Study of Concentrations of Nitrates and Heavy Metals in the Soil and Lettuce and Risk Assessment of its Consumption

This study is conducted to evaluate the concentration of nitrate and heavy metals in soil and edible organs of lettuce in Varamin plain farms for one year during 2017-2018. For this porouse, 30 lettuce fields in Varamin plain are selected and in the lettuce harvest season, soil and crop sampling are performed and the average concentrations of nitrate and heavy metals in the soil and lettuce were compared statistically with the standard limits by one paired t-test. The average concentrations of nitrate, lead and cadmium in lettuce are 2756, 1.46, and 0.11 mg / kg in fresh weight, respectively, which are 1.8, 7.3, and 1.1 times greater than the standard limit, declared by the National Standards Organization of Iran, respectively. The mean concentrations of nitrate and total concentrations of lead, cadmium, and nickel in the soil of lettuce fields are 27, 42, 0.64, and 42.5 mg /kg, respectively, while the concentrations of nitrate and lead have been 35% and 180% higher than the allowable limits, respectively. Risk assessments for heavy metals and non-cancerous diseases are performed, using formulas provided by the US Environmental Protection Agency (USEPA, 2006). In this regard, the risk index for non-cancerous diseases (HQ) is used. The risk factor for non-cancerous diseases for all contaminants is less than one, indicating that there is no risk for consumption. Accordingly, consuming 40 grams of lettuce per day does not pose a problem for an adult consumer. The bioaccumulation index for all the studied metals has been less than one. According to this study, the highest bioaccumulation factor belongs to the heavy metal cadmium, which indicates the tendency of lettuce to absorb and accumulate cadmium compared to other heavy metals. In order to reduce the concentration of nitrate and lead in the soil and prevent contamination of lettuce soils, it is recommended to avoid excessive use of fertilizers containing nitrogen and phosphorus and fertilizer application should be based on soil test. According to the results of this study, there is no serious possibility of exposure to non-cancerous diseases caused by nitrate and heavy metals from eating lettuce, but monitoring the concentration of nitrate and heavy metals in soil and lettuce at different intervals is necessary.