Fate in the Environment and Long-Range Atmospheric Transport of the Organophosphorus Insecticide, Chlorpyrifos and Its Oxon - Reviews of Environmental Contamination and Toxicology - page 60

Table 10 Estimates of the transformation of CPY and concentrations in air at various distances
downwind of an application
Distance km Transit time h F (reacted) Conc. ng m −3 Comment
1-3 0.1-0.2 <0.05 20-100 Application area
10 0.67 0.14 5 Local
30 2 0.38 0.7 Regional
60 4 0.62 0.15 One CTD
120 8 0.84 0.022 Two CTDs
180 12 0.94 0.005 Three CTDs
240 16 0.98 0.001 Four CTDs
300 20 0.99 0.0003 Five CTDs
1,000 67 >0.999 <0.0001 Fifteen CTDs
A wind speed of 14.4 km h −1 is assumed. The fraction reacted, F, is calculated assuming a half-life
of 3 h as e − 0.231 × t where t is the transit time and the transformation rate constant is 0.231 h −1
Fig. 4 Concentrations of CPY and CPYO modelled at various times and distances downwind
from an application
Concentrations of CPY in air would have decreased to 0.022 ng CPY m −3 (0.16 nPa).
At this distance, transformation would have become a greater proportion of the total
dissipation, and concentrations of CPYO would be expected to exceed those of CPY
by a factor of 2, but may be affected by differing deposition rates. At steady state,
rain water would be predicted to have a concentration of 0.1 ng CPY L −1 and snow
a concentration of 1.5 ng CPY L −1 . If a very conservative CPY half-life of 12 h were
assumed, the fraction of CPY transformed would be only 38% and much greater
concentrations are expected. At a distance of 180 km and 12 h transit time, that is
equivalent to three CTDs, 94% of CPY would be predicted to have been