Risk assessment for humans using physiologically based pharmacokinetic model of diethyl phthalate and its major metabolite, monoethyl phthalate.

Diethyl phthalate (DEP) belongs to phthalates with short alkyl chains. It is a substance frequently used to make various products. Thus, humans are widely exposed to DEP from the surrounding environment such as food, soil, air, and water. As previously reported in many studies, DEP is an endocrine disruptor with reproductive toxicity. Monoethyl phthalate (MEP), a major metabolite of DEP in vivo, is a biomarker for DEP exposure assessment. It is also an endocrine disruptor with reproductive toxicity, similar to DEP. However, toxicokinetic studies on both MEP and DEP have not been reported in detail yet. Therefore, the objective of this study was to evaluate and develop physiologically based pharmacokinetic (PBPK) model for both DEP and MEP in rats and extend this to human risk assessment based on human exposure. This study was conducted in vivo after intravenous or oral administration of DEP into female (2 mg/kg dose) and male (0.1-10 mg/kg dose) rats. Biological samples consisted of urine, plasma, and 11 different tissues. These samples were analyzed using UPLC-ESI-MS/MS method. For DEP, the tissue to plasma partition coefficient was the highest in the kidney, followed by that in the liver. For MEP, the tissue to plasma partition coefficient was the highest in the liver. It was less than unity in all other tissues. Plasma, urine, and fecal samples were also obtained after IV administration of MEP (10 mg/kg dose) to male rats. All results were reflected in a model developed in this study, including in vivo conversion from DEP to MEP. Predicted concentrations of DEP and MEP in rat urine, plasma, and tissue samples using the developed PBPK model fitted well with observed values. We then extrapolated the PBPK model in rats to a human PBPK model of DEP and MEP based on human physiological parameters. Reference dose of 0.63 mg/kg/day (or 0.18 mg/kg/day) for DEP and external doses of 0.246 µg/kg/day (pregnant), 0.193 µg/kg/day (fetus), 1.005-1.253 µg/kg/day (adults), 0.356-0.376 µg/kg/day (adolescents), and 0.595-0.603 µg/kg/day (children) for DEP for human risk assessment were estimated using Korean biomonitoring values. Our study provides valuable insight into human health risk assessment regarding DEP exposure.

Multi-pathway human exposure assessment of phthalate esters and DINCH.

Phthalate esters are substances mainly used as plasticizers in various applications. Some have been restricted and phased out due to their adverse health effects and ubiquitous presence, leading to the introduction of alternative plasticizers, such as DINCH. Using a comprehensive dataset from a Norwegian study population, human exposure to DMP, DEP, DnBP, DiBP, BBzP, DEHP, DINP, DIDP, DPHP and DINCH was assessed by measuring their presence in external exposure media, allowing an estimation of the total intake, as well as the relative importance of different uptake pathways. Intake via different uptake routes, in particular inhalation, dermal absorption, and oral uptake was estimated and total intake based on all uptake pathways was compared to the calculated intake from biomonitoring data. Hand wipe results were used to determine dermal uptake and compared to other exposure sources such as air, dust and personal care products. Results showed that the calculated total intakes were similar, but slightly higher than those based on biomonitoring methods by 1.1 to 3 times (median), indicating a good understanding of important uptake pathways. The relative importance of different uptake pathways was comparable to other studies, where inhalation was important for lower molecular weight phthalates, and negligible for the higher molecular weight phthalates and DINCH. Dietary intake was the predominant exposure route for all analyzed substances. Dermal uptake based on hand wipes was much lower (median up to 2000 times) than the total dermal uptake via air, dust and personal care products. Still, dermal uptake is not a well-studied exposure pathway and several research gaps (e.g. absorption fractions) remain. Based on calculated intakes, the exposure for the Norwegian participants to the phthalates and DINCH was lower than health based limit values. Nevertheless, exposure to alternative plasticizers, such as DPHP and DINCH, is expected to increase in the future and continuous monitoring is required.

A margin of exposure approach to assessment of non-cancerous risk of diethyl phthalate based on human exposure from bottled water consumption.

