Surface mining and low birth weight in central appalachia.

BACKGROUND: Surface mining has become a significant method of coal mining in the Central Appalachian region of the eastern United States alongside the traditional underground mining. Concerns have been raised about the health effects of this surface mining, particularly mountaintop removal mining where coal is mined upon steep mountaintops by removing the mountaintop through clearcutting forests and explosives. METHODS: We used a control group design with a pretest and a posttest to assess the associations of surface mining in Central Appalachia with low birth weight and other adverse birth outcomes. The pretest period is 1977-1989, a period of low surface mining activity. We consider three posttest periods: 1990-1998, 1999-2011 and 2012-2017, with 1999-2011 as the primary analysis and the other periods as secondary analyses. Surface mining in Central Appalachia increased after 1989, partly resulting from the Clean Air Act Amendments of 1990 which made surface mining in Appalachia more financially attractive. For the primary analysis, we fit a logistic regression model of the primary outcome (low birth weight, <2500 g) on dummy variables for county and year; individual level maternal/infant covariates (maternal race, maternal age, infant sex and whether birth was a multiple birth); and the amount of surface mining during the year of the birth in the maternal county of residence. RESULTS: Our analysis sample consisted of 783,328 infants -- 482,284 infants born from 1977 to 2017 to women residing in substantial surface mining activity counties and 301,044 infants born from 1977 to 2017 to women residing in matched control counties. Compared to the pre-period of low surface mining from 1977 to 1989, for the primary analysis posttest period of 1999-2011, there was an estimated relative increase in low birth weight in surface mining counties compared to matched control counties that was not statistically significant (odds ratio for a 5 percentage point increase in area disturbed by surface mining: 1.07, 95% confidence interval (0.96, 1.20), p-value: .22). For the secondary analysis posttest period of 1990-1998, there was no increase (odds ratio: 0.91, 95% confidence interval: (0.74, 1.13), p-value: .41). For the secondary analysis posttest period of 2012-2017, there was a statistically significant relative increase (odds ratio: 1.28, 95% confidence interval: (1.08, 1.50), p-value: .004). Qualitatively similar results were found for the outcomes of very low birth weight, preterm birth and small-for-gestational age. CONCLUSIONS: We examined the hypothesis that surface mining activity in Central Appalachia contributes to low birth weight using an observational study. We found evidence in secondary analyses that surface mining was associated with low birth weight in the 2012-2017 time period and potentially beginning in the early to mid 2000's. Evidence for an association was not found prior to 2000. A potential explanation for this pattern of association is that surface mining caused an increase in low birth weight but its onset was delayed. Future research is needed to clarify the findings and if replicated, identify the mechanism necessary to mitigate the impacts of mining on adverse birth outcomes.