Ecotoxicity of 3,4-dichloroaniline in enclosed freshwater plankton communities at different nutrient levels

The sensitivity of Daphnia magna to 3,4-dichloroaniline (DCA) was studied in a multispecies mesocosm study and its response was compared to those of naturally occurring zooplankton species. A series of DCA concentrations was tested during two experiments conducted in 1.2 m3 plastic enclosures, which contained water and natural plankton from Lake Markermeer (The Netherlands) and laboratory-cultured D. magna. Low concentrations of 2.7 and 27 mu g l-1 were tested during the first experiment and additional nutrients were supplied to half of the enclosures. Cladocerans were found to be the zooplankton group most sensitive to DCA. The addition of nutrients resulted in a more marked reduction of cladoceran populations at 27 mu g l-1. In the second experiment, additional DCA concentrations (27, 90 and 270 mu g l-1) were tested under nutrient-enriched conditions only. The EC50 for D. magna, calculated from the integrated density over the first 21 days, was 3.2 (1.9--5.5) mu g l-1 DCA when the results of the two experiments were combined. Two naturally occurring dominant cladoceran species were more sensitive to DCA than was D. magna. Less sensitive rotifer and copepod species profited from the reduced competition. The opportunisitic response of the less sensitive species could not prevent an increase in phytoplankton densities at high nutrient supply. The results show that both the effects of DCA on zooplankton and the diminished control exerted by zooplankton on phytoplankton are intensified under nutrient-enriched conditions[PUBLICATION ABSTRACT]