RESUMEN
In the present study, during a three-month exposure lethal and sublethal effects of ammonium and its products on typical brook organisms (Gammarus pulex, Amphipoda; Radix ovata, Gastropoda; Limnephilus lunatus Trichoptera) were monitored in microcosms approximating field conditions. Every 24 h during this period the microcosms were contaminated with ammonium at five different nominal concentrations, which by chemical reactions produced a mixture of the toxic products ammonia and nitrite. G. pulex proved the most sensitive to the ammonia and nitrite contamination resulting from the ammonium load. In contrast. L. lunatus and R. ovota exhibited clearly effects only at concentrations 10 times higher. It is appropriate to investigate ammonium pollution with its reaction products as a mixture, because in natural bodies of water receiving ammonium input (e.g., from sewage-treatment plants) the substances ammonium/ammonia and nitrite are likewise present simultaneously.