Introduction

Bena-Yungur (ISO 639-3 yun) is a language from the Bena-Mboi group traditionally classified as a subgroup of Adamawa, in which it occupies an isolated position according to Kleinewillinghöfer (to appear). We have not yet attempted to determine its genealogical classification, but we have noted so many clear cognates with Benue-Congo languages that an affiliation to that family will be our working hypothesis. The speakers refer to their languages as e ̃ː ɓə̃ńā 'the Bena language'. The name Yungur is originally an exonym, but today it is regularly used by the Bena themselves. Since speakers of the Lala varieties of the Bena-Mboi group identify themselves as Bena as well, [START_REF] Kleinewillinghöfer | Nominalklassen im Mboi und Ɓəna-Lala der Yungur bzw. Ɓəna-Mboi-Gruppe[END_REF] proposes to use Bena-Yungur as the name of the language, a convention we will follow.

This paper is based on original data from field work we carried out in Nigeria. We gathered initial data with about ten speakers in the village of Dumne during a pilot study in Adamawa State. Due to the insecurity in the region, we subsequently invited native speaker consultants to come and work with us in Kwara State for periods in 2013, 2014 and 2015. Our main consultants are Sabeta Bukta and Bitrus Andrew, two male mother tongue speakers from Dumne in their early thirties who use Bena-Yungur on a daily basis. Their variety of Bena-Yungur is the Pra (pə rá) dialect of Dumne, also our reference dialect. We recorded many texts, including dialogues, which are partly transcribed and translated. However, the data used in this paper are almost entirely elicited. Also, although we have started working on Bena-Yungur several years ago, our work has been frequently interrupted and is not yet very much advanced. Since the tone system in African languages with lots of tonal morphology is often among the last things that are fully understood, the analysis presented in this paper might have to be refined in the future. However, enough aspects of Bena-Yungur tone are already understood to warrant a publication, especially since so little is known about the languages of the Bena-Mboi group or the other languages of the area referentially classified as Adamawa.

We begin by presenting a concise grammatical overview of Bena-Yungur in Section 2. Section 3 concentrates on the tone rules of the language, viz. tone spread (3.1), tone absorption (3.2) and floating tone attachment (3.3). The joint application of these tone rules is briefly illustrated in Section 3.4. Section 4 is concerned with the distribution of tones over syllables and lexemes. Sections 4.1 and 4.2 comment on the exceptional nature of contour tones on monosyllabic lexemes (4.1) and the marginal occurrence of the three-tone contour HLH on these lexemes as a result of tone spread (4.2). The analysis of the distribution of tones in lexemes allows for an internal reconstruction of the current three level Bena-Yungur tone system as a formerly two level system (Section 4.3). The major factor behind the increase of the number of tone levels in Bena-Yungur is the effect of stem-initial voiced stops as tone depressor consonants. Section 5, finally, provides a description of the morphological operations in Bena-Yungur that consist exclusively of tone changes. Nouns may acquire tone schemes different from their lexical tone patterns in certain syntactic positions (5.1) and a number of morphological processes applied to nouns and verbs assign tone schemes that override lexical tones (5.2). 1

Grammatical overview

In our current analysis Bena-Yungur has twenty six consonant phonemes : /b, p, d, t, ʧ, g, k, gb, kp, ʔ, ɓ, ɗ, f, z, s, ʃ, h, m, n, ɲ, ŋ, l, ⱱ, r, y, w/. So far, we found the labialdental flap /ⱱ/ in one ideophone only, viz. pàⱱàɗ '(appear) suddenly'. We analyse geminates and pre-nasalised stops as successions of two phonemes. Bena-Yungur distinguishes six phonological vowel qualities /i, e, a, ə, o, u/. All can be phonologically nasal, with the possible exception of /ə/. Vowel length is contrastive throughout the vowel system. This brings the vowel inventory to twenty two phonemes. Utterance-initially, vowels are often pre-glottalised and voiced stops partially or fully devoiced, with the exception of /gb/, but including implosives. Optional initial devoicing is especially common with fricatives.

Both open and closed syllables are possible. In their citation form, most words end in an open syllable. In lexical words that consist of one open syllable, the vowel is always long. In function words, such as personal pronominals, the vowel is normally short but can be pronounced long in very slow careful speech. Final closed syllables are more common in minor word classes, such as adverbs. The difference in laryngeal settings is neutralized in coda stops, which normally lack audible release. 2 In utterance-final position, glottalisation is regular with stops and also occurs with 1 We use the term tone pattern to refer to a tone or succession of tones that is part of the lexical representation of a linguistic form and the term tone scheme for a tone or succession of tones that is imposed on a linguistic form by the application of a morphological operation.

2 By default, we use implosive stop symbols for coda stops of the labial and coronal places of articulation, where the neutralization is between voiced, voiceless and implosive stops, and the voiceless stop symbol for coda stops of the velar place of articulation, where the neutralization is between voiced and voiceless stops. However, if depending on the construction a given stop can occur both in the syllable-final position and in the context before a vowel, we consistently use the stop symbol corresponding to the laryngeal setting found in the context before a vowel. continuants, nasals, [l] and vowels. Utterance-internally, word final vowels are often reduced and in some constructions deleted. When the final vowel is deleted, the result is a word-final closed syllable. Vowel-initial syllables are rare. They are found mostly in function words and borrowings. Consonant clusters are possible across word boundaries and within words, either across syllable boundaries or in syllable onsets, but there are no pre-pausal or phrase-internal word-final consonant clusters in Bena-Yungur. Consonant clusters in syllable onsets are of two types. The first one involves a sequence of a homorganic nasal and a voiced stop. The second one involves a sequence of a stop and /w/, /l/ or /r/. In careful speech, and for some types of clusters also at a normal speech rate, some of the clusters of the second type are broken up by a schwa transforming a monosyllabic sequence into a bisyllabic one, as in tə wá (careful) ~ twá (casual) 'guinea fowl' with an optional schwa vs. twáːtwá(ː) 'wide' where no such option exists. We note such an optional schwa as ə . The two cluster types can combine, provided that the first consonant is a homorganic nasal, as in mbə ̯ ra ̃᷄ (ː)

'water'. Bound segmental morphology is mostly suffixing. The noun class system of Bena-Yungur is analysed in [START_REF] Van De Velde | Morphological classes and gender in Ɓə ńá-Yungur[END_REF], where a distinction is made between morphological classes (defined as sets of nouns that have the same class/number markers), noun classes (defined as sets of nouns that trigger the same agreement pattern) and genders (defined as singular-plural pairings of noun classes). Defined this way, Bena-Yungur has three noun classes, eight genders and about thirty morphological classes. Figure 1 provides an overview of the gender system. Noun classes are represented by the form of demonstratives.

Modifiers follow the element they modify. Demonstratives, indefinite determiners, possessive pronouns, adjectives and participles agree with their head noun in noun class and number. Basic clause structure is SVO, although in some TAM constructions first and second person pronominal objects are preposed to the verb. Negative polarity is marked by a clause-final negation marker réʔ in combination with some negative morphology earlier in the clause. Basic TAM categories, including Perfective, Habitual, Progressive and Future, are marked syncretically on the verb and the subject pronominal. Pronominal agreement targets agree in animacy with their controller, where animacy basically reflects the ability of self-locomotion of the referent. Inanimate pronominal targets are mostly realized as absence of a pronominal. Nonselective interrogative pronominals make a distinction between human yānā 'who?' and non-human mbīː 'what?'. A clusivity distinction is made in 1PL between inclusive and exclusive pronominals, both as subjects and non-subjects. Dedicated singular and plural logophoric forms exist for animate subject and possessive pronominals.

Tone rules

Bena-Yungur distinguishes three surface tone levels: L(ow), M(id) and H(igh) that can combine to form all logically possible contour tones: HM, HL, LH, LM, MH and ML. There is no phonological downstep. Bena-Yungur has two tone rules that apply to linked tones: tone spread (Section 3.1) and tone absorption (Section 3.2). Floating tones normally dock to the right and any floating tone that has not docked by the end of the derivation is deleted (Section 3.3).

Tone spread

Every tone can (and normally does) spread one position to the right across word boundaries, provided the tone occupying this position to the right is followed by a pause or by an identical tone (1). Moreover, a L does not spread onto a following M (2) and a M does not spread onto a following L (3).

