Environmental Fate, Toxicity, and Bioaccumulation of Perfluorinated Chemicals

Found in such diverse products as pesticides, popcorn bags, and Prozac(TM), fluorinated organic compounds are widely used in many commercial and industrial applications. Perfluorinated chemicals (PFCs), in which all carbon-hydrogen bonds are replaced with carbon-fluorine bonds, are both hydrophobic and oleophobic and are commonly used in carpet and textile coatings (e.g., ScotchGard(TM) and Stainmaster(TM)) and surfactants (e.g., fire-fighting foams). Despite their many uses, little is known about the environmental fate of PFCs once they are released from industrial, commercial, and residential waste streams. However, these compounds are thought to bioaccumulate and have been detected in fish, birds, marine mammals and humans from around the globe.

The Luthy group's PFC research aims to understand the fate, transport, and bioavailability of these compounds in aquatic environments. For example, sediment processes may play an important role in the movement of PFCs from waste streams into the food chain. In a survey of San Francisco Bay Area sediments, PFCs were found in sediments from all locations.  Furthermore, in collaboration with Alexandria Boehm's group (Stanford EES), correlations between sediment PFC concentrations and various water quality parameters at these sites suggest that domestic sewage is the dominant source of some PFCs to the local environment.

In evaluating the potential role of sediments in moving PFCs into the food web, it is often useful to know how much of each PFC is sorbed to the sediment and how much remains in the aqueous phase. To that end, sorption experiments have been conducted to determine the extent to which these compounds sorb to sediments and soils, and how that sorption is related to the specific chemical structure of the PFC (i.e. chain length), sediment-specific parameters such as the fraction of organic carbon, and solution specific parameters (i.e., pH). Current Luthy group research efforts are also now addressing how sediment-bound PFCs and sediment-bound PFC precursor molecules bioaccumulate in sediment dwelling organisms. 

In collaboration with David Epel's research group (Stanford Biological Sciences), we have studied the dynamic uptake and loss of a variety of perfluorochemicals in the gill tissue of the marine mussel, Mytilus californianus, as well as their inhibition of the efflux transporter, p-glycoprotein, in M. californianus. We found that perfluorochemicals with fluorinated carbon chain lengths between 7-9 act as chemosensitizers by inhibiting p-glycoprotein and therefore potentially allow other more toxic substrates to accumulate intracellularly. As many organisms, including humans, share efflux transporters as a first line of defense against environmental toxins, these results have implications for the ecotoxicology of these PFCs. These studies also aim to elucidate the relationships between molecular size/structure and biological toxicity and bioaccumulation.