Occurrence and fate of atmospheric short/medium chain chlorinated paraffins: Size distribution and inhalation exposure.

Chlorinated paraffins (CPs) are intricate industrial compounds synthesized through alkane chlorination. Researches on the size distribution of short-chain (SCCPs) and medium-chain chlorinated paraffins (MCCPs) in atmospheric particulate matter (PM) are limited. Here, we conducted a thorough investigation on the size-dependent distribution characteristics, deposition behavior in respiratory tract, and health risks associated with CPs in atmospheric PM. The concentration of SCCPs in atmospheric particulate matter (PM10) was much higher than MCCPs, with concentration ranges of 2.53-31.8 and 1.07-4.62 ng m-3, respectively. Concentrations of CPs increase with decreasing PM size, peaking at aerodynamic diameters (Dp) < 0.49 μm. Physicochemical properties influence the distribution of CP homologs in PM. Those with lower vapor pressure, higher octanol-air and octanol-water partition coefficients tended to accumulate in PM with larger geometric mean diameters. Most of the inhaled CPs in PM deposited in the upper airways, with a small amount in the trachea and alveolar regions. The estimated daily intakes values were highest when Dp < 0.49 μm. Particle size is an essential determinant for the deposition of inhaled CPs in PM and should be considered in health risk assessments.