EPA's Upcoming Regulation On Strontium — What You Need To Know

In October, the U.S. Environmental Protection Agency (EPA) made a preliminary determination to regulate strontium in the nation's drinking water. This decision is being made under the Safe Drinking Water Act (SDWA), which calls for the creation of a "contaminant candidates list" (a CCL) for regulation every five years (we are currently on CCL3). The latest batch of chemicals off CCL3 for which preliminary regulatory determinations were made identified strontium as the only chemical that potentially requires regulation. Following this action, a 60-day public comment period is planned, and assuming a final determination to regulate is made, then a rule is prepared.

Strontium occurs naturally in the environment. Air, dust, soil, foods, and drinking water all contain small amounts of strontium. Ingestion of small amounts of strontium is not harmful. However, high levels of strontium can occur in water drawn from bedrock aquifers that are rich in strontium minerals. Strontium occurrence is also linked to other sources such as air contamination from milling processes, coal burning, and phosphate fertilizers.  In some cases, low levels of strontium have been administered to osteoporosis patients as a treatment of their condition. However, the EPA says strontium is at “levels of concern” in just 7 percent of U.S. public water systems.

The risk posed by strontium depends on the concentration ingested and on exposure conditions. EPA current reference concentration indicates that ongoing exposure to strontium at levels of more than 1,500 parts per billion per day may lead to negative health effects. There is no evidence that drinking water with trace amounts of naturally-occurring strontium is harmful. However, exposure to high levels of naturally-occurring strontium during infancy and childhood can affect bone growth and cause dental changes, and there is some evidence that strontium increases bone density in adults. The isotope strontium-90 has been linked to bone cancers and leukemia, but the radioactive form is not the subject of this determination.

There are still large uncertainties in setting a specific maximum contaminant level for strontium.  EPA needs to provide a stronger justification for its use of Uncertainty Factors (UFs) in calculating the Reference Dose (RfD).  In the regulatory determination, EPA used a factor of 10 for Database Uncertainty when 3 had been used in previous calculations.  There are questions of how the certainty factors were adjusted when the RfD calculation includes an age-specific adjustment component.  In addition, EPA should provide stronger justification for using a Relative Source Contribution (RSC) of 20 percent as the RSC has a significant impact on the RfD

Given there are known water systems with higher levels of strontium, EPA should consider performing human epidemiology studies in those water systems and use the results to better inform the RfD.  Strontium is likely one of the relatively few drinking water chemical exposure scenarios that can be addressed for resolution with human epidemiology. The candidate water supplies are easily identifiable, water and dietary doses are determinable, and the potential skeletal effects can be determined with non-invasive methods. Other potential negative and positive effects of treatment can also be simultaneously evaluated. Some of the treatment options would also remove calcium, which is beneficial in blocking the adverse health effects of strontium.

There are a lot of questions about setting the Maximum Contaminant Level (MCL) and the cost of treatment, particularly when this will impact many small systems who cannot afford the expensive treatment (and disposal of a potentially hazardous waste). Let’s take the time to collect sound scientific information to make solid decisions for strontium control.  EPA should move carefully with this important decision — there's a lot to consider.