Dermal uptake of 18 dilute aqueous chemicals: in vivo disappearance-method measures greatly exceed in vitro-based predictions

Estimation of multi-route exposures to various chemicals during Children's clay toy use

Clay toys have been used as play materials and educational tools for children. Clay toys exhibit adherent properties, and may facilitate chemical ingestion via dermal absorption and oral (hand-to-mouth, HTM) exposures. Inhalation exposure also be considered when contain volatile chemicals. The purpose of this study was to estimate the exposure dose for chemicals in clay toys via three exposure routes, and to evaluate the relationship between the exposure contribution of each route considering both the chemical properties and children's age. Chemical analysis was conducted for 9 semi-volatile organic compounds (SVOCs), 17 volatile organic compounds (VOCs), and 7 metal elements in clay toys (n = 66) purchased from Korean market. Exposure factors for usage pattern of clay toys were conducted based on a nationally representative survey in Korea. A total of 12,144 (60.7%) children responded positively to playing with clay toys. Exposure to SVOCs and VOCs in clay toys via HTM, inhalation, and dermal absorption were estimated. The exposure level was the highest in styrene with 5.2 × 10^-3 mg/kg-bw/day (95th percentile population), which was approximately 13% of the acceptable daily dose for styrene. In 3-year-old children, dermal absorption route contributed the highest at 59.2-100%. Chemicals with higher octanol-water partition coefficient (K_ow) had the greater the contribution of the dermal absorption route and the weaker the contribution of the HTM route. In infants (0-2 years), the contribution via HTM exposure was higher than that in the other age groups. The contribution of inhalation exposure differed depending on the volatility of the chemicals. Furthermore, the exposure route contribution significantly differed due to age-dependent behavioral changes in children. These results suggest that the exposure assessments for children could be considered with multiple exposure routes related to chemical properties.

A decision tree approach to screen drinking water contaminants for multiroute exposure potential in developing guideline values

The consideration of inhalation and dermal routes of exposures in developing guideline values for drinking water contaminants is important. However, there is no guidance for determining the eligibility of a drinking water contaminant for its multiroute exposure potential. The objective of the present study was to develop a 4-step framework to screen chemicals for their dermal and inhalation exposure potential in the process of developing guideline values. The proposed framework emphasizes the importance of considering basic physicochemical properties prior to detailed assessment of dermal and inhalation routes of exposure to drinking water contaminants in setting guideline values.

Reassessment of MTBE cancer potency considering modes of action for MTBE and its metabolites

A 1999 California state agency cancer potency (CP) evaluation of methyl tert-butyl ether (MTBE) assumed linear risk extrapolations from tumor data were plausible because of limited evidence that MTBE or its metabolites could damage DNA, and based such extrapolations on data from rat gavage and rat and mouse inhalation studies indicating elevated tumor rates in male rat kidney, male rat Leydig interstitial cells, and female rat leukemia/lymphomas. More recent data bearing on MTBE cancer potency include a rodent cancer bioassay of MTBE in drinking water; several new studies of MTBE genotoxicity; several similar evaluations of MTBE metabolites, formaldehyde, and tert-butyl alcohol or TBA; and updated evaluations of carcinogenic mode(s) of action (MOAs) of MTBE and MTBE metabolite's. The lymphoma/leukemia data used in the California assessment were recently declared unreliable by the U.S. Environmental Protection Agency (EPA). Updated characterizations of MTBE CP, and its uncertainty, are currently needed to address a variety of decision goals concerning historical and current MTBE contamination. To this end, an extensive review of data sets bearing on MTBE and metabolite genotoxicity, cytotoxicity, and tumorigenicity was applied to reassess MTBE CP and related uncertainty in view of MOA considerations. Adopting the traditional approach that cytotoxicity-driven cancer MOAs are inoperative at very low, non-cytotoxic dose levels, it was determined that MTBE most likely does not increase cancer risk unless chronic exposures induce target-tissue toxicity, including in sensitive individuals. However, the corresponding expected (or plausible upper bound) CP for MTBE conditional on a hypothetical linear (e.g., genotoxic) MOA was estimated to be ∼2 × 10(-5) (or 0.003) per mg MTBE per kg body weight per day for adults exposed chronically over a lifetime. Based on this conservative estimate of CP, if MTBE is carcinogenic to humans, it is among the weakest 10% of chemical carcinogens evaluated by EPA.

Dermal exposure from transfer of lubricants and fuels by consumers

Consumer uses of fuels and lubricants in Europe are subject to the Registration, Evaluation, Authorization and restriction of CHemicals (REACH) legislation. Ten volunteers completed a series of exposure situations to simulate filling a vehicle fuel tank with diesel (ES1 Diesel), adding lubricant to a car engine (two situations, one filling point easier to reach (ES2 Easy) than the other (ES3 Hard)) and lubricating a bicycle chain (ES4 Bike). Dermal exposure to the hands and forearms was assessed using a wipe sampling method. A high proportion of samples was less than the limit of detection (ES1=38%, ES3=60%, ES2 and 4, both 78%). In ES1 Diesel, dermal exposure to the hands and forearms ranged from <0.25 μg/cm(2) to 96.21 μg/cm(2). Significantly higher dermal exposure was observed when a lower level of care was taken to complete the task. In ES2 Easy and ES3 Hard, the hand and forearm results ranged from <0.1 μg/cm(2) to 3.33 μg/cm(2) and from <0.1 μg/cm(2) to 3.54 μg/cm(2), respectively. In ES4 Bike, the hand and forearm exposures ranged from <0.35 μg/cm(2) to 5.25 μg/cm(2). Not all volunteers fully complied with the ES4 instructions, thus highlighting that this situation may have more variability in consumer behaviour. The ratio of the amount measured on the hands and forearms to the amount of product handled for ES1 Diesel, ES2 Easy and ES3 Hard was less than 0.0001%, for ES4 Bike it was 0.04%. Mixed effect models showed that the between and within volunteer variations are small for all except ES1 Diesel, where the within volunteer variation was relatively large (likely due to the few high measurements). This study reports dermal exposure measurement data, which will be of value when updating REACH and other exposure assessments for these, and similar, petroleum products.

Dermal versus total uptake of benzene from mineral spirits solvent during parts washing

Quantitative approaches to assessing exposure to, and associated risk from, benzene in mineral spirits solvent (MSS), used widely in parts washing and degreasing operations, have focused primarily on the respiratory pathway. The dermal contribution to total benzene uptake from such operations remains uncertain because measuring in vivo experimental dermal uptake of this volatile human carcinogen is difficult. Unprotected dermal uptake involves simultaneous sustained immersion events and transient splash/wipe events, each yielding residues subject to evaporation as well as dermal uptake. A two-process dermal exposure framework to assess dermal uptake to normal and damaged skin was applied to estimate potential daily dermal benzene dose (Dskin ) to workers who used historical or current formulations of recycled MSS in manual parts washers. Measures of evaporation and absorption of MSS dermally applied to human subjects were modeled to estimate in vivo dermal uptake of benzene in MSS. Uncertainty and interindividual variability in Dskin was characterized by Monte Carlo simulation, conditioned on uncertainty and/or variability estimated for each model input. Dermal exposures are estimated to average 33% of total (inhalation + dermal) benzene parts washing dose, with approximately equal predicted portions of dermal dose due to splash/wipe and to continuous contact with MSS. The estimated median (95th percentile) dermal and total daily benzene doses from parts washing are: 0.0069 (0.024) and 0.025 (0.18) mg/day using current, and 0.027 (0.085) and 0.098 (0.69) mg/day using historical, MSS solvents, respectively.