Background and Purpose: Accumulation of heavy metals and petroleum hydrocarbons lower than the dangerous range can still threaten human health by entering the food chain. Therefore, this research investigated the effect of inorganic and organic Zinc (Zn) sources and Piriformospora indica (P. indica) fungus on reducing the risk of cadmium (Cd) and lead (Pb) for humans due to lettuce consumption.
Materials and Methods: This research was done as a factorial arrangement in a completely randomized design. Statistical analyses were performed using SAS software, version 9.1. A total of 54 treatments were prepared consisting of organic and inorganic Zn fertilizers at the rates of 0, 20, and 40 kg Zn/ha in a Cd- and Pb-contaminated soil that was simultaneously polluted with crude oil (0%, 4%, and 8% w/w) under cultivation of lettuce inoculated with P. indica. After 4 months, the lettuce plant was harvested, and the Pb and Cd risk assessment was calculated according to the US Environmental Protection Agency formula.
Results: Plant inoculation with P. indica significantly decreased the hazard quotient (HQ) factor by 11.4% (0.4 units) for consumers of the lettuce cultivated in the soil polluted with 8% w/w crude oil. Furthermore, using 40 kg/ha pure Zn from a Zn-EDTA source in the crude oil-polluted soil (4% w/w) significantly decreased the HQ factor by 14.3%. 
Conclusion: Plant inoculation with P. indica and inorganic and organic Zn sources significantly decreased the HQ factor. Although this decrease depends on the type of plant, the kind of pollution and the physicochemical characteristics of the soil should be investigated in separate studies.