Watershed-Scale Risk to Aquatic Organisms from Complex Chemical Mixtures in the Shenandoah River.

River waters contain complex chemical mixtures derived from natural and anthropogenic sources. Aquatic organisms are exposed to the entire chemical composition of the water, resulting in potential effects at the organismal through ecosystem level. This study applied a holistic approach to assess landscape, hydrological, chemical, and biological variables. On-site mobile laboratory experiments were conducted to evaluate biological effects of exposure to chemical mixtures in the Shenandoah River Watershed. A suite of 534 inorganic and organic constituents were analyzed, of which 273 were detected. A watershed-scale accumulated wastewater model was developed to predict environmental concentrations of chemicals derived from wastewater treatment plants (WWTPs) to assess potential aquatic organism exposure for all stream reaches in the watershed. Measured and modeled concentrations generally were within a factor of 2. Ecotoxicological effects from exposure to individual components of the chemical mixture were evaluated using risk quotients (RQs) based on measured or predicted environmental concentrations and no effect concentrations or chronic toxicity threshold values. Seventy-two percent of the compounds had RQ values <0.1, indicating limited risk from individual chemicals. However, when individual RQs were aggregated into a risk index, most stream reaches receiving WWTP effluent posed potential risk to aquatic organisms from exposure to complex chemical mixtures.

Synergistic Treatment of Mixed 1,4-Dioxane and Chlorinated Solvent Contaminations by Coupling Electrochemical Oxidation with Aerobic Biodegradation.

Biodegradation of the persistent groundwater contaminant 1,4-dioxane is often hindered by the absence of dissolved oxygen and the co-occurrence of inhibiting chlorinated solvents. Using flow-through electrolytic reactors equipped with Ti/IrO2-Ta2O5 mesh electrodes, we show that combining electrochemical oxidation with aerobic biodegradation produces an overadditive treatment effect for degrading 1,4-dioxane. In reactors bioaugmented by Pseudonocardia dioxanivorans CB1190 with 3.0 V applied, 1,4-dioxane was oxidized 2.5 times faster than in bioaugmented control reactors without an applied potential, and 12 times faster than by abiotic electrolysis only. Quantitative polymerase chain reaction analyses of CB1190 abundance, oxidation-reduction potential, and dissolved oxygen measurements indicated that microbial growth was promoted by anodic oxygen-generating reactions. At a higher potential of 8.0 V, however, the cell abundance near the anode was diminished, likely due to unfavorable pH and/or redox conditions. When coupled to electrolysis, biodegradation of 1,4-dioxane was sustained even in the presence of the common co-contaminant trichloroethene in the influent. Our findings demonstrate that combining electrolytic treatment with aerobic biodegradation may be a promising synergistic approach for the treatment of mixed contaminants.

Advanced Electrochemical Oxidation of 1,4-Dioxane via Dark Catalysis by Novel Titanium Dioxide (TiO2) Pellets.

1,4-dioxane is an emerging groundwater contaminant with significant regulatory implications. Because it is resistant to traditional groundwater treatments, remediation of 1,4-dioxane is often limited to costly ex situ UV-based advanced oxidation. By varying applied voltage, electrical conductivity, seepage velocity, and influent contaminant concentration in flow-through reactors, we show that electrochemical oxidation is a viable technology for in situ and ex situ treatment of 1,4-dioxane under a wide range of environmental conditions. Using novel titanium dioxide (TiO2) pellets, we demonstrate for the first time that this prominent catalyst can be activated in the dark even when electrically insulated from the electrodes. TiO2-catalyzed reactors achieved efficiencies of greater than 97% degradation of 1,4-dioxane, up to 4.6 times higher than noncatalyzed electrolytic reactors. However, the greatest catalytic enhancement (70% degradation versus no degradation without catalysis) was observed in low-ionic-strength water, where conventional electrochemical approaches notoriously fail. The TiO2 pellet's dark-catalytic oxidation activity was confirmed on the pharmaceutical lamotrigine and the industrial solvent chlorobenzene, signifying that electrocatalytic treatment has tremendous potential as a transformative remediation technology for persistent organic pollutants in groundwater and other aqueous environments.