Accumulation of Perfluoroalkylated Substances in Oceanic Plankton.

[NNadir]

A paper with the title of this post appears in the current issue of the journal Environmental Science and Technology.

The link is here: Environ. Sci. Technol., 2017, 51 (5), pp 2766–2775

Perfluoroalkylated compounds are now widely considered to join some well known toxic species like, for instance, PCBs (Perchlorobiphenyls) and PBDE's (Polybrominated diphenyl ethers) and DDT and many others as members of a class of compounds known as persistent organic pollutants (POPs).

Many of these compounds were originally contained in consumer products; PBDE's for one example were originally developed as flame retardants in fabrics and electronic devices. Sometimes these POP's were utilized in important industrial infrastructure systems important in every day life. PCB's were widely used (and are still present) in transformers on which our electricity depends as well as in other devices, like capacitors in TV's.

Perfluroakylated products were used in a wide variety of products, PFOA (perfluorooctanoic acid) for example is a degradation product of Teflon. Spray on products designed to protect fabrics in furniture and clothing often utilized perfluorinated organic compounds.

The introductory text of the paper gives some insight to the level of concern associated with these compounds.

To wit:

Perfluoroalkylated substances (PFASs), including perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs), are ubiquitous in the global environment. PFASs have been detected in wildlife and human tissues and have been associated with a broad array of adverse effects, including neurodevelopmental alterations,(1) reproductive,(2) immunologic(3) and metabolic effects.(4) The occurrence of PFASs has also been described in remote oceanic and polar regions.(5-8) Concerns regarding the persistence, toxicity, and environmental effects(9, 10) led to the inclusion of perfluorooctanesulfonic acid (PFOS), its salts, and perfluorooctane sulfonyl fluoride (PFOSF), in the list of Persistent Organic Pollutants (POPs) regulated under the Stockholm Convention.(11) Perfluorooctanoate (PFOA) is currently under consideration for its inclusion in this list. However, ongoing production of PFOS and its precursors, of PFCAs and their respective precursors, as well as new alternative PFASs(12-15) requires continuous monitoring and fate assessment of PFASs in the global environment.

The biogeochemistry and long-range transport of POPs depends largely on their physico-chemical properties. The water solubility of ionizable PFASs is higher than that of chlorinated POPs, such as polychlorinated biphenyls (PCBs) or polychlorinated dibenzo-p-dioxins (PCDDs). For that reason, although PFAS neutral precursors undergo atmospheric transport(16) reaching remote regions,(17, 18) oceanic transport of PFASs has been suggested as an important transport vector from source regions to remote marine environments.(19-21) Due to the importance of the marine system in the global distribution of PFASs, previous surface seawater monitoring has already been reported.(7, 9, 22, 23) The occurrence of PFASs in deeper seawater has received little attention in terms of vertical profiles(22) and vertical transport.(24)

I have an interesting book on the topic of these compounds in my personal electronic library:

Toxicological Effects of Perfluoroalkyl and Polyfluoroalkyl Substances

In it one can read all about the fun physiology of these compounds and find lots of interesting references like this one:

Neurobehavioral teratogenicity of perfluorinated alkyls in an avian model (Neurotoxicology and Teratology Volume 32, Issue 2, March–April 2010, Pages 182–186) (It's about chickens, and not humans, although - to allow a little innuendo, it could also be about humans. I often think one might need to be neurologically impaired to vote for certain kinds of people and, to recall, Ronald Reagan was known as the "Teflon President&quot

Anyway, the scientists in the paper originally cited here investigated the concentration of perfluoroalkylated compounds in oceanic plankton, a key element in our biosphere, and what they found was disturbing, at least to me, since I am professionally involved in the measurement of compounds at physiologically relevant levels.

PFOS and PFOA were ubiquitously detected in plankton samples with concentrations ranging from 0.1 to 43 ng g dry weight (dw)–1 and from 0.5 to 6.7 ng gdw^–1, respectively. Short chain PFCAs were generally more frequently detected than longer chain PFCAs (detection frequency among all samples: PFBA - 65%, PFPeA - 100%, PFHxA - 7%, PFHpA - 100%, PFOA - 100%, PFDA - 21%, PFUnA - 69%, PFDoA - 7%, PFTrA - 3%, PFTeA - 3%). Regarding other PFSAs, PFHxS, and PFDS were not always detected in plankton (found in 59% and 14% of the samples, respectively), and their concentrations were always low (<LOQ to 0.9 ng gdw–1).

"ng" here refers to nanograms, billionths of a gram, and gdw^–1 refers to "per gram dry weight." If you are comforted by the concentrations being at a billionths of a gram, don't be. Most important drugs of physiological importance, things like antibiotics, blood pressure drugs, heart drugs, cancer drugs, etc, etc, etc exert their effects at similar concentrations, and some do it pictogram (trillionths of a gram) levels.

Many of the other persistent organic pollutants are also halogenated, for instance PCB's have carbon chlorine bonds, and PBDE's have carbon bromine bonds, both in aromatic rings.

