Aluminum is a chemical included in a water treatment agent (aluminum sulfate) that is often used by water utilities during the coagulation process to purify drinking water. Consequently, it is common in tap water. However, it has recently also been found in the deposits of lead scale that form on the inside of lead water pipes.

While the presence of aluminum in water pipes is not surprising, nor a health issue at the levels observed by researchers, its presence could have other, as yet unknown, implications in terms of drinking water quality.

In particular, Daniel Giammar, a Professor of Environmental Engineering in the McKelvey School of Engineering at Washington University in St. Louis, was curious as to how the aluminum was affecting the behavior of lead in the scale on the interior surface of the pipes. "As long as the lead is bound to the scale, it doesn't enter the water system," he explained.

Giammar and his colleagues, including Guiwei Li, a visiting PhD student from the Chinese Academy of Sciences, conducted several laboratory experiments and discovered that aluminum can effect the solubility of lead when conditions are favorable. The results of the study were recently published in the scientific journal Environmental Science & Technology. As the paper has been nominated as the ACS Editor's Choice, online access to the paper is free to the public.

For the study, the researchers used simplified models to assess how aluminum, phosphate and a combination thereof, affected lead placed in a container of water with a similar composition to that found in municipal water systems. Their primary aim was to gain a clearer understanding of how these chemicals affected the solubility of lead, or more specifically, how much lead would dissolve and enter the water when exposed to these chemicals.

They found that the container into which aluminum only was added, the solubility of lead remained unchanged, with concentrations of lead dissolving into the surrounding water at around 100 micrograms/L. In the container into which phosphate only was added, the solubility of lead decreased significantly from around 100 micrograms/L to less than 1 microgram/L. In the container into which both phosphate and aluminum were added, lead levels decreased from around 100 micrograms/L to around 10 micrograms/L of water.

While lead concentrations of 10 micrograms/L do not exceed the safety standards for drinking water, Giammar points out that lead levels are still higher than those observed in the container without aluminum.

"This showed us things that were surprising," he said. "Some people would have thought that aluminum wasn't doing anything because it's inert. But then in our work, we saw that it actually affects lead solubility."

"This tells us what our next experiment should be," said Giammar, who together with his team plan to expand this study by conducting similar experiments on real lead water pipes next.

Journal Reference Guiwei Li, Yeunook Bae, Anushka Mishrra, Baoyou Shi, and Daniel E. Giammar. Effect of Aluminum on Lead Release to Drinking Water from Scales of Corrosion Products. Environmental Science & Technology; 2020 54 (10), 6142-6151; DOI: 10.1021/acs.est.0c00738