Water Pollution by Insecticides in an Agricultural River Basin. II. The Zooplankton, Bottom Fauna, and Fish

In 1959 and 1960, zooplankton, bottom fauna, and fish populations were studied in a drainage system polluted with insecticides in northern Alabama. Toxaphene and BHC (benzene hexachloride) were present in all water samples collected in 1959 and 1960 in concentrations considered to be sublethal to aquatic animals in a single dose. There was no convincing evidence that continuous toxaphene and BHC contamination resulted in gross damage to zooplankton, bottom fauna, and fish populations. Zooplankton was sparse at all times. However, this scarcity was attributed to other unfavorable environmental conditions such as changes in discharge and high turbidity. A considerable variety of bottom fauna taxa was noted in all collections. There were fluctuations in the abundance of bottom fauna during the period of study. However, the data did not suggest that these were caused by insecticide contamination. Fish collections from two stations in June and September of 1959 and 1960 contained a variety of fishes represented by many size classes. There was additional evidence that the drainage system supported a sizable fish population of diverse taxonomic structure.