Non-negligible vector effect of micro(nano)plastics on tris(1,3-dichloro-2-propyl) phosphate in zebrafish quantified by toxicokinetic model

Micro(nano)plastics (MNPs) inevitably interact with coexisting contaminants and can act as vectors to affect their fate in organisms. However, the quantitative contribution of MNPs in the in vivo bioaccumulation and distribution of their coexisting contaminants remains unclear. Here, by selecting tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) as the typical coexisting contaminant, we quantified the contribution of MNPs to bioaccumulation and distribution of TDCIPP with toxicokinetic models. Results indicated that MNPs differentially facilitated TDCIPP bioaccumulation and distribution, and NPs slowed down TDCIPP depuration more significantly than MPs. Model analysis further revealed increasing contributions of MNPs to whole-fish TDCIPP bioaccumulation over time, with NPs (33-42%) contributing more than MPs (12-32%) at 48 h exposure. NPs contributed more than MPs to TDCIPP distribution in the liver (13-19% for MPs; 36-52% for NPs) and carcass (24-45% for MPs; 57-71% for NPs). The size-dependent vector effect might be attributed to the fact that MNPs promote contaminant transfer by damaging biofilm structure and increasing tissue membrane permeability, with NPs exerting stronger effects. This work demonstrated the effectiveness of using modeling tools to understand the relative importance of MNPs as contaminant vectors in the TK process and highlighted the higher contaminant transfer potential of NPs under combined exposure scenarios.

A toxicokinetics approach using Enchytraeus crypticus to evaluate the efficiency of hydroxyapatite to remediate soils contaminated with rare earth elements

Extensive rare earth element (REE) mining activities pose threats to agricultural soils surrounding the mining areas. Here, low and high REE-contaminated soils from farmlands around mine tailings were remediated with hydroxyapatite. A toxicokinetic approach was applied to assess whether the use of hydroxyapatite reduced the bioavailability of REEs and thus inhibited their accumulation in the terrestrial organism Enchytraeus crypticus. Our results showed that addition of hydroxyapatite increased soil pH, DOC and anion contents. CaCl2-extractable REE concentrations significantly decreased, indicating the stabilization by hydroxyapatite. The influence of hydroxyapatite on the REE accumulation in enchytraeids was quantified by fitting a toxicokinetic model to dynamic REE body concentrations. The estimated uptake (Ku) and elimination rate constants (Ke), and bioaccumulation factor (BAF) for REEs were in the range of 0.000821 - 0.122 kgsoil/kgworm day-1, 0.0224 - 0.136 day-1, and 0.00135 - 1.96, respectively. Both Ku and BAF were significantly reduced by over 80% by hydroxyapatite addition, confirming the decreased REE bioavailability. Low atomic number REEs had higher BAFs in slightly contaminated soil, suggesting a higher bioaccumulation potential of light REEs in soil organisms. Overall, chemical stabilization with amendments can attenuate the bioavailability of REEs and reduce the potential ecological risk of contaminated agricultural soils near REE mining areas.

Community-facing toxicokineticmodels to estimate PFAS serum levels based on life history and drinking water exposures

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are drinking water contaminants. Tools to assess the potential body burden associated with drinking PFAS-contaminated water may be helpful for public health assessment of exposed communities.

METHODS

We implemented a suite of one-compartment toxicokinetic models using extensively calibrated toxicokinetic parameters (half-life and volume of distribution). We implemented the models both in the R programming language for research purposes, and as a web estimator for the general public (built in typescript.js). These models simulate exposure to PFAS water concentrations for individuals with varying characteristics such as age, sex, weight, and breastfeeding history. The models account for variability and uncertainty in parameter inputs to produce Monte Carlo-based estimates of serum concentration. For children, the models additionally account for gestational exposure, lactational exposure, and potential exposure through formula feeding. For adults who have borne children, the models account for clearance through birth and breastfeeding. We ran simulations of individuals with known PFAS water and serum concentrations to evaluate the model. We then compared the predicted serum PFAS concentrations to measured data.

RESULTS

The models accurately estimate individual-level serum levels for each PFAS for most adults within ½ order of magnitude. We found that the models somewhat overestimated serum concentrations for children in the tested locations, and that these overestimates are generally within an order of magnitude.

