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(70-17) Long-term effects of Zn contamination on soil microbial processes. Smolders, E.*,1, Van den Brande, K.1, Lombi, E.1, McGrath, S.P.1, 1 Katholieke Universiteit Leuven, Heverlee, Belgium ABSTRACT- Soil microbial processes are sensitive to zinc (Zn) and may control the soil limits for Zn when based on laboratory toxicity tests. Toxicity tests based on Zn salt spiked tests have been frequently criticised for not mimicking effects of Zn in the field. The objective of this study is to compare the toxicity of Zn to the soil nitrification potential between soils where Zn enrichment has been equilibrated for several years and soils that are freshly spiked with Zn. Four transects were sampled around galvanised steel pylons and roadsides An uncontaminated soil was collected close to each of the contaminated soils and was spiked with Zn salt at concentrations similar to that in the contaminated and aged soils. Total Zn concentration in soil significantly increase with decreasing distance to the source reaching 200-1100 mg Zn/kg. The nitrification potential is consistently reduced by increasing soil Zn concentration in spiked soils. In contrast, there is no relation between soil Zn and nitrification in the 40m or 60 m pylon transects up to the highest soil Zn concentration at which nitrification is more than 50% inhibited in spiked control soils. Nitrification potential was significantly reduced in one roadside sample collected under a crash barrier, whereas no adverse effects were found in all other roadside sampled. Ageing of the soil after spiking (1d-28 d) did not significantly change the EC50 on nitrification. In contrast, leaching soil after spiking followed by 4 weeks incubation significantly increased the EC50 by more than a factor of two. Pore water Zn concentration in spiked soils were consistently above these in field contaminated soils at corresponding total Zn and soil pH. Pore water Zn explains higher effects of soil Zn on nitrification in spiked, unleached soils than in field contaminated soils. Key words: zinc, pylons, nitrification, soil solution |
