The continuing persistence and biomagnification of DDT and metabolites in American robin (Turdus migratorius) fruit orchard food chains

DDT is an organochlorine insecticide that was widely used in fruit orchards in the South Okanagan Valley from the late 1940s and in the 1990s, this was documented to have caused extensive contamination of American robin (Turdus migratorius) food chains. Due to the environmental persistence of DDT and its metabolite, p,p'-DDE, the objective of this study was to re-sample previous orchards, as well as several new agricultural areas with the prediction that DDT and metabolite concentrations would significantly decline twenty-six years after a similar sample collection was conducted in 1993-1995. This was done by: 1) collecting soil, earthworms and American robin eggs from orchard and non-orchard areas in the South Okanagan Valley, 2) comparing previous and current contaminant burdens for DDE, DDT and DDD metabolites, and 3) calculating biomagnification factors for earthworms and robins on a lipid normalized basis. All robin eggs contained DDE, DDT and DDD, with the highest concentration being p,p'-DDE at 107 ug/g (wet weight), confirming that contamination is still present at similar and high levels relative to the 1990s. DDE and DDT levels in robins were significantly higher than Aporrectodea and Lumbricidae earthworms, and earthworm-robin regressions for DDE showed a significant positive relationship. Biomagnification factors were generally > 1 and were higher for DDE than DDT and DDD. Concentrations of p,p'-DDE in American robins in this study were comparable to and/or exceeded published levels in other migratory birds nesting in fruit orchards, including the eastern bluebird (Sialia sialis), where reproductive and immunostimulation effects were observed. The relatively high concentrations of DDE in the South Okanagan Valley may pose a health risk to local predators and birds of prey, such as Accipiter hawks and falcons, who often feed at higher trophic levels where DDE and other contaminants are biomagnified.