Photochemical processing of aldrin and dieldrin in frozen aqueous solutions under arctic field conditions

Organochlorine (OC) contaminants are transported to the Polar Regions, where they have the potential to bioaccumulate, presenting a threat to the health of wildlife and indigenous communities. They deposit onto snowpack during winter, and accumulate until spring, when they experience prolonged solar irradiation until snowmelt occurs. Photochemical degradation rates for aldrin and dieldrin, in frozen aqueous solution made from MilliQ water, 500 μM hydrogen peroxide solution or locally-collected melted snow were measured in a field campaign near Barrow, AK, during spring–summer 2008. Significant photoprocessing of both pesticides occurs; the reactions depend on temperature, depth within the snowpack and whether the predominant phase is ice or liquid water. The effect of species present in natural snowpack is comparable to 500 μM hydrogen peroxide, pointing to the potential significance of snowpack-mediated reactions. Aldrin samples frozen at near 0 °C were more reactive than comparable liquid samples, implying that the microenvironments experienced on frozen ice surfaces are an important consideration.

► Photodegradation rates for aldrin and dieldrin in frozen aqueous solutions made from MilliQ water, H2O2 or melted snow are reported.
► Photoprocessing depends on temperature, depth beneath the snowpack surface and dominant phase.
► Species present in natural snowpack have a photosensitizing effect comparable to 500 μM H2O2.
► Aldrin samples frozen at near 0 °C were more reactive than comparable liquid samples.
► Collectively we find that frozen aqueous surfaces play a unique role in aldrin and dieldrin photochemistry.