Bayesian toxicokinetic modeling of cadmium exposure in Chinese population

Bayesian analysis of physiologically based toxicokinetic (PBTK) modeling for pentachlorophenol exposure in pregnant women

Pentachlorophenol (PCP) is a persistent organic compound that is widely present in the environment. The estimation of internal exposure levels for a given external exposure using toxicokinetic models is key to the human health risk assessment of PCP. The present study developed a physiologically based multicompartmental pharmacokinetic (PBTK) model to describe and predict the behavior of pentachlorophenol (PCP) in an organism. The model consists of stomach, intestines, adipose tissue, kidneys and fast- and poorly perfused tissues that are interconnected via blood circulation. We constructed a PBTK model of PCP in rats and extrapolated it to human dietary PCP exposure. The toxicokinetic data of PCP in human tissues and excreta were obtained from the published literature. Based on the collected PCP dietary survey and internal exposure data of pregnant women in Shanghai, Bayesian statistical analysis was performed for the model using Markov chain Monte Carlo (MCMC) simulation. The posterior distributions of the sensitive parameters were estimated, and the model was parameter optimized and validated using the pregnant women's test dataset. The results showed that the root mean square error (RMSE) improved 37.3% compared to the original model, and a systematic literature search revealed that the optimized model achieved acceptable prediction results for other datasets in China. A PCP metabolism model based on the exposure characteristics of pregnant women in China was constructed in the present study. The model provides a theoretical basis for the study of PCP toxicity and risk assessment.

Assessment of human exposure to cadmium and its nephrotoxicity in the Chinese population

BACKGROUND

Cadmium (Cd) is a toxic heavy metal that widely detected in environment and accumulated in kidney, posing a great threat to human health. However, there is a lack of systematic investigation of exposure profile and association of Cd exposure with renal function in the Chinese population.

METHODS

Related articles were searched from PubMed, Web of Science, China National Knowledge Internet, and Wanfang to construct an aggregate exposure pathway (AEP) framework for Cd and to explore the correlation between Cd and renal function using random effects models.

RESULTS

A total of 220 articles were included in this study, among which 215 investigated human exposure and 12 investigated the association of Cd with renal outcomes. The AEP framework showed that 96.5 % and 62.5 % of total Cd intake were attributed to dietary intake in nonsmokers and smokers, respectively. And 35.2 % originated from cigarette smoke inhalation in smokers. In human body, Cd was detected in blood, urine, placenta, etc. Although the concentrations of Cd in blood and urine from subjects living in polluted areas showed a sharp downward trend since the early 21st century, higher concentration of Cd in the environment and human body in polluted areas was found. Kidney was the target organ. The level of blood Cd was positively associated with urinary β2-microglobulin [β2-MG, r (95 % CI) = 0.12 (0.05, 0.19)], albumin [0.13 (0.06, 0.20)], and retinol-binding protein [RBP, 0.14 (0.03, 0.24)]. Elevated urinary Cd was correlated with increases in β2-MG [0.22 (0.15, 0.29)], albumin [0.23 (0.16, 0.29)], N-acetyl-β-d-glucosaminidase [NAG, 0.33 (0.22, 0.44)], and RBP [0.22 (0.14, 0.30)].

CONCLUSIONS

Foods and cigarette smoke were two major ways for Cd intake, and Cd induced renal injury in the Chinese population. This study enhanced the understanding of human exposure and nephrotoxicity of Cd, and emphasized the need for controlling Cd level in polluted areas.

