203 - OECD

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203 GUIDELINE FOR TESTING OF CHEMICALSA do pte d by the Co unc il o n 1 7th July 1992Fish, Acute Toxicity new version of the guideline, originally adopted in 1981 and first updated in 1984, isbased on a proposal from the United Kingdom to reduce the numbers of fish in tests of acute aquatictoxicity. The proposal was discussed at a meeting of OECD experts convened at Medmenham (UnitedKingdom) in November main differences in comparison with the earlier versions are the reduction in group-sizeallowing the use of seven fish per group, the extension of the concentration range by allowing aspacing factor of instead of 2 and the introduction of a limit test at 100 mg/l of test OF THE fish are exposed to the test substance preferably for a period of 96 hours.

(Binomial theory dictates that when 10 fish are used with zero mortality, there is a 99.9 % confidence that the LC50 is greater than 100 mg/l. With 7, 8 or 9 fish, the absence of mortality provides at least 99% confidence that the LC50 is greater than the concentration used in …

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