Introduction

Soil pollution by potentially toxic elements (PTEs) has spread worldwide, provoking the ecosystem and health risks to humans, owing to their stable, persistent, and irreversible properties (1). Crops grown in contaminated soils may accumulate PTE in their edible parts, resulting in an excessive human intake, which eventually poses adverse impacts to humans via the food chain (2–4). PTE can enter the human body in three ways including ingestion, inhalation, and dermal contact, while food consumption (>90%) has been recognized as the major pathway for human exposure (5). Therefore, from the perspective of both environmental security and human health, it is critical to pay more public attention to PTE contamination.

Being the most crucial toxic elements to humans, prolonged exposure to arsenic (As), chromium (Cr), cadmium (Cd), and lead (Pb) can make some threats even at low concentrations, such as kidney dysfunction, musculoskeletal systems, cholesterol balance, and central nervous system (6, 7). Nickel (Ni) is a carcinogenic element and its extraordinary amount can pose lung cancer, diabetes, and uremia (8, 9). Of note, although zinc (Zn) is beneficial to healthy human growth, it may defect in stomach cramps and reproduction (10, 11). According to the World Health Organization [World Health Organization (WHO) 2002 (12)], although fluorine (F) can help to strengthen bones and teeth (1–4 mg/kg normally), a daily intake (>6 mg/day) may be correlated with skeletal fluorosis, and a daily intake (>14 mg/day) may further cause serious risk of fracture (13). In recent decades, researchers have concentrated on the human health risk posed by PTE exposure in the food chain.

Wheat and wheat-derived foods play indispensable roles in human growth and have a critical position in food production, circulation, and ingestion (14, 15). China is one of the greatest wheat producers worldwide, accounting for 18% of the global wheat grain products (16). Durum wheat is consumed in a number of countries typically as pasta, noodles, and breakfast cereals; therefore, the demand for its production is increasing gradually (17). In terms of nutritional value, bran layers and embryo fractions of wheat produced by milling are abundant in minerals, fibers, and folate (18, 19). However, wheat can absorb some hazardous elements (e.g., Pb, Cd, and Ni), and the intake of excessive PTE through wheat and wheat-derived foods may pose health risks to humans (20). Research conducted in Baoji city showed a non-carcinogenic risk (CR) in wheat grains for children and adults due to Cr, Ni, Cu, Zn, Cd, and Pb exposure (21). Ali et al. (22) showed that the mean Pb concentration was above the permissible limit of the Food and Agriculture Organization (FAO), and its hazard quotient (HQ) was the highest (2.118) among different PTEs (e.g., Cr, Cd, As, and Zn). Nevertheless, few studies focused on wheat polluted by the co-exposure of F and other toxic elements so far.

To the best of our knowledge, two kinds of techniques including deterministic and probabilistic (Monte Carlo simulation) are well applied to estimate the human health risk due to several pollutants (23). The deterministic risk approach regarding PTE has been carried out in previous studies (24–26). Hu et al. (27) showed that HQ values for elements were significantly lower than 1 of the limit value using the deterministic without considering other variables, such as body weight (BW), ingestion rate (IR), and exposure durations (EDs), which eventually may underestimate the risk outcomes. Studies by Ihedioha et al. (24) and Guo et al. (28) were consistent with the study by Hu et al. Herein, the deterministic risk technique may exist some uncertainties during exposure assessment, leading to less persuasive risk results. In contrast, the probabilistic approach has attempted to emphasize the reliabilities and uncertainties of risk results based on the probability distributions of the PTE concentrations and related parameters (29). Actually, the probabilistic assessment in several studies has been applied. However, Jiang et al. (30) only considered for children to reduce the uncertainty of deterministic risk using the Monte Carlo simulation. Besides, Kukusamude et al. (5) performed the approach for exposure to elements in rice via consumption. Unfortunately, related exposure parameters (BW, IR, and ED) were not identified during probabilistic modeling (31). Based on the discussions earlier, the probabilistic assessment was applied in this study, considering essential parameters (C*, BW, ED, and IR), and the populations were divided into three groups based on age (children, adult females, and adult males), which will make the results more objective.

Southwestern China is the largest karst region worldwide and has been confirmed that the natural background of PTE was initially controlled by the lithology of parent rock and soil type-dependent (32). Various studies indicated that the maximum values of mean concentrations for PTE were distributed in karst regions such as Guizhou, Guangxi, and Yunnan provinces, which were attributed to unique geochemistry in the process of the soil formation (32, 33). As one of the most essential karst regions, Southwestern Guizhou has been reported that the background value for Cd (0.659 mg/kg) in soils was far higher than the standard value (0.097 mg/kg) in China, and the mean concentration for F was highly up to 1,200 mg/kg (34). Furthermore, the study region has been considered a typical fragile area for the well-developed industry (35). However, as one of the main cereals, any study is still not aware of the wheat pollution by PTE in this critical area.

In light of these facts, 149 wheat grains were collected and their PTE (Cr, Ni, As, Pb, Cd, and F) concentrations were measured by the inductively coupled plasma mass spectrometer (ICP-MS) and fluoride-ion electrode methods to (1) determine the concentration of PTE; (2) identify the pollution sources of PTE; and (3) assess the probabilistic risks (non-carcinogenic and carcinogenic) for children, adult females, and adult males. It will provide a new scope for pollution control and a scientific basis for local governance and will ensure the health of the populace.

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*Original full-text article online at: https://www.frontiersin.org/articles/10.3389/fnut.2022.934919/full