Risk assessment of combined exposure to lead, cadmium, and total mercury among the elderly in Shanghai, China

Lead (Pb), cadmium (Cd) and total mercury (THg) are toxic heavy metals (THMs) that are widely present in the environment and can cause substantial health problems. However, previous risk assessment studies have rarely focused on the elderly population and have usually targeted a single heavy metal, which might underestimate the long-term accumulative and synergistic effects of THMs in humans. Based on the food frequency questionnaire and inductively coupled plasma mass spectrometry, this study assessed external and internal exposures to Pb, Cd and THg in 1747 elderly people in Shanghai. Probabilistic risk assessment with the relative potential factor (RPF) model was used to assess the neurotoxicity and nephrotoxicity risks of combined THMs exposures. The mean external exposures of Pb, Cd and THg in Shanghai elderly were 46.8, 27.2 and 4.9 μg/day, respectively. Plant-based foods are the main source of Pb and THg exposure, while Cd is mainly from animal-based foods. The mean concentrations of Pb, Cd and THg were 23.3, 1.1 and 2.3 μg/L in the whole blood, and 6.2, 1.0 and 2.0 μg/L in the morning urine, respectively. Combined exposure to THMs leading to 10.0 % and 7.1 % of Shanghai elderly at risk of neurotoxicity and nephrotoxicity. The results of this study have important implications for understanding the profiles of Pb, Cd and THg exposure in the elderly living in Shanghai and provide data support for risk assessment and control of nephrotoxicity and neurotoxicity from combined THMs exposure in the elderly.

Tracking cadmium pollution from source to receptor: A health-risk focused transfer continuum approach

Cadmium (Cd) exposure poses a substantial risk to human health. Despite this, the multi-stage process through which Cd is released to the environment before being taken up and impacting human receptors has rarely been investigated. Here we utilized an integrated model involving Cd emissions, atmospheric transport, deposition, uptake by rice, receptor ingestion and metabolic processing in quantifying the critical emission sources and human health risks of Cd. Atmospheric Cd emissions in the study area in southeastern China were estimated at 147 kg (2016), with >53 % of emissions from non-ferrous metals (NFM) smelting activities. Atmospheric Cd depositions caused elevated Cd content in soil and rice, accounting for 3-79 % and 50-85 % of, respectively, soil and rice Cd. Cumulative frequency analysis showed that an estimated 1.3 % of predicted urine Cd through the consumption of Cd-contaminated rice and exceeded existing safety standards (1 μg g^-1), thus highlighting the risks posed to health from high levels of Cd pollution. Applying stricter industrial emission standards to the NFM sector in particular and effective soil management practices could substantially reduce exposure to Cd pollution. The results contribute to understanding of the Cd transfer process and draw attention to the relative health benefits of interventions aimed at mitigating Cd levels and exposure risks at different stages along the Cd transfer continuum from source to receptor.

Health risk assessment of cadmium exposure by integration of an in silico physiologically based toxicokinetic model and in vitro tests

Cadmium (Cd) is a common environmental pollutant that can damage multiple organs, including the kidney. To prevent renal effects, international authorities have set health-based guidance values of Cd from epidemiological studies. To explore the health risk of Cd exposure and whether human equivalent doses (HEDs) derived from in vitro tests match the current guidance values, we integrated renal tubular epithelial cell-based assays with a physiologically based toxicokinetic model combined with the Monte Carlo method. For females, the HEDs (μg/kg/week) derived from KE2 (DNA damage), KE3 (cell cycle arrest), and KE4 (apoptosis) were 0.20 (2.5th-97.5th percentiles: 0.09-0.48), 0.52 (0.24-1.26), and 2.73 (1.27-6.57), respectively; for males the respective HEDs were 0.23 (0.10-0.49), 0.60 (0.27-1.30), and 3.11 (1.39-6.78). Among them, HED_KE4 (female) was close to the tolerable weekly intake (2.5 μg/kg/week) set by the European Food Safety Authority. The margin of exposure (MOE) derived from HED_KE4 (female) indicated that risks of renal toxicity for populations living in cadmium-contaminated regions should be of concern. This study provided a new approach methodology (NAM) for environmental chemical risk assessment using in silico and in vitro methods.

