Validation of a four‐day Ceriodaphnia toxicity test and statistical considerations in data analysis

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Abstract
This study evaluated the technical feasibility of a shorter alternative to the U.S. Environmental Protection Agency (EPA)‐recommended 7‐d chronic toxicity test with Ceriodaphnia dubia. The results of 4‐d and 7‐d Ceriodaphnia dubia toxicity tests, conducted concurrently, were compared using treated municipal effluent, metals, PCP, ethylene glycol, phenol and surfactants. The experimental technique was similar for both studies with the exception of the duration and age of the test species at test initiation. The 4‐d static‐renewal test was initiated with 3‐day‐old Ceriodaphnia dubia, and 1‐day‐old organisms were used in the 7‐d tests. The chronic values of the replicated studies, based on survival and young production, were within a factor of two in approximately 70% of the total tests conducted and in all tests conducted with municipal effluent. Based on the available results, the 4‐d toxicity study appears to be a technically valid alternative to the EPA‐recommended 7‐day test, particularly for treated municipal effluent. An important factor in toxicity testing is the use of valid statistical procedures. The validity of the various methods for Ceriodaphnia dubia depends upon their appropriate use; however, it is difficult to justify the widespread use of multiple comparison methods, particularly Dunnett's procedure.