Impact of Long-Term Reclaimed Water Irrigation on Trace Elements Contents in Agricultural Soils in Beijing, China

The rapid increase of reclaimed water irrigation on agricultural soils requires investigation of its impact on soil health. In this study, a simulation experiment for various lengths of long-term reclaimed water irrigation time (98, 196 and 236 years, respectively) was conducted in the southeast suburb of Beijing, China. Unirrigated soil served as the control. The environmental behavior of seven trace elements (As, Cd, Cr, Cu, Hg, Pb and Zn) at different soil depths in 0-600 cm profiles was analyzed. Results showed that the 0-30 and 200-300 cm soil layers were more likely to accumulate trace elements under long-term reclaimed water irrigation, although the accumulation in the 0-600 cm profiles was not particularly obvious. Correlation analysis showed that the trace element concentrations and distribution were significantly related to clay fraction and organic matters (OM), whereas they were not related to redox potential (Eh). The potential ecological risk assessment showed that the long-term reclaimed water irrigation did not result in a significantly increased ecological risk. However, Cd and Hg were identified as the metals with the highest potential ecological risk in the study area and the trace element contents in the top 0-30 cm soil layer should be carefully monitored. Future studies are required to clarify the environmental risks of trace elements under long-term reclaimed water irrigation as they might slowly accumulate in soil with time.