4 ms·

> forever chemicals Sorry, but that phrase really annoys me.[0] What does it actually mean? [0] full disclosure: PhD in organic chemistry

mdrew 3y ago
Totally agree. You can blame the Washington Post. But we choose to use it because a lot of people don't know the chemistry but recognize this label.
azinman2 3y ago
As a layman, my understanding is that it doesn't break down over time. Is that not right?
philipkglass 3y ago
It generally refers to polyfluoroalkyl substances, often abbreviated PFAS. The "bad" ones are hydrophobic compounds that can accumulate in fat tissue. There are some PFAS that do not appear harmful because they're nonreactive solids (e.g. pure PTFE) or because they're not hydrophobic enough to biomagnify (e.g. trifluoroacetic acid). Discussion of PFAS among non-chemists tends to elide the differences between all fluorinated organic molecules and the ones of environmental concern. These compounds are not literally "forever" but they have long half-lives once released into the environment, due to the strength of C-F bonds and due to pollutants partitioning into low-degradation-activity environments. For example, a certain compound may be degraded by ultraviolet light from sun exposure, but tend to adsorb to soil where it's shielded from light. PFAS share a lot of characteristics with the earlier-known "persistent organic pollutants" like polychlorinated biphenyls: - Polyhalogenated organic compounds - Low acute toxicity - Endocrine disruptor activity - Low rate of natural breakdown in the environment In fact PFAS of concern share so many characteristics with the historically known PoPs that I am not sure why they got their own phrase "forever chemicals." They don't actually seem to have longer half-lives than those PoPs known by the 1970s. For further reading, here is a page on PFAS from the Stockholm Convention on Persistent Organic Pollutants: https://chm.pops.int/Implementation/IndustrialPOPs/PFAS/Overview/tabid/5221/Default.aspx https://chm.pops.int/Implementation/IndustrialPOPs/PFAS/Over... And one from the Environmental Protection Agency: https://www.epa.gov/pfas/pfas-explained https://www.epa.gov/pfas/pfas-explained

mdrew 3y ago

Totally agree. You can blame the Washington Post. But we choose to use it because a lot of people don't know the chemistry but recognize this label.

azinman2 3y ago

As a layman, my understanding is that it doesn't break down over time. Is that not right?

philipkglass 3y ago

It generally refers to polyfluoroalkyl substances, often abbreviated PFAS. The "bad" ones are hydrophobic compounds that can accumulate in fat tissue. There are some PFAS that do not appear harmful because they're nonreactive solids (e.g. pure PTFE) or because they're not hydrophobic enough to biomagnify (e.g. trifluoroacetic acid). Discussion of PFAS among non-chemists tends to elide the differences between all fluorinated organic molecules and the ones of environmental concern. These compounds are not literally "forever" but they have long half-lives once released into the environment, due to the strength of C-F bonds and due to pollutants partitioning into low-degradation-activity environments. For example, a certain compound may be degraded by ultraviolet light from sun exposure, but tend to adsorb to soil where it's shielded from light. PFAS share a lot of characteristics with the earlier-known "persistent organic pollutants" like polychlorinated biphenyls: - Polyhalogenated organic compounds - Low acute toxicity - Endocrine disruptor activity - Low rate of natural breakdown in the environment In fact PFAS of concern share so many characteristics with the historically known PoPs that I am not sure why they got their own phrase "forever chemicals." They don't actually seem to have longer half-lives than those PoPs known by the 1970s. For further reading, here is a page on PFAS from the Stockholm Convention on Persistent Organic Pollutants: https://chm.pops.int/Implementation/IndustrialPOPs/PFAS/Overview/tabid/5221/Default.aspx https://chm.pops.int/Implementation/IndustrialPOPs/PFAS/Over... And one from the Environmental Protection Agency: https://www.epa.gov/pfas/pfas-explained https://www.epa.gov/pfas/pfas-explained