Following the definition of per- and polyfluoroalkyl substances (PFAS) suggested by Buck et al.(1) and adopted in the Organization for Economic Co-operation and Development (OECD) report(2) and in the U.S. Environmental Protection Agency (EPA) PFAS inventory,(3) the recent letter titled “Scientific Basis for Managing PFAS as a Chemical Class” by Kwiatkowski et al.(4) proposes a class-based regulatory action for thousands of fluorinated chemicals. Kwiatkowski et al. claim that all PFAS, which the article defines as any chemical with at least one aliphatic perfluorocarbon moiety (-C_nF_2n-, where n ≥ 1), are or could lead to substances that are persistent, can accumulate in the environment and living organisms, and could impact human and ecological health. The Montreal Protocol (MP) for the protection of the ozone layer is an example of a wide regulatory action that controls the production and consumption of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and other chemicals.(5) The MP has been evaluated and ratified on the basis of extensive scientific knowledge for all targeted compounds and, even more so, lists all of the controlled substances in its annexes. The MP relies on a periodic scientific assessment that evaluates the impact of halogenated compounds on the stratospheric ozone layer and climate change based on >1000 scientific studies.(6) Before a class-based approach for PFAS like that suggested by Kwiatkowski et al. is adopted, the process should follow the well-justified path of previous regulatory actions and rely on an extensive scientific evaluation of each PFAS subgroup and compounds within. Several C₂–C₄ HCFCs, HFCs, and hydrofluoroolefins (HFOs) are categorized as PFAS in ref (4) and in the EPA’s and OECD’s inventories. HCFCs, HFCs, and HFOs were or are used in various applications (refrigeration, blowing agents, and others). HFOs are the latest-generation CFC substitutes with a negligible contribution to climate change and stratospheric ozone layer depletion, compared to their predecessors.(6−8) HCFCs, HFCs, and HFOs are gaseous substances, and their atmospheric lifetimes and degradation pathways and products are well-documented in reviews, assessments, and references therein.(6,9−13) A majority of HCFCs, HFCs, and HFOs degrade fully in the environment (common end products are CO₂, H₂O, and CaF₂ or other minerals). Some, but not all, of the commercially available HCFCs, HFCs, and HFOs degrade in the environment to trifluoroacetic acid (TFA), the simplest of the perfluorocarboxylic acid (PFCA) group of substances.(9,10) TFA is vastly different from the larger PFCAs (PFOA and other PFCAs), which are anthropogenic substances of regulatory interest. The sources, fate, and associated risks of TFA have been documented.(6,14−16) TFA occurs in the environment from natural and anthropogenic sources and does not bioaccumulate in the food chain.(14,16−20) Although TFA is considered environmentally persistent, a few degradation pathways that require further research to evaluate their importance have been suggested in the literature.(16,21,22) HFO-1234yf (CF₃CF═CH₂) is a characteristic example of the HFO class because it is a low-global warming potential (GWP_100yrs < 1) alternative for HFC-134, a MP-regulated substance with high CO₂-eq emissions, in mobile air conditioning (MAC).(6−8,23) Because HFO-1234yf produces ∼5 times more TFA than HFC-134a, which it replaces, atmospheric modeling studies evaluated the TFA environmental impact if complete conversion to HFO-1234yf is assumed for MAC.(14,16,24,25) It has been concluded that the use of HFO-1234yf in MAC will lead to insignificant amounts of TFA being deposited on the surface and oceans that pose no threat to humans or the ecosystem.