Clay Karen, Portnykh Margarita, Severnini Edson
Carnegie Mellon University and NBER, 4800 Forbes Avenue, Pittsburgh, PA 15213, United States.
Carnegie Mellon University, 4800 Forbes Avenue, Pittsburgh, PA 15213, United States.
Econ Hum Biol. 2019 May;33:181-192. doi: 10.1016/j.ehb.2019.03.001. Epub 2019 Mar 3.
Surface soil contamination has been long recognized as an important pathway of human lead exposure, and is now a worldwide health concern. This study estimates the causal effects of exposure to lead in topsoil on cognitive ability among 5-year-old children. We draw on individual level data from the 2000 U.S. Census, and USGS data on lead in topsoil covering a broad set of counties across the United States. Using an instrumental variable approach relying on the 1944 Interstate Highway System Plan, we find that higher lead in topsoil increases considerably the probability of 5-year-old boys experiencing cognitive difficulties such as learning, remembering, concentrating, or making decisions. Living in counties with topsoil lead concentration above the national median roughly doubles the probability of 5-year-old boys having cognitive difficulties. Nevertheless, it does not seem to affect 5-year-old girls, consistent with previous studies. Importantly, the adverse effects of lead exposure on boys are found even in counties with levels of topsoil lead concentration considered low by the guidelines from the U.S. EPA and state agencies. These findings are concerning because they suggest that legacy lead may continue to impair cognition today, both in the United States and in other countries that have considerable lead deposition in topsoil.
表层土壤污染一直被公认为是人类铅暴露的重要途径，如今已成为全球关注的健康问题。本研究估计了表层土壤中铅暴露对5岁儿童认知能力的因果效应。我们利用了2000年美国人口普查的个人层面数据，以及美国地质调查局（USGS）关于美国广泛县份表层土壤中铅含量的数据。通过采用基于1944年州际公路系统规划的工具变量法，我们发现表层土壤中较高的铅含量显著增加了5岁男孩出现学习、记忆、集中注意力或做决定等认知困难的概率。生活在表层土壤铅浓度高于全国中位数的县份，5岁男孩出现认知困难的概率大约会翻倍。然而，与之前的研究一致，这似乎对5岁女孩没有影响。重要的是，即使在美国环境保护局（EPA）和州机构指南认为表层土壤铅浓度较低的县份，也发现了铅暴露对男孩的不利影响。这些发现令人担忧，因为它们表明遗留的铅可能至今仍在损害认知能力，在美国以及其他表层土壤中有大量铅沉积的国家都是如此。
