Effects of lindane on macroinvertebrates and periphyton in outdoor artificial streams.

A system of six outdoor artificial streams (dimensions 5.0 X 0.35 X 0.25 m) was used to study the biological effects of lindane in flowing water. Lindane was continuously applied during 28 days to four of the streams while two were left as untreated controls. The nominal concentrations were 4.0, 8.0, 16.0, and 32.0 micrograms liter-1 and the mean measured concentrations of lindane in stream water over 28 days were 3.1, 5.7, 11.1, and 20.3 micrograms liter-1. Effects were observed on population densities of the freshwater shrimp Gammarus pulex, drift of G. pulex and mayflies (Baetis spp.), and on community photosynthesis. An increase in photosynthetic production of oxygen, a result of increased periphyton standing crop, followed the loss of macroinvertebrates, via drift, from the treated streams. This established a clear link between a direct effect of lindane on macroinvertebrates and an indirect effect on periphyton production. Drift and community photosynthesis were the most sensitive of the biological parameters measured and effects were detected in all treated streams. During a 28-day experiment with lower concentrations of lindane, nominally 0.25 and 1.0 micrograms liter-1, there were minor effects on the drift of Baetis spp. but only at the higher concentration. There were no detected effects on population densities or on community photosynthesis. Results from the two experiments provided a measured no observed effect concentration for lindane of 0.2 micrograms liter-1 and the threshold concentration for sustained effects on the stream communities was in the range 0.8 to 3.1 micrograms liter-1.