Flame Retardant Exposure in Vehicles Is Influenced by Use in Seat Foam and Temperature

Abstract

Flame retardants (FRs) are added to vehicles to meet flammability standards, such as US Federal Motor Vehicle Safety Standard FMVSS 302. However, an understanding of which FRs are being used, sources in the vehicle, and implications for human exposure is lacking. US participants (n = 101) owning a vehicle of model year 2015 or newer hung a silicone passive sampler on their rearview mirror for 7 days. Fifty-one of 101 participants collected a foam sample from a vehicle seat. Organophosphate esters (OPEs) were the most frequently detected FR class in the passive samplers. Among these, tris(1-chloro-isopropyl) phosphate (TCIPP) had a 99% detection frequency and was measured at levels ranging from 0.2 to 11,600 ng/g of sampler. TCIPP was also the dominant FR detected in the vehicle seat foam. Sampler FR concentrations were significantly correlated with average ambient temperature and were 2-5 times higher in the summer compared to winter. The presence of TCIPP in foam resulted in ∼4 times higher median air sampler concentrations in winter and ∼9 times higher in summer. These results suggest that FRs used in vehicle interiors, such as in seat foam, are a source of OPE exposure, which is increased in warmer temperatures.

Keywords: TCIPP; TCPP; flame retardant; flammability standards; human exposure; organophosphate ester; silicone passive sampler; vehicle; wristband.

Figure 1

Comparison of TCIPP levels (ng/g) among the three vehicle engine types (hybrid, gas, and electric) in both winter (n = 101) and summer (n = 54) silicone samplers. TCIPP levels are graphed on a logarithmic scale. A Kruskal–Wallis (p < 0.05) global test indicated significant differences by engine type. Statistical significance (p < 0.05) in post hoc nonparametric Wilcoxon Each Pairs Test indicated by orange bars with asterisk.

Figure 2

Concentrations (graphed on a log scale) of the four most abundant (>60% detection) OPEs detected in both winter and summer sampling periods, restricted to vehicles sampled during both seasons (n = 54). Box plots inside violin plots depict the 25th percentiles, medians, and 75th percentiles. Orange bars with an asterisk represent a significant difference (p < 0.001) between summer and winter values by Wilcoxon Signed Rank (paired) Test.

Figure 3

Plots of average ambient temperature (°C) vs log silicone sampler concentration (ng/g) for the four most detected compounds (a) TEP, (b) TIBP, (c) TNBP, and (d) TCIPP. Concentrations are log_10- transformed to better show the spread in the data and allow for overlay of linear model results. All data are displayed including winter (blue) and summer (orange) time points and imputed values for detections < MDL. β = exponentiated fixed effect coefficient generated from the mixed effect model (see Table S5). A significant relationship (p < 0.0001) between temperature and concentration was found for all four compounds, represented by the dashed lines.

Figure 4

TCIPP concentrations in silicone samplers (ng/g) in both winter (n = 51) and summer (n = 28) sampling periods from vehicles where a foam sample was provided. TCIPP concentrations are graphed on a logarithmic scale for clarity. Statistical significance (p < 0.05) in nonparametric Wilcoxon Rank Sum Test indicated by orange bars with asterisk.