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ORGANI C CHEMISTR

Y OF LEA

D I N NATURA L WATE RSYSTEMS

By R . L . WERSHA W

I Natura l soil-wate r an dsediment-wate r

system s ar e extremel y complex , consistin g of amyria dof

interactin g organi c an dinorgani c components

. I n thi s sectio n w e shal l b e concerne dwid i tine interactio n of on e of th e inorgani c components , lead , wit hth e organi c component s of

thes e systems

. Th e organi c component s of asoil-wate r

syste mar e a n extremel y divers e grou p o f compound s (Saxby , 1969) , includin g carbohydrates , amin o acids , phenoli c an d quinoni c compounds , organi c acids , nuclei c acids , enzymes , porphyrin s an dothe r heterocycli c compounds , lipids , terpinoids , an dhumi c materials

. (See Saxby , 1969 ; Spakho v an dSpakhova , 1970 ; Greave s an dWilson , 1969 ; Kowalenk o an dMcKercher , 1971 ; Ivarso n an dSowden , 1969 ; an dKononova , 1966 , fo r mor e complet e discussion s o f th e organi c compound s i n soils. ) I n additio n t o th e natura l organi c compound s presen t i n soil , stream s an dlake s contai n organi c sediment s an d suspende dsolid s tha t

hav e bee n derive dfro mmunicipal , agricultural , an dindustria l wastes

. Thes e waste s ar e mad e u p of carbohydrates , proteins , nuclei c acids , enzymes , lipids , an dman y of

th e othe r organi c compound s of

livin g systems

. Oils , plasticizers , polymers , an da n enormou s numbe r of ome r organi c compound s ar e discharge dt o natura l waterway s b y manufacturin g an dchemica l industries

. Th e interactio n of

lea dwit hth e organi c component s of soil-wate r

an dsediment-wate r

system s i s stil l no t

wel l understood , bu t

w e shal l revie w th e wor k tha t ha s bee n don e an dattemp t

t o dra w wha t

conclusion s w e ca n fro m th e dat aavailable

. A numbe r

o f studie s hav e show n tha t di e organi c matte r of soil s an dstrea msediment s apparentl y bind s metal s an d reduce s fJiei

r mobility

. However , a s Mortense n (1963 ) ha s pointe dout , althoug hman y worker s hav e suggeste dtha t soi l organi c matte r

form s complexe s wit hmetals , an dtha t thes e complexe s ar e importan t i n soi l formatio n an dplan t nutrition , th e evidenc e fo r existenc e of

metal-soi l organi c matte r complexe s i n natur e i s largel y circumstantial

. Althoug harelativel y larg e numbe r of publication s ar e availabl e o n th e interactio n of metal s wiri i organi c material s of

soil s an dwater s (se e Mortensen , 1963 ; Saxby , 1969) , ver y fe w of th e paper s hav e deal t

wit hinteraction s o f lea dan dorgani c material , an dof these , mos t

hav e bee n concerne dwit hlea di n soil-wate r systems ; ther e ar e very fe w o n th e interactio n of

lea dwit horgani c material s i n stream s an dlakes

. SURFAC E WATER-SEDIMEN T SYSTEM S Herri g (1969 ) an dHellma n (1970a , b , 1971 ) hav e studie d th e heav y metal s i n di e water s an dsediment s o f th e Rhin e Rive r an dit s tributaries

. Herri g foun dtha t bot hinorgani c an dorgani c lea dcompound s wer e bein g introduce dint o river s a s industria l an dmunicipa l wastes ; th e mos t commo n of

thes e wer e lea doxide , metalli c lead , lea d stearate , lea dpalmitat e an dtetraediy l lead

. Muc hof thi s lea dwa s concentrate di n di e suspende dan dbotto msedi

ment s of hig horgani c content

. Th e sediment s wer e mor e effectiv e i n removin g lea dtha n i n removin g coppe r o r zin c (Hellman , 1970a)