( When tone spreads onto an utterance-final monosyllabic word that already had a complex tone, the result is a more complex tone (7). However, for the reasons discussed in Section 4.2, the only possible combination of three tones on such an utterance-final monosyllabic word is HLH. Thus, M and L do not spread onto a contour tone, which follows from the restrictions on tone spread described above. Also, when H spreads onto a MH contour, the last H tone becomes floating, as in ( 21). ( 7) hóːrá # dǒː → hóːrə̃́ do 'the liver of the duiker'

When tone spreads onto a syllable with an optional schwa (see Section 2), the result of the tone spread is somewhat different from other contexts. The only situation where tone spread may affect the tone of an optional schwa is when the optional schwa is in the word-initial syllable. With the exception of the word ŋmgbə ra ̯ (ː) 'elegant sand racer, Psammophis elegans', the tone of the optional schwa ə in this position is identical to the tone of the following syllable, as in gə ràːgəǹ 'glutton', or if it is a complex tone, the initial part of the latter, as in mbə ̯ ra ̃᷄ (ː) 'water'.

The tone spreading across word boundaries from the left replaces the tone of the optional schwa ə and spreads to the next syllable if its tone (or the initial part of its contour) is identical to the tone of the optional schwa, as in mbə ̯ ra ̃᷄ (ː) 'water' (8a) and gə ràːgəǹ 'glutton' (8b). However, in the case of ŋmgbə ra ̯ (ː) 'elegant sand racer,

Psammophis elegans' where the tone of the optional schwa is L and the tone of the following syllable is M, such further spread is blocked (8c). Apparently, in (8c) the H spreading on the L of the optional schwa first creates a HL contour, whose L part is then exceptionally absorbed by the following M because the syllable with an optional schwa cannot host two tones. The tone absorption is exceptional here because elsewhere the absorption of L in a HL contour by a following M is only possible across word boundaries (see Section 3.2).

(8) a. été # mbə ̯ ra ̃᷄ (ː) → ét mbə ra ᷇ (ː) H 'white person, European' (lit.: 'person of water', meaning 'person from overseas') b.

tóː # gə ràːgəǹ → tóː gə râːgəǹ 'take the glutton!' c.

tóː # ŋmgbə ra ̯ (ː) → tóː ŋmgbə ra ̯ (ː) 'take the elegant sand racer!'

The formulation "can (and normally does) spread" in the description of the tone spread rule is intended to reflect the fact that while the application of tone spread one position to the right across word boundaries is extremely productive, in principle tone spread remains optional and a tone may spread further than one position to the right. This is illustrated in (9) with the example of the genitive construction 'the eye of a bean', where nṹː 'eye' is the head and dàsè 'bean' is the genitive modifier. The normal realization of this phrase by our main consultants irrespective of the speech rate is (9b)

where the H tone of nṹː spreads one position to the right across the word boundary (with the subsequent absorption of the L part of the HL contour created by H tone spread, cf. Section 3.2). However, in principle the H tone may also fail to spread as in (9a) or spread two positions to the right, instead of one, as in (9c). The variability in the application and the range of tone spread may be subject to contextual, individual and dialectal differences the extent of which is difficult to ascertain without a big corpus study. Yet, we do have some indications that tone spread is likely to be less prominent in the Guto dialect as compared to our reference dialect Pra. For instance, the word gìràŋgó 'crocodile' in Pra corresponds to gìráŋgó in Guto. This example also provides evidence in support of our hypothesis that the tendency for the tone of the second syllable in disyllabic words to be identical to the tone of the first syllable must be due to the application of rules of tone spreading (cf. Section 4.3).

Tone absorption

The second tone rule is the rule of tone absorption. This rule simplifies complex tones that are followed by a tone that is identical to their final part, e.g. HL#L → H#L in (10).

(10) kálsâ # bəmbəm → kálsə̃́ bəmbəm 'fat monkeys (sp.)'

Unlike tone spread, tone absorption also productively applies within words. This explains the difference in outcome of tone spread in (1a, 11), on the one hand, and (1bd, 12a), on the other. Thus, a spreading tone sometimes forms a contour with the tone it encounters at its right (1a, 11) and sometimes replaces it (1b-d, 12a). Replacement can easily be analysed as the outcome of the successive application of spreading and tone absorption, as spelled out in (12b).

(11) tóː # gòː → tóː gôː 'take a chicken!' (12) a. tóː # gòːsà → tóː góːsà 'take chickens!' b. tóː # gòːsà → tóː gôːsà → tóː góːsà 'take chickens!'

L and M tones often behave as if they were identical in the application of the tone absorption rule too, so that a HL contour tone followed by a M can be reduced to H, as illustrated in ( 13).

(13) kwáːnô # yā → kwáːnə̃́ yā 'this plate' Note that a HL contour must be separated from the following M by a word boundary for the tone absorption to be applied. This is illustrated in ( 14), where the L part of the lexical HL contour is not absorbed by the following M within the same word, and in (15), where the HL contour is created by the application of tone spread and its L part is not absorbed by the following M within the same word either. The only exception to the requirement that a HL contour must be separated from the following M by a word boundary for the tone absorption to be applied is represented by the case where the HL contour would be created by the application of tone spread on a syllable with an optional schwa, which cannot host two tones (see Section 3.1 and example 8c). ( 14) kwîllā 'fish (sp.)' (15) été # bèɓtā → ét bêɓtā 'disrespectful person' (lit.: 'person of disrespect')

Floating tone attachment

In Bena-Yungur, tones of all three levels can float, viz. H , M and L . No sequences of floating tones exist. When a morphological process results in the creation of a sequence of two floating tones, the second of these two tones is deleted, as in (32b) in Section 5.1 where the deletion of the final vowel of bwálô 'cooking' leaves a sequence of a floating H and a floating L but then the latter floating tone is also deleted. We have so far found no morphemes that consist only of a floating tone. Floating tones are usually lexically specified, as in ə̯n H 'with', à M 'on, at' and áy L '3SG.AN.be', but may sometimes result from the application of tone rules, as in (21). With the exception of the word àtwa᷇ ŋ (H) 'grasshopper (sp)', whose floating H is optional, floating tones are found only in the lexical specifications of function morphemes. In a limited number of function morphemes, H tone is variably specified in the lexicon as linked or floating. So far we found such variation with two prepositions, viz. 'with', varying between ə̯n H and ə̃ń, and 'in', varying between ɗā(ː) H and ɗáː. As is apparent from the examples of morphemes with floating tones in this section, a floating tone is always the last tone in the lexical specification of a morpheme. The linked tone preceding a floating tone is always different from the latter. Furthermore, floating L tones are found only after H. Floating M tones can be found after both L and H. Floating H tones are usually found after M and in a few cases after L.

The rules governing the docking of floating tones are largely similar to the rules of tone spread (Section 3.1) and tone absorption (Section 3.2). Thus, any floating tone is absorbed by a following identical linked tone. Furthermore, a floating M is absorbed by a following linked L and a floating L is similarly absorbed by a following linked M. All floating tones first try to dock to the right. If they cannot dock to the right, floating H and M are deleted, while a floating L may also dock to the left if the preceding syllable is H. Otherwise it is deleted. Furthermore, neither a floating M nor a floating L can dock to the right if the following tone is a linked H itself followed by either linked M or L or floating M or L .

Example ( 16) illustrates three possible realizations of the floating L tone of áy L '3SG.AN.be'. The floating L is absorbed by the following linked L in (16a) and the following linked M in (16b). In (16c), the floating L can dock to the right because it is followed by a linked H tone which is not itself followed by L or M. The H tone of the resulting LH contour is then regularly absorbed by the following H. In (16d), the floating L docks to the left to the preceding H syllable since it cannot dock to the right because it is followed by a linked H tone which is itself followed by M.

(16) a.

áy This plural word has another lexically conditioned allomorph ám L with a floating L . It is not always possible to say which allomorph is used, as is the case in (17a), where both the allomorph with a floating M and the allomorph with a floating L would have the same realization. However, in (17b, c) and ( 18), the two allomorphs can be distinguished. Thus, compare (17c), where the floating M followed by H.M is deleted, and ( 18), where the floating L equally followed by H.M docks to the left, since it cannot dock to the right, just as the floating L in (16d).

(18) ám L # kálā → âm kálā 'bellies'

3.4. Illustration: tones tend to be realised one position to the right of their lexical attachment site

The

Tone patterns

With the exception of syllables formed by an optional schwa ə (cf. Sections 2, 3.1 and 3.2), every syllable can host two tones, irrespective of its weight or position. At the same time, as discussed in Section 4.1, there is only a handful of monosyllabic words with a lexical two-tone contour pattern. In a very limited number of cases, the application of tone rules can lead to three surface tones being realised on one syllable. As discussed in Section 4.2, the only possible three tone contour is HLH on a heavy syllable before pause. Finally, in Section 4.3 we analyse the distribution of tones in lexemes, which allows us to formulate some hypotheses on the internal reconstruction of the tone system of Bena-Yungur.

Two tones on monosyllabic words

Monosyllabic words very rarely have complex tones. The six exceptional words we found are listed in (20).

