Bioaccessibility and Human Exposure Assessment of Cadmium and Arsenic in Pakchoi Genotypes Grown in Co-Contaminated Soils

Effects of four amendments on cadmium and arsenic immobilization and their exposure risks from pakchoi consumption

Exposure to heavy metal(loid)s (HM) through contaminated food chains poses significant health risks to humans. While soil amendments are known to reduce HM bioavailability, their effects on bioaccessibility and health risks in soil-pakchoi-human systems remain unclear. To address this knowledge gap, we conducted a greenhouse pot experiment coupling soil immobilization with bioaccessibility-based health risk assessment for Cd and As exposure from pakchoi consumption. Four amendments (attapulgite, shell powder, nanoscale zero-valent iron, and biochar) were applied to soil, resulting in changes to soil characteristics (pH and organic matter), plant dry weight, and exchangeable fractions of As and Cd. Among the tested amendments, biochar exhibited the highest effectiveness in reducing the risk of Cd and As exposure from pakchoi consumption. The bioaccessibility-based health risk assessment revealed that the application of 5% biochar resulted in the lowest hazard index, significantly decreasing it from 1.36 to 0.33 in contaminated soil. Furthermore, the structural equation model demonstrated that pH played a critical role in influencing remediation efficiency, impacting the exposure of the human body to Cd and As. In conclusion, our study offers a new perspective on mitigating exposure risks of soil HM and promoting safe crop production. The results underscore the importance of considering bioaccessibility in health risk assessment and highlight the potential of biochar as a promising amendment for reducing Cd and As exposure from pakchoi consumption.

Effects of foliar applications of Brassinolide and Selenium on the accumulation of Arsenic and Cadmium in rice grains and an assessment of their health risk

Arsenic and cadmium pose a potential health risk to human beings via rice grain consumption. In the current study, a pot experiment was conducted to evaluate the effect of Br (5 mM and 20 mM) and Se (1 mM) at rice tillering and filling stages on Cd and As accumulation in rice grain and their health risk indices. The results showed that Br or Se applications at different stages of rice improved the photosynthesis, reduce MDA content in flag leaves by 17.41%-38.65%, increased rice biomass and grain yield by 10.50%-29.94% and 10.50%-36.56%, and enhanced grain N and P uptake by 3.25%-34.90%, and 22.98%-72.05%, respectively. Applications of Br and Se effectively decreased Cd and As concentration in rice grain by 31.74%-86.97% and 16.42%-81.13% respectively. Compared to the individual treatment, combined 20 mM Br and 1 mM Se at the filling stage showed the lowest accumulation of As (0.149 mg·kg^-1) and Cd (0.105 mg·kg^-1) in grain, and its health risk index was below the acceptable limits (HRI < 1). This implies that application of Br and Se at the filling stage is a promising strategy for the safe production of rice in As and Cd co-contaminated regions.

Screening of Leafy Vegetable Varieties with Low Lead and Cadmium Accumulation Based on Foliar Uptake

Leafy vegetables cultivated in kitchen gardens and suburban areas often accumulate excessive amounts of heavy metals and pose a threat to human health. For this reason, plenty of studies have focused on low accumulation variety screening. However, identifying specific leafy vegetable varieties according to the foliar uptake of air pollution remains to be explored (despite foliar uptake being an important pathway for heavy-metal accumulation). Therefore, in this study, the lead (Pb) and cadmium (Cd) contents, leaf morphology, and particle matter contents were analyzed in a micro-area experiment using 20 common vegetables. The results show that the Pb content in leaves ranged from 0.70 to 3.86 mg kg⁻¹, and the Cd content ranged from 0.21 to 0.99 mg kg⁻¹. Atmospheric particles were clearly scattered on the leaf surface, and the particles were smaller than the stomata. Considering the Pb and Cd contents in the leaves and roots, stomata width-to-length ratio, leaf area size, enrichment factor, and translocation factor, Yidianhongxiancai, Qingxiancai, Baiyuanyexiancai, Nanjingjiangengbai and Sijixiaobaicai were recommended for planting in kitchen gardens and suburban areas as they have low accumulation characteristics. Identifying the influencing factors in the accumulation of heavy metals in vegetables through foliar uptake is important to help plant physiologists/environmentalists/policy makers to select suitable varieties for planting in air-polluted areas and thus reduce their threat to human health.

