Bioassays for evaluating toxicity of soil treated with sewage sludge

摘要

In this study, bioassays were used to evaluate soil toxicity after treatment with domestic sewage sludge (DSS). Soil samples were taken in a commercial production area where eucalyptus (Eucalyptus grandis) seedlings were treated with 0.0, 7.5, 15 and 22.5 t/ha (dry base) of DSS. The bioassays were conducted using three test organisms: Lactuca sativa, Daphnia magna, and Pseudokirchneriella subcapitata. Root growth test with L. sativa was ineffective to assess toxicity in DDS treated soil, due to the lack of relation between root growth and elutriate dilution. For D. magna, the LC<,50> (48h) values showed a slightly increase in soil toxicity related to increasing DSS dose. For P. subcapitata, the IC<,50> (72h) values indicated higher soil toxicity associated with DSS doses than the LC<,50> values. Both LC<,50>, and IC<,50> values were effective to show potentially toxic impacts on soil due to DSS application, however, the bioassay with P. subcapitata was more sensitive to DSS than D. magna. The ecotoxicity tests permitted to conclude that the DSS application in soil provides both nutrients and contaminants, and do not cause harmful impact on forest system, when compared with soil-eucalyptus system without DSS treatment.