Loss rates of polycyclic aromatic hydrocarbons from sediment and deposit-feeder fecal pellets

Deposit feeders modify sediment by aggregating individual particles into fe cal pellets. Loss of contaminants may be either more (enhanced bacterial de gradation) or less (hindered diffusion and desorption) rapid for sediment i ncorporated into pellets. We studied the loss of 10 polycyclic aromatic hyd rocarbons (PAHs) from historically contaminated estuarine sediment and the same sediment after it had been pelletized by Capitella sp, I. a polychaete worm typically found in disturbed environments. Fecal pellets initially ha d higher concentrations of organic carbon and PAHs (enrichment factors 1.03 -1.21) due to selective feeding. Over 60 d. desorption of PAHs was minimal, with an average loss of 4 to 5%. Biodegradation accounted for an additiona l 28% loss. A two-component model fit the data well and indicated that the slowly desorbing fraction was close to one for all PAHs. For low molecular weight PAHs, biodegradation rate constants were greater than desorption rat e constants; for high molecular weight PAHs, the opposite was found. Desorp tion rate constants were similar for fecal pellets (0.0002-0.037/d) and sed iment (0.0002-0.031/d). Biodegradation rate constants were also similar for fecal pellets (0.0006-0.022/d) and sediment (0.0002-0.018/d). Thus, incorp oration of sediment into robust fecal pellets (half-life on the order of de cades) did not affect the loss rates of PAHs.