Prenatal exposure to fine particles and polycyclic aromatic hydrocarbons and birth outcomes: a two-pollutant approach

BACKGROUND Previous epidemiologic studies have considered the effects of individual air pollutants on birth outcomes, whereas a multiple-pollutant approach is more relevant to public health policy. OBJECTIVES The present study compared the observed effect sizes of prenatal fine particulate matter (PM2.5) and polycyclic aromatic hydrocarbons (PAH) (a component of PM2.5) exposures on birth outcome deficits, assessed by the single vs. two-pollutant approaches. METHODS The study sample included 455 term infants born in Krakow to non-smoking mothers, among whom personal exposures to PM2.5 and PAH were monitored in the second trimester of pregnancy. The exposure effect estimates (unstandardized and standardized regression coefficients) on birth outcomes were determined using multivariable linear regression models, accounting for relevant covariates. RESULTS In the single-pollutant approach, each pollutant was inversely associated with all birth outcomes. The effect size of prenatal PAH exposure on birth weight and length was twice that of PM2.5, in terms of standardized coefficients. In the two-pollutant approach, the negative effect of PM2.5 on birth weight and length, adjusted for PAH exposure, lost its significance. The standardized effect of PAH on birth weight was 10-fold stronger (β = -0.20, p = 0.004) than that estimated for PM2.5 (β = -0.02, p = 0.757). CONCLUSION The results provide evidence that PAH had a greater impact on several measures of fetal development, especially birth weight, than PM2.5. Though in the single-pollutant models PM2.5 had a significant impact on birth outcomes, this effect appears to be mediated by PAH.