Hazard assessment of heavy metal contamination by the paper industry, north-eastern India

Abstract

The spatial distribution and hazard assessment of heavy metals in the paper mill contaminated area of Jagiroad, Assam, India were investigated using statistics, geostatistics and geographic information system techniques. The amounts of Cr, Cd, Ni and Pb were determined from 188 samples collected within the contaminated area. Log-transformation was applied in order to achieve normality in the data-set. The ordinary kriging estimates of Cr, Cd, Ni and Pb maps showed that high concentrations of heavy metals were located in the low-lying areas like bils (lakes). Indicator kriged probability maps of soil Cr, Cd, Ni and Pb were prepared based on the concentrations to exceed the respective Food and Agriculture Organization maximum permissible limit (MPL) value of 100, 3, 30 and 50 mg/kg, respectively. It was seen that more than 80% of the studied area has a higher than 50% probability to exceed the MPL value of Ni. Smaller areas in the north and west side of the study area displayed a higher concentration than the MPL value of Pb. For Cr, only a small portion at the centre of the study area had a higher concentration than the MPL value. In an attempt to identify the source of heavy metals through multivariate analysis, it was concluded that Cr, Ni and Pb mainly originated from paper mill effluent and soil Cd was associated with natural concentration.