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The use of in situ assays, which was initially proposed by Nebeker et al. (1984), is presently recognised as an effective tool to study the effects of contaminated sediments (Burton 1992). The placement of caged organisms to study short-term effects of exposure to contaminated environments has been employed for a number of aquatic species, both fish and invertebrate. This paper describes the application of this techniques to study the toxicity of Lake Orta sediments using both resident (Daphnia obtusa, D. longispina) and non-resident (D. magna, Echinogammarus stammeri) invertebrate species. In each of the selected stations, a group of four chambers, each containing 10 individuals, were deployed by scuba divers at 10 m depth and collected after 48 h. For each chamber, the surviving animals were counted, transferred to the laboratory and kept in Lake Orta water until their death. The number of neonates produced by each female in the laboratory was recorded daily in order to determine if the short exposure period could affect the reproductive behaviour of the animals. The technique and results reported here indicate the utility of in situ testing and suggest that, under certain conditions, this method of testing may yield results which are more representative of actual environmental conditions by avoiding the sample manipulation required for traditional laboratory toxicity tests.
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