A review of models for near-field exposure pathways of chemicals in consumer products

Abstract

Exposure to chemicals in consumer products has been gaining increasing attention, with multiple studies showing that near-field exposures from products is high compared to far-field exposures. Regarding the numerous chemical-product combinations, there is a need for an overarching review of models able to quantify the multiple transfers of chemicals from products used near-field to humans. The present review therefore aims at an in-depth overview of modeling approaches for near-field chemical release and human exposure pathways associated with consumer products. It focuses on lower-tier, mechanistic models suitable for life cycle assessments (LCA), chemical alternative assessment (CAA) and high-throughput screening risk assessment (HTS). Chemicals in a product enter the near-field via a defined "compartment of entry", are transformed or transferred to adjacent compartments, and eventually end in a "human receptor compartment". We first focus on models of physical mass transfers from the product to 'near-field' compartments. For transfers of chemicals from article interior, adequate modeling of in-article diffusion and of partitioning between article surface and air/skin/food is key. Modeling volatilization and subsequent transfer to the outdoor is crucial for transfers of chemicals used in the inner space of appliances, on object surfaces or directly emitted to indoor air. For transfers from skin surface, models need to reflect the competition between dermal permeation, volatilization and fraction washed-off. We then focus on transfers from the 'near-field' to 'human' compartments, defined as respiratory tract, gastrointestinal tract and epidermis, for which good estimates of air concentrations, non-dietary ingestion parameters and skin permeation are essential, respectively. We critically characterize for each exposure pathway the ability of models to estimate near-field transfers and to best inform LCA, CAA and HTS, summarizing the main characteristics of the potentially best-suited models. This review identifies large knowledge gaps for several near-field pathways and suggests research needs and future directions.

Qualitative Approach to Comparative Exposure in Alternatives Assessment

“…Alternative assessments such as those on printed circuit boards conducted by the USEPA (2015) Design for the Environment program follow these same standard approaches. High-throughput data (e.g., the USEPA's Chemistry Dashboard; Williams et al 2017) and models (e.g., Huang et al 2016) are becoming more and more available to predict physicochemical properties when measured data are missing. Although some parameters may be measured, this is not feasible for all, in which case estimation is used (e.g., the molecular weight for substances of unknown or variable composition [UVCBs]).…”

“…No existing AA that addressed fundamental product design change was found to be adequate for a case study; thus, that aspect of the methodology has not been fully evaluated. Huang et al (2016) provide an overview of a wide range of potentially relevant pathways and modeling approaches for characterizing these pathways in an AA context. Finally, the focus of the present effort was to explore a qualitative comparative approach.…”

“…Although some parameters may be measured, this is not feasible for all, in which case estimation is used (e.g., the molecular weight for substances of unknown or variable composition [UVCBs]). High-throughput data (e.g., the USEPA's Chemistry Dashboard; Williams et al 2017) and models (e.g., Huang et al 2016) are becoming more and more available to predict physicochemical properties when measured data are missing.…”

“…Initial quantitative frameworks for exposure assessment are already available for application in AA (NRC 2014a;, but these need to be extended to different product exposure scenarios and respective exposure pathways that might become relevant as a function of assessed product exposure scenario. Huang et al (2016) provide an overview of a wide range of potentially relevant pathways and modeling approaches for characterizing these pathways in an AA context.…”

Evaluating the consumption of chemical products and articles as proxies for diffuse emissions to the environment

“…These studies employ either measured emission factors or models requiring chemical and/or article-specic parameters, including material-ambient phase diffusion and partitioning coefficients. [38][39][40][41][42] A more generic model based on molecular structure has been developed to predict emissions of additives from polymers (evaluated for two phthalates in vinyl-ooring). 43 High-throughput estimates of emissions from articles are hampered by the fact that information on service life is required and models for multiple layer products are lacking.…”