Chinese scientists demonstrate complete mineralization of the persistent pollutant PFOA.

[NNadir]

Recently in this space, we learned about the pollution of wells, fish in a Michigan unincorporated area:

200 Homes In Oscoda, MI Using Bottled Water; PFAS From Closed Airbase In Wells, Lake Huron, Fish

PFAS is a broad chemical class of compounds and is an abbreviation for "perfluoroalkylated substances."

Since the US EPA has been effectively shut down to serve the interests of a corrupt member of the Trump crime family, who squanders money on first class flights for himself and his friends in order to prevent it being spent on the Environment, it is necessary to refer to a document from a European agency, in this case the European Food Safety Authority, to give a comprehensive description of what these compounds are, and something about their health implications: Perfluoroalkylated substances in food: occurrence and dietary exposure

One may find a list of the compounds in this document.

The report, which is a report in meta-analysis of a wide variety of published data, assembles data from studies involving over 50,000 samples, and concludes that most concentrations in food stuffs in Europe are below actionable limits, the "TDI" or "Tolerable Daily Intake" but are nonetheless clearly detectable in pretty much everything. The data evaluated was collected over six years from 2006 to 2012.

The compounds do accumulate in tissue, particularly adipose tissue, and they do not degrade in tissue, nor are they generally excreted.

Although the report indicates that the problem is not yet represent a major health risk from the foodstuffs analyzed, it does list the toxicological and human health concern after stating the sources of these pollutants:

Public health concern towards PFASs was raised after several studies indicated that PFOS and PFOA are present in the environment including the human body. Several adverse health effects e.g. hepatotoxicity, developmental toxicity, neurobehavioral toxicity, immunotoxicity, reproductive toxicity, lung toxicity, hormonal effects, as well as a weak genotoxic and carcinogenic potential have been demonstrated in experimental studies in animals (Lau et al., 2007; Zhang et al., 2008; Shi et al., 2009; Peden-Adams et al., 2009; Eriksen et al., 2010; Pinkas et al., 2010). Recently, an epidemiological study performed on a children cohort in the Faroe Islands indicated that high exposure to PFASs was associated with reduced humoral immune response to immunisations in children (Grandjean et al., 2012). Many studies have reported the presence of PFASs in food indicating fish and other seafood as the most contaminated commodities (Berger et al., 2009; Delinsky et al., 2009; Haug et al. 2010a; Schuetze et al., 2010)...

In the general scientific literature the most commonly mentioned PFAS that I see are PFOS and PFOA, respectively perfluorooctanoic sulfonic acid and perfluorooctanoic acid.





The paper I will site below referring to the title here - happily it is open access - refers to the latter compound.

If you're wondering by the way, where these compounds come from, they were widely used in a wide range of consumer products and materials, one of the most famous of such compounds was the now reformulated (and not necessarily harmless) product Scotch Guard, which keeps your furniture stain free. (Aren't you lucky?)

When reading the post above about the unfortunate Oscoda region, in a response I proposed to write about an interesting paper I came across in my general reading about a new kind of laser material for putting out short wavelength (high energy) UV radiation at wavelengths that have been shown to degrade PFOA, albeit slowly, UV radiation at 185 nanometers. This material was said to lase at wavelengths at 177 nm, and therefore should work. This paper is here:

CsSiB3O7: A Beryllium-Free Deep-Ultraviolet Nonlinear Optical Material Discovered by the Combination of Electron Diffraction and First-Principles Calculations (Sun et al, Chem. Mater., 2018, 30 (7), pp 2203–2207)

As interesting as this paper is, it appears that this material is still a laboratory curiosity, an impurity discovered in a similar compound, a single mm scale crystal does not appear to have been grown, so with dreams of beryllium free UV lasers aside for now, I did a quick search to see the latest and greatest path to actually remediating this worldwide environmental problem via radiation, radiation being the only tool for degrading PFAS that will work.

So, I won't be discussing this interesting paper on this website any further.

You may not like that bolded statement, an inconvenient truth if you will, but having just returned from my local "March for Science" nominally dedicated to "facts" and having heard a pompous airhead from the Sierra Club having no facts to support his absurd argument, I'm trying to still believe that facts matter, whether people who hate them are nominally either on the left or the right.

Ignorance from the leadership of the leadership of putative self declared "Environmental Organizations" is no less toxic than ignorance on the far right. Sorry but it's true. Your Sierra Club calendar at Christmas may not be helping to address environmental problems; it may be hurting.

