### Biologic a l Report 85(1.5) Contaminant Hazard Reviews October 1985 Report No. 5



## SELENIUM HAZARDS TO FISH, WI LDLIFE, AND I N VERTEBRATES: A SYNO PTIC REVIEW

By

Ronald Eis l er

Patuxent Wildlife Research Center U.S. Fish and Wildlife Service Laurel, MD 20708SUMMARY Ecologi cal a n d toxicologi ca l aspe cts of selenium (S e) in the environ ment are reviewe d , inclu d ing its chemi s try, ba ckgro und re si due s in biolo g ical a nd oth e r mate rials, and toxic, su blethal, and l a tent effects (incl udin g the effects of Se deficie ncy). Recom m en dati ons a r e p r e s e n ted, inclu d in g prop osed S e crite r ia for prote c tion of sen s itive sp e c ie s of fish an d wildlife.

Most autho riti es ag ree o n five points. First, Se defic ie ncy is not a s well do cum e n t ed as Se poi soni ng, but may be equal ly significa nt. Secon d , Se relea s ed a s a resu lt of anthropog eni c acti vities (incl udi ng fossil fuel comb ustio n a nd metal sm e l ting), as well as that in nat ura lly sel enife rou s area s, pose s the grea test threat of poisoning to f i sh an d wildlif e. Third, addit i onal re se arch is req u ired on ch emical and biol ogical transfo rmatio ns among vale n c e state s , allo tropic fo rm s, and isome r s ofSe. Fourth, Se metabolism and deg ra dation are bot h signifi cantly modified by intera ction wit h variou s hea vy metals, agricultural chemic a l s , mic r oo r g an isms , an d

nume r ou s ph ysico c h e mica l factors, and until these int e ra ctio n s are resolved it wil l be difficult to meaningfully interpret Se res i dues in various ti ssue s. And fifth, documented bi ol ogical re spo n s e s to Se deficien c y or to sele no sis vary widely, even among clo s ely related ta xonomic g r o u p s. It is generallyagree d that Se deficien c ymay be prev ent ed in fish, small lab o ratory mammal s , and livestock by feeding di ets co ntainin g 50 to 100 p pb of Se. The con c entratio n rang e of total inorg ani c selenite curren tly

recomme nde d for aquati c life protectio n --35 pp b in fre s h w aterto 54 ppb in mari n e waters--i s b e low the rang e of 60 to 600 pp b that is fatal to sen s itive aq uatic spe c ie s. In fresh w ater, it is also bel ow the ra nge of 47 to 53 pp b

asso ciated wi th growth in hi bition of fresh w ater al gae, anemia a nd redu ced h a tch i ng in trout, and shifts in spe c ie s comp osition of fre s hwate ralga e comm unitie s . Acco rdin gly, curre n t reco mmend ation s for Se with respe c t to aquatic life app ear to afford an ade quate measur e of protectio n . Ho wever, some studie s have sho w n that Se water con c entratio n s of 9 to 12 ppb are asso ciat ed with in hibited re prod uction of cert ain freshwate r teleost s , sug gestin g that the cu rrent Se criteri on for p r otectio n of fresh w ate rlife sho u ld be revised d o wnwa rd. Also, high bio c on ce ntration and accum u l a tion of Se fr om wate r by nume r ou s sp ecie s of alga e, fish, and inverteb rate s is well d o cum ented at level s of 0.015 to 3.3 ppb, whi c h are sub s tan t ially below th e recomme nd ed rang e of 35 to 54 ppb. Th e signifi can c e of Se residu es in aq uatic biota is still u n cle a r, and m o re research appe ars to be neede d on Se pharma co ki netics in aqu atic enviro n m ents.

Aero sol con c entration s ex cee d ing 4.0 u g Se/m 3 are con s id ere d p o tentially harmful to huma n health; however, no comp arable d a ta base for b i rds a nd othe r wildlife sp eci e s is avail abl e at this time.

Selenium in n a tural food s i s less toxic th an are p u rifie d forms of Se. The c o ns ens u s is that Se toxic i ty is prevente d in livestock if die t ary Se con c e n tration s do n o t exceed 5,0 00 ppb in n a tural forage, o r2,000 pp b in feeds sup p le mented with purified Se. Minimum toxic co ncent rati ons of Se in the rat (a sen s itive speci e s), fed diets containi ng natural Se were 1,4 00 p pb of Se as ju dged by evid ence of liver cha nge s, and 3,000 ppb a s estimated fro m longevity and histo patho logy; these valu e s we re o n ly 350 and 7 50 ppb, re sp e c tively, when diets low in natu r al Se were fo rtified with purifi ed Se. The e v idence is in complete for m i grato ry waterfowl and oth e r bird s, but diets co ntainin g more tha n 5,000 pp b of Se are de mon s trably harmful

.

This repo rt sh ould be cited as:

Eisler R. 198 5. Selenium hazard s to fish, wildlife and invertebrates: a synoptic review. U.S. Fish an d Wild life Service Biolo g ical Rep o rt 85 (1.5 ).



### 2SUMMARY INTRODUCT I ON ENVIRONME N TAL CHEMI S TRY BACKGR O U ND CO NCE N T RATIO N S DEFICIENCYAND PROTECTIVE EFFECTS TOXICITY MAMMALS AND BIRDS AQUATIC O R GANISMS SUBLETHAL AND LATE NT EFFECTS AQUATIC O R GANISMS TERRESTRI AL INVERTE BRATES BIRDS MAMMALS CU R R ENT R E COMME ND ATIONS LITERATU R E CITED

TABLES Numb er 1 Selenium con c entration s in nonbiol ogical material s. 2 Selenium con c entration s in field populati ons of sele cted sp eci e s offlora and fau na. Values sh own are in total Se (mg/kg, or ppm) fresh weight (F W), dryweight (D W )

, or ash wei g ht (AW). Hyphe nated numbe rs sh o wran ge an d singl e numb e r s the me an; whe r e both a ppea r, the ra nge is in p a r en th es es

. 3 Toxicity of sel enium salts to aquati cbiot a. Values sho w n are in ug/l (ppb ) in medi um fatal to 50% of the orga nism s duri ng expo sure for vario u s interval s. 4 Propo se d sel enium criteri a for preventio n of Se deficiency an d for prote c tion ag ainst selen o si s.

AC K N O W LE DGME NTS I thank L. Garrett, M. Shawe and B. Graf f for library serv ices; I. Moore for secretaria l help; J. Jacknow, D.J. Hoffman, H. M. Ohlendo rf, and T.P. Lowe for reviewi ng the manu script; and P.H. Eschmeye r and J. R. Zub o y for editorial servic es

.



### 3INTRODUCT I ON Selenium (S e ) wa s first ide n tified as an element in 18 17 by the Swedish ch emistBerzeli u s. It is no w firmly establi s h ed that Se is ben eficial or e s se ntial in amou nt s from tra c e to part-pe r-bi llion co ncentrations for h u mans and some pla n ts and a n im als, but toxic at some con c entration s p r e s ent in the en vironme n t. Selenium d e fici ency
wa s re cently repo rted am o ng cattle gr azing in the Florida Evergla d e s , whi c h sho w ed evid en ce of anemia, sl ow gro w th, and redu ced fertilit y (Morri s et al . 1984). Co nverse ly, calves of Indian buffaloe s died of Se poiso ning after eating ri ce hu sks g r o w n in natu r all yseleniferou s soil s (P rasa d et al. 1982); severe rep r o ductive an d developm ent al abno rmaliti e s were o b se rved in aqu atic bi rd s ne stin g at Se-co n ta minated irriga tion drain w at er pond s in the San Joa quin Valley, California (Ohle ndo rf et al. 1986); and fish co n t ained hig h b ody burd e n s of Se and failed to repro d u c e in a lake re ceivin g dissolved S e by way of a powe rplant fly ash slui ce water return (Cu m bie a nd Van Ho rn 19 78). Seleni u m poiso ning i s an an cie n t and well-d o cumented di se ase (Ro s e n fe ld and Beath 1964 ). Signs of it we re re porte d a m ong do me stic livesto ck b yMarco Polo in we stern Ch ina nea r the bord e rs of Tu rke s tan a nd T i bet in about the year 12 95; among livest o ck, chi c ken s , and child ren in Columbi a , South Ameri c a, by Father Pedro Simo n in 1560; amo ng huma n ad ults in Irapu ato, Mexico, in about 17 64; a nd among h o rse s of the U.S. Cavalry in So uth Da kota in 1857 an d ag ain in 189 3 (Ro s enfel d an d Beath 1964 ). In 1907 -08, mo re than 15,00 0 shee p died i n a regio n no rth of Medici n e Bow, Wyo m ing, after grazin g on sele nifero us plants. The in cide nts have contin ued, an d the re cent tech nical litera t ure abo und s with isol ated example s of sele no sis am ong dom esti c animals.

Selenium h a s been the sub j ect of many reviews (R ose n feld and Be ath 1964; Fro s t 1972; San dholm 19 73; Zingaro and Cooper 1974; Frost and Ingvoldstad 19 75; Anon. 1975; NAS 1976; Harr 1978; EPA 1980; Lo and Sandi 198 0; Shambe rge r 1981; Wil ber 1980, 19 83; Fishb e in 19 7 7 , 1983; NRC 1983; Re ddyand Massa r o 1983 ). The s e authoritie s a g ree that Se i s wid e ly distri buted in natu r e, being e s pe cially abu nda nt with sulfide minerals of variou s metal s , such a s iron , lead, and co pper. Th e major so urce of environ menta l Se is the weath e rin g of natural rock. The amo unt of Se enterin g the atmosp here a s a result of anthrop ogeni c a c tivities is estimated to be 3,500 met r ic ton s ann u a lly, of which most is attrib uted to comb ustion of coal ; however, a s ide from highly lo cali zed conta m ination, the contri bution o fSe by man's activities is small in com p arison with th at attributable to natural sou r ces. Coll ective ly, all authorit ies ag ree that Se may favorably or adve r sely affect gro w th, su rvival, and rep r o ductio n of alg ae and hi ghe r plants, ba cte r ia and yea s t s , crusta ce an s, molluscs, inse cts, fish, bird s, and ma mmals (i ncl u ding hum an s). Most ackno w led ge that s ensitivity to Se and its comp oun ds i s extremely variabl e in all classe s of org anism s an d, except for so me instan ce s of Se deficiency or of selen o si s, metaboli c pat hway s and m ode s of actio n are imp e rfe c tly understo od. For exam ple, sele nium “indi cato r” pla n ts ca n accu mulate Se to con c e n tration s of thousand s of part s per million witho u t ill effects; in these pl ants Se promote s gro w th, whe r eas in cro p pl ant s a c cumul a tions a s lo w as 25 to 50 p p m may be toxic. Thus, pla n ts and waters hi gh in Se are con s id ere d p o tentially hazardo us to live s tock an d to aquati clife and other natu r al resou r ces in sele nifero us zon e s.

In this accou n t I briefly review the techni cal literat u r e on ecologi cal and toxicol ogi cal a s pe cts ofseleni um (with em pha sis on fish a n d wildlife and t heir p r ed ators and p r ey), a nd provid e cu rre nt re comm endatio ns for the prote c tion of sen s itive sp e c ie s of con c e r n to the U.S. Fish and Wil d life Service. This is part ofa continui ng seri es of synoptic revie w s prep ared in resp on se to in fo rmation a l re que sts from e n vironm ental spe c iali sts of the Servic e.

ENVIRONME N TAL CHEMISTRY
Selenium i s chara c te rized by an atomic weig ht of 78. 96, an atomic numbe r of 34, a melting point of 271° C, a boiling poi nt of 685° C, and a density of 4.26-4.7 9 . Ch emical p r o perties, use s , an d environ men t al persi sten ce of sele nium were documente d by a numbe r of resea r ch ers wh os e works cons titute the major source material for this se ction: Ro senfel d an d Beath (19 6 4 ); Bowe n (1 966); La kin (1 973); Stadtm an (19 74, 19 77); Frost an d Ingvoldsta d (1975 ); Cha u et al. (1976 ); Harr (1 978 ); Wilbe r(1 980, 1983); Zieve and Peterso n (1981 ); Rob berecht and Von Gri e ken (19 8 2 ) ; Ca ppon a nd Sm ith (1982 ); an d Nria gu an d Won g (19 8 3 )

. There wa s ge neral a g reem ent on four p o ints. First, that seleni um chemist ry is co mplex, and that additional

resea r ch is warranted o n chemical and biochemi c al tran sform a tion s amon g vale nce states, all o tropi c form s, and isome r s of se lenium. Seco nd, that selen i um metaboli s m and d e g r a dation is signi ficantly modified by intera ction with heavy metals, agri c ult u ral chemi c al s, microo rgan isms, a nd a variety of physico chemi c al f a ctors. Thi r d, that anthro pog eni c activities (in c ludi ng fossil fuel comb usti on and metal smelting ) an d naturally sel enifero us a r e a s pose the gre a t est hazard s t o fish and wil d life. And fourth, that selen i um deficie ncy is not as we ll docum ente d as



### 4Se poiso ning, but may be equally sig n ificant. These po ints are d e vel oped h e re in greate rdetail.

Selenium che m istry is com p lex (Ro s e n feld and Beat h 1964; Harr 1978; Wil ber 1983 ). In nature, sel eniu m exists: as six stable i s otop es (Se

- 74, -76

, -77,-7 8,-80, and -8 2), of which Se -80 a nd -78 a r e th e most comm on,
accou n ting fo r 50 and 2 3 .5 %, respe c tive ly; in three allotropi c form s; and in five valen c e state s . Chang es in the valence state of Se from -2 (hydro gen se lenide ) thro ug h 0 (elem enta l Se), +2 (sel enium dioxid e), +4 (sel enit e ), and +6 (selen ate) are asso ciated with its geologi c di stribution, redi stribution, and use. Solubl e sele nate s occur in alkali ne soils, are slo w ly re duced to sel e nites, and a r e then readily take n up by pl ants. In drin ki ng wate r, sele nate s rep r esent the do minant ch emi c al spe c ie s. Selenites a r e less sol uble t han the corre s po ndin g sele nate s an d are ea sily redu ced to ele m ental Se. In sea w ater, se lenites a r e th e domina n t chemical sp eci e s unde r so me condition s (Ca ppon a nd Sm ith 1981). Sel enium dioxid e is forme d b ycombu s tion of elemental Se pre s ent in fossil fuels o rru bbish. Seleni um is the mo st stro ngly en rich ed ele m e n t in coal, bei ng pre s e n t as an orga no sele ni um com pou n d , a chelate d spe c ie s, or a s an ad so rbe d element. O n comb ustio n of fossil fuels, the sulfur di oxide formed redu ce s the sel eni um to elemen tal Se.

