3 September 2019
The polyfluoroalkyl substances (PFAS) are chemical substances of increasing importance for the environment and public health. There are about 5000 commercial available PFAS but most information is available for two of these: perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) and their salts, which have been addressed in previous News releases (March and December 2016, May and August 2017, September 2018 and January, April and July 2019).
A selection of recent research is discussed briefly in the following:
Short PFAS in focus
An American research group has published a literature review on short- and ultrashort fluorinated substances with 2-3 and 4-7 fully fluorinated carbon atoms, respectively (Atea et al. 2019). The paper has a focus on analytical methods for short-chain PFAS and occurrence and mobility in natural waters and removal techniques of short-chain PFAS from such water.
Accumulation of PFAS in plants and vegetables
An Italian research group has published a literature review of accumulation of PFAS in agricultural plants (Ghisi et al. 2019). They found that the main sources of PFAS for plants were polluted water and soil amendment with biosolids such as sewage sludge. Further, the content and type of soil organic matter were affecting plant uptake of PFAS. In addition, the extent of PFAS accumulation in plants depended on the chain length and functional groups of the PFAS.
Thus, the uptake decreased in general with increasing chain-length and sulfonated PFAS were commonly less taken up than those with carboxylic groups and the same number of carbon atoms. It was found that leaf of cereals, vegetables and fruits were able to accumulate high levels of short-chain PFAS that can transfer to humans through the food chain.
After the phase-out of PFOA as catalyst in the production of fluoropolymers other fluorinated chemicals have been introduced instead, for example “perfluoralkyl ether carboxylic acids”. The most known is GenX.
GenX (2,3,3,3-Tetrafluoro-2-(heptafluoropropoxy)propanoic acid)
Now, these emerging PFAS and other PFAS have been determined in relatively high concentrations in river water downstream a production plant in the Netherlands using GenX and in drinking water produced hereof (Gebbink et al. 2017).
Concentrations of perfluoroalkyl substances (PFASs) in human embryonic and fetal organs
A Danish-Swedish study (Mamsen et al. 2019) has for the first time measured a dozen different PFAS (PFOS > PFOA > PFNA > PFDA = PFUnA = PFHxS in human embryonic and fetal organs from first, second, and third trimester pregnancies. A total of 78 pregnancies were included, from which a total of 296 individual tissue samples were obtained. Maternal blood samples were available in 63 cases.
In general, PFAS concentrations in embryo/fetal tissue (ng/g) were lower than maternal serum (ng/ml) but similar to placenta concentrations. The total PFAS burden was highest in lung tissue in first trimester samples and in liver in second and third trimester samples. The burden was lowest in CNS samples irrespective of fetal age. The placenta/maternal serum ratios of PFOS, PFOA and PFNA increased across gestation suggesting bioaccumulation in the placenta. The ratios were higher in pregnancies with male fetuses compared to female fetuses.
Effect on bone mineralization in children
Identifying factors that impair bone accrual during childhood is a critical step toward osteoporosis prevention. Exposure to polyfluoroalkyl substances (PFAS) has previously been associated with lower bone mineral density. In a new study (Cluett et al. 2019) participated 576 children with an average age of about 8 and living in the Boston area. Their plasma concentrations of several PFAS were determined, and the areal bone mineral density (aBMD) was measured by dual-energy X-ray absorptiometry (DXA).
The highest PFAS plasma concentrations were of perfluorooctanesulfonic acid (PFOS) [median 6.4 ng/mL] and perfluorooctanoic acid (PFOA) [median: 4.4 ng/mL]. Using linear regression, children with higher plasma concentrations of PFOA, PFOS, and perfluorodecanoic acid (PFDA) had lower aBMD z-scores. Thus PFAS exposure may impair bone accrual in childhood and peak bone mass, an important determinant of lifelong skeletal health.
Interaction of PFAS with thyroid hormones in children.
The blood serum concentrations of five PFAS (PFOS, PFOA, PFHxS, and PFNA) were measured In 186 children and youth among indigenous people in Canada (Caron-Beaudoin et al. 2019). The levels of PFOS, PFOA, PFHxS, were low. However, the serum levels (GM) of PFNA in participants aged 12 to 19 years old were with 3 µg/L three times higher than the Canadian average. Participants aged 6 to 11 years old had even higher serum PFNA concentrations (GM) of 9.44 μg/L, which should be the highest exposure to PFNA in children ever reported.
After adjusting for relevant confounders, the PFNA concentrations were positively and statistical significantly associated with free thyroxine (T4) levels, but not with thyroid-stimulating hormone (TSH) and thyroglobulin levels. No association was observed between other PFAS and thyroid hormones parameters.