( A closer look at the (presumed) lexical frequencies and positional preferences of these six lexemes suggests that the rules of tone spread and absorption are responsible for the rarity of their lexical tone pattern. One of our main consultants distinguishes between gǎː 'sun; God' and gàː H 'day', where the latter form has a more regular surface tone pattern. We believe that regularisation of the tone pattern of this word in the meaning 'day' is due to frequency effects. One reason for this is that the meanings 'sun' and 'God' are more often expressed by other words, viz. óː and líwrá respectively. The fact that this word is used more frequently in the meaning 'day' accounts for the divergent development of the word in this meaning, as compared to the meanings 'sun' and 'God'. In addition to the relative frequency of this word in the meaning 'day', its absolute frequency in speech in this meaning is also likely to be relevant. It can account for the fact that the tone pattern has been regularized in gàː H 'day' but not in dǒː 'duiker', wa ̰᷅ ː 'tree (sp.)' and we ̃ːɗ ~ wêɗ 'grasshopper (sp.), which must be rather infrequent in speech. Finally, the difference between gàː H 'day' and the remaining two exceptional words listed in (20), viz. gbǎː 'be big; very much' and lǎː 'like this', which must be at least as frequent as 'day', is likely to be accounted for by differences in their frequency of occurrence in two kinds of environments, viz. before an utterance-final pause vs. phrase-internally. Due to their predicative and adverbial function, the latter two words must be more common before an utterance-final pause, while there is no such expectation for the word 'day'. In fact, it is likely to be more common phrase-internally. Following the application of tone rules (see Section 3), in an utterance-internal position a monosyllabic word with the lexical LH tone pattern is most often realized as L, while before an utterance-final pause the LH contour is preserved. That is, while gbǎː and lǎː usually occur in the environment where their LH contour is preserved, gǎː in the meaning 'day' frequently surfaces as simply L, which readily accounts for the reanalysis of its lexical tone as L H .

Three tones on one syllable: HLH contour

In some rare cases the application of tone rules can lead to three surface tones being realised on one heavy syllable before a pause (see Section 3). Only one combination of three tones is possible on a single syllable, viz. HLH. This is due to several reasons. Most importantly, M and L do not spread onto a contour tone, which already drastically reduces the number of possible three tone contours. Moreover, when H spreads on a two-tone contour and one of its two tones is M, the last tone becomes floating, as in ( 21) where H spreads on a MH contour and the final H delinks, resulting in a HM contour followed by a floating H. In other words, the only words that may be realised with three tones on one syllable before a pause due to the application of tone rules are the four monosyllabic words with a LH tone pattern cited in (20), viz. dǒː 'duiker', gǎː 'sun; God' (for some speakers also in the meaning 'day'), gbǎː 'be big; very much' and lǎː 'like this'. We found only two words where a HLH contour is lexical, viz. dènde᷉ n 'numerous, many' and gəmgə᷉ m 'mature person who died without being married and without having children'. It is obvious that the HLH contour on the second syllable of the two words results from H tone spread from the first syllable and that the current L.HLH tone pattern comes from an earlier *LH.LH pattern. Note that the relation between the two tone patterns is diachronic and not synchronic in terms of the application of tone rules. Although the two words look like reduplications, they are both fully lexicalized. Thus, for dènde᷉ n no related base form is found. As for gəmgə᷉ m, although there is a related simple form gəm 'useless', its tone is L and not LH and the semantic relation between 'useless' and 'mature person who died without being married and without having children' is idiosyncratic.

In open syllables and in closed syllables whose coda is not a nasal,4 the final H part of the HLH contour is often realized lowered so that in this context we can either say that the distinction between H and M is neutralized or that H is lowered to M. However, we prefer to analyse the final tone of this three tone contour as H for two reasons. First, lexically this final tone should be H and it still behaves as such in the phonology as soon as it is followed by anything else than a pause. Second, if an open syllable with the three-tone contour becomes closed by a nasal coda, such as the perfective assertive clitic =n, as in ( 22), its final part is normally realized on the regular H level.

The distribution of tones in lexemes and the internal reconstruction of the tone system

In this section we will look at the distribution of tones in lexemes, which shows very interesting patterns that allow us to formulate some hypotheses on the internal reconstruction of the tone system of Bena-Yungur. The two properties that are most relevant in this respect are the strong correlation between the laryngeal settings of stem-initial consonants with the tone of stem-initial syllables and the similarities between L and M in Bena-Yungur phonology.

As shown in Table 2, the number of H monosyllabic nouns and verbs more or less equals the sum of L and M words. Table 2. Tone patterns of monosyllabic nouns and verbs Moreover, there is a very strong correlation between the laryngeal settings of stem initial consonants and the first tone of stems, such that voiced stops (i.e. b, d, g and gb)

are almost exclusively followed by a low tone and voiceless stops almost exclusively by a M or a H tone. Exceptions to the rule that initial voiced stops are followed by a low tone are very rare. Some are obviously recent borrowings and others are names for animals, which tend to have exceptional shapes. An exhaustive list of the exceptions found so far is provided in ( 23).

(23) bə̃ŕkə̃mrā 'mangoose' góndà ⁓ gwándà 'pawpaw' góːdê 'to thank' (from Hausa góːdè 'to thank')

gwéːvà

'guava'

5 The data used for this section is a subset of 1161 double checked entries from our lexical database.

Counterexamples involving initial voiceless stops followed by a L tone are slightly more numerous. They also tend to be borrowings or names for biological species and are listed in (24).

( Most other phonemes and NC clusters (mb, n, nd, ŋg, ŋmgb, r, l, f, h, ɓ and ɗ) largely pattern with the voiceless stop consonants. For m there is no clear pattern. Perhaps many borrowings start in m. The case of r is not very clear either, but it seems to be typically followed by M or H tones as well. The voiceless fricative s shows no clear preference for a following tone, which is due to recent neutralisation of the opposition between s and z in the Pra dialect of Bena-Yungur. Comparison with the Guto dialect spoken to the south of Pra shows that all nouns with an initial z in that dialect have a L tone in Pra, as illustrated in (25). Words that start in s in the Guto dialect are mostly M or H in Pra. Exceptions can be attributed to the hypothesis that devoicing of z is currently spreading through the Guto lexicon.

The distributional facts cited so far could be accounted for by a three step historical scenario, schematised in Figure 2, that starts with a two tone system in which tones are distributed more or less randomly over lexemes, i.e. irrespective of the quality of the stem-initial consonant. In step two, the distinction between L and H is neutralised after stem-initial voiced obstruents, which act as depressor consonants that change all H tones into L. Finally, the subsequent lowering of tones after stem-initial voiced obstruents gave rise to tonogenesis, splitting L tones into low and extra low, respectively M and L in the current tone system. The straightforward relation between consonants and tones was later blurred by the application of tone rules (see Section 3), devoicing of stem-initial voiced obstruents and the erosion of segmental material leading to the emergence of floating tones.

The second step of this historical scenario, viz. the split of an earlier L into M and L, is further corroborated by the fact that in many ways current M and L are treated as similar in Bena-Yungur phonology. For instance, as discussed in Section 3.1, L and M are treated as identical for the purpose of the rule of tone spread. First, L and M do not spread onto each other. Second, L and M do not spread on the following H if the latter is immediately followed by either L or M. In certain contexts, L is also treated as identical to the following M for the purposes of the rule of tone absorption. Thus, as described in Section 3.2, when a HL contour happens to be followed by M across a word boundary, L is absorbed by M.

In disyllabic words, the tone of the second syllable tends to be identical to that of the first, which must be due to the application of rules of tone spreading (cf. Section 3.1). Interestingly, in disyllabic verbs, it is the L pattern that is almost as frequent as H and M combined, as is shown in Table 3. In Tables 3 and4 the rows show the tone of the first syllable and the columns that of the second syllable. Disyllabic nouns also tend to have identical tones on the first and the second syllable, with the notable exception of L.M nouns, as shown in Table 4. Although the general pattern for disyllabic nouns in Table 4 is similar to that for disyllabic verbs in Table 3, there is clearly much more noise in Table 4. The difference is primarily due to the fact that a large majority of disyllabic nouns are not monomorphemic. The second syllable is often a morphological class/number marker (see Section 2). Another important factor must be a higher rate of borrowings among nouns, as borrowings are more likely to have irregular tone patterns. Finally, it is relevant that the CVCCV shape is much more common among disyllabic nouns than disyllabic verbs, which are normally CVCV. This is relevant because CVCCV words are likely to derive from earlier *CVCVCV, whereby the original three tones had to be accommodated on two syllables.

