Drinking water treatment residuals reduce toxicity to fish from metal-contaminated sediments

Drinking water treatment residuals (DWTRs) produced as a result of the coagulation-flocculation process during water treatment are considered waste materials. Characterization of this material shows its ability to sequester metals and other anionic and cationic chemicals. Drinking water treatment residuals from two different drinking water treatment plants located in Wyoming and Oregon were evaluated for their ability to function as viable capping materials of metal-contaminated sediments. The contaminated sediments tested were either spiked with a mixture of metals, 1 mg/kg of Cu, Zn, Cd, and Pb, or coming from an intertidal sediment collected at a U.S. Naval Air Station. A Gust chamber experiment was used to determine metal fluxes from these sediments into the overlying water with applied hydrodynamic stress of 0.05 and 0.4 Pa in the absence and presence of DWTR as a capping material. The DWTR effectively reduced the amount of metal released to the overlying waters to a value below the National Recommended Aquatic Life Criteria for Cr, Cu, Pb, and Zn, but slightly above the value for Cd. The toxicity of these waters was tested with an in vivo 96 hr fathead minnow survival assay. In the absence of capping, all the fry died within 1 hr. Capping with DWTR from Wyoming effectively reduced contamination, and 95% of the fish survived. The DWTR from Oregon was less successful, but the survival of fish was equivalent to diluting the original contaminated waters by a factor of 100. Drinking water treatment residual effectively reduced metallothionein in fish, a biomarker of metal contamination, corroborating the survival experiments. These results suggest that DWTRs may be very effective for remediation of metal-contaminated sites.