. Th e sediment s of

di e lowe r

Rhin e containe dabou t 1 0 time s th e amoun t

of heav y metal s foun di n thos e of th e uppe r Rhin e an dit s tributaries

. Lea dconcentration s a s hig ha s 0. 2 percen t

wer e foun di n som e o f

th e sediments ; hig hheavy-meta l concentration s i n th e sediment s wer e associate dwit hhig hconcentration s i n th e river water

. Th e hig hconcentration s ar e order s of magnitud e highe r tha n di e natura l backgroun dlevel s an dca n onl y b e du e t o municipa l an dindustria l pollution

. Th e hig h concentratio n of

lea di n sewag e sludg e indicate s tha t municipa l wast e ca n b e amajo r contributo r

o f lea d pollutio n i n som e stream s (Gross , 1970)

. Eve n dioug hdi e sediment s remov e larg e quantitie s of heav y metal s fro m th e wate r o f rivers, die y ar e stil l no t efficien t enoug ht o totall y decontaminat e di e water , an dtherefor e th e rive r wate r ofte n contain s hig hheavy-meta l concentrations

. Hellma n (1970a) measure dlea dconcentration s i n di e wate r a s hig ha s 8 5 ns^h an ^ di e averag e fo r di e lengt ho f di e Rhin e rive r

wa s 5 1 /tg/1

. Th e lea di n di e organi c component s of asedimen t

enter s di e sedimen t

fromtw o sources : (1 ) Th e plan t an danima l remain s tha t

provid e di e organi c compound s t o di e sediment , an d(2 ) th e wate r tha t come s int o contac t

wit h di e sediment

. Th e chelatio n of lea db y di e chemica l component s of

livin g organism s tend s t o caus e lea dt o accumulat e i n livin g tissu e (MacLea n an dodiers , 1969 ;
1 3P. 3

1 4 LEA D IN TH E ENVIRONMEN T Danielson , 1970 ; Bryce-Smith , 1971)

. Thi s accumulatio n of lea di s n o doub t

amajo r sourc e of

lea di n organi c sediments

. However , bot hth e orgarai c an dinorgani c component s of

sediment s wil l als o remov e lea dfro m water

. Therefore , a s ha s bee n pointe dou t b y Hellma n (1970a) , organi c sediment s wil l ten dt o decontaminat e surfac e water s contaminate dwit hlea dan dothe r heav y metals

. However , on e mus t als o remembe r

tha t sediment s wil l ten dt o suppl y lea dt o water s wid i lo w lea d concentration s i n orde r t o maintai n chemica l equilibrium

. Therefore , eve n i f th e lea dpollutio n of

a surfac e wate r

wer e t o ceas e immediately , th e sediment s woul dcontinu e t o suppl y lea dt o di e wate r an dt o it s faun a an dflora

. CHEMISTRY O F TH E INTERACTION S Saxb y (1969 ) ha s reviewe ddi e literatur e o f metal

organi c chemistr y i n th e geochemica l cycle

. H e foun dtha t lea dha s bee n detecte di n th e carbonaceou s fraction s of soils , coals , petroleum , bituminou s rock s an dasphalts , shales , sedimentar y sulfides , an dphosphat e rocks

. I n general , however , ver

y littl e i s know n abou t

th e molecula r association s of

metal s i n geologica l materials

. Therefore , i n ou r discussio n w e shal l hav e t o dra w heavil y upo n studie s tha t

hav e bee n mad e o n syntheti c organi c system s an dmedicall y importan t biologica l systems ; however , th e genera l chemica l principle s elucidate di n thes e studie s shoul dals o hol dtru e for natura l soil-wate r

systems

. Tw o differen t

type s o f organi c lea dcompound s ma y b e foun di n nature : (1 ) th e so-calle dorgan©-lea dcompounds , i n whic hdi e lea di s covalentl y bonde dt o carbo n atom s an dth e meta l complexes , an d(2 ) chelates , i n whic hth e lea di s ionicall y bonde dt o organi c ligands

