Low doses of contaminants, long ignored, can have vast consequences

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Low doses of contaminants, long ignored, can have vast consequences

Scientists found cocaine – and a lot of other chemicals – in Minnesota snow

In 2016, four billion prescriptions were filled within the US. That's about 12 prescriptions filled per US citizen over the course of a single year.

Although hugely beneficial in terms of public health and longevity, manmade pharmaceuticals and other compounds have downsides that are typically out of sight, out of mind. At the tippy top of the "con" list rests "environmental persistence" – as the enormous volume of manmade pharmaceuticals and chemicals produced and consumed each year doesn't *poof* and disappear after humans consume or use a given compound. Pharmaceuticals and other human pollutants stick around for minutes, days, weeks, years, decades, or even millennia in the environment, and have a sneaky way of showing up where they aren't welcome.

Like in snow. A recently published study by Mark Ferrey of the Minnesota Pollution Control Agency and colleagues found man-made contaminants like pharmaceuticals, surface-coating chemicals, and cocaine in snow from Minnesota. Alarming? Yes. Dangerous? Probably not, as the pollutant levels found were, thankfully, quite low.

Yet low doesn't translate to negligible. Seventeen emerging human contaminants were found in Minnesotan air, rain, and snow. Emerging contaminants (ECs) are created compounds that are relatively new on the scene and are understudied in terms of their chronic ecological and human health impacts. Compounds found in the snow included alkylphenols – used in surfactants and soaps – derivatives of benzotrioles used in anti-corrosive coatings, caffeine, several antibiotics, an x-ray contrasting agent, cocaine, and the active ingredient from household insect repellants, DEET.

The concentrations found in this study are in the parts per billion (ppb) to parts per trillion (ppt), ranging from below detection limits to approximately 228 ppt. A typical therapeutic pharmaceutical dose is somewhere in the parts per million (ppm) range, meaning exposure to the concentrations found in snow and rain as documented in Ferrey’s study are very, very unlikely to cause acute effects in humans or wildlife.

But here's the rub: pharmaceuticals and other ECs are created to be biologically active at low doses, and have been found to accumulate in the environment or living organisms more than we thought possible. Toxicity testing currently centers around lethality or observed acute effects in a lab setting and doesn't account for chronic effects from continued low-level exposures or complicating real-world conditions. Just because an organism doesn’t go belly up doesn’t mean its chemical environment isn’t impacting it, and such assessments underestimate or miss what low EC concentrations can do in living systems over extended periods of time.

Unfortunately, chronic harm from low EC concentrations isn’t just a hypothesis. Synthetic hormones have been found to cause collapse of fish populations with prolonged exposure to amounts as low as five to six ppt in surface water. Environmentally relevant concentrations of ECs have been found to change how fish eat, alter predator-prey dynamics, suppress respiration or primary productivity, or skew fish population sex ratios.

While the impacts of chronic low concentrations of ECs may be surprising, Ferrey and his team noted that finding these compounds in snow isn’t necessarily surprising. The presence of ECs in natural water bodies is well-established. A 2002 study in the US found that 80 percent of US streams contained detectable concentrations of pharmaceuticals or other personal care products. More recently, EC concentrations in the ppb – ppt range have been found within freshwater, estuarine, and coastal bodies of water across the US and globe. ECs have also been detected in air and rain, confirming these compounds are capable of jumping into the atmosphere from surface water source areas. Finding ECs in snow is just an additional line of evidence that atmospheric transport of these compounds is a viable pathway contributing to their ubiquity in the environment today.

The chemical cake

When I bring up pharmaceuticals in water or air as part of conversation, I’ve gotten asked what other conspiracy theories I believe in, heard imitations of Alex Jones and his ridiculous frog theory, or received a glazed smile and nod. To me, such responses are symptomatic of a larger lack of concern about ECs; there’s scant public outcry about understudied synthetic chemicals in air and water despite the fact that production and diversification of human-created chemicals have outpaced every other identified agent of global change, particularly in developed countries.

Decreased EC research and popular attention may relate to less-than-perfect assumptions about them, particularly pharmaceuticals. Decades of meticulous research are required to show pharmaceutical structure, function, and fate within the human body before it's approved for public use, but environmental fate is less thoroughly vetted. Instead, scientists often rely 'quantitative structure activity relationships' and lab testing to make predictions about a chemical's fate. This involves using established empirical data to estimate a compound's biological impacts and environmental fate based on its structure, and then validating these assumptions in a controlled laboratory environment. It’s cost-effective and provides good insight, yet it’s not a perfect approach: these sorts of educated deductions inform assumptions of EC environmental fate and biological impact, rather than comprehensive in situ data collection.

