Toxicity of Dieldrin to Fish

Abstract
Toxicity bio‐assays of run‐off water from an area treated with dieldrin at the rate of 4.66 pounds per acre indicated that the run‐off from the first rain following treatment was toxic to fathead minnows, Pimephales promelas, at a dilution of one in three. Mortality in run‐off from the third rain was less than 50 percent, and a few fish exhibited the characteristic effects of dieldrin when placed in run‐off from the fourth rain following treatment. It is evident that run‐off from an extensive area treated with dieldrin would adversely affect fish life. A time‐of‐effect concentration curve was prepared by exposing fish to known concentrations of dieldrin. Tests with samples, the concentrations of which were unknown to the investigators, indicated that within the range of 0.03 to 0.5 p.p.m., the dieldrin concentration could be estimated within 25 percent. By using this curve it was estimated that the composite sample of run‐off contained 0.128 p.p.m. of dieldrin. Bio‐assays with different formulations of dieldrin showed that it was extremely toxic to three different species of fish. The 96‐hour TL/m values ranged from 0.0056 to 0.042 p.p.m., depending on the formulation and the kind of fish. Tests, when using dilution waters with different characteristics, indicated that dieldrin was somewhat more toxic in hard than in soft waters. While larger volumes per fish of the test solution appeared to be slightly more toxic, evidence was not sufficient to establish that absorption of dieldrin by fish reduced the toxicity of test solutions.

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