Evaluation of Complex Mixture Toxicity in the Milwaukee Estuary (WI, USA) Using Whole-Mixture and Component-Based...

Area of Science:

• Environmental Toxicology
• Ecotoxicology
• Aquatic Chemistry

Background:

• Anthropogenic activities introduce complex chemical mixtures into aquatic ecosystems.
• Traditional risk assessments often focus on single chemicals, potentially underestimating mixture toxicity.
• Evaluating mixture toxicity is crucial for comprehensive environmental risk assessment.

Purpose of the Study:

• To demonstrate alternative approaches for mixture evaluation in a target watershed.
• To characterize chemical composition, in vitro bioactivity, and in vivo effects of whole aquatic mixtures.
• To identify priority chemicals and mixtures contributing to cumulative effects.

Main Methods:

• Deployment of caged fathead minnows (Pimephales promelas) and composite samplers over 96 hours.
• Chemical characterization, in vitro bioactivity assays, and in vivo toxicity testing of collected water samples.
• Grouping chemicals by structure/mode of action and using random forest regression for predictive assessments.

Main Results:

• Identified 14 mixtures and 16 chemicals as high or medium priority for further evaluation.
• Characterized site-specific mixture effects, identifying targets for industrial/urban and pharmaceutical assessments.
• Provided a comprehensive evaluation of cumulative mixture effects, complementing single-chemical prioritizations.

Conclusions:

• The study successfully demonstrated the utility of multiple tools for complex mixture assessment in aquatic environments.
• Identified priority substances and sites for targeted ecotoxicological evaluation and regulatory action.
• Highlights strategies for future complex mixture risk assessments in watersheds.