DISCUSSION

This paper presents scientifically robust models that allow users to estimate serum PFAS concentrations based on known PFAS water concentrations and physiologic information. However, accuracy in historical water concentration inputs, exposure from non-drinking water sources, and life-history characteristics of individuals present a complex problem for individual estimation. Additional refinements to the model suite to improve the prediction of individual results may consist of including duration of exposure and additional life-history characteristics.

Toxicokinetic analyses of naphthalene, fluorene, phenanthrene, and pyrene in humans after single oral administration

Polycyclic aromatic hydrocarbons (PAHs) are generated by incomplete combustion of organic matter. They have health effects in multiple organs and can cause lung, skin, and bladder cancers in humans. Although data regarding their toxicity is available, information on the absorption, distribution, metabolism, and excretion of PAHs in humans is very limited. In the present study, deuterium-labeled naphthalene (Nap), fluorene (Flu), phenanthrene (Phe), and pyrene (Pyr) were orally administered as a single dose (0.02-0.04 mg/kg) to eight healthy adults. Both serum and urine samples were monitored for 72 h after the exposure. Parent compounds and PAH metabolites (monohydroxy-PAHs; OH-PAHs) were measured by headspace-solid phase microextraction coupled with gas chromatography-mass spectrometry and high-performance liquid chromatography-tandem mass spectrometry, respectively. Based on the time-concentration profiles in serum and urine, non-compartmental analysis was performed, and two-compartment models were constructed and validated for each PAH. Subsequently, all of the parent compounds were rapidly absorbed (T_max: 0.25 to 1.50 h) after oral administration and excreted in urine with a biological half-life (T_1/2) of 1.01 to 2.99 h. The fractional urinary excretion (F_ue) of OH-PAHs ranged from 0.07 % to 11.3 %; their T_1/2 values ranged from 3.4 to 11.0 h. The two-compartment models successfully described the toxicokinetic characteristics of each PAH and its metabolites. F_ue and the two-compartment models could be useful tools for exposure simulation or dose-reconstruction of PAHs. The results of this study will provide useful information for interpreting biomonitoring data of PAHs.

Organ-specific accumulation of cadmium and zinc in Gammarus fossarum exposed to environmentally relevant metal concentrations

One of the best approaches for improving the assessment of metal toxicity in aquatic organisms is to study their organotropism (i.e., the distribution of metals among organs) through a dynamical approach (i.e., via kinetic experiments of metal bioaccumulation), to identify the tissues/organs that play a key role in metal regulation (e.g., storage or excretion). This study aims at comparing the organ-specific metal accumulation of a non-essential (Cd) and an essential metal (Zn), at their environmentally relevant exposure concentrations, in the gammarid Gammarus fossarum. Gammarids were exposed for 7 days to ¹⁰⁹Cd- or ⁶⁵Zn-radiolabeled water at a concentration of 52.1 and 416 ng.L^-1 (stable equivalent), respectively, and then placed in clean water for 21 days. At different time intervals, the target organs (i.e., caeca, cephalons, intestines, gills, and remaining tissues) were collected and ¹⁰⁹Cd or ⁶⁵Zn contents were quantified by gamma-spectrometry. A one-compartment toxicokinetic (TK) model was fitted by Bayesian inference to each organ/metal dataset in order to establish TK parameters. Our results indicate: i) a contrasting distribution pattern of concentrations at the end of the accumulation phase (7^th day): gills > caeca ≈ intestines > cephalons > remaining tissues for Cd and intestines > caeca > gills > cephalons > remaining tissues for Zn; ii) a slower elimination of Cd than of Zn by all organs, especially in the gills in which the Cd concentration remained constant during the 21-day depuration phase, whereas Zn concentrations decreased sharply in all organs after 24 h in the depuration phase; iii) a major role of intestines in the uptake of waterborne Cd and Zn at environmentally relevant concentrations.

