Human health risk assessment of potentially toxic elements in soils and rice grains (Oryza sativa) using a combination of probabilistic indices and carcinogenic risk modelling

Agricultural soils and crops are increasingly vulnerable to contamination by potentially toxic elements (PTEs), exacerbated by anthropogenic activities. This study evaluated the human health risks associated with PTEs (Cd, Cr, Hg, Cu, As, Zn, and Ni) contamination in agricultural soil and rice grains from different cultivated paddy soils. In this research, a modified Susceptible-Infected-Removed-Susceptible (SIRS) model, based on mathematical derivatives, was employed alongside the carcinogenic and non-carcinogenic risk assessment method to evaluate associated health risk through various indices. A total of 100 samples including soils and rice grains (Oryza sativa) were analysed using inductively coupled plasma–mass spectrometry (ICP-MS) (Perkin Elmer Nixon 300Q). The mean concentration of Cr (43.56 mg/kg) in the soil of Vele, as well as Cr (43.48 mg/kg) and Ni (36.24 mg/kg) in the soils of Zoulla, exceeded the geochemical background values. The concentrations of Cd, Cr, Cu, Hg, Ni, and Zn in rice grains were within the limits set by the WHO/FAO, except for Ni in Djogoidi, which exceeded the WHO/FAO recommended value of 0.1 mg/kg. Additionally, Ni content in rice grains from Droumka was twice as high as the recommended WHO/FAO value. Similarly, the bioaccumulation factor (BAF) of Cd, (3.53 mg/kg), Cu (3.25 mg/kg) and Zn (2. 59 mg/kg) for Djogoidi and Cd (4.44 mg/kg), Cu (3.22 mg/kg), Zn (2.44 mg/kg) for droumka were one to two-fold higher than one denoting higher potential to bioaccumulates toxic metals in the rice grains. Also, the carcinogenic risk factor assessment (CRFS) indicates a higher Hi value (4.49E+02) for children exceeding the critical value (threshold = 1) for carcinogenicity standards, indicating a very potential health risk. The results of the carcinogenic dynamic risk model also confirm a higher susceptibility to mortality over time due to the ingestion of contaminated crops. This is particularly evident for the following PTEs: As, Cr, Cu, Ni, and Zn, which show an increasing trend in $I_h\left(t\right)$, as the contamination factor increase, with α = 0.25. Therefore, targeted mitigation measures are necessary to be adopted for agricultural food protection from PTEs pollution in the area.