Acute (96-hour) bioassays were performed with endrin and the following estuarine organisms: American oyster (Crassostrea virginica), pink shrimp (Penaeus duorarum), grass shrimp (Palaemanete's pugio). sailfin molly (Poecilia latipinna) and sheepshead minnow (Cyprinodon variegatus). Endrin was acutely toxic to all organisms tested, except oysters, whose shell growth was appreciably inhibited by 56 ug/1 (parts per billion) of the chemical. Pink shrimp were the most sensitive animal tested, but significant numbers of both species of shrimps and fishes died when exposed 10 concentrations of one ug/1 or less, In a separate test, embryos and fry of the sheepshead minnow were exposed to concentrations of endrin ranging from 0.046 to 1.0 ug/1 (nominal) for 33 days in an intermittant-flow bioassay. Embryos were not affected by the concentrations to which they were exposed, but the estimated LC50 (prohit analysis. a=.05) of fry was 0.27 ug/1.
