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| the compounds in question Credit: C&EN |
The US Environmental Protection Agency is doubling down on efforts to
decrease a backlog of new pesticide active ingredients waiting for EPA approval to enter the marketplace. Since April, the agency has proposed registering four of them—cyclobutrifluram, diflufenican, isocycloseram, and trifludimoxazin.All four pesticides contain a fully fluorinated methyl or methylene group, raising concerns that they will persist in soil and water for many years. Environmental groups argue that the chemicals are per- and polyfluoroalkyl substances (PFAS) under the definition recommended by the Organisation for Economic Co-operation and Development (OECD) in 2021. PFAS are notoriously difficult to remove from the environment, and some of them are toxic at extremely low levels.
The proposed active ingredients have half-lives of over 3 years, which means that half of what is sprayed today will still be contaminating soil and water in 3 years, at the time of the next US presidential election, Nathan Donley, environmental health science director at the Center for Biological Diversity, said during a meeting of the EPA’s Pesticide Program Dialogue Committee (PPDC) on June 17. Donley is a member of the PPDC, representing the environmental group’s perspective.
“It’s like PFAS pollution on steroids these past few months,” he said, referring to the EPA’s plan to approve the four pesticides. The EPA’s pesticides office “appears to have absolutely no plan to account for the fact that actives are getting more persistent and fluorinated breakdown products are essentially going to be around forever.”
The proposed pesticide active ingredients can degrade into trifluoroacetic acid, which persists in the environment for more than 100 years, Donley noted.
Of course, there actually IS an apparent definition of PFAS:
The EPA’s Office of Pesticide Programs considers PFAS to be chemicals containing at least two saturated, fully fluorinated carbons, either CF2 or CF3. The OECD defines PFAS as any chemical with at least one saturated CF2 or CF3. The European Union has adopted a definition that is closer to that recommended by the OECD.
I am rather shocked that a legal definition of PFAS is about the number of saturated CF2 or CF3 and that is set so low. I mean, perfluorooctanoic acid has, I dunno, fifteen of them? But what do I know, I'm not a PFAS expert, I'm just a dumb organic chemist.
I think the relevant question would be if the metabolic products can't be broken down further - if you get TFA and TFA can't be further degraded in the environment, then anything that ends up generating it should likely be treated as persistent. The problem could be that metabolism likely depends on what other functional groups are nearby (and what bugs are nearby) - CF3 and CF2 groups aren't all created equal.
ReplyDeleteThe OECD definition seems overly broad - I don't think they have a core property to identify PFAS by and don't want companies hopping to PFAS that haven't been tested and so don't have negative data for them, so the OECD just wants to ban everything that looks close to a PFAS. That seems bad, but I don't know what to do. - Hap
Agreed - I think TFA is the primary concern. Given that there's already a measurable level of TFA in much ground water and there's no biological breakdown mechanism, I think it's far safer to apply a flat out ban except perhaps for some pharmaceuticals.
Deletenot sure funny how
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