(6,14−16,24,25) TFA is a well-studied compound that is completely miscible with water. As one would expect with most very water-soluble chemicals, its octanol–water partition coefficient shows there is a negligible risk of bioaccumulation;(19,20) therefore, any future regulatory action on the premise of bioaccumulation should exclude TFA and its anthropogenic precursors. Kwiatkowski et al. list the major PFAS subclasses, which, among others, include perfluoroalkyl acids (PFAAs) and substances that could potentially transform to PFAAs in the environment. While several longer-chain PFAAs (≥C₄) are of regulatory interest due to their widespread environmental presence, this subclass represents only <10% of PFAS in inventories.(2,3) PFAA precursors make up a large fraction of the PFAS group (several subgroups and thousands of compounds in inventories). Longer-chain PFCAs are among the most studied PFAAs in the literature. The manufacture, use, and disposal of PFCA are their main sources of direct environmental release, and their distribution occurs via oceanic and atmospheric circulation.(26−29) The contribution of PFCA precursors to the total PFCA environmental concentration, although uncertain, is relatively small (<10%).(26−29) The atmospheric emissions, observations, chemistry, and contribution to PFCA environmental concentration of fluorotelomer alcohols (FTOHs) and other long-chain PFCA precursors are discussed in the literature.(29−40) FTOHs typically yield <10% of the corresponding PFAS, but the exact magnitude depends on emissions and chemistry assumptions that remain a large source of uncertainty in atmospheric models. Critical parameters for an accurate model representation are the magnitude and geographical distribution of precursor emissions, the NO_x, HO₂, and RO₂ concentrations in the modeled domain, and the kinetic and mechanistic information for critical reactions and their dependence on perfluorinated-chain length, temperature, and pressure.(29,30,33−36) As discussed in past studies, these parameters require further research and are crucial for assessing the significance of PFCA precursors before any wide class-based regulation of >1000 compounds. Perfluoro-alkanes, -amines, and -ethers are also suggested to be PFAS by Kwiatkowski et al.(2−4) These have long atmospheric lifetimes and are on the radar of regulatory bodies due to their high GWP.(6,23,41) Their atmospheric degradation does not lead to any PFAS of concern. In fact, their atmospheric chemistry is distinctly different from those of other fluorochemicals because these substances fully degrade at altitudes of >50 km (mesosphere) by Lyman-α radiation.(41,42) Lastly, the PFAS structural definition in ref (1) (i.e., must contain the C_nF_2n+1- moiety) is different from the broader one of Kwiatkowski et al. and others (presence of the -C_nF_2n- group).(2−4,43−47) On the basis of the latter definition, a number of HCFCs, HFCs, and other fluorochemicals that have only -CF₂- groups in their structure are included in PFAS inventories.(2,3) Using established atmospheric oxidation pathways, many of these compounds are not expected to degrade to persistent, bioaccumulative, and/or toxic substances.