Wednesday, March 12, 2008

What’s in Your Fav Five? Five top contaminants

I’d been blabbing away for the past hour or so about chemical contaminants, imparting my imperfect knowledge upon my seven brilliant college students.

“So, what do you think are the five most important contaminants?” asked Beth, my student who has been investigating atrazine, one of the most ubiquitous pesticides in this country.

I was speechless. “Um..” I wavered, “well….” I pondered, before finally copping-out with “that’s a really good question.”

“I guess that’ll be my assignment,” I grimaced, “but I’m not sure I’d be able to come up with just one list.” Although it seemed a fair if not daunting assignment, since I’d been asking them to stretch their brains all semester, I’m guessing if you asked ten toxicologists for their “Fav-Five” they’d come up with at least twenty different lists.

As with anything in toxicology, there are some basic questions about exposure, toxicity, how the stuff behaves in the environment, and who’s most at greatest risk? For example, we might use some pretty nasty stuff to clean our ovens, paint our toenails or kill rats but we might not expose ourselves to concentrations that are of concern (though that might be debatable), unless we drink them.

Then there’s toxicity. Does it cause cancer? Impair reproduction? Contribute to the development of asthma? Which is worse? Or maybe it’s more insidious, as one of my students, Liz, revealed about a group of fragrances, used in more consumer products that I can name, called synthetic musks. Some of these compounds impair the ability of our cells to spit out foreign chemicals. Finally, there’s the question of how the chemical behaves in the environment, and in us. Does it accumulate? Do we metabolize it? Does it seep into water? Is it spewed into the air? And this is just considering human toxicity. Finally there’s the ‘at risk’ question. Are we talking most problematic for humans? The Environment? Wildlife?

My brain was off in all directions. There are just too many variables. Even David Letterman hasn’t attempted at top-ten list for chemical contaminants I checked.

But I already copped-out once. I couldn’t do it again. So I did some academic soul-searching (A.K.A: A Google Search).

Maybe there are some existing lists that hordes of experts, policy makers and regulators have already developed? But no such luck (although please correct me if I’m wrong. I’d love to see one.) Then I dared write to representatives from USGS and EPA’s Office of Water, but got no response other than a boiler plate answer from the EPA's press office assuring me that in addition to protecting us from acute problems like pathogens, "EPA is concerned that water systems protect their sources of drinking water, address replacement of aging infrastructure, have properly trained operators, and charge sufficient rates to ensure that they have the revenue needed to provide access to safe drinking water."

So for better or worse it seems I’m on my own (with help from the universe of information available on the web – and these are in no particular order – they are about as random as my selection process,) though I’d love to see a poll of those in various fields to see what they’d come up with, here goes – not in any particular order:

1) Arsenic is linked to many different types of cancer, and occurs naturally in soil and water (and may occur in drinking water). It's a chemical once used widely as a pesticide. As a result it may be found in the neighborhood playground (arsenic is one of a triumvirate of metals in CCA or chromated copper arsenate,) or contaminate the soil of old fruit orchards (and elsewhere) thanks to its effectiveness as a pesticide. In terms of large scale environmental release, mining industries – like the Newmont Mining Corporation, in Nevada which describes itself as one of the leading gold companies in the world - may be most important. According to Scorecard a site originally created by Environmental Defense (and now "owned" by Green Media) that digests and synthesizes EPA’s Toxic Resource Inventory into a more readable format, arsenic is the number one cancer concern, and Newmont releases almost 300 millions pounds of arsenic a year into the surrounding environment.

Arsenic also tops the Agency for Toxic Substances Disease Registry Top 20 List which is based on contaminants most commonly found at National Priority List or Superfund sites and which are considered most important in terms of potential for exposure and potential for causing adverse health effects.

Finally, in 2002, the EPA dropped the drinking water standard from 50 part-per-billion (ppb) down to 10 ppb, after considering even lower standards of 3 and 5 ppb.

2) Lead. This is not only important as a neurotoxic contaminant now because it exists in old house paint and other paint (e.g. on old peeling highway bridges), courtesy of the lead industry who once encouraged Americans to paint their houses with white lead, and advertised, yes actually advertised that “Lead Takes Part in Many Games,” (see Deceit and Denial for some fascinating reading,) but it’s also in our water having been used for pipes and solder. The EPA estimates that twenty percent of human lead exposure is the result of contaminated drinking water. Lead also tops NRDC’s Scorecard for number one, non-carcinogenic contaminant, this time thanks in part to Red Dog Ops in Alaska, another mining company.

Several years back, as a pregnant mother of a toddler, I dutifully tested the window sills of our new 1860’s home for lead paint – when the hardware store lead-test stick turned a shade of hot-pink I hadn’t seen since the psychedelic ‘70s. I immediately (and maybe not so wisely) purchased some gel non-toxic stripper and scraped away. Sometimes we do dumb things. And sometimes we just don’t learn. Maybe we will this time around.

