ARTICLE pubs.acs.org/est
Source Elucidation of Perfluorinated Carboxylic Acids in Remote Alpine Lake Sediment Cores Jonathan P. Benskin,†,§ Vanessa Phillips,‡,|| Vincent L. St. Louis,‡ and Jonathan W. Martin*,† †
Division of Analytical and Environmental Toxicology, Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, Alberta T6G 2G3, Canada ‡ Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
bS Supporting Information ABSTRACT: Atmospheric deposition of perfluorinated carboxylic acids (PFCAs) in remote regions might arise from transport and degradation of precursors (e.g., perfluorooctanesulfonyl fluoride (PFOSF)-based products or fluorotelomer alcohols (FTOHs)) or direct transport (e.g., PFCAs in the vapor phase or on particles). To probe the dominant atmospheric source of PFCAs, historical trends in environmental FTOH, PFOSF, and direct perfluorooctanoate (PFOA) emissions were compared to the flux of PFCAs (sum of C7 C13 perfluoroalkyl chain lengths) and PFCA isomer signatures in dated sediment cores from two remote alpine lakes in the Canadian Rocky Mountains. Contributions from PFOSF-based substances and direct transport of PFOA were ruled to be minimal because no branched isomers were detected in either core and temporal trends for direct emission of PFOA did not match the flux measurements. PFCA flux to Lake Opabin sediment agreed well with reported FTOH emissions, including a peak in mid-2003 and subsequent decline. In Lake Oesa, agreement between PFCA flux and FTOH emissions was also good up to 2004, but a subsequent decline was only detected for some PFCA congeners through 2008, while others continued to increase. Overall, both the isomer profiles and the temporal trend data suggest that FTOH oxidation is the dominant atmospheric source of PFCAs to these high alpine lakes. The efficacy of recent industry phase-out initiatives was difficult to assess due to the divergent temporal trends in samples after 2003; thus, continued monitoring is suggested at remote sites such as these.
’ INTRODUCTION Perfluorinated compounds (PFCs) have been manufactured for over 60 yr for various commercial and consumer applications and are widely disseminated in the environment. Among these diverse materials, the perfluorinated carboxylates (PFCAs) are some of the most frequently detected in remote Arctic ecosystems,1 and these compounds can have significant adverse health effects in laboratory animals.2 Identifying the major manufacturing source(s) and pathway(s) involved in transporting PFCAs to remote locations is important for predicting how environmental concentrations will respond in the future following recent changes in fluorochemical production practices and phase-out initiatives. In remote locations that are influenced only by atmospheric transport, the occurrence of PFCAs may arise from one of three deposition pathways: (i) direct atmospheric transport of PFCAs via the gas phase,3,4 marine aerosols,5 or particulate matter,6 (ii) atmospheric transport and degradation of semivolatile perfluorooctanesulfonyl fluoride (PFOSF)-derived species (e.g., N-alkylsubstituted perfluorooctanesulfonamides),7,8 or (iii) atmospheric transport and degradation of semivolatile fluorotelomer alcohols (FTOHs).9 It is unclear which of these sources predominate; however, temporal trends in manufacturing and emissions of PFCAs, r 2011 American Chemical Society
FTOHs, and PFOSF-based substances have been markedly different over the past 60 yr.5,10 For example, manufacturing of PFCAs and PFOSF-based substances by electrochemical fluorination (ECF) started in the 1950s and was phased out in 2002, while production of telomer-based PFCAs and related substances (e.g., fluoroacrylate polymers and surfactants) began in the 1970s and continues today, with recent stewardship initiatives focusing on removing “free”, or unreacted, FTOH from commerical material.11 Owing to the distinct ECF and telomerization manufacturing processes, PFCAs, FTOHs, and PFOSF-based substances can have unique isomer profiles, depending on how they are produced. For example, PFOSF-based compounds were manufactured exclusively by ECF, a process that yields a mixture of branched and linear isomers (70 80% linear). In contrast, FTOH-based materials (and their associated free FTOH residuals) were manufactured exclusively by telomerization and are usually 100% linear molecules. Large-scale manufacturing of Received: April 3, 2011 Accepted: July 16, 2011 Revised: July 5, 2011 Published: July 16, 2011 7188
dx.doi.org/10.1021/es2011176 | Environ. Sci. Technol. 2011, 45, 7188–7194
Environmental Science & Technology
Figure 1. Map of sampling locations in the Canadian Rocky Mountains relative to Banff, Yoho, and Kootenay National Parks.
perfluorooctanoate (PFOA) (and presumably unintentional manufacturing of non-C8 chain lengths) was historically by ECF (i.e., branched + linear), but the use of telomerization for PFOA production has increased in recent times. Here we hypothesize that a historic record of PFC emissions to the northern hemisphere should be reflected by temporal trends of PFCA deposition and PFCA isomer profiles in remote alpine sediment cores. The idea was that this should allow identification of the dominant sources (i.e., ECF or telomer and direct transport versus degradation of PFCA precursors) while also allowing an evaluation of phase-outs and the global stewardship program on mitigating future environmental exposures. Remote alpine lake sediment cores were collected in the Canadian Rocky Mountains and dated using 210Pb. Temporal trends in PFCA flux and isomer profiles were compared to historical emissions of PFOA, FTOHs, and PFOSF-based substances to assess the dominant atmospheric source of PFCAs to this region.
’ EXPERIMENTAL PROCEDURES Sampling Sites. One sediment core from Lake Oesa and one sediment core from Lake Opabin (Figure 1) in Yoho National Park were collected in the summer of 2007 as part of a previous study on historical mercury loadings.12 Both lakes are small (
