Impact of physical activity on ethoxy- and propoxypropanol human toxicokinetics in vivo

Abstract

Organic solvents such as propylene glycol ethers (PGEs) represents more than 20 different substances and are incorporated in thousands of commercial and professional products. Two PGEs commonly used in Europe and found mainly in cleaning and water-based paint products are propylene glycol ethyl ether (PGEE) and propylene glycol propyl ether (PGPE). Given their volatile properties, inhalation is the most common route of exposure. The aim of this study was to characterize human toxicokinetics following PGEE and PGPE inhalation exposure. The participants were exposed (4 h) at rest to a single PGE (between 15 and 35 ppm) under controlled conditions and blood, urine, and exhaled breath were collected. Our study shows that both PGEs were rapidly detected in blood (absorption rate: 0.01 µg/mL/h*ppm) and elimination was more important through urine (half-life: 1 h) than exhaled breath (half-life: 2 min). We also evaluated the impact of a moderate physical activity (30 min, 100 W) during exposure. A significant increase of blood absorption (absorption rate: 0.03 µg/mL/h*ppm) and internal dose (increase of 48%) was observed. Our results confirm that both PGEs are easily absorbed at rest and even faster with a moderate physical activity. The biomonitoring approach we have developed here allow the measurement of the "real" internal dose in workers handling these solvents. The existing occupational exposure limits do not consider workload, which may lead to their underestimation. Therefore, we recommend the use of biomonitoring for future studies and the consideration of physical workload for future exposure limits settings as an important parameter for risk assessment.

Keywords: Absorption; Activity; Chemical exposure; Elimination; Propylene glycol ethyl ether; Propylene glycol propyl ether.

Fig. 1

Exposure design for participants exposed to PGEE or PGPE vapors at rest (including three different air concentrations) and with physical activity

Fig. 2

External-internal exposure dose relationship curves in blood (µg(mL) over the time (minutes) following four hours inhalation exposure to PGEE or PGPE at rest. Each grey curve represents the data from one participant. Black curves are the average (± standard deviation) for all participants (n = 5). The large square represents the time in the exposure chamber. a PGEE concentrations in blood as a function of time for a 25 (●), 30 (▲) and a 35 (■) ppm exposure to PGEE vapors. b PGPE concentrations in blood as a function of time for a 15 (●), 20 (▲) and a 25 (■) ppm exposure to PGPE vapors

Fig. 3

External-internal exposure dose relationship curves in blood (µg(mL) over the time (minutes) following exposure at rest (■) or with physical activity (□). Each dotted line represents the data of one participant. Bold points are the average (± standard deviation) for all participants (n = 9). The large square represents the time in the exposure chamber (4 h). The grey rectangle represents the 30 min of physical activity. a Exposure sessions with 35 ppm of PGEE. b Exposure sessions with 25 ppm of PGPE

Fig. 4

External-internal exposure dose relationship curves in urine (µg/mL) and exhaled breath (ppm) over the time (minutes) following four hours inhalation exposure to PGEE or PGPE at rest. Each grey points represent the data for one participant. Black points are the average (± standard deviation) for all participants (n = 5). The large square represents the time in the exposure chamber. Urinary (a) or exhaled breath (c) PGEE concentrations as a function of time for a 25 (●), 30 (▲) and a 35 (■) ppm exposure to PGEE vapors. Urinary (b) or exhaled breath (d) PGPE concentrations as a function of time for a 15 (●), 20 (▲) and a 25 (■) ppm exposure to PGPE vapors