EVALUATION OF JOINT TOXICITY OF CHLORINE AND AMMONIA TO AQUATIC COMMUNITIES

Periphytic communities on artificial substrates were exposed to chlorine and ammonia, alone and in combinations. The species richness of protozoans decreased with increasing toxicant concentrations. Species richness was reduced by 20% in 2.7 μg/l chlorine, 15.4 μg/l un-ionized ammonia, and a combination of 1.2 μg/l chlorine and 16.8 μg/l ammonia. Interaction between toxicants was significant and effects of mixtures were less-than-additive, especially at higher concentrations. Multiple regression was used to derive a response surface model accounting for 73.4% of the variation in species richness. Algal biomass and community metabolism measures were less sensitive to stress and showed different patterns of joint action. © 1990.