In-situ stabilization of heavy metals in agriculture soils irrigated with untreated wastewater

• Effects of amendments on heavy metal stability in wastewater irrigated soils
• Farm yard manure (FYM) was effective in stabilizing Cr, Fe, Mn, Ni, and Pb in soil.
• Di-ammonium phosphate (DAP) was more effective in immobilizing Cd, Cu, and Zn in soil.
• FYM at 10 t ha− 1 and DAP at 120 kg P ha− 1 are recommended for in-situ stabilization.

A field experiment was conducted to assess the effectiveness of various organic and inorganic amendments on the in-situ stabilization of common heavy metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) added to soil through wastewater irrigation. Analysis of wastewater samples indicated higher concentrations of Cr, Cu, Fe, and Pb as compared to the safe limits set by the NEQS for effluents and wastewater, indicating a potential buildup of the metals in soil, whereas the concentrations of Cd, Ni, Mn and Zn were within the safe limits for use as irrigation water. The soil of the experimental plots (size: 1 × 2 m, design: RCBD) was loam with an alkaline pH of 8.1 and an EC of 0.32 dS m− 1 (1:5 soil water suspension). Organic matter content of the soil was 1.08% while lime content was 9.04%. The analysis of soils post-experiment indicated a varied effect of different amendment on the stability of different metals. The concentration of Ni and Pb buildup in wastewater irrigated plots was higher in comparison to control plot receiving tap water and may cause soil toxicity if untreated wastewater is used for long term. Farm yard manure (FYM) was effective in stabilizing Cr, Fe, Mn, Ni, and Pb in soil. Di-ammonium phosphate (DAP) was more effective in immobilizing Cd, Cu, and Zn in soil. The use of FYM at 10 t ha− 1 and DAP at 120 kg P ha− 1 reduced the metal mobility in soil probably by forming insoluble complexes with metals and are thus recommended as soil amendments where untreated wastewater is used in urban agriculture so as to limit the entry of heavy metals into the food chain.