Elemental Se is insol uble a nd larg ely un available to the bio s ph ere, although it is still capa ble of satisfying metaboli c nut ritional requi rements. Hydrogen sele nid e is highly toxic (at 1-4 ppb in air), un stab le, acidi c , and irritative. Selenide s of mercury, silver, co pper, an d c a d m ium are ve ry insolubl e, although thei r insol ubility may be the ba sis f o r the re porte d detoxificatio n of methylme rcury by diet ary sele nite, and for the d e crea sed h e a vy metal toxicity associated wi th selenite. M e tallic selenide s are thus bi ologi cally import ant in sequesteri ng both Se and he avy metals in a larg ely unavailabl e form.

In area s of acid or neut ral soils, the amo unt of biol ogi cally availabl e Se shoul d steadily declin e. The de clin e may be accel e rated by a c tive agricultura l or indu strial pr a c tice s. In dry are a s, wit h alkali ne soils and oxidi z in g
con d ition s , elemental Se a nd sel enide s i n rocks and v o lc a n ic soil s may oxidize sufficiently to maintain the availability of biologi cally active sele nium. Concentrations of sel eni um in wa ter are a function of seleni um levels in the drain a g e system a n d of water p H . In Colorado, fo r exampl e, stream s with p H 6.1-6.9 u s u a lly contain <1 ppb of Se, bu t those with p H 7.8-8.2 m a y contain 27 0 to 400 ppb (Laki n 197 3).

Selenium vol a tilizes from soils at rates that are modified bytemperature, moi s ture, time, season of year,

con c e n tration of water-sol u ble sel enium, and microbi o l ogical activity. Conversi on of inorgani c and organi c sele nium co mpoun ds to volatile sel eniu m comp oun d s (su c h a s dimethyl seleni de, dimethyl disel enide, a nd an unkno wn co mpoun d) by microorgani sms ha s bee n observed in l a ke sedim ent s ofthe Sudb ury are a of Ontario. This conve r si on may have been effe cted by pure cultu r es of Ae rom ona s , Flavo b a cteriu m , Pseudom ona s , or an unide ntified fungu s, all of whi c h are fou nd in methyla t ed lake sedi ments. Pro d u c tion of volatile sele nium is temperature depe ndent. Compa r ed with the amount o f(CH 3 ) 2 Se p r odu ce d at an incub a tion te mperature of
20° C, 25% less wa s pro d u c ed at 10 °C a nd 90% less at 4°C. Detail s of Se redu ction and oxid ation by microorgani sms are not cl ear. On e sug geste d mech anism fo r sel enite red u ctio n in certai n m i cro o rgani sm s involves attachment to a ca rrie rprotein a nd tran sform a ti on from sel enite to elem ental Se, whi c h in turn m a y be oxidize d to se lenite by the action of Baci llus spp., as o ne example. It is apparent that much a d d i tional re sea r ch on this proble m is wa rra nte d

. Selenium i s a n essential n u trient for so me plants a n d animal s ; it constitute s an integral p a rt o fthe enzyme glutathion e p e roxida se a n d may have a role in othe r biologi cally a c tive comp ou nds, e s pe ciall yvitamin E a nd the enzyme fo rmi c dehyd r og en ase. Some a n imals req u ir e Se-containi ng amino a c i d s (viz. selen o cystei ne, sele no cystine

, selenom ethi onine, selen o c ysta thio nine, Se-methylsel eno cystein e , and Semethylsele no methionin e ), but repo rtedlyare incapa bl e of produ cin g them. Selenium also forms pa rt of certain protein s , incl uding cytoch rome C, hem o g lobin, myogl obin, myosin, and variou s ribonu cleo proteins. It now appe ars that sele nate s an d sele nites a r e absorb ed b ypl ants, redu ced, an d then incorpo r ated in amino a c id s synthe sis. Th e biologi cal a v ailability of Se is high er in plant food s than in food s of animal ori g in (Lo and Sa n d i 1980 ). The n e t effect of soil, plant, and animal meta b o lism is to co nvert Se to inert and in solu ble form s su ch as elemental Se, metallic sel e nide s, and co mplexes of selenite with fe rri c oxide s

. Selenium was used in the early 1900' s as a pestici d e to control plant pests, and is still used sparingly to control pe sts of green hou se chry santh e m ums a nd ca rnat ion s (Ro s enfeld an d Beath 196 4). It has be en u s ed to control cotton pests (in Tri n idad), mite s a nd spi ders th at attack cit r u s , and mite s that damag e a pple s . Although no insect-re s i s tant strain s have develo p ed, the use ofseleni um pe sticid es h a s b een di scontin ued, owi ng to their stability in soi l s and resulta n t contamin ation of food crops, their hi g h price, and their p r oven to xicity to mammals



### 5and birds. Sel enium sham p oos, which co ntain abo ut 1% se leniu m sulfide, are still used to control dand ruff in human s an d derm a titis an d mange in d ogs. Seleni u m is used extensively in th e manufa c ture and produ ct ion of glass, pigme n ts, rub ber, metal alloys, textiles, pet rol eum, medi cal therape utic a gents, an d ph otogra phi c emulsi on s.

Air and surfa c e waters ge nerally contai n nonh azard o u s con c entrations of Se. Significa nt increases of Se in spe c ific a r ea s are attribute d exclu s ively to industri a l s ource s, and to leaching of grou nd wate r from selenife rous soil s. In the United States, about 4.6 mill ion kg of se le nium are rele ase d ann uall yinto the environm ent: 33 % from co mbu s t i on of fossil fu els, 59% from industri a l lo sse s , and 8% from muni cip a l waste s . Of the total, abou t 25% is in the form of atmospheri cemi s si ons, an d the rest in ash. Mining an d sme l ting of copp e r-ni c kel ores at Sudbu ry, Ontario, Ca nad a, alone rel e a s es ab out 2 metr ic ton s of Se to the environment daily, and pro bably rep r e s ent s the greate s t poi nt source of Se relea s e in the worl d. In 1977, 68 0,00 0 kg of Se wa s pro d u c ed at Sudbu ry, but only about 10 % was recovered, sugg est i ng that about90% was lo st to the environment. Of the amount lo st, perh a p s 50 m e tric ton s wa s dispe n sed in to the atmosp here, p r ob abl y as sele nium dioxide (ai r b o rne Se levels 1-3 km from Sud bury we re a s high a s 6.0 μg/m 3 ). The rest was pr obably associ ated with mine tailings,

wa stewater, and sco r ia, a nd is a lo cal source of Se c ontaminatio n, most notablyin lake s. The present ann u a l rates of Se a c cumulatio n in lake sedim ent s in the Su dbury a r ea ra nge from 0.3 to 12.0 mg/m 2 ; these de po sition rates ex cee d those of p r e-colonial time s by factors of 3 to 18, and a r e amo ng the highe st recorded in North America (Nria gu and Won g 1983).

Selenium i s a serio u s h a za rd to livestock and pro bablyto people in a wide semia r id belt that extends from insid e Ca nad a south w a r d across the United States into Mexico (NRC 19 83). Selenium ten d s to be p r esent in large a m ou nts in are a s wh ere the soils have bee n de riv ed from Cretac eous rock s

. Total Se in s u c h soils averag es a b o u t 5 ppm, but is som e time s as hig h as 8 0 ppm. Lack ofrainfall ha s p r evented the solutio n of the Se mineral s a nd the rem o val of their salt s in drai nag e waters. In so me are a s, mo dern fe rtilizati on pra c tices and the buildup of sulfates in the soil due to acid precipitation partl y lessen the avail ability of Se to plants and forage

cro p s. In the United States, highly seleni ferou s natu r al area s (2 00-3 00 ppb in fora ge) a r e mo st abun dant in the Ro cky Mou n tain and High Central Plain s are a s; a r ea s with lo wer concentratio n s (20-30 pp b) i n forage a r e typical in the Pacific North w e s t and the Southea st. Ho weve r, huge variations a r e not uncom mon from on e spe c ific lo cati on to anothe r. Among plan ts, prima ry an d se con dary sele nium a c cumulato rs a r e almost always implicate d in ca se s of acut e or ch ro nic selenium p o isoni ng of livest o ck. Primary Se ac cumul a tor plant s, su ch as

v a riou s sp eci e s of Astra galus , O o no ps is

, Stanelya

, Z y

lo r h iz a , and M a ch aeranthe ra , may require 1 to 50 ppm Se in either soil or wate r for g r owth, an d m a y contai n 1 0 0 to 10,000 p p m Se as a gl utamyl dipept ide or sela no cystant hionin e . Seco ndary a c cum u lator pla n ts (rep re sentativ e gene ra: As t o r

, Gutierrezi a , Atriplex

, Grindelia

, Castilleja , and Com andra ) gro win either sel enifero us o rn onselenife rou s soil s an d may contain 2 5

- 100 ppm Se. Non a ccum ula t or plants g r o w ing o n sel e n i fero u s soil s contain 1-25 p p m fresh wei ght of Se. Meat and eg gs of d o mesti canim a ls may co ntain 8-9 p p m o fSe in seleniferou s a r ea s, comp ared wit h 0.01-1.0 p p m in

non sele nifero us area s. Tissue s from a n i m als mai n tai ned on hi gh-Se feeds ge n e rally co ntain 3-5 ppm Se f r esh weig ht vs. up to 20 ppm in animal s dying of Se poisoni ng (Harr 197 8).

Selenium i s n u tritionally im portant a s an essentia l tra c e element, bu t is harmful atslightly highe r
con c e n tration s . Although n o rmal Se diet ary levels req u ired to en su re human h eal th range from 0.04 to 0.1 ppm, toxicity may occur if food contain s as little as 4.0 ppm. Minimum Se con c e n tration s req u ired are usu a lly high er in livestock than in human s. In area s with highly sel enifero u s soils, e x cess Se is a d so rbe d onto a variety of plants and grain s an d can b e fatal to grazin g livesto ck. Th ere is gene ral ag reem ent, however, that sel enium inade qua cy can be of gre a t er con c e r n to health than i s se l enium to xicity. Studies in human s a nd small a n i m als indicated thatSe deficien cy (in part) un derlie s vari ou s ch roni c di se ase s , increa si ng su sceptibil ity to cance r , arthriti s, hype rtensi on, hea rt disea s e, an d possibly pe riodo ntal dise ase a nd cataracts. Seleni u m repo rtedly prote c ts ma m m als an d so me bird s ag ai nst the toxic effe cts of mercury, cadmiu m, arse nic, th allium, and th e herbi cid e paraquat (Hill 19 75; Wilbe r19 83). The r e is no dou bt that high dieta ry levels of these comp oun ds, as well a s of salt s of cop per, zinc, and silver, contribute to seleni um def icien c y effect s. Ho wever, t oo little is kno w n of the chemi c al mech ani sms to enabl e sci entist s to account for the s e ph enom en a. Selenium h a s a comp aratively short effect ual biologi cal life in various sp e c ie s of organi sms fo r whi c h data a r e available. Studies with radi osele n ium-75 indi cated that its biologi cal half-l i fe is 10 to 64 days: 10 in p hea sant s, 13 in guppi es a n d voles, 15 in a n ts, 27 in eel s, 28 in lee c h e s, and 6 4 in earth wo rms (Wilbe r198 3). Many investigators co ncl u ded that the great est cu rrent an d dire ct use o fselenium i s in the tran spo r tation of grai ns grown in seleniferou s areas to Se-defici e n t areas as ani mal and hu m an food.



### 6Table 1. Selenium con c e n tration s in n onbiol ogical material s.

Sample, and unit of con c e n tration Con c e n tratio n Referen c e a

TERREST RI AL (ppm )
Earth' s crust 0.05 Fro s t and Ing v oldstad 1 9 7 5 Soils 0.2 Ebens a nd S hacklette 19 8 2
Limesto n e s 0.08 Sandsto ne s up to 0.05 Shales 0.6 Cho ndrite s 8.0 Oce an sedim ents 0.34-4.8 de Goeij et al . 1974 Coal 3.36(0.4 6 -10. 65) NAS 1976; Kuhn et. al. 1980
Fossil fuels 1-10 Harr 19 78
Lake se dime nts NY, Lake Ge orge 0.22 Heit et al. 1980 Great L a ke s 0.35-0.7 5 Adams a nd John son 1 977
Fre s h w ater la ke s, Can ada 0.2-14.5 Speyer 19 80 AQ UATI C (p pb)
Drin kin g wate r Wo rldwi d e 0.12-0.4 4 Rob berecht and Grou nd wate r Von Grie ke n 1982
Neb r a s ka, USA <1-480 Argentin a 48-6 7 Australi a 0.008-0.33
Fran ce <5-75 Israel 0.9-27 Italy < 0 .002-1.9 Sewag e wate rs USA
Ra w se wa ge 280 NAS 1976 Primary efflu ent 45 Secon d a ry effluent 50
Wo rldwi de Jap a n 480-700 Ebens a nd S hacklette 19 8 2 USA 10-2 80 USSR 1.8-2.7 Germ any 1.5
Riv e r w a ter s Jap a n 0.03-0.0 9 Nria gu an d Wong 19 83 Germ any 0.015 Ebens a nd S hacklette 19 8 2
Amazo n Rive r, South America 0.021 USA



### 7Ohio Rive r <0.01 Rob berecht and
Missi ssippi Ri ver 0.14 Von Grie ke n 1982 Michig an 0.8-10
N e br as ka < 1 -2 0 Colo rad o Riv e r 30
Lake wate rs Swede n 0.04-0.2 1 Nria gu an d Wong 19 83 USA 0.04-1.4 NAS 1976 Great L a ke s 0.001-0.036 Adams a nd John son 1 977 Sea wate r Wo rldwi d e 0.009-0.045 Fro s t and Ing v oldstad 1 9 7 5 ; Ebens a nd S hacklette 19 8 2
Wo rldwi d e 0.09-0.4 5 Whittle et al. 1977
Wo rldwi d e 0.09-<6.0 NAS 1976 Israel, Dead Sea 0.8 Rob berecht and
Von Grie ke n 1982 Jap a n 0.04-0.0 8 AIR (μg/m 3 )
Nea rSe indu strial pla n t 0.7 NAS 1976 Control area 0.001
Nea rSudb ury (Cana da ) smelter up to 6.0 Nria gu an d Wong 19 83
INTEGRATE D STUDIES (ppb) California
Rain wate r 0.05 Rob berecht and
Lake wate r 0.018 Von Grie ke n 1982 Sea wate r 0.058-0.08 Irrigatio n drai n water Subsu r fa ce 300-1,400 Ohlen dorf et al. 1986 Surface 300 Vicinity of nickel-co ppe r smelte r, Sudbury, Ontari o Lake wate rs 0.1-0.4 Nria gu an d Wong 19 83
Lake se dime nts 2,000-6,000
Lake se dime nts 240 km
south of Sud bury 1,000-3,000 Cu-Ni o r e s 20,000 -80,0 0 0 Fly ash pon d s Sediment 14,000 Furr et al. 1979
Wate r 350

a Each refere nce a pplie s to the values i n the same ro w, and in the rows that follow for which no other reference is indi cated.



