Office of Research and Development Publications

Letter to the Editor on Brent et al. (2022): “A Novel Approach to Developing Thresholds for Total Dissolved Solids Using Standardized and Experimental Toxicity Test Methods”

Citation:

Cormier, S. AND G. Suter II. Letter to the Editor on Brent et al. (2022): “A Novel Approach to Developing Thresholds for Total Dissolved Solids Using Standardized and Experimental Toxicity Test Methods”. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 43(2):241-243, (2024). https://doi.org/10.1002/etc.5800

Impact/Purpose:

The development of ecological benchmark values for major ions in fresh water, measured as total dissolved solids (TDS) or specific conductivity (SC), is a difficult problem with multiple proposed solutions. Brent et al. (2022) presented a new site-specific method based on laboratory tests of synthetic ion mixtures. Their method has appealing attributes, but some aspects in there paper were misleading or incorrect. This letter to the editor clarifies the issues and contributes to improved methods for assessing and developing TMDL thresholds for mixtures of ions.

Description:

The development of ecological benchmark values for major ions in fresh water is challenging and a site-specific method based on laboratory tests of synthetic ion mixtures has recently been published by Brent et al. (2022). Although the method has some appealing attributes, their critique of the U.S. EPA’s field-based method is faulty in some respects. The U.S. EPA’s field-based method has withstood much scrutiny. It has been positively reviewed by the Agency’s Science Advisory Board (SAB, 2011), it has been described and demonstrated in peer-reviewed journals is consistent with independent studies (Cormier et al., 2020). It has starred as key evidence in legal cases (Chambers, 2014). Contrary to comments by Brent et al., the first conductivity benchmark is specific to Central Appalachia (Cormier et al. 2013) and background itself can be used with a model to predict 5% extirpation levels in streams (Cormier et al. 2018). Brent et al. (2022) are to be commended for their investigation of a potential benchmark for dissolved ions as a toxic agent and not just individual ions and for making their benchmark values site specific. However, we believe that the evidence shows that field exposures of entire communities provide genuinely protective ecoregion-specific benchmark values and can also be a viable choice for protecting stream ecosystems.