Impact of wastewater on soil properties and accumulation of heavy metals
Nationally, the use of sewage water for irrigation of agricultural crops has increased over the last twenty years. However, its prolonged use can cause soil degradation and pollution. The objective of this study was to determine the effect of untreated, treated and mixed (1:1 ratio) sewage water on bulk density (Da), hydrogen potential (pH), electric conductivity (CE), cationic exchange capacity (CIC), organic matter (MO), exchangeable sodium percent (PSI) and concentrations of copper (Cu), lead (Pb), and cadmium (Cd) at three soil depths. The investigation was conducted in soils irrigated with sewage water for ten years. The results indicate significant differences among types of water in Da with values of 1.21, 1.25 and 1.50 g cm-3, for the soils irrigated with untreated, treated and mixed sewage water, respectively. Highly significant differences in pH were found: 8.04, 8.60 for the soils irrigated with untreated and treated sewage water. Soil PSI had percentages of 1.64, 4.64 and 6.44 for untreated, treated, and mixed sewage water, respectively. The highest concentrations of copper, lead and cadmium were 1.48, 2.91 y 0.16 mg kg‑1 in soil irrigated with untreated sewage water without exceeding the maximum permissible limits established in the Official Mexican Standard. The highest values of Da were observed at depth 60-90 cm for untreated and treated sewage water with values of 1.32 and 1.42 g cm-3, respectively. The highest concentrations of Pb and Cu were observed at the depth of 0-30 cm with values of 2.26 and 1.44 mg kg-1, respectively. The use of untreated sewage water negatively modifies soil physical-chemical properties and increases heavy metal content in the topsoil.