The Effect of an Increase in Lead in the Water System on Fertility and Birth Outcomes: The Case of Flint, Michigan
Discussant: Ludovica Gazze
Our results suggest that women in Flint following the water change had a general fertility rate (GFR) of approximately 7.5 fewer births/1,000 women 15-49 (a 12% decrease). The ratio of male to female live births decreases by 0.9 percentage points in Flint. We also use synthetic control methods (Abadie and Gardeazabal 2003). The average treatment effect in Flint is comparable (-5.9 live births/1,000 women) and greater than the average treatment effect for all other cities (p-value of 0.07).
This result of a decrease in the fertility rate is plausible given the broader literature. Edwards (2014) studies an increase in lead in drinking water in Washington, D.C. in the early 2000s, and using somewhat different methods finds a 12% decrease in the fertility rate, identical to our result.
The GFR drop suggests that 198-276 more children would have been born had Flint switched water sources. Our results also suggest that in Flint following the change in water supply, an additional 18 female infants were born.
We also untangle scarring and selection (as in Bozzoli et al. 2009). We assume that the pre-water change birthweight distibriution in Flint is normally distributed and that the 12% reduction came from the left tail of the birthweight distribution, as birthweight is often thought of as a proxy for infant health. Using the formula for the mean of a truncated normal, we calculate the birthweight of the surviving newborns, without any scarring and compare it to the observed mean in Flint in the post period. Removing the pre-post difference in the rest of Michigan results in a 4.9 percent decrease.
Michigan State University recently received a large grant to create a voluntary registry of affected individuals. It is possible that many residents who miscarried during the water switch do not realize that exposure increased their risk of these outcomes. Therefore, this work may inform citizens that they should sign up for this registry as they were more affected by the water switch than they may have previously realized.
This study is of great importance as the current legislative environment includes calls for a substantial decrease in funding for the EPA. Our results suggest that a more lax regulatory environment in the context of drinking water may have substantial unforeseen effects on maternal and infant health, including large reductions in the number of births.
References:
Abadie, A and J Gardeazabal. 2003. The Economic Costs of Conflict: A Case Study of the Basque Country. AER, 93(1): 113-132.
Bozzoli, C, A Deaton, and C Quintana-Domeque. 2009. Adult Height and Childhood Disease. Demography, 46(4): 647-669.
Edwards, M. 2014. Fetal Death and Reduced Birth Rates Associated with Exposure to Lead-Contaminated Drinking Water. Environ. Sci. Technol., 2014, 48 (1): 739–746.