Impact of long-term reclaimed wastewater irrigation on agricultural soils: a preliminary assessment

The effect of reclaimed wastewater irrigation on the alteration of soil properties and accumulation of trace metals in soil profiles was investigated by monitoring different plots from Palmdale, California that had been irrigated with effluents for various lengths of time (3, 8, and 20 years, respectively). The non-effluent-irrigated plot served as the control and provided reference "background" values. Total metals at different soil depths were analyzed by acid digestion, and EDTA-extractable metals were analyzed as available fraction. Results show that soil pH values were significantly (p<0.05) lowered in plots with 20-year irrigation to a depth of 140 cm, while EC was elevated for all three plots compared with control. OM, TC and TN contents increased in the top 10-cm soil layers in plots with 8- and 20-year effluent irrigation. Irrigation with effluents also increased both the total and EDTA-extractable metals in the fields. It showed that long-term effluent irrigation could be of agricultural interest due mainly to its organic matter concentrations and nutrients input, however, trace contaminants such as heavy metals in the upper horizons may be accumulated, which may eventually lead to deterioration of soil and groundwater quality and affect the sustainability of land-based disposal of effluent.