Risk assessment of available and total heavy metals contents in various land use in calcareous soils

Heavy metals (HMs) are regarded as a high priority monitoring contaminant and have been identified as a major environmental concern. The forms of land use may have an impact on the movement and accumulation of HMs. The mobility and accumulation of HMs were examined in topsoils of various land use using different soil test methods. Sixty-three soil samples were taken from various land use including garlic, orchard, pasture, potato, vegetable, wheat, and polluted lands. The availability of Cd, Cu, Mn, Ni, Pb, and Zn were determined using CaCl 2 , HCl, HNO 3 , EDTA, and DTPA extractants. Amongst all extractants and land use, the mean available contents of Cd, Cu, Mn, Ni, Pb, and Zn were 0.81, 4.95, 58.60, 2.41, 14.94, and 7.95 mg kg −1 , respectively. Among the extractants, the mean contents of all HMs in all land use decreased in following order: HNO 3 (34.39 mg kg −1 ) > EDTA (19.41 mg kg −1 ) > HCl (13.52 mg kg −1 ) > DTPA (5.26 mg kg −1 ) > CaCl 2 (1.36 mg kg −1 ). Generally, among the various land use, after polluted land (26.2 mg kg −1 ) the orchard land (17.3 mg kg −1 ) presented the highest contents of HMs, and the wheat (8.35 mg kg −1 ) and pasture (9.94 mg kg −1 ) lands presented the lowest contents. The results from the geo-accumulation index ( I geo ) and the ecological risk index ( RI ) showed that except for polluted land in other land use the HMs categorized as unpolluted ( I geo < 0) and low risk (RI ≤ 150). The results from the availability ratio ( AR ) showed that among the extractants, the mean AR calculated for all HMs and land use decreased in the following order: HNO 3 (28.08%) > EDTA (26.36%) > HCl (21.55%) > DTPA (7.11%) > CaCl 2 (3.19%). It also indicated that the vegetable land (average of all extractants) presented the highest (25.1%) of HMs extractability while the pasture land (average of all extractants) presented the lowest (12.7%). The hazard index ( HI ) showed that for all HMs in various land use the non-carcinogenic risk were not significant. Generally, Pb and Mn are the main contributors to the total health risks, while Zn and Cu were the least risks. When utilizing the EDTA extractant, Mn and Ni were combined into one cluster by using AR of HMs, but Cu and Pb were combined into one cluster when using the both EDTA and DTPA extractants. The noteworthy feature of this clustering is the use of AR of HMs rather than available ones, which considers both available and total HMs in soil. This study highlights the importance of extractants, land use and AR in assessing risk assessment caused by HMs, bioavailability of HMs and exposure health risk. Lastly, we emphasize the significance of employing AR to evaluate soil enrichments with HMs and suggest considering available background level of HMs rather than the total background levels that is currently utilized to assess soil contamination.