Clover and cress as indicator species of impacts from limed sewage sludge and landfill wastewater land application

Abstract

This study evaluated the performance of cress and clover as bioindicators to evaluate the impact of limed sewage sludge and landfill wastewater application on soil. The use of these two species, and the subsequent parameters measured, were also compared for their effectiveness in evaluating potential effects. Sewage sludge was added to the soil at a rate of 23 mg ha −1 and also at twice this dose. Wastewater was added at a level of 2 and 10% of the soil volume. Germination rate, height increase per week and final dry biomass were measured for both species. Heavy metal (Cd, Pb, Fe, Cu, Ni, and Zn) concentration was determined only for the shoot and root of clover. In general, the results showed that, compared to the control, the overall performance improved for plants exposed to both treatments. However, plants appeared to respond better to the wastewater addition than the sewage sludge amendment. The germination rate as well as other traits indicate that clover may be more sensitive to these fertilizers than cress. The lime addition did not appear to influence growth, nor heavy metal accumulation in clover. There were major differences in heavy metal accumulation in the root vs. shoot of clover. Hence, the concentrations of Cd, Cu, Fe, Zn, and Pb did not vary in the shoots of the plants under either treatments. The concentrations of the heavy metals in the roots however, greatly varied according to the type of metals. The concentrations of these metals appeared to increase with the increase of the addition treatments. The results suggest that for both species, the levels of fertilizers used in the present study were below the toxicity levels. Since the types of soils and the doses of fertilizers influence the rate of heavy metal absorption and their effects on plants, methods for rapid evaluation/monitoring as well as the types of indicators used should be explored as in the present study.