Comparative evaluation of in vivo relative bioavailability and in vitro bioaccessibility of arsenic in leafy vegetables and its implication in human exposure assessment

Arsenic (As) contamination in vegetables is a severe threat to human health. However, the evaluation of As relative bioavailability (As-RBA) or bioaccessibility in vegetables is still unexplored. The study sought to evaluate the As-RBA in commonly consumed ten leaf vegetables collected from As-polluted farmlands. Additionally, the As-RBA was determined using rat bioassay and compared with As bioaccessibility through five commonly used in vitro methods, including UBM (Unified BARGE Method), SBRC (Solubility Bioavailability Research Consortium), DIN (Deutsches Institut für Normung e.V.), IVG (In Vitro Gastrointestinal), and PBET (Physiologically Based Extraction Test). Results showed that the As-RBA values were 14.3-54.0% among different vegetables. Notably, significant in vivo-in vitro correlations (IVIVC) were observed between the As-RBA and the As bioaccessibility determined by the PBET assay (r² = 0.763-0.847). However, the other assays (r² = 0.417-0.788) showed a comparatively weaker relationship. The estimation of As-RBA using derived IVIVC to assess As exposure risk via vegetable consumption confirmed that As exposure risk based on As-RBA was lower than that the total As concentrations. Therefore, it was concluded that PBET could better predict the As-RBA in vegetables than other in vitro assays. Furthermore, As-RBA values should be considered for accurate health risk assessment of As in vegetables.

In Vivo-In Vitro Correlations for the Assessment of Cadmium Bioavailability in Vegetables

The correlation of in vitro and in vivo assays for determining bioavailable Cd amounts in vegetables is limited. Herein, the correlations between Cd relative bioavailability (Cd-RBA) in rat models and Cd bioaccessibility in four in vitro assays were examined in vegetables. Results showed that the combined liver plus kidney data provided the appropriate endpoint and was used as a biomarker to estimate Cd-RBA. The Cd-RBA was negatively correlated with the mole ratio of Ca/Cd and Fe/Cd in vegetables. Strong in vivo-in vitro correlations were found from physiologically based extraction test (PBET) and in vitro gastrointestinal (IVG) (R² = 0.66-0.69). We concluded that PBET and IVG were optimal models for Cd-RBA determination in vegetables. The nutritional elements in the vegetables could affect Cd absorption. Furthermore, the Cd bioavailability in vegetables should be considered because risk estimates solely based on the total Cd concentration in vegetables would overestimate Cd intake.

Cadmium phytoextraction by Helianthus annuus (sunflower), Brassica napus cv Wichita (rapeseed), and Chyrsopogon zizanioides (vetiver)

The use of phytoextraction plant species to accumulate soil metals into harvestable plant parts is a method used for managing soils with high cadmium (Cd). We evaluated three Cd accumulating species recently recommended for such use in cacao farms where Cd removal is needed to maintain markets: Helianthus annuus (sunflower), Brassica napus (rapeseed), and Chyrsopogon zizanioides (vetiver). Plants were grown in two greenhouse pot experiments with different Cd-spiked growth media: (sand plus perlite) and a natural soil. Plant total Cd and Cd uptake in shoot biomass of all species, across both experiments, increased linearly with increasing amounts of added Cd. Rapeseed had the highest plant total Cd and sunflower had the highest Cd uptake in shoot biomass. The highest application of Cd corresponded to the highest plant total Cd and shoot biomass Cd uptake, regardless of species. The bioconcentration factor (BCF) for each species increased in a curvilinear manner with added Cd, with maximum BCF values for plants grown in the sand and perlite matrix at 2.5 mg kg^-1 added Cd and in the natural soil at 5.0 mg kg^-1 added Cd. We conclude that the Cd uptake (shoot biomass only) capability of the three species examined is greatest for sunflower given its increased uptake with Cd additions, its BCF value > 1, and lack of observed visual Cd toxicity symptoms, fungus and insect damage. Although these species had BCF >1, the potential annual removal of Cd would have been too small to support a meaningful phytoextraction practice.