Tonal morphosyntax

Tone plays a crucial role in the expression of morphosyntactic categories in Bena-Yungur in three ways. First, morphemes can partly consist of floating tones (see Section 3.3). Second, lexical forms can have different tones depending on their syntactic position. Thus, nouns may acquire tone schemes different from their lexical tone patterns when used as dependents in the genitive construction, as complements of some prepositions and as complements of nominalised verb forms (Section 5.1). Third, a tone scheme can override the lexical tone pattern of the base due to the application of a morphological operation. For instance, verbs may be assigned different tone schemes overriding their lexical tones in the positive perfective construction (Section 5.2) or the dependent tone scheme of a noun can be changed to derive a different noun (Section 5.1).

Tonal syntax: dependent tone schemes of nouns

Bena-Yungur nouns are morphotonologically interesting in that they have a higher number of tone schemes as dependents in genitive constructions than in other contexts.

We will call the tone scheme of nouns in that position their dependent tone scheme The dependent tone schemes of nouns are purely lexically determined, i.e. not by the type of genitive relation, and are unpredictable. We therefore specify the genitive tone scheme of every L or H noun in our lexical database. As is illustrated by nouns whose citation forms have a different tone pattern in the singular and the plural, such as H.H ándá 'place' versus H.HL ánsâ 'places', tone patterns are a property of words, not of stems. This is also true for dependent tone schemes, as illustrated by the word for 'arrow' ɓwáː, which has DTS A (33a), and its plural ɓwáːmé, which has DTS B (33b). For a number of nouns, our consultants sometimes accepted both dependent tone schemes as free variants. Such examples should probably be analysed as cases of analogical levelling, viz. original DTS B → more regular DTS A . DTS A is more regular both in the sense that it is much more frequent and in the sense that it can be construed as the default option: the dependent tone scheme of a noun is the same as its lexical tone pattern.

We also found two pairs of nouns which are identical except for their DTS and their meaning (34). Examples illustrating the difference between the members of each pair are provided in (35)(36)(37). Obviously, the difference in DTS cannot be analysed as regularisation here. We treat the members of these pairs as homonyms in our lexical database.

( Note that the list in (34) is probably not exhaustive, as is suggested by two facts. First, the nouns in the two pairs in (34) are clearly related and they are related in a similar way. The noun with DTS B has a concrete spatial semantics while the noun with DTS A looks like a metonymical extension with a more abstract meaning, viz. some abstract object associated with the space denoted by the formally identical noun with DTS A . Therefore, we can say that DTS change, viz. the change DTS B → DTS A , can be used as a derivational tool. Second, the two pairs in (34) are not just frozen relics, as the change DTS B → DTS A appears to be available to the speakers as a morphological process. Thus, one of our main consultants volunteered the derivation by the change DTS B → DTS A in (38), when asked which of the two DTS options is correct for the noun káɲtá in the genitive construction as the dependent of the word été 'person', viz. ét káɲtá 'a person from the Káɲtá clan' (DTS A )

Tonal morphology: tones of verbs

As described in Section 4.3, monosyllabic verbs have three possible lexical tone patterns, viz. H, M and L, while disyllabic verbs have five, of which the three most common patterns are similar to monosyllabic verbs in that they consist of the same tone in both syllables, viz. H.H, M.M, L.L, and two marginal patterns have different tones in the two syllables, viz. H.HL and L.H. All trisyllabic verbs we have found so far are similar to monosyllabic verbs in that they have the same tones in all three syllables. In all but one TAMP (tense-aspect-mood-polarity) construction, verbs preserve their lexical tone patterns. 7 The exception is the positive perfective construction, where monotonal verbs of certain tone patterns are assigned a tone scheme that overrides their lexical tones. These changes are summarized in ( 40), where a notation such as H(.H…) refers to monotonal verbs irrespective of the number of syllables.

(

Figure 1 .

 1 Figure 1. The Bena-Yungur gender system

  (9) a. nṹː # dàsè → nṹː dàsè 'the eye of a bean' b. nṹː # dàsè → nṹː dásè 'the eye of a bean' c. nṹː # dàsè → nṹː dásê 'the eye of a bean'

  → ét mbə ra ᷇ (ː) H 'white person, European' (lit.: 'person of water', meaning 'person from overseas')

'

  Enough of this!' ('Stop arguing!') (lit.: 'it has actually stopped like this!')

  5

  Figure 2. A scenario for the evolution of tones in stem-initial syllables in Bena-Yungur

  ɓwáːmē 'in the arrows' (DTS B )

  (39a) with DTS B or (39b) with DTS A . The Káɲtá clan does not exist, but it would be a possible clan name, since Bena clans are often associated with particular villages and the names of clans are sometimes identical to names of villages. ét káɲtā 'a person from the village of Káɲtá ' (DTS B ) b.

  Example (17) illustrates two possible realisations of the floating M tone of the plural marker ám M , which is related to the short form ám of the plural ámbá 'children' (compare the singular form áwé 'child'). Thus, the floating M is absorbed by the following linked L in (17a), docks to the right creating a MH contour whose H part is subsequently absorbed by the following H in (17b), and is deleted in (17c) because it cannot dock either to the right or to the left.

	b. c. d.	L # bəm áy L # ʧēɓʧēɓ → áy ʧēɓʧēɓ '(s)he is black' '(s)he is large' → áy bəm áy L # ɓwáláŋ → áy ɓwàláŋ '(s)he is tall' áy L # lósã᷄ → ây lósã᷄ '(S)he is like that'
	(17) a. b. c.	ám M # bwà(ː) → ám bwà(ː) 'dogs' ám M # túɓâ 'hares (sp.)' → ám tūɓâ ám M # tóːnā → ám tóːnā 'girls'

  application of tone rules may result in output tones that are very different from the structural tones in the input, as illustrated in(19). Here the floating H of the 3SG.PFV pronominal ā H docks to the right on the L tone of the perfective form of the verb bàː 'scoop' and the two tones first form a HL contour. The L tone of the perfective form of the verb bàː 'scoop' spreads on the following H of the 1SG pronominal nə̃́ and the two tones first form a LH contour. The H tone of the 1SG pronominal nə̃́ itself spreads on the following L of bàːrā 'lie' and the two tones first form a HL contour. The L part of the first HL contour on the verb is absorbed by the following L part of the LH contour on the 1SG pronominal, while the H part of the latter LH contour is itself absorbed by the following HL contour of 'lie'. That is, the original input tone pattern M

	(19) ā |āH	báː bàː	nə̀ bâːrā nə̃́ bàːrā|
	3SG.PFV scoop\PFV 1SG lie
	'He lied to me.' (lit.: 'He scooped me a lie') 3

H L H L.M comes out as M H L HL.M.

Table 3 .

 3 Tone patterns of disyllabic verbs (imperative forms)

Table 4 .

 4 Tone patterns of disyllabic nouns

  (DTS). Nouns that are entirely H in isolation are split into two dependent tone schemes. The DTS of one class remains H (26), which we refer to as dependent tone scheme A (DTS A ). That of the other class becomes M (27-28), which we refer to as dependent tone scheme B (DTS B ). Note that rules of tone spread and tone absorption apply in the examples. DTS B noun bùtò 'ground', and in complements of nominalised verb forms, as in (32b) where a DTS B noun búrá 'porridge' is a complement of the nominalisation ɓwálô 'cooking', which in this environment takes the short form ɓwál with the final vowel deleted. Both constructions are likely to have their origin in genitive constructions. However, since the relevant prepositions are not used as nouns elsewhere, only the construction with nominalised verb forms can be analysed as a genitive construction synchronically.

	with a (31) a. b. c.	'ground' 'on the ground' ɗā bûtô 'in the ground' bùtò à bùtô
	(32) a. b.	ɓwál búrá 'cook porridge!' ɓwál búrā 'cooking (of) porridge, to cook porridge'
	(26) a. b.	sífé da ̀ːrə̀ sìfé wa᷇ 'the skin of the herbalist' 6 'herbalist'
	(27) a. b.	ɓə̃ńá e ̃ː ɓə̃ńā 'the Bena language' 'Bena'
	(28) a. b.	'cow' bwàːrə̀ nāː 'cow dung' náː
	Nouns that are entirely L in isolation and that are not monosyllabic are likewise split
	into two tone classes. Again, the DTS of one class is identical to the tone scheme in
	isolation, i.e. L (29), which we refer to as DTS A . The other class has a DTS with a
	final HL contour (30), which we refer to as DTS B .
	(29) a. b.	'iroko tree' līŋgē dùŋgà 'the top of the iroko tree' dùŋgà
	(30) a. b.	dòɓrà tȭːrə̯̄ dòɓrâ	'bush' 'the road of the bush'
	We have so far identified two other syntactic contexts in which the DTS of nouns is used, viz. in complements of the prepositions ɗāH 'in' and à M 'on, at', as in (31b-c)

  'They are fighting for the land.' (lit.: 'They fight them(selves) on the land')

	34)		DTS B	DTS A
	a.	bùtò	'ground, soil' (35)	'land' (36)
	b.	líwrá	'sky, heaven' (37a)	'God' (37b)
	(35) ɓān |ɓān H 3PL.IPFV fight 3PL on ground[DTS B ] yám ɓāː á bùtô yāmā ɓáː à M bùtô|
	'They are fighting on the ground.' (lit.: 'They fight them(selves) on the ground')
	(36) ɓān |ɓān H 3PL.IPFV fight 3PL on land[DTS A ] yám ɓāː á bùtò yāmā ɓáː à M bùtò|
	(37) a. b.	ɗā líwrā ɗā líwrá	'in the sky, in heaven' (DTS B ) 'in God' (DTS A )

  In monotonal verbs, H becomes M and M becomes H, while L remains L. In nonmonotonal verbs, all tones stay put.

