Dermal bioaccessibility and cytotoxicity of heavy metals in urban soils from a typical plateau city: Implication for human health

In vitro tungsten bioaccessibility in Chinese residential soils: Implications for human health risk assessments and soil screening level derivation

Tungsten (W) contamination presents emerging environmental challenges, necessitating the need to establish soil screening levels (SSLs), especially for residential soils. This study assessed the health exposure risk and derived national and regional residential SSLs for W in Chinese residential soils, incorporating machine-learning prediction of in-vitro soil W bioaccessibility. We analyzed 204 residential soil samples collected across 24 provinces, recording a wide range of W concentrations (0.01-3063.2 mg/kg). Synchrotron-based X-ray fluorescence spectroscopy, chemical extractions, and random forest modeling indicated that the key determinants of soil W bioaccessibility were soil pH, cation exchange capacity, organic matter, and clay contents. Monte Carlo simulations demonstrated that soil W contamination predominantly results in noncarcinogenic health risks to residents via oral exposure, especially in mining-affected regions. A national residential SSL (NRSSL) of 35.5 mg/kg and regional residential SSLs (RRSSLs) of 34.5-49.2 mg/kg were established. Incorporating predicted bioaccessibility increased the NRSSL to 73.8 mg/kg and the RRSSLs to 69.8-112.5 mg/kg. Southern China, which is rich in W ore, exhibited lower RRSSLs, underscoring a need for enhanced safety management. Our framework and findings provide a robust scientific foundation for future soil contamination risk assessment studies, and we present customized SSLs that can guide targeted W risk control strategies.

Health risk assessment of heavy metal(loid)s in road dust via dermal exposure pathway from a low latitude plateau provincial capital city: The importance of toxicological verification

The human health risk assessment through the dermal exposure of metal (loid)s in dust from low latitude and high geological background plateau cities was largely unknown. In this study, the road dust samples were harvested from a typical low-latitude plateau provincial capital city Kunming, Southwest China. The total concentration and dermal bioaccessibility of heavy metal (loid)s in road dust were determined, and their health risks as well as cytotoxicity on human skin keratinocytes were also assessed. The average concentrations of As (28.5 mg/kg), Cd (2.65 mg/kg), Mn (671 mg/kg), and Zn (511 mg/kg) exceeded the soil background values. Arsenic had the highest bioaccessibility after 2 h (3.79%), 8 h (4.24%), and 24 h (16.6%) extraction. The dermal pathway when bioaccessibility is considered has a higher hazard quotient than the conventional method using total metal(loid)s in the dust. In addition, toxicological verification suggested that the dust extracts suppressed the cell viability, increased the reactive oxygen species (ROS) level and DNA damage, and eventually activated the mitochondria-mediated apoptosis pathway, evidenced by the upregulation of Caspase-3/9, Bax, and Bak-1. Cadmium was positively correlated with the mRNA expression of Bax. Taken together, our data indicated that both dermal bioaccessibility and cytotoxicity should be considered for accurate human skin health risk assessment of heavy metal(loid)s in road dust, which may provide new insight for accurate human health risk assessment and environmental management.

Natural peloids originating from subsea depths of 200 m in the hupo basin, South Korea: physicochemical properties for potential pelotherapy applications

The present study firstly reports surface sediment from the subsea depth of 200 m as a potential natural peloid. The fine-silt sediment exhibited a consistent clay mineral composition dominated by illite, chlorite, kaolinite, and diatomite. The most abundant clay mineral was illite/mica, with other minerals loosely packed in a face-to-face orientation. The thermal conductivity, specific heat capacity, and cation-exchange capacity of the sediment were in the range 0.855-0.885 W/m K, 2.718-2.821 J/g °C, and 23.06-32.96 cmol/kg, respectively. The concentrations of most toxic elements in the sediment were considerably lower than the limits set by domestic cosmetic regulations and other international standards. The analyzed samples exhibited similar properties to those of previously reported peloids, thus making them suitable for use in the field of pelotherapy; furthermore, the consistency in data across a wide peloid-distribution area is expected to enable economically viable mining. Future investigations should aim to to evaluate the long-term effects on the skin, the bioavailability of potentially hazardous substances, and the therapeutic efficacy for various skin conditions.

Loss of mutant p53 in HaCaT keratinocytes promotes cadmium-induced keratin 17 expression and cell death

BACKGROUND

Cadmium exposure induces dermatotoxicity and epidermal barrier disruption and leads to the development of various pathologies. HaCaT cells are immortalized human keratinocytes that are widely used as alternatives to primary human keratinocytes, particularly for evaluating cadmium toxicity. HaCaT cells bear two gain-of-function (GOF) mutations in the TP53 gene, which strongly affect p53 function. Mutant forms of p53 are known to correlate with increased resistance to various stimuli, including exposure to cytotoxic substances. In addition, keratin 17 (KRT17) was recently shown to be highly expressed in HaCaT cells in response to genotoxic stress. Moreover, p53 is a direct transcriptional repressor of KRT17. However, the impact of TP53 mutations in HaCaT cells on the regulation of cell death and keratin 17 expression is unclear. In this study, we aimed to evaluate the impact of p53 on the response to Cd-induced cytotoxicity.

