Endosulfan is a semivolatile organochlorine pesticide that was globally distributed before it was banned, and it continues to cycle in the Earth system. The chemical kinetics of the reaction of α-endosulfan with the hydroxyl radical (OH) was studied by means of pulsed vacuum UV flash photolysis and time resolved resonance fluorescence (FP-RF) as a function of temperature in the range of 348–395 K. The experimentally determined rate coefficient, kOH = 5.8×10-11 exp (-1960 K/T) cm3 s-1 (uncertainty range 7×10-12 exp (-1210 K/T) to 4×10-10 exp (-2710 K/T) cm3 s-1) suggests photochemical atmospheric half-lives ranging from 2-6 months (assuming a temperature of 298 K and an OH concentration of 1 ×10-6 cm-3). Comparing the atmospheric concentrations observed after the global ban of endosulfan with multimedia model predictions, we conclude that photochemical degradation in the atmosphere is slower than biodegradation in soil. Lifetimes in soil or water must be underestimated, in particular in temperate and warm climate.
