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Initial deposits of aerially applied fenitrothion insecticide over a boreal forest area near Searchmont, Ontario, was studied. Two plots (PI, 23 ha and P2, 49 ha) were sprayed with an emulsion formulation of fenitrothion at 280 g in 1.5 L per ha using a Cessna 188 aircraft equipped with 4 Micronair® AU3000 atomizers. Kromekote® card/glass plate collection units were placed around the sample trees to determine spray deposit at ground level. Balsam fir and white birch foliage, caged and wild pollinators, moths and wild flower species were collected for deposit assessment. Water samples were collected, at different intervals of time after treatment, from a creek inside the spray plot (P2), and from a nearby river into which the creek drained. All samples were analysed by gas-liquid-chromatography.
Droplet analysis on Kromekote cards showed that the mean droplet frequency (droplets/cm2), number and volume median diameters were nearly the same at all sampling sites in both plots. Fenitrothion deposits (in ng/cm2) at mid-crown level of the sample trees were slightly higher on birch leaves than on fir foliage. The tubular chokecheery flowers showed higher deposits than the bell-shaped blueberry flowers, The caged pollinators showed higher fenitrothion concentrations than the wild pollinators.
The insecticide concentration in the creek rose to a maximum of 31.0 μg/L within five min after treatment, but fell to 0.5 μg/L after 24 h. The concentration-time profile showed that nearly half of the initial concentration in the creek water was lost within 21.8 min. In the river water sampled outside the spray area, the post-spray concentration, on average, was 2.2 μg/L.
Fenitrothion, spray deposit, aerial treatment, forest ecosystem, droplet size spectra, water concentration, ground deposit
Research Scientist and Project Leader for Insecticide Chemical Accountability Project, Forestry Canada, Forest Pest Management Institute, Sault Ste. Marie, Ontario