Five Metropolitan Areas Across the US

Water Environment & Reuse Foundation (WE&RF)

University of Cincinnati, University of Michigan, US EPA

Our Expert:

Trace organic compounds (TOrCs) discharged in municipal wastewater effluents have potential to adversely affect aquatic communities. The Water Environment & Reuse Foundation (WE&RF) funded a study (CEC6R12) and contracted with the LimnoTech team to further develop and validate a diagnostic framework and assessment tools for assessing the risk of TOrCs to aquatic life. The framework will help utility managers assess the importance of TOrCs in their wastewater effluents as a potential ecosystem stressor in their local waterways.

The Challenge

Thousands of trace organic compounds (TOrCs), such as pharmaceuticals, personal care products, plasticizers, pesticides, flame retardants, and other organics, are regularly released into the aquatic environment, and little is known of their cumulative effects on human health and aquatic life. Targeted studies have suggested exposures to TOrCs could have negative ecosystem impacts. Establishing a cause and effect link between TOrCs in water resource recovery facility (WRRF) effluent discharges and adverse impacts to aquatic life in the receiving waters is challenging due to several factors, including:

  • not knowing which TOrCs are endocrine disruptors;
  • lack of information on TOrC bioavailability;
  • the importance of other receiving water stressors; and
  • whether the presence of TOrCs is a reliable indicator of aquatic life impairment.

Because of the uncertainty associated with the potential risks of TOrCs, management actions might focus on the wrong sites, and/or the wrong compounds, and might not yield the expected improvement of water quality and ecological integrity. Receiving waters often have numerous sources of nonpoint and point source pollution and several stressors including habitat, flow modification, nutrients, suspended solids, metals, and organics.

WRRF managers need to understand which stressors contribute to aquatic life impairments in their receiving waters. A weight-of-evidence (WoE) approach can reduce uncertainty where there are multiple stressor linkages. WE&RF researchers, led by LimnoTech, refined and validated site screening tools to assist water quality managers in evaluating the potential for adverse aquatic life impacts associated with TOrCs exposure from treated effluent discharges.

The Outcome

Using a risk- and management-based approach, the LimnoTech team developed assessment tools and a WoE framework for assessing the potential impact of TOrCs on aquatic life in receiving waters. The framework employs a two-level approach and integrates on-site physical, chemical, and biological characterizations to characterize whether TOrCs are of “Lower”, “Possible”, “Moderate”, or “Higher Concern.” The LimnoTech team applied the first tier of the framework at five sites across the US, using existing data provided by site utility partners. Two of the five sites then underwent a refined second tier assessment, including new field work, to reduce uncertainty and to better support management planning and decisions.

Going beyond merely identifying TOrC exposures in stressed systems, this work provides an effective and practical screening framework for WRRF managers to assess the potential risk to aquatic life from discharges that may contain TOrCs, taking into account non-TORC stressors, and to support planning of future monitoring and/or treatment technology investments. The science of TOrC exposures and their ecological impacts is evolving rapidly, and the WoE framework can be adapted to reflect new information and understanding.


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