A toxic family tree

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PFAS "family tree"

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November 26, 2018

Critical Commentary

Substantive Caption:

“PFASs as a whole, much more than solely PFOS, PFOA, and their precursors, are an intractable, potentially never-ending chemicals management issue” (Wang 2017, 2511).

This image depicts the “family tree” of the chemicals PFOS (perfluoroctasulfonic acid) and PFOA (perfluorooctanoic acid). PFOA and PFOS are persistent environmental chemicals associated with a range of toxic effects including increased incidence of liver disease, thyroid disease, high cholesterol, decreased vaccine efficacy, decreased fertility, pre-eclampsia, and several types of cancer (ATSDR 2018). PFOS—formerly the key ingredient in the stain-resistant coating Scotchgard—is among the two-dozen persistent organic pollutants restricted or banned under the UN’s Stockholm Convention. PFOA—a key constituent in Teflon production until the mid-2000s—is under consideration for addition to the Stockholm Convention in April 2019.

As these two toxic chemicals have been phased out, they have been replaced, Hydra-like, by diverse related chemicals from the broader class of PFCs or PFASs (perfluoro chemicals / per- and polyfluoroalkyl substances). Environmental toxicologists are concerned that the same structural similarities that make other PFASs useful substitutes for the industrial uses of PFOA and PFOS may also make the entire class just as hazardous as these two substances that have become major public health concerns. This figure, from a 2017 review article addressing PFAS toxicology, is intended to illustrate the molecule-by-molecule breadth of this toxic hazard and the comparatively narrow scope of research and regulation.

The authors of this article explain, “The most common current industrial practice of phasing out one PFAS is to replace it with another (or multiple other) structurally similar PFAS. Such a strategy is easier and less costly than identifying a nonfluorinated substance to be used in the same or similar process (i.e., chemical replacement) or inventing a new process that does not require PFASs (i.e., functionality replacement).…. [B]ut such a replacement strategy will not solve issues in relation to PFASs as a whole group—it will only increase the numbers of PFASs on the market and the difficulties in tracking them” (Wang 2017).

Design Statement:

  • Scientists, regulators, and those who wish to work within scientific and regulatory frames typically address environmental toxicity on a chemical-by-chemical basis, where chemical substances are defined by their molecular identity.
  • Framed in this way, the problem of toxicity appears to be well-nigh intractable.
  • There are just too many molecules. But maybe molecules are the wrong toxic subjects to be looking for. So maybe we can figure out how discussions of environmental toxicity got framed in molecular terms in the first place.

This image portrays environmental toxicology and toxic substances regulation as trapped in a molecular double bind. On the one hand, the quantity of studies dedicated to PFOA and PFOS attest to how much work it takes to begin to understand the long-term, low-dose toxicity of a specific chemical compound—let alone to take action to address it. On the other hand, the molecule-by-molecule list of PFASs at right illustrates how focusing on specific compounds risks missing the chemical forest for the molecular trees. And yet this forest—the white noise of ubiquitous multiple chemical exposure (Murphy 2006)—is precisely the white noise that makes it take so much work to pick out a toxic signal associated with an individual substance in the first place.

In sum, according to this figure, there are too many molecules to know, and it’s very hard to know anything at all about any of them, in large part because there are so many of them to know. This is a fruitful starting point for asking historical and ethnographic questions about the ontology of the agents of environmental toxicity. Where did we get the idea that the environment (or the hazardous anthropogenic bits of it, anyway) is made up of molecules? What is a molecule? Are there alternative ontologies on offer, within or outside of the chemical and toxicological sciences?

One place to start: The impression that there is just too much to know is a general feature of the “informating of environmentalism” (Fortun 2004). Historically, such concerns have tended to emerge in the wake of novel technologies that afford new practices and imaginaries and scales of information management (Blair 2010).

References:

ATSDR (Agency for Toxic Substances and Disease Registry, United States Department of Health and Human Services). 2018. Toxicological Profile for Perfluoroalkyls (Draft for Public Comment). https://www.atsdr.cdc.gov/toxprofiles/tp200.pdf.

Blair, Ann. 2010. Too Much to Know: Managing Scholarly Information before the Modern Age. New Haven: Yale University Press.

Fortun, Kim. 2004. “From Bhopal to the Informating of Environmentalism: Risk Communication in Historical Perspective.” Osiris 19: 283–96. doi: 10.1086/649407.

Murphy, Michelle. 2006. Sick Building Syndrome and the Problem of Uncertainty: Environmental Politics, Technoscience, and Women Workers. Durham: Duke University Press.

Wang, Zhanyun et al. 2017. “A Never-Ending Story of Per- and Polyfluoroalkyl Substances (PFASs)?.” Environmental Science & Technology 51 (5): 2508–18. doi: 10.1021/acs.est.6b04806.

Source

Reprinted with permission from Zhanyun Wang et al., “A Never-Ending Story of Per- and Polyfluoroalkyl Substances (PFASs)?,” Environmental Science & Technology 51, no. 5 (March 7, 2017): 2508–18, https://doi.org/10.1021/acs.est.6b04806. Copyright 2017 American Chemical Society.

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