Strontium is an alkaline earth metal that naturally occurs in air, dust, soil, foods and drinking water. It can occur at high levels in bedrock aquifers as an adverse contamination result of milling, coal burning and phosphate fertilizers. An on-going exposure to strontium at more than 4,200 ppb (4.2 mg/l) may lead to negative health effects by replacing calcium in bone affecting skeletal development in people who do not consume enough calcium. There is no evidence that the trace levels, typically 0.3 to 1.5 mg/l, found in drinking water will cause harm.
Nonetheless, the Health Reference Level has been revised by the National Inorganics and Radionuclides Survey lowering the strontium health risk level from 4.2 mg/l to 1.5 mg/l. Therefore, the U.S. Environmental Protection Agency (EPA) plans to elevate the element from its third contaminant candidate list (CCL3) and mandate its treatment. Because of strontium’s effects on development, the EPA is concerned about the potential consumption by infants, children and adolescents. The EPA announced the forthcoming regulation in an October 2014 news release.
The Safe Drinking Water Act mandates that every five years the EPA must develop a contaminant list and then make a regulatory determination for at least five contaminants on that list. The EPA’s decision to regulate strontium in drinking water marked the final stage of the process for regulating a CCL3 contaminant. The first two stages require health and occurrence assessments. A 60-day public comment period on the decision ended Dec. 19, 2014. The agency plans to make the final decision on the strontium regulation sometime in 2016. Following that decision, a rule must be proposed within 24 months and a final decision on the rule within 18 months after that.
An American Water Works Association (AWWA) report on the potential regulatory implications of strontium notes the metal is found in all drinking water sources in the country at an average concentration range of 0.3 to 1.5 mg/l. Conventional treatment is ineffective in removing strontium from water, per the EPA. The agency has identified ion exchange and reverse osmosis as the best available technologies to treat drinking water for strontium.
The AWWA and Water Research Foundation have joined forces to create the “Critical Review of Treatment Options and Considerations for Strontium Removal from Water.” The project is reviewing existing literature on strontium removal from water and will conduct lab-scale evaluations. The project will issue a final report that includes findings and recommended treatment options, as well as identify needs for future research.
The links below provide additional information on Strontium.