Silent Spring Institute, 320 Nevada Street, Suite 302, Newton, MA, 02460, USA.
Environmental Working Group, 1436 U St. NW, Suite 100, Washington, DC, 20009, USA.
Environ Health. 2019 Jan 17;18(1):3. doi: 10.1186/s12940-018-0442-6.
Low-income and minority communities often face disproportionately high pollutant exposures. The lead crisis in Flint, Michigan, has sparked concern about broader socioeconomic disparities in exposures to drinking water contaminants. Nitrate is commonly found in drinking water, especially in agricultural regions, and epidemiological evidence suggests elevated risk of cancer and birth defects at levels below U.S. EPA's drinking water standard (10 mg/L NO-N). However, there have been no nationwide assessments of socioeconomic disparities in exposures to nitrate or other contaminants in U.S. drinking water. The goals of this study are to identify determinants of nitrate concentrations in U.S. community water systems (CWSs) and to evaluate disparities related to wealth or race/ethnicity.
We compiled nitrate data from 39,466 U.S. CWSs for 2010-2014. We used EPA's Safe Drinking Water Information System (SDWIS) to compile CWS characteristics and linked this information with both city- and county-level demographic data gathered from the U.S. Census Bureau. After applying multiple imputation methods to address censored nitrate concentration data, we conducted mixed-effects multivariable regression analyses at national and regional scales.
5.6 million Americans are served by a CWS that had an average nitrate concentration ≥ 5 mg/L NO-N between 2010 and 2014. Extent of agricultural land use and reliance on groundwater sources were significantly associated with nitrate. The percent of Hispanic residents served by each system was significantly associated with nitrate even after accounting for county-level cropland and livestock production, and CWSs in the top quartile of percent Hispanic residents exceeded 5 mg/L nearly three times as often as CWSs serving the lowest quartile. By contrast, the percent of residents living in poverty and percent African American residents were both inversely associated with nitrate.
Epidemiological evidence for health effects associated with drinking water above 5 mg/L NO-N raises concerns about increased risk for the 5.6 million Americans served by public water supplies with average nitrate concentrations above this level. The associations we observed between nitrate concentrations and proportions of Hispanic residents support the need for improved efforts to assist vulnerable communities in addressing contamination and protecting source waters. Future studies can extend our methods to evaluate disparities in exposures to other contaminants and links to health effects.
低收入和少数族裔社区通常面临不成比例的高污染物暴露。密歇根州弗林特的铅危机引发了人们对饮用水污染物暴露方面更广泛的社会经济差异的关注。硝酸盐通常存在于饮用水中，特别是在农业地区，流行病学证据表明，在低于美国环保署饮用水标准（10mg/L 硝酸盐氮）的水平下，癌症和出生缺陷的风险会升高。然而，目前还没有对美国饮用水中硝酸盐或其他污染物的暴露情况进行全国性的社会经济差异评估。本研究的目的是确定美国社区供水系统（CWS）中硝酸盐浓度的决定因素，并评估与财富或种族/族裔相关的差异。
我们从 2010 年至 2014 年收集了 39466 个美国 CWS 的硝酸盐数据。我们使用美国环保署的安全饮用水信息系统（SDWIS）来收集 CWS 特征，并将这些信息与美国人口普查局收集的城市和县一级人口统计数据相联系。在应用多种插补方法处理有截尾的硝酸盐浓度数据后，我们在国家和区域尺度上进行了混合效应多变量回归分析。
2010 年至 2014 年间，有 560 万美国人的饮用水来自硝酸盐浓度平均值≥5mg/L 硝酸盐氮的 CWS。农业用地面积和地下水来源的广泛程度与硝酸盐显著相关。每个系统所服务的西班牙裔居民的百分比与硝酸盐显著相关，即使在考虑到县一级的耕地和牲畜生产之后也是如此，而西班牙裔居民比例最高的 CWS 超过 5mg/L 的频率几乎是服务于最低四分位数的 CWS 的三倍。相比之下，生活在贫困中的居民的百分比和非裔美国人居民的百分比都与硝酸盐呈反比关系。
与饮用水中硝酸盐浓度超过 5mg/L 硝酸盐氮相关的健康影响的流行病学证据引起了人们对超过 560 万美国人的担忧，这些人通过公共供水系统供水，其平均硝酸盐浓度高于这一水平，他们面临着更高的风险。我们观察到的硝酸盐浓度与西班牙裔居民比例之间的关联支持了加强努力，帮助弱势社区应对污染和保护水源的需要。未来的研究可以扩展我们的方法，以评估对其他污染物的暴露情况和与健康影响的关联。
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