Studies on bioaccumulation and mobilization of heavy metals in crops and vegetables grown around industrial environments

Abstract

Crops and vegetables provide essential nutrients to human diet. Plants import chemical elements and nutrients directly from the soil or water by root absorption, resulting in accumulation within different tissues. The most common route for metals to enter into the food chain and human body is the cultivation of crops and vegetables in industrially contaminated soil. Heavy and toxic metals concentrations in contaminated water, soil, crops, and vegetables from two different study areas are investigated in this study. One of the study areas was selected and recognized as highly contaminated area (Savar, Dhaka) and another area was identified as long range contaminated area (Kalihati, Tangail). The samples were collected directly from the study areas following the standard procedures and protocols. Different soil, crops, and vegetables were digested using a mixture of HNO3, H2SO4, HClO4 in a ratio of 5:1:1, and the resulting mixtures were analyzed for heavy and toxic metals using the Flame AAS method. A total of seven metals (Cu, Pb, Fe, Ni, Mn, Cd, and As) have been analyzed in crops, vegetables, arable soil, and irrigation water and the results were compared with the permissible values reported by FAO, WHO, USEPA, EU, and others. All the studied samples collected from Savar area showed heavy and toxic metal concentrations relatively higher than the tolerable limits. However, most of the environmental samples obtained from Kalihati Upazila contained different metal concentrations which were lower than the safety levels of FAO, WHO, and USEPA. Heavy metal concentrations in different parts of crops and vegetables plants were also investigated in the present study to understand the mobilization and transportation trend of these metals from roots to shoots. Pollution Load Index (PLI) was calculated for better understanding of pollution levels in irrigation water, contaminated soil, crops and vegetables. Bioconcentration factor (BCF) of metals was evaluated to visualize the transfer rate of heavy metals from soil to food plant bodies. Health risks due to the consumption of contaminated food items were investigated for both adult and children in terms of non-carcinogenic risk and carcinogenic risk. Almost all the studied crops and vegetables showed higher non-carcinogenic risk for both adult and children. Non-carcinogenic risks associated with samples collected from Savar area were observed to be higher than those obtained from Kalihati Upazila. Considerable carcinogenic risks were realized in all the studied samples for both adult and children. In addition, carcinogenic risks were higher in crops and vegetables samples collected from Savar area than those grown in the long range contaminated site, Kalihati Upazila. The risks assessment data suggested that children are of at a higher risk than adult in terms of both carcinogenic and non-carcinogenic risks. Metal Pollution Index (MPI) was determined in each of the crops and vegetables samples and the order of MPI values was: Green spinach > Water spinach > Spinach > Red spinach > Rice > Lady's finger > Brinjal grown in Savar area whereas the MPI trend in crops and vegetables collected from Kalihati, Tangail area was: Spinach > Water spinach > Rice > Lady's finger > Red spinach > Brinjal > Green spinach. These MPI data indicated that the crops and vegetables grown in the Savar area are highly contaminated than those obtained from the Kalihati Upazila. The present research findings has revealed that long time consumption of metal contaminated crops and vegetables grown in and around the industrial polluted areas could cause a severe health risks to the local people who are directly consume them. Keywords: Waste water irrigation, Heavy metals, Soil pollution, Crops and Vegetables, Transfer factor, Health risk, Metal pollution.