	40) Lexical tone	𝑝𝑓𝑣 + tone
	H(.H…)	→ M(.M…)
	M(.M…)	→ H(.H…)
	L(.L…)	→ L(.L…)
	H.HL	→ H.HL
	L.H	→ L.H
	Glosses
	AN	animate
	ASS	assertive
	DTS	dependent tone scheme

PFV perfective

7 Lexical tone patterns of verbs are most directly observable in the 2SG imperative construction without overt subject as no other tones interfere there.

In the examples, |the second line| presents structural forms of the respective morphemes.

This generalization is most likely to hold true for all kinds of sonorants. However, for the moment nasals are the only type of sonorants that we found in coda position in syllables with a HLH contour.

The final element wā here is a demonstrative which agrees in gender with the head noun 'skin'. In genitive constructions, the use of a demonstrative agreeing in gender with the possessed noun seems to be generally obligatory when the possessor is human.

The tone system of Bena-Yungur Dmitry Idiatov & Mark Van de Velde LLACAN (CNRS -INALCO/USPC)


Fran De Aquino

The origin of the Ultra-high-energy cosmic-ray particles

Keywords: Cosmic-ray particles Energy, Gravitational Mass, Mini-blackholes

In this paper, we show that the extremely-high energies of some cosmic-ray particles can be related to the strong increase of their gravitational masses when they have been generated.

Introduction

The energy spectrum of cosmic-ray particles extends to ~10 20 eV [1]. The origin of these ultra-high-energy cosmic-ray particles is not yet firmly established [1,2,[3][4][START_REF] Belotsky | Advances in High Energy Physics[END_REF][START_REF] Belotsky | [END_REF]. Actually, this is one of the great challenges of modern Astrophysics [7,8]. In this paper, we show that the extremely-high energies of these cosmic particles can be related to the strong increase of their gravitational masses when they have been generated.

Theory

In 1974, Stephen Hawking shown that black holes could emit particles (neutrinos, electrons, protons, nucleons, etc.) and so evaporate [9]. The Hawking's theory [9,10] establishes that the internal temperature ( ) T of a black hole, its lifetime ( ) τ and the number ( )

N
of particles emitted from it, are respectively given by ( ) In a previous paper [START_REF] De Aquino | of the Relativistic Theory of Quantum Gravity[END_REF] it was shown that there is a correlation between the gravitational mass,

1 10 26 m T ≈ ( )
, and the rest inertial mass , which is given by

g m 0 i m ( ) 4 1 1 2 1 2 2 0 0 ⎪ ⎭ ⎪ ⎬ ⎫ ⎪ ⎩ ⎪ ⎨ ⎧ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ - ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + - = = c m Un m m i r i g χ
where U is the electromagnetic energy absorbed or emitted by the particle;

is the index of refraction of the particle and is the light speed.

r n c

In the particular case of thermal radiation, it is usual to relate the energy of the photons to the temperature, through the relationship is the Boltzmann's constant. Thus, in that case, the energy absorbed by a particle will be

kT h U η ν η ≈ =
, where η is a particledependent absorption coefficient ( 1 . 0 ≅ η , see [START_REF] De Aquino | Gravitation and Electromagnetism Correlation and Grand Unification[END_REF]). Therefore, Eq.( 4) can be rewritten in the following form:

( ) 5 1 1 2 1 2 2 0 0 ⎪ ⎭ ⎪ ⎬ ⎫ ⎪ ⎩ ⎪ ⎨ ⎧ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ - ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + - ≈ c m kTn m m i r i g η
According to Eq. ( 1), the temperature ( ) T of mini black holes can be very high, in such way that the term 2 0 c m kTn i r η in Eq. ( 5), can become very greater than 1. In this case, Eq. ( 5) shows that, the gravitational masses of the particles emitted from a mini black hole will be given by:

( ) ( 6
1 ; 10 2 41 2 r r g n T c kTn m - - ≈ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ - ≈ η )
Thus, these particles will have energy, E , expressed by [START_REF] De Aquino | of the Relativistic Theory of Quantum Gravity[END_REF]: with masses down to ~10 -5 g could have be created in the initial stages of the formation of the Universe [START_REF] Hawking | [END_REF].

( )

  ) is the inertial mass of the black hole.

  m

≈

  In the case of mini black holes with inertial masses g m 1000 < * , the temperature, T , according to Eq.(1), is . Then, Eq. (8), tells us that the particles emitted from these mini black holes can have energy, This energy corresponds to the extremely-high energies of the spectrum of the cosmic-ray particles. Consequently, we can conclude that, possibly the ultra-high-energy cosmic-ray particles can have originated in mini black holes.* In 1971 Hawking shows that many mini black holes ( )


Suchanya Wongrod

Stéphane Simon
email: stephane.simon@unilim.fr

Eric D Van Hullebusch

Piet N L Lens

Gilles Guibaud

Assessing arsenic redox state evolution in solution and solid phase during As(III) sorption onto chemically-treated sewage sludge digestate biochars

Keywords: Sewage sludge digestate biochar, As(III) removal, arsenic redox distribution, sorption

This work aimed to determine arsenic redox state distribution during As(III) sorption onto chemically-modified biochars. A solid-liquid extraction protocol using phosphoric (0.3 M) and ascorbic (0.5 M) acids at 80 °C for 20 min was established to ensure a quantitative recovery and stability of As(III) during the extraction. During sorption experiments, the redox conversions of As occurred and As(III) was either stable or partially oxidized in solution. The As distribution strongly varies depending on the biochar chemical treatment

Introduction

Elevated concentrations of arsenic (As) in water bodies represent a global environmental and health issue because of its toxic features. The increasing threats of As contamination mainly originate from anthropogenic sources, particularly mining, industrial and agricultural activities [START_REF] Vithanage | Interaction of arsenic with biochar in soil and water: A critical review[END_REF]. Arsenic toxicity in targeted organisms is strongly linked to its chemical speciation, especially its redox state. Indeed, organic forms of As such as monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) present intermediate toxicity, whereas inorganic As species, i.e. arsenite (As(III)) and arsenate (As(V)), are known as the most toxic ones [START_REF] Hughes | Arsenic exposure and toxicology: A historical perspective[END_REF].

Regarding the acute toxicity of As, efforts have been made to efficiently remove As from polluted water streams by using several treatment techniques such as oxidation, coagulation-flocculation, ion exchange, phytoremediation, membrane separation and adsorption [START_REF] Jadhav | Arsenic and fluoride contaminated groundwaters: A review of current technologies for contaminants removal[END_REF][START_REF] Jain | Technological options for the removal of arsenic with special reference to South East Asia[END_REF][START_REF] Singh | Arsenic contamination, consequences and remediation techniques: A review[END_REF]. Among these methods, sorption is well known as a cost effective approach to remediating metal(loid)s polluted water [START_REF] Ahmad | Biochar as a sorbent for contaminant management in soil and water: A review[END_REF]. Biochar is a charcoal obtained from pyrolysis of biowaste materials in an oxygen-limited environment [START_REF] Novotny | Biochar: Pyrogenic carbon for agricultural use -A critical review[END_REF]. Because of the low-cost and the great abundance of biowaste feedstocks (e.g. sewage sludge digestate obtained from wastewater treatment streams), biochars are considered as alternatively potential sorbents for metal(loid)s removal from water [START_REF] Mohan | Organic and inorganic contaminants removal from water with biochar, a renewable, low cost and sustainable adsorbent -A critical review[END_REF]. Most of the sewage sludge biochars were used to sorb cationic metals like lead (Pb(II)) and chromium (Cr(VI)) [START_REF] Ifthikar | Highly efficient lead distribution by magnetic sewage sludge biochar: Sorption mechanisms and bench applications[END_REF][START_REF] Lu | Relative distribution of Pb 2+ sorption mechanisms by sludge-derived biochar[END_REF]Zhang et al., 2013), and to a lesser extent to metalloids like arsenic (As) and antimony (Sb). Thus, the development of sewage sludge biochar with chemical modification to improve As sorption [START_REF] Sizmur | Biochar modification to enhance sorption of inorganics from water[END_REF] as well as the investigation of As speciation is of great interest. To date, As redox species repartition during the adsorption process onto biochar, and the role of biochar on redox modifications of As are not known. Hence, it is worthwhile to investigate the redox transformation of As(III) during its sorption onto biochars, since As(III) is more toxic and weakly bound to solid material than As(V) [START_REF] Manning | Arsenic(III) oxidation and arsenic(V) adsorption reactions on synthetic birnessite[END_REF]. Therefore, the As(III) oxidation induced by biochars is an important reaction that can possibly decrease As toxicity in As polluted water bodies. Arsenic speciation in solid-phase samples can be accessed via X-ray absorption near edge structure (XANES) spectroscopy (Niazi et al., 2018a(Niazi et al., , 2018b)). However, the use of this technique is limited due to the very high operation cost and the accessibility to synchrotron

