Toxicity and biodegradability screening of nonionic surfactants using sediment-derived methanogenic consortia

The objective of this study was to screen and select biologically-compatible surfactants for subsequent use in enhancing the bioavailability and reductive dechlorination of sorbed-phase chlorinated organic contaminants. Sixteen surfactants commonly used in surfactant-enhanced bioavailability experiments were examined: polyoxyethylene (POE) alcohols (Brij 30/35, Witconol SN-70/90/120), POE sorbitan fatty acid esters (Tween 20/21/40/60/61/65/80/81/85), the octylphenol ethoxylate Triton X-100, and the anionic sodium dodecyl sulfate. Two hexachlorobenzene-dechlorinating, mixed enrichment cultures -- one glucose-fed and the other lactate-fed -- were developed at 22°C using anaerobic media and contaminated estuarine sediment as inoculum. Serum bottle methanogenesis assays using these two cultures were performed at a surfactant concentration of 200 mg/L. Tween surfactants were found to be the least inhibitory and also partially degradable. Some Tween surfactants accelerated the rates of methanogenesis for the lactate-fed culture, but no enhancement was observed for the glucose-fed culture. Cultures amended with Tween 20, 21, and 80 had the slowest methane production, while those amended with Tween 40, 60, and 85 had the fastest methane production. All non-Tween surfactants inhibited methanogenesis. The results of this study indicate that the biological compatibility of nonionic surfactants, even those from the same homologous series, appear to be system-specific and can vary significantly.