A toxic family tree (revised)


PFAS "family tree"




Creative Commons Licence


Created date

January 21, 2019

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 molecule-by-molecule detail of the figure is overwhelming, inscrutable, frustrating, intractable. That is the point. The authors wish to argue that, as long as environmental science, law, and politics hew to molecule-by-molecule conceptions of what's toxic, the task of controlling environmental toxicity will remain overwhelming, inscrutable, frustrating, and intractable, too.

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).

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).

Design Statement:

In this essay, I take data visualization and image-based arguments as subject matter for historical and ethnographic analysis. My particular interest is in the relationship between, on the one hand, genres and conventions for making and interpreting images, and on the other hand, databases and reference works containing data that gets visualized in such images. By attending to the connection between information infrastructure (Bowker and Star 1999) and image-making, we can investigate the interdependence between the ways data gets stored and the “ways in which [a community of practice] attunes to, interacts with, and shapes its objects in its various and varied practices.” (Mol 2002, vii; see also Hacking 2002). To oversimplify: visualization method + data structure = ontology.

Methodologically, this essay aims to model the sort of approach that ethnographers and historical ethnographers might apply reflexively to assess their own methods of data visualization and image-making—especially methods drawing on data and techniques developed within other fields. My work shows how, as chemical databases and visualization methods are taken up outside their fields of origin, cross-disciplinary user communities can fall into a “certainty trough” (Mackenzie 1990), taking inscriptions created as index terms (where can you find data about a certain substance?) and granting them ontological status (what substance is this data about?). This is not necessarily a bad way of enacting the world, but we should be aware that we’re doing it!

Cover image

I want to avoid the temptation of getting lost in a hall of mirrors of representation and re-mediation, when it comes to this screenshot of a database-accessed copy of a digital scan of a newsmagazine article with a figure reproducing a soft-focus photograph of a chemical typewriter typing a diagrammatic representation of a chemical substance that never was. Instead, I want to emphasize the proliferation of articles containing figures like this in mid-20th century chemical journals, extolling the capacity of this or that chemical typewriter to type legible and interpretable structural formulas rather than hand-drawing them (or employing a professional graphical artist to do so). Across pen-and-paper, chalk-and-slate, mechanical, and digital media, the genre of the structural formula representing the molecular structure of a chemical substance has remained remarkably consistent since the late 1860s. Digital ethnographers might ask whether phenomena of interest are best explained in terms of digital media, in terms of genre, and/or along other dimensions of continuity and change.

This image

The taxonomic tree is a common visual genre for expressing a collection of relationships. Taxonomic trees reflect, imply, or constitute a hierarchical classification, pinning down entities to specific positions within it. Yet these trees also afford a certain flexibility, permitting the viewed to lump or split, emphasize sameness or difference, depending on which specific taxa or taxonomic level one chooses to privilege. Indeed, natural historians have at times interpreted trees as illustrations of the unreality of species as natural kinds. By this view, what’s arboreal is arbitrary.

Rhetorically, such images are frequently employed to overwhelm, confronting the viewer with a surfeit of complexity, employing an all-encompassing order to emphasize the incomprehensible scope of specifics. The tree in this figure, for instance, presents an impression of order-cum-overload supporting the article authors’ argument that the variety of fluorine-rich synthetic chemical substances subsumed in this hierarchy is in part responsible for their “Never-Ending Story” (per the article’s title) as persistent organic pollutants.


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.

Bowker, Geoffrey C., and Susan Leigh Star. 1999. Sorting Things Out: Classification and Its Consequences. Cambridge, MA: MIT Press.

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

Hacking, Ian. 2002. Historical Ontology. Cambridge, MA: Harvard University Press.

Mackenzie, Donald A. 1990. Inventing Accuracy: A Historical Sociology of Nuclear Missile Guidance. Cambridge, Mass: MIT Press.

Mol, Annemarie. 2002. The Body Multiple: Ontology in Medical Practice. Durham: Duke University Press.

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.

(Revision of May 9, 2019)


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.




United States