Relative source allocation of TDI to drinking water for derivation of a criterion for chloroform: A Monte-Carlo and multi-exposure assessment

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.

Urinary levels of 1-hydroxypyrene and health risk assessment in children living in Mexican communities with a high risk of contamination by polycyclic aromatic hydrocarbons (PAHs)

Health complications have been associated with polycyclic aromatic hydrocarbons (PAHs) exposure, a widespread environmental pollutants family. Therefore, the objective of this investigation was to develop a probabilistic health risk evaluation (using Monte-Carlo simulation) in an infantile population living in areas with a high risk of pollution by PAHs (indoor wood combustion, brick kiln industry, municipal landfill, and low and high vehicular traffic) in Mexico. Urine samples were obtained from Mexican children (n = 135) and urinary 1-OHP concentrations (used as a PAHs biomarker) were quantified. Highest urinary 1-OHP concentrations were detected in children living in areas that use wood combustion as the principal indoor fuel (3.50 ± 0.95 µg/L). Nevertheless, estimated hazard quotients (HQ) lower than 1 were found in all assessed sites after Monte-Carlo analysis. Although HQ <1.0 (a toxic effect is not expected), more data are necessary to determine the real impact of PAHs exposure on children health status.

Assessment of indirect inhalation exposure to formaldehyde evaporated from water

Volatilization volumes and health risks associated with indirect inhalation exposure to formaldehyde evaporated from water have not been investigated quantitatively. We experimentally investigated formaldehyde volatility, compared with chloroform volatility, predicted formaldehyde inhalation exposure concentrations in Japanese bathrooms, and then re-evaluated drinking water quality standards. Although the Henry's law constant of formaldehyde is 1/10⁴ that of chloroform, with a 30-min exposure period, the formaldehyde non-equilibrium partition coefficient (K'_d) was 1/500th the chloroform value because of formaldehyde's faster volatilization rate. We used this ratio to estimate the cumulative probability distribution of formaldehyde concentrations in bathroom air. For a formaldehyde concentration in water of ≤2.6 mg/L-water (WHO tolerable concentration), the probability that the incremental formaldehyde concentration due to volatilization would exceed 100 μg/m³-air (WHO indoor air quality guideline) was low. However, major sources of formaldehyde in indoor air are building materials and furniture. We therefore calculated the allowable concentration in water by allocating a small percentage of the indoor air guideline value to indirect inhalation exposure via volatilization from tap water. With an allocation factor of 20% (10%), the allowable concentration was 0.52 (0.26) mg/L-water. These concentrations are similar to the Health Canada guideline concentration but they are 3-6 times the Japanese water quality standard.

Monte-Carlo and multi-exposure assessment for the derivation of criteria for disinfection byproducts and volatile organic compounds in drinking water: Allocation factors and liter-equivalents per day

The probability distributions of total potential doses of disinfection byproducts and volatile organic compounds via ingestion, inhalation, and dermal exposure were estimated with Monte Carlo simulations, after conducting physiologically based pharmacokinetic model simulations to takes into account the differences in availability between the three exposures. If the criterion that the 95th percentile estimate equals the TDI (tolerable daily intake) is regarded as protecting the majority of a population, the drinking water criteria would be 140 (trichloromethane), 66 (bromodichloromethane), 157 (dibromochloromethane), 203 (tribromomethane), 140 (dichloroacetic acid), 78 (trichloroacetic acid), 6.55 (trichloroethylene, TCE), and 22 μg/L (perchloroethylene). The TCE criterion was lower than the Japanese Drinking Water Quality Standard (10 μg/L). The latter would allow the intake of 20% of the population to exceed the TDI. Indirect inhalation via evaporation from water, especially in bathrooms, was the major route of exposure to compounds other than haloacetic acids (HAAs) and accounted for 1.2-9 liter-equivalents/day for the median-exposure subpopulation. The ingestion of food was a major indirect route of exposure to HAAs. Contributions of direct water intake were not very different for trihalomethanes (30-45% of TDIs) and HAAs (45-52% of TDIs).

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.