Higher Risks of Copper Toxicity in Turbid Waters: Quantifying the Bioavailability of Particle-Bound Metals to Set Site-Specific Water Quality Criteria

In coastal waters, particulate metals constitute a substantial fraction of the total metals; however, the prevalent water quality criteria are primarily based on dissolved metals, seemingly neglecting the contribution of particulate metals. Here we developed a method to quantify the toxicity risk of particulate metals, and proposed a way to calculate modifying factors (MFs) for setting site-specific criteria in turbid waters. Specifically, we used a side-by-side experimental design to study copper (Cu) bioaccumulation and toxicity in an estuarine clam, Potamocorbula laevis, under the exposure to “dissolved only” and “dissolved + particulate” 65Cu. A toxicokinetic-toxicodynamic model (TK-TD) was used to quantify the processes of Cu uptake, ingestion, assimilation, egestion, and elimination, and to relate mortality risk to tissue Cu. We find that particulate Cu contributes 40–67% of the Cu bioaccumulation when the suspended particulate matter (SPM) ranges from 12 to 229 mg L–1. The Cu-bearing SPM also increases the sensitivity of organisms to internalized Cu by decreasing the internal threshold concentration (CIT) from 141 to 76.8 μg g–1. MFs were derived based on the TK-TD model to consider the contribution of particulate Cu (in the studied SPM range) for increasing Cu bioaccumulation (MF = 1.3–2.2) and toxicity (MF = 2.3–3.9). Water quality criteria derived from dissolved metal exposure need to be lowered by dividing by an MF to provide adequate protection. Overall, the method we developed provides a scientifically sound framework to manage the risks of metals in turbid waters.