Perfluorobutanesulfonic acid

Perfluorobutanesulfonic acid (PFBS) is a chemical compound with a four carbon fluorocarbon chain and a sulfonic acid functional group. As an anion it functions as a stable fluorosurfactant because of the strength of carbon–fluorine bonds.
Since June 2003, 3M has used PFBS as a replacement for the persistent, toxic, and bioaccumulative perfluorooctanesulfonic acid (PFOS) in its Scotchgard stain repellents. 3M markets surfactant with PFBS in two fluorosurfactants.
Safety.
PFBS has a half-life of a little over one month in humans, much shorter than PFOS with 5.4 years. PFBS is persistent in the environment. Studies have not yet been specifically conducted to determine safety in humans.
The ECHA decision adding PFBS and its salts to the REACH Regulation Candidate List of Substances of Very High Concern states:“The combined intrinsic properties justifying the inclusion as a substance for which there is scientific evidence of probable serious effects to human health and the environment which give rise to an equivalent level of concern are the following: very high persistence, high mobility in water and soil, high potential for long-range transport, and difficulty of remediation and water purification as well as moderate bioaccumulation in humans. The observed probable serious effects for human health and the environment are thyroid hormonal disturbances and reproductive toxicity seen in rodents, and effects on liver, kidney and haematological system in rats, hormonal disturbances and effects on reproduction in marine medaka fish and effects on expression of hormone receptors in tadpoles. Together, these elements lead to a very high potential for irreversible effects.”
Legislation.
European Union.
On 2020-01-16, PFBS and its salts were added to the REACH Regulation Candidate List of Substances of Very High Concern (SVHCs) on the grounds of "Equivalent level of concern having probable serious effects to human health (Article 57(f) - human health)" and "Equivalent level of concern having probable serious effects to the environment (Article 57(f) - environment)".