Determination of ED50 in a Calcareous Soil Contaminated with Different Concentrations of Ni

Abstract

Background and Objectives: Soil microbial properties such as biomass, microbial respiration and nitrogen mineralization can be used as indicators to show the stress caused by heavy metal pollution on soil quality. The aim of this study was the measurement soil microbial activity to evaluate the effect of soil Ni contamination on soil quality and determination of ecological dose 50 (ED50). Method: This study was conducted as a factorial experiment in year 2016 based on a randomized completely design with three replications. The experiment factors including Ni concentration in six levels (0, 50, 100, 150, 300 and 600 mg Ni kg-1) and two incubation times (15 and 60 days). Soils sample was spiked uniformly with different concentrations of NiCl2. Microbial respiration, microbial biomass carbon, heterotrophic population and metabolic quotient were measured after incubation times of 15 and 60 days, then according to the results, ED50 was determined by using the dose-response curve. Findings: Soil Nickel contamination on the indicator was significantly effective at P<0.01 level. Heterotrophic population, respiration and microbial carbon biomass decreased significantly (P<0.01) compared to control by increasing the Ni concentration and incubation times, whereas the increase of Ni concentration and incubation times were not significantly affected on metabolic quotient. The minimum amount of microbial respiration, microbial biomass carbon, and the heterotrophic population was observed at the end of incubation times and 600 mg Ni kg-1 with 77.07, 75.72 and 99.99% decrement compared to the control, respectively. ED50 value (mg/kg soil) of microbial respiration, microbial biomass carbon, and heterotroph population increased from 77.55, 78.63, 81.34 to 97.84, 111.04 and 84.67 respectively, with increased incubation time. Discussion and Conclusion: The soil contaminated with Nickel acutely decreased the biological activity of soil and the ecological dose increased with increasing the incubation time, suggesting that toxicity of Ni to soil microbial activity was decreased with increased incubation time. Ni concentration of 100 mgNikg-1 soil can be considered as the critical range of Ni for soil quality at which negative effect was observed.