Heavy Metals in Agricultural Soils in Nigeria: A Review
This review paper presents the health risks of heavy metals such as: lead (Pb), chromium (Cr), zinc (Zn), cadmium (Cd), copper (Cu), mercury (Hg), nickel (Ni) and arsenic (As) etc contamination in soils. The review reveals the major sources of these metals which are urban and industrial effluents, deterioration of sewage pipe, treatment water works, sewage sludge, fertilizers and pesticides. It also reveals the adopted standard for drinking water (maximum tolerable limit) by FAO, JECFA and WHO which are as follows: 0.05mg/L, 0.05mg/L, 1.5mg/L, 0.001mg/L, 0.02mg/L, 15mg/L, 0.3mg/L, 0.5mg/L, 0.01mg/L, 0.05mg/L and 0.05mg/L for Pb, Cr, Cu, Hg, Ni, Zn, Fe, Mn, Se, As and Cd respectively. The accumulation of heavy metals in agricultural soils is of increasing concern because of food safety issues, potential health risks such as neurological disorder, cancer, kidney damage, fragile bone etc and their detrimental effects on soil ecosystem. However, the regular monitoring of levels of these metals from dump sites, effluents and sewages in soil and drinking water is essential to prevent excessive buildup of these metals thereby increasing toxicity and elevating the public health risk.