### 8BA C K G R O U ND CO NCE N T RA TIONS
Selenium con c entration s in nonbiol ogical material s ext end over sev e ral o r de rs ofmagnitude (Table 1 ) . In terres t rial materials

, c o nc entrations in exc e ss of 5 pp m Se are ro utinely recorde d in meteorite s , cop per-ni c kel

ore s , coal a n d other fo ssil fuels, lake se diments in th e vi cinity of a nickel-co ppe r smeltery, an d in sedim ent s of fly ash settlin g pond s. Wat e r co ncentrations ex cee d in g 50 ppb Se have bee n do cume nted in grou nd wate r, esp e ci ally in area s with sel enifero us soil s, in se wag e wa stes, in irri gation drain water, an d in water of fly ash settling po nd s. Selenium concentratio n s in air sam p le s we re >0.5 μg/m 3 in the vicinity of Se produ ction pla n t s, and the s e we re at least 50 0 times high e rthan in a co ntrol area. As a result of na tural and a n th ropo geni c pro c e s ses, compa r atively high con c entrations of sele nium in non bi ologi cal mate rials m a y pose signifi cant ri sks to fish and wil d life (this poi nt is discu s se d later).

Selenium con c entration s in represent ative spe c ie s of freshwater, m a rine, an d terrest r ial flora a nd fauna a r e listed in Tabl e 2. Additiona l information on body an d tiss ue bu rde n s of sele nium was give n by Birkne r (1 97 8), Jen k in s (1 98 0), Lo and Sa ndi (19 8 0 ) , Eisler (19 81), a nd Wilb er (19 83). It is emp hasi z e d that, for all org ani sms, Se con c ent ra tions tend ed to be sig n ifica n tly higher when co lle cted from local e s having certai n cha r a c teri st ics: highly sel eniferou s soils o r sedime nts ( in Comp arative studie s of food an d environmental con t amination. Int. Atomic Energ yAgency, Vienna.de G oeij et al. 1974; Bi rkn e r 1 978; Speyer 19 80; Wilbe r198 3); high huma n popul ation de nsitie s (Beal 1974 ); heavy accumul a tion s of Se-lad en waste s , su ch as effluents f r om sy stem s
use d to colle ct fly ash scru bber slud ge o rbottom ash (Cu m bie a nd Van Ho rn 19 78; Soren s e n et al. 1982, 1984); and Se-co n ta minated sub s urface irri gati on drai nwater (O hlen do rf et al. 1986). Th ere is evid en ce that Se

con c e n tration s are p o sitivel ycorrelated with mercu r y resi due s in pi scivo rou s ma mmals (Reij n ders 198 0; Wren 1984 ) and tel eost s (G anth e r et al. 1972; Leon zio et al . 1982), altho ugh the evide n ce for tele osts is co nflictin g (Tamu r a et al . 1975; Speyer 198 0; Mah e r 198 3), an d that Se varies se asonally i n cru s ta cea n s (Zafi r opo ulo s and Grima n is 1 9 7 7 ). In gene ral

, concentratio n s of Se in va riou s tissue s are u s ually hi gher in ol de r than in youn g e r orga nisms; a m ong ma rine vertebrates, Se increa se s were espe cial ly pronou nce d among the older spe c im ens of pred atory, lon g -lived spe c ie s (Eisl e r 19 84 ).
All reporte d Se levels in tissue s of mari n e inverteb rate s and pl ants have bee n le ss tha n 2 pp m Se on a we t weig ht basi s , or 12 pp m dry weight. Hig her level s are r outinely re corde d in liver and ki dney tissue s of mari n e and coa s tal verteb rate s, includi ng teleo s ts, bird s, and mamma l s . Livers fro m adu lt seals were comp aratively rich in sele nium (Table 2 ) ; however, high co nce n tration s i n liver of maternal Califo r n i a sea lio ns were not reflect ed in liver of newb o rn pu ps (Ma r tin et al. 1976). Mean con c entra tion s of Se in kidney s of seven sp ecie s of co ast a l bird s coll ecte d from the hig h ly industri a li zed Corpu s Christi, Texa s, area u s u a lly varied bet we en 1.7 and 5. 6 ppm Se fre s h weight, but were 10.2 p p m in one bird. Acco rdi ng to White et al. (1980 ), Se co nce n tration s of this magnitud e m a y be sufficie n t to impair re prod uctio n in sho r ebi rd s.

Selenium lev e ls in fre s h w a t er biota are relatively low, c o mpared wit h thos e in their marine c ounterparts . In fresh w ate rorgani sms, ab o u t 36% of the total Se was pre s ent a s se lenate, and th e rest a s sele nite and sele nide. In marine sa mples, only 2 4 % of the total Se was p r e s ent a s sel e n a te (Ca ppo n and Smith 19 82). The implications of this difference are not now understood , but have great relevance i n the ability of Se to complex and detoxify variou s poten tially toxic heavy metals, su ch a s me rcu ry and ca dmi u m. In the most re cent Nation wide m onitorin g of selenium a nd other contami nants in fre s h w ater fi she s , Se rang ed fro m 0.05 to 2.9 ppm (fre sh weight, whole fish) a nd avera ged about 0.6 pp m; st ations where con c e n trations in fish excee ded 0.8 2 ppm (>85th p e rcentile ) we re in three a r e a s: Atlantic c oastal strea m s; Mississippi River sy stem ; and Californ i a (May and M c Kinney 1981 ). Among fish from Atlantic coas tal strea m s, those from the Dela wa re River nea r Camd en, Ne w Je rsey, had elevated whol e bo dy co nce n tration s (i.e., >1.0 and <3.0 ppm Se ), which were attributed to the indu striali z ed ch ara c te r of the ri ver. In the Big Horn and Yello wst one Rive rs, hi gh Se

con c e n tration s in fish may result from ge ologi c so urce s of the elem ent, includi ng coal, pho sp h a te, and sedim enta ry rock. Fish fro m the South Platte River n ear Denve r , Colo rad o , ma y receive Se from ind u stri al effluents, or from natural an d anthro pog e n ic a c tivities asso ciated wi th the remova l of deposit s of coal, barite

, and sulfur. In California, wh ere Se was el evated in fish from the San Jouq uin Rive r, it was spe c ulated that Selocid e , an Se-containi ng pestici de re g i stere d for u s e on citru s fru i ts in the 196 0's, may have been a source, althoug h co ntaminated i rrig a tion drai n water wa s con s id e r ed a m o re likely po ssi bility (Ohlend orf et al. 1986 ).
Among terre s trial plants, selenium a c cu mulation s in speci e s of As t e r

, Astra galus , and severa l other gen era are sometime s sp ecta cul a rl y high (Tabl e 2). Astra galus is the mo st widely di strib u t ed. About 2 4 of its more than 200 spe c ie s are Se a c cu mulators that requi re Se to gro w well . T he high est re ported Se co nce n tration in plants



### 9wa s 15,00 0 p p m dry wei g h t, in loco wee d

, Astragalus racem o sus (Wilbe r198 3). Con s umptio n of these an d other Se-accumulating fo rage pla n ts bylivestock ha s induced illne ss a nd de ath from sel eniu m poiso ning. Even at much lo we r con c e n tratio ns, Se may harm anim a ls t hat eat con s i dera b le am ou nts of the fora ge. Plants tha t accumul a te Se tend to be d eepe r ro oted than the gra s se s and survi v e more seve re ari d ity, thus rem a inin g (unfo r tunately ) as the p r in ci pal forag e for grazi ng in time of drou gh t (Wilbe r198 3).

Table 2. Sel e nium con c e n tration s in fiel d pop ulation s of se l e cte d speci e s of flora and faun a. Values sho w n are in total Se (mg/kg, or pp m) fresh weight (FW), dry we i ght (DW), o rash weig ht (AW). Hyp henat ed numb e rs sho w rang e and sin g le numb e rs the mean; wh ere both a p p ear, the ra ng e is in parent heses.

Ecosy s tem, taxonomi cgro up, Con c e n tratio n Referen c e a

orga nism, tissue, lo cation, and (ppm)
other vari able s

MARI NE Algae and m a crophyte s

Whol e 0.04-0.2 4 DW Cha u and Riley 1970;
Lund e 197 0; Tijoe et al. 1979
Edible se awe eds, whole 0.16-0.3 9 DW; Nod a et al. 1979
0.047 F W
Molluscs
American oyster, Cra s so st re a virgi n ica Red w o od Cre e k, San Fran cisco, CA

Mantle 4.8 DW Oka z a k i an d Panietz 19 81 Dige stive gla n d 8.8 DW Kidney 4.7 DW
T o m a l e s B a y , C A
Mantle 2.2 DW Dige stive gla n d 6.4 DW Kidney 2.5 DW
Tran sfe rre d from Red w o o d Cree k
to Tomale s Bay for 56 days
Mantle 3.5 DW Dige stive gla n d 6.5 DW Kidney 3.8 DW
Bivalve molluscs Shell 0.03-0.0 6 DW Bertine an d Goldb e rg 1 9 7 2 Soft parts 0.1-0.9 F W ; Lund e 197 0;
1.3-9.9 DW Bertine an d Goldb e rg 1 9 7 2 ; Karbe et al. 1 977;

Hall et al. 197 8;



### 10Fukai et al. 1 978;
Luten et al. 1980
Muscle 1.1-2.3 DW Mahe r 198 3
Visce ra 1.6-2.5 DW

Edible fre s h, 3 spp. Total Se 0.22(0.1 6 -0.3 1) FW Cap pon a nd Smith 1982
As sele nate 0.05 FW
As sele nite a nd sel enide 0.17 FW Mussel, Mytilu s ed ulis Gills 2.0-16.0 DW Stump et al. 1979
Visce ra up to 5.0 DW Mussel, Mytilu s gall oprovi n ciali s Gills 7.0 DW Fowler and Soft parts 6.0 DW Benayoun 1 9 76c
Mantle 5.2 DW
Visce ra 3.2 DW
Muscle 1.9 DW Shell <0.05 DW
Echino de rms Whol e, 7 spp. 0.8-4.4 DW Papado poul u et al.1976 C r us tac e an s Dige stive system, 3 spp. 3.0-3.5 DW Mahe r 198 3
Edible tissue s sol d for hu man co nsum ption

17 sp p. 0.2-2.0 F W Hall et al. 197 8;
Nod a et al. 1979;
Luten et al. 1980
Edible tissue s, 2 spp.

Total Se 0.21 FW Cap pon a nd Smith 1982
As sele nate 0.05 FW
As sele nite a nd sel enide 0.16 FW Muscle, 5 sp p. 2.4-4.4 DW Mahe r 198 3 Soft tissue s , 2 spp. 2.0-2.8 DW Cop epo ds, whole 1.8-3.4 DW Zafirop oulo s and G r iman is 19 77 ; Tijoe et al. 1977 Euphau sid, M egan yctipha n e s no rvegi ca Visce ra 11.7 DW Fowle ran d Benayou n Eyes 7.8 DW 1976 a Muscle 1.8 DW
Exoskel e ton 0.8 DW Shrimp, Lysm ata seticaud a t

a Visce ra 7.0 DW Fowle ran d Benayou n 197 6c Eyes 4.8 DW
Whol e 2.6 DW



### 11Muscle 1.9 DW
Exoskel e ton 1.5 DW
Molts 0.3 DW Sharks
Muscle 0.2-0.8 F W Glover 19 79
Fish Dige stive system, 4 spp. 1.0-2.4 DW Mahe r 198 3
L i v e r 2 spp. 2.6-6.6 DW Grima n is et a l . 1978 74 sp p. 0.6-5.0 F W de Goeij et al . 1974;
Hall et al. 197 8;
Luten et al. 1980 13 sp p. 5.0-30.0 F W Hall et al. 197 8 Meals, 3 spp. 1.0-4.0 DW Kifer and Payne 196 8
M u s c l e 4 spp. 0.5-1.5 DW Mahe r 198 3 182 spp. 0.1-2.0 F W Bebbingto n e t al. 1977; Grima n is et a l

. 1978;
Kari and Kau r anen 1 978;
Hall et al. 197 8;
Nod a et al. 1979;