. Lea dnormall y exhibit s bod i divalen t an dtetravalen t state s i n organi c compounds

. Whe n lea di s covalentl y bonde dt o carbo n i t

i s generall y mor e stabl e i n th e tetravalen t

state ; relativel y stabl e divalen t lea dderivative s ar e known , however

. (Se e Shapir o an dFrey , 1968 , for a mor e complet e discussio n of lea dbendin g i n organi c compounds. ) Covalentl y bonde dorgano-lea dcompound s i n natura l system s underg o slo w oxidatio n b y ai r an dphotolysi s whe n expose dt o light

. Mos t of dies e compound s excep t thos e i n whic hdi e lead-carbo n bond s ar e highl y polar , suc ha s th e perfluoroalky l lea dcompound s an dRjPb X an dRjPb X compound s i n whic hX i s a n anion , ar e no t hydrolyze db y water

. I n coordinatio n compounds , suc ha s meta l complexe s an dchelates , ioni c lea di s normall y divalent ; however , organo-lea dcation s i n whic hth e lea di s tetravalen t

ma y als o b e complexe db y organi c ligands

. Mos t of di e detaile dstudie s o n di e eomplexin g of lea d an dothe r metal s by organi c ligand s hav e bee n conducte d by biochemist s o n th e component s of livin g systems ; th e sam e ligand s howeve r

ar e presen t

i n di e organi c materia l o f soils , natura l waters , an dsewag e effluents

. Lea di s generall y mos t strongl y boun dt o sulfur containin g ligand s an dt o phosphory l group s (Passow , 1970) , bu t

i t als o form s coordinatio n bond s wit hothe r ligands

. Valle e an dWacke r

(1970 ) hav e reviewe dth e chemistry of metalloprotein s an dhav e pointe dou t tha t leadinteract s wit hprotein s an denzyme s b y bindin g t o carboxy l group s o r sulfhydry l groups
. Th e bindin g of lea dan dothe r

heavy metal s t o awid e variet y of enzyme s inhibit s th e activity o f th e enzyme s (Morro w an dothers , 1969 ; Hernber g an d .Nikkanen , 1970 ; Valle e an dWacker , 1970)

. L i an d Mannin g (1955 ) hav e demonstrate ddiat , i n general , lea d form s mor e stabl e complexe s wit hprotein s tha n d o cadmium , zinc , o r

copper
. Th e bindin g o

f lea dt o enzyme s an dth e consequen t inhibitio n of

enzymati c activit y wil l undoubtabl y affec t di e biologica l reaction s tha t tak e plac e i n streams , soils , an dsewag e treatmen t

facilities , bu t

unfortunatel y there ar e ver y fe w dat ao n di e interaction s o f lea dwit hsoi l an d wate r biochemica l systems

. However , th e poisonin g o f enzym e system s i n natura l water s b y heav y metal s can be expecte dt o drasticall y alte r th e rate s o

f decompositio n o

f organi c waste s i n thes e systems

. Heavy-meta l cation s ma y no t alway s ac t

a s enzyme poison s i n soi l systems

. Lad dan dButle r (1970 ) hav e show n tha t

divalen t cation s ar e effectiv e i n reducin g th e inhibitio n of

th e enzym e proteas e by humi c acid

. It appear s tha t

di e humi c aci dbind s t o th e enzyme , thereb y preventin g i t

fro mcombinin g wit hsubstrate

. I f meta l cation s ar e presen t

i n th e system , activ e site s o n th e humi c aci dwil l apparentl y preferentiall y bin dt o th e cation s an d b e unavailabl e fo r

bindin g th e enzyme
. Lea dals o interact s wid i polynucleotide s an dviruses

. Lea dion s wil l caus e th e depolymerizatio n o

f som e polynucleotide s suc ha s ribonuclei c aci d(RNA ) (Farkas , 1968 ) an d deoxyribonuclei c aci d(Eichhorn , 1962 ; Izat t an dothers , 1971)