Here’s a little ditty I found on EPA’s site:

Hence gout and stone afflict the human race;
Hence lazy jaundice with her saffron face;
Palsy, with shaking head and tott'ring knees.
And bloated dropsy, the staunch sot's disease;
Consumption, pale, with keen but hollow eye,
And sharpened feature, shew'd that death was nigh.
The feeble offspring curse their crazy sires,
And, tainted from his birth, the youth expires.
(Description of lead poisoning by an anonymous Roman hermit,
Translated by Humelbergius Secundus, 1829)

3) Priority Air Pollutants. Air is not my field, but no top-five list can be complete without at least a few air pollutants. These include particulate matter - released by power plants, motor vehicles, (especially older diesel vehicles), and some factories; ground-level ozone (primarily from motor vehicles and industry), carbon monoxide (from burning fossil fuel), sulfur oxides (fuel again, particularly coal burning plants), nitrogen oxides (yup, burning fuel again) and finally lead (again – so now you see it’s a double assault.)

We’ve all heard how asthma rates are going up. At least a few of those pollutants listed above aggravate asthma, and are known to cause or aggravate other respiratory conditions (for a historical perspective on the killing smog of Donora Pennsylvania, When Smoke Ran Like Water is a sobering read)

Although thanks to the Clean Air Act, smoke no longer runs like water, it’s still a pervasive pollutant, as anyone with a respiratory condition will tell you. As a parent who watched her asthmatic toddler’s every breath, and then watched as he bounced off the walls following massive doses of Ventolin (he’s thankfully grown out of it), I cannot imagine living in fear of the air. But people do, every day, and it’s criminal. Unfortunately, unlike water, until the sources clean up their act, there is no choice when faced with contaminated air (except perhaps, to visit one of those oxygen bars.)

4) Trichloroethylene, the “miracle” solvent of the twentieth century. I don’t know of too many contaminants that have their own blog, except for TCE (there’s also a very active TCE list serve run by Lenny Siegel, director for Center for Public Environmental Oversight). Though it may or may not reflect the importance of this developmental immuno - , neuro – (basically you name it) toxic and potentially carcinogenic contaminant, it does reveal the importance of this chemical. According to the EPA, TCE is present in 60% of their National Priority (NPL) or Superfund sites around the country, not to mention all the tens of thousands non-NPL sites contaminated with TCE as a result of past industrial, military, small business, or legal and illegal dumping. TCE not only contaminates water – including drinking water, but, depending on the depth of the water table and soil conditions, TCE vapors from contaminated ground water can and have intruded into homes, businesses and schools. Several years back, a class of mine worked with residents in North Adams, MA – a town where seventeen houses were bought-out and razed because of concerns about TCE vapor intrusion.

5) Bisphenol-A. Actually, I don’t know that anyone might consider this one a top-five, though it’s certainly among the top-five in “Buzz.” Bisphenol A is one of those seemingly all too-common estrogenic plasticizers. As we’ve all heard by now, this is the stuff that leaches from polycarbonate bottles – including those colorful Nalgene bottles that college students carry around (to make a statement about their environmental mindfulness) baby bottles, metal can linings, and even tooth sealants. Way back when, in the dark ages of 1993, when the realization that very small amounts of chemicals could really tweak developing reproductive systems was just dawning, the EPA’s Integrated Risk Information System (IRIS) stated, “The developmental toxicity of bisphenol A has been adequately investigated. Confidence in the RfD, therefore, is high.” Consequently the EPA set the “Reference Dose,” an amount considered as safe, at 50 parts per billion per day. Recent studies now suggest concentrations nearing this reference dose may cause reproductive and developmental toxicity. Bisphenol A now contaminates rivers, streams, with unknown impacts on wildlife, and because of its use in consumer products, its in us as well, at concentrations nearing the EPA reference dose.

Phew. That about does it for me, I now submit to class for grading. Comments, corrections, additions and subtractions are welcome.


JLowe said...

Very nicely done! My top five: 1) bisphenol-a; 2) PBDEs (I'm assuming classes can be counted as "one"), 3) phthalates, 4) dioxins/furans and 5) Lead. If I was given a 6th, it would be high-fructose corn syrup :-). There's some alignment here with the organic compounds - they're all hormonally active, have developmental and/or neurobehavioral effects and have widespread body burdens in humans.

Emily Monosson said...

Thanks jlowe, your list will make my student happy. She was expecting a more interesting list of contaminants - not the old dinosaurs that I pulled out!

As you write, the contaminants you list are insidious and can cause more subtle yet potentially very important effects (see the most recent post by guest blogger Cal - who writes about different ways of prioritizing.)

I also agree with you on the high-fructose corn syrup - it's like a plague, and raises an interesting question about characterizing contaminants vs "food product" additives that cause disease.