#tthms

Caption: Preparing TTHM samples in support of Flint Water Study. (Photo Credit Xuyen Mai)

A friend sent me a text last weekend. She was concerned about a news article from one of her local outlets summarizing the results of a recently released database on drinking water quality from the Environmental Working Group (EWG). In short, the article states that 5 contaminants were found in her family's water “above recommended health guidelines”. The headline was worrisome, so I prepared myself to see some pretty bad results. However, after digging into the EWG numbers a bit more, my concern was replaced by a bit of frustration. Here’s what I saw:

(NOTE: I focused on 1 of the 5 contaminants noted in the article: Total Trihalomethanes (TTHMs). These compounds are squarely in my area of expertise, and a reoccurring theme on this blog. I did not seriously examine the other 4 contaminants, but I suspect that the situation facing them may be similar.)

First, a quick overview of TTHMs: They are formed in treated drinking water as an unintended and unavoidable consequence of adding chlorine when other naturally occurring organic matter (NOM) is present. These compounds can cause cancer and are regulated by the EPA. Right now, the regulatory limit is 80 parts per billion (ppb), averaged over the 4-quarters of the year. The first TTHMs regulations were promulgated about 35 years ago, set the limit at 100 ppb, and have since been tightened.

The water system of my friend (part of the Aqua PA System) had a reported TTHM concentration of 48 ppb, ~40% less than the EPA standard. Seems pretty safe. But, the EWG database and subsequent article compares this 48 ppb to the draft public health goal defined by the California Office of Environmental Health Hazard Assessment (COEHHA) of 0.8 ppb (or 800 parts per trillion**). Should I now be worried? 

The short answer is no. 0.8 ppb is an fairly absurd standard for TTHMs. First, 0.8 ppb is not intended to be a standard, the COEHHA number is a draft goal, as stated (in fine-ish print) in the EWG database. There is a clear and important difference between goals and standards. A difference the EPA itself recognizes in its own guidance on water treatment contaminants. 

Second, the cancer risk from 48 ppb is already fairly low. There are peer-reviewed methods for estimating the cancer risk from TTHMs, that I have described in a previous post. Using the same model, and assuming all TTHMs are chloroform, I get approximately 7 cancers per 100,000 people, as a result of drinking (and cooking with and showering in, etc.) my friend’s water over a lifetime.

EWG has links to a website where one can purchase water filters on the same page where they present this worrisome data. The implication here is that a Brita-type filter or similar will protect you from these TTHMs. Science tells us, however, that this is flawed thinking, and most of our exposure to TTHMs comes not from actually drinking tap water, but from inhaling. This exposure occurs in a steamy bathroom during a hot shower, or while boiling pasta in the kitchen, etc. So, unless you are willing to filter all water used in the home (and stop swimming in chlorinated pools), simply buying a drinking water filter won’t protect you from this major TTHMs exposure pathway. 

The article in question contains a quote from EWG President Ken Cook: 

 “It’s time to stop basing environmental regulations on political or economic compromises, and instead listen to what scientists say about the long-term effects of toxic chemicals and empower Americans to protect themselves from pollutants even as they demand the protective action they deserve from government.” 

With respect to Mr. Cook, I disagree. I’m a scientist, and I want people to listen to my expertise. But, I also believe that to effectively regulate is to inherently make economic and political compromises, and that is exactly what the EPA and other agencies should do. It’s a good thing! We readily accept this type of regulation compromise in other facets of our life. For example, in the US ~35,000 people died in automobile accidents in 2015 (note: this is about 11 per 100,000 people, per year). If we wanted to completely remove this risk of death we probably could get close. Some places to start would include dropping the federal speed limit to 30 MPH on highways and outlawing driving after dark. Obviously, we would reject this out of hand due to the major negative impacts it would have on our life, and on our nation. So, we compromise. We strike a balance between risk and reward, between benefit and cost. As it turns out, I have roughly a 11/100,000 risk of dying in a car accident, but I can get from Boston to Philadelphia in 5 hours of driving (traffic not considered). I can also live far enough away from work to find affordable housing. Most Americans agree with me, and make similar trips without thinking twice about the inherent risk of death. (Some folks seem to think that a 70 MPH federal speed limit is too low, and choose to further compromise on their risk of dying to arrive somewhere a few minutes earlier).

Our national political discourse now includes regular (also silly) accusations regarding who “believes in science” and who does not. I don’t subscribe to this type of name-calling, but I humbly submit that if my friend drives a car (11/100,000 risk of death) to go buy a water filter in order to remove TTHMs in her water (~7/100,000 risk of cancer) then she not making a rational “science-based” choice. 

For some reason, we sometimes hold the water we drink to a ‘zero risk’ standard, as this article, and the EWG is encouraging us to do. Don’t get me wrong: I want all people to have access to safe, plentiful, cheap water but thats different than risk-free water. In fact, these things are probably incongruent, meaning that completely pure water would be very expensive to make and deliver, and all of this comes at a time of growing concerns related to water affordability and social justice issues. We demand so much from our water systems. We (increasingly) want to live in densely populated areas, near rich employment and social opportunities, but with more anthropogenic pollution. We also demand ~200 gallons of water per day, ready the instant we want it; and without any risk of waterborne disease, of course. 

These are very appropriate goals, but this is a fundamentally different conversation from safety and the role of regulations. I also deeply appreciate the important role the EWG has played in compiling massive amounts of data and making it publicly available, drastically increasing the transparency in our drinking water systems. It will help hold everyone accountable, and I’ve used some of the data in my research. That said, I’m concerned that comparing water quality data to draft goals while dismissing regulatory limits and compromise may cause unnecessary worry. 

--JEG