Overview
ISO/TS 23893-2:2007 specifies a standardized laboratory procedure for measuring ethoxyresorufin-O-deethylase (EROD) enzyme activity in fish as a water quality biomarker. The method quantifies EROD activity in the post‑mitochondrial (S9) fraction of fish liver homogenate using a fluorimetric assay (microplate or cell/test‑tube format). It applies to fish sampled from freshwater or marine environments or from laboratory exposure studies. The method is intended for EROD activities ≥ 1 pmol/(min·mg protein), with higher sensitivity achievable using the cell procedure.
Key Topics and Requirements
- Analyte and matrix: EROD activity measured in the S9 subcellular fraction of fish liver homogenate.
- Measurement principle: Fluorometric detection of resorufin produced from 7‑ethoxyresorufin; quantification via external calibration (resorufin or rhodamine B).
- Sensitivity: Applicable for activities ≥ 1 pmol/(min·mg protein); cell (test tube) method can improve sensitivity.
- Temperature control: All handling of S9 fractions near 4 °C (ice); enzymatic reaction at 20 °C ± 2 °C.
- Sampling guidance: Sample groups of fish (recommend at least 10 individuals of same species/sex/size); avoid spawning season and record environmental/biological covariates (water temperature, sex, length, liver mass).
- Reagents & equipment: Specifies use of analytical‑grade reagents (resorufin, 7‑ethoxyresorufin, NADPH, buffers), cryogenic storage (≤ −70 °C or liquid nitrogen), homogeniser (Potter‑Elvehjem), centrifuge, and a cell or 96‑well microplate spectrofluorimeter.
- Data expression: EROD activity normalized to protein content in S9 fraction; includes instructions for calibration, calculation and statistical processing.
Applications and Users
- Environmental monitoring programs assessing exposure of fish to P4501A inducers such as PCBs, PAHs and dioxins.
- Ecotoxicology and fisheries research investigating early biological effects of organic contaminants.
- Accredited environmental laboratories and regulatory agencies performing biomarker‑based surveillance of aquatic ecosystems.
- Consultants and industry labs conducting laboratory exposures or effluent impact studies.
Note: EROD induction indicates exposure to certain organic inducers, but a lack of induction does not necessarily mean absence of contamination (inhibition, bioavailability and low exposure levels can affect results).
Related Standards
- ISO 23893-1: Sampling of fish, handling and preservation of samples - normative reference for sample collection and pre‑analytical procedures.
Keywords: ISO/TS 23893-2:2007, EROD, ethoxyresorufin‑O‑deethylase, fish liver, water quality, biomarker, fluorimetric, S9 fraction, microplate assay.