Seasonal Variation of Heavy Metal Concentrations in Farm Soils of Sreepur Industrial Area of Gazipur, Bangladesh: Pollution Level Assessment

A study was conducted to measure the seasonal variation of different heavy metal contents in farm soils of Sreepur Upazila of Gazipur district and to assess their pollution level. Industrial affected and non-affected soil samples were collected from 5 locations in three seasons viz. pre-monsoon (April), monsoon (August), and dry season (January), thus a total of 30 soil samples were analyzed for this study. Concentrations of different heavy metals (Cd, Pb, Cr, Ni, Cu, and Zn) in soil samples were determined by an Atomic Absorption Spectrophotometer (AAS). The mean total concentration of Cd, Pb, Cr, Ni, Cu and Zn in industrial affected soils were trace, 12.05, 101.10, 51.32, 20.79 and 55.40 mg kg^-1, respectively in the pre-monsoon, trace, 28.54, 40.96, 22.70, 2.46 and 7.72 mg kg^-1, respectively in the monsoon and 0.27, 10.49, 39.45, 20.69, 1.85 and 4.11 mg kg^-1, respectively in the dry season. All heavy metal concentrations in industrial affected soil samples were higher than the corresponding non-affected sites. The study results revealed that Cd contents in the dry season and Pb contents in the monsoon season for industrial affected soils were higher compared to the average earth’s crust abundance value. The geoaccumulation index (I_geo) values for Pb of industrial affected soils ranged from 0.30-0.85 in the monsoon that means I_geo class 1, indicating unpolluted/moderately polluted soil quality. Furthermore, the calculated I_geo value for one industrial affected location revealed moderate soil pollution by Cr in the pre-monsoon season and unpolluted/moderately polluted soil quality by Ni and Cd in the pre-monsoon and the dry season, respectively. The measured pollution load index (PLI) values were also higher in all industrially polluted sites than corresponding non-polluted sites in three seasons, which indicates pollution load due to anthropogenic sources.