Impact of nitrogen and sulfur fertilizers on leaching behavior of heavy metals from aquifer sediments to groundwater

Abstract

Background

The groundwater of the Bathinda district of Punjab is contaminated with heavy metals, nitrate (NO₃), and sulfate (SO₄) exceeding the BIS limits for drinking water in many areas. The article attempts to understand the role of fertilizers, nitrate and sulfate, in the mobilization of heavy metals from the aquifer minerals.

Method

Heavy metal mobilization from aquifer sediments was studied through batch experiments using artificial groundwater (AGW) with varying concentrations of NO₃ and SO₄. For actual field conditions, column experiments were conducted with artificial groundwater containing 50 ppm NO₃ as mobile phase and 1 ml/minute flow rate. The leached metal ions from the sediments were analyzed with ICP-MS.

Significant findings

It was found that compared to the AGW without NO₃ and SO₄, the heavy metal mobilization potential of AGW with NO₃ and SO₄ was significantly enhanced. The presence of nitrate significantly influenced the leaching of Cr, Co, Ni, Zn, and Hg, moderately affected the mobilization of As, and least impacted the mobilization of Fe, Mn, Cu, Cd, Pb, and U. An increase in leaching of Cr, Mn, Ni, Zn, As, and U was observed with the increase in SO₄ concentration from 0 to 400 ppm, however, drastic reduction was observed with SO₄ concentration of 500 ppm indicating high concentration of SO₄ is posing an inhibitory action. The concentration of Cr, Fe, Co, Ni, Cu, Zn, Se, and Pb were significantly positively correlated indicating similar processes driving the mobilization of these metals. To reduce the mobilization of toxic heavy metals from the aquifer sediments, the NO₃ and SO₄ from the wastewater and agricultural run-off should be removed/reduced to the extent possible through optimized fertilizer usage, use of organic fertilizers, and treating the wastewater before discharging in the environment.