Material and methods

Biochar production and chemical modification

Sewage sludge digestate (SSD) was collected from a wastewater treatment plant (WWTP) located in Limoges (France), after its dewatering and drying processes. Biochar was produced from the SSD sample under slow pyrolysis conditions (at 350 °C for 15 min) (Wongrod et al., 2018a). The SSD biochar (100 g) was then modified with a 1 L of 10% H 2 O 2 solution (modified from Xue et al., 2012) or with a 2.5 L of 2 M KOH solution (modified from [START_REF] Jin | Biochar pyrolytically produced from municipal solid wastes for aqueous As(V) removal: Adsorption property and its improvement with KOH activation[END_REF]. For each biochar modification, the mixed biochar-solution was continuously stirred at room temperature for 2 h.

Raw and modified biochars were further washed with ultrapure water (18.2 MΩ, MilliQ Gradient A10, Millipore SAS 67120, Molsheim, France) in a batch system (triplicate in a row) followed by a continuous column washing (Wongrod et al., 2018a). These washing steps were performed to eliminate releasable organic compounds and inorganic ions (i.e. PO 4

3-, HCO 3 -, CO

Biochar characterization

The pH of the biochar was measured using a pH-meter (LPH 330T, Tacussel, France) after stirring 1 g biochar in 20 mL deionized water for 5 min and allowed it to settle for 15 min.

The electrical conductivity (EC) of biochar was measured using a conductivity meter at 20 In all these experiments, samples were collected at 1, 3, 7, 16 and 24 h. The total sampled volume was less than 5% of the initial volume to avoid any disturbance on the sorption equilibrium. Solutions were filtered through a 0.2 µm PES syringe filter and stored in a dark cold room at 4 °C until analysis.

Arsenic redox state distribution in biochars

Total As and its redox state distribution in raw and chemically-modified biochars before and after As(III) sorption experiments were determined through solution analysis, extraction and acid digestion as described in the following subsections.

Arsenic analysis in solution and deduction of sorbed arsenic.

Total arsenic analysis was performed using graphite furnace atomic absorption spectrometry (GF-AAS) (240Z, Agilent Technologies, USA) at λ 193.7 nm. The standard calibrations of As were prepared in the ranges of 10-50 µg L -1 . The detection limit was estimated from the mean of the blank and standard deviation, and the analyte solution was measured to produce a signal of at least 3 times higher signal than the noise level.

The arsenic redox distribution was assessed by liquid chromatography coupled to atomic fluorescence spectroscopy (LC-AFS) with hydride generation (HG) (PS Analytical Millennium Excalibur, PS Analytical, UK). The chromatographic separation was performed using a Hamilton PRP-X100 column with a phosphate buffer solution as the mobile phase at pH 6.9 and at a flow rate of 1 mL min -1 . The details of the experimental conditions for speciation analysis can be found in a previous study reported by [START_REF] Wan | Distribution of As trapping along a ZVI/sand bed reactor[END_REF]. To avoid any transformation between As(III) and As(V), arsenic speciation on both liquid and extracted solutions was performed within 5 h after sample recovery.

The amount of As sorbed onto the biochar was calculated from differences between initial and final concentrations of arsenic during sorption experiments. The sorbed As onto biochar can be calculated following Equation ( 1):

( (1),
where Q sol. is the amount of arsenic sorbed onto biochar (µg) (based on 0.15 g of biochar in this study), C i and C f are, respectively, initial and final equilibrium concentrations of arsenic in the solution, and V is the total volume of the solution (L).

Extraction of As(III) and As(V) from biochar

Due to the lack of a soft extraction procedure for arsenic from biochar in the literature, this study designed one extraction method based on the extraction procedures described by The extraction was operated using microwave assistance (Multiwave GO, Anton Paar, France) by heating at 80 °C for 20 min. The resulting solution was then centrifuged (Multifuge X3 FR, Thermo Fisher Scientific) at 3400 rpm for 20 min. The supernatant was collected and filtered through a 0.2 µm PES syringe filter and diluted to a constant volume of 50 mL. Samples were analyzed for As speciation using LC-AFS as mentioned in section 2.4.1.

Biochar acid digestion for total arsenic measurements

After the sorption experiments, the biochar (about 0.15 g) was rinsed with ultrapure water and transferred into a digestion tube (Teflon). Concentrated nitric acid (HNO 3 , 69.5% w/w, Panreac ITW) (6 mL) was added to the digestion tube. Hydrogen peroxide (H 2 O 2 , 30%

w/w, Carlo ERBA) (6 mL) was then slowly added into the digestion tube with a caution regarding its strong oxidizing property. The digestion tube was left overnight (12 h) to oxidize and digest organic matter in biochar prior to a microwave acid digestion (in order to avoid over-pressure due to the high initial release of CO 2 ). Finally, 3 mL of concentrated hydrochloric acid (HCl, 37% w/w, VWR) were added before starting the digestion that was operated at 180 °C for 4 h (4 cycles) using a microwave digestion (1 cycle per 1 h) to sufficiently digest all biochar particles. After digestion, the resulting solution was recovered and the dilution in a 50 mL volume was made with ultrapure water. It was filtered through a 0.2 µm PES syringe filter before analysis. Total arsenic content was analyzed by GF-AAS as previously mentioned in section 2.4.1. Regarding the analysis of total arsenic in the biochars, the As content that is already present in each biochar (before sorption) was deduced from the sorbed As after the As(III) sorption experiments. This deduction was made to avoid errors in the experimental results.

Statistical analysis

The biochar characteristics and As(III) sorption experiments were carried out in triplicate.

Results are reported as the mean value followed by standard deviation. Constants for sorption parameters were obtained by the non-linear regression using Statistica software (v6.1, StatSoft). Statistical analysis of the experimental data was performed by the t-test with two-tailed distribution at a statistical significance level of p ≤ 0.01.

Results and discussion

Characterization of raw and chemically-modified biochars

The total As content in the raw and chemically-modified biochars is given in Table 1.

Results show a significant (p ≤ 0.01 decrease of the As content after treating the raw biochar with H 2 O 2 or KOH from 47 (± 1) µg g -1 for BSS to 29 (± 1) and 13 (± 1) µg g for BKOH bat to 13 (± 1) µg g -1 for BKOH, was found after the subsequent continuous column washing.

The pH values of all biochar suspensions are also provided in Table 1. The pH of BSS (6.4 ± 0.1) increased to 8.4 (± 0.1) and 10.1 (± 0.1) for BKOH and BKOH bat , respectively, whereas H 2 O 2 induced no significant change (p ≤ 0.01 on the pH suspension of biochar.

The electrical conductivity (EC) of biochar suspensions remained in similar ranges from 4.0 (± 0.1) to 4.1 (± 0.3) and 6.2 (± 0.5) µS cm -1 for BSS, BH 2 O 2 and BKOH, respectively.

However, a significantly higher EC value (324 ± 2 µS cm -1 ) for BKOH bat was found, compared to BKOH (Table 1). This highlights the ability of BKOH bat to release a relatively high amount of dissolved ions as previously reported by Wongrod et al. (2018a).

The pH PZC and zeta potential (at pH 5) values of the raw and chemically-modified biochars are given in Table The biochar properties reported in Table 1 highlight that the total As content, zeta potential and S BET are the key indicators that were significantly affected by the biochar treatment.

Due to its lower negative charge and its higher S BET , BKOH can potentially sorb more As compared to other biochars. Furthermore, the biochar washing procedure is an important parameter to be considered after the chemical treatment, since the biochar properties significantly change between BKOH and BKOH bat . showed the high potential oxidation of As(III) (up to 25%) induced by the dissolved organic matter from sugar beet tailing and Brazilian pepper derived biochars.

As redox state evolution during sorption kinetics by BKOH bat and its dissolved solutions

Extraction procedure for As redox state distribution in biochars

In order to assess the redox state distribution of As sorbed onto biochar by LC-AFS, it was first necessary to validate an extraction procedure that allows a quantitative As recovery without any conversion of As species, especially As(III) being oxidized to As(V).

