Non-parametric method

This chapter presents ^II rev1c,v of the thcorcticnl con1cx1 \\'1th1n ,,h,ch the stud) ,vns cnrried out. II provides information as regards the origin and nature of the

mcu11loid, its sources, its chemistry and geo-chem,str), the health effects of arsenic poisoning as well os n rcvic\\ of methodological aspects of arsenic 1nvestigotion

Allcn1p1 was also made to provide nvailoblc relevant tnforrnotion os rcgnrds hydro·

geological infom1a1ion of each of the bos,n into "hich the study locauons belong

2.1. Sou ^{recs n} nd occu ^rrcncc or ^{n rscnic}

2.1.1. Ori�in nnd Nniurc or Arsenic

1 lumnn 1;xposurc to n1ctols dates b"ck 10 38008(' \\'llh the use of mercury, arsenic and siher I 111h: ,vas ho,,·e,·er kno,vn as regards 1he1r potential d ^an ger, but the current pic1ure or human exposure 1s one 1n "hich not onl ^{) 1111\} c the)' been dispersed into our env1ronmen1, but o1so the variet} of metals lo ,vtuch man is occupationally and ulhmntel) cnvironmentall) exposed is also incrc11sing (Clurkson, 1995) Heavy metals and their salts including I lgCI and NuAsO, h.1vc become one of n1nn) contan11nan1S found in the environment nnd ore l..no,,11 nephro1oxican1s.

Arsenic is dcri,ed from 'al"\enikon' a Greek ,vord for ·potent' (C,rJeme and Pollack , 1998). Arsenic is a metul, likc substance (n1ctnlloid, semi-metal) found in 5m11II 111noun1� in nutun.:. It can bi: grouped ,,i1h clemcnis like lithi ^um cbro1niu111, Ouoridc:, boron, and aluminiu,n which are commonly lbund in most organic mnucrs in lrocc runounts 11nd exhibit binlogic;il nc1ivi1y but \\hich cnn also be to,,c \\ilh high

cxpo5urc (Gochfold 1111d Goldsh:111, 1999) rt1c clcn,cnt 1s �,c:cl yre), ^\C:I) briule, cry Mnllinc, scmi,mcllilhc solid, \\l11d1 ^I 1r111shcs 111 ulr (D,I\ 1s ,Uld Reich, I '>94).

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Arsenic is a naturally occurring clement that has been recognized as a human poison since ancient times (Osbaldo, 1995). It occurs naturally in the earth's crust and in seas (USE.PA, 2002: WHO, 2006) fhc clement occurs naturally in rock. soil, \\'liter.

air and in plants and animals (USEP1\, 2002: \\'110, 2006) as \\ell n s 1n sediments in fonn of large numbers of minerals including arsenic of copper, lead, gold, or ns the sulphide. IL is a natural component of bedrock ¹ n areas \Vlth granite and is somet1n1cs found in drinking \\'Uter at levels high enough to raise concern for human health. II is ,videly distributed and forms ^5x Io· ^{1 %} of the earth crust (Lenihan and Flecther. 1997;

Lchnnno and Alfi than, 1998). II is one of the 189 elements that hove been idenulied os pollutants of special concern and arc being regulated b) Clean Air Act,(CAA) 1970

and the amendments of 1990 (Chappel and 1\bcmath ₎ , 1994) In addition to lh1s, the clement top the list of 126 toxic \Wier pollutants being n1onitorcd ^b) the 1977 Clean

\Voter Act ^(C\VA) (Gorb), ^I 990) and listed an1ong the top ^IO 1nos ¹ commonly found hllZllfdous chemicals in the USA (Marquitn, 1997, USEPA, 2002),

Arsenic content of the eru1h crust is 1,5-2.0nig/kg (\VJ-10, 1981 ). It ranks 20 ^th in abundance in relation to other clements and an: found in their oxidized fom1s ¹ n sedimentary deposits. :,,,1njor arsenic containing mincmls arc nrserop) rite (FcAsS);

rcalgor (As�s�) Wld orpimcnt (As2S,) (\VI 10. 1981 ). 1'-hncraliscd 1.oncs of sulplud ¹ c ores may contain much higher concentration of an;cnic. It 1s believed that higher levels occur

1n son1c coals. Unconta1n ¹ nulcd soil \\Us round to contain levels bctv,ecn 0.2 �Omg,'kg

\\hile arsenic treated soil may contain up to ^SSOmg/kg. Contnn1inntcd soil contains highe ^r concentration of1he element (\VHO, 1981 ).

2.1.2. Occurrence of Arsenic

Arsenic is n \\'idcly distributed clement present in vonous compounds throughout the earth's crust. II 1s mainly transponcd 1n the cnv1ronn1cnt by \\Utcr.

Arsenic is pn:�ent 1n soil ot levels mng1ni• fron1 0.2 to 40 µg-' kg, in urban oi ^r ot le\ els around 0.02 µg/m ³ nnd in \\illcr at level$ ovcra1i1ng around 0.00 I nip., I in lhc Un1tt:d 51at� ^(IARC 1980) The general popul;11ion i s ei.poscd to inol'Ranic ,ind organic U11>Cnic 1hrou11h ntcthdnill, cnvnonmcninl, and occupational situ,1 ¹ 1on� Oru�. con1nin1ng ino ^r 1:.1anic 11r,cn1c huvc bcc:n used fo ^r the: trc:,llmcnt of lcukc,miu, p,ona\l., and chronic

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AFRICAN DIGITAL HEALTH REPOSITORY PROJECT

bronchial asthma and as a home remed}. Both inorganic nnd organic arsenic are present in varying amounts in food. Seafood, for example, contains relative!) high concentrations of organic arsenic. Ho,vcvcr, inorganic forms of arsenic arc much more toxic than organic forms. Cigarcllc smokers may be exposed to an;enic in tobacco, but the chemical form of arsenic 1n smoke remains unclear \Vorkcrs involved in the processing of copper, gold, and lead ores; 1n the use of arsenic as p1gn1cnts and dye, 1n

the production nnd use of agricultural pesticides: in the manufacturing of glass and various phnrmnccutical substances; und in the chimnc} S\\'Ctp1ng business may h:I\ e a

high exposure to arsenic, I lo,vevcr, for the general population, the ,nnin ex1>0s11re to inorganic arsenic is through ingestion of high-arsenic drinking ,, ntcr (\\ 110, I 981, Nriugu, 1994a).

