Arsenic Drinking Water Violations Decreased across the United States Following Revision of the Maximum Contaminant Level.

Arsenic poses a threat to public health due to widespread environmental prevalence and known carcinogenic effects. In 2001, the US EPA published the Final Arsenic Rule (FAR) for public drinking water, reducing the maximum contaminant level (MCL) from 50 to 10 µg/L. We investigated impacts of the FAR on drinking water violations temporally and geographically using the Safe Drinking Water Information System. Violations exceeding the MCL and the population served by violating systems were analyzed across the conterminous US from 2006 (onset of FAR enforcement) to 2017. The percentage of public water system violations declined from 1.3% in 2008 to 0.55% in 2017 (p < 0.001, slope = -0.070), and the population served decreased by over 1 million (p < 0.001, slope = -106 886). Geographical analysis demonstrated higher mean violations and populations served in certain counties rather than evenly distributed across states. The decline in violations is likely due to the adoption of documented and undocumented treatment methods and possibly from reduced environmental releases. Considering other studies that have shown decreased urinary arsenic levels in the population served by public water systems since the new standard, it may be inferred that the FAR is facilitating the reduction of arsenic exposure in the US.

Influence of infrastructure on water quality and greenhouse gas dynamics in urban streams.

Streams and rivers are significant sources of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) globally, and watershed management can alter greenhouse gas (GHG) emissions from streams. We hypothesized that urban infrastructure significantly alters downstream water quality and contributes to variability in GHG saturation and emissions. We measured gas saturation and estimated emission rates in headwaters of two urban stream networks (Red Run and Dead Run) of the Baltimore Ecosystem Study Long-Term Ecological Research project. We identified four combinations of stormwater and sanitary infrastructure present in these watersheds, including: (1) stream burial, (2) inline stormwater wetlands, (3) riparian/floodplain preservation, and (4) septic systems. We selected two first order catchments in each of these categories and measured GHG concentrations, emissions, and dissolved inorganic and organic carbon (DIC and DOC) and nutrient concentrations biweekly for 1 year. From a water quality perspective, the DOC : NO3 - ratio of streamwater was significantly different across infrastructure categories. Multiple linear regressions including DOC : NO3 - and other variables (dissolved oxygen, DO; total dissolved nitrogen, TDN; and temperature) explained much of the statistical variation in nitrous oxide (N2O, r2 = 0.78), carbon dioxide (CO2, r2 = 0.78) and methane (CH4, r 2 = 0.50) saturation in stream water. We measured N2O saturation ratios, which were among the highest reported in the literature for streams, ranging from 1.1 to 47 across all sites and dates. N2O saturation ratios were highest in streams draining watersheds with septic systems and strongly correlated with TDN. The CO2 saturation ratio was highly correlated with the N2O saturation ratio across all sites and dates, and the CO2 saturation ratio ranged from 1.1 to 73. CH4 was always supersaturated, with saturation ratios ranging from 3.0 to 2157. Longitudinal surveys extending form headwaters to third-order outlets of Red Run and Dead Run took place in spring and fall. Linear regressions of these data yielded significant negative relationships between each gas with increasing watershed size as well as consistent relationships between solutes (TDN or DOC, and DOC : TDN ratio) and gas saturation. Despite a decline in gas saturation between the headwaters and stream outlet, streams remained saturated with GHGs throughout the drainage network, suggesting that urban streams are continuous sources of CO2, CH4, and N2O. Our results suggest that infrastructure decisions can have significant effects on downstream water quality and greenhouse gases, and watershed management strategies may need to consider coupled impacts on urban water and air quality.