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

Deposit feeders modify sediment by aggregating individual particles into fecal pellets. Loss of contaminants may be either more (enhanced bacterial degradation) or less (hindered diffusion and desorption) rapid for sediment incorporated into pellets. We studied the loss of 10 polycyclic aromatic hydrocarbons (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 had 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 additional 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 rate constants; for high molecular weight PAHs, the opposite was found. Desorption rate constants were similar for fecal pellets (0.0002-0.037/d) and sediment (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, incorporation of sediment into robust fecal pellets (half-life on the order of decades) did not affect the loss rates of PAHs.

Pore structure of soot deposits from several combustion sources.

Soot was harvested from five combustion sources: a dodecane flame, marine and bus diesel engines, a wood stove, and an oil furnace. The soots ranged from 20% to 90% carbon by weight and molar C/H ratios from 1 to 7, the latter suggesting a highly condensed aromatic structure. Total surface areas (by nitrogen adsorption using the Brunauer Emmett Teller, BET method) ranged from 1 to 85 m2 g(-1). Comparison of the surface area and meso-pore (pores 2-50 nm) surface area predicted by density functional theory (DFT) suggested that the soot was highly porous. Total meso-pore volume and surface area ranged from 0.004-0.08 cm3 g(-1) and from 0.33-6.9 m2 g(-1) respectively, accounting for up 33% of the BET surface area. The micro-pore volume (pores <2 nm) calculated from CO2 adsorption data (by DFT) ranged from 0.0009 to 0.013 cm3 g(-1) and micro-pore surface area was 3.1-41 m2 g(-1), accounting for 10-20% of the total intra-particle (meso-plus micro-pores) pore volume and 70-90% of the total intra-particle surface area. Higher pore volume and surface area values were computed using the Dubinin Radushkevich plot technique; ranging from 0.004-0.04 cm3 g(-1) to 11-102 m2 g(-1) for micro-pore volume and surface area, respectively. Comparison of the C/H ratio and the micro-pore structure showed a strong correlation, suggesting a relationship between the condensation of the skeletal structure and micro-porosity of the soot. These data contradict literature reports that soot particles are non-porous and are consistent with recent literature reports that soil organic matter has large micro-pore surface areas.

Induction of suspension feeding in spionid polychaetes by high particulate fluxes.

The feeding behavior of three species of spionid polychaetes varied with water velocity. At moderate flows the worms ceased deposit feeding, formed their feeding tentacles into helices, and lifted them into the water column to capture material in suspension. This behavior was apparently a response to increased flux of suspended matter at high flows rather than to flow velocity alone. Organisms capable of switching their feeding behavior may be common in dynamically variable benthic environments.