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The impact of Squoxin on aquatic invertebrates and an assessment of its fate in the aquatic environment Staley, George Stephen

Abstract

Squoxin, 1,1'-methylenedi-2-naphthol, is a pesticide developed to eradicate the northern squawfish, Ptychocheilus oregonensis. Investigations concerning the acute toxicity of the pesticide to aquatic invertebrates and an assessment of its fate in aquatic ecosystems are reported. Squoxin was found to be much less toxic to aquatic invertebrates than it was to squawfish. It was proposed that the toxicity of squoxin to aquatic invertebrates is inversely proportional to their adaptations to habitats having low levels of oxygen availability. The most sensitive invertebrate species tested was the blackfly larva, Simulium canadense, which is distributed in streams having high current velocity and abundant dissolved oxygen. These larvae exhibit an LC50 value of 60 ug/l in 48 hours. Chaoborus trivittatus larvae, known to tolerate anoxic conditions, were resistant to treatments up to 10 mg/1, exhibiting a maximum response of 30 percent in 96 hours. The degradation of Squoxin was monitored in surface waters of diverse origin. Degradation was most severe in water having a high pH and high alkalinity. Degradation was also found to occur due to the presence of dissolved organic compounds of high molecular weight. Freshwater bacteria did not exhibit any ability to utilize Squoxin as a carbon source in short term tests. A 100 ug/l Squoxin treatment depressed the natural heterotrophic activity of bacteria by nearly 25 percent based on studies of uptake of ¹⁴C-glucose over a 2 hour period. ¹⁴C-Squoxm residues initially adsorbed to phyto-plankton and organic sediment in simple laboratory microcosms. However, the residues steadily desorbed from these components and became increasingly soluble throughout the test period. Daphnia pulex and Hyalella azetca in the microcosms took up Squoxin rapidly in the first 24 hours after treatment. Uptake then levelled off and tissue concentration of Squoxin increased only at a very slow rate during the remainder of the test. Only small amounts of Squoxin were transferred to organisms feeding on contaminated food items when compared to the dose obtained from a contact exposure. C. trivittatus fed contaminated D. pulex retained only 6 percent of the ingested Squoxin residues. These residues, however, appeared to be retained for a longer period than tissue residues gained through a contact exposure. Invertebrates exhibited an ability to excrete Squoxin residues given time and an uncontaminated environment. D. pulex excreted over 90 percent of the toxicant in 96 hours; H. azteca required 275 hours. It was postulated that because of Squoxin's water solubility, low partition coefficient, rapid degradation, and the ability of a wide variety of organisms to excrete it, the toxicant would not be biologically magnified to a significant degree in aquatic ecosystems.

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