Urinary Arsenic and Cadmium Associations with Findings from Cranial MRI in American Indians: Data from the Strong Heart Study

BACKGROUND

Arsenic and cadmium are known cardiovascular toxicants that pose disproportionate risk to rural communities where environmental exposures are high. American Indians have high vascular risk, which may be attributable in part to these exposures.

OBJECTIVE

We examined urine metal concentrations in association with magnetic resonance imaging findings of vascular brain injury or cerebral atrophy in adult American Indians.

METHODS

We measured arsenic and cadmium in American Indian participants from the Strong Heart Study (1989-1991) and evaluated these associations with later (2010-2013) measures of infarct, hemorrhage, white matter hyperintensity (WMH) grade, brain and hippocampal volume, and sulcal and ventricle atrophy using nested multivariate regression analyses.

RESULTS

Among participants with available data (N=687), the median urine arsenic:creatinine ratio was 7.54μg/g [interquartile range (IQR): 4.90-11.93] and the cadmium:creatinine ratio was 0.96μg/g (IQR: 0.61-1.51). Median time between metal measurement and brain imaging was 21 y (range: 18-25 y). Statistical models detected significant associations between arsenic and higher burden of WMH [grade increase=0.014 (95% CI: 0.000, 0.028) per 10% increase in arsenic]; and between cadmium and presence of lacunar infarcts [relative risk (RR)=1.024 (95% CI: 1.004, 1.045) per 10% increase in cadmium].

DISCUSSION

This population-based cohort of American Indian elders had measured values of urine arsenic and cadmium several times higher than previous population- and clinic-based studies in the United States and Mexico, and comparable values with European industrial workers. Our findings of associations for arsenic and cadmium exposures with vascular brain injury are consistent with established literature. Environmental toxicant accumulation is modifiable; public health policy may benefit from focusing on reductions in environmental metals. https://doi.org/10.1289/EHP6930.

Study amino acid contents, plant growth variables and cell ultrastructural changes induced by cadmium stress between two contrasting cadmium accumulating cultivars of Brassica rapa ssp. chinensis L. (pak choi)

Cadmium (Cd) is an inauspicious abiotic traction that not only influences crop productivity and its growth parameters, but also has adverse effects on human health if these crops are consumed. Among crops, leafy vegetables which are the good source of mineral and vitamins accumulate more Cd than other vegetables. It is thus important to study photosynthetic variables, amino acid composition, and ultrastructural localization of Cd differences in response to Cd accumulation between two low and high Cd accumulating Brassica rapa ssp. chinensis L. (pak choi) cultivars, differing in Cd accumulation ability. Elevated Cd concentrations significantly lowered plant growth rate, biomass, leaf gas exchange and concentrations of amino acids collated to respective controls of both cultivars. Electron microscopy indicated that the impact of high Cd level on ultrastructure of leaf cells was associated to affecting cell functionalities, i.e. irregular cell wall, withdrawal of cell membrane, and chloroplast structure which has negative impact on photosynthetic activities, thus causing considerable plant growth suppression. Damage in root cells were observed in the form of enlargement of vacuole. The energy dispersive micro X-ray spectroscopy of both cultivars leaves indicated that cellular structure exhibited exudates of Cd-dense material. Ultrastructural damages and phytotoxicity were more pronounced in high accumulator cultivar as compared to the low accumulator cultivar. These findings are useful in determining the mechanisms of differential Cd-tolerance among cultivars with different Cd tolerance abilities at cellular level.

