Aqua regia and ethylenediaminetetracetic acid (EDTA) trace metal levels in agricultural soil

Soil samples were collected from irrigation farmlands along the bank of Mada River and analysed for aqua regia and ethylenediaminetetracetic acid (EDTA) extractable trace metal (Cd, Cr, Cu, Pb, Zn Ni, Fe and Mn) concentrations. Water samples at source were also collected for analysis. Metal levels were quantified using atomic absorption spectrometry (AAS). Aqua regia and EDTA extractable Fe and Cd concentrations were the highest and lowest, respectively. The highest and lowest aqua regia and EDTA trace metal concentrations were recorded at sites 1 and 3, respectively. Aqua regia trace metal levels were generally higher than that of EDTA, but below the critical values for irrigation soil. Soils were extremely enriched with Cd (153 – 289), and deficient in Fe (0.5 – 1.0) contents. Fe Kd was generally the highest (21.45 – 44.35 kgl-1) and Zn (0.03 – 0.08 kgl-1) the lowest. Higher total metal contents result in a lower proportion of metal being sorbed, because potential absorption sites are filled in decreasing order of affinity. Strong and positive correlations existed for Cr/Zn (0.9879) and Cu/Ni (0.8077) at Site 1, Cu/Ni (0.9229) and Pb/Pb 0.9581) at Site 2, and Ni with Cr (0.9440) and Cu (0.8153) at Site 3. Significant correlations for soil-water indicated contributions of irrigation water to total metal contents in soil.