Laserfiche WebLink
<br />Dc}'orcst, 8rix, and Adams <br /> <br />Debate/Commentary <br /> <br />discussed below, some coldwater fish may be more scnsitivc Lhan warmwatcr <br />fish. Another unccrtainty is lhc paucity of warl1lwatcr spccies fur which ovalY <br />data are availablc. FUl'lher testing should bc conducted to understand thc <br />variability in sensitivitics betwccn spccies. <br />Whole Body. The whole body guidclinc of 4 mg/kg dw recommended by <br />Lemlr (1993a) is based on mortality of rainbow trout cxposed to aqucous <br />selcnHe (Hunn el at" 1987). In rcvicwing Ihc whole 1J0dy rcsiduc-bascd toxi- <br />cological data, ,,:e nO,ted,t.wo potcntially significant rclationships that may cxist. <br />Thc first potcntlally slglllhcant relationship is heavily dcpcndent on the chinook <br />salmon c~ata from Hamiltun el at. (1990). As discussed ahovc, the toxicity <br />rcsults altcr 90 days are clucstionable duc to the rapid dcclinc in sUlvival of <br />~ontrollis~1 betwccn day 60 and 90 of the test. [f thc results aftel' 90 days are <br />mdeed rehablc, and the obscrved mortality can be alll"ilmted to seleniulII, thc <br />resu~l~ suggcsl coldwater fish (rcprescnted by chinouk salmon) may hc more <br />~ensHlvc than warmwater fish (rcprcscntcd by IJlucgill) (Figure 4). Howcver, <br />If thc results aftcr 50 days are more reOectivc of the sensitivity of chinuok <br />salmon to selcniulll, there wonld IJc limited cvidcnce to suggest I hat coldwater <br />fish are more sensitive than warlllwatcr fish. In lact, the sensitivity of coldwaler <br />and warmwatcl' fish appear to he qnitc similar bascd on thc day GO data (Figlll'c <br />4). The second potclllially significant rclalionship that becamc apparenl was <br />that effects are observed in fish atlowcr whulc body selenium concentralions <br />when they arc exposed to only waterborne seleniulll than when they arc <br />expos,ed to dietary seleni~m. Cleveland el at, (1993), for example, exposed <br />bluegtlls to an aqueous 6: I sclenatc:selenite mixture lor 50 days, and in a <br />separate expel"im.ent, cxp?sed IJlucgills to dictalY organoselcninm lor 90 days. <br />Obsctved mOl'lahty was htghcr at lowcr whole 1J0dy residnes in fish cxposcd <br />onl,y to ~aterbOl:ne, inorganic selcnium (Figurc 5). This has impol'lant impli- <br />callons m estabhslnng a whole body selcnium guidelinc bccausc, as discusscd <br />previously, natural fish populations arc pl"imarily cxposcd to selcniulII via Iheir <br />diet. Cleveland el at. (1993) support this ohscrvation, lIl>linH Ihat toxicily to <br />, natural populations of bluegill and probalJly othcr aquatic OlWlIIislllS would <br />probably occur at much lowcl' waterbol"lle concentratious than thosc tcstcd iu <br />this study owing to food-chain exposure. <br />~csscr el at. (1993) also obsclved thatlJlucgills from both aqucous and fooel- <br />cha~n cxposures to seleno-mcthioninc accumulated greater selenium conccn- <br />tl:allons tha~l bl~legills in cOlllparalJle exposures with inorganic selcniulII spc- <br />CICS. .81uegtlls III fO,od-chain cxposures accumulated consistenlly greater <br />selenium concentrallons than Ihose in aqncous exposurcs, and bluegills ex- <br />posed to both aqucons and foodbornc selcnium accumulated most of Iheir <br />total selenium residnes frollllheir food. Bertralll and Brooks ( I U8fi) mcasured <br />diflcret~tnptakc ~inctics between walcrborne 5e1cniulII and dietalY selcniulII, <br />snggesllng the eXlstcnce of two functional compartmenls for selcniulII accu- <br />mulation in fish. Onc cOlllpartmentmay contain an unbound inorganic pool <br />and thc othcr may contain organically bound compounds. The depuralion <br />rate of the unbound inorganic pool is rapid. Thc aUlhol's noted Ihat acculllu- <br />lation ofwaterbornc selenium and diclalY seleninlll is appl'llximately addilivc, <br /> <br />and that in all cascs Ihe potcnliallJurdcn of selcnium in fish tissues is rclated <br />to the conccntriltion of selenium in the fish diet. <br />We hypothesize that waterlJorne inorganic selenium exposures result in <br />toxicity at lower whole 1J0dy residucs than those based on dictary <br />organoselcniulll cxposures bccausc thc inorganic selcnium in fish is rapidly <br />depurated. [n natural populations, most of the selcnium exposure and result- <br />ing bioacculllulalion is from dictalY organoselenium, resulting in higher <br />whole body conccntrations, Comparison of whole body selenium concentra- <br />tions in field-collected fish to laboratory-dcrivcd toxicity data lJased on water- <br />bornc cxposnres to inorganic selcnium is, therefore, not a valid comparison, <br />Givcn that Lemly's (1993a) I'ecolllmended whole body rcsidue guidelillt: of <br />4 mg/kg dw is based on a study involving water only exposures, we recolII- <br />mcnd guidelines based only on studics including dietary exposures. <br />For coldwater fi5h, Ilamilton el at. (1990) is the only study in which fish were <br />fed diets conlaining organoselenium. As discusscd above, the whole body <br />chronic values in Lhis study are 7.4 mg/kg dw for reduced growLh and 7,6 IIIg/ <br />kg dw lor reduced slllvival following 60 and 90 days of exposure, respectively. <br />Bascd on Ihe probit and logit models, the ECw. EC20, and EC50 values for <br />mortality in Ihis study are 12, 17, and 27 mg/kg dw after 60 days and 1.7, 2,8, <br />and 7,0 mg/kg dw after 90 days (Figure 6). Bascd on the growth endpoinl, <br />ECI\l. EC2\l. and EC5\l values are 6, II, and 20 mg/kg dw aftcr 60 days of <br />exposurc to selenium, and 5, 7, and 14 mg/kg dw aftcr 90 days (Fib'1.lre 7). <br />The lowcst wholc body chronic value for warmwater fish from a dietary <br />study, 10.5 mg/kg dw, is lJased onlalval mortality (Coyle el at" 1993). Similar <br />to the ovary data discussed above, we poolcd thc wholc body selenium and <br />Ialval mortalilY studies from all relcvant studies for wannwater fish (i.e" Ogle <br />and Knight, J 989, Hcrmanllu el at" 1992, Coylc el at" 1993). Thc whole body <br />ECIIl, EC2\l' and EC50 values, using bOlh thc pmbit and logh models, are 9, II, <br />and 15 mg/kg dw, respectivcly (Figure 8). It should be noted thal the concen- <br />tralion-response rclationship is not wcll defined as thcre are only two wholc <br />body conccnlralions where lalval mortality was greater than 10% following <br />Ahhou's correcliun for conlrul mortality. As for thc ovaries, we recommend <br />Ihc ECIO valucs as whole body thrcsholds, Given that the results of the Hamilton <br />elllt, (1990) stndy after 90 days are questionalJle and neeo 10 be confirmed, we <br />rccommend that the ECIO for growth at (iO days (i,e" 6 mg/kg dw), the most <br />sensitivc endpoint measured, be considered thc whole body threshold for <br />lalval culdwater anadrolnous fish; Ihe EC,o of9 mg/kg dw is recommended as <br />Ihe Ihreshold lor wannwatcr fish, 1L is important to notc that the coldwater <br />ilnadromous lish threshold is for larval /ish, while thc wannwater threshold is <br />for adults. The coldwater anaoromous lish threshold specifically does not <br />apply to adultlish as maternal transfer of selenium has not becn evaluatcd in <br />thesc lisla. <br />/Jie/IllY. The Hamilton el (lL (1990) chinook salmon study is currcntly the <br />most relevant lor delennilling a dictal)' threshold for coldwatcr fish lJecausc <br />it is Ihe only coldwater study in which fish were fed organosclenium. I'rolJit <br /> <br />HUIlI, Eeul. Risk Asscss. Vul. 5, Nu, 6, 1999 <br /> <br />1215 <br />