Amendments and plant cover influence on trace element pools in a contaminated soil

Abstract

A 30-month experiment was carried out in field containers to evaluate the potential of various amendments and/or a plant cover (Agrostis stolonifera L.) for reclamation of a soil contaminated with As, Cd, Cu, Pb and Zn. Five amended treatments with plant were established: leonardite (LEO), litter (LIT), municipal waste compost (MWC), biosolid compost (BC) and sugar beet lime (SL). Two controls were also set up: control without amendment but with plant (CTRP) and control without amendment and without plant (CTR). A widely accepted sequential extraction procedure was used to assess changes in trace element pools in soil following remediation. Results showed that trace element distribution in soil was highly influenced by the origin of the contamination (mine sulphides): trace elements were mainly associated with the residual fraction (in form of sulphides) and to a lesser extent with the reducible fraction, where Fe oxides and oxyhydroxides are expected, as a consequence of sulphide oxidation. The addition of amendments and/or establishment of a plant cover showed no clear effect on Cd and Pb distribution. The influence on As fractionation was also small and restricted to the most labile fraction, where higher concentrations of As were found in SL, MWC and BC. In contrast, Cu concentrations in the most labile fraction decreased in MWC, BC, LEO and LIT, while Cu recovery within the organic matter-associated fraction increased in these treatments. Zinc concentration in the most labile fraction was significantly lower in CTRP than in CTR, whereas Zn recovery in this fraction increased in MWC due to Zn input. In some cases redistribution of amendment-derived trace elements from slow-releasing fractions to the residual pool seemed to occur. Since the increase in As and Zn only accounted for a small proportion of the total pool and soil quality improved in treated soils, the use of soil amendments and/or revegetation might be a reliable option for long-term reclamation of soils moderately contaminated with trace elements. Nonetheless, high quality by-products should be employed to minimize trace element input to soil.