Substance-specific water quality criteria for the protection of South African freshwater ecosystems: methods for derivation and initial results for some inorganic toxic substances

Freshwater ecosystems form the resource base on which water users, such as the agricultural, recreational, domestic and industrial sectors, depend. These essential resources therefore need to be protected and maintained in a healthy state. The Department Water Affairs and Forestry is currently developing water quality criteria for the protection of South African freshwater ecosystems, to complement the existing National Water Quality Guidelines for domestic, industrial, agricultural and recreational use. This paper descriptionbes the methodology for the derivation of in-stream water quality criteria for inorganic toxic substances. Criteria are calculated from the results of acute and chronic toxicity tests on a number of representative species, using local data where available, and relying on international databases to supplement local information.