Framework for risk assessment of PFAS utilizing experimental studies and in-silico models

Perfluoroalkyl substances (PFAS), especially PFOS and PFOA, are two widely used synthetic chemicals that can impact human health based on evidence from animal and epidemiologic studies. In this paper, we have reviewed and summarized the influence of PFAS exposure on health, pointing the quality of evidence, and applied translational techniques to integrate evidence for PFAS policy making. This is the first review where highly referred articles on PFAS used for policymaking by several regulatory agencies were collected and evaluated based on the review guidelines developed by the US National Toxicology Program's Office of Health Assessment and Translation (OHAT) review guidelines. Several limitations were observed, including co-exposure to multiple chemicals and limited measurement of primary and secondary outcomes related to specific toxicity. However, data from all the studies provided a moderate to strong level of confidence for link between PFAS exposure and different adverse outcomes. Secondly, for translating the risk to humans, an in-silico model and scaling approach was utilized. Physiologically based pharmacokinetic model (PBPK) was used to calculate the human equivalent dose (HED) from two widely accepted studies and compared with tolerable daily intakes (TDIs) established by various regulatory agencies. Inter-species dose extrapolation was done to compare with human the relevance of dosing scenarios used in animals. Overall, a framework for translation of risk was proposed based on the conclusions of this review with the goal of improving policymaking. The current paper can improve the methodological protocols for PFAS experimental studies and encourage the utilization of in-silico models for translating risk.

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.

The added value of Bayesian inference for estimating biotransformation rates of organic contaminants in aquatic invertebrates

Toxicokinetic (TK) models refer to the process of contaminant bioaccumulation as a balance between rate of uptake from different sources (e.g., water or food), and rate of elimination via different processes such as excretion, growth and/or biotransformation. Biotransformation can considerably modify the fate of chemicals in an organism, especially their bioavailability, residence time, and toxicity. Invertebrate models generally neglect this process as they assume a low metabolic activity. However, some species such as Gammarus sp. amphipods are able to metabolize a vast range of organic compounds. Some recent TK models include biotransformation, but they prove limited for estimating related parameters by giving negative values and/or large uncertainties for biotransformation rate(s). Here we propose a generic TK model accounting for biotransformation using a Bayesian framework for simultaneously estimating the parameters. We illustrated the added value of our method by fitting this generic TK model to 22 published datasets of several benthic invertebrate species exposed to different chemicals. All parameters are estimated simultaneously for all datasets and showed narrow estimates. Furthermore, the median model predictions and their 95% credibility intervals showed that the model confidently fitted the data. In most cases the uncertainties around biotransformation rate(s) were reduced in comparison to the original studies. From a methodology standpoint, this paper reflects that Bayesian inference has real added value for simultaneously estimating all TK parameters for parent chemicals and their metabolite(s) based on all available data, while accounting for different types of data and the correlation between parameters. Bayesian inference was able to overcome the limits of previous methods, since no parameters were fixed and no irrelevant negative values were obtained. Moreover, the 95% credibility intervals around model predictions, which are core uncertainties for Environmental Risk Assessment, were easily acquired.

A Bayesian framework for estimating parameters of a generic toxicokinetic model for the bioaccumulation of organic chemicals by benthic invertebrates: Proof of concept with PCB153 and two freshwater species

Toxicokinetic (TK) models are relevant and widely used to predict chemical concentrations in biological organisms. The importance of dietary uptake for aquatic invertebrates has been increasingly assessed in recent years. However, the model parameters are estimated on limited specific laboratory data sets that are bounded by several uncertainties. The aim of this study was to implement a Bayesian framework for simultaneously estimating the parameters of a generic TK model for benthic invertebrate species from all data collected. We illustrate our approach on the bioaccumulation of PCB153 by two species with different life traits and therefore exposure routes: Chironomus riparius larvae exposed to spiked sediment for 7 days and Gammarus fossarum exposed to spiked sediment and/or leaves for 7 days and then transferred to a clean media for 7 more days. The TK models assuming first-order kinetics were fitted to the data using Bayesian inference. The median model predictions and their 95% credibility intervals showed that the model fit the data well. From a methodological point of view, this paper illustrates that simultaneously estimating all model parameters from all available data by Bayesian inference, while considering the correlation between parameters and different types of data, is a real added value for TK modeling. Moreover, we demonstrated the ability of a generic TK model considering uptake and elimination routes as modules to add according to the availability of the data measured. From an ecotoxicological point of view, we show differences in PCB153 bioaccumulation between chironomids and gammarids, explained by the different life traits of these two organisms.

