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Abstract-To develop a guideline for a simulation test for aerobic degradability in surface water, the fate of [ 14 C]lindane (␥-hexachlorocyclohexane) was studied in laboratory systems using natural river water and sediments. No sterilized controls were set up. Thus, measured data reflect the sum of biotic and abiotic processes. Tests were carried out under various experimental conditions to investigate which of these would affect the feasibility of the test, the fate of lindane, the physicochemical state, and the biological activity within the sediment-water systems. Lindane (37.7 nmol) was applied either to the water (3 L) or the sediment (0.33 L). Sediments remained nonreducing, and there was no serious decline of nutrients nor enzymatic activities. In one experiment up to 14.1% of the applied lindane was mineralized to 14 CO 2 within 50 d and in a second one up to 35.3%. At day 91 of the latter experiment up to 46.8% were found to have been mineralized. Among the experimental factors tested, the method of lindane application and temperature predominantly affected mineralization. The type of aeration and the semicontinuous addition of organic nutrients were of minor importance. Sediments and water collected at the same site but at different times showed variation in carbon content as well as in esterase and dehydrogenase activities. Nevertheless, these parameters could not be correlated with mineralization of lindane during the tests. Between 1 and 9% of the radioactivity volatilized during the tests. At the end, 23 to 66% were bound to sediments and 15 to 45% of the total activity was neither extractable by water nor by cyclohexane.

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