Sorption of atrazine and metolachlor by burrow linings developed in soils with different crop residues at the surface.

Atrazine and metolachlor sorption by earthworm (Lumbricus terrestris L.) burrows was measured by introducing herbicides into the burrows and collecting the effluent between 0 to 3, 3 to 6, and 6 to 9 min of simulated burrow flow. On average, sorption by burrow linings reduced the herbicide concentration to 78% (atrazine) and 74% (metolachlor) of the applied herbicide solution concentration. For both herbicides, the amount sorbed was dependent on the food source available to the earthworm, as well as the duration of burrow flow. On average, soybean-fed- and corn-fed-earthworm-burrows significantly retained more herbicides relative to the Control Treatment (unfed-earthworms). More herbicides were transported through the burrows with time because the lateral flow movement from the burrow wall into the soil matrix decreased. It is also likely that herbicides retained on burrow linings during the first 3 min of flow saturated the adsorption sites on the burrow wall, which decreased the subsequent retention potential of herbicides in flow between 3 to 9 min. Based on these results, we conclude that herbicide transport through earthworm burrows in the field will be related to crop and crop residue management practices.

Transfer of DDT and metabolites from fruit orchard soils to American robins (Turdus migratorius) twenty years after agricultural use of DDT in Canada.

Wildlife contamination studies found high levels of DDT and associated metabolites in bird eggs from Canadian orchard sites during the early 1990s. The present study investigated local dietary uptake of DDT and geographic variability in tissue concentrations in the same orchards. A soil-earthworm-robin food chain was chosen for study, as early surveys showed that robins contained the highest levels of DDT of several avian species and because published research indicated that earthworms were a probable dietary exposure route. Organochlorine pesticides and PCBs were measured in soil, earthworm, robin egg, and robin nestling samples collected from fruit orchards and reference sites. High average DDE (soil: 5.2 mg/kg; earthworm: 52 mg/kg; robin egg: 484 mg/kg dry weight) and DDT (soil: 9.2 mg/kg; earthworm: 21 mg/kg; robin egg: 73 mg/kg dry weight) concentrations in Okanagan (British Columbia) samples confirmed that previously recorded contamination was common in the region. Concentrations detected in Simcoe, Ontario, orchards were not as high but were still significantly elevated relative to levels in soils and robins from reference areas. Significant positive linear regressions between soil and earthworm concentrations and consistent trends in food chain accumulation suggested that robins were acquiring DDT and metabolite (DDTr) burdens locally. Low concentrations of DDT and DDTr in robin eggs collected from nests in nearby nonorchard and post-DDT orchard habitats suggested that the local sources were in orchards. Persistence of DDT in orchard food chains is likely due to a combination of retarded degradation rates for DDT in soil and its extensive use historically. DDT concentrations in some robin eggs and earthworms were at levels comparable to those observed in field studies where mortality or reproductive effects occurred.

DDT in forest streams.

Water was sampled from a tributary of the Miramichi River of New Brunswick before, during, and up to two years after the final operational application of DDT to this area of forest. Gas chromatographic analysis of petroleum ether extracts of the water showed that only during and for a few hours after actual spray application did the DDT concentration in the stream exceed a steady background level of 0.5 ppb. pp 'DDT (<17 ppb.), and this DDT flush occurred mainly as a surface film associated with the formulating oil. Bottom sediments, extracted with hexane-acetone (2/1) for chromatographic analysis, showed a downstream dilution gradient of DDT residue from tributary to estuary, and these averaged only 12.5 per cent of the DDT concentration found in the soils of surrounding forests. Much of the pp' DDT applied in the original technical spray was decomposed to DDE and DDD in the bottom sediments of forest streams.