Riverine macroinvertebrate responses to chlorine and chlorinated sewage effluents - Acute chlorine tolerances of Baetis harrisoni (Ephemeroptera) from two rivers in KwaZulu-Natal, South Africa

Abstract

Chlorine is widely used in South African sewage treatment works, and despite its volatility is likely to have a considerable impact on riverine ecosystems. This paper considers the results of acute (96 h) toxicity responses to chlorine of riverine mayfly nymphs Baetis harrisoni collected from the small, relatively uncontaminated suburban Westville, Stream, KwaZulu-Natal and from the more severely impacted Umbilo River, which flows through the industrial area of Pinetown, KwaZulu-Natal, South Africa. The 96 h LC50 value for total residual chlorine for nymphs from Westville Stream was 4.1 μg/l and from the Umbilo River 4.8 μg/l. This value is well below the general effluent standard of 100 μg/l (General and Special Standards, Regulation 991, 1984), but correlates with the acute effect value guideline of 5 μg/l (South African Water Quality Guidelines, No 7. 1996).