Assessment of contamination status and potential health risk of heavy metals in soil and vegetables of Savar Tannery adjacent area

Abstract

Monitoring of heavy metal concentration in soil of newly shifted tannery industry in Savar tannery village and the accumulation of heavy metals in vegetables grown on tannery area and its nearby area is crucial for public health. Because, the toxic heavy metals present in soil and vegetables may pose potential non-carcinogenic and carcinogenic risks to human health. For quantifying and assessing the risks, six heavy metals (e.g., Cr, Pb, Cu, Zn, Ni, and Cd) concentration were determined by an atomic absorption spectrophotometer of 45 soil and 27 vegetable samples collected from four different zones of the tannery and its nearby area. The analyzed results revealed that Cr was in highest concentration in soil and found to be 3222 mg/kg (mean value of four zone) which is 32 fold greater than the maximum permissible limit set by WHO/FAO and 10 times more than EU/UK safe limit. Amount of Pb, Cu, and Ni in the studied soil was far below the all standard limit. The heavy metal Zn was in slightly to moderately higher than the EU and Chinese standard as well as control and background concentration and met India standards and the WHO/FAO concentration. The mean concentration of Cd was 1.97 mg/kg and the greatest concentration was found in zone 3 (5.11mg/kg) which is far beyond the acceptable value set by China, EU and WHO limit. The statistical analysis such as contamination factor, enrichment factor, degree of contamination, pollution load index, geoaccumulation index, marked the area as moderately to very highly contaminated and enriched with heavy metals, thus leading to significant pollution of soil. The ecological risk factor, risk index, non-carcinogenic risk and cancer risk for soil contaminated with heavy metals posed moderate to very high ecological risks and some of the zone with value of hazard index greater unity showed high potential non cancer risks. In addition, analyzed total target cancer risks exceeded the acceptable range (1×10-6-1×10-4) by all of the zones for soil and posed more risks to child population than adult. The main exposure pathway of heavy metal in soil to human was oral ingestion (97.83-99.90%). Concentration of heavy metals in consumable vegetables collected in this study was alarming, especially Cr, Pb, Zn and Cd and was found to cross the boundary limit set by WHO/FAO, Chinese national standards and EU/UK limits. The calculated mean hazard index for vegetable samples in four zones was 8.71, showing elevated level of potential non-carcinogenic risks to the human, when the target cancer risks by Cr and Cd are far beyond the acceptable value 1×10-4, indicating serious cancer causing probability of human by consumption of these vegetables. From the calculated results, it can be concluded that soils and vegetables particularly in the tannery area are enriched with high amount of heavy metals which are well above the maximum permissible limit suggested by international organizations. Therefore, there is a critical need to remedy the soil of contaminated zones by applying proper techniques. After a vigorous feasibility study of different developed and practiced technology of soil remediation, phytoremediation has been selected for its cost, simplicity, environmental aspects and public acceptance to remedy the heavy metals from the contaminated soil of Hemayetpur, Savar tannery area and its adjacent area. Policy have been suggested to prevent the soil pollution caused by tannery effluent which is suitable, logical and adjustable to this modern era in this study. Finally, individual awareness should be raised to stop cultivating and eating of vegetable in the study area.