Effects of Dietary Supplements on the Bioaccessibility of Se, Zn and Cd in Rice: Preliminary Observations from In Vitro Gastrointestinal Simulation Tests

Trace elements such as selenium (Se) and zinc (Zn) are essential elements in the human body, while cadmium (Cd) has no physiological function. A high proportion of people consume dietary supplements to enhance the performance of the body or alter the nutrient contents within the body. Therefore, this study was conducted to evaluate the interaction effects of several popular dietary supplements on the bioaccessibility of Se, Zn and Cd in rice with the hope of identifying dietary supplements that can increase rice Se and Zn bioaccessibility but decrease rice Cd bioaccessibility. The results from in vitro gastrointestinal simulation tests showed that the bioaccessibility of these elements in rice was in the order of Cd (52.07%) > Zn (36.63%) > Se (10.19%) during the gastric phase and Zn (26.82%) > Cd (18.72%) > Se (14.70%) during the intestinal phase. The bioaccessibility of Se during the intestinal phase was greater than that during the gastric phase, and the bioaccessibility of Zn and Cd were the opposite. The bioaccessibility of Se significantly increased in response to vitamin C (VC), vitamin E (VE), vitamin B6 (VB6) and vitamin B9 (VB9), especially VC, which also increased the bioaccessibility of Zn and decreased that of Cd. Procyanidins (OPC), methionine (Met) and coenzyme Q10 (Q10) significantly reduced the bioaccessibility of Se. These results suggest that the reasonable use of dietary supplements can effectively regulate the in vivo contents of trace elements, which provide valuable information for developing health interventions to address problems for specific people, especially selenium-deficient people.

Comparative assessment of Brassica pekinensis L. genotypes for phytoavoidation of nitrate, cadmium and lead in multi-pollutant field

Information is needed for comparative assessment and agronomic practices for phytoavoidation in multi-pollutant field. A field study was conducted to explore 97 Brassica pekinensis L. genotypes with permissible limit of contaminants growing in a severely Cd, moderately nitrate and slightly Pb multi-polluted field. Thirteen genotypes, i.e. KGZY, CXQW, CAIB, JINL, JQIN, JFEN, WMQF, XLSH, TAIK, BJXS, JUKA, XYJQ and GQBW, were identified with permissible limit for nitrate, Cd and Pb based on their resistance to heavy metal and nitrate accumulation in leaves when grown in co-contaminated soils. Furthermore, the correlation between essential and toxic elements concentrations in plant of B. pekinensis were inconsistent. Generally speaking, application of increasing Ca, K and S fertilizers in appropriate forms and dosages tended to increase the yield and quality of B. pekinensis cultivated in multi-pollutant field.

Ameliorative Effect of Selenomethionine on Cadmium-Induced Hepatocyte Apoptosis via Regulating PI3K/AKT Pathway in Chickens

Selenium (Se) is a trace element for human and animal health. Cadmium (Cd) is a known human carcinogen. The effects of Cd on the environment and humans are well known. Because chickens are at the top of the food chain, it is a good experimental animal model for assessing heavy metal toxicity and its potential threat to humans. Selenomethionine (Se-met) is a suitable form for nutritional Se supplementation. Therefore, the toxicity of Cd to the chicken liver and the antagonistic effects of Se-met on Cd were examined at the molecular level in the present study. The results showed that oxidative stress indicators (apoptosis-related genes, P13K/AKT pathway-related genes, and heat shock proteins (HSPs)-related genes) in the Cd group have changed significantly, indicating Cd induced hepatocyte stress and apoptosis. Interestingly, the changes in oxidative stress indicators (apoptosis-related genes, P13K/AKT pathway-related genes, and HSPs-related genes) in the Cd-Se-met group were mitigated compared with the control group. Our results indicated that Cd can induce hepatocyte apoptosis and stress in the chickens. Se-met has an ameliorative effect on Cd-induced apoptosis of chicken hepatocyte by regulating PI3K/AKT pathway. Our findings will provide a new insight for better understanding of the detoxification function of Se-met to heavy metals.

