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Background: Particulate matter (PM) has been documented to contribute to preterm delivery. However, few studies have investigated the relationships between individual constituents of fine PM (PM2.5 ) and preterm delivery, and factors that may modify their associations.Methods: In this study, we examined the associations between several prenatal exposure metrics to PM2.5 and 23 constituents of PM2.5 and preterm delivery in California from 2000 to 2006. In a retrospective cohort study including 231 637 births, we conducted logistic regression analyses adjusting for maternal, infant, temporal, geographic, and neighbourhood characteristics.Results: We observed increased risk for preterm delivery with full-gestational exposure for several PM2.5 constituents. Per interquartile range increase, ammonium (21.2%, 95% confidence interval (CI) 17.1, 25.4), nitrate (18.1%, 95% CI 14.9, 21.4) and bromine (16.7%, 95% CI 13.2, 20.3) had some of the largest increased risks. Alternatively, some PM2.5 constituents were inversely associated with preterm delivery, including chlorine (-8.2%, 95% CI -10.3, -6.0), sodium (-13.2%, 95% CI -15.2, -11.3), sodium ion (-11.9%, 95% CI -14.1, -9.6) and vanadium (-19.2%, 95% CI -25.3, -12.6). Greater associations between PM2.5 constituents and preterm delivery were observed for Blacks and Asians, older mothers, and those with some college education compared to their reference groups, as well as for births with gestational ages from 32 to 34 weeks.Conclusions: PM2.5 constituents ammonium, nitrate and bromine, often linked to traffic and biomass combustion, were most associated with increased risk of preterm delivery in California. Certain demographic subgroups may be particularly impacted. [ABSTRACT FROM AUTHOR]

Background While most research on temperature and mortality has focused on the elderly, little has concentrated on infants, who may also lack thermoregulatory responses to heat exposure. Methods We examined mean daily apparent temperature, a combination of temperature and humidity, and infant deaths in California during the warm season of May through October 1999 to 2011. Deaths from all causes and specifically from congenital malformations, sudden infant death syndrome, abnormal gestation duration, respiratory causes, and circulatory causes were considered in a time-stratified case-crossover analysis of 12 356 infant deaths. Results For all-cause mortality, excess risk was 4.4% (95% confidence interval −0.3, 9.2) per 5.6° C increase for average of same day and previous 3 days apparent temperature (lag 03). The associations for apparent temperature and both all-cause mortality and deaths caused by gestation duration were highest for Black infants (13.3%, 95% CI 0.6, 27.6 and 23.7%, 95% CI −3.3, 58.2, respectively), while White infants had elevated risk for deaths from respiratory causes (44.6%; −0.7, 110.5). We further observed differential effects for neonates (infants aged 28 days and under) and post-neonates (infants above 28 days and under 1 year), and coastal and non-coastal regions. These associations remained even after considering criteria air pollutants. Conclusions This study suggests that infants are a vulnerable subgroup to heat exposure. Further studies should be conducted with a sufficient number of cases of infant deaths in other locales. [ABSTRACT FROM AUTHOR]