Luten et al.19 80 5 spp. Total Se 0.4(0.2

- 0.6) F W Cap pon a nd Smith 1982
As sele nate 0.1 FW
As sele nite a nd sel enide 0.3 FW
Whol e, 21 sp p. 0.3-2.0 F W Kari and Kau r anen 1 978;
Hall et al. 197 8;
United Nation s 197 9 Jap ane se t u n a s, 4 sp p. Liver 10.0-1 5 .0 FW Tamura et al. 1975
White mu scle 0.5-1.3 F W
Red mu scle 3.5-9.1 F W
B l a c k m a r l i n , Makai r a in dica
Muscle 0.4-4.3 F W MacKay et al. 1975
Liver 1.4-13.5 F W
B l u e m a r l i n , Makai r a ni gri can s Kidney 23.0 FW Schultz a nd Ito 1979
Blood 1.0 FW Gill 1.0 FW
M u s c l e Total Se 3.3(2.5

- 4.1) F W Cap pon a nd Smith 1982

As selenate 0.2(0.09 -0.3 ) FW
As s e lenite
and sele nid e 3.1(2.4

- 3.8) F W



### 12Striped ba ss, Morone saxatilis
Muscle 0.3 FW Heit 197 9
Liver 0.6 FW Tuna, canne d 1.9-2.9 F W Ganthe r et al. 1982 Swordfish, Xiphia s gladius Muscle 0.3-1.3 F W Freem an et a l

. 1978
Birds

Kidney, 12 sp p. 1.2-5.6 F W Turn er et al. 1978;

White et al. 1980 White-f a ced ibis, Plegadi s chihi Egg 0.3-1.1 F W King et al. 1980 Royal tern, Sterna m axim a Egg 0.4-2.1 F W King et al. 1983 Sooty tern, Sterna fuscata Egg 1.1-1.4 F W Ohlen dorf an d Harri s on 1 9 86
Brown peli c a n ,

Peleca nus occide ntalis Egg 0.19-0.3 8 FW Blus et al. 1977
Liver 1.0-4.2 F W
Wed ge-tail ed shea rwater,

Puffinus pac i fic us Egg 1.1-1.3 F W Ohlen dorf an d Harri s on

1986
Red

- footed b ooby, Sula sula Egg 0.8-0.9 F W Oy st er cat c he r,

Haem atopus ostral egus Kidney 12.7(2.3

- 1 7 .5 ) DW Hutton 19 81
Liver 12.8(5.0

- 2 0 .5 ) DW Herring gull,

Larus a r ge ntatus Kidney 14.1(8.6

- 1 9 .4 ) DW
Liver 7.9(6.9

- 9.3) DW Great Skua, Catharac ta sk ua Kidney 32.8(1 3 .3-89. 1) DW
Liver 19.7(6.7

- 3 4 .6 ) DW
Mammal s Pilot whale, Globi cep hala m a crorhynch u s Blubbe r 0.8-1.4 F W Stonebu rne r 1978
Liver 22.8-6 1 .6 FW Kidney 3.0-10.0 F W



### 13Ring ed seal,
Phoca hi spi d

a saim ensi s Muscl e 0.2-2.8 F W Kari and Kau r anen 1 978
Liver 29.0-1 70.0 F W Kidney 0.3-3.0 F W
Blubbe r 0.06-0.1 1 FW
Harbor s e al, Phoca vitulin a Juv enil e s Kidney 0.6(0.0

- 1.3) F W Reijn ders 19 80
Liver 2.8(2.6

- 6.5) F W
Brain 1.1(0.0

- 7.4 F W
Adults Kidney 3.5(1.9

- 7.3) F W
Liver 109.0(409.0 Max.) FW
Brain 3.7(1.5

- 8.2) F W Seals Liver, 4 spp. 6.1-17 0.0 FW Kari and Kau r anen 1 978;

Smith and Armstro ng

1978; van de Ven

et al. 1979 California sea lion, Zaloph us cali fornian u s Mothers with norm a l pup s Liver 260.0 DW Martin et al. 1976 Kidney 22.0 DW
Normal pu ps Liver 4.1 DW Kidney 6.1 DW
Mothers with prem ature p u p s Liver 79.0 DW Kidney 12.0 DW Pups bo rn p r ematurely
Liver 2.9 DW Kidney 3.7 DW FRESHWATER

Algae and hi g her pla n ts

Algae, whol e <2.0 DW Jen k in s 19 80 High er pla n ts 0.1 DW Ro ssi et al. 1 976 Aquatic mo sses 0.8 DW
Filamento u s algae Se-contamin ated are a 35.2(1 2 -68) DW Ohlen dorf et al. 1986



### 14Control area <0.5 DW
Roote d plant s Se-contamin ated are a 52.1(1 8 -79) DW Control area 0.4 DW
Molluscs
Mussel s, 3 sp p., NY State

Soft parts 2.0-4.0 DW Heit et al. 1980
A s iat i c clam, Corbicula flum inea
Whol e, Florid a 0.7 FW Wing er et al. 1984 Arthrop oda Zoopla n kto n 0.8-3.9 DW Adams a nd John son 1 977
Plankton Se-contamin ated are a 85(5 8 -124 ) DW Ohlen dorf et al. 1986 Control Site 2(1.4

- 2.9) DW
I n se ct s Se-contamin ated are a 20-2 18 DW Control site 1.1-3.0 DW
M a y f l y , Hexa genia sp. 0.3-0.5 F W Wing er et al. 1984 Amphibia n s Liver 0.7-4.7 F W Jen k in s 19 80 Reptile s Wate r sn ake, Natrix sp. Whol e, Florid a 0.3-0.5 F W Wing er et al. 1984
Fish C o m m o n c a r p , C y

pr

in us ca r p io
Whol e 1.0(0.7

- 1.4) DW Wien er et al. 1984
Liver 3.6(2.2

- 5.2) DW Bluegill, Lepo m i s m a crochi rus From water containin g <5 ppb Se
White mu scle 0.04 FW Lemly 1982 b
Liver 0.7 FW Spleen 1.6 FW Erythro c ytes 0.04 FW

H e a r t 1

. 0 F W
From water containin g 22. 6 ppb Se
White mu scle 3.1 FW
Liver 11.2 FW Spleen 17.7 FW Erythro c ytes 7.2 FW
H e a r t 1 2

. 8 F W
U p p e r M i s s i s s i p p i R i v e r Whol e 1.2(0.7

- 1.4) DW Wien er et al. 1984 Larg e mo uth bass, Micropterus salm oides



### 15From water containin g <5 ppb Se
White mu scle 0.05 FW Lemly 1982 b
Liver 0.8 FW Spleen 1.8 FW Erythro c ytes 0.07 FW
H e a r t 1

. 2 F W
From water containin g 22. 6 ppb Se
White mu scle 1.7 FW
Liver 10.2 FW Spleen 16.6 FW Erythro c ytes 8.0 FW
H e a r t 1 2

. 0 F W Apalachicola River, Flori d a Whol e Female s 0.3-0.4 F W Wing er et al. 1984
Males 0.3-0.5 F W
Juvenil e s 0.3-0.5 F W Eggs 0.7-1.0 F W Cha nnel catfish,

Ic talurus punc tatus Apalachicola River, Flori d a

Whol e Female s 1.1-0.3 F W
Males 0.2-0.3 F W
Juvenil e s 0.4-0.6 F W Eggs 0.8-2.1 F W
Thre adfin sha d

, Doro som a petene nse Whol e 0.3-0.5 F W Gree n su nfish, Lepom is cyan ellus F r o m w a t e r contai ning 1 3 ppb Se

Liver 7.0-21.4 F W Soren s e n et al. 1984
Muscle 2.3-12.9 F W
From control site
Liver 1.3 FW
Muscle 1.3 FW

Trout, 2 sp p., Wyoming
F r o m w a t e r contai ning 1 2

. 3-13.3 pp b Se

Liver 50.0-7 0 .0 FW Kaise ret al. 1979
M u s c l e < 2

. 0 F W Skin Max. 4.8 FW
Mos q uitofis h

, Gam busia af finis , whol e From Se -cont aminated i rrig a tion



### 16drain w ate rpo nd 170(115 -28 3 ) DW Ohlen dorf et al. 1986 Control site 1.3(1.2

- 1.4) DW Coho s a lmon, Onco rh yn ch us ki sut ch
Muscle 0.7-1.0 DW Ran c itelli et a l . 1968
Liver 3.8 DW Chin oo k salm on, Oncorhy n chus ts hawytsch a Muscle 1.6 DW
Fish
M u s c l e 25 sp p. 0.0-0.5 Uthe an d Bligh 1971; Willford 1 971; Tonget al. 19 71;
Pakkala et al. 1972;
Ro ssi et al. 1 976;
Luten et al. 1980 18 spp. 0.5-1.0 F W Willford 1 971; Tong etal.19 7 2;
Pakkala et al. 1972 3 spp. 1.0-2.0 F W Schroed er et al. 1970;

Pakkala et al. 1972 3 spp.
Total Se 0.25 FW(0.15

- 0.34 ) Cap pon a nd Smith 1982
As sele nate 0.09 FW
As sele nate a nd
sele nide 0.16 FW
10 sp p. We stern Lake Erie 0.4-1.5 F W ; 1.8-8.1 DW Adams a nd John son 1 977
L i v e r 17 sp p. 0.0-0.5 F W Lucas et al. 1 970
7 spp. 0.5-1.0 F W 4 spp. 0.6-5.0 F W Luten et al. 1980
Whol e Nation wide, USA
1972 0.60(0.5 7 -0.6 4) FW May and McK i nney 198 1
1973 0.46(0.4 2 -0.4 9) FW
1976 -77 0.58(0.5 3 -0.6 2) FW 5 spp. 0.5-1.9 F W Pratt et al. 1972 4 spp. 0.2-0.3 DW Ro ssi et al. 1 976 6 spp. 0.0-0.5 F W Wal s h et al. 1977
12 sp p. 0.5-1.0 F W
6 spp. 1.0-2.0 F W



### 176 spp. 2.1-6.0 F W
B i r d s C o m m o n l o o n , Gavia im mer Egg 0.4(0.3

- 0.7) F W Ha seltine et a l

. 1983
R e d- br e a s t e d me r g an se r , Merg us serra t or Egg 0.47-1.0 F W Ha seltine et a l

. 1981
M a l l a r d

, Anas platyrh y

n ch o s Egg 0.28-0.8 1 FW
From Ke sterson Natio nal Wildlife Refu ge, California, ne sting on Se -contaminate d irrig a tion drai nwate rpon ds - 1983
American coo t, Fulica am eri cana Liver 37.2(2 1 -63) DW Ohlen dorf et al. 1986 Egg 54.0(3 4 -110 ) DW
Du ck s, Anas spp. Liver 28.6(1 9 -43) DW Egg 9.9(2.2

- 46 ) DW
Bla c k- ne ck ed s t ilt,
Him ant opus m e xican u s Egg 32.7(1 2 -74) DW
American avo c et, Re curvi r o s tra am erican a Egg 9.1 DW

Eared g r eb e, Podice ps ni gricolli s Liver 130.0 DW Egg 81.4(7 2 -110 ) DW

From Volta Wildlife Area, California, Co ntrol Site -19 83
American coo t Liver 5.0(4.4

- 5.6) DW
Du ck s, 2 sp p. Liver 4.1(3.9

- 4.4) DW
Bla c k- ne ck ed s t ilt
Liver 6.1 DW From Apal achicol a River, Florid a Little green h e ron, B u t o ri d

e s vi re sc en s Whol e 0.1-0.5 F W Wing er et al. 1984 TERREST RI AL Fungi <2.0 DW Jen k in s 19 80 Macrop hytes

We stern whe a t grass, Agropyron sm ithii



### 18South Da kota , plant top 11.5(0.0

- 8.4 ) DW
Little blueste m, Andropog on scop arius Plant top 0.0-6.0 DW
As paragus , Aspa rag u s offi cinal e We stern U.S. 2.7-11.0 DW Aster, wh ole
As te r ca er u l

es ce ns 560.0 DW
A. c o mmu ta tu s Max. 590.0 DW
A. m u ltiflora Max. 320.0 DW
A. occide ntali s 284.0 DW
Milk vetch, Astragalus argillosus Top 385.0 DW
Root 27.0 DW
A. beathii Top 1,963.0 DW
Root 66.0 DW
A. bisulcatus Top Max. 10,239.0 DW Seed 305.1 DW
A. confertiflorus Top 1,372.0 DW
A. crotula r iae Top 2,000.0 DW
Root 45.0 DW Locoweed, Astragalus sp p. Max. 46,000.0 AW;
Max. 6,000.0 DW Saltbush, Atriplex spp. 300.0-1,734. 0 DW Oats

, Ave na sativa 2.0-15. DW Buffalo gras s , Bouteloua d a c tyloi d

e s 2.7(0.0

- 12.0 ) DW
Indian pai nt brush, Castilleja spp

. 0.0-1,81 2.0 DW Gumweed, G r indeli a

s q ua rr os a 38.0(0.0

- 2,1 6 0 .0) DW
Broom wee d s, Gutierrezia spp. up to 723.0 DW Hapl opap pus spp. up to 4,800.0 DW
Toba cco, Nicotiana taba cum Leaf 5.8 DW Stem 44.2 DW
R i c e , Or yz a s a t i va



### 19Grain 0.09-0.1 1 FW Pear, P y

r u s c o m m unis
Fruit 0.02 FW
R y e , S e cale cer eale 0.9-25.0 DW Potato, Solanum tuberosum Tube r 0.2-0.9 DW Wheat, Triticum aestivum Grain 1.1-35.0 DW Stem and lea f 17.0 DW
Root 36.0 DW C o r n , Zea m ays Grain 1.0-20.0 DW Grap e, Vitis sp. R a i s i n < 0

. 0 0 1 F W
Annelid s Earthworm s , whol e From n o rmal soil 2.2 FW Birkn e r 19 78
From selenite - enri c he d soil 7.5 FW
From soil am ende d
with se wa ge slud ge Whol e 15.0-2 2 .4 DW Helm ke et al. 1979 Ca sts 0.6-0.7 DW
From control field
Whol e 22.1 DW C a s t s 0

. 6 D W
Ar th r o po ds Sow bug, Porcellio sp. 0.9 FW Jen k in s 19 80 Cra ne fly, larva, Tipula sp. 0.9 FW “Fly larvae,” whol e, from Astragalus plant with 18 00 ppm Se 20.0 FW
Birds Blackbird, Turdus m e rula
Whol e 2.1 DW Niel sen a nd Gissel-Niel s e n197 5 H o us e s p ar row , Passer d o m esticus
Whole 0.6 DW Pheasant, P hasia nus col ch i cus Whole 0.6 DW
Mammal s Beaver, Ca st or ca nad en si s Liver 0.2 FW Wren 198 4 Kidney 0.9 FW



### 20Intestine 0.04 FW
Muscle 0.09 FW Otter, Lutra canad en sis
Liver 2.1 FW Kidney 1.9 FW
Intes t ine 1.1 FW
Muscle 0.2 FW
W o od ch uc k

, Marm ota m onax From fly ash l andfill vicinity
A d u l t s Liver 2.2-10.7 DW Fleming et al. 1979 Lung 1.4-4.4 DW
J u veniles
Liver 3.9-6.4 DW Lung 2.1-2.8 DW
From control area A d u l t s Liver 0.4 DW Lung 0.4 DW
J u veniles
Liver 0.2-0.4 DW Lung 0.2 DW
Field mole, M i crotus ag re st is
Whol e 0.5 DW Niel sen a nd Gissel-Niel s e n197 5 White-t a iled d eer, Odocoileus vi rginianus
Muscle 0.16(0.0 5 -0.4 9) DW Ullrey et al. 1981
Ra ccoon, Pro c yon lotor
Liver 1.8 FW Wren 198 4 Kidney 1.9 FW
Muscle 0.2 FW Rat, Rattu s n o rv egi cus Whol e 0.4 DW Niel sen a nd Gissel-Niel s e n197 5
Ro ck squi rrel, Sperm ophilus variegatus Kidney 8.9-53.0 Sharma a nd Shupe 19 77 (Max. 90.0) DW Mole, Talpa e u rop aea Whol e 2.6 DW Niel sen a nd Gissel-Niel s e n197 5

a Each refere nce a pplie s t o the value s in the sam e row, and i n the ro ws that fo llow for whi c h no other refe ren c e is indi cated.