Phthalates may be present in food due to their widespread presence as environmental contaminants or due to migration from food contact materials. Exposure to phthalates is considered to be potentially harmful to human health as well. Therefore, determining the main source of exposure is an important issue. So, the purpose of this study was (1) to measure the release of diethyl phthalate (DEP) in bottled water consumed in common storage conditions specially low temperature and freezing conditions; (2) to evaluate the intake of DEP from polyethylene terephthalate (PET) bottled water and health risk assessment; and (3) to assess the contribution of the bottled water to the DEP intake against the tolerable daily intake (TDI) values. DEP migration was investigated in six brands of PET-bottled water under different storage conditions room temperature, refrigerator temperature, freezing conditions (40 °C ,0 °C and -18 °C) and outdoor] at various time intervals by magnetic solid extraction (MSPE) using gas chromatography-mass spectroscopy (GC-MS). Eventually, a health risk assessment was conducted and the margin of exposure (MOE) was calculated. The results indicate that contact time with packaging and storage temperatures caused DEP to be released into water from PET bottles. But, when comprising the DEP concentration with initial level, the results demonstrated that the release of phthalates were not substantial in all storage conditions especially at low temperatures (<25 °C) and freezing conditions. The daily intake of DEP from bottled water was much lower than the reference value. However, the lowest MOE was estimated for high water consumers (preschooler > children > lactating women > teenagers > adults > pregnant women), but in all target groups, the MOE was much higher than 1000, thus, low risk is implied. Consequently, PET-bottled water is not a major source of human exposure to DEP and from this perspective is safe for consumption.

Identification of Drosophila-based endpoints for the assessment and understanding of xenobiotic-mediated male reproductive adversities.

Men are at risk of becoming completely infertile due to innumerable environmental chemicals and pollutants. These xenobiotics, hence, should be tested for their potential adverse effects on male fertility. However, the testing load, a monumental challenge for employing conventional animal models, compels the pursuit of alternative models. Towards this direction, we show here that Drosophila melanogaster, an invertebrate, with its well characterized/conserved male reproductive processes/proteome, recapitulates male reproductive toxicity phenotypes observed in mammals when exposed to a known reproductive toxicant, dibutyl phthalate (DBP). Analogous to mammals, exposure to DBP reduced fertility, sperm counts, seminal proteins, increased oxidative modification/damage in reproductive tract proteins and altered the activity of a hormone receptor (estrogen related receptor) in Drosophila males. In addition, we show here that DBP is metabolized to monobutyl phthalate (MBP) in exposed Drosophila males and that MBP is more toxic than DBP, as observed in higher organisms. These findings suggest Drosophila as a potential alternative to traditional animal models for the prescreening of chemicals for their reproductive adversities and also to gain mechanistic insights into chemical-mediated endocrine disruption and male infertility.

Pharmacokinetics of di-isononyl phthalate in freely moving rats by UPLC-MS/MS.

Di-isononyl phthalate (DINP) is a general-purpose plasticizer for polyvinyl chloride. However, this industrial chemical plasticizer used as a clouding agent has recently contaminated food and beverages that had been inspected by Taiwan Food and Drug Administration. This study develops a sensitive and specific method combining ultra-performance liquid chromatography with electrospray ionization tandem mass spectrometry (UPLC-MS/MS) to investigate the pharmacokinetics of DINP in freely moving rats. Multiple reaction monitoring (MRM) was used to monitor the transition of the protonated molecule m/z of 419 [M+H](+) to the product ion 149 for DINP. The analyte was analyzed by UPLC-MS/MS with C18 column (100×2.1mm, 1.7 µm) which was equilibrated and eluted with an isocratic mixture of acetonitrile-ammonium acetate water solution (90:10, v/v) at a flow rate of 0.3 mL/min. Linear calibration curves were obtained for DINP concentration ranges of 0.05-2.5 µg/mL in plasma and feces. The feces were homogenized mechanically using 50% acetonitrile as the medium. The pharmacokinetic curve demonstrates that the disposition of DINP in rat plasma was fitted well by the two-compartment model after DINP administration (10 mg/kg, i.v.). The elimination half-life of DINP was 364±146 min and 150±58 min for intravenous (10 mg/kg) and oral (100 mg/kg) administration, respectively. The pharmacokinetic data indicate that the oral bioavailability of DINP in freely moving rats was about 1.19%. The total DINP excretion up to 48 h was 13.64±3.99% in feces.

Exposure assessment of phthalates in French pregnant women: results of the ELFE pilot study.

The ubiquitous use of phthalate esters in plastics, building material, medical devices, personal care products and food packaging materials results in a widespread exposure of general population. This study reports measurement of urinary concentration of phthalate metabolites in France and provides a first assessment of the exposure of French pregnant women to this chemical class. For the majority of the phthalate metabolites, concentrations measured in urine were similar to those reported in previous studies except for two phthalates that were characterized by high concentrations of metabolites if compared to previous European and American studies: DiNP (Di-iso-nonylphthalate) and DEHP (Di(2-ethylhexyl)phthalate). In a second part of the study, a pharmacokinetic model was used in order to gain understanding on exposure to DEHP. A high concentration of the primary metabolite of DEHP, MEHP (Mono(2-ethylhexyl)phthalate), was thus identified probably because of a very recent exposure to perfusion materials at the hospital. Pharmacokinetics modelling highlighted that gathering data on the time gap between exposure and biomonitoring is an essential information requirement for reconstructing the dose of non persistent pollutants. Information about exposure pathway is also crucial for conducting effective reverse dosimetry.

