Do high soil geochemical backgrounds of selenium and associated heavy metals affect human hepatic and renal health? Evidence from Enshi County, China

High-selenium exposure is associated with modulation of serum lipid metabolism

At present, there is no consensus on the relationship between selenium (Se) exposure and human serum lipid metabolism. The etiological role of high-Se exposure in lipid markers, dyslipidemia, and nonalcoholic fatty liver (NAFLD) remains unclear. We used serum untargeted metabolomics analysis to evaluate whether high-Se exposure is cross-sectionally associated with lipid metabolism in adults from high-Se exposure area (n = 112) and control area (n = 101) in Hubei Province, China. An untargeted liquid chromatography/mass spectrometry (LC/MS)-based metabolomic analysis identified 144 differential pathways and yielded 204 differentially abundant metabolites, including 32 lipid metabolites associated with lipids profiles. To further explore the correlation between Se exposure and serum lipid metabolism, we measured serum levels of lipid profiles among all the people, including serum cholesterol (CHOL), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and apolipoprotein B (APOB). The average serum Se level of the high-Se exposure group was 537.18 μg/L, significantly higher than 72.98 μg/L in the control group (p < 0.0001). The measurement levels of serum TG, LDL-C, HDL-C, and APOB in the high-Se exposure group were 1.03 (0.76, 1.34) mmol/L, 2.25 ± 0.48 mmol/L, 1.12 ± 0.24 mmol/L, and 0.77 ± 0.15 g/L, respectively, while the control group were 1.13 (0.84, 1.80) mmol/L, 2.56 ± 0.61 mmol/L, 1.02 ± 0.22 mmol/L, and 0.83 ± 0.16 g/L, respectively (all p values <0.05). Correlation analysis showed a significant negative correlation between serum Se and CHOL (r = -0.201, p < 0.01), serum Se is also associated with metabolomics markers, the negative correlation includes glyceric acid and ect., the positive correlation includes phosphorylcholine and ect. Our study suggests that high-Se exposure is negatively associated with serum lipid profiles and decreases the risk of high-TC and HDL-C dyslipidemia.

Effects and mechanisms of different exogenous organic matters on selenium and cadmium uptake by rice in natural selenium-cadmium-rich soil

Many natural selenium (Se)-rich rice plants are being polluted by cadmium (Cd). In this study, for reducing Cd concentrations in rice grains while maintaining Se concentrations, the effects of different exogenous organic matters (OMs), such as humic acid (HA), cow manure (CM), and vermicompost (VC), on Se and Cd uptake in rice growing in natural Se-Cd-rich paddy soils were investigated by pot experiments. The Se and Cd concentrations in the soil solution, their species in the soil, and their concentrations and translocations in rice tissues were determined. Results showed that different exogenous OMs exhibited distinct percentage changes in Se and Cd levels in rice grains with amplitudes of -19.42 % and -56.90 % (significant, p < 0.05) in the HA treatments, +10.79 % and -1.72 % in the CM treatments, and +15.83 % and -15.52 % in the VC treatments, respectively. Correlation analysis showed that the concentrations of Se and Cd in rice grains might be primarily influenced by their concentrations in the soil solution, rather than the Se/Cd molar ratios in the soil solution or their translocations in rice tissues. HA decreased Se and Cd bioavailability in soil by increasing HA-bound Se and residual Cd, respectively. Meanwhile, HA increased soil solution pH, which was negative for Cd bioavailability but positive for Se bioavailability. This additive effect made HA lowered Cd concentration more than Se concentration in both soil solution and grain. CM and VC did not have this additive effect and thus have limited effects on grain Se and Cd concentrations. In addition, according to grain Se and Cd concentrations, to prioritize reducing Cd in rice, use HA; to prioritize increasing Se in rice, use VC. This study enhances the understanding of Se and Cd uptake mechanisms in rice with the applications of various OMs and offers potential remediation methods for Se-Cd-rich paddy soils.

Rhizosphere enrichment and crop utilization of selenium and metals in typical permian soils of Enshi

Enshi, China, is renowned as "Selenium(Se) Capital" where widely distributed soils derived from Permian parent rocks are notably rich in Se, as well as metals, particularly cadmium(Cd). However, the soil enrichment and crop uptake of Se and metals in these high-Se and high-Cd areas are not well understood. To propose the optimal crop planting plan to ensure the safety of agricultural products, we investigated the soils and corresponding typical crops (rice, tea, and maize). The results showed significant soil enrichment of elements, with average contents (mg/kg) as follows: Cr (185), Zn (126), Cu (58.8), Pb (31.1), As (15.7), Se (6.85), Cd (5.41), and Hg (0.211). All soil Se contents were above 0.4 mg/kg, indicating Se-rich soils. Se primarily existed in an organic-bound form, accounting for an average proportion of 61.3%, while Cd was mainly exchangeable, with an average of 62.5%. Cd exhibited higher activity according to the Relative Index of Activity (RIA). Nemerow single-factor index analysis confirmed significant soil contamination, with Cd showing the highest level, followed by Cr and Cu, while Pb had the lowest level. Tea exhibited a high Se rich ratio (82.0%) without exceeding the Cd standard. In contrast, corn and rice had relatively lower Se-rich ratios (42.0% and 51.5% respectively) and high rates of Cd exceeding the standard, at 49.0% and 61.0% respectively. Canonical analysis revealed that rice was more influenced by soil factors related to Se and Cd compared to maize and tea crops. Therefore, tea cultivation in the Enshi Permian soil area is recommended for safe crop production. This study provides insights into the enrichment, fractionation, and bioavailability of soil Se, Cd, and other metals in the high-Se and high-Cd areas of permian stratas in Enshi, offering a scientific basis for selecting local food crops and producing safe Se-rich agricultural products in the region.

Effects of Selenium and Cadmium on Human Liver and Kidney Functions in Exposed Black Shale Areas

Animal experiments suggest that selenium (Se) may alleviate cadmium (Cd) toxicity in animal liver and kidneys, but its effect on human liver and kidneys remains uncertain. In China, areas with black shale have shown elevated levels of Se and Cd. According to the USEPA (U.S. Environmental Protection Agency) evaluation method, the soil and rice in these areas pose significant risks. In black shale regions such as Enshi and Zhuxi County, residents who long-term consume local rice may surpass safe Se and Cd intake levels. Significantly high median blood Se (B-Se) and urine selenium (U-Se) levels were detected in these areas, measuring 416.977 μg/L and 352.690 μg/L and 104.527 μg/L and 51.820 μg/L, respectively. Additionally, the median blood Cd (B-Cd) and urine Cd (U-Cd) levels were markedly elevated at 4.821 μg/L and 3.848 μg/L and at 7.750 μg/L and 7.050 μg/L, respectively, indicating substantial Cd exposure. Nevertheless, sensitive liver and kidney biomarkers in these groups fall within healthy reference ranges, suggesting a potential antagonistic effect of Se on Cd in the human body. Therefore, the USEPA method may not accurately assess Cd risk in exposed black shale areas. However, within the healthy ranges, residents in the Enshi study area had significantly greater median levels of serum creatinine and cystatin C, measuring 67.3 μmol/L and 0.92 mg/L, respectively, than those in Zhuxi did (53.6 μmol/L and 0.86 mg/L). In cases of excessive Se and Cd exposure, high Se and Cd levels impact the filtration function of the human kidney to some extent.