Significantly higher numbers of aquatic insects were sampled in treated ponds than in untreated, and insect numbers at high-treatment ponds were significantly higher than at low-treatment ponds. Chironomids were dominant and significatnly increased after a certain level of treatment. Chironomids comprised 74 percent of samples from high-treatment ponds, but only 43 and 42 percent respectively fro untreated and low-treatment ponds. Methoxychlor residues were not detectable in pond-bottom mud samples.

Bluegills and channel catfish were exposed to four applications of malathion at two concentrations in ponds over an 11-week summer period. Fish losses ranged from 8 to 44 percent but could not be correlated to treatment levels. Neither acute nor chronic pathology developed, nor were depressions in the brain cholinesterase activity significant or reproducible. The total number of aquatic insects from plate sampling the low-treated ponds was not significantly lower than that from the untreated ponds, but the number of organisms from the high-treated ponds was significantly lower than that from either the low-treated or untreated ponds. Chironomidae was the dominant family of aquatic insects, and formed about 70 percent of the total benthos. This group showed a significant reduction in numbers in both low- and high-treated ponds after the third application of malathion.

A Special Publication of the Society of Environmental Toxicology and Chemistry (SETAC) Aquatic Mesocosm Studies in Ecological Risk Assessment discusses the methods currently used for conducting simulated field studies and provides a series of case histories in which mesocosm type studies have been used to assess the impact of pesticides on aquatic ecosystems. Specific chapters address the dosing and exposure components of such studies and how they influence experimental design. Advantages and disadvantages of various statistical designs are addressed in detail. Regulatory aspects of the design and interpretation of these studies are also covered. The book will be a superb reference for aquatic biologists, ecologists, toxicologists, environmental toxicologists, environmental chemists, and regulatory personnel.