Induction of micronuclei in hemocytes of Mytilus edulis and statistical analysis

A genotoxicity test focusing on micronucleus production in the blood cells (hemocytes) of blue mussel M. edulis has been developed as a possible indicator for marine pollution. A linear dose-response relationship was found when M. edulis was exposed to low concentrations (0, 12.5, and 25 mg/liter) of the alkylating agent ethyl methanesulfonate under laboratory conditions, while higher concentrations (50 and 100 mg/liter) resulted in cytotoxic effects. Furthermore the micronuclei (MN) frequencies in wild mussels from four different field locations have been determined. Mussels collected from two polluted sites showed an elevated MN frequency, indicating the presence of genotoxic pollution. A method to determine the micronuclei background level is suggested and the further implications for applying the method in biomonitoring investigations are discussed. The considered M. edulis exhibits a high biological variation, emphasizing the importance of application of a correct statistical method. A systematic approach to the statistical evaluation of the mussel MN test is outlined. The statistical model includes three different situations: (a) estimation of parameters of a single sample, (b) estimation and comparison of two samples, and (c) estimation of a dose-response relationship. Cases (a) and (b) are especially relevant in biomonitoring investigations while case (c) primarily concerns laboratory experiments.