Water Effect Ratio

Water quality criteria are the numeric conditions (e.g., contaminant concentrations) that need to be maintained or attained to protect aquatic ecosystems and human health. To provide for protection of aquatic life, it is necessary to consider both short term “acute” (survival) effects and long-term “chronic” (survival, growth, reproduction) effects. When appropriate information on these effects exists, regulatory agencies are able to develop Ambient Water Quality Criteria using existing protocol.

However, the U.S. EPA acknowledges that these criteria can sometimes be either under-protective or over-protective of the aquatic environment since site-specific water quality conditions can strongly influence a compounds bioavailability and toxicity. To address this issue, the EPA has provided a mechanism for the development of appropriate site-specific water quality-based limits for sites for which a compound (e.g., aluminum, copper) that has had ambient water quality criteria developed and the concentration of the compound exceeds existing ambient water quality criteria through the implementation of water effect ratio (WER) determinations, taking into account site-specific conditions.

Pacific EcoRisk is very experienced in development of ambient water quality criteria as well as the evaluation of current criteria and the studies required for development of site-specific criteria.

Services that we provide in the determination of ambient water quality criteria, site specific criteria, and water effect ratios (WERs):

• Critical review of regulatory reports                                                

• Preparation of information (e.g., literature) reviews

• Performance of acute, chronic, life-cycle toxicity tests

• Performance of water effect ratio studies using current EPA guidance

• Derivation of numeric limits using Biotic Ligand Model (BLM)