Exposure to violence and socioeconomic deprivation in susceptibility to nitrogen dioxide on term infant birthweight in New York City.

Introduction: Air pollution has been associated with adverse birth outcomes, with variation by socioeconomic position (SEP). However, it remains unknown which aspects of lower SEP - comprised of myriad physical and psychosocial stressors - may best explain observed pollution susceptibilities. Building upon previous studies that estimated joint associations of air pollution and socioeconomic deprivation on term birth weight in New York City (NYC), this study seeks to identify specific social stressors underlying that relationship.

Methods: We examined records for 243,853 term births in NYC from 2007-2010. Residence-specific pregnancy-average NO₂ was estimated using NYC Community Air Survey (NYCCAS) and EPA regulatory data. Twenty-six community social stressor indicators were tested as modifiers of NO₂-birthweight associations in linear mixed-effects models, adjusting for particulate matter (PM_2.5), individual-level maternal characteristics, and other covariates. In sensitivity analyses, we also examined non-linear interactions between continuous NO₂ and census-tract level violence and deprivation terms.

Results: Consistent with previous work, a 1-IQR (6.2 ppb) increase in average prenatal NO₂ exposure was associated with a 12.6 (SE = 2.7)-gram decrease in term birthweight.We observed similar values in independent models for most stressors related to violent crime or SEP and significantly lower birthweights with higher stressor exposures. In models of effect modification, however, we found that - despite lower average birthweights in high-stressor communities - NO₂-birthweight associations were weaker in higher-stressor communities, particularly for violence-related stressors. For example, in the highest-quartile communities for assault, a 1-IQR increase in NO₂ exhibited a decrement of only 7.3 g, on average, compared to 16.9 g in the lowest-assault quartile (p = .01 trend across quartiles). Exposures to non-violent stressors were not significantly associated with lower birthweights, nor modified observed NO₂-birthweight associations.

Conclusions: We found significantly lower term-infant birthweights with higher NO₂ or community stressors. Counter to hypotheses, however, in communities with very high stressor exposures (esp. violent crimes), despite lower overall birthweights, associations for NO₂ were weaker than in low-stressor communities. Our results suggest a possible saturation effect in stress-pollution interactions, wherein very high stressor exposures appear to overwhelm any effects of pollution. In addition, we observed stronger effects for violent crimes, in relation to other social stressors.