METHODS AND RESULTS

Employing the MTT assay and Annexin V/propidium iodide staining, we demonstrated that knockout of TP53 leads to a decrease in the sensitivity of HaCaT cells to the cytotoxic effects of cadmium. Specifically, HaCaT cells with TP53 knockout (TP53 KO HaCaT) exhibited cell death at a cadmium concentration of 10 μM or higher, whereas wild-type cells displayed cell death at a concentration of 30 μM. Furthermore, apoptotic cells were consistently detected in TP53 KO HaCaT cells upon exposure to low concentrations of cadmium (10 and 20 μM) but not in wild-type cells. Our findings also indicate that cadmium cytotoxicity is mediated by reactive oxygen species (ROS), which were significantly increased only in TP53 knockout cells treated with 30 μM cadmium. An examination of proteomic data revealed that TP53 knockout in HaCaT cells resulted in the upregulation of proteins involved in the regulation of apoptosis, redox systems, and DNA repair. Moreover, RT‒qPCR and immunoblotting showed that cadmium toxicity leads to dose-dependent induction of keratin 17 in p53-deficient cells but not in wild-type cells.

CONCLUSIONS

The connection between mutant p53 in HaCaT keratinocytes and increased resistance to cadmium toxicity was demonstrated for the first time. Proteomic profiling revealed that TP53 knockout in HaCaT cells led to the activation of apoptosis regulatory circuits, redox systems, and DNA repair. In addition, our data support the involvement of keratin 17 in the regulation of DNA repair and cell death. Apparently, the induction of keratin 17 is p53-independent but may be inhibited by mutant p53.

Evaluation of Cd-induced cytotoxicity in primary human keratinocytes

An increasing number of studies have investigated the effects of Cd on human health. Cd-induced dermatotoxicity is an important field of research, but numerous studies have focused on the effects of Cd on the human skin. Moreover, most studies have been performed using HaCaT cells but not primary keratinocytes. In this study, we provide the results describing the cytotoxic effects of Cd exposure on primary human epidermal keratinocytes obtained from different donors. The subtoxic concentration of cadmium chloride was determined via MTT assay, and transcriptomic analysis of the cells exposed to this concentration (25 µM) was performed. As in HaCaT cells, Cd exposure resulted in increased ROS levels, cell cycle arrest, and induction of apoptosis. In addition, we report that exposure to Cd affects zinc and copper homeostasis, induces metallothionein expression, and activates various signaling pathways, including Nrf2, NF-kB, TRAIL, and PI3K. Cd induces the secretion of various cytokines (IL-1, IL-6, IL-10, and PGE2) and upregulates the expression of several cytokeratins, such as KRT6B, KRT6C, KRT16, and KRT17. The results provide a better understanding of the mechanisms of cadmium-induced cytotoxicity and its effect on human epidermal skin cells.

Estimate of the maximum amount of dust adhering to skin and the upper limit of dust-skin adherence factor for young adults: An example from Changchun, China

Contaminants present in dust adhering to the skin can pose a significant risk to human health through dermal absorption and hand-to-mouth contact. The adhesion capacity of dust differs significantly from that of soil due to its physicochemical properties. Therefore, applying the raw soil exposure parameters to estimate the health risks associated with dermal exposure to dust may lead to erroneous conclusions. In this study, we quantified the maximum amount of dust that adhered to the skin (MADmax) and the upper limit of dust-skin adherence factor (DSAFmax) in 26 adults using element markers as a proxy for dust. The volunteers were exposed to dust and rinse water samples were collected from their hands, forearms, lower legs, and feet. We analyzed both the raw dust samples and the rinse water samples for 11 element markers, including Be, V, Cr, Mn, Co, Ni, Cu, Zn, Se, Ba, and Pb. The results showed that the MADmax of indoor dust and outdoor dust increased by 0.08-0.62 mg and 0.33-0.56 mg following a 1 cm2 increase in skin surface area, respectively. Based on best dust element markers, the body part-weighted dust-skin adherences (WDSAFmaxs) of indoor dust and outdoor dust were 0.35 and 0.64 mg/cm2, respectively. A smaller particle size and higher moisture content resulted in a larger DSAFmax. Only when indoor dust concentrations exceed 24.2 mg/m3 or outdoor dust concentrations exceed 44.3 mg/m3, can the WDSAFmax be applied directly in the health risk assessment of dermal exposure to dust. The method from this study can be re-applied in different regions, and the adherence data can help to improve future studies on the health effects of dermal exposure to dust.

