Uptake of hazardous elements by spring onion (Allium fistulosum L.) from soil irrigated with different types of water and possible health risk

Bio-concentration of elements such as Mo, As, Se, Fe, Cu, Zn, Ni and Pb was analyzed in spring onion (Allium fistulosum L.) in three different locations of central Punjab, Pakistan. At location GW, relatively low level of hazardous elements was found in spring onion, suggesting that groundwater is a safe source of water for irrigating food crops. The pH of soil at wastewater irrigation was found less acidic (pH 7.4) than the other sites. The range of concentration in the different samples of spring onion was as follows: 6.15–8.16 mg kg−1 for Mo, 2.77–4.28 mg kg−1 for As, 0.395–0.705 mg kg−1 for Se, 36.73–48.17 mg kg−1 for Fe, 10.58–16.26 mg kg−1 for Cu, 28.87–39.79 mg kg−1 for Zn, 6.66–8.75 mg kg−1 for Ni and 4.33–6.09 mg kg−1 for Pb, respectively. High bio-concentration of Zn (15.37) from soil to spring onion was found at canal water irrigated location. The estimated daily intake of metal for spring onion was less, but the health risk index was higher than 1 for Mo, As, Cu, Pb and Ni, respectively. This was due to higher proportion of spring onion in diet, which consequently increased the health risk index for metals. Therefore, it is recommended to avoid growing vegetables in untreated urban and rural wastewater containing elevated amounts of metals.