Fate in the Environment and Long-Range Atmospheric Transport of the Organophosphorus Insecticide, Chlorpyrifos and Its Oxon - Reviews of Environmental Contamination and Toxicology - page 40

Table 5 Key physical-chemical properties of CPY
Property Units Value Comments

Melting point (mp) °C 42

Molar mass g/mol 350.6

Fugacity ratio (FR) - 0.68 Estimated from mp

Vapor pressure (VP) of solid Pa 0.0023 EPA gives 0.00249

Vapor pressure of sub-cooled
liquid

Pa 0.0034 Consistent with FR and solid

VP

Solubility of solid in water g m −3 or mg L −1 0.73 EPA gives 1.43

Solubility of sub-cooled
solid

g m −3 1.07 Consistent with FR and solid

solubility

Henry's Law constant Pa m −3 mol −1 1.11 VP/Solubility, EPA gives 0.628

Air-water partition coeff.
K AW

- 0.00045

Log is −3.35

Calculated from H/RT

Octanol-water partition
coeff. K OW

- 100,000

Log is 5.0

EPA gives 4.7

Octanol-air partition coeff.
K OA

- 2.2 × 10 8

Log is 8.34

Log is 8.34, K OA = K OW /K AW

Organic carbon-water
partition coeff. K OC

L/kg 8,500

Log is 3.93

EPA gives 5,860, 4,960, 7,300

Data from Mackay et al. ( 1997 ); Muir et al. ( 2004 ); Racke ( 1993 ); USEPA ( 2011 ). Values are at
25 °C unless otherwise stated

minimum, maximum, and mean or median concentrations. Such results are reported
as three points. Given these limitations, only an approximate distribution of observed
values can be obtained.
Concentrations in air that exceed 20 ng CYP m −3 were generally near sources
(areas of application), while those in the range 0.01-10 ng CYP m −3 were regarded
as “regional”, corresponding to distances of up to 100 km from sources.
Concentrations less than 0.01 ng CYP m −3 were considered to be “remote”. There is
a possibility that lesser concentrations could have been measured close to sources if
the prevailing wind direction is not from the source region. Approximately 70% of
the data for concentrations in air were in the range of 0.01-1.0 ng CPY m −3 . For
rain, the greatest frequency (40%) was in the range 1-10 ng CPY L −1 . The distribu-
tion of concentrations of CPY in snow exhibited similar patterns, but with more
concentrations in the range 0.01-0.1 ng CPY L −1 .

Physical-chemical properties of chlorpyrifos and chlorpyrifos-oxon . The model
developed here was designed to describe transport and fate of CPY from source to
remote destinations and thus obtain a semi-quantitative assessment of its LRT char-
acteristics and provide estimates of exposure concentrations at remote locations.
Estimates can then be compared with measured concentrations from monitoring
programs. The sensitivity of the results to uncertainty in the various input parame-
ters can also be determined. Fundamental to assessing and predicting LRT of CPY
and CPYO are reliable values for physical-chemical properties and rates of
reaction by different processes that determine partitioning and persistence in the
environment. Data from the literature were compiled and critically assessed to
obtain consistent values of these physical-chemical properties (Tables 5 , 6 , and 7 ).