Refining health risk assessment of arsenic in wild edible boletus from typical high geochemical background areas: The role of As species, bioavailability, and enterotoxicity

Arsenic (As) is easily accumulated in wild Boletus. However, the accurate health risks and adverse effects of As on humans were largely unknown. In this study, we analyzed the total concentration, bioavailability, and speciation of As in dried wild boletus from some typical high geochemical background areas using an in vitro digestion/Caco-2 model. The health risk assessment, enterotoxicity, and risk prevention strategy after consumption of As-contaminated wild Boletus were further investigated. The results showed that the average concentration of As was 3.41-95.87 mg/kg dw, being 1.29-56.3 folds of the Chinese food safety standard limit. DMA and MMA were the dominant chemical forms in raw and cooked boletus, while their total (3.76-281 mg/kg) and bioaccessible (0.69-153 mg/kg) concentrations decreased to 0.05-9.27 mg/kg and 0.01-2.38 mg/kg after cooking. The EDI value of total As was higher than the WHO/FAO limit value, while the bioaccessible or bioavailable EDI suggested no health risks. However, the intestinal extracts of raw wild boletus triggered cytotoxicity, inflammation, cell apoptosis, and DNA damage in Caco-2 cells, indicating existing health risk assessment models based on total, bioaccessible, or bioavailable As may be not accurate enough. Given that, the bioavailability, species, and cytotoxicity should be systematically considered in accurate risk assessment. In addition, cooking mitigated the enterotoxicity along with decreasing the total and bioavailable DMA and MMA in wild boletus, suggesting that cooking could be a simple and effective way to decrease the health risks of consumption of As-contaminated wild boletus.

Influence of sebum proportion in synthetic sweat on dermal bioaccessibility and on permeation of metal(loid)s from contaminated soils

Even if dermal exposure to metal(loid)s from contaminated soils has received less attention than oral and inhalation exposure, the human health risk can be significant for some contaminants and exposure scenarios. The purpose of this study was to assess the influence of sebum proportion (1% v/v and 3% v/v) in two synthetic sweat formulations (EN 1811, pH 6.5 (sweat A) and NIHS 96-10, pH 4.7 (sweat B)) on As, Cr, Cu, Ni, Pb, and Zn dermal bioaccessibility and on subsequent diffusion through synthetic skin. A Franz cell with a Strat-M® membrane was used to quantify permeation parameters of bioaccessible metal(loid)s. Sebum's presence in synthetic sweat formulations significantly modified bioaccessibility percentages for As, Cr, and Cu. However, sebum proportion in both sweats did not influence the bioaccessibility of Pb and Zn. Some metal(loid)s, namely As and Cu, permeated the synthetic skin membrane during permeation tests when sebum was added to sweat while no permeation was observed without sebum in sweat formulations. Depending on sweat formulation, the addition of sebum (1% v/v) increased or decreased the Cr permeation coefficients (Kp). In all cases, bioaccessible Cr was no longer permeable when extracted with 3% sebum. Ni transdermal permeation was not influenced by the presence of sebum, and no permeation was observed for Pb and Zn. Further studies on the speciation of metal(loid)s in bioaccessible extracts in the presence of sebum are recommended.

The spatial distribution, health risk, and cytotoxicity of metal(loid)s in contaminated field soils: The role of Cd in human gastric cells damage

The spatial distribution and pollution level of heavy metal(loid)s in soil (0-6 m) from a typical industrial region in Jiangmen City, Southeast China was investigated. Their bioaccessibility, health risk, and human gastric cytotoxicity in topsoil were also evaluated using an in vitro digestion/human cell model. The average concentrations of Cd (87.52 mg/kg), Co (106.9 mg/kg), and Ni (1007 mg/kg) exceeded the risk screening values. The distribution profiles of metal(loid)s showed a downward migration trend to reach a depth of 2 m. The highest contamination was found in topsoil (0-0.5 m), with the concentrations of As, Cd, Co, and Ni being 46.98, 348.28, 317.44, and 2395.60 mg/kg, respectively, while Cd showed the highest bioaccessibility in the gastric phase (72.80 %), followed by Co (21.08 %), Ni (18.27 %), and As (5.26 %) and unacceptable carcinogenic risk. Moreover, the gastric digesta of topsoil suppressed the cell viability and triggered cell apoptosis, evidenced by disruption of mitochondrial transmembrane potential and increase of Cytochrome c (Cyt c) and Caspases 3/9 mRNA expression. Bioaccessible Cd in topsoil was responsible for those adverse effects. Our data suggest the importance to reduce Cd in the soil to decrease its adverse impacts on the human stomach.