Effects of lindane on the planktonic community in freshwater microcosms

Effects of lindane on natural planktonic communities were investigated in aquatic indoor microcosms. Lindane was dosed to eight 300-liter microcosms for 2 weeks, and effects and recovery processes were monitored over 12 weeks. Mean measured water concentrations of lindane during the exposure period were 3, 6, 13, 27, 55, 102, 230, and 455 micrograms/liter. Zooplankton was severely affected by lindane. The most sensitive organisms were nauplii of copepodes which were affected at all treatment levels > or = 6 micrograms/liter during exposure (Days 2-14). Recovery of nauplii abundance was concentration-dependent at concentrations < or = 55 micrograms/liter lindane, whereas at concentrations > or = 102 micrograms/liter recovery was negligible. Cladocera abundance decreased during exposure to > or = 102 micrograms/liter lindane and did not recover to original levels until the end of the study. For phytoplankton, decreased population densities of Chlorophyceae and microalgae ( < 5 microns) were observed at lindane concentrations < or = 55 micrograms/liter, where zooplankton was only temporarily affected. At higher lindane, concentrations ( > or = 102 micrograms/liter) effects on phytoplankton were not clear, as also increases in abundances were observed, probably as a consequence of minimized grazing pressure, due to high zooplankton mortality. Comparison of these results with data obtained in complex outdoor systems demonstrates the practicability and sensitivity of indoor microcosms and emphasizes the importance of long-term testing and assessment of recovery processes for prediction of environmental effects.