As a result, many ECs have been thought to degrade too readily in the environment to impart harm or be transported any significant distance in air or water. Results like Ferrey’s, and additional observational evidence suggesting we have underestimated the persistence of ECs, mean that their atmospheric and water-based transport cannot be written off as unlikely or insignificant.

The icing on the chemical cake is the phenomenon known as mixture toxicity. We are inundated with synthetic chemicals on a daily basis, and have faint idea how all these small ambient exposures add up. Research suggests that sustained, low-dose exposures to complex mixtures of pharmaceuticals, ECs, and other pollutants may impact humans or wildlife in sublethal, chronic ways we have yet to fully understand and can’t really predict from toxicity testing focusing on the limited effects of one type of chemical in one or two types of study organisms.

'Divide and conquer'

To even begin understanding the ramifications of chronic EC exposures or mixture toxicity, researchers must be able to measure pollutant concentrations. Ferrey's study used a combination of two analytical techniques, chromatography and mass spectrometry, to measure pollutant concentrations in carefully prepared water and air samples. The two techniques are a chemical equivalent of "divide and conquer," as in combination they act to separate different compounds from each other to allow identification by weight.

The methods and analysis employed in this work aren’t groundbreaking. Environmental chemists the world over use similar approaches to prepare environmental samples and screen them for various pollutants. But it's expensive and time-consuming. Coupled chromatography/mass spectrometry systems are pricey, running anywhere from around $100,000 to north of $500,000, effectively limiting use to those agencies or institutions who can afford them, or afford to pay for sample analysis elsewhere.

Lack of systemic access to appropriate measurement instrumentation means for most of the globe, ambient concentrations of pharmaceuticals and other ECs remains a big, fat question mark. This isn't cause for mass hysteria, as no one can claim they are getting viable doses of medication from a dip in their local water body. But, we do know that low concentrations of ECs have both local and far-reaching ecological consequences that are mostly under the radar, to the detriment of humans and wildlife.

Although we certainly can't do away with pharmaceuticals or other life-saving compounds, seek out personal care products with environmentally safe active chemical ingredients and refrain from flushing any prescriptions down the drain to prevent contributing to ECs in your waterways, air, and winter's swirling snowflakes.

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Devang Mehta


University of Alberta

Thanks for writing this – it’s an excellent primer for a topic I’ve wanted to try to understand for a while now. I just have a question about the points you make in the last paragraph, i.e. what can we do about low-concentration ECs? Like you say, It seems unrealistic to do away with medicines, but is there a list somewhere of “environmentally safe active chemical ingredients”? And have these been tested? On the other hand, are there any clean-up solutions, or waste-treatments that could prevent ECs from entering water systems and the atmosphere?

Anna Robuck responds:

I think there are a few ways to tackle ECs in the environment.

Primarily we could encourage more environmentally responsible chemistry by industry. For many ECs, existing data or empirical relationships can roughly suggest whether a compound will be environmentally persistent or bioaccumulative (the QSARs mentioned in the article, etc). Those compounds that seem biologically or environmentally risky could undergo increased environmental fate testing before chemical production or use (current version of this under US law is pretty shoddy). Or a more environmentally safe compound could be swapped in from the get go?

Beyond that idealistic approach, we can be smart consumers to avoid ECs in common products/materials, decreasing market demand and ambient concentrations of ECs in our households. There are a few lists of environmentally safer active chemicals; I link to one curated by Environmental Working Group in the article. The list essentially points you to use personal care and household products that contain the “lesser of two evils” or some kind of natural alternative…for example, for sunscreens its advisable to avoid products with oxybenzone (an EC) and swap in something mineral based. Can’t vouch for every alternative on the EWG list, but seems to be a sizable body of evidence supporting use of one active ingredient vs. another for the examples I’m familiar with.

Pharmaceuticals are way trickier though. They obviously aren’t created to be environmentally friendly, they are created to for utmost efficacy within the human body. So choosing a more environmentally safe alternative isn’t really an option to the best of my knowledge? Could be wrong there, I have no background in pharma design. There are a few wastewater designs that have been tested to remove pharmaceuticals and other ECs more so than others (e.g. like this). The most effective removal mechanisms are beyond just basic primary or secondary treatment employed by many WWTPs. Perhaps continued data elucidating the impacts of ECs, and increased subsequent concern for ECs and pharma could help raise capital needed to improve wastewater infrastructure to include more effective EC treatment processes? Not sure…big expensive dreams…