The paper I found is this one: Complete mineralization of perfluorooctanoic acid (PFOA) by ?-irradiation in aqueous solution (Sheng et al, Scientific Reports volume 4, Article number: 7418 (2014))

Although the paper is open sourced and you can read it yourself at the link, I'll take the liberty of reproducing the opening paragraphs here:

A class of fully fluorinated hydrocarbons known as perfluorocarboxylic acids (PFCAs, CnF2n + 1COOH) has been widely applied in various ranges for several decades. They are receiving increasing attention because of their easy bioaccumulation and persistent toxic environment impact. Perfluorooctanoic acid (C7F15COOH, PFOA), as a PFCA has already been detected in environment waters, human bodies and wildlife1,2,3,4. As a ubiquitous environmental contaminant, PFOA has the following features: extremely resistant degradation, bioaccumulation in food chains, and long half-lives in human bodies, all of which present characteristics of persistent organic pollutants5,6. The major human exposure sources to PFOA and other PFCs include drinking water7 and edible fish8 etc, and can lead to several chronic and developmental problems, such as children attention deficit/hyperactivity disorder9 and lowered immune response to vaccinations10. Statistic survey shows that its concentration in human bodies and wildlife continues to increase in certain location globally11.

However, PFOA is very stable and considered almost non-biodegradable under natural environments because of the strong C-F bonds (116 kcal/mol). Besides, some researchers reported that PFCAs could almost not be degraded by advanced oxidation process. The principal reason may be that C-F bonds can't be destroyed effectively by hydroxyl radicals (·OH)12,13. Various treatments for PFCAs including adsorption14, photocatalysis15,16, photolysis17, thermolysis18, sonochemical19 and other methods20,21 have been tested for decomposing PFCAs. However, harsh reaction conditions at high temperatures and high pressures are usually needed18,19. Furthermore, the mineralization and defluorination of PFCAs always could not be achieved completely, and toxic by-products might be formed during the decomposing processes12. Thus, it is highly desirable not only to decompose the PFCAs, but also to defluorinate the toxic by-products for complete mineralization of PFCAs. A novel method for PFCAs mineralization with high efficiency is still highly desired.

...highly desired indeed.

They have such a method, and its described in the paper, which again you can read without traveling to a science library.

Here's a relevant graphic from the paper:



The best pathway involves basic solutions, so it's not a slam dunk direct drinking water approach, although it is very easy to remove calcium hydroxide from water simply by bubbling air through it, especially now since our air is so enriched in the dangerous fossil fuel waste carbon dioxide. Calcium hydroxide would be preferred since calcium fluoride, a component of many dental preparations, is completely insoluble, thus negating any effects from either hydrogen fluoride or soluble fluoride salts.

But it works apparently.

In this paper, the source of ? radiation was cobalt-60. My personally preferred source of ? radiation is cesium-137, which is readily available from used nuclear fuel, and in fact is available to USDOE licensees from stock, as I noted in a previous post in this space.

16 Years of (Radioactive) Cesium Recovery Processing at Hanford's B Plant.

The Ba-137m gamma ray available from the decay of cesium-137 is only about half as energetic as the Co-60 gamma ray, but it is well known to produce solvated electrons, which according to this paper on PFOA degradation is the key intermediate.

The degradation pathway, which is something along the lines I imagined, but also slighly different, is also shown:



This shows that the pathway is sequential and takes place at the functionalized end of these molecules. It is entirely possible that other pathways, removing fluorine atoms on the interior chain might have a toxicological footprint that is worse - possibly, but not definitively - and so the shown mechanism is to be preferred, since these intermediate perfluoro shorter chained alkanoic acids are already in the environment, some still in commercial products. Thus stopping the radiation process before completion is not likely to make things worse as opposed to better.

Nevertheless, with enough exposure, they will definitely entirely degrade these compounds to carbon dioxide and calcium fluoride, the mineral fluorite.

Have a nice Saturday evening.

[NNadir]

1. Errata.

In my original post here, to which I referred this morning, I noticed that a typo existed, the word not having been missed in the statement, here corrected,

The compounds do accumulate in tissue, particularly adipose tissue, and they do not degrade in tissue, nor are they generally excreted.

Like lead, PFOA, thus accumulates over a lifetime of eating contaminated food.