Are We Justified in Modeling Human Exposure to Chlorinated Paraffin Mixtures Using the Average Properties of Congeners and Homologues?

Concern over human exposure to chlorinated paraffin (CP)
mixtures
keeps increasing. The absence of a comprehensive understanding of
how human exposure varies with the physicochemical properties of CP
constituents has hindered the ability to determine at what level of
aggregation exposure to CPs should be assessed. We answer this question
by comparing exposure predicted with either a “complex”
method that utilizes isomer-specific properties or “simplified”
methods that rely on median properties of congener, homologue, or
short-/medium-/long-chain CP groups. Our results demonstrate the wide
range of physicochemical properties across CP mixtures and their dependence
on molecular structures. Assuming unit emissions in the environment,
these variances translate into an extensive disparity in whole-body
concentrations predicted for different isomers, spanning ∼11
orders of magnitude. CPs with 13–19 carbons and 6–10
chlorines exhibit the highest human exposure potential, primarily
owing to moderate to high hydrophobicity and slow environmental degradation
and biotransformation. Far-field exposure is dominant for most CP
constituents. Our study underscores that using average properties
of congener, homologue, or S/M/LCCP groups yields results that are
consistent with those derived from isomer-based modeling, thus offering
an efficient and practical framework for future risk assessments and
human exposure studies of CPs and other complex chemical mixtures.