Making sense of the NYT on water safety

| Comments (4) | Biology
I'm probably late to the party here but I wanted to make note of the NYT's recent article on water safety. (þ Melanie Schoenberg). While there's certainly some stuff here one might be distressed about, the article is written in such a way that it's pretty hard to evaluate how serious the issue actually is.

The article seems to make three major factual claims:

  • The Safe Water Drinking Act only regulates a small fraction of the potentially hazardous chemicals potentially found in drinking water.
  • Many municipal water systems contain chemicals at levels which, while legal, may be unsafe (e.g., are above EPA safe levels).
  • People are getting sick from this.
I don't doubt that the first of these is true: according to the article, 60,000 plus chemicals are used within the US (I'm actually surprised it's this low, since the PDR has over 4000 drugs and MSDS.COM claims to have 3.5 million data sheets), and it's not clear how you would plausibly analyze all of these, let alone determine permissible levels for each of these. I'm not saying this is desirable, but it's not necessarily a disaster either. Ultimately, you can either have an "default accept" or "default deny" policy here; given how sensitive modern analytic techniques are, if your policy is "default deny" you're going to spend a lot of time removing trace concentrations of harmless chemicals from your water supply. On the other hand if it's "default accept" you're going to end up with a lot of chemicals in your water that you don't really know are safe.

Given the first point, the second isn't surprising either. With that said, I'm not sure that the Times is really representing the situation that accurately. For instance, here's the report for Palo Alto, where I live. The Times reports "1 contaminant below legal limits, but above health guidelines", with the contaminant being alpha particle activity at a mean rate of 4.56 pCi/L. Let's see if we can put this in perspective. Assume humans are made entirely of water and rescale into kg, so we have 4e-12 Ci/kg of human body mass. A Ci is 37e+9 disintegrations/s so multiplying out we have .148 disintegrations/kg/s. If we assume that all the alpha particles are from U-238, and the alpha particles are being emitted at 4.270 MeV (~ 7e-13 J), then we get 1e-13 J/kg/s. If we assume that all of these are absorbed (not crazy since alpha particles have a very short path in the body) then we're getting 1e-13 Grays/s or 2e-12 Sv/s (multiply by the 20 Q factor for alpha particles) or .03 mSv/year. For comparison, the background level of radiation is 2.4 mSv/year. Obviously this isn't something you should be that thrilled about, but it's not clear to me that a 1% increase in your radiation dose is that bad either.

Given that, why does the NYT list this as above the health level? The answer seems to be that their safe value for alpha particles is zero (the legal limit is 15 pCi/L): the maximum level of alpha particle activity in neighboring Mountain View is 2.56 pCi/L, but it's still listed as having 5 "above health" samples (Chicago had one reading of .88 pCi/L and is also listed as a positive). This all makes me wonder if something is wrong here and the NYT is showing false positives. Of course, when you're processing a lot of data it's easy to make mistakes—assuming this is a mistake. It could be that I'm confused or that it's just the alpha particle threshold that's too low. I e-mailed the times to ask them for a copy of the raw data, but I haven't heard anything yet.

This brings us to the final point: the Times writes:

All told, more than 62 million Americans have been exposed since 2004 to drinking water that did not meet at least one commonly used government health guideline intended to help protect people from cancer or serious disease, according to an analysis by The Times of more than 19 million drinking-water test results from the District of Columbia and the 45 states that made data available.

...

And independent studies in such journals as Reviews of Environmental Contamination and Toxicology; Environmental Health Perspectives; American Journal of Public Health; and Archives of Environmental and Occupational Health, as well as reports published by the National Academy of Sciences, suggest that millions of Americans become sick each year from drinking contaminated water, with maladies from upset stomachs to cancer and birth defects.

This seems to conflate a bunch of issues. There seems to be a lot of variance in the data, with some tests showing positive results and some negative results (or low levels) for the same toxin even in the same area. It's very different to drink water with a toxin in it once than it is to drink it ever day for 10 years. I spent a couple days in Boston in 2007, but I'm not overly concerned about the fact that I might have been exposed to twice the legal limit of haloacetic acids in the two to four liters of water I drank while I was there. More generally, while one positive test may qualify as an exposure, it's not clear what that means as far as the real level of risk people are incurring. And of course there's a difference between cumulative toxins (e.g., arsenic) and acute toxins (e.g., e. coli). Speaking of e. coli, "maladies from upset stomachs to cancer and birth defects" covers a lot of territory; it's one thing if a sewer system occasionally fails to remove all the bacteria from the water supply (not that that's good) and another if it delivers hot and cold running cyanide from the tap.

Obviously, when you read this article you're supposed to be scared, but the way the article is written (and the opaque data presentation) doesn't make me feel like I have enough data to know if I should be or not.

P.S. San Francisco really does have great water. Almost good enough to make up for destroying Hetch Hetchy..

4 Comments

Alpha emitters are a bit more dangerous to your genetic material than, say, gamma radiation at the same energy levels, but your point is otherwise reasonable. I can't see how one can call the safe level zero, given that this is completely unachievable with current technology.

Yes, that's why you multiply by 20 to convert Grays to Sieverts for alpha particles....

How many ads for bottled water were in the print edition carrying that article or series?

A while ago the NYT talked a shredder manufcturer into a big ad buy, and then they had to run a long profile of some crazy guy who goes through Bob Dylan's trash.

In this case I'm guessing that the story had to be spun in the direction of “OMG radioactive tap water” no matter what, and unrealistic minimum safe concentrations make that easier.

Bottled water probably has the same problems, since you can't get to zero levels of contaminants unless you are combining hydrogen and oxygen directly. And even then the purity probably goes away when it contacts plastic.

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