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The assimilation of [14C]2,4,5,2′,4′,5′-hexachlorobiphenyl (HCBP) from Lake Michigan sediments by oligochaete worms was determined in laboratory microcosms using dual tracer techniques. Particle size selective feeding by oligochaetes makes single tracer calculations of assimilation from bulk feces subject to errors resulting from the changing distribution coefficients of adsorbed constituents as a function of particle size. 51Cr3+ adsorbed to sediments passes through the guts of worms without being assimilated and serves as a conservative tracer of ingestion. Assimilation efficiencies for HCBP decreased from 36 to 15% over the initial 10 d of active feeding and was inversely related to average defecation rate which increased from 0.05 to 0.25 mg sediment∙mg worm−1∙h−1 over the same period. In combination with measured defecation rates, assimilation efficiencies were used to estimate HCBP uptake rates of 3.9–8.1 pmol∙mg worm−1∙h−1. Assimilation efficiencies appear to be dependent upon gut clearing times which are a function of both gut volume and feeding rate and which are estimated to vary from <1 to >5 h.

In situ radon-222 flux experiments conducted in benthic chambers in Cape Lookout Bight, a small marine basin on the North Carolina coast, reveal that enhanced chemical transport across the sediment-water interface during summer months is caused by abiogenic bubble tube structures. Transport rates for dissolved radon, methane, and ammonium more than three times greater than those predicted on the basis of molecular diffusion occur when open tubes are maintained by semi-diurnal low-tide bubbling.