Development of physiologically based toxicokinetic models for 3-monochloropropane-1,2-diol and glycidol

3-Monochloropropane-1,2-diol (3-MCPD), glycidol, together with their fatty acid esters are commonly presented in various food and have shown carcinogenicity in various laboratory animals. Public health risk assessment of 3-MPCD and glycidol exposure relies on quantitative tools that represent their in vivo toxicokinetics. In order to better understand the absorption, distribution, metabolism, and excretion profiles of 3-MCPD and glycidol in male rats, a physiologically based pharmacokinetic (PBTK) model was developed. The model's predictive power was evaluated by comparing in silico simulations to in vivo time course data obtained from experimental studies. Results indicate that our PBTK model successfully captured the toxicokinetics of both free chemicals in key organs, and their metabolites in accessible biological fluids. With the validated PBTK model, we then gave an animal-free example on how to extrapolate the toxicological knowledge acquired from a single gavage to a realistic dietary intake scenario. Three biomarkers, free compound in serum, urinary metabolite DHPMA, and glycidol-hemoglobin adduct (diHOPrVal) were selected for in silico simulation following constant dietary intakes, and their internal levels were correlated with proposed external daily exposure via reverse dosimetry approaches. Taken together, our model provides a computational approach for extrapolating animal toxicokinetic experiments to biomonitoring measurement and risk assessment.

Physiologically-based toxicokinetic model for the prediction of perchlorate distribution and its application

Perchlorate is a stable and readily transportable thyroid hormone disruptor, and prevalent exposure to perchlorate through food and drinking water has raised public concern about its health effects. The physiologically based toxicokinetic (PBTK) model as a dose prediction method is effective to predict the toxicant exposure dose of an organism and helps quantitatively assess the dose-dependent relationship with toxic effects. The current study aimed to establish a multi-compartment PBTK model based on updated time-course datasets of single oral exposure to perchlorate in rats. With adjustment of the kinetic parameters, the model fitted well the toxicokinetic characteristics of perchlorate in urine, blood, and thyroid from our experiments and the literature, and the coefficient of determination (R²) between the fitting values and the experimental data in regression analysis was greater than 0.91, indicating the robustness of the current model. The results of sensitivity analysis and daily repeated exposure simulations together confirmed its effective renal clearance. According to the distribution characteristic of perchlorate, a correlation study of internal and external exposure was conducted using urinary perchlorate as a bioassay indicator. The developed multi-compartment model for perchlorate updates important toxicokinetic data and kinetic parameters, providing analytical and modeling tools for deriving total exposure levels in the short term.

Experimental and theoretical studies on the adsorption characteristics of Si/Al-based adsorbents for lead and cadmium in incineration flue gas

Si/Al-based adsorbents are effective adsorbents for capturing heavy metals in incineration flue gases at high temperatures in the furnace. In this work, the adsorption characteristics and adsorption mechanisms of Si/Al-based adsorbents for lead and cadmium vapors were studied using a combination of experimental and density functional theory (DFT) calculations. The trapping performance of a series of Si/Al-based adsorbents for Pb and Cd vapors was investigated using a self-designed gas-solid two-phase rapid adsorption experimental system. The results showed that kaolinite and montmorillonite exhibited better heavy metal adsorption capacity than SiO₂ and Al₂O₃, and were significantly stronger for Pb than for Cd. Chemisorption dominated the capture of Pb/Cd by Si/Al-based adsorbents at high temperatures. The results of DFT calculations indicated that the chemisorption mechanisms dominated the adsorption of Pb and Cd species on the metakaolinite (001) surface, and the adsorption energy of Pb species on the metakaolinite surface was greater than that of Cd species. The exposed O atoms and unsaturated Al atoms of metakaolinite (001) surface were effective adsorption active sites for heavy metals and their chlorides. In the adsorption reaction, the binding of Pb/Cd atoms and surface exposed O sites, as well as the strong interaction between Cl and unsaturated Al atoms, were responsible for the capture of Pb and Cd chlorides by metakaolinite.