Policy relevant results from an expert elicitation on the health risks of phthalates.

BACKGROUND: The EU 6th Framework Program (FP)-funded Health and Environment Network (HENVINET) aimed to support informed policy making by facilitating the availability of relevant knowledge on different environmental health issues. An approach was developed by which scientific agreement, disagreement, and knowledge gaps could be efficiently identified, and expert advice prepared in a way that is usable for policy makers. There were two aims of the project: 1) to apply the tool to a relevant issue; the potential health impacts of the widely used plasticizers, phthalates, and 2) to evaluate the method and the tool by asking both scientific experts and the target audience, namely policy makers and stakeholders, for their opinions. METHODS: The tool consisted of an expert consultation in several steps on the issue of phthalates in environmental health. A diagram depicting the cause-effect chain, from the production and use of phthalates to potential health impacts, was prepared based on existing reviews. This was used as a basis for an online questionnaire, through which experts in the field were consulted. The results of this first round of consultation laid the foundation for a new questionnaire answered by an expert panel that, subsequently, also discussed approaches and results in a workshop. One major task of the expert panel was to pinpoint priorities from the cause-effect chain according to their impact on the extent of potential health risks and their relevance for reducing uncertainty. The results were condensed into a policy brief that was sent to policy makers and stakeholders for their evaluation. RESULTS: The experts agreed about the substantial knowledge gaps within the field of phthalates. The top three priorities for further research and policy action were: 1) intrauterine exposure, 2) reproductive toxicology, and 3) exposure from medical devices. Although not all relevant information from the cause-effect chain is known for phthalates, most experts thought that there are enough indications to justify a precautionary approach and to restrict their general use. Although some of the experts expressed some scepticism about such a tool, most felt that important issues were highlighted. CONCLUSIONS: The approach used was an efficient way at summarising priority knowledge gaps as a starting point for health risk assessment of compounds, based on their relevance for the risk assessment outcome. We conclude that this approach is useful for supporting policy makers with state-of-the-art scientific knowledge weighed by experts. The method can assist future evidence-based policy making.

Toxicological review and oral risk assessment of terephthalic acid (TPA) and its esters: A category approach.

Polyethylene terephthalate, a copolymer of terephthalic acid (TPA) or dimethyl terephthalate (DMT) with ethylene glycol, has food, beverage, and drinking water contact applications. Di-2-ethylhexyl terephthalate (DEHT) is a plasticizer in food and drinking water contact materials. Oral reference doses (RfDs) and total allowable concentrations (TACs) in drinking water were derived for TPA, DMT, and DEHT. Category RfD and TAC levels were also established for nine C(1)-C(8) terephthalate esters. The mode of action of TPA, and of DMT, which is metabolized to TPA, involves urinary acidosis, altered electrolyte elimination and hypercalciuria, urinary supersaturation with calcium terephthalate or calcium hydrogen terephthalate, and crystallization into bladder calculi. Weanling rats were more sensitive to calculus formation than dams. Calculi-induced irritation led to bladder hyperplasia and tumors in rats fed 1000 mg/kg-day TPA. The lack of effects at 142 mg/kg-day supports a threshold for urine saturation with calcium terephthalate, a key event for calculus formation. Chronic dietary DMT exposure in rodents caused kidney inflammation, but not calculi. Chronic dietary DEHT exposure caused general toxicity unrelated to calculi, although urine pH was reduced suggesting the TPA metabolite was biologically-active, but of insufficient concentration to induce calculi. Respective oral reference doses of 0.5, 0.5, and 0.2 mg/kg-day and total allowable drinking water concentrations of 3, 3, and 1 mg/L were derived for TPA, DMT, and DEHT. An oral RfD of 0.2 mg/kg-day for the terephthalate category chemicals corresponded to a drinking water TAC of 1 mg/L.

Challenges in the application of quantitative approaches in risk assessment: a case study with di-(2-ethylhexyl)phthalate.

The constantly evolving science of risk assessment is currently faced with many challenges, not only from the interpretation of the volume of data being generated with new innovative technologies, but also in attempting to quantitatively incorporate this information into understanding potential risk of adverse events in human populations. The objective of the case study described was to use the more recent data for di-(2-ethylhexyl)phthalate (DEHP) to investigate the impact of innovative quantitative approaches on the risk assessment of a compound, specifically as it can be used to move towards the new vision of risk assessment involving the integration of the available toxicological data to understand underlying biological processes. What emerged were several outcomes that demonstrated clearly the importance of the integration of the toxicological data, specifically to understand the biological processes being impacted, because standard statistical modeling approaches may not be adequate to describe the dose-response relationships observed. Alternative approaches demonstrate that a definitive mode of action is not needed to justify the shape of the low-dose region or a threshold, when the integration of the available data assist risk assessors in understanding the shape of the dose-response curve for both noncancer and cancer endpoints. Many of the challenges described as part of this case study would likely be encountered with compounds other than DEHP, especially other receptor-mediated compounds or compounds that "perturb" biological pathways, such as endocrine disruptors. This case study also highlights the importance of communication between risk assessors and the research community to focus on the generation of data most relevant for assessing the potential for chemicals to impact biological systems in the human.