Animal carcass- and wood-derived biochars improved nutrient bioavailability, enzyme activity, and plant growth in metal-phthalic acid ester co-contaminated soils: A trial for reclamation and improvement of degraded soils

Reclamation of degraded soils such as those with low organic carbon content and soils co-contaminated with toxic elements and phthalic acid esters (PAEs) is of great concern. Little is known about the efficiency of plant- and animal-derived biochars for improving plant growth and physicochemical and biological properties of co-contaminated soils, particularly under low content of organic matter. Hence, a pot trial was carried out by growing pak choi (Brassica chinensis L.) to assess the influence of different doses (0, 0.5, 1, 2, and 4%) of animal (pig carcass) and wood (Platanus orientalis) derived biochars on soil properties, nutrient availabilities, plant growth, and soil enzyme activities in two soils containing low (LOC) and high (HOC) organic carbon contents and co-contaminated with di-(2-ethylhexyl) phthalic acid (DEHP) and cadmium (Cd). Biochar applications improved pH, salinity, carbon content, and cation exchange capacity of both soils. Addition of biochars significantly increased the bioavailability and uptake of phosphorus and potassium in the plants in both soils with greater effects from pig biochar than wood biochar. Biochar additions also significantly enhanced urease, sucrase, and catalase activities, but suppressed acid phosphatase activity in both soils. The impact of pig biochar was stronger on urease and acid phosphatase, while the wood biochar was more effective with sucrase and catalase activities. The biomass yield of pak choi was significantly increased after biochar addition to both soils, especially in 2% pig biochar treatment in the LOC soil. The positive response of soil enzymes activities and plant growth for biochar addition to the Cd and DEHP co-contaminated soils indicate that both biochars, particularly the pig biochar can mitigate the risk of these pollutants and prove to be eco-friendly and low-cost amendments for reclaiming these degraded soils.

Differences in cadmium absorption by 71 leaf vegetable varieties from different families and genera and their health risk assessment

Leaf vegetables have strong capabilities to take up cadmium (Cd) compared to other vegetable varieties. Until now, the differences in Cd uptake and accumulation by leaf vegetables from different families and genera and the related health risks were unknown. To remedy this, we studied 71 leaf vegetables (multiple genotypes within 17 categories of vegetables) in soil cultivation experiments (3 Cd treatment levels). Results showed that at 2.12 mg kg^-1 Cd treatment, the dry weight of only five genotypic varieties from the families Brassicaceae and Asteraceae significantly decreased compared to the control, suggesting their weak Cd tolerances. Vegetables from the Brassicaceae, Asteraceae, Apiaceae, and Convolvulaceae families had stronger Cd absorption capabilities, whereas those from the Liliaceae and Amaranthaceae families had weaker ones. Cluster analysis found that the 17 vegetable categories could be divided into three groups: vegetables with high Cd accumulation capabilities were Lactuca sativa L.var. ramosa Hort. and Lactuca sativa var. longifoliaf. Lam. Vegetables with moderate Cd accumulation capabilities were bok choy, napa cabbage, choy sum, leaf mustard, Lactuca sativa L., Sonchus oleraceus L., celery, coriander, and water spinach. Vegetables with low Cd accumulation capabilities were cabbage, crown daisy, garlic chive, Allium ascalonicum, Gynura cusimbua, and edible amaranth. Estimated daily intake (EDI) and target hazard quotient (THQ) analysis results showed that 100% genotypes of vegetables from the Apiaceae and Convolvulaceae families had health risks; 100% genotypes of Lactuca sativa L., Sonchus oleraceus L., Lactuca sativa L. var. ramosa Hort., and Lactuca sativa var. longifoliaf. Lam from the Asteraceae family carried high risks. Of vegetables in the Brassicaceae family, 42.9% showed risks. Vegetables from the Amaranthaceae and Liliaceae families, Gynura cusimbua and crown daisy from the Asteraceae family, and cabbage from the Brassicaceae family all displayed relatively low risks (all 100%).

A transcriptomic (RNA-seq) analysis of genes responsive to both cadmium and arsenic stress in rice root

