No abstract

Investigations of potential risk from biosolids generally indicate that land application does not threaten human or ecosystem health, but questions continue to arise concerning the environmental effects of this practice. This research project was initiated to evaluate ecotoxicity resulting from the amendment of soils with biosolids from municipal wastewater treatment plants. Toxicity was evaluated using standard tests, including earthworm mortality, growth, and reproduction; seedling germination and root elongation; microbial respiration; and nematode mortality and reproduction. Nineteen municipal wastewater treatment plants were identified to participate in an initial screening of toxicity, and five were chosen for a more detailed evaluation. In addition, two soils with historically high applications of high‐metal biosolids were evaluated. Contaminants examined were zinc, copper, nickel, chromium, arsenic, cadmium, lead, and coplanar polychlorinated biphenyls (PCBs). Single applications had no effect on soil metal concentrations. Coplanar PCBs were not detectable in any of the soils or biosolids. All target organisms were sensitive to reference toxicants. Limited toxicity was observed in a small number of the amended soils, but no patterns emerged. Approximately one‐half of the negative effects of biosolids on bioindicators could be attributed to routine properties, such as slight depression of pH and/or elevated salinity. None of the accumulated metal concentrations were excessive, and most would not be considered elevated. These observations suggest that current regulations for application of biosolids to soils are providing adequate ecosystem protection.

No abstract

Phytoremediation has been demonstrated to be a viable cleanup alternative for soils contaminated with petroleum products. This study evaluated the application of phytoremediation to soil from a manufactured gas plant (MGP) site with high concentrations of recalcitrant, polycyclic aromatic hydrocarbons (PAHs). Two greenhouse studies investigated the potential dissipation and plant translocation of PAHs by fescue (Festuca arundinacea) and switchgrass (Panicum virgatum) in the first experiment and zucchini (Curcubita pepo Raven) in the second. The MGP soil was highly hydrophobic and initially inhibited plant growth. Two unplanted controls were established with and without fertilization. In the first experiment, concentrations of PAHs decreased significantly in all treatments after 12 mo. Plant biomass and microbial numbers were statistically equivalent among plant species. PAH concentrations in plant biomass were negligible for fescue and switchgrass. In the second experiment, zucchini enhanced the dissipation of several PAHs after 90 d of treatment when compared to the unvegetated soil. Plant tissue concentrations of PAHs were not elevated in the zucchini roots and shoots, and PAHs were not detectable in the fruit.

Several biological assays were used to evaluate the toxic effects of contaminants in soil after phytoremediation. During the treatment process, significant decreases in overall toxicity were observed. Specifically, earthworm survivability and lettuce germination increased over the study period. Microbial respiration improved, but only in planted treatments. Toxicity and total polycyclic aromatic hydrocarbon concentrations showed some correlation, but the relationships generally were not significant. Soil moisture was less of a predictor for biological responses. The presence of plants did not provide a clear advantage for improving toxicity compared to unplanted treatments.