Heavy Metal Concentrations and an Effect of Phosphate Fertilizer Application in Greenhouse Soil Samples

Abstract

Recently, it has been pointed out that fertilizer application beyond optimum level should cause heavy metal accumulation in agricultural soil. In this study, we analyzed concentrations of some heavy metals: chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), arsenic (As), cadmium (Cd) and lead (Pb), in greenhouse soils sampled from farmers’ field and neighboring non-cultivated field in southern Kyushu in Japan. A possibility of heavy metal accumulation in the soils was investigated by comparing both soils. The heavy metal concentrations in an acid-labile fraction of the greenhouse soils ranged 18.5-190 mg/kg (Cr), 304-952 mg/kg (Mn), 10.1-36.8 mg/kg (Fe), 2.32-13.6 mg/kg (Co), 7.80-24.7 mg/kg (Ni), 19.8-71.4 mg/kg (Cu), 73.1-250 mg/kg (Zn), 4.40-22.7 mg/kg (Ga), 18.1-74.5 mg/kg (As), 0.0824-0.438 mg/kg (Cd) and 6.79-43.1 mg/kg (Pb), respectively. The concentrations of Cr, Mn, Ni, Cu, Zn and Cd in the greenhouse soils were higher than those in the neighboring non-cultivated soils, which indicates that these six elements have accumulated in the greenhouse soils. In particular, concentrations in the acid-labile Cu, Zn and Cd showed a significant and positive correlation with total concentration of phosphorus in the soils. These correlations suggest that Cr, Cu, Zn and Cd should be derived from phosphate fertilizer which is the major source of phosphorus nutrient for greenhouse culture. The concentration of water-soluble Cr, Mn, Ni, Cu, Zn and Cd also elevated in the most of greenhouse soils, suggesting an increased risk of the element uptake by crops.