The high levels of PFNA in the blood of these children may be explained by the fact that PFNA (perfluorononanoic acid) is the most abundant perfluoroalkanoic acid (PFAA) in Arctic wildlife. Especially high levels of PFNA have been determined in the livers of seals and polar bears.
Immunotoxicity of 8:2 Fluorotelomer alcohol
8:2 Fluorotelomer alcohol (8:2 FTOH) is a polyfluoroalkylated substance widely distributed in the environment after previous intensive usage. The substance is a PFOA and PFNA precursor, and therefore no more allowed to be used in most countries.
8:2 FTOH has been linked to hepatoxicity, nephrotoxicity, and reproductive toxicity, as well as endocrine-disrupting effects. A new study by Wang et al. (2019) showed that 8:2 FTOH (by gavage ≥ 10 mg/kg bw. for 28 days) also caused disturbances of immune system function in mice.
Modifying effect of vitamin C
In a study of 141 elderly Korean people (Kim et al. 2016) levels of perfluorooctane sulfonic acid (PFOS) and perfluorododecanoic acid (PFDoA) in their blood serum were positively associated with insulin resistance and oxidative stress.
Double-blind supplementation once a day for 4 weeks of 1000 mg vitamin C (ascorbic acid) resulted, however, in protection against this adverse effect. Supplementation of placebo had no protective effect.
POLICIES AND REGULATIONS
In 2008 the European Food Safety Authority (EFSA) established tolerable daily intakes of 150 ng PFOS/kg b.w. and 1500 ng PFOA/kg b.w. This assessment was mainly based on evidence from animal experiments, although it is known that such animals eliminate PFOS and PFOA much easier than humans.
The EFSA Panel on Contaminants in the Food (CONTAM) concluded in 2008 that the exposure to the general population for PFOS and PFOA was well below the derived TDI, and in 2012 EFSA confirmed that dietary exposure to PFOS and PFOA was highly unlikely to exceed the TDIs established by EFSA in 2008.
However, these TDIs have been criticized for being too high, and in March 2018 the EFSA CONTAM Panel also proposed much lower provisional tolerable weekly intakes (TWIs) of 13 ng/kg b.w. for PFOS and 6 ng/kg b.w. for PFOA. https://www.efsa.europa.eu/en/efsajournal/pub/5194
The assessment was based on human epidemiological studies. For PFOS, the increase in serum total cholesterol in adults, and the decrease in antibody response at vaccination in children were identified as the critical effects. For PFOA, the increase in serum total cholesterol was the critical effect. Also reduced birth weight (for both compounds) and increased prevalence of high serum levels of the liver enzyme alanine aminotransferase (ALT) (for PFOA) were considered.
The new TWIs are per day 80 and 1750 times lower than the previous TDIs for PFOS and PFOA, respectively. Since the chemicals are accumulating in the body, and the cumulative long-term exposure is most important, it is correct to use weekly intakes instead of daily intakes.
For both compounds, exposure of a considerable proportion of the population exceeds the proposed TWIs thus something has to done!
It showed up that the European Chemical Agency (ECHA) with support of some national institutions disagreed with and questioned the proposed EFSA TWIs. An Expert meeting with the various parties involved was organized by EFSA in Parma on 24 September 2018. The minutes of the meeting was agreed on 10 December 2018. The meeting concluded that the divergence was considered not to be substantive due to the different scopes of the CONTAM Panel risk assessment and the ECHA restriction procedure. The participants agreed that further discussion was needed on these substances, and that collaboration on future assessments would be needed. Final TWIs for PFOS and PFOA are expected from EFSA in December 2019. https://www.efsa.europa.eu/sites/default/files/news/efsa-contam-3503.pdf
Short‑chain perfluoroalkyl acids are substances of very high concern (SVHC)
Some scientists at the German EPA have made a scientific paper suggesting a strategy for regulation of short-chain PFAS under REACH (Brendel et al. 2018). They concluded that an effective regulation was urgently needed to minimize human and environmental exposure, because of the increasing use of these chemicals, their high mobility in soil and water, their extremely persistent degradation products and their enrichment in edible parts of plants; all resulting in food drinking water contamination with these substances.
Denmark will ban all polyfluorinated substances (PFAS) in food contact materials
This is according to a press release by Mogens Jensen, the Danish Minister of Food.
Addition of PFAS to food contact materials, such as paper and paperboard packaging, results in a fat- and water repellent effect, which protects the food content. Use areas are, for instance, fast food wrappers, microwave popcorn, cereal packing, and paper wrappers for cake’s and deserts.
A recent study from the USA concluded that 56 %, 38% and 20% of the measured dessert and bread wrappers, sandwish and burger wrappers, and paperboard for pommes frites, respectively, on the market had a content of fluorine compounds, which can migrate into the food.
It is expected that the ban will come into force in July 2010.