The importance of adding ascorbic acid in the extraction solution to stabilize As(III) was assessed by applying the extraction procedure to a biochar sample with and without spiking with a known amount of As(III) just before performing the extraction step. In this study, the BKOH bat was selected due to its release of dissolved compounds and its ability to oxidize As(III) as previously reported by Wongrod et al. (2018aWongrod et al. ( , 2018b)).

Table 2 shows the recoveries of the arsenic species and total As after the extraction using H 3 PO 4 with or without addition of ascorbic acid onto the BKOH bat sample, and with and without As(III) spiking just before the extraction. Results show that all spiked arsenic was recovered by the extraction procedure. The results also highlight that when using only 0.3 M H 3 PO 4 , a significant amount of spiked As(III) was oxidized. Indeed, the addition of 12.5 µg of As(III) to the biochar before performing the extraction step resulted in an increase of 8.8 (± 0.7) µg and 3.5 (± 0.3) µg for As(III) and As(V), respectively. Thus, 29% of spiked As(III) was converted into As(V). In contrast, no oxidation of As(III) was observed during extraction with H 3 PO 4 and ascorbic acid: the difference between the As(III) amount before and after spiking is 12.6 (± 0.7) µg, which is in agreement with the amount of As(III) added (12.5 µg). Therefore, the addition of ascorbic acid is essential to ensure As(III) stability during the extraction step. The findings are also in agreement with the study of Xu et al.

(2015) who reported the efficiency of using both phosphoric and ascorbic acids as extracting agents to quantitatively recover As(III) and As(V) from fly ash.

To estimate the extraction yield of As sorbed onto the biochar after the As(III) sorption experiments, the biochars were recovered and submitted to both acid digestion and extraction procedures (see section 2.4). The corresponding results are presented in Table 3.

For BSS and BH 2 O 2 , the amount of total sorbed As was too low to allow an accurate determination after the acid digestion and/or extraction. As a result, no extraction yield was calculated. For BKOH bat , the total amount of sorbed As was quantitatively recovered by the extraction procedure. In the case of BKOH, most of the sorbed As was recovered but about one fourth could not be extracted under the applied conditions. This difference in the extraction efficiency may result from different sorption mechanisms of As from one biochar type to the other. Nevertheless, the majority of As could be extracted from the biochars and thus the identification of the As species in the extracted solutions gives the main As species sorbed onto the biochars.

Determination of As(III) and As(V) sorbed onto biochars

Different types of biochars were exposed in the solution containing an initial As(III) amount of 146 µg. After 24 h of As(III) sorption, the biochars were recovered and the exposure solutions were analyzed to determine the remaining amount of As and to assess its distribution between As(III) and As(V). The biochars were separately submitted to acid digestion for the determination of the total quantity of sorbed As and to the extraction for the assessment of the redox distribution of sorbed As. The amounts of As(III), As(V) and total As in the exposure solutions and sorbed onto the biochars (determined after acid digestion and extraction steps) are shown in Table 4.

Results showed that the total As (i.e. As(III) + As(V)) remaining in the final exposure solutions of BSS and BH 2 O 2 were not significantly different from the initial As(III), indicating that no As was sorbed onto these biochars. In contrast, As was removed from the exposure solutions by both BKOH and BKOH bat , corresponding to an As sorption efficiency of 67% and 50%, respectively. These results are in agreement with the sorption yield estimated with the amount of As quantified in the digestate-based biochars (Table 4).

The arsenic redox distribution in the final exposure solution shows almost no As(III) oxidation for both BSS and BH 2 O 2 as the final amount of As(III) remained the same as the initial As(III) amount (Table 4). For the KOH treated biochars, the assessment of the redox distribution only concerned the unsorbed As. In the case of BKOH, no significant oxidation of As(III) was observed, whereas for BKOH bat about 28% of the remaining As was oxidized to As(V) (Table 4). These findings are in agreement with a previous study from Wongrod et al. (2018b) with a large oxidation of As(III) in BKOH bat and a partial oxidation in BKOH during As(III) sorption. As previously discussed (Fig. 1a and1b), the majority of As(III) oxidation was induced by the biochar solid compounds.

Considering As(III) and As(V) extracted from the biochars after the sorption experiment, a similar distribution of the As species was found for BKOH and BKOH bat (Table 4). Arsenic was mainly sorbed as As(III) (90-92%) and only 8-10% was sorbed as As(V) onto the KOH biochars. In the case of BKOH, the redox distribution of As sorbed onto the biochar is quite similar to the distribution observed in the final exposure solution. However, for BKOH bat , the evolution of the As species in solution and on the biochar was different:

As(V) represents only 8% of the sorbed arsenic whereas it corresponds to 28% of the dissolved As(V) (Table 4). This suggests that the As(III) sorption onto the KOH biochar was favored compared to As(V) sorption. This finding is consistent with results previously reported by Wongrod et al. (2018b) when comparing As(III) and As(V) sorption onto such biochars. Another possible explanation would be that As(V) could be reduced into As(III)

during the sorption process, as observed by Niazi et al. (2018aNiazi et al. ( , 2018b) ) who studied the speciation of As onto wood and leaf derived biochars using the solid-phase XANES technique. Depending on the nature and chemical treatment applied to the biochar, it could also contain chemical functions that act as electron donors to facilitate the As reduction [START_REF] Choppala | Differential effect of biochar upon reduction-induced mobility and bioavailability of arsenate and chromate[END_REF].

Comparison of the two KOH biochars showed that the adsorption capabilities for As(III)

were quite similar for both the BKOH (410 µg g -1 ) and BKOH bat (385 µg g -1 ) at As(III) concentration ranges of 0-4000 µM (or 0-54 µg L -1 ) and the initial solution pH at 5.0.

Nevertheless, a much higher As(III) sorption was observed onto the Japanese oak wood derived biochar (3,890 µg g -1 ) (concentrations of 27-144 µg L -1 and at pH 7.0 ± 0.1) (Niazi et al., 2018b). This is probably due to different biochar properties between the SSDbased biochars and the Japanese oak wood biochar. For instance, the specific surface area was substantially lower with the KOH modified biochars from SSD (3.0-7.9 m 2 g -1 ) (Table 1) compared to the oak wood biochar (475 m 2 g -1 ) (

Conclusions

The extraction using phosphoric and ascorbic acids allowed recovering sorbed arsenic, while preserving As(III) oxidation state. Arsenic redox distribution could thus be assessed in both solid and liquid phases. Arsenic was mainly sorbed onto biochar as As(III) but during sorption, As(III) oxidation may occur over time. This oxidation, mainly induced by biochar solid compounds rather than by soluble compounds released from biochar, can strongly vary depending on the chemical treatment and efficiency of washing procedures applied to biochar after chemical treatment. The KOH modification efficiently improves the biochar sorption capacity but also promotes As(III) oxidation, especially with an incomplete washing. 1

Tables Table 1 a S BET refers to Brunauer-Emmett-Teller surface area of biochar.

b CEC refers to cation exchange capacity of biochar.

Note: all values reported are mean of triplicate followed by standard deviation, except pH PZC and zeta potential. As(III)+As(V)).

Biochar

b Value close to limit of quantification.

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  facilities. Solid-liquid extraction followed by separation techniques, for instance liquid chromatography (LC) coupled to spectrometric detection techniques such as atomic fluorescence spectroscopy (AFS) or inductively coupled plasma mass spectrometry (ICP-MS), could be an effective and more accessible technique to determine the As species sorbed onto the solid-phase samples. The present study focused on the determination of the inorganic As redox distribution in raw sewage sludge digestate (SSD) biochar and the H 2 O 2 and KOH modified biochars before and after As(III) sorption using an analytical approach based on a solid-liquid extraction. At present, no study has reported on the implementation of an extraction method to recover As(III) and As(V) from the solid-phase of biochar. An extraction method using phosphoric and ascorbic acids as extracting agents was thus investigated before studying the possibility of redox transformations of As(III) during sorption experiments onto the biochar. The main objectives of this work were to: (1) validate the extraction procedure for As(III) and As(V) speciation in the biochars; (2) investigate the sorption ability for As(III) by the raw and chemically-modified biochars; and (3) report on the redox conversions of arsenic during the sorption experiments.

  Thomas et al. (1997), Montperrus et al. (2002) and Zhang et al. (2015). The extractant was prepared from 0.3 M phosphoric acid (H 3 PO 4 , 85% w/w, Carlo ERBA) with or without the addition of 0.5 M ascorbic acid (99.5% w/w, Fluka). Ascorbic acid was used to prevent the oxidation of As(III) in the solution during the extraction (Xu et al., 2015).After the sorption experiments, 0.15 g of biochar was quickly rinsed 3 times with ultrapure water and transferred into a Teflon digestion tube with 25 mL of the extracting solution.

