Land application has become a promising method for recycling energy and resources from sewage sludge; however, the changes that occur to the toxic metal concentrations in soil following the application of sewage sludge have been poorly investigated in China. The present study attempted to investigate the spatiotemporal variations of toxic metal concentrations in soil due to the land application of sewage sludge and the critical influencing factors. Overall, the results indicated that an increasing ratio of sewage sludge for land application, the concentrated disposal measures, and a shallower soil may lead to elevated toxic metal concentrations in soil. The worst scenario simulation showed that the cumulative discharge of toxic metals through sludge disposal were ranked as: Zn > Cu > Cr > Pb > Ni > As > Cd > Hg. After sewage sludge was applied to previously unaffected soil, i.e., background soil, the toxic metal concentrations in the soil increased annually over the period from 2006 to 2017. However, with respect to the affected soil, the concentrations of Zn and Cu increased, whereas the concentrations of As, Cd, Cr, and Pb decreased annually over the period from 2006 to 2017. The results indicate that, in practice, the selection of soil for sewage sludge disposal depends on the background and actual concentrations of toxic metals in a soil as well as the stress caused by the amount of sewage sludge application to cultivated land. We propose to use sewage sludge containing relatively lower concentrations of metals than the disposal soil for land application. Furthermore, land application of sewage sludge should be suited to local conditions in the future sewage sludge management.
Keywords: Land application; Sewage sludge; Spatiotemporal variations; Toxic metals.
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