The acute toxicity to the marine copepod Acartia tonsa Dana of four technical grade insecticides was determined by bioassay using standardized procedures, homogeneous populations and constant laboratory conditions. At a water temperature of 17 plus or minus 1C, the 96-hour median lethal concentrations or tolerance limits for methyl parathion, Azodrin, diazinon and toxaphene were computed as 0.89 milligrams per liter, 0.24 milligrams per liter, 2.57 micrograms per liter and 7.2 nanograms per liter, respectively. Residue analysis for diazinon at zero and 96-hour exposure time revealed that the amounts of diazinon uptake by three algal organisms is greater than amounts concentrated by the copepod. The toxicity of higher concentrations above 2.0 ppm (2 milligrams per liter) has offset copepod uptake, while at lower concentrations, quantities concentrated by Acartia are negligible.

"Contract no. 68-01-0151." Includes bibliographical references (pages 24-26).