Cyprinids EROD activities in low contaminated rivers: A relevant statistical approach to estimate reference levels for EROD biomarker?

In an attempt to estimate the levels of fish EROD activity in low polluted rivers, three species of cyprinids were collected in four French river sites in the Rhône watershed area. Chemical contamination of fish and sediment was measured. Physiological indices, including condition factor, liver somatic index and gonadosomatic index were calculated to assess fish condition and reproductive status. No significant difference was observed for EROD levels between three sites. A fourth site (Saône) showed a small induced EROD level. Hence, we concluded that EROD levels measured in Ain, Ardèche and Drôme may be considered as useful and relevant control values to be compared with levels in other areas where no suitable upstream values can be obtained. Such a preliminary approach is a first step for the estimation of reference levels which are necessary in the future environmental biomarker monitoring.