Ecotoxicological assessment of heavy metals in sewage sludge amended soils |
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| Institution: | 1. Laboratory of Soils and Agricultural Chemistry, Department of Natural Resources and Agricultural Engineering, Agricultural University of Athens, Athens GR-118 55, Greece;2. Laboratory of General and Agricultural Microbiology, Department of Crop Science, Agricultural University of Athens, Athens GR-118 55, Greece;1. Faculty of Engineering, Architecture and Urbanism and Geography (FAENG), Federal University of Mato Grosso do Sul (UFMS), Av. Costa e Silva, S/N, Cidade Universitária, Campo Grande, MS 79.070-900, Brazil;2. Department of Environmental and Sanitary Engineering, Federal University of Santa Catarina (UFSC), Trindade, Florianópolis, SC 88040-970, Brazil;3. Institute for Water and Wastewater Technology (IWWT), Durban University of Technology (DUT), PO Box 1334, Durban 4000, South Africa |
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| Abstract: | Contamination of soils by potentially toxic elements (PTEs) (e.g. Zn, Cu, Ni, Cr, Pb, Cd) from amendments of sewage sludge is subject to strict controls within the European Community in relation to total permissible metal concentrations, soil properties and intended use. This paper highlights the need for ecotoxicological data for the assessment of PTE impacts in addition to geochemical data alone. The soil microflora plays an essential role in determining levels of soil fertility, being intimately associated with the biogeochemical cycling of essential plant nutrients and the turnover of organic carbon. The measurement of soil microbiological parameters can provide insight into the impact of PTEs upon soil fertility, where geochemical analysis alone can often be inadequate to assess contaminant effects on essential components of the soil ecosystem. Microbial investigations were conducted on soils sampled from a well-controlled field experiment previously amended with specific types and rates of sewage sludge. Key microbiological parameters measured included the activity of the dehydrogenase enzyme and the presence and number of effective nitrogen fixing cells of Rhizobium leguminosarum biovar trifolii capable of nodulating the host plant, white clover (Trifolium repens). Results were evaluated with respect to maximum permissible concentrations of PTEs in sludge amended soils, as stipulated under UK limit values and the European Directive 86/278/EEC. Important effects on the size of the Rhizobium population and dehydrogenase activity were apparent in soils samples in relation to the soil pH, sludge type, addition rates and the concentrations of PTE present. |
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