Implication of sewage sludge increased application rates on soil fertility and heavy metals contamination risk

Abstract

This paper aims to assess soil fertility and risk contamination parameters in response to increased amendment rates of sewage sludge application, under semi-arid climatic conditions of Morocco, using two soil textures: soil A (clay-silty) and soil B (sandy-clay) over two years. To this end, sewage sludge and soils treatments physicochemical parameters, heavy metals content, degree of pollution and associated risks were evaluated and compared to controlled soils. The results showed that all studied parameters changed significantly (p < 0.05) in a dose-dependent manner for both soils compared to the untreated control soils. Indeed, there were significant increase in organic matter (OM), total organic carbon (TOC) and nutrients content (N, P and K) of both sols as a response to increased sewage sludge amendment rates. Overall, sewage sludge application showed a positive agronomic potential for both soil and plant. However, there were concern about some heavy metals contamination risks, the results showed a gradual increase of heavy metals concentration in this order: Cu > Pb > Zn > Ni > Cd > Cr. Nevertheless, their concentrations were below the critical values established by the European Union for the agronomic use of soil. The obtained results of assessed parameters indicating SS degree of pollution and associated risks showed a low to a moderate contamination risks of heavy metals. Accordingly, environmental risks of sewage sludge application will be related to increase of heavy metals mainly in a long-term agricultural reuse. Thus, optimal management of sewage sludge application is recommended to ensure sustainability and benefits at the same time to master the contamination risks.