University of Pittsburgh Researchers Reveal Hidden Impacts of Drinking Water Treatment on Urban Streams
Aging lead-pipe drinking water systems, along with the public health measures implemented to reduce their risks, are reshaping the chemistry and health of nearby urban streams. New research from University of Pittsburgh biogeochemists, hydrologists, and environmental engineers uncovered previously overlooked environmental impacts of a common water treatment practice: adding orthophosphate to drinking water systems to prevent lead pipe corrosion. Published in PLOS Water, the study reveals that phosphate used in drinking water treatment can leak into urban streams, altering their chemistry and potentially accelerating eutrophication, the process where such nutrients lead to excessive growth of algae and aquatic plants..
And such lead-pipe networks are widespread throughout the Northeast, Great Lakes region and Midwest — meaning as many as 20 million Americans and their nearby streams may face similar challenges.
In collaboration with local water authorities, the scientists studied five urban streams to look for changes in the pre- and post-implementation of orthophosphate-based corrosion control on stream chemistry. Their findings show statistically significant increases in phosphorus and metal concentrations in streamwater following the treatment, indicating that subsurface infrastructure is not a closed system. Phosphorus concentrations in urban streams increased by over 600% following orthophosphate dosing, while trace metals such as copper, iron, and manganese also rose by nearly 3,500%, suggesting co-transport of corrosion byproducts.
“We were surprised by how clearly the effects of drinking water treatment appeared in stream chemistry. This finding suggests that our underground infrastructure isn’t as sealed off from the environment as we often assume,” said first author Dr. Anusha Balangoda, Assistant Teaching Professor in Geology and Environmental Science in the Kenneth P. Dietrich School of Arts & Sciences. “Our study is the first to examine urban stream chemistry and the influence of drinking-water additives.”
"We absolutely need to protect people from lead in drinking water," said co-author Dr. Emily Elliott, co-founder and chair of the Pittsburgh Water Collaboratory and professor in Geology and Environmental Science. "But we also need to understand how these treatments affect our rivers and ecosystems." Elliott collaborated with co-authors Sarah-Jane-Haig, an associate professor, and Isaiah Spencer-Williams, a doctoral student, both also in Civil and Environmental Engineering. Their paper, titled "From Pipes to Streams: The Hidden Influence of Orthophosphate Additions on Urban Waterways," was published November 13 in PLOS Water.
Public-health emergencies arising from corroded, lead-water pipes are nothing new— contaminations have made the news in the past decade in Flint, Michigan, Washington, D.C., and more recently in the study area of Pittsburgh. Phosphate corrosion inhibitors are used in water systems across North America, the United Kingdom, and parts of Europe. The researchers noted that the potential ecological consequences of this dosing of drinking-water system pipes does to streams, rivers, and groundwater remain “largely unexplored, particularly in the U.S.”
The study examined a pathway of phosphorus pollution that has received little attention: leakage from drinking water pipes rather than traditional sources like wastewater discharge or industrial runoff. The researchers monitored five above-ground urban stream reaches, selecting these because most Pittsburgh streams are buried in an underground pipe network, and collected detailed water chemistry samples monthly over a two-year period spanning before, during, and after orthophosphate treatment implementation (February 2019 to June 2020). They also conducted nutrient addition bioassays at three key time points, using both streamwater and tap water controls, to assess the ecological impacts on algal growth.
The scientists offer four corrective actions to address phosphate leakage from buried water infrastructure systems:
1. Repair Aging Infrastructure. Urgently address the issue of drinking water pipe networks losing 40-50% of treated water through leaks and breaks, thereby preventing phosphate-enriched water from reaching urban streams and groundwater.
2. Upgrade Wastewater Treatment. Implement tertiary treatment processes at wastewater treatment plants to remove excess phosphorus. The study shows effluent phosphorus increased 26% after dosing began, yet many plants lack phosphorus removal capabilities that can achieve an 80-99% reduction.
3. Optimize Dosing Concentrations. Determine the minimum effective orthophosphate concentration that protects human health from lead exposure while minimizing ecological harm to receiving waters.
4. Develop Innovative Approaches to Monitor Infrastructure-Ecosystem Interactions. Create new monitoring and assessment methods to understand how additives in drinking water systems reach and affect urban streams through subsurface connections.
"Pittsburgh isn't unique—millions of Americans are served by water systems with lead pipes and aging infrastructure," Elliott said. "Our findings suggest this issue extends far beyond one city, particularly in the Midwest and Northeast where both lead pipes and phosphate treatment are common. We need a national conversation about infrastructure and water quality."
This research was supported by the National Science Foundation RAPID funding program (grant NSF No. 1929843), as well as the Pittsburgh Water Collaboratory. The Pittsburgh Water and Sewer Authority contributed drinking water sample collection, chemical analysis and water treatment information.
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