Sulfur dioxide reduction at coal-fired power plants in North Carolina and associations with preterm birth among surrounding residents

Abstract

Coal-fired power plants (CFPP) are major contributors of air pollution, including the majority of anthropogenic sulfur dioxide (SO₂) emissions, which have been associated with preterm birth (PTB). To address a 2002 North Carolina (NC) policy, 14 of the largest NC CFPPs either installed desulfurization equipment (scrubbers) or retired coal units, resulting in substantial reductions of SO₂ air emissions. We investigated whether SO₂ air emission reduction strategies at CFPPs in NC were associated with changes in prevalence of PTB in nearby communities.

Methods: We used US EPA Air Markets Program Data to track SO₂ emissions and determine the implementation dates of intervention at CFPPs and geocoded 2003-2015 NC singleton live births. We conducted a difference-in-difference analysis to estimate change in PTB associated with change in SO₂ reduction strategies for populations living 0-<4 and 4-<10 miles from CFPPs pre- and postintervention, with a comparison of those living 10-<15 miles from CFPPs.

Results: With the spatial-temporal exposure restrictions applied, 42,231 and 41,218 births were within 15 miles of CFPP-scrubbers and CFPP-retired groups, respectively. For residents within 4-<10 miles from a CFPP, we estimated that the absolute prevalence of PTB decreased by -1.5% [95% confidence interval (CI): -2.6, -0.4] associated with scrubber installation and -0.5% (95% CI: -1.6, 0.6) associated with the retirement of coal units at CFPPs. Our findings were imprecise and generally null-to-positive among those living within 0-<4 miles regardless of the intervention type.

Conclusions: Results suggest a reduction of PTB among residents 4-<10 miles of the CFPPs that installed scrubbers.

Figure 1.

Location of the 14 North Carolina coal-fired power plants included in this study characterized by their 2003 capacity, intervention strategy, and operating status as of 31 December 2015. CFPP indicates coal-fired power plant; MW, megawatt; NG, natural gas.

Figure 2.

Monthly SO₂ emissions reported by 14 coal-fired power plants in North Carolina (2002–2015). A, Summed monthly SO₂ emissions grouped by CFPP-scrubber and CFPP-retired. B, CFPP-scrubber (left) and CFPP-retired (right) monthly SO₂ emissions grouped by 1-year LMP exposure window pre- and postintervention. (Data source: US EPA’s AMPD.) CFPP indicates coal-fired power plant; LMP, last menstrual period; SO2, sulfur dioxide.

Figure 3.

Mean difference and 95% confidence intervals in the proportion of preterm birth by distance in miles from coal-fired power plants. Mean difference = postintervention minus preintervention. A) CFPP-scrubber cohort. B) CFPP-retired cohort. C) CFPP-all cohort. *For <1 mile from CFPP-all and CFPP-scrubber, the 95% CIs extend past the shown y axis due to small numbers of observations (−9.4 to 11.3 and −15.3 to 12.4, respectively). For <1 mile from CFPP-retired, the mean difference and 95% CI could not be calculated because no cases of PTB occurred within that distance. CFPP indicates coal-fired power plant; PTB, preterm birth; 95% CI, 95% confidence interval.

Figure 4.

Absolute difference in proportions of preterm birth pre-intervention versus post-intervention to reduce sulfur dioxide emissions at coal-fired power plants in North Carolina. Overall results: A, D, G. Stratified by early and moderate-to-late PTB: B, E, H. Stratified by gestational parent race/ethnicity: C, F, I. Top row (A–C) shows CFPP-scrubber cohort results. Middle row (D–F) shows CFPP-retired cohort results. Bottom row (G–I) shows CFPP-all cohort results. No results provided for Asian, nH in (F) and (I) because models did not converge. Distance categories are 0 miles to less than 4 miles (circles) and 4 miles to less than 10 miles (triangles), compared with 10 miles to less than 15 miles. CFPP indicates coal-fired power plant; DiD, difference-in-differences; nH, non-Hispanic; 95% CI, 95% confidence interval.