Fig. 1a shows

  Fig.1ashows the As redox state distribution in the solution during adsorption experiments for As(III) onto BKOH bat . The results demonstrate that while As was gradually sorbed onto BKOH bat (corresponding to the decrease of total As over time), the oxidation of As(III) to

Figure 1 .

 1 Figure 1. Arsenic redox distribution in solution during adsorption kinetics for As(III) by BKOH bat (a) and for the control with only released dissolved compounds (RDC) from BKOH bat (b).

FigureFig. 1 .

 1 Figure

  -1 , respectively, for BH 2 O 2 and BKOH. These reductions can be due to the ability of KOH to dissolve ash contents[START_REF] Lin | Water extractable organic carbon in untreated and chemical treated biochars[END_REF][START_REF] Liou | Characteristics of microporous/mesoporous carbons prepared from rice husk under base-and acid-treated conditions[END_REF][START_REF] Liu | Modification of bio-char derived from fast pyrolysis of biomass and its application in removal of tetracycline from aqueous solution[END_REF]) and H 2 O 2 to oxidize organic matter present in the solid phase of the biochars (Xue et al., 2012). As a result, the As bound to the biochar matrix could be chemically altered and thus the As contents were lower in the chemically-modified biochars compared to the raw biochar (Table1).Considering BKOH and BKOH bat , an almost 2 times decrease of As, from 23 (± 2) µg g -1

  1. Results showed similar pH PZC ranges (2.7-3.4) among the raw and modified biochars. Currently, there is still a lack of information regarding pH PZC of biochars reported in the literature. Nevertheless, these findings are consistent with previous studies from Qiu et al. (2009) who reported a pH PZC of 1.9 on straw biochar and Petrovic et al. (2016) with pH PZC values of 4.5 and 6.0, respectively, on grape pomace biochar and its KOH modified biochar. Moreover, the negative zeta potential values of the biochars implied that all biochars carried net negative charges at pH 5, particularly for the BH 2 O 2 (-16.5 mV) and BKOH bat (-17.1 mV). These negatively charges may hinder the sorption ability for arsenic oxyanions at pH 5.The BET surface area (S BET ) of all biochars is reported in Table1. The S BET was significantly improved by 7-20 times after H 2 O 2 or KOH modification of the biochar

	compared to the non-treated biochar. In this case, the S BET increased from 0.4 (± 0.1) (the
	raw biochar) to 5.7 (± 0.1) and 7.9 (± 0.1) m 2 g -1 for BH 2 O 2 and BKOH, respectively. This
	implies that H 2 O 2 and KOH induced higher porosity on the modified biochars, thus As
	sorption can be enhanced for these biochars (Mohan et al., 2014). These S BET results are in
	agreement with those reported for sewage sludge biochars (4.0-14.3 m 2 g -1 ) (Agrafioti et

[START_REF] Agrafioti | Biochar production by sewage sludge pyrolysis[END_REF] Yuan et al., 2015)

, but lower than biochar made from wood (475 m 2 g -1 )

(Niazi et al., 2018b)

. Nevertheless, they remain very low compared to activated carbon which displays specific surface area beyond 1000 m 2 g -1 in most cases (Gonzalez-Garcia, 2018) (e.g. 1215.0-1316.0 m 2 g -1 for activated carbon prepared from coal)

[START_REF] Gong | Adsorption of arsenic from micro-polluted water by an innovative coal-based mesoporous activated carbon in the presence of co-existing ions[END_REF]

.

The CEC values for all biochars are also given in Table

1

. Results demonstrate a similar CEC of the biochar after H 2 O 2 modification, i.e. from 2.0 (± 0.1) to 3.0 (± 0.1) cmol + kg -1 , whereas the CEC values were much higher (7-10 times) for BKOH (13.4 ± 0.1 cmol + kg -1 ) and BKOH bat (20.8 ± 0.1 cmol + kg -1 ) (Table

1

). Nevertheless, in the literature much higher CEC values are reported for wood and straw derived biochars, ranging from 45.7 to 483.4 cmol + kg -1

[START_REF] Ding | Removal of lead, copper, cadmium, zinc, and nickel from aqueous solutions by alkali-modified biochar: Batch and column tests[END_REF][START_REF] Jiang | Effect of crop-straw derived biochars on Pb(II) adsorption in two variable charge soils[END_REF]

.

  Niazi et al., 2018b).In the case of BH 2 O 2 , the amount of sorbed As being low, the results of the As redox distribution were less accurate and should thus be taken with caution. The percentage of

	As(V) sorbed onto the H 2 O 2 -modified biochar appears to be higher than into solution,
	highlighting a potential oxidation of As(III) during sorption. This phenomenon was also
	observed by Niazi et al. (2018a, 2018b), who suggested that redox active species present at
	the biochar surface such as NO 3	-or FeO(OH) could induce As(III) oxidation. Therefore,
	the presence of iron (Fe) (65 g kg -1 ) and manganese (Mn) (769 mg kg -1 ) on the SSD

biochar, that could be partially in metal oxide forms

(Wongrod et al., 2018a)

, could promote the redox transformation of As(III) to As(V) on metal oxides associated onto the biochars

[START_REF] Vithanage | Interaction of arsenic with biochar in soil and water: A critical review[END_REF]

. Such a phenomenon is also reported by several studies

[START_REF] Han | Oxidation of As(III) by MnO 2 in the absence and presence of Fe(II) under acidic conditions[END_REF][START_REF] Manning | Arsenic(III) oxidation and arsenic(V) adsorption reactions on synthetic birnessite[END_REF][START_REF] Wang | Manganese oxide-modified biochars: Preparation, characterization, and sorption of arsenate and lead[END_REF]

.

Table and figure legendsTable 1 .

 1 pH, electrical conductivity and surface area of the raw and chemically-modified biochars.

Table 2 .

 2 Arsenic speciation stability using H 3 PO 4 with or without ascorbic acid (BKOH bat sample, with and without As(III) spiking just before extraction).

Table 3 .

 3 Comparison of total amount of sorbed arsenic determined after acid digestion or extraction procedure.

Table 4 .

 4 Comparison of As speciation and total As in exposure solutions and sorbed onto biochars (initial As(III) amount in exposure solution: 146 µg).

Table 2

 2

	Extraction method		Extracted arsenic (µg)	Spiking recovery a (%)
			As(III)	As(V)	As(III)	Total As
	No ascorbic acid	Before As(III) spiking	0.3 b ± 0.1	1.1 ± 0.1	-	-
		After As(III) spiking	9.1 ± 0.7	4.6 ± 0.3	71	99
		(12.5 µg)
	With ascorbic acid	Before As(III) spiking	0.4 b ± 0.1	0.8 b ± 0.1	-	-
		After As(III) spiking	13.0 ± 0.7	0.8 b ± 0.1	101	101
		(12.5 µg)

a Recovery: amount of spiked As(III) recovered by extraction either as As(III) or total arsenic (i.e.

Table 3 a

 3 na refers to not available due to very low values detected by liquid chromatography coupled to atomic fluorescence spectroscopy (LC-AFS) and/or graphite furnace atomic absorption spectrometry (GF-AAS).

	Biochar	Total arsenic (µg)		Recovery from extraction (%)
		Extraction	Acid digestion
	BSS	0.2 ± 1	1 ± 1	na a
	BH 2 O 2	3 ± 1	6 ± 1	na
	BKOH	70 ± 3	93 ± 3	75 ± 4
	BKOH bat	63 ± 4	60 ± 3	105 ± 9

Table 4

 4

	Biochar	Exposure solution			Sorbed As onto biochar
		Initial	Final			Acid digestion	Extraction
		As(III)	As(III)+	As(III)	As(V)	Total	Sorption	As(III)+	As(III)	As(V)
		(µg)	As(V)	(%)	(%)	As	yield (%)	As(V)	(%)	(%)
			(µg)			(µg)		(µg)
	BSS	146	145 ± 2	99	1	1 ± 1	<1	0.2 ± 1	na a	na
	BH 2 O 2	146	143 ± 3	96	4	6 ± 1	4	3 ± 1	76	24
	BKOH	146	48 ± 3	98	2	93 ± 3 64	70 ± 3	90	10
	BKOH bat 146	72 ± 5	72	28	60 ± 3 41	63 ± 4	92	8

a na refers to not available due a value close to limit of quantification.

Acknowledgments

Patrice Fondanèche (Université de Limoges, France) is acknowledged for technical assistance with arsenic analysis. This research work was economically supported by the Marie Sklodowska-Curie European Joint Doctorate in Advanced Biological Waste-to-Energy (ABWET) under the European Union's Horizon 2020 framework [grant agreement N° 643071].

Conflict of interest

The authors declare no conflict of interest.