Environ. Sci. Technol. 2010, 44, 849–850
Response to Comments on “Degradability of an Acrylate-Linked, Fluorotelomer Polymer in Soil” We thank Russell et al. (1) (hereafter “Russell”) for their careful comments (see preceding pages) on our paper (2). We address their comments below, however, in all this detail, we emphasize that it is important not to lose track of several overarching issues that we address here and in Supporting Information (SI): (1) We observed an excess of reaction products in our experiment, including sec-alcohols (SI), that cannot be explained without invoking degradation proceeding with half-lives for commercial acrylate-linked fluorotelomer polymers (AFTPs) on the scale of years, assuming AFTP-particle interiors do not participate in degradation (SI); (2) The high AFTP-residual content of Russell obfuscates detection of AFTP-degradation rates having half-lives as short as those we estimated in our study (SI), thereby depriving the study of a legitimate basis for rejection of our conclusions; and (3) The moisture status of the Russell microcosms left an unknown, but probably large, fraction of the test-AFTP surfaces dry, rendering the experimental design ineffective for defending a conclusion of slow degradation (SI). Here, we respond to their specific comments.
Recovery of FTOH and PFOA from Day-0 Soil/AFTP Microcosms The FTOH and PFOA recoveries of 137% and 123% reported in the comments are new intriguing data that could not have been computed with precision from the original Russell paper (1) because the actual loadings of soil and the AFTP in the microcosms were not reported. Based on our experience with loading soil-AFTP microcosms, using nominal values to calculate recovery is a dubious exercise. To illustrate this point, calculation of recoveries for 8-2FTOH in Russell’s sterile microcosms (Table S13 of ref 1) using the nominal loadings of soil (25 g) and AFTP (20 mg) yields recoveries of 46%-220%, a range that clearly is too wide to evaluate recovery with satisfactory resolution. Regardless of not being reported previously, the larger size of our AFTP particles, ∼300 µm for our study and
