The Effects of Heavy Metals on Enzyme Activity and Microbial Biomass of the Soil Around the Waste Disposal Site (Case Study of Saravan - Iran)

Abstract

ABSTRACT Municipal solid waste is considered an environmental threat in Iran. The study was performed on soil near the Saravan dumpsite and measured the concentrations of 8 metals (Zn, Cu, As, Hg, Pb, Cr, Cd, and Ni) in soil, by inductively coupled plasma mass spectrometry. The average content of As, Cu, Cr, Pb, Zn, Hg, Ni, and Cd in soil were 10.48, 20.22, 19.07, 24.95, 28.83, 0.13, 19.91, and 0.1 mg/kg, respectively. The mobility factors based on water-soluble and exchangeable fractions were As (8.85%), Zn (4.19%), Pb (1.85%), Cu (1.60%), and Cr (0.02%), and not detectable for Hg, Ni, and Cd. Evaluation of metals contamination by pollution index, integrated pollution index, and Nemerowʼs pollution index for each metal showed that PI for all metals except Hg was in the range of low to moderate, and for Hg, 50% in high pollution grade; the average of the IPI (1.21), indicated a moderate pollution condition; the mean value of the PINemerow (1.20), which was in slight pollution grade. The correlations between total concentrations of metals, and bioavailable fractions with microbial biomass carbon, basal respiration, microbial quotient, metabolic quotient, urease, and alkaline phosphatase activities were moderate (r = 0.4-0.6). The activity of urease was from 37.79 to 1414.31 µg N gˉ1 dm.2 hˉ1 and alkaline phosphatase from 34.66 to 698.78 µg nitrophenyl gˉ1 dm. hˉ1. Due to the rainy climate and the continuous leaching of the surface soil, we suggested performing waste separation and the treatment of leachate produced before flowing downstream.