. I n th e depolymerizatio n of RN A i t appear s tha t

th e lea dbind s di e phosphat e groups
. Thi s neutralize s th e charg e o n th e phosphat e group s an drender s th e phos

phodieste r

bond s mor e susceptibl e t o hydrolysi s b y hydroxy l group s (Farkas , 1968)

. I n di e bindin g of lea dt o tobacc o mosai c viru s molecule s th e lea dma y displac e proton s o

f th e hydroxy l group s (Fraenkel-Conrat , 1965)

. I n a amin o acids , i n mor e comple x molecule s con
tainin g a amin o acids , an di n molecule s simila r t o 8

- hydroxyquinolin e an dquinolin e acid , lea dan dman y odie r metal s formfive-membere dchelat e ring s wit h reactiv e ligands

. Charle s an dFreise r (1952) , i n thei r

work o n five-membere dchelat e rings , hav e measure dth e stabilit y constant s of

lea dchelate s of

o-aminopheno l an d o-aminobenzenediiol

. Thei r dat aindicat e tha t

theordero f decreasin g stabilit y for

meta l o-aminopheno l i s a s follows : Cu , Ni , Zn , Co , Pb ; for

o-aminobenzenethiol , however , th e orde r i s Cu , Ni , Pb , Zn , Co

. Lea dform s mor e stabl e complexe s wit ho-aminobenzenethio l dia n wit ho
-P. 4

ORGANI C CHEMISTRY O F LEA D I N WATE R 1 5

*

h aminophenol , apparentl y becaus e th e lead-sulfu r bon di s stronge r dia n th e lead-oxyge n bond

. Othe r group s of

compound s suc ha s carbohydrates , carboxyli c acids , lipids , phenols , an doxygenate d isoprenoid s tha t

hav e electro n dono r

ligand s simila r

t o thos e of th e protein s mentione dabov e woul dals o b e expecte dt o comple x lead

. I n thi s regar dHoogevee n (1970 ) ha s demonstrate dtha t

lea di s boun db y phospholipids

. Martin , Ervin , an dShepher d(1966 ) an dMarti n an d Richard s (1969 ) hav e show n tha t copper , zinc , iron , an d aluminu mformcomplexe s wit hsoi l polysaccharides

. Thes e metal-polysaccharid e complexe s ar e generall y mor e resistan t t o decompositio n i n soil s tha n ar e uncomplexe d polysaccharides

. Althoug hther e ar e n o experimenta l dat a o n lead-polysaccharid e complexe s i n soil , on e woul d expec t the mt o hav e propertie s simila r t o thos e of

othe r heavy-meta l polysaccharid e complexes

. I t i s wel l establishe dtha t

soi l humi c material s suc ha s humi c aci dan dfulvi c aci dfor mcomplexe s wit hmetal s (Kononova , 1966)

. Aleksandrov a(1967 ) ha s classifie dth e interaction s of

metal s wit hhumi c material s int o thre e categories : (1 ) Formatio n of heteropola r

salt s (a n io n exchang e phenomeno n betwee n stron g base s an dhumi c materials) , (2 ) formatio n of coordinatio n complexes , (3 ) formatio n of

adsorptio n complexe s wit hnonsilicat e sesquioxide s (adsorptio n o f humu s o n sesquioxid e gels)

. Mos t of di e interaction s of

lea dwit hhumi c material s tha t hav e bee n studie dfal l unde r th e secon dcategory

. Humi c acid s an dfulvi c acid s for mstabl e complexe s wit hlea d(II ) ion s an dothe r meta l ions ; thes e complexe s may b e separate dfro mamixtur e o f humi c aci do r

fulvi c aci dmeta l complexe s b y ge l permeatio n chromatograph y (Muck e an dKleist , 1965 ; Klbckin g an dMiicke , 1969)

