Sources and Occurrence of Dacthal in the Canadian Atmosphere

Abstract

Dacthal is a herbicide that can undergo long-range atmospheric transport. Due to limited use in Canada, its occurrence in the Canadian environment is likely associated with transboundary flow from the United States where 100 times more dacthal is used. To investigate its atmospheric distribution and possible sources, two sampling strategies were applied. First, polyurethane foam-disk passive air samplers were deployed across the country from the spring to summer of 2004 and 2005. Results showed highest dacthal concentrations at two sites in southern Ontario (max: 50 pg m(-3)) and much lower concentrations in other agricultural regions across Canada. Second, daily high-volume air samples were collected at a field site in north Toronto (Downsview). Sampling at this site was triggered by real-time meteorological forecast models that indicated when air flow to the site originated in the United States. Two such events, one in late June and one in late September 2005, were sampled. In both cases, elevated dacthal concentrations were captured (e.g., up to 319 pg m(-3) in the June event) and they were well correlated with transboundary flow from the United States. Finally, the octanol--air partition coefficient (K(OA)) of dacthal and other current-use pesticides was measured. K(OA) was used to derive a particle--gas partitioning coefficient (K(p)) for dacthal (Log K(p) = -4.1), indicating that this compound should exist mainly in the gas phase.

Influence of Asian and Western United States Agricultural Areas and Fires on the Atmospheric Transport of Pesticides in the Western United States

“…Dacthal undergoes atmospheric transport (11,41) and is used intensively in Eastern Oregon/Washington and Central California (Figure S1) (42). Dacthal concentrations at MBO were significantly positively correlated (p-value < 0.05) with only Σendosulfan concentrations (Table S3) and dacthal use areas in the Western U.S. overlap with endosulfan use areas (Figure S1).…”

Currently used pesticides, hexachlorobenzene and hexachlorocyclohexanes in the air and seawater of the German Bight (North Sea)

“…The pre-emergence herbicide dacthal has been reported to be one of the most frequently detected CUPs in the air of North America, [28,29] but its occurrence in the European environment has been rarely reported. Dacthal has been frequently detected in snow and rain.…”

Persistent Organic Pollutants

“…However, few studies have performed targeted air sampling of organic contaminants from suspected source regions as triggered by real-time meteorological forecast models (Yao et al, 2007). To the best of our knowledge, our study represents the first attempt to both (i) use model predictions driven by a priori information on emissions of POPs to trigger air sampling as well as (ii) retrospectively evaluate the source regions for measurements collected during predicted episodes.…”

“…While the current strategy is appropriate for the purpose of assessing long-term trends (years, decades), the intermittent sampling approach may not effectively capture key longrange atmospheric transport (LRAT) episodes (e.g. Yao et al, 2007), which are often associated with the highest POP concentrations (Eckhardt et al, 2007;Yao et al, 2007).…”