The burrow microbial communities were markedly different from those of surrounding surface and subsurface sediments. Differences in microbial biomass were attributed to burrow structures, textures of the burrow lining sediments, and organic carbon content. No significant reduction of microbial biomass or of several distinctive signature PLFA (phospholipid fatty acid) was detected in bromophenol-contaminated burrows, when compared to non-bromophenol-containing burrows. All three types of sediments (burrow, surface, and subsurface) examined for each worm species were distinct.