AbstractTo simulate the bioaccumulation of neutral organic contaminants by infaunal benthos, the partitioning of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) between a contaminated estuarine sediment and admixed C‐18‐coated silica particles was measured. The concentrations of lower chlorinated PCB congeners (less than five chlorine atoms per molecule) on the C‐18‐coated silica particles reached apparent steady state within 300 h while congeners with greater numbers of chlorine atoms required much greater time periods (greater than 1 year) to reach apparent steady state. Polycyclic aromatic hydrocarbons showed less partitioning from sediment to the C‐18 particles than PCB congeners, although the log Kow ranges of the compounds in these comparisons were similar. The biota sediment accumulation factors, defined as the lipid‐normalized contaminant concentration in an exposed organism divided by the organic carbon‐normalized contaminant concentration of the sediment, were calculated for these exposures using the C‐18 of the particles as the lipid. The results from these exposures agreed closely with those measured in studies where living benthic organisms were exposed to contaminated sediment.