Physiologically based pharmacokinetic (PBPK) modeling of BDE-209 following oral exposure in Chinese population

The wide usage of decabromodiphenyl ether (BDE-209) as additive brominated flame retardant has caused its widespread occurrence in the environment and high exposure risk in humans. Estimating its internal exposure dose and reconstruction of external exposure dose using physiologically based pharmacokinetic (PBPK) modelling approach is a key step in the risk assessment of BDE-209. However, the PBPK model for BDE-209 is currently unavailable. This study has established two oral permeability-limited PBPK models of BDE-209 without enterohepatic recirculation (EHR) (model 1) and with EHR (model 2) for Chinese population. Using the in vitro experiments, the average binding of BDE-209 to human plasma protein (99.64% ± 2.97%) was obtained. Moreover, blood sample analysis and systematic literature review were performed to obtain internal and external exposure data of BDE-209 used for model calibration and validation. The predictions of both models were within 2-fold of the observed, and a longer half-life of serum BDE-209 was observed in model 2 than model 1. Based on the models, a human biomonitoring guidance value (HBM-GV) of 93.61 μg/g lw was derived for BDE-209, and there is no health risk found for Chinese population currently. This study provides new quantitative assessment tools for health risk assessment of BDE-209.

Chain modeling for the biogeochemical nexus of cadmium in soil-rice-human health system

This paper presents a novel chain model named soil-food-human (SFH) for clarifying the biogeochemical cascades among the triple challenges of cadmium contamination, food safety, and related public health effect. The model was developed based on the integration of spatial distribution pattern of soil environment and the biogeochemical process of cadmium in soil-rice-human health, and it was validated through a case study. In soil environment terms, SFH predicted the spatial distribution of soil properties with an average prediction accuracy of 82.28%. In food production terms, the SFH can identify the safe production zones for planting rice and unsafe area for adjusting croppingsystems with a relative error of 39.41%. In food consumption terms, SFH mapped the high-resolution map of cadmium exposure dose, which gives a new solution to assess the food safety risks for self-sufficient populations. For the health effect of rice cadmium exposure, SFH simulated the spatiotemporal pattern of urinary cadmium based on toxicokinetic which revealed the health effect of rice cadmium exposure. The chain model provides a new insight in understanding the biogeochemical cascades between food production, food safety, and public health, making it possible to develop a comprehensive strategy to tackle cadmium pollution in soil-rice-human health system.

Estimation of the bio-accessibility of methylmercury from aquatic foods using a PBTK model with an approximate Bayesian computation method in Chinese pregnant women

BACKGROUND

Fish are the primary source of protein and docosahexaenoic acid (DHA) for pregnant women and children, but methylmercury (MeHg) pollution is the potential hazard of fish consumption. In risk assessments, the bio-accessibility of MeHg is usually assumed to be 100%, which could lead to overestimation of dietary exposure.

METHOD

An existing PBTK model was adapted to estimate parameters of the bio-accessibility based on MeHg exposure data from a cohort of 397 Chinese pregnant women. The posterior distributions of parameters were determined by using the ABC - MCMC. RMSEP and Spearman's rank correlation coefficients (Rho) were calculated to determine the goodness of model fitting. The Monte Carlo analysis was performed for the parameter distributions to estimate the model variability.

RESULT

The median of daily MeHg intake and maternal MeHg levels were 0.018 μg/kg bw and 3.01 μg/kg in the early and middle terms of pregnancy. The estimated bio-accessibility of freshwater fish, marine fish and others were 46.1, 17.3 and 58.2%, separately. The RMSEP improved from 11.18 to 2.54 and the Rho improved from 0.19 to 0.22 after bio-accessibility optimization. The model variability was estimated to be 2.6.

CONCLUSION

The bio-accessibility estimated in this study was comparable to that determined in previous in vitro studies. The optimized model could improve the prediction performance on the MeHg body burden by dietary exposure.

