Optimization of Ethoxyresorufin‐ O ‐deethylase Determination in the Microsomes of Earthworms and Its Induction by Polycyclic Aromatic Hydrocarbons

In this study, a fluorometric method was established to measure the ethoxyresorufin‐ O ‐dealkylase (EROD) activity in the microsomes of earthworm after a series of parameter modification (including excitation wavelengths; kinds, pH, and volumes of buffer solutions; kinds and volumes of sensitizers). Earthworms were exposed to increasing concentrations of benzo[ a ]pyrene (B[ a ]P) (0.009–90 µg cm −2 ) in filter papers to validate the modified method and to find out the possible effects of B[ a ]P to EROD activity. Results showed that 560 nm was the optimal excitation wavelength for detecting resorufin. The linear range was 0.05–20 pmol mL −1 with the correlation coefficient of 0.9996. The detection limit was 0.045 pmol mL −1 and the relative standard deviation was <1.3%. Based on the established method, we also found that EROD activity in earthworms was significantly induced by B[ a ]P at 0.009 and 0.09 µg cm −2 , suggesting that the EROD activity in earthworms could be served as a sensitive biomarker in the monitoring of soil contamination within low dosage range.