Probabilistic risk assessment (Monte Carlo simulation method) of Pb and Cd in the onion bulb (Allium cepa) and soil of Iran

Recently, the exposure to heavy metals through the consumption of vegetables has become a global concern. In this regard, the current study was aimed to measure the concentrations of lead (Pb) and cadmium (Cd) in the collected onion bulb samples as well as the surrounded soil using a flame atomic absorption spectrometer (FAAS). Additionally, the target hazard quotient (THQ) for males and females in all age groups of consumers were estimated by using Monte Carlo Simulation (MCS) method. Furthermore, the soil threshold values (STVs) were evaluated to investigate the heavy metal contents in the soil based on the established standard limits. In this context, 45 onion bulbs (HashtBandi region, 25 and Ravang region, 20) and 41 soil (HashtBandi region, 21 and Ravang region, 20) samples were collected (March–May of 2016). The average concentrations of Pb in the onions from HashtBandi and Ravang regions were determined as 0.0052 ± 0.0011 and 0.0061 ± 0.0022 mg/kg, and for Cd were 0.0095 ± 0.0024 and 0.0011 ± 0.0035 mg/kg, respectively. The average concentration of Pb in the soil from HashtBandi and Ravang regions were measured as 3.99 ± 3.77 and 2.03 ± 0.69 mg/kg, and for Cd, the corresponding values were determined as 2.21 ± 3.17 and 2.22 ± 0.92 mg/kg, respectively. The average concentration of Pb and Cd in both investigated onion bulb and soil were lower than Iranian national (onion bulb: Pb = 0.1 mg/kg, Cd = 0.05 mg/kg) and FAO/WHO (onion bulb: Pb = 0.3 mg/kg, Cd = 0.1 mg/kg; soil: Pb = 50 mg/kg, Cd = 0.3 mg/kg) standard limits. Moreover, the THQ and total target hazard quotient (TTHQ) for males and females in all age groups were less than 1 value. Therefore, no risk of the exposure to Pb and Cd as result of onion bulb consumption was reported. STVs for Pb and Cd in the HashtBandi region were calculated as 3.99 and 2.21 mg/kg, and Ravang as 2.03 and 2.22 mg/kg, respectively. Due to the higher calculated STVs for Cd while compared with the established standard limit for the soil, the further revisions regarding the heavy metal standard limits in the soil were recommended.