Factors affecting the evaluation of biomonitoring data for human exposure assessment.

Measuring trace levels of multiple environmental chemicals in biological tissues (i.e., biomonitoring) with a high degree of accuracy and precision is possible thanks to sophisticated analytical chemistry techniques and highly trained laboratory personnel. Selection and validation of biomarkers of exposure are critical. We present examples of the use of biomonitoring in exposure assessment for non-persistent chemicals using phthalates as model compounds. We also discuss several factors relevant to interpreting and understanding biomonitoring data, including the impact of metabolism of the chemicals and matrix composition in the selection of biomarkers of exposure, as well as temporal stability considerations that may affect the biomarkers' concentrations.

Estimated exposure to phthalates in cosmetics and risk assessment.

Some phthalates such as di(2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate (DBP) and their metabolites are suspected of producing teratogenic or endocrine-disrupting effects. To predict possible human exposure to phthalates in cosmetics, the levels of DEHP, diethyl phthalate (DEP), DBP, and butylbenzyl phthalate (BBP) were determined by high-performance liquid chromatography (HPLC) in 102 branded hair sprays, perfumes, deodorants, and nail polishes. DBP was detected in 19 of the 21 nail polishes and in 11 of the 42 perfumes, and DEP was detected in 24 of the 42 perfumes and 2 of the 8 deodorants. Median exposure levels to phthalates in cosmetics by dermal absorption were estimated to be 0.0006 g/kg body weight (bw)/d for DEHP, 0.6 g/kg bw/d for DEP, and 0.103 g/kg bw/d for DBP. Furthermore, if phthalates in cosmetics were assumed to be absorbed exclusively via 100% inhalation, the median daily exposure levels to phthalates in cosmetics were estimated to be 0.026 g/kg bw/d for DEHP, 81.471 g/kg bw/d for DEP, and 22.917 g/kg bw/d for DBP, which are far lower than the regulation levels set buy the Scientific Committee on Toxicity, Ecotoxicity, and the Environment (CSTEE) (37 g/kg bw/d, DEHP), Agency for Toxic Substances and Disease Registry (ATSDR) (7000 g/kg bw/d, DEP), and International Programme on Chemical Safety (IPCS) (66 g/kg bw/d, DBP), respectively. Based on these data, hazard indices (HI, daily exposure level/regulation level) were calculated to be 0.0007 for DEHP, 0.012 for DEP, and 0.347 for DBP. These data suggest that estimated exposure to-phthalates in the cosmetics mentioned are relatively small. However, total exposure levels from several sources may be greater and require further investigation.

Mono(2-ethyl-5-hydroxyhexyl) phthalate and mono-(2-ethyl-5-oxohexyl) phthalate as biomarkers for human exposure assessment to di-(2-ethylhexyl) phthalate.

Exposure to di-(2-ethylhexyl) phthalate (DEHP) is prevalent based on the measurement of its hydrolytic metabolite mono-(2-ethylhexyl) phthalate (MEHP) in the urine of 78% of the general U.S. population studied in the 1999-2000 National Health and Nutrition Examination Survey (NHANES). However, despite the high level of production and use of DEHP, the urinary MEHP levels in the NHANES samples were lower than the monoester metabolites of phthalates less commonly used than DEHP, suggesting metabolic differences between phthalates. We measured MEHP and two oxidative DEHP metabolites, mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) and mono (2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) to verify whether these other metabolites account for a greater proportion of DEHP metabolic products in 127 paired human urine and serum samples. We found that the urinary levels of MEHHP and MEOHP were 10-fold higher than levels of MEHP; concentrations of urinary MEOHP and MEHHP were strongly correlated (r = 0.928). We also found that the serum levels of MEOHP and MEHHP were comparatively lower than those in urine. Furthermore, the glucuronide-bound conjugates of the oxidative metabolites were the predominant form in both urine and serum. MEOHP and MEHHP cannot be formed by serum enzymes from the hydrolysis of any contamination from DEHP potentially introduced during blood collection and storage. Therefore, concentrations of MEHHP and MEOHP in serum may be a more selective measure of DEHP exposure than is MEHP. However, additional data on the absorption, distribution, metabolism, and elimination of these oxidative metabolites are needed to completely understand the extent of DEHP exposure from the serum concentrations of oxidative DEHP metabolites.