Detection of Chlorodifluoroacetic Acid in Precipitation:  A Possible Product of Fluorocarbon Degradation

Abstract

Chlorodifluoroacetic acid (CDFA) was detected in rain and snow samples from various regions of Canada. Routine quantitative analysis was performed using an in-situ derivatization technique that allowed for the determination of CDFA by GC-MS of the anilide derivative. Validation of environmental CDFA was provided by strong anionic exchange chromatography and detection by 19 F NMR. CDFA concentrations ranged from <7.1 to 170 ng L -1 among all samples analyzed. Monthly volume-weighted CDFA concentrations in rain event samples showed a seasonal trend between June and November 1998, peaking in late summer and decreasing in the fall for Guelph and Toronto sites. Preliminary toxicity tests with the aquatic macrophytes Myriophyllum sibiricum and Myriophyllum spicatum suggest that CDFA does not represent a risk of acute toxicity to these aquatic macrophytes at current environmental concentrations. A degradation study suggests that CDFA is recalcitrant to biotic and abiotic degradation relative to dichloroacetic acid (DCA) and may accumulate in the aquatic environment. On the basis of existing experimental data, we postulate that CDFA is a degradation product of CFC-113 and, to a lesser extent, HCFC-142b. If CFC-113 is a source, its ozone depletion potential may be lower than previously assumed. Further work is required to identify alternative atmospheric and terrestrial sources of CDFA.

Variation, Replication, and Power Analysis of Myriophyllum Spp. Microcosm Toxicity Data

“…Because n ϭ 3 and k ϭ 2, the degrees of freedom are 4. have reported EC25 values [32,33,37,38]. By including the minimum detectable difference with the result of the power of a test, a meaningful estimate of the true sensitivity of the test is obtained [22].…”

Gas-phase acidity, bond dissociation energy and enthalpy of formation of fluorine-substituted benzenes: A theoretical study

“…We also compare the structure-reactivity trends in these heterolytic C-H bond dissociation energies (BDEs) with the corresponding homolytic C-H BDEs for the same species. These latter quantities are important as hydrogen atom abstraction is a key step in the atmospheric degradation of hydrofluorocarbons (HFCs) [5].…”

Chlorodifluoroacetic acid fate and toxicity to the macrophytesLemna gibba, Myriophyllum spicatum, andMyriophyllum sibiricumin aquatic microcosms

“…Chlorodifluoroacetic acid (CDFA) is an environmental contaminant that has only recently been detected and quantified [1, 2]. The main input into the environment is hypothesized to be from the degradation of 1,1,2‐trichloro‐1,1‐difluoroethane (CFC‐113) and, to a lesser extent, 1‐chloro‐1,1‐difluoroethane (HCFC‐142b).…”

“…Current concentrations of CDFA in southern Ontario, Canada, rainwater range from <7.1 to 39 ng/L, and it has been shown to be slightly phytotoxic to the rooted macrophytes Myriophyllum spp. in laboratory tests [2]. Phytotoxicity is a property CDFA shares with other haloacetic acids (HAAs) [3–5].…”

“…Phytotoxicity is a property CDFA shares with other haloacetic acids (HAAs) [3–5]. It has also been shown to be resistant to degradation under normal environmental conditions, undergoing neither biotic or abiotic transformation over 35 d in test chambers [2]. Trifluoroacetic acid (TFA) is another HAA with similar properties to CDFA.…”