EPA announced today that it made a "preliminary determination to regulate strontium in drinking water." If this goes final, there's still an awful lot of work to do. What is involved?
The "preliminary determination" is being made under the Safe Drinking Water Act, which calls for the creation of a "candidates list" (a CCL) for regulation every five years (we are 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 (which likely would be published by the end of 2015).
To "regulate" strontium involves the derivation of both technology- and health-based allowable limits. The former are called "maximum contaminant goals" are considered a "maximum permissible level of a contaminant in water delivered to users of a public water system." The latter are more complicated to derive and is where the bulk of the remaining work lies.
To derive a health-based limit for a chemical that is protective of human health requires the derivation of a toxicity reference value (TRV), such as a "Reference Dose" (RfD). To do this, the Office of Water will request that the Office of Research & Development IRIS program establish a TRV. Actually, the IRIS program has already done this, but the work is from 1992 and not reliable by today's risk and regulatory standards. The Agency for Toxic Substances and Disease Registry has actually done a more up-to-date and thorough review of strontium toxicology and exposure (from 2004); however, it approached its derivation of a TRV differently -- despite using the exact same study as EPA.
(ATSDR is a public health agency of the Department of Health & Human Services and mandated to serve specific functions by Congress: public health assessments of waste sites, health consultations concerning specific hazardous substances, health surveillance and registries, response to emergency releases of hazardous substances, applied research in support of public health assessments, information development and dissemination, and education and training concerning hazardous substances.)
WARNING!! Tox Geek Alert!! As one might imagine, there's not a ton of tox literature out there for strontium and the work that the current TRVs are based on were done in the 60s and 80s. Complicating the interpretation of the body work is the fact that it is naturally occurring, occurs in radioactive and radiostable forms, and has been used therapeutically in humans (to treat osteoporosis). EPA IRIS based its RfD on rachitic bone effects observed in a 20-day oral study using young and adult female rats. ATSDR based its TRV (called a "minimal risk level") on the same study. In both cases, a "no effects level" was interpreted from the study and combined with uncertainty factors to produce the TRV, and the differences are notable:
- EPA defined the "no effects" level as 190 mg/kg-day and combined this with total UF of 300 to yield an RfD of 0.6 mg/kg-day.
- ATSDR defined the "no effects" level as 140 and used a total UF of 90 to yield an MRL of 2 mg/kg-day (3x higher than EPA). Additionally, it also set health limits based on its radioactivity (which is carcinogenic, as opposed to the radiostable versions which are not).
Given that this work is over 20 years old, a renewed TRV derivation will have to be done following the new IRIS procedures (which I have written about before). This will involve "systematic review" of the available evidence, including any relevant human/clinical data which may have been reported in the intervening years. This will also involve a long, laborious process that will have multiple comment periods, public meetings, etc and probably 3-5 years total.
Once the IRIS process is successfully navigated, then there are additional SDWA mandates to follow. For example, EPA has since introduced a policy where "lifetime health advisories" will be calculated for all SDWA contaminants. regardless of carcinogenicity status. The available evidence on the radiostable versions of strontium found in drinking water (such as strontium carbonate and strontium nitrate) shows it is not carcinogenic at the highest dose tested (263 mg/kg-day) following 3-year oral exposures in male adult rats.
If you use strontium in your manufacturing or laboratory processes, you may want to follow these proceedings and press EPA IRIS to use all available data and to use modern methods if it needs to derive a new TRV). M³ Technical & Regulatory Services can help!