Methoxychlor Residue Studies in Caged and Wild Fish from the Athabasca River, Alberta, Following a Single Application of Blackfly Larvicide

On June 4, 1974, the Athabasca River was treated with methoxychlor for control of blackfly larvae. Pesticide was introduced into the water in a manner calculated to generate a 15-min pulse of treated water containing 300 μg methoxychlor/ℓ. A preliminary experiment with rainbow trout (Salmo gairdneri) indicated that liver or kidney residues of methoxychlor would be suitable for monitoring likely times and places to expect toxic effects on fish in the river. Fish (Salmo gairdneri, Catostomus commersoni, C. catostomus, and Hybopsis gracilis) were caged in order to observe residues and mortality. Caged fish were not killed by methoxychlor but they contained lower liver residues than wild fish of the same species captured near cages. Contaminated wild fish were found upstream of the treatment site after treatment. Residues were below detection limits by June 16. Residue measurements suggested that the most likely times to expect fish poisoning were the 2 wk following treatment and that the most likely places were those river areas extending a few kilometres in both directions from the point of application. Evidence of fish movements and low pesticide residues in caged individuals reduced confidence in residue methods as monitoring tools. </jats:p

Effects of Chronic DDT/DDE Exposure on Anesthetic Induction and Recovery Times in Rainbow Trout (<i>Salmo gairdneri</i>)

In rainbow trout (Salmo gairdneri) fed pellets containing 4.55 μg/g of p,p′-DDT and 6.81 μg/g of p,p′-DDE every other day, anesthetic induction and recovery times of phenoxyethanol (PE) were less than those in trout fed control pellets. No interactions were observed in fish fed DDT/DDE and anesthetized with ethyl m-aminobenzoate methanesulphonate (M.S. 222). Differences observed between fish fed DDT/DDE and anesthetized with PE as compared to M.S. 222 could be due either to enhanced metabolism of PE or to the fact that PE and M.S. 222 have different modes or sites of action. </jats:p

Effects of Biotreated Bleached Kraft Mill Effluent on Fingerling Chinook Salmon (<i>Oncorhynchus tshawytscha</i>)

Fingerling chinook salmon (Oncorhynchus tshawytscha) were chronically exposed in the laboratory to nonlethal biologically treated bleached kraft mill effluent (TBKME) at concentrations and temperatures typical of the Fraser River. Laboratory exposure was for 144 d in freshwater followed by 66 d in seawater without TBKME. Exposed fish bioconcentrated chlorophenols, chloroguiacols, and extractable organochlorine substances in proportion to the aqueous concentrations of the substances. Polychlorinated dibenzo-p-dioxins (PCDD's) and polychlorinated dibenzofurans (PCDF's) were also bioaccumulated, but the low body burdens compared with wild fingerling chinook indicated that the laboratory environment did not account for biomagnification via the food chain. Growth, mortality, hematocrit, protein and fat content, liver somatic index, sorbitol dehydrogenase, and tolerance to hypoxia were not affected by TBKME exposure. Increased nuclear diameters of interrenal cells among TBKME-exposed fish indicated that these fish were experiencing chronic stress. Hepatic and renal granulomas of Bacterial Kidney Disease origin were observed in some TBKME-exposed fish, but there was only a tenuous link between TBKME exposure and disease resistance. Hepatic ethoxyresorufin-O-deethylase (EROD) activity was correlated with dioxin toxic equivalency (TEQ). From this analysis, we estimated a threshold for EROD induction between 0.3 and 1.0 ng TEQ∙kg−1. </jats:p