Association Among Sources Exposure of Cadmium in the Adult Non-smoking General Population of Tehran

Acute and chronic exposure to cadmium can cause numerous health effects including poisoning, as well as, bone, liver, and kidney diseases. Cadmium competes with iron absorption in blood and can induce anemia. Cadmium body burden can be measured through urine and blood samples. Urine reflects chronic and blood indicates recent and cumulative exposures to cadmium. Dietary is considered as the main source of exposure to cadmium in non-smoking general population. The study was conducted to determine cadmium level in blood, urine, and in diet of 120 non-smoking adults in Tehran. Dietary components and consumption pattern of participants estimated by a food frequency questionnaire. Next, the correlation investigated between them. Moreover, serum ferritin measured as a marker of iron storage in blood to determine its association with cadmium. The prediction of cadmium fate in the body is determined by toxicokinetic models. This study tried to evaluate one of these models' validity which is developed to predict urinary cadmium from dietary. Afterwards, the predicted urinary compared with the measured urinary cadmium. The correlation coefficient between dietary and blood cadmium equaled 0.66 which was statically significant, but the correlation between dietary and urinary cadmium was minimal and not statically significant (p > 0.05). An inverse and negative correlation was found between serum ferritin and blood cadmium. The mean predicted urinary cadmium calculated by the model was 2.5-fold higher than the measured value in the total population. Results of the present study revealed that blood cadmium reflected mainly acute exposure. There was no correlation between chronic and acute exposures to cadmium. The low serum ferritin level increased cadmium amount in blood. Moreover, the mean predicted urinary cadmium by the model was greater than the measured value. It can because of characteristics of populations and type of dietary exposure. Thus, it is suggested that the model coefficients are determined in each society based on their characteristics.

Dose reconstruction in workers exposed to two major pyrethroid pesticides and determination of biological reference values using a toxicokinetic model

A toxicokinetic model has been optimized to describe the time profiles of common biomarkers of exposure to permethrin and cypermethrin: trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acids (trans-DCCA) and 3-phenoxybenzoic acid (3-PBA). The model then served to reproduce urinary time courses in exposed agricultural workers and predict corresponding absorbed doses. It allowed for the prediction of the main routes of exposure in workers during the study period. Modeling showed that simulating exposure mostly by the oral route, during the 3-day biomonitoring period, provided best-fits to the urinary time courses of most workers. This is compatible with an inadvertent oral exposure during work. According to best-fit scenarios, absorbed doses in workers reconstructed with the model reached a maximum of 2.4 µg/kg bw/day and were below the absorbed dose limits associated with an exposure to the reference dose values established by the U.S. Environmental Protection Agency (0.06 and 0.25 mg/kg bw/day for cypermethrin and permethrin, respectively) and the Acceptable Operator Exposure Level set by the European Commission (0.06 mg/kg bw/day for cypermethrin). Modeling was further used to derive biological reference values for cypermethrin and permethrin exposure. Respective values of 7 and 29 nmol/kg bw/day of trans-DCCA, and 3 and 13 nmol/kg bw/day of 3-PBA were obtained. None of the workers presented values above these biological reference values.

Long-term time trends in human intake of POPs in the Czech Republic indicate a need for continuous monitoring

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) from the group of persistent organic pollutants are detected in human tissues years or even decades after their ban. Exposure to PCBs and OCPs can pose risks to human health. In the present study, we calculated the daily intakes of PCBs and OCPs in the Czech population and investigated the long-term trends of human exposure to POPs. Data on POP concentrations from a 16-year period of breast-milk monitoring were used. A toxicokinetic model with consideration of compound-specific elimination half-lives was used to calculate the mothers' daily intake of PCBs and OCPs representing the intake of POPs by all exposure routes. The calculated intakes were compared with dietary intakes calculated by the Czech National Institute of Public Health. The comparison shows good agreement of both intake estimates with decreasing intake trends of POPs in the Czech population in the time period studied. However, several fluctuations with peaks of higher levels were observed in both datasets which are not typical for the period after the ban of use and production of POPs. The available evidence suggests that the increases in chemical concentrations might be caused by food contamination. The calculated intakes of compounds with longer elimination half-lives, such as higher-chlorinated PCBs, were higher in older mothers. This "memory effect" was already observed in other studies and indicates higher exposure in earlier life periods of the mother. Our results suggest that exposure to POPs is still relevant for the Czech population in the period after the ban of the use and production of POPs (post-ban period), especially via food ingestion, though the intake trends are decreasing. Possible food contamination by POPs in the post-ban period requires further assessment.