Previous studies - primarily in high income countries - have shown that high prenatal temperatures are associated with adverse birth outcomes. However, these studies are mostly focused on average exposure across the full gestational period or short-term exposure immediately prior to delivery and may miss important sensitive windows of exposure in utero. Further, nearly all use ambient air temperature data, which neglect physiologically important interactions between air temperature and humidity. The Ghana Randomized Air Pollution and Health Study (GRAPHS) recruited pregnant individuals from 2013 to 2015 from communities in the Kintampo North Municipality and Kintampo South District of Ghana. We estimated daily maximum shaded wet bulb globe temperature (WBGTmax) and heat index (HImax) during pregnancy and examined associations with birth weight, birth length, head circumference, and incidence of low birth weight, preterm birth, and small for gestational age. Using linear regression analyses, trimester average models identified that higher WBGTmax in the first trimester was associated with larger head circumference; second trimester was associated with shorter birth length, lower birth weight and higher odds of preterm birth, and third trimester was associated with shorter gestational age and larger head circumference. Time-varying analyses using distributed lag nonlinear models find that, compared to the median, lower WBGTmax and HImax (25th percentile) during the first half of pregnancy was associated with higher birth weight and longer birth length. Compared to the median, lower WBGTmax and HImax (25th percentile) in the second half of pregnancy was associated with smaller head circumference while higher wet bulb globe temperature (75th percentile) was associated with larger head circumference. Overall, our study identified that higher WBGTmax and HImax are associated with pregnancy duration and newborn size. Given the overall trend in our study area of rising temperatures, these data suggest that adaptation strategies are urgently needed to protect child health.

Human endogenous retroviruses (HERVs) are transposable genomic elements generally repressed through DNA methylation. HERVs can be demethylated and expressed in response to environmental stimuli. Therefore, more research is needed to understand the influence of environmental exposures on HERV methylation. Air pollutants are commonly linked with global hypomethylation, and as HERVs comprise of nearly 8% of repetitive elements in the human genome, our objective was to examine the association between air pollutant exposure and HERV methylation. We investigated 180 students with asthma participating in the School Inner-City Asthma Intervention Study, which evaluated the efficacy of classroom air filters and school-wide pest management on air pollutant/allergen exposure and asthma. Both air pollutants measured in classrooms and asthma outcomes assessed by surveys were collected pre- and post-intervention. Buccal swabs were also collected pre- and post-intervention, and methylation levels from 9 transposable genomic elements (HERV-E, -FRD, -K, -L, -R, -W, -9, and HRES and LINE1) were measured. Adjusting for relevant covariates, the overall air pollutant mixture was cross-sectionally associated with higher HERV-W and lower HERV-L and LINE1 methylation. Coarse PM was cross-sectionally associated with higher HERV-K methylation and CO₂ with lower LINE1 methylation. These results suggest that exposure to air pollutants is associated with HERV-W and HERV-K hypermethylation and HERV-L and LINE1 hypomethylation in children with asthma. Future studies are needed to characterize the links between HERV methylation and possible adverse outcomes.

Diesel exhaust (DE) is a major traffic-related pollutant linked to adverse health outcomes, but existing methods for estimating indoor DE exposure fall short, as common surrogates like black carbon (BC), NOx, and PM2.5 are not sufficiently specific to diesel sources. 1-Nitropyrene (1-NP), a nitro-PAH preferentially formed during diesel combustion, has rarely been studied as an indoor exposure indicator. We measured 1-NP and isomeric nitro-PAHs (2-nitropyrene, 2-nitrofluoranthene) in indoor air and house dust from 40 homes in the eastern San Francisco Bay Area, CA, across two sampling events, alongside continuous indoor BC monitoring. We assessed 1-NP’s utility as a DE proxy using summary statistics, diagnostic nitro-PAH ratios, correlations with monitored pollutants, and single-predictor mixed-effects models relating 1-NP to spatial DE predictors. 1-NP was frequently detected in air (74%) and dust (97%), with median concentrations of 0.42 pg/m³ (IQR 0.32 - 0.54) and 340 pg/g (IQR 190 - 620), respectively. Air and dust 1-NP were moderately correlated (r=0.40, p = 0.02), as was BC with 1-NP (air r=0.38, dust r=0.47; p<0.01). Diagnostic ratios (2-NFl:1-NP <5) indicated dominant primary emission sources. Dust 1-NP showed numerous significant associations with spatial DE predictors, while air 1-NP showed fewer. Overall, 1-NP shows promise as a diesel-specific indoor exposure proxy integrating longer-term exposure and aligning with spatial DE predictors.