Assessment of the Effects of Bioturbation in Contaminated Sedi- Ments

Oligochaete worms are often the dominant organisms present in contaminated sediment in the field. Bioturbation, the reworking of sediments or soils by organisms, can be a significant fate and transport mechanism in contaminated sediment systems. The fate of pyrene, a polycyclic aromatic hydrocarbon, subjected to oligochaete bioturbation is the focus of this paper. Limnodrilus cervix, a representative oli-gochaete, were introduced into small laboratory microcosms containing beds of contaminated sediment with a continuous flow of overlying water. Through their feeding, respiration, and burrowing activities, the worms physically changed the porosity of the sediment and significantly influenced the fate and transport of pyrene by several mechanisms. Over a seven-month experiment, the amount of pyrene released into the overlying water was about 250% greater in bioturbated than in undisturbed cells. Pyrene loss in the upper 15 mm due to biotic processes was 170% greater than undisturbed cells due to enhanced microbial processes and/or direct worm degradation. The pyrene remaining in the upper 15 mm of sediment bed at the end of the experiment was 15% for bioturbated cells compared to 52% for undisturbed controls. Experimental results suggest that native oligochaetes can enhance natural attenuation of contaminated sediments in the field.