### 21DEFICIEN CYAN D PROT ECTIVE EFFECTS
Selenium i s a critical n u trie nt and a key comp one nt of several e n zy mes. The r e i s a general co nse n sus that Se deficien c yin livestock is increa si n g in many cou n tries, resulting in a need for adde d Se in the food. Sele nium deficie ncy is con s id ere d b ysome re se a r ch ers to co n s ti tute a great er thre at to health than sel enium poi so n i ng. Studies with animal s and human s have sugg este d that Se deficien c y, in part, un derlie s susce p tibility to cancer, arthriti s, hype rtensi on, hea rt disea s e, an d possibly pe riodo ntal dise ase a nd cataracts (Frost an d Ingvoldsta d 1975; Sham b e rge r19 81; Robbe re cht an d Von Grie ke n 1982 ). The s e lin kag e s h a ve not yet been dem on strated

con c lu sively; for example, eye lens cata ract wa s indu ced in 1 0 -d ay-old mal e rats by selenate, sele nite, sele nomethi o n ine, and sel eno cystine, p r esuma b ly through inte rference with glut athione meta bolism (O sta dalova and Babi cky 1980 ). On the other han d, adverse effects of Se inade qua cyhave b een cl early d o cum ented fo r a wide vari ety of organi sm s, inclu d ing ba ct eria, protozoa ns , Atlantic salmon, rai nbo w trout, Ja pa nese quail, d u cks, poultry, rats, dog s, horse s, shee p, swi n e , cattle, antelope s, gazelle s, deer, mo nkeys, and hum ans (Je n sen 1968; Frost a nd Ingvold s ta d 1975; Methanococcus vanniellii: cultu r e and effect s of seleni um a nd tung sten o n gro w th. J. Bacteriol. 13 0:1 404-140 6.

Jon e s a nd Stadtman 19 75; Fishbei n 197 7; Harr 197 8; Kaise ret al. 1979; Hilton etal. 1980; Shambe rge r 1981; Bovee and O'B r ien 1 982; Ro bbe re cht and Von Grie ken 1 982 ; NRC 1 983; Levand er 19 8 3 , 1984; Mor r i s et al. 1984). Sel enium defi c ie ncy, wheth e r indu ced exp e r iment ally by use of lo w Se feeds suppl e m ented with alpha tocop herol or by chro nic in gestio n of low Se diets, has cau s ed a n u mber of mala dies: hig h em bryoni c morta lity in cattle and she ep; anemi a in cattle; po or growth a n d r eprodu ction in she ep an d rats; re du ced viability of newly hatch ed qu ail ; nutritional m y opathy (whit e muscle di se as e ) in sh eep , swine, an d cattle; hepatic necro sis a nd lamene ss in dog s, horse s, and bre edin g bulls; hair lo ss and sterility in rat offspri n g; and sp erm a tozo an abno rmalitie s in rats. Defi ci enci e s were usu a lly preve n t ed or reversed by suppl ements with sodium selen a t e or sele nite at 10 0 ppb Se in the diet, or 20 μg Se/kg bod y weight admi n istered pa re nterally.

The availabilit y of Se to pla n ts may be le ssene d by m odern ag ricultural p r a c tice s, eventually contributin g to Se deficiencyin animal consum ers. For example, fert ilizers containing nitrogen, su lfur, and phosphorus all influen ce Se uptake by pla n ts thro ugh di fferent mode s of action, the net effect being a red u ctio n in Se uptake (Frost an d Ingvoldsta d 19 75). The b u ild up of sulfur (a s sulf ate s ) in the soil, due t o acid rain, fertilize r s, an d other

sou r ces, inte rferes with Se accumul a tion by crop s (F ro st and Ingvo l dstad 1 975 ). In addition, hi gh dietary lev e ls of various h e a vy metals (i nclu ding cop per, zin c , silv er, and me rcury) contri b u te to Se deficiency in anim a ls (Frost an d Ingvoldsta d 19 75; Harr 19 78 ), pre s uma b ly as a re sult ofSe binding with the metal into biologi call y unavailabl e form s (Harr 1 978; Kaise re t al. 1979).
The protectiv e action of se lenium ag ain s t the adverse or lethal effects in du ced by various m e tals an d metalloid s is well do cum e n t ed for a wide variety of plant and animal spe c ie s. Among ma rine o r gani sm s, for example, sel enium p r ote c ts agai nst toxic levels of me rc u ry in alga e (Gotsi s 19 82 ), shri mp (L ucu and Skrebli n 1982 ), crab s and oyste r s (Glickstei n 19 78), fish (S he li ne and Sch m idt-Ni elsen 1977 ), and m a mmal s (Koe man et al. 1975). Si milar ob se rva t ions have b e en re co rde d for co ppe r an d marin e alga e (Got sis 1 9 8 2 ); cad m ium and fresh w ate rsn ails (Wilbe r1 983), ma rine cra b s (Bjerra gaard 198 2), earth wo rms (Helm k e et al. 1979; Beyer et al. 1982 ), and ra ts (Harr 1978 ); mercury o rmethylmercu r y and rats (Cappo n and S m ith 1982 ), eggs of la ke trout (Klaverkam p et al. 1983b), fresh w ate rtel eost s (Kim et al. 1975, 197 7) and (temp o ra rily) Ja pan ese q uail (ElBerge a rmi et al. 1977, 198 2; Beijer and Jernelov 19 7 8 ); and a r seni c and fresh w ater and m a ri ne teleo s ts (L uten et al. 1980; Orvini et al. 1980). Not all te sts were con c lusi ve. Studie s with some speci e s of fre s hwate rteleo s ts demon strated negligible a n t agoni sm of Se again s t mercur y (Klave rkamp et al. 1983a) o rcadmi u m (Dun can and Klaverkamp 1 983). Sele niu m repo rtedly prote c ts ma m m als an d poi kilothe r m s ag ainst poi so nin g by thallium, the herbi cid e paraquat, ca dmi u m, mercury, lead, arseni c, and co ppe r (Wilbe r198 3).

Rea s o n s, to accou n t for the antago nism of Se and he a vy metals (h ere me rcury i s used a s an example ) incl ude dietary so urce and chemi c al form of Se, influence of sulf ur, biol ogi cal tran slo c ati on of Se or m e rcury to less critical body p a rts, an d che m ical lin kag e of Se to me rcury on a linea r basi s . The e x act mode of intera ction is prob ably co m p lex and ha s not yet been resolve d . In regard to diet, Se of animal origin a nd in the form of sele nate is le ss effe ctive than Se from pl ant and ino r g ani c sou r ces i n preventin g methylmercu ry neurotoxicit y in experim ental animal s (Cap pon an d Smith 1982 ). Disrupti on of sulf ur metab o lism by Se, the sulfur b e ing repla c e d by seleno -amin o acid s an d oth e r cell con s tit uents contai n i ng Se in living orga nisms, is one p r ob ab le

cau s e of Se p o iso n ing. It is con c eiva ble that Se-Hg co mpoun ds fo rmed within th e orga nism would be suffici ently



### 22nonrea ctive biologi cally to interfere with sulfur kineti c s, presu m ably -S H group s (Koeman et al . 1975; Beijer and Jernelov 19 7 8 ; Capp on an d Smith 1982 ; Gotsis 19 82 ). Different ial redi strib u tion of Se or Hg to less critical body parts m a y partly accou n t for observe d an tagoni sms. Pretr eatme nt of marine min n o ws with Se prote c ts ag ai nst Hg poi so ning and cau s e s a marked re distribution of Hg among o r g ans, presuma b ly to non-crit ical bo dy part s , and this tra n sfer may partlyaccount for t he ob serve d Se-Hg antag onism s in tha t speci e s (Sh e line an d Sch m idtNiel sen 1 977 ). Some investigators h a ve repo rted that Se results in i n crea sed Hg accumul a tion s. Increa sed retention of Hg and othe r metals may l ead to a high er le vel of bio m agnification in the food chain an d high er body burd en in the individual, wh ich might cou n tera ct the po siti ve effect of decrea s ed in toxication (Be ijer and Je rne l ov 1978 ). Extensive re sea r ch is unde r wayon the chemi c al lin kag e of Se and Hg. In marine ma m m als an d human s, Se and Hg co ncentration s a r e closely relate d, almost line a rly in a 1:1 molar ratio, but this relatio n blurs in teleost s in whi c h Se is in abund an ce, and fails in bi rds (Koem an et al. 1975; Beijer an d Je rn elov 1978; Orvini et al. 1980; Cappo n and S m ith 1982 ).
TOXICITY
MAMM ALS AN D BI RDS
“The el ementseleni um ca n be tra c ed in an orde rly se quen ce fro m its origin in th e ear th' s cru s t to specific geolo g ical fo rmation, to distribution of sp ecific g ene ra and group s ofplants which requi re the el ement for thei r gro w th, to the accumulatio n in vegetatio n, and to its s ubsequ ent toxicity to birds or mamm als t hat con s um e the sele nifero us f ood s” (Ro s e n f eld and Beat h 1964 ). Sele nium poi soni ng in livesto ck, discu s sed here, was la rgely extracted fro m reviews by Ro senfel d an d Beath (19 6 4 ), Fro s t (19 7 2 ), Fi sh bein (1977 ), Ha rr (1978 ), Sham berg e r (198 1), NRC (198 3), an d Wilbe r(1 983 ).

In livestock, there a r e thre e basi ctypes of seleni um p o is o n ing: a c u t e, resulting from con s u m pt ion (u sually in a singl e feedi ng) of a sufficient quantity of highly sele ni ferou s wee d s; “blin d sta ggers,” from con s um ption of mode rately toxic amount s of selenife rou s we ed s over an extended perio d of time; and "alkali d i sea s e," ca used by the con s u m ption of mo derately sele niferou s g r ain s and fo rage gra s ses ove r a perio d of se veral we eks to months.
Acute poi soni ng is a s soci ated with pla n t material s con t aining 40 0 to 800 ppm Se: shee p died whe n fed amount s of plant material rangin g from 8 to 16 g/kg bo dy weight, or about 3.2 to 1 2 .8 mg Se/kg body weig ht. The minimu m lethal dose o fSe administ e red o r ally a s selenite (mg Se per kg bo dy weight) ra nged fro m 3.3 for horse s and m u les to 11 for cattle and 1 5 for swine. Ot her mo de s of admini s tratio n were more toxic, e.g., 2 and 1.2 mg Se/ kg body wei g h t given sub c u t aneou sly kill ed swine in 4 hours an d 5 d a ys, re spe c tively; and 1.5-6

. 0 mg Se/kg bo dy weight giv en intraven ou sly or intra peritonea lly to ra ts and rabbits were fatal. Acci dental toxi co sis of shee p and cattle from ov ertre a tment with comme rci a l mi xtures ofSe salts and vitamin E are also d o cume nted for Australia and New Ze a l and. Acute S e poisoning i n dome s tic livesto ck i s ch aracteri ze d by abno rmal movement s, lowe red h ead, droop ed ea rs, diarrhe a , el evated tempe r ature, rapid pulse, labore d breathi ng, bloating with abdomi nal pa in, incre a sed urinatio n, and d ilated pupil s . Before deat h, which is du e to respirato ry failure, there is co mplete p r ostratio n and lethargy. Du rati on of illness extend s fro m a few hou rs to seve ral d a ys, depe nding o n the toxicity of plant materia l ingeste d. In thes e ca se s, Se is distri but ed bythe circulatory syste m to all body org a n s, the co nce n tration s bein g highe st in liv er, blood, ki dney, sple en and brain, an d lowe st in muscle, ski n, hair an d bone. Elimin ation is pri m a r ily in the urin e; smalle r qu antities are e x creted with the fece s, bre a th, perspi r ation, and bile. Post mortem exam ination s indicate many pathologi cal cha nge s in the h eart, lung s, ru men, liver, kidney, and othe r org ans. No effective treatment is kno w n for cou n tera cting toxic effects of large am ou nts of ingeste d selenium.

