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Environmental fate & pathways

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Stability of the C4 fluorinated isonitrile was addressed in a phototransformation study and a study of hydrolytical stability in aquatic toxicology test media. Additional information on hydrolytic stability is derived from Henry's Law, water solubility, and octanol-water partition studies. In the atmosphere the isonitrile undergoes reaction with hydroxyl radical in the gas phase. The rate of reaction was monitored v. HFC-125 or methane, with the isonitrile reacting less quickly than either. The average lifetime obtained by comparing relative reaction rates with known atmospheric lifetimes of the reference compounds is 35 years.


The isonitrile is also hydrolytically unstable, forming the corresponding fluorinated amide when held in contact with aqueous phases. The isonitrile is also subject to hydrolysis in water-saturated octanol, and may also form imidate adducts which could not be detected by the analytical methodology used in the log P experiment. The fluorinated amide was not confirmed in the Henry's Law or water solubility experiments, and was not quantified in the log P coefficient experiment. However, the presence of the amide was confirmed in the log P experiment and the results obtained in the other experiments were consistent with the log P result. The exact rate of hydrolysis is not well defined, since the process involves both hydrolysis and distribution to the aqueous phase. However, trials were conducted to evaluate the potential to perform aquatic toxicology tests on the gas. Small volumes of gas were injected into sealed containers completely filled with medium, and then held for 48 hours. Time points for chemical analyses were as soon as possible after test vessel assembly, at 24 hours, and at 48 hours. The parent was analyzed in the limited headspace and in solution, and the hydrolysis product was measured in solution only. Average mass balances during these tests were 98-108%, indicating that all parent and degradation product were recovered. In the daphnia medium experiment (unshaken), ca. 75% of the parent gas remained in the headspace. The aqueous concentration of parent declined from 200 µg/L to 30 µg/L within 48 hours, while the concentration of hydrolysis product increased from 700 µg/L at time zero to 40,000 µg/L at 48 hours. The total process (entry into the aquatic phase and hydrolysis) showed first-order kinetics, indicating that the process was limited by transport into the dissolved phase. In the test of algae medium (with shaking), ca. 80% of parent was lost from the headspace within 24 hours and 90% within 48 hours. The initial and 24-hour parent aqueous concentrations were similar (ca. 600 and 800 µg/L) but declined at 48 hours (ca. 200 µg/L). The remaining mass of parent had been converted to dissolved hydrolysis product (ca. 90 % by 48 hours, >100 mg/L). The overall process did not follow first-order kinetics, which is expected since the flasks were shaken and limitation by transport was at least partially mitigated. The extent of increase in the hydrolysis product's concentration indicates that the parent can only be maintained in solution by replacement from an adequately large headspace, while concentration of the hydrolysis product would increase throughout the test. If the headspace were removed, the remaining dissolved parent would quickly hydrolyze to form the amide. Consistent test concentrations of the parent and its hydrolysis product cannot be maintained even in a closed container.


Given the relatively long atmospheric lifetime of C4 fluorinated isonitrile and the ready hydrolysis of the vapor when in contact with liquid water, the possibility of hydrolysis in the atmosphere cannot be discounted. However, no information on rate is available for the atmospheric compartment. The net effect of hydrolysis in the atmosphere would be to reduce atmospheric lifetime of the isonitrile, with deposition of amide to the terrestrial and the aquatic compartments.