An extensive database of organochlorine (OC)
pesticide concentrations measured at the Norwegian Arctic
monitoring station at Ny-Alesund, Svalbard, was analysed to
assess longer-term trends in the Arctic atmosphere. Dynamic
Harmonic Regression (DHR) is employed to investigate the
seasonal and cyclical behaviour of chlordanes, DDTs and
hexachlorobenzene (HCB), and to isolate underlying interannual
trends. Although a simple comparison of annual mean
concentrations (1994–2005) suggest a decline for all of the
OCs investigated, the longer-term trends identified by DHR
only show a significant decline for p,p0-DDT. Indeed, HCB
shows an increase from 2003–2005. This is thought to be
due to changes in source types and the presence of impurities
in current use pesticides, together with retreating sea
ice affecting air-water exchange. Changes in source types
were revealed by using isomeric ratios for the chlordanes
and DDTs. Declining trends in ratios of trans-chlordane/cischlordane
(TC/CC) indicate a shift from primary sources, to
more “weathered” secondary sources, whereas an increasing
trend in o,p-DDT/p,p-DDT ratios indicate a shift from use
of technical DDT to dicofol. Continued monitoring of these
OC pesticides is required to fully understand the influence
of a changing climate on the behaviour and environmental
cycling of these chemicals in the Arctic as well as possible
impacts from “new” sources.