Chroni c sel e n o si s may be indu ced bydi etary exposure to natural selenite, sel e n a te, or sele niferou s feedstuffs at dietary co nce n tration s bet wee n 1 ppm (rat) an d 44 p p m (ho r se), o rfrom water containin g 0.5 to 2.0 ppm of Se. Cattle fed 0.5 mg Se/kg bo dy weight 3 times wee k ly lost their ap pe tite; sheep fe d up to 75 mg sele nite daily develop ed m y ocardial de g eneration a n d fibrosi s , pul mona ry con g e stion, an d e dema. The minimum toxic co ncentrati on of Se in lifetime exposu r e of rats (a compa r atively sen s itive sp e c ie s) fed Sedeficie nt diets fortified with Se was 0.3 5 mg Se/kg di et , as judge d b ychang es in l i ver che m istry; and 0.75 mg Se/kg diet, as judged by lo ngevity, and histolo g ical chang es in h e a rt, kidney, a nd spl een. Th ese con c e n trations are 10 time s the nutrition al threshold fo r Se, and abou t 25% of the minimum lifetime exposure to Se in natural feedstuffs tha t produ ce s si milar effect s unde r the sa me experim e n tal con d ition s . Signs of ch roni c sel eno si s inclu de skin l e sio n s, lymph chan nel infla mmation, lo ss of hair an d nails, an emia , enlarge d organ s (splee n, pan cre a s, liver), fatigue, la ssitu de, and dizzine s s. “Blind stag gers” is ch ara c te rized by anorexia, emaciatio n , and sud den colla pse, follo wed by death. Typically , the upp er intestin al tract is ul cera ted. In “alkali dise ase,” in cattle,



### 23hog s, and ho rse s that had eaten selenif e rou s g r ain s , t he sign s were deform a tion and slo ughi n g of the hooves, hair lo ss, la ssitude, ero s ion of the ar ticul a r ca rtilag e s, redu ce d co nception, increa sed reab so rpt i on of fetuse s, and de gen eration of heart, kidney, and li ver. It is likely that Se displace s sulfur in keratin, resul t ing in stru ctu r al cha nge s in h a ir, nails, an d hooves (Fish bein 19 77).
Among birds, it appears that domesti c chicken s are e x tremely sen s itive to Se; redu ced h a tch i ng of egg s
wa s re co rde d at 7 to 9 ppm Se in feed (Ort and L a tsh a w 19 78). Si milar re sult s were ob se rve d by El-Berge armi et al. (1977 ) in Jap ane se q uail at 6 and 12 ppm dieta ry se lenite. Studie s in pro g ress at the Patuxent Wildlife Re sea r ch Ce nter with ad ul t mallard s ind i cated that 10 0 ppm dieta ry seleni um (a s sodium sele nite) wa s fata l within one month, but that survival was high at 25 ppm after 3 months. Poor egg hatchability was recorded in the 25 ppm selen i te group, but not in the 10 ppm sel enite gr ou p; however, hatching p e rcent wa s re duced in eg g s of adults fed 1 0 ppm of Se as selen o methi onine (Dr. G. Hein z, pers. comm.). It appears obviou s that additiona l

resea r ch is n eede d on the toxicology of orga no sele ni um com pou n d s.

Seleno sis in warm bloo de d orga nisms i s modified by numerou s factors, inclu d in g method of a d minist ration, chemi c al fo rm of Se, dietary com p o s ition, and ag e a nd nee ds of the org ani sm. For exampl e, Se admini s tered in natural fee d st uffs is only ab out one-fo urt h as toxic a s are si milar ex posure s in water or p u rifie d feeds (Ha rr 1978 ). Con c u rre nt inge stio n of mineral s and ro ugh o r high protein feed s red u ces Se toxicity, a nd expo sure by diet is less to xic than expo sure pa rente r ally or by inhalation.
Many com p o und s are kno w n to preve n t or red u ce toxic ef f e ct s ofs uba cut e an d chr oni c sel e n o si s in pig s , beef cattle, a nd other wa rmblood ed o r g anism s. A partial list includ es arse nic, st ry chni ne sulfate, tungsten, germ anium, a n timony, beet pectin, high -fat diets, ACT H inje ction s , sulfate, incre a se d dietary protein s , lactalb u min, ovalbumin, wheat protei n, dried b r e w e r ' s yeast, de siccated liver, lin see d oil meal , gluco s amin e, hemo c ystein e, creatin e, methionin e , an d choli ne. Nota ll of these compou nd s afforde d equ al p r otectio n agai nst variou s Se formulatio ns; th e rea s on s for the differen c e are not cle a r, but it appears that the sub j ect of sele nop rote ctive agents wa rra nts ad ditio nal re sea r ch effort.

AQ UATI C O R G ANISMS Among sen s itive spe c ie s of aquatic o r ga nism s, death wa s ob serve d at water co nce n tration s betwe en 60 and 60 0 ppb Se; early life history stage s that we re subje c ted to compa r atively lengthy expo sures a c cou n t ed for most of these data (Tabl e 3). Latent mo rtality after ex posure to co mparatively high Se con c e n tration s ha s been documente d , but not extensively. For exam ple, all em bryos of the zebrafi s h ( B r a ch y

da nio re ri o) su rv iv ed exposure to 3

, 000 ppb of S e durin g deve l opment, but more tha n 90 % of the resul t ant larvae di ed so on after hatchi ng; at 1,000 ppb, survival was simi lar to that in control s (Niimi and La Ham 1 975). It has b een sugg este d (EPA 1980) t hat selenite is more toxic than sel enate a nd is preferentially conc entrated over sel enate by mussel s, Myti lus gall oprovi n ciali s

(M ea sure s and Bu rton 198 0). Sel enite is ge nerally more toxic to early life history stage s and effe cts are mo st pro noun ce d at elevat ed tempe r atures (Klaverkamp et al. 1983 a). Also, Se salts m a y be conve r ted to methylated forms by mi cro o rg a n isms, a nd these are readily a c cu mulated by a quatic vertebrates (Klaverkamp e t al. 1983a). Among fre s h w ater al gae speci e s, it has been d e mon s trated that sel enite, sele nate, sel enomethi onin e , and sel eno purin e are all toxic, but that sulph u r, as sulphate, ha s a signifi cant prote c tive rol e again s t Se toxicity (Kuma rand Pra k a s h 1971 ). Num e rou s ad ditio nal ch emical comp oun ds a nd mixtures p r ob ably prote c t again s t Se toxicity, much a s Se prote c ts a gain s t toxic effects of mercury salt s and other chemi c als, but data are spa r se on Se protective agents.
Almost 50 ye ars a go, Ellis et al. (1937 ) reco rde d a lon g lis t of sign s of seleni um p o iso n ing in tel eost s : loss of equilib rium, lethargy, co ntraction of de rmal ch romato phor es, lo ss of coordinatio n, muscle sp asm s , prot rud i ng eyes, swolle n abdome n , liver deg ene rati on, redu ction in blood h e m oglobi n and e rythro c yte nu mber, an d increa se in white blood cell s. Soren s e n et al. (1984 ), observed m o st of these si gns in Se -poi son ed green sunfi s h toget her with el evated liver Se con c e n tration s , redu ce d bl ood hem atocrit, enlarged li ver, histopath o logy of kidney an d heart, swolle n gill lamellae with extensiv e cellul a r vacuolization, an d necrotic a n d dege neratin g ovarian folli cl es.



### 24Table 3. Toxicity of seleniu m salts to aq uatic biota. Value s sh own are in μg/l (p p b ) in medi um fatal to 50% of the orga nisms d u r ing expo su re for variou s in tervals.

Medium, taxo nomic Exposu r e LC-50 Referen c e a grou p, and sp ecie s interval (ppb ) in hours (h), days (d ), or lif e cy cle (L C )

FRESHWATER Algae
Anabae na va riabili s 96 h 15,000 -17,0 0 0 Kumar an d Prakash 197 1 Anacysti s

nid u lan s 96 h 30,000 -40,0 0 0 Oedogonium cardia cum 48 h <10 0 Na ssos et al. 1980
Molluscs Snail, Phy s a

sp. 96 h 24,000 Rea d ing 19 7 9 Snail, Phy s a

sp. 48 h >10,0 0 0 Na ssos et al. 1980
I n se ct s Mosq uito larv ae, Culex fatigans 4 8 h < 3 ,1 00 Midge, Tanyt a rsus di ssim ilis 96 h 42,400 EPA 1980 C r us tac e an s Clad ocera n , Dap hnia m a gn a 48 h <25 0 Na ssos et al. 1980
" 96 h 710 Halter et al. 1 980
" 14 d 430
" 28 d 240 EPA 1980
" LC 70-1 20 Scud, 96 h 760 Adams 1 976 Hyallela azteca 96 h 340 Murp hy 1981
" 14 d 70 Halter et al. 1 980 Clad ocera n , Dap hnia pul e

x 96 h 3,870 Rea d ing 19 7 9 LC 600-800 EPA 1980 Amphibia n s Frog, Xeno pus lae v is Embryo 27 h 20,000 Browne an d Dumo nt 1979
" 61 h 10,000
" 96 h 4,000
" 113 h 2,000 Tadpol e 3 d 8,000
" 5 d 2,600
" 7 d 1,500
Fish Goldfish, Carassius auratus 96 h 26,100 Cardwell et al. 1976
" 14 d 6,300
W h ite suck er , Catostom us 48 h 48,600 Dun c a n and Klaverkamp

c o mme r s o n i 96 h 31,400 1983



### 25Comm on carp, 24 h 72,000 Sato et al. 1980 Cyprin us ca rpio 96 h 35,000 Speha r et al. 1982
Northern pike, Esox lu cius 75 h 11,100 Klaverkamp e t al. 1983a Mosq uitofish, 48 h >>6,000 Na ssos et al. 1980

Gam busia aff i nis 96 h 12,600 Rea d ing 19 7 9 Cha nnel catfish, Ictalu rus pun ctatus 96 h 13,600 Cardwell et al. 1976 Flagfish, Jord anella flori d

a e 96 h 6,500 Bluegill, Lepo m i s m a crochi rus 96 h 28,500
" 14 d 12,500
" 48 d 400-2,000 Adams 1 976 Coho s a lmon, Onco rh yn ch us ki sut ch Fry 43 d 160
Yellow pe rch, Perca flave scens 10 d 4,800 Klaverkamp e t al. 1983a
Fathead mi nn ow, Pim ephal es prom elas Fry 96 h 2,100 Cardwell et al. 1976
Juvenil e 96 h 5,200
Adult 96 h 2,200-12,50 0 Adams 1 976
" 96 h 620-970 EPA 1980
" 96 h 1,000 Halter et al. 1 980
" 9 d 2,100 Cardwell et al. 1976
" 48 d 1,100 Adams 1 976 LC 83-153 EPA 1980
Rainbow trout, Salm o gairdneri 96 h 8,100 Speha r et al. 1982
" 96 h 4,200-4,500 Adams 1 976
" 96 h 12,500 EPA 1980
" 96 h 7,200-8,800 Hod s o n et al. 1980
" 9 d 5,400-7,000
" 21 d 460 Adams 1 976
" 96 d 290
" LC 60-130 EPA 1980
Brook trout, Salveli n us fontinalis 96 h 10,200 Cardwell et al. 1976
MARI NE
Molluscs
P a cif i c oy st e r , Cra s sostrea gigas
Larvae 48 h >10,0 0 0 Glickstei n 19 78 C r us tac e an s Cop epo d, Acartia cla u si 96 h 1,740 EPA 1980 Cop epo d, A. tonsa 96 h 800
Blue crab, Ca llinecte s sapi dus 96 h 4,600 Wa rd et al. 1981 (2,700 -7,8 00)
Dun gen ess crab, Ca ncer m agister
Larvae 96 h 1,040 Glickstei n 19 78 My sid sh rimp

, Mysid opsi s

bahia



### 26Adult 96 h 1,500 Wa rd et al. 1981 (1,100 -2,1 00)
Juvenil e 96 h 600 EPA 1980 Egg LC 127-143
Brown sh rimp

, Penaeus a z t e cus 96 h 1,200 Wa rd et al. 1981 (800 -1,8 00)
Fish Fourspi ne sti ckl eba ck, Apeltes quadracus 96 h 17,350 EPA 1980 Sheep she ad minno w, Cyprinodo n va riegatus Adult 96 h 7,400-67,10 0 Egg throu gh j u venile LC 470-970 Wa rd et al. 1981 Pinfish, Lago don rh om boid e s 96 h 4,400 (2,900 -6,7 00)
H a dd oc k

, Mel anog ram m u s aeglifinus Larvae 96 h 600 EPA 1980
Atlantic silverside, Meni dia m enidia 96 h 9,725 Summer flou nder, Paralichthys dentatus Larvae 96 h 3,500
Winter flou nd er, Pseu dopl euro n e c tes a m erican us Larvae 96 h 14,250 -15,1 0 0

a Each refere nce a pplie s to the values i n the same ro w, and in the rows that follow for which no other reference is indi cated.

SUBLET H A L AN D LATE N TEFFECTS
Re sults of lab o rato ry studie s and field inv e stigatio ns wi th fish, mammals, and bi rds have le d to gene ral agre e me nt that elevated concentratio n s of selenium i n diet or wate r we re a s soci ated with re produ ctive abno rmalitie s includi ng con genital malfo r mations, sele ct ive bioa ccu m ulation by the org ani sm, and growth retardation. Not as extensiv ely docum ent ed, but never t hele ss imp o rt ant, are re ports of seleni u m -ind uced chromo som a l aberration s, intestinal le sio n s, shifts in speci e s comp osition of fre s hwate ralgal comm unitie s , swim ming im pairm ent of protozoan s, an d behavio ral modificatio n s.