The big difference with perfluorocompounds, which have carbon fluorine bonds, is that the carbon fluorine bonds are extremely strong, and therefore far more difficult to break.

All of these compounds can be remediated by exposure to radiation but the energy of the radiation required is a function of the bond strength. It is possible in some cases, to break chloro and bromo carbon bonds with UV light, particularly in the presence of catalysts, the most notable being titanium dioxide and various derivatives know in the class of titanates.

A caveat is that UV light requires in general, um, energy. This is described in a nice "opinion" paper a few issues back in Environmental Science and Technology:

Photocatalytic Water Treatment: So Where Are We Going with This?

The author writes:

During the Cold War era race to the moon between the United States and the USSR, the Soviets are now believed to have possessed a working lunar orbiter, lunar lander, and functional moon suits at the time of the Apollo 11 success. They lacked, however, a reliable rocket capable of getting this payload to the moon. While the quest for photocatalytic water treatment (PWT) is a bit less awe-inspiring, parallels can be drawn between the moon race story and the failures of this enticing form of water treatment. In a 1996 interview with Chemical & Engineering News, chemist James R. Bolton commented on the surge of recent studies within this new field: “This may be a strong statement, but I think the interest in TiO2 [in aqueous systems] is a good example of scientific hype.”(1) Twenty years later, it is surprisingly difficult to argue that he was wrong. The field has ballooned within academia and spawned a growing number of subfields pursuing new applications of PWT, improved catalysts, and reaction mechanisms. And yet, the fundamental technology has scarcely demonstrated a capability to survive outside the lab. While I am a hopeful believer in PWT and active participant in the field, “hype” is perhaps still the best descriptor of its present driving forces and academic allure. In fact, among the water treatment fields, photocatalytic processes arguably show the widest disconnect between research directions and the actual needs of the water industry.

In any case, UV radiation is not strong enough in most circumstances to break carbon fluorine bonds.

A very nice (open sourced) paper in the Nature sponsored journal Scientific Reports describes this nicely.

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

Complete mineralization of perfluorooctanoic acid (PFOA) by ?-irradiation in aqueous solution (Scientific Reports 4, Article number: 7418 (2014))

The authors were able to completely mineralize (convert the perflurooctanoic acid to fluoride salts and carbon dioxide) under relatively mild conditions, but they required gamma radiation to do it.

I always have the same agenda:

In the 1950's and 1960's there was some discussion of utilizing gamma radiation to routinely purify water, and of course, there are still some people who know quite well what a good idea this was.

Since when I was a dumb and easily distracted kid, I can still remember some looney somewhere shouting at some anti-nuke demonstration I was at that this was horrible since gamma radiation came from "nuclear waste" and this was "our" water!!!!!

Our waters are all turning to shit.

Fear and ignorance have won the day, and in those times, when I was attending anti-nuke demonstrations, I was part of the reason for spreading that same fear and ignorance.

Recently, since this is the sixth anniversary of an event in which close to 20,000 people were killed by, um, drowning and collapsing buildings in an earthquake in Japan, I've been hearing a lot on this website about the reactors that failed in the same event. I've commented on this picayune garbage in my usual acerbic way, but it will do no good.

What is done cannot be undone.

Environmentally, the reactors at Fukushima are meaningless in the sense that they are of small consequence in the big picture. Perfluoroalkylated substances are far more important, and even they fall far behind climate change and air pollution in terms of their overall threat to humanity and the planet's biosphere as a whole.

We make fun of the Republicans for representing that saluting the flag is a more important issue than, say, um, climate change as if we are immune to trivializing distractions.

We are not.

Have a nice evening.

[KT2000]

1. we will not evolve out of this

we will adapt to the damage and the changes in what humans are.

[eppur_se_muova]

2. Heck, I have heard from some who are afraid to heat water in the microwave ...

because they have read you can produce dangerous free radicals that way. No clear response when I asked how long these radicals supposedly persisted.

AFAIK they still use the microwave for cooking ... just not heating water.

[NNadir]

3. "Normal" free radicals are not generally strong enough to break C-F bonds...

...in alkyl fluorides, and by "normal" I mean the very powerfully oxidizing ^.OH radical.

Apparently one needs a healthy dose of solvated electrons to do the trick. I would not be surprised to learn that the effectiveness of gamma radiation on mineralizing PFOA is also connected to direct cleavage of the C-F bond at least in rare cases.

Gamma radiolysis can destroy many of the common contaminants that are becoming more and more problematic from personal care products, pharmaceuticals and their metabolites, insecticides, electronic waste, and things like flame retardants.

The obvious best source for this would be fission products, which are readily available and relatively easy to place in insoluble forms.

They are an excellent source of gamma radiation, x-rays, and can in fact be stepped down to make a continuous source of UV. All of these forms of radiation can be utilized to break problematic bonds in contaminants in water and in air. It's a shame that we are not utilizing them as such.