The short-term toxicity of NH3 and low oxygen was determined for different species of aquatic insects (mayflies and stoneflies). The experiments were carried out in laboratory channels. Compared with fish species, the investigated macroinvertebrates were much less sensitive. Hence, if ecotoxicological criteria for the wet weather situation are developed for ammonia and oxygen, the requirements of sensitive fish species should be considered first.

In Switzerland, exceedences of the NH3 short-term threshold concentration caused by combined sewer overflow occur mostly in (too) small receiving waters during summer thunderstorms.

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