Perfluorinated chemicals stay in people for years not days.

What did they do?

Olsen et al. took annual blood samples from 26 retired employees of 3M for five years (1998 - 2004) to determine how long it takes for PFCs to degrade in humans after exposure to the chemicals.

The study followed 2 women and 24 men who worked at 3M plants in either Decatur, Ala. or Cottage Grove, Minn.

They were selected because, as employees, they would have had higher exposure, and therefore, PCFs levels above the detection limit of the laboratory instruments used to measure the compounds.

The subjects worked as electrochemical fluorination cell operators, chemical operators, maintenance workers, foremen, laboratory technicians, warehouse workers and engineers prior to their retirement between 1995 and 1998. After retiring, participants had minimal exposure to PFCs.

Blood levels of PFOS, PFOA and PFHS were measured by high performance liquid chromatography and mass spectrometry. For each individual, the blood concentration of each PFC was plotted over time. The half-life was estimated using multiple regression analysis and calculated based upon the measured decrease in blood level over the course of the study period. The half life of a chemical is a measure of how long it takes for half of the original amount to be eliminated, either by excretion in urine or feces.

What did they find?

PFOS was the most prevalent chemical in these retired workers and was detected at average levels of 799 nanograms per milliliter (ng/ml) (range 145 to 3,490). PFOA was the second most common (average 691 ng/ml, range 72 to 5,100) and PFHS was detected at the lowest levels (290 ng/ml, range 16 to 1,296).

These levels are much higher than those routinely measured in the general population. Average human blood PFOS is approximately 30 to 40 parts per billion (ppb), whereas mean PFOA levels range from about 4 to 7 ppb (ng/ml is equivalent to ppb.)

In all subjects, blood levels of the three compounds decreased over time. Estimates of mean half-lives (when half of total amounts were eliminated) of serum elimination were calculated to be 3.8 years for PFOA, 5.4 years for PFOS and 8.5 years for PFHS.

What does it mean?

These findings suggest that humans have a much lower capacity to remove PFC chemicals from the body compared to other animals.

This is one of the first studies to systematically examine how long PFCs stay in people. The time frame of years instead of days or months means longer, continual exposures than previously thought. The health effects, if any, from these exposures is not known.

PFC levels in people who worked with the chemicals fell continuously for up to five years after they retired and were no longer exposed to such high levels of the pollutants. However, the three PFCs tested during the study were estimated to be in the workers' blood for between 4 and 8 years after exposure ended.

Laboratory animal studies suggest that the biological half-life of PFOA varies greatly among species. Half-lives range from 4 hours (rat) to 22 days (dogs). Large sex differences in PFOA elimination rates have been observed in rats (Vanden Heuvel et al. 1991).

The half-life of PFOS is estimated at 14 to 40 days in monkeys.

The authors suggest the differences among species is related to a reduced net transport of these chemicals from the kidney to the urine. Most chemicals in the body cannot passively diffuse across cell membranes. Rather, they are carried by transporters from inside the cell to the extracellular space, or vice versa. It is possible that humans do not have high levels of the particular transporter that would carry PFCs from kidney cells to the urine, although this hypothesis has not yet been tested.