Studies on Ground Water Toxicants in Food Chain

Abstract

Many of the metals are considered as essential nutrients for maintaining sound human health throughout life. But intake of heavy metal contaminated vegetables, rice, meat, fish, drinking water and dust may pose a risk to human health. Arsenic in groundwater and its fate and transport in the environment have become matters of great concern in Bangladesh. Lead and cadmium pollutions are also considered to be global issues. Considering these, two separate studies were carried out to find out the potential ways for remedy of arsenic, cadmium and lead toxicity in food grains as well as to assess human health risk due to arsenic, cadmium and lead exposures from dietary food products collected from two villages of Rajshahi City Corporation in Bangladesh. In this investigation, six natural organic fertilizers that the Bangladeshi farmers use frequently were used to assess their potentials towards reduction of arsenic, cadmium and lead toxicity in corns. These were rotten cow-dung, rotten Dhunca, compost, drain mud, earthworm mud and water hyacinth. The selected corn plants grown in open field were paddy, sesame, maize and foxtail, and were irrigated with the contaminated water having concentrations of 4.8 mg L-1 of As, Pb and Cd simultaneously. The concentrations of arsenic, cadmium and lead in the environmental samples were determined by Graphite Furnace– Atomic Absorption Spectroscopy (GF-AAS) technique. To assess human health risk due to consumption of dietary products, drinking water and dust, US Environmental Protection Agency’s (USEPA) guidelines were applied. The overall efficiency of the studied organic fertilizers towards simultaneous reduction of arsenic, cadmium and lead toxicity in food grains was found as follows: CM (Compost) >> EW( Earthworm mud ) ≈ CD (Cow-dung) ≈ DM (Drain mud) >> RD (Rotten Dhuncha) ≈ WH (Water hyacinth). Since compost, earthworm mud, cow-dung, drain mud and rotten Dhuncha were able to reduce the concentration of arsenic, cadmium and lead in the food grains simultaneously with respect to control, they could be recommended for remedy of arsenic, cadmium and lead toxicity in corns. The observed concentration range of arsenic, cadmium and lead in the studied food grains were: (0.329 - 2.105), (0.002 - 0.121) and (0.002 -1.495) mg kg-1 on fresh weight basis. Based upon the accumulated concentrations of the concerned metals, the studied crops could be arranged in the follow the order: Paddy >Sesame > Maize > Foxtail. In the human health risk assessment investigation, arsenic, cadmium and lead concentration ranges in all the studied diet were found as dust (1.154-3.441 μg g-1), rice ( 0.016-0.154 μg g-1) and Fish ( 0.017-0.507μg g-1) respectively (ww). Generally, the concentrations of the concerned metals in the studied samples follow the order: Dust > Rice > Fish > Vegetables > Drinking water. It was found that 99.29% of meal exposure was due to ingestion, while only 0.71% due to inhalation. Sample wise contribution towards average total Hazard Quotient (HQ) values was found as follows: For Arsenic : Dust > Rice > Fish > Vegetables > Drinking water For Cadmium : Rice > Dust = Drinking water > Fish > Vegetables For Lead : Dust > Rice > Fish > Vegetables > Drinking water As, Cd and Pb contribute to 60.79%, 20.89%, 18.32% of exposures respectively for children. But for average person, As, Cd and Pb contributions are 75.26 %, 24.48 % and 0.26 %. respectively. For senior person, the contributions are 70.15%, 17.50% and 12.38% respectively. In case of children population sub-group average HI value was 2.215. It reflects that all children are at risk due to consumption of the studied diet. The HI values for Average Person and Senior population sub-group are 0.909 and 0.871 respectively. Hence both population sub-groups are in safe limit due to consumption of the same diet. Comparison among HI values suggests that the population sub-groups should be arranged in following order: Children > Average Person > Senior.