(6,9−13) We disagree that there is a scientific basis for regulating thousands of compounds as one class, as well as with the overgeneralization of PFAS physicochemical behavior based on an assessment of a relatively small number of substances. The relative importance and the state of knowledge for each subclass (and compounds within) as well as important scientific gaps are not discussed in depth by Kwiatkowski et al. There is clearly a need for a more accurate, science-driven, and methodological approach upon which regulatory bodies can rely for future PFAS actions, as is the case for previous landmark regulations such as the MP. The views expressed in this article are those of the authors and do not necessarily represent the views of Honeywell International Inc. The authors declare the following competing financial interest(s): The authors of this Correspondence are affiliated with Honeywell International Inc., a manufacturer of fluorinated chemicals. The authors declare the following competing financial interest(s): The authors of this Correspondence are affiliated with Honeywell International Inc., a manufacturer of fluorinated chemicals. This article references 47 other publications.

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评论“将PFAS作为化学类别进行管理的科学依据”

遵循Buck等人（1）提出的并在经济合作与发展组织（OECD）报告（2）和美国环境保护署（EPA）中采用的全氟烷基物质和多氟烷基物质（PFAS）的定义。 PFAS清单（3），最近由Kwiatkowski等人（4）撰写的题为“将PFAS作为化学类别进行管理的科学依据”的信提出了针对数千种氟化化学品的基于类别的监管措施。Kwiatkowski等。要求将所有PFAS（本文定义为具有至少一个脂肪族全氟化碳部分（-C _n F _{2 n-}，其中n≥1），是或可能导致持久存在的物质，会在环境和生物体内积聚，并可能影响人类和生态健康。保护臭氧层的蒙特利尔议定书（MP）是广泛管制行动的一个例子，该行动控制氯氟烃（CFC），氢氯氟烃（HCFC），氢氟烃（HFC）和其他化学品的生产和消费。（5）根据对所有目标化合物的广泛科学知识，对MP进行了评估和批准，甚至在其附件中列出了所有受控物质。MP依靠一项定期的科学评估，根据超过1000项科学研究评估了卤代化合物对平流层臭氧层和气候变化的影响。（6）在基于类的PFAS方法之前，像Kwiatkowski等人所建议的那样。如果采用此方法，则该过程应遵循先前的监管措施的合理化路径，并依赖于对每个PFAS亚组和其中的化合物的广泛科学评估。几个C_{2 –} C ₄ HCFC，HFC和氢氟烯烃（HFO）在参考文献（4）中以及在EPA和OECD的清单中归为PFAS。HCFC，HFC和HFO已经或已经用于各种应用（制冷，发泡剂和其他用途）。氢氟碳化合物是最新一代的氟氯化碳替代品，与它们的前代产品相比，对气候变化和平流层臭氧层消耗的贡献微不足道。（6-8）氟氯烃，氢氟碳化合物和氢氟碳化物是气态物质，它们的大气寿命，降解途径和产物（6,9-13）大多数HCFC，HFC和HFO在环境中会完全降解（常见的最终产品为CO ₂，H ₂ O和CaF _2）。或其他矿物质）。在市场上，部分但并非全部的HCFC，HFC和HFO会降解为三氟乙酸（TFA），这是最简单的全氟羧酸（PFCA）类物质。（9,10）TFA与以下物质有很大不同较大的PFCA（PFOA和其他PFCA），它们是具有监管意义的人为物质。已经记录了TFA的来源，命运和相关风险。（6,14-16）TFA在环境中来自自然和人为来源，并且不会在食物链中生物累积。（14,16-20）尽管TFA是考虑环境持久性，需要进一步研究，以评估其重要的几个降解途径已经被建议在文献中。（16,21,22）HFO-1234yf的（CF ₃ CF = CH ₂）是HFO类的典型示例，因为它是HFC-134（一种受MP管制的高CO ₂物质）的低全球变暖潜能值（GWP _100yrs <1）。移动空调（MAC）中的当量排放量。（6-8,23）由于HFO-1234yf产生的TFA比其替代的HFC-134a高约5倍，因此大气模型研究评估了如果完全转化为HFA-1234yf，TFA对环境的影响MAC假定使用HFO-1234yf。（14,16,24,25）已经得出结论，在MAC中使用HFO-1234yf将导致少量的TFA沉积在水面和海洋上，不会对人类构成威胁（6,14−16,24,25）TFA是一种经过充分研究的化合物，可以与水完全混溶。正如人们对大多数水溶性非常高的化学品所期望的那样，其辛醇-水分配系数表明生物蓄积的风险可以忽略不计；（19,20）因此，任何未来在生物蓄积前提下的管制措施都应排除TFA及其人为前体。Kwiatkowski等。列出了主要的PFAS子类别，其中包括全氟烷基酸（PFAA）和在环境中可能转化为PFAA的物质。而几个较长链的PFAA（≥C₄）由于其广泛的环境存在而受到监管关注，该子类仅占库存中PFAS的<10％。（2,3）PFAA前体占PFAS组的很大一部分（库存中的几个子组和数千种化合物） 。较长链的PFCA是文献中研究最多的PFAA之一。PFCA的生产，使用和处置是其直接环境释放的主要来源，其分布是通过海洋和大气循环来实现的。（26-29）PFCA前体对PFCA总环境浓度的贡献虽然不确定，但相对小（<10％）。（26−29）大气排放，观测，化学，文献中讨论了氟调聚物醇（FTOH）和其他长链PFCA前体对PFCA环境浓度的贡献。（29-40）FTOH通常产生相应PFAS的<10％，但确切的数量取决于排放量和化学成分这些假设仍然是大气模型不确定性的主要来源。精确模型表示的关键参数是前体排放量，NO的大小和地理分布。_x，HO ₂和RO ₂建模域中的浓度，关键反应的动力学和机理信息及其对全氟链长度，温度和压力的依赖性。（29,30,33-36）正如过去的研究所讨论的，这些参数需要进一步的研究和对于在> 1000种以上的化合物进行任何基于类别的广泛管制之前，评估PFCA前体的重要性至关重要。Kwiatkowski等人（2-4）也建议使用全氟烷烃，-胺和-醚为全氟辛烷磺酸。它们的大气寿命很长，并且由于它们的高全球升温潜能值而备受监管机构的关注。（6,23， 41）它们的大气退化不会导致任何关注的PFAS。实际上，它们的大气化学与其他氟化物明显不同，因为这些物质会在>_n F _{2 n + 1-}部分）与Kwiatkowski等人的较宽泛的文章不同。（-C _n F _{2 n-}基团）。（2-4,43-47）根据后一个定义，许多仅含-CF ₂的HCFC，HFC和其他含氟化合物-PFAS清单中包括其结构中的基团。（2,3）使用已建立的大气氧化途径，预计其中许多化合物不会降解为持久性，生物蓄积性和/或有毒物质。（6,9-13）我们不同意将一千种化合物作为一类来进行调节具有科学依据，并且基于对相对少量物质的评估而过度泛化了PFAS的理化行为。Kwiatkowski等人未深入讨论每个子类（及其中的化合物）的相对重要性和知识水平以及重要的科学空白。显然，需要一种更准确，科学驱动和方法论的方法，监管机构可以依靠该方法来执行未来的PFAS行动，像MP等以前的地标性法规就是这种情况。本文中表达的观点仅代表作者的观点，并不一定代表霍尼韦尔国际公司的观点。作者声明以下相互竞争的财务利益：本通讯的作者与制造商霍尼韦尔国际公司有关联。氟化物。作者声明存在以下竞标的经济利益：本通讯的作者与氟化化学品制造商Honeywell International Inc.有关联。本文引用了其他47种出版物。该通讯的作者隶属于霍尼韦尔国际公司，后者是氟化物生产商。作者声明存在以下竞标的经济利益：本通讯的作者与氟化化学品制造商Honeywell International Inc.有关联。本文引用了其他47种出版物。该通讯的作者隶属于霍尼韦尔国际公司，后者是氟化物生产商。作者声明存在以下竞标的经济利益：本通讯的作者与氟化化学品制造商Honeywell International Inc.有关联。本文引用了其他47种出版物。