AQ UATI C O R G ANISMS In green sunfi s h from a la ke in North Ca rolina re ceivi ng sel enium (as fly ash wa stes from a coal-fired po wer station), reprodu ction faile d and the po p u lation de clin ed marke d ly. In these fish, Se levels we re elevated in liver (up to 21.4 p p m fresh wei ght) and oth e rtissue s; ki dn ey, heart, liver, and gill sh o w ed hi stop athology; and b l ood chemi s try wa s altere d. Ovarie s of fish h ad nume r o u s necrotic a nd rupture d egg f o llicle s that may have contri buted to the populatio n extinction (Soren se n et al. 1984). It is proba ble thatSe uptake byplankto n (co n tainin g 4 1 -97 p p m dryweight) from lake water (9-12 ppb ) intro duced Se to the food chain where it ultimately

rea c he d elev ated levels in fish throu gh b i omagnifi catio n (Cu m bie a n d Van Ho rn 1 978). In labo ratory tests, however, egg s of comm on carp hatched norm a lly whe n incu bated i n media cont aining 5,0 00 ppb of Se (Hu c kab ee a nd Griffith 19 74), as did eg gs of lake tro u t ( Salv elinus nam aycush ) at 10,000 pp b of Se (Klaverkam p et al. 1983b). In frogs ( X e n opus laevis), cra n ial an d verteb ral defo r mities and lo wered surviv al were do cum e nted duri ng d e velopme n t in water with Se con c ent ra tions of 2,000 ppb or hig h e r(Bro wn e an d Dumo nt 1979 ).

At water co ncentration s of 47 to 53 ppb, Se was a s so ci ated with an emia and red u ce d hatch of rainbo w tro u t (Ho d son et al . 1980), growt h retardation of fresh w ate rgr ee n alga e (Hutchin son a nd Stoke s 19 75; Klaverka mp et al. 1983a ), an d shifts in spe c ie s com p o s ition of fres h w ater algal co mmunitie s (P atrick 197 8). At 250 ppb Se, gro w th wa s redu ced in rai nbo w trout fry after exposu r e for 21 d (Ad a ms 19 76 ), and goldfi s h d e mon s trate d an avoidan ce re spo n se after 48 h (Weir a n d Hine 1 970 ). At Se water con c e n tration s of 7,930 -11, 000 pp b, gro w th



### 27was inhibited in freshwater and ma rine al gae (Patri ck 1978; EPA 1980), and sw i mming rate was reduced in the proto z oa n Te trahym e n a py riform is (Bov ee and O'B r ie n 1982 ). Egg s of cha nnel catfish exp o sed to ce rtain metals (incl udin g ca dmium, mercury, and co pp er) p r od uced an increa se d percenta ge ofalbino fry; however, eg gs exposed to 2 50 ppb Se p r odu ced fry wi th norma l pi g m entation (Westernma n an d Birge 19 78).
A significa nt numbe r of ch romo som a l a ber ration s wa s indu ce d in the edibl e gob y, Boleophtha lm us dussum i eri, b ySe after intramuscul a r a n d water exp o s ures (Kri shn aja and Reg e 1982). Intra m uscula r inje ction s of Se as low as 0.1 mg/ k g body wei ght, or 3,200 p pb i n the water column, we re asso ciated wi th a marked enha ncementof polyploid cells 76 -96 h p o stadmi n ist r a t i on; some de aths were re corde d at high er test
con c e n tration s . Selenite was mo re effective than sele nate in indu ci ng ch rom o so mal abe rratio n s. The a u tho r s
con c lu ded th at a relatively narrow rang e of Se con c e n trat ion s lead to a mutagen ic rathe rthan a lethal effect

. Accu mulatio n of Se by aquatic org ani sm s is hig h ly variabl e. In sho r t-term (48 h ) laboratory test s at Se water

con c e n tration s of 0.015 to 3.3 ppb, Na sso s et al. (19 80) repo rted biologi cal con c entration factors (B CF ) of 460 for mosquitofi sh to 32,00 0 for a fre s h w at er ga stro pod; values were i n terme d iate for dap hnid s (2,100), pla n kt on (2,600 ), and Fundulus kan s ae (3,300), the freshwater k illifish. High BCF's (>680) were recorded for freshwater diatoms subj ected to maxi mum co ncent ration s of 40 ppb Se (Patri ck 1 978 ). Livers from rai n bow tro u t and brown trout may con t ain from 50 to 70 ppm Se fresh weig ht durin g lifetime exposure in selenife rou s (12.3

- 13.3 p p b ) water, an d ha ve BCF value s of 3,759 to 5,691 (Kai se r et al. 1979); BCF value s were 361 to 3 90 for skin, a nd about 18 0 for muscle (Kai ser et al. 1979 ). In short

- term exposu r e s , most of the Se was p r o b a b ly adso r be d to the body su rface (Fo w ler a nd Benayoun 1 9 76c ), and wa s then rapidlylost on tran sf er to Se-fre e media (B ro wne and Dumo nt 1979 ). In longer ex posure s , the BCF value s in aquati c org anism s were lowe r after im mersion in hi gh ambient Se concentratio n s over extende d perio ds. Th us, mari ne crabs exp o sed to a water co nce n tration of250 ppb of Se for 29 days a c cu mulated Se o v er wate r co n c entra tion lev e l by a factor of 25 for ca ra pace, and 3.8 for gill; accumula tions in mu scl e and he pato pan cre a s we re negligibl e . Cadmi u m in solution en han ced Se upta k e (Bjerrag aard 1982 ). Exposure of commo n carp to 1,00 0 ppb Se for 85 days resul t ed in a whol e body BCF o f6; addition al stu d ies of 7 wee ks exp o sure plus 7 wee k s postexp osure at Se concen trations b e tween 50 0 and 5,000 ppb (Sato et al. 1980) yiel ded a BCF ra nge of 0.6 (5, 000 pp b) to 1

. 8 (500 pp b). High est BCF' s in ca rp were 50 for kidn ey an d 80 for liver after exposur e of the fish to 100 pp b Se for 7 wee k s plus 7 wee k s in Se-free m e dia. For carp, Se tende d to accumulate in ki dney, liver, gill, gall bladde r, heart, bone, and muscle, in that genera l orde r (Sato etal. 1980). Studie s with fre s h w ater o r g a n is m s coll ect ed from a farm pond conta m inated by fly ash with high Se l e vels (F urr et al. 1979), an d with mari ne bivalves and nerei d wo rm s held for 4 mo nths in sea w a t er flowing throu gh co al fly ash contai ning 6,200 pp b Se (R yther et al. 1979), sho w ed that accu mulation was slight. Contraste d to this are the o b se rvation s o fCherry et al. (1976 ) an d Ohlen dorf et al. (1986 ). Ch erry an d his

co worke r s col l ected mo sq u i tofish from a drain age syst em that recei v ed high coal fly ash con c e n tration s at one end an d thermal discha rg es at the othe r; mosq uitofish c ontai ned u p to 9.0 ppm Se whole b o d yfresh weigh t. Of 40 eleme n ts examined, on ly Se, zinc, and cal c ium were a c cumul a ted in exce ss of the levels measured in the water. O h len dorf et al. found mean re si due s of 172 p p m dry wei g h t (rang e 110 -280 ppm ) in whol e mosqui tofish from irri gation drain w ate rp ond s co ntami nated by abo ut 300 ppb of Se; based o n a wet/dry factor of 4, the BCF for whol e mo squitofi sh wa s >9 1.

Selenium a ccumulation i s modified by water tempe r at ur e, age of th e orga nism, organ o rtissue spe c ificity, mode of admi n istratio n, an d other fa ctors. In the mari ne mussel, M ytilus galloprovinciali s , an inc r eas e in water temperature f r om 13 to 29 ° C dou bled th e BCF in 13 d a ys (Fo w le r a nd Benayou n 1976b ). Mussel s prefe r e n tially accumul a ted sele nite over sele nate (F o w ler a nd Ben a youn 19 76b ); however, m u ssel s did notreach a stea dy state in 63 da ys (Fo w ler a n d Benayoun 1976 c), indi cating t hat Se kineti cs in so me spe c ie s a r e difficult to eluci date in short-te rm stu d ies. Accum u lation rate s we re hig h e rin small than in l a rge m u ssel s (Fowl e r an d Benayoun 1 9 76b), a s they were in fre s h w ater tele ost s (F u rr et al. 1979 ). Ho we ver, the reverse was d o cu mented for marin e m a mmal s and t e leo s ts (Ei s le r 1984 ). Wh e n Se was ava ilable from b o t h the diet and the medium

, con c e n tration s we re hig h e s t in liver, kid ney, and gills of teleosts (Soren se n et al. 1982; Furr etal. 1979; Kaiser et al. 1979), e x oskeleton ofcru s ta cean s (Fo w ler a nd Benayoun 1 9 76c; Bjerrag a a rd 19 82 ), an d visce ral ma ss and gill s of molluscs (Fo w l e r and Be nay oun 19 76 c). Whe n Se wa s admini s te re d in food to marine sh rimp s,
con c e n tration s we re hig h e s t in visce ra a nd exoskel e ton, sug g e s tin g that ingeste d Se is rea d il y translo cate d from internal to external tissu e s (Fo w ler a nd Benayoun 1 9 76c). Con c e n t rations of Se in cru s ta cea n s u s ually we re highe r in feca l pellets than i n the diet; fecal pellets ma yrepresent a possibl e biolo g ical me ch ani sm for do wn ward vertical tra n sport of Se in the se a (Fo w l e r and Be nay oun 19 76a ), as well as in f r eshwater e n vironme n ts.



### 28The time for 50% excretio n of accumul a ted Se has r ange d from 1 3 to 181 days in various sp ecie s of mari ne and fre s h w at er fauna. Biol ogical half-life of Se accum u lat ed from th e medium h a s bee n estim a ted at 28 da ys for carp (Sato et al. 1980), 37 days for the marin e eup ha usid cru s ta ce an Mega nycti phan es no rv egica (Fo w ler and Benayoun 1 9 76a), 63 to 8 1 days for the marine mu ssel Mytilus gall oprovinciali s

(Fowle r an d Benayou n 197 6b), 58 to 60 days for the marin e shri mp Ly sm ata caudata (Fowl e r an d Benayoun 1 9 76b), an d, as reviewed by Stadtman (19 74, 1977 ), 13 days for gup pies, 27 d a ys fo r eels, and 28 days for le ech e s. Studie s by Lemly (198 2a ) with bluegill s and l a rge m outh b a ss sh owed e l evated tissue levels after e x posu r e to 10 ppb of Se for 120 days. Time fo r 50% excretion in 30-dayelimination tri a ls was a bout15 days from gill and eryth r ocyte s ; however, there was e s sentially no el imination fro m splee n , liver , kidney, or muscle. It appears that re search is n eed ed on prefe r ential ti ssue rete ntio n of Se and its implication s for bioch e mi cal an d meta bolic tra n spo rt mechani sm s.

TERREST RI AL INVERTE BR ATES
Con c e n tratio ns of Se de creased in whol e earth wo rms fr om 22.4 to 15.0 ppm (dry weight) a s the rate of slud ge ap plication increa sed from 15 to 60 metric ton s / ha. Co ncen trations of Se in soil and sl udge were 0.3 and 0.5 ppm dry weig ht, resp e c tively (Helm k e et al. 1979 ). Other stu d i e s indi cate d that some m e tals, notably cadmi u m, de cre a sed in worm s living in soil s amen de d with se wa g e slud ge but that Se con c e n tration s we re not affected (Bey er et al. 1982 ). The biolo g i c al half life of Se in earth wo rms i s estim a ted to be 64 d a ys, a perio d

con s i s tent wit h values of 1 0 to 81 days documente d for ants, bi rd s, mammals, a nd aqu atic bi ota (Stadtma n 1974, 19 77).

BIR D S Embryos of t he dome s tic chi c ken ( Ga llu s dom esti cus) are extrem ely sensitive to Se. The hatchability of egg s is re du ced by con c e n t rations of Se in feeds(6 to 9 ppm) that were too lo w to produ ce p o isoning in oth e r avian sp eci e s. Dietary Se excess was a s so ciated wi th decrea s e d eg g weig ht, decrea s ed e gg p r odu ction a n d hatch ability, anemia, elevat ed kid ney Se resi due s in chic ks, an d a high in ciden ce of gro ssly d e forme d emb ryos with missing or disto r ted e y es, bea ks, wings a nd feet (Ort an d Latshaw 1 978; Harr 1 979 ). Selenomethi onin e
wa s more effective than sodium selenit e in raisi ng th e Se content of tissue s an d egg s (Mo ksnes 1 983 ). Until recently, there wa s little credi ble evide n c e that sel eni um adverselyaffect ed wild bird s. Ho wev e r, Ohlen d o r f et al. (198 6) repo rt ed seve re rep r odu ctive effects in du cks ( Anas spp.), A m eri c an coot ( Fuli ca am eri can a ), and ot her spe c ie s of aq uatic birds n e s ting at irri gat ion drai nwate rpond s in the San Joaq uin Valley, California. Water in these p ond s contai ned a b norm a lly high con c entratio n s of abo ut 300 ppb of Se, but low or no n-dete c tabl e levels of silver, ch ro mium, arseni c, cad m ium, mercury, lead , and zin c . Of 347 ne sts ex amined from this site, ab ou t 40% had at le ast one d ead embryo a nd a bout 20% ha d at least one embryo or ch ick with obvio us extern al anomali e s, in cludi ng missi ng or ab no rm al bea ks, eye s , wing s, leg s , or feet. In a ddition, brai n, heart, liver, and skeletal an o m alies we re reco rde d . Con c entration s of seleni um (p p m , dry weight ) we re 2-110 i n egg s and 1 9

- 130 in livers of birds, 12 -7 9 in plants, 2 3 -20 0 in in vertebrate s , and 110-280 in fish from the po nds, or 7 to 130 times tho s e found at a ne a r by cont rol area. It wa s co nclu ded that Se was the p r obabl e ca use of poor rep r od uctio n and devel op mental abn ormalities in the aquat ic n e sti ng bird s, due to interfere n ce with their rep r od uctive pro c e s ses. T he co ncentrat i ons of Se in br ea st mu scl e of coots we re suffi ciently high (u p to 11 .0 ppm fre s h we ight) to indu ce State agen cie s to post the are a , advising a gain s t the co nsumpti on of more th an one meal pe r we e kof this sp eci e s, or of any coot s by child ren o rpre gna nt women (O hlend orf et al. 1986).