Skerfving et al ( I 999) n:vic,\fed the conccntmtion or arsenic nlongs1dc that of similar metals 1n the Bollie region and concluded 1lu1t \\hilc populnllon hod levels of lead and cadmium in sufficient amount likely 10 cause ill health, the level of arsenic ,vns generally lo,v CVCl)"\'hcrc in the 13alt1c region Robinson (2000) observed that higher

levels of arsenic hos been found in ground\\ater supplies 111 some plnccs of Bangladesh in the region of 10 10 40 times higher than the �la-.1mum Permissible Le,cl (MPI.)

Being pnmnrily of natural origin ur.;cn1c nlU)' be n sign11icun1 cons11tuen1 even 1n areas in ,vhich induslrinl or other polluuon is e11:tremely limited. It occurs bo� ¹ from nulurnl sources os wi:11 ^ilS from human activity (USEPA, 2002) •\ccording to I.Jhem10 el al ( 1998), the most important source of arsenic is nrscnopyrite (FeAsS) and thus it is high ^Ill nri:as of increasing sulphide mincralizolion ofien 1n connection \\ith occurrences of n1nlic rocks such ns gabbros, nmphibohtcs and pcndotites. ^1\II rock ^I) pcs have been said 10 contain As in vnrJ1ng quo.nlilics. Block shales has been clo1mcd 10 contain about IOOppnl of ·\s while sandstones contain lc�ser ( I.Oppm) nnd igneous. limestone nnd

�hale containing I .8ppm, 2 Sppn1 und I Sppm rcspcctlvel) (Users. ^JOOJ) \\'c:11hcrcd materials from such rocks ^\\Ill therefore contmn much higher levels than other rock

I} pcs as well as subsequent groundw111cr that come in contncl ,vith it

Arsenic can be further relc,1scd into the c:11v1ronmllnl thn1ugh 11.11uml ncti\ itics such us \'Olcaruc action, erosion of rock., soil, l11�M lire� und other hu1n1111 ,1c1 ¹ ons

According to L SGS ( 1999), noturolly occurrini: ,\s b co11 ¹ 1nnnl) lountl 111 volc,1n1c

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glass of rhyolitic to intcnnediate composiiion; adsorbed to nnd co prccipita1ed \\ ith rnetal oxides, especially iron oxides; adsorbed lo clay-mineral surfaces; and associated

\Vith sulphide minerals and organic carbon. In some countries, parucularly in the USA, about 90% of industrial nrscnic is currently used os a wood prcscrvauve {Kwon cl nl.

2004). Apart from this ^it also finds its \\'DY into the environment through arsenic based paints. n1etnls. dn1gs, soaps and semi-conductors.

Other in1portant contribuling sources of arsenic ¹⁰ the cnvirorunenl arc ognculturaJ applications, n1ining and sn1elting. Industrial effiuents also contribute arsenic to ,v.iter

1n some arcns.

Inorganic arsenic predominates in environmental media that is in soil, ,,111cr nnd air and also 1n co1111ncrcial uses and has bl!cn disco,ercd to bt: more toxic than the organic especially in solution (Bcnromdonc, 1999). II rs still a dangerous polluung agent for industrial \\'Orkcrs i1nd people living ,n the vic,nll} of en1ission sources (Benromdnne ( 1999) Arsenic is found ,v,dely 1n surfnce and ground,vutcr 1n mnn) parts

of the ,vorld (Nriagu. 1994b).

Arsenic 1s n ,vc:ll-docun1en1ed drinking ,,·ater problem due to ^its ubiquity in the earth crust. In spite of its significance as ^a problem, �lcArthur, Rnvenscron. Safiullo and lhirhvall ⁽²⁰⁰ I) posited that n1orc studies would bl! required to investigate its mobility and fotc 1n \\'Iller.;. I hgh As ground,v:itcr has been said (Finkelman. I 999, l\,lcArtln1r ct al ²⁰⁰¹⁾ to 1yp1call) contnin lo,vcst iron conccntmlions suggesting that simple mobilization from f·e-oxyhydroxidcs 1s not the n1ain As source ^It hos been hypothesized b) l'vtccall and lus group that ,\s is liberated to ground ^\\ atcr from oxidah\'c dissolution of 1\s-bl!aring p)'rilc 1n rclutivcly fresh gluciol dn n ^{It 1s found}

locnliud from aquifers interspersed with thick grey cln) layers. I he natural

concentrations of urscnic 1n 1hc soil rnngc from ^0.1 10 -IOml!lkg ,v11h on O\crogc

concentration of 5-6 mg/kg (Scott, 2000; USFPA, 2000). I hrough erosion. dissolu11on

and \\C:Ulhcring. urscnu: can � released to groundwater and surfncc ,,oter wlulc

gc:othcm1ill ,,utc:rs could aho he: sources of nrscn1c pollution of ground ,vntcrs (Users,