Biological Effects and Persistence of Dursban® in Freshwater Ponds12

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Abstract
An experiment was conducted in ponds near Bakersfield, California, to determine the effects of the insecticide Dursban® (O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate) on mallard ducklings, Anas Platyrhynchos L.; mosquitofish, Gambllsia affinis (Baird and Girard); corixids, Corisella spp. (Hemiptera); and several zooplankton species. Dursban was applied 4 times at 2-week intervals to small ponds at 0.0, 0.01, 0.05, 0.10, and 1.0 Ib per acre. Total duckling mortality was 42% on the treated ponds and 0% on the control ponds; the difference was significant (P >0.05). Mortality appeared to be independent of treatment rate. At all except the highest rate, Dursban caused only slight (>10%) mortality of caged mosquitofish and did not appear to inhibit their reproduction. Fish exposed to 0.05 lb/acre had Dursban residues of 2.8 ppm at 4 hours, 1.7 ppm at 24 hours, and 0.1 ppm at 2 weeks after treatment. Reduction of Corisella populations was variable but approximately proportional to treatment rate. Except in ponds treated at 1.0 Ib/acre, Corisella populations recovered well from the 1st treatment but less well from subsequent treatments. Cyclops vernalis Fischer and Moina micntra Kurz, the dominant zooplankton species, were markedly affected by the 1st treatment, but populations in ponds receiving the lower rates recovered Within 2 weeks. No C. vernalis or M. micrura population recovered from the 2nd and subsequent treatments. Populations of the crustacean Diaptomus pallidus Herrick and the rotifer Asplanchna brightwelli Gosse were initially low but developed rapidly in those ponds where C. vernalis and M. micrura were reduced by Dursban treatment. A. brightwelli was even abundant in ponds treated at 1.0 Ib/acre. D. pallidus populations did not develop in ponds receiving 1.0 Ib/acre but showed no evidence of being susceptible at the 3 lower rates. Dursban residues in water were very low 4 hours after treatment (at 1.0 Ib/acre, 0.2 ppm) and declined rapidly (0.006 ppm at 7 days). Initial residue levels in mud were even lower (0.01 ppm) but increased to a maximum (0.3 ppm) at 7 days and presumably declined gradually thereafter. Vegetation residues were high initially but declined rapidly (at 1.0 Ib/acre, 26 ppm at 4 hours, 1.1 ppm at 7 days).

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