In studie s at the Patuxent Wildlife Rese arch Ce nter, Dr. G. Hei n z ( per s. com m

. ) is evaluatin g effects of dietary Se on mallard rep r odu ction. Du cks give n diets containi ng 1 00 ppm of ino r gani c selenit e usu a lly died within a mont h; for some ti me before de ath they exhi bited red u ced food intake s (bo r de ring o n repelle nce) a nd signifi cant we ight loss. In birds re ceiving 25 ppm, su rv i v al was hi gh after 3 month s , but gro w th and re produ ction were dramati c ally red u ced

. Teratoge nic effects were ev ident at 3 months in d u ckli n g s of mallard s re ceivin g 10 ppm, and p r el iminary evide n ce sug g e s te d that selen o m ethi onin e at 10 ppm dieta ry Se was m o re effective th an inorg ani c sel enite in pro d u c ing d e velop m ental abn orma lities. Du cks a nd their p r oge ny appe a r ed no rmal af ter 3 months of ex posure to 5 p p m and le ss of dietary sel enite.

MAMM ALS Harr (1 978 ) a nd NRC (198 3) su mma rize d nonleth a l effect s of sel eni um on mamm als, incl uding rep r od uctive anomali e s. S e leno si s ca used co nge nital malformation s in rat s , mice, swin e, and cattle. In general, young b o rn to females wit h sele no sis were em aci a te d and un able to nurse. Mice given Se in drin king wate r rep r od uced

norm a lly for three g ene rati ons, but litters we re fewer and sm alle r whe n com p a r ed to cont rols, pups were runts with high mo rtality before wea n ing, a n d most su rv iv ors wer e inf e rt i l e.



### 29In rats, sel eni um did not in duce cirrh o si s or ne opla s i a ; howeve r , intestinal le sio n s were o b se rved amo ng those fed di ets co ntainin g 0.8 to 1.0 ppm Se during li fe time exposure. The th re shol d req u ire m ent for opti m al rat nutrition un de r simila r co nd itions is a bout0.08 ppm, ag ain demo n st rating the relat i vely narro w range sep a rati ng sele nium defi c ien c y from selenium p o isoning. Absorption of oral radio s elenite by rats was a s high a s 95 t o 100%. A singl e dose of radi osel enite con c entrated in the pan crea s, intestine, eryt hro c ytes, liver, kidney an d testes, in thatgeneral orde r; tissu e dist ri bution s from chroni c expo sure we re si milar. As exp e cted, level s of Se in poisone d rats were hi ghe stin liver and ki dney. Rats, a nd pro bably o t her mamm al s, can regul ate dietary Se accumul a tion s. Dieta ry con c entration s in excess of 54

- 84 pp b we re usu a lly excret ed in urin e; howeve r , whe n Se intake ex cee ded 1,00 0 pp b, pulmona ry excretio n wa s acti ve. Excre t ion of Se in fece s, bile, sal i va, and hair appe ars to be relatively con s tant re gardle ss of the am o unt of exposu r e. Yonemoto et al. (1983) demon strated that some sel enotoxic effe cts in mi ce, in cludi ng abo rti on and mate rnal death, we re pr evented by prior tre a tment with vitamin E, but exacerbated by red u c ed gl utathio ne; the mech anism s for th ese inte ra ctio ns are un kno w n, and me rit add itional re sea r ch.

Table 4. Proposed seleni um crite r ia for prevention of Se deficien cy and for prot ection a gain s t seleno si s.
Selenium C r iter io n c o n c en tr a t io n R e fe re nc e
PREVENTION OF SE DEFICIENCY
Rain bo w trou p, Salm o gairdneri (wate rlevel s of 0.4 ppb Se ) 70 ppb in di et Hilton et al. 1980 Poultry 30-5 0 ppb in diet Fishb e in 19 7 7 Rats 54-8 4 ppb in diet Harr 19 78 Cattle 20 ppb in di et Fishb e in 19 7 7 Gra z ing she e p and cattle 100 pp b in di et Shambe rge r 1981
Huma ns 40-1 00 pp b in diet Wilbe r198 3
" 50-2 00 pp b in diet Harr 19 78
" 60 μg daily (range 2 2 -2 20 ) Rob berecht and
Von Grei ch en 1982
" 100-200 μg d a ily Shambe rge r 1981

" 20 ppb in d r in king water Rob berecht and (if water sole Se sou r ce, 2 liters/day ) Von Grei ch en 1982

PROTE C TION AGAINST SELENOSIS

Aquatic life protection
F r es hw a t e r As inorgani c selenite Up to 35 ppb in water EPA 1980 (24 h ravera g e ), not to exceed 26 0 ppb at any time
As inorgani c selenate <760 ppb EPA 1980 Great L a ke s 10 ppb in wat e r Won g et al. 1978 Saltwater, as inorgani c sel enite Up to 54 ppb in water EPA 1980 (24 h ravera g e ), not to exceed 41 0 ppb at any time
Livesto ck p r o t ection
Drin kin g wate r <50 p p b NAS 1974; Wilber 19 83 Diet (total) <2,00 0 ppb (dry wt.) NRC 19 83



### 30Diet (natu r al ) <4,00 0 ppb Wilbe r198 3
Feed s (n atural <2,00 0 ppb Fro s t 1972
Fora ge (n atural) <5,00 0 ppb Fro s t 1972 Cro p protecti on Irrigatio n wat e r <50 p p b Birkn e r 19 78;
Wilbe r 198 3
Huma n healt h prote c tion

Seafood Not to excee d 2,000 pp b Bebbingto n e t al. fresh wt. 1977
Drin kin g wate r <50 0 ppb Rob berecht and (as sole Se source ) Von Grei che n 1982 Food (natural ) <5,00 0 ppb Wilbe r198 3
Milk or water <50 0 ppb Wilbe r198 3 Daily intake (all sources)
A d u l t s Safe 200 μg Shambe rge r 1981
Normal 60-2 50 μg Lo and San d i 1980
Maximum tolerabl e level <50 0 μg Levand er 19 8 4 Infants 4-35 μg Lo and San d i 1980 C h i l d r e n Age 1-3 20-8 0 μg Levand er 19 8 4 Age 4-6 30-1 20 μg Levand er 19 8 4 Age 7-1 1 + 50-2 00 μg Levand er 19 8 4
Air

J a pa n < 1 00 μg /m 3 NAS 1976

USSR < 1 00 μg/m 3 NAS 1976

USA < 2 00 μg/m 3 NAS 1976

- 1 to 4 μg/m 3 Harr 19 78

CU R R ENT R E COMME ND ATIO NS All investigators a ppe ar to agree o n fou rpoints. Fi rst, that insufficie n t seleni um in the diet may have harmf ul and sometim e s fatal co nseque nces. Se con d , that exposure to g r o ssly elevate d levels of Se in the diet or water, is inevitably fatal over time to terrest rial and aq uatic o r gani sm s. Thi r d, that there is a co mpa r at ively narro w
con c e n tration range sep a rating effects of seleni um d e ficien cyfro m those of se leno sis. And fourth, that ad ditional fundame n tal and ba si c re search is req u i r ed on sele ni um me taboli s m, physiology , recyclin g, intera ction s with other comp ou nds o rformul ations, an d chemical sp eci a tion in ord e r to elucid ate its nutritive rol e as well as it s toxic effects. Acco rdi ngly, the pro p o s ed sele nium crit er ia sho w n in Table 4 for p r evention of Se deficien c yand for prote c tion of aquatic life

, livestock, crops, an d hum an health, sh ould be vie w e d as gui delin es, pen ding acq u isitio n of addition al, more definitive, data.
Reg a rdi ng Se deficien c y, it appe ars that diets c ontaini ng 50 to 100 ppb Se provide ade quate prote c tion to human s an d to variou s sp e c ie s of fish, small labo rato ry mammals, and livesto ck (Tabl e 4). Fa ctors contrib u t ing to Se deficiency in crops include incr easi ng use of agri c ultural fertilizers a nd increasing atmospheri c fallout of sulfur; furth e rmore, foliar a pplication s of sele nate, alth ough effici entin raisin g Se levels in plant s, have only



### 31sho r t-te rm value (F ro st and Ingvoldstad 1975 ). There is a gen eral consen su s tha t Se deficiency in livestock in many cou n tri e s is in crea si ng, resulting i n a need for adde d Se in the food chain

. Curre n t reco mmend ation s for prote c tion of fresh w ater aquatic life a r e that inorga ni c selenite concentratio n s in the water should n o t exceed 35 p pb o n a daily average, or 26 0 p pb at any time (Tabl e 4). T hese value s are highe r for saltwater life: 54 ppb daily ave r age, 41 0 pp b at any time. The co nce n tration ran ge of35 to 54 ppb

recomme nde d for prote c tio n of aquatic li fe is belo wthe r ang e of 60 to 600 ppb th at is fatal to variou s sen s itive spe c ie s of marine a nd fre s hwate rfauna, and in this re sp e c t afford s an ade quate measure of protectio n . It is very near the ran g e (47 to 53 p pb) that ha s b een a s soci ated with growt h inhibition offresh w ate ral gae, anemi a and redu ce d hatch in rainb o w t r out, and shifts in sp eci e s co mpo s ition offresh w ate ral gal com m unit i es. But studi es by Cumbie a nd Van Ho rn (197 8) a nd Soren s e n et al. ( 1984 ) sho w ed that water con c e n tration s of 9 to 12 ppb of Se were asso ciated with re duced re prod uction of fre s hw ate rfishe s , and their re sult s strongly indicated that some d o wnward mo dificati on of the Se freshwater a q uatic life prot ection crite r io n may be app rop r iate. Furthe rmo r e, high bio c on centration a nd accumul a tion ofSe from the water colu mn by numerous spe c ie s o f algae, fish, a nd inverteb rat e s is well do cumented at le vels between 0.015 an d 3.3 ppb, whi c h is sub s tantially belo wthe re commen ded range of 35 to 54 ppb. The significa nce of Se resi due s i n aquati c biot a in terms of bioavailabilityand Se re ce ptor site s is i m perfe ctly un der stood, an d it appears that much ad ditional re se arch is

warra n ted on Se pharm a co kineti cs in a q uatic environ ments.

Livesto ck a p p ear to be p r ot ected a gain s tselen o si s pr ovided that their diets cont ain less than 4,000 pp b of natural (i.e., nonsuppl emen ted) sel eniu m (Table 4 ) . Th is co ncentrati on is some wh at higher tha n levels rep o rt ed for rats (Wil b er 198 3). Mini mum toxic co nce n tration s of Se in lifetime exposure of rats given diets containi ng natural Se we re 1,400 p pb dietary Se, as judged by ev iden ce of liver cha nge s, an d 3,000 pp b a s estim a ted from longevity and histologi cal chang es in h e a rt, kidney, a nd spl een. Th ese valu es were only 35 0 and 75 0 ppb, respe c tively, whe n rat diet s co ntaine d p u rified, rath er than natural, Se. This relati onship emp h a si ze s that accide ntal poi soni ng of livestock, and p r esum ably fish and wildlife, may occur when soils a r e delibe r ately sup p leme nte d with purifie d Se, or whe n soil s or aq u i fers a r e cont aminated a s a result of faulty waste disp osal pra c tice s. Althoug h the co nce n tration of<50 pp b for livestock d r inki ng wate r and irrig a tion water for cro p prote c tion is i n co nsi s tent with that of < 35 ppb for aq u a tic life prote c tion, neithe rlivestock no r cro p s a ppe ar threaten ed atthe higher le vel. Since ma ny waterways t hat abut agri c ultural land s or are a s of hi gh anthropo g enic loadin g s of Se contai n valuable a nd de sira ble aq uati c sp eci e s, it woul d appe ar that some do wn ward modificatio n of the currentlivestock drin ki ng water co nce n tration ofSe is nece ssary.

Re cent field studies d e mon s trated th at migrato ry wa terfowl we re he avily and adversely affecte d while nestin g at Se-co n tamin a te d irrig a tion drainwater po n d s in Californi a, where food chain o r ga ni sm s co ntaine d betwe en 12,0 00 and 2 80,0 00 ppb of Se. The so urce a nd fate of Se in irrig a tion drainwater po n d s are largely unkno wn; the ymust be det ermin ed so that alternate te ch n o logie s fo r Se cont rol can be imple m ented to prot ect waterfo w l in that geog rap h i c al re gion.

Aero sol con c entration s in exce ss of 4.0 μg Se/m 3 are potentially harmful to hu man health (Harr 19 78);

c o nc en tr a t io ns in e x c e ss o fthis value (6. 0 μg Se/m 3 ) were re gula r l yencou ntere d in the vicinity of the smeltery at Sudbury, Canad a (Nriag u and Wong 1983 ). It is not now kn own wheth e r respi r ation rates ofwildlife, particula rly birds, a r e comp arabl e to those of human s, or wh ethe r Se absorptio n energetics a r e simila r, or wheth e r wil d li fe spe c ie s that frequent p o int sou r ces of air conta m i nated by high Se levels for protracte d pe riod s are at greater risk than hu mans. Until additional an d more con c lu sive data beco m e available, aero s ol

con c e n tration s of less than 4.0 μg Se/m 3 are recom m ende d for the prote c tion ofsen s itive speci e s of wil d life.

Acute lethal d o se s for livest o ck sp eci e s range d from 3

, 300 μg/kg b o d y weight of Se for horse s and mule s to 15,000 μg/ k g for swine; ap petite loss in cattle wa s not ed at 500 μg/ k g. For h u ma ns, the maxi mum tolera nce level is usuall yset at 500 μg of Se daily (Lo and San d i 1980), an d the “safe” leve l at 200 μg/da y(Shambe rg er 1981 ). Seleni um dietary le vels for man sho u ld not ex cee d 5,000 p pb; however, recomme nde d maximum d i etary levels in othe r mammal s ra nged fro m 1,000 pp b for rats to 4,000 p pb for ho rses. For all sp eci e s, incl udin g man, there is a ten den cy to list Se dosa ge le vels in term s of “natural” a nd “suppl eme n ted” level s , with the tacit unde rsta ndin g that “natura l ” levels a r e a bout one -fou rth as toxic as “su pple m ente d ” value s . Given the compl e xities of Se metabo lism and spe c iation, it appe ars that g r eat er preci s io n a nd cla r ity are necessa ry in formulatin g Se crite r ia if these crite r ia are to bec om e admini s trativ ely enforced stand ard s through p a ssa g e of approp riate le gislatio n.



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