A survey of 40 US Red Cross blood donors in 2005 reported an average PFOS concentration of 20.2 nanograms per millilitre and 3.5ng/ml of PFOA. A similar survey of 100 blood donors in 2000 had reported levels of 43.3 and 5.7ng/ml respectively.
3M, the main manufacturer of PFOS, phased out production between 2000 and 2002 following concerns about its toxicity, persistence and ability to bioaccumulate (ENDS Report 354, pp 28-31 
).
Manufacturers are now under pressure from the US Environment Protection Agency to phase out PFOA emissions (ENDS Report 373, pp 16-17 ). DuPont has already agreed to stop producing the compound (ENDS Report 386, pp 9-10 ).
The findings are consistent with the rate of breakdown in the human body of PFOS and PFOA, the half-lives of which are five and four years respectively.
The study was a pilot, based on donors living around Minneapolis-St Paul, where 3M’s PFOS production was based. Further work is needed to unpick the links between PFOS and PFOA levels and expand the study geographically, the authors say.