Cadmium physiologically based pharmacokinetic (PBPK) models for forward and reverse dosimetry: Review, evaluation, and adaptation to the U.S. population

The goal of this study was to assess a cadmium (Cd) physiologically based pharmacokinetic (PBPK) model to evaluate Cd toxicological reference values (e.g. reference dose, tolerable intake, minimum risk level) adapted to the U.S. population. We reviewed and evaluated previously published Cd PBPK models and developed further adaptations to the 1978 Kjellström and Nordberg (KN) model. Specifically, we propose adaptations with updated U.S.-specific bodyweight, kidney weight and creatinine excretion models by using NHANES data as well as a stochastic PBPK model that provides credible intervals of uncertainty around mean populational estimates. We provide our model review and adaptations as well as present estimates from the newly adapted models using observed U.S. urinary Cd values as a function of gender and age and given dietary exposure as evaluated from NHANES/WWEIA and U.S. Total Diet Study data. Results show all newly adapted models provide acceptable mean estimates of urinary Cd in the U.S. The stochastic model provides credible intervals to further inform regulatory decision making. Validation of the estimated K-Cd concentration values was not possible as data for a representative population was not available. We developed a web-based tool implementing these models and other potential adaptations to facilitate PBPK model estimate comparisons.

Urinary cadmium in relation to bone damage: Cadmium exposure threshold dose and health-based guidance value estimation

Cadmium (Cd) is a widespread heavy metal with osteotoxicity, and bone mineral density (BMD) is often used as an early sensitive biomarker of bone damage. This study retrieved worldwide epidemiological studies to conduct a systematic meta-analysis to explore the association between Cd exposure and bone damage. A random effect model was used to establish the relationship between urinary Cd (U-Cd) and BMD and explore the influence of covariate factors. The benchmark dose method was used to calculate the safety threshold of U-Cd when the BMD decrease within an acceptable range. Toxicokinetic (TK) model was used to estimate the health-based guidance value (HBGV) of dietary Cd exposure based on the U-Cd threshold. The 95% lower confidence interval of benchmark dose of U-Cd derived in this study was 1.71 μg/g Cr, and the HBGV of dietary Cd exposure was determined to be 0.64 μg/kg bw/day. Gender had the greatest influence on BMD, followed by body mass index (BMI), age, and race. This study conducted a comprehensive systematic analysis of global research and was the first exploration to quantify the decreased BMD caused by Cd exposure in a large-scale population. The results provided reference for the risk assessment of Cd exposure and the formulation of dietary exposure standards.

Dose-response evaluation of urinary cadmium and kidney injury biomarkers in Chinese residents and dietary limit standards

BACKGROUND

Cadmium (Cd) is a common heavy metal that mainly causes renal damage. There is a lack of research on the large-scale and systematic evaluation of the association between urinary Cd (U-Cd) and various effect biomarkers among Chinese residents.

METHODS

Based on the establishment process of dietary Cd limit standards by European Food Safety Authority (EFSA), the dose-response relationships between U-Cd and four biomarkers, β₂-microglobulin (β₂-MG), N-acetyl-β-glucosidase (NAG), microalbumin (mALB), and retinol binding Protein (RBP) were explored, respectively. Toxicokinetic model was used to derive the dietary Cd exposure limit for Chinese residents after critical U-Cd concentration was calculated.

RESULTS

As the sensitive biomarkers of renal injury, β₂-MG and NAG were selected to estimate the 95% confidence interval lower limit of the U-Cd benchmark dose (BMDL₅) to be 3.07 and 2.98 μg/g Cr, respectively. Dietary Cd exposure limit was calculated to be 0.28 μg/kg bw/day (16.8 μg/day, based on the body weight of 60 kg), which was lower than the average Chinese Cd exposure (30.6 μg/day) by the China National Nutrient and Health Survey.

CONCLUSION

This study established an overall association between U-Cd and renal injury biomarkers, and explored the Chinese dietary Cd exposure limits, which helps improve Chinese Cd exposure risk assessment and provides a reference basis for formulating reasonable exposure standards.