Near and far field exposure to organic contaminants through multiple parallel exposure pathways, including consumer product use, as a complement to ToxCast

Abstract

Background A list of 229 concerning organic chemicals was selected by the United States Environmental Protection Agency to investigate exposure modeling to complement ToxCast high-throughput toxicology data. Chemicals often have multiple exposure pathways that must be consistently assessed. Aims We aim to identify the chemicals' parallel exposure pathways, determine population-scale exposure for each pathway, and compare their relative magnitudes. Methods Several US government databases are used to categorize chemicals into potential exposure pathways via their likely uses (e.g. personal care products, pesticides). For far field environmental exposure, we run available exposure and fate models (e.g., USEtox) to estimate intake fractions (iF) ([kg intake per kg applied per use]. Intake through pesticide residue is determined using the Dynamicrop model. Near field consumer product intake fractions characterize direct dermal intake and subsequent far field population exposures after product wash-off (e.g. cosmetics permeate the skin during use, and may contaminate drinking water after use). Results The 229 chemicals are split into 13 categories corresponding to combinations of possible exposure routes and subsequent near and far field iF. Among them, 14 are banned, 97 are agricultural and 47 are household pesticides, and 43 are in cosmetics. Many have multiple exposure pathways. For cosmetics, generally, exposure to environmental media amounts to iF ~10-6 [kg intake/ 1 daily application] versus iF ~10-1 [kg intake/ 1 daily application] through skin permeation during use. However, iF through environmental media are important if a cosmetic is mostly washed off during use, especially when the chemical partitions into drinking water and has a high bio concentration factor. Conclusions Chemical uses can be identified through existing databases and dominant exposure pathways may be estimated using available exposure and fate models. The results demonstrate the necessity of exploring parallel exposure multiple pathways to understand cumulative exposure.