Fate in the Environment and Long-Range Atmospheric Transport of the Organophosphorus Insecticide, Chlorpyrifos and Its Oxon - Reviews of Environmental Contamination and Toxicology - page 41

Table 6 Estimated reaction half-lives of CPY in various media as used in the modeling of LRT
Medium Value Comment

•OHradicalreaction
in air

9.1 × 10 −11 cm 3
molecules −1 s −1

2nd order rate constant

Half-life in air 1.4 h

3.0 h

•OHradicalconc.of1.5×10 6 molecules cm −3
•OHradicalconc.of0.7×10 6 molecules cm −3

Half-life in air 3 h Conservative value assuming lesser

concentrationof•OH

Half-life in soil 7-30 d 168-720 h

Half-life in surface water 30-50 d 720-1,200 h

Half-life in sediment 50-150 d 1,200-3,600 h

Table 7 Estimated and measured physical-chemical properties of CPYO
Property Value Comment

Molar mass 334.6

Vapor pressure 0.00088 Pa (USEPA

2011 )

Goel et al. ( 2007 ) give 0.0000062

Solubility in water 26 mg L −1 (USEPA

2011 )

Octanol water partition
coefficient K OW

776 (USEPA 2011 ). Log
is 2.89

Appears very low compared to K OW for
CPY

Half-life in air 11 h

7.2 h

•OHradicalconc.of1.5×10 6 molecules
cm −3 (Aston and Seiber 1997 )
•OHradicalconc.of1.56×10 6 molecules
cm −3

Half-life in air 11 h Conservative value assuming lesser

concentrationof•OH

Half-life in soil 9-30 d

Half-life in water 13.2 d (USEPA 2011 )

40 d, pH = 4, 20 °C
4.7 d, pH = 7, 20 °C
1.5 d, pH = 9, 20 °C
(Tunink 2010 )

The more conservative value of 13.2 d
was used in the modeling

Half-life in sediment 132 d 10× half-life in water assumed
Note that some of these values are only illustrative and are subject to considerable error

Selected values presented for CPY in Tables 5 and 6 are well established and judged
to be accurate within a factor of approximately 2 but, in some cases, ranges are
given to reflect the variability and uncertainty in values. Since CPYO has been less
studied, the values presented in Table 7 are subject to more uncertainty than those
for CPY and must be treated as tentative.
The vapor pressure and solubility were used only to estimate the air-water parti-
tion coefficient K AW and the Henry's Law constant, H. The octanol-water partition
coefficient (K OW ) was used only indirectly to estimate the organic carbon water
partition coefficient (K OC ) in the TAPL3 LRT model but, since there are extensive
empirical data on K OC , these empirical values were used directly. The octanol-air