. Therefore , i t

shoul db e possibl e t o isolat e intact , humic

meta l complexe s fro msoil s an dsediments

. Bondarenk o (1968 ) foun ddia t th e presenc e of

fulvi c aci d i n wate r increase ddi e rat e of

solutio n of

lea dsulfid e 10-6 0 time s ove r

awate r solutio n a t

th e sam e p H tha t

di dno t contai n fulvi c acid

. At

p H value s nea r

7 , solubl e lead

fulvi c aci dcomplexe s were presen t i n solution ; a t

initia l p H value s betwee n 7. 4 an dabou t 9 , di e lead-fulvi c complexe s partiall y decomposed , an dlea dhydroxid e an d carbonat e wer e precipitated

. At initia l p H value s of

abou t 10 , th e amoun t

of lead-fulvi c aci dcomplexe s agai n increased

. Bondarenk o (1968 ) attribute ddii s increas e t o dissociatio n of

phenoli c group s a t

hig hp H values , a phenomeno n whic hincrease s di e complexin g capacit y o f di e fulvi c acid

. I n additio n t o interaction s i n whic halea dio n i s boun d by asingl e organi c molecule , asingl e meta l io n ca n b e boun db y tw o differen t

organi c molecules

. I t

ha s bee n demonstrated , for

example , tha t

polyvalen t

cation s ac t

a s bridge s betwee n clay mineral s an dhumi c an dfulvi c acid s (Greenland , 1971)

. SUMMARY AN D CONCULSION S Th e complexin g o

f lea dby mos t

of th e commo n sulfur- , phosphorus- , oxygen
- an dnitrogen-containin g ligand s mean s tha t

lea dwil l accumulat e i n bot hth e livin g an d nonlivin g organi c component s of soil-wate r

an d sediment-wate r

systems

. Th e livin g an dnon-livin g organi c component s ar e no t independen t

of eac hother , bu t ar e constantl y interacting , a s th e livin g component s metaboliz e di e nonlivin g component s of th e syste man d the n die , contributin g thei r remain s t o th e poo l o f

non
livin g compound s i n th e system

. Som e o f th e lowe r

form s of lif e ar e consume di n th e proces s b y th e highe r form s o f lif e an di n dii s way chemica l element s fro mth e sediment s ar e introduce dint o th e foo dchai n of th e system ; thi s foo d chai n ofte n end s wit hman
. Th e fate of heav y metal s i n thi s proces s ha s no t

bee n elucidated ; however , th e sedimen t i n acontaminate dsurface-wate r bod y wil l serv e a s alarg e reservoi r whic hca n provid e lea dan dothe r metal s t o th e biot aof di e syste meve n afte r

heav y meta l pollutant s hav e cease dt o b e introduce dint o th e system

. Unfortunately , i n th e cas e o f

heav y metals , muc hmor e attentio n ha s bee n pai dt o heav y metal s dissolve di n th e wate r phas e o f surfac e wate r tha n t o di e complexe dmetal s i n th e sedimen t phas e which , i n general , probabl y contai n aconsiderabl y highe r amoun t of metal s tha n th e water

. Th e sediment s wil l als o ac t a s areservoi r

fo r providin g dissolve dheav y metal s t o th e wate r whe n contaminatio n level s ar e low

. Hig hconcentration s of

lea di n soil s an dsediment s wil l hav e amarke deffect

upo n enzym e systems , actin g i n som e instance s t o reduc e inhibitio n b y othe r component s o f

th e systems

. Th e alteratio n of th e activit y of

som e of th e mos t basi c component s of

livin g system s i s certai n t o hav e a profoun deffect

upo n th e biologica l an dchemica l pro
cesse s takin g plac e i n natura l systems

.

ACKNOWLEDGMEN T Thi s wor k

coul dno t

hav e bee n complete dwithou t th e diligen t effort s of

Mis s Sara hBooke r

wh o di dmos t

of th e literatur e search

.

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# rm>immmP* mmmm 

# ' mimmmmmmmmmm IPPP WP. 5

1 6 LEA D I N TH E ENVIRONMEN T
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