Cadmium (Cd) and arsenic (As) are nonessential and toxic elements in rice that often occur together in contaminated paddy field soils. To understand whether rice has a common molecular response mechanism against Cd and As toxicity, 30-day seedlings (Oryza sativa L. indica) were exposed separately to Cd and As³⁺ in hydroponic cultures for up to 7 days. Root transcriptomic analysis of plants exposed to Cd and As for 3 days revealed that a total of 2224 genes in rice roots responded to Cd stress, while 1503 genes responded to As stress. Of these, 841 genes responded to both stressors. The genes in common to Cd and As stress were associated with redox control, stress response, transcriptional regulation, transmembrane transport, signal transduction, as well as biosynthesis and metabolism of macromolecules and sulfur compounds. In plants exposed to Cd and As separately or in combination for 3 and 7 days, qRT-PCR verification revealed that the glutathione metabolism associated gene Os09g0367700 was significantly up-regulated with respect to unexposed controls and had a positive synergistic effect under combined Cd and As stress. In addition, the redox control related genes Os06g0216000, Os07g0638300 and Os01g0294500, the glutathione metabolism related gene Os01g0530900, the cell wall biogenesis related genes Os05g0247800, Os11g0592000 and Os03g0416200, the expression regulation related genes Os07g0597200 and Os02g0168200, and the transmembrane transport related genes Os04g0524500, also varied significantly with respect to an unexposed control and displayed synergistic effects after 7 days of simultaneous exposure to Cd and As. Our identification of a novel set of genes in rice which responded to both Cd and As³⁺ stress may be of value in mitigating the toxicity of co-contaminated soils. These results also provide a deeper understanding of the molecular mechanisms involved in response to multi-metal/loids stress, and may be used in the genetic improvement of rice varieties.

Risk assessment of bioaccessible arsenic and cadmium exposure through rice consumption in local residents of the Mae Tao Sub-district, Northwestern Thailand

Consumption of contaminated rice is a toxin exposure route in Asian populations. Since total concentrations generally overestimate health risks, the objectives of this study were to determine the levels of bioaccessible As and Cd in rice cultivated in the Mae Tao, Tak Province and evaluate their potential health impacts in local adults. In total, 59 locally grown rice samples were analyzed for their total and bioaccessible concentrations. Bioaccessible concentrations were obtained from an in vitro digestion process. Inorganic As concentrations were estimated assuming that 63.2-63.5% of the total As is inorganic As. Rice contained inorganic As (45.2% of white rice and 57.1% of sticky rice) and Cd (51.6% of white rice and 32.1% of sticky rice) levels exceeding the Codex standards. The bioaccessibilities of As (16.3-70.0%) and Cd (Null to 83.7%) in rice varied widely. The concentrations of bioaccessible As, which were 1-1.2 times greater than those of bioaccessible Cd, indicate a higher possibility of As absorption into the human body. Positive significant relationships were found between total and bioaccessible As (R² = 0.568 for white rice and R² = 0.704 for sticky rice) and Cd (R² = 0.874 for white rice and R² = 0.862 for sticky rice). The hazard quotient (HQ) of inorganic As exposure accounted for approximately 93.4% of hazard index (HI). Approximately 2-6 in 10,000 residents over a lifetime of 75 years could suffer from cancer as a result of daily rice consumption. Therefore, the consumption of the home-grown rice in this study should be limited.

Oral Bioaccessibility and Exposure Risk of Metal(loid)s in Local Residents Near a Mining-Impacted Area, Hunan, China

Metal(loid) contamination of food crops and soils resulting from mining activities has been a major concern due to the potential risk to humans. In this study, a total of 36 rice (home-grown and market rice), 38 vegetable, 10 drinking water, 4 river water, 18 soils and 30 urine samples were collected from an abandoned mining area or the local residents in China. Results showed that metal(loid) levels in some of the soil and drinking water samples exceeded the Chinese standard. Rice Cd concentration, rice Pb levels, and vegetable Pb levels exceeded the maximum permissible concentrations in 49%, 68%, and 42% of the samples, respectively. In gastric phases, the average Cd, Pb and As bioaccessibilities in rice were 72%, 70%, and 82%. In gastrointestinal phases, the average Cd, Pb and As bioaccessibilities in rice were 49%, 39%, and 94%. Vegetables (pak choi was selected) showed lower metal(loid) bioaccessibility than rice. The median concentrations of Cd, Pb and As in urine were 3.99, 4.82 and 64.8 µg L⁻¹, respectivley. Rice had the highest contribution rates of Cd and Pb for daily intake, accounting for 114% and 210%, respectively. Vegetables contributed less, and very little contribution came from drinking water. Based on the bioaccessibility data, metal(loid) contamination around the mining area poses a great exposure risk to the local residents through consumption of food crops.