Environmental Engineering Reference
In-Depth Information
Table 1 Key physicochemical properties of chlorpyrifos
Parameter
Value
Source
Chemical name
O,O-diethyl
o-(3,5,6-trichloro-2-pyridyl
phosphorothioate
USEPA ( 2011 )
Chemical Abstracts Service (CAS)
Registry Number
2921-88-2
USEPA ( 2011 )
Empirical formula
C20H17F5N2O2
USEPA ( 2011 )
Molecular mass
350.6 g/mol
Mackay et al. ( 2014 )
Vapor pressure (25 °C)
1.73 × 10 −5 torr
Mackay et al. ( 2014 )
Water solubility (20 °C)
0.73 mg/L
Mackay et al. ( 2014 )
Henry's law constant
1.10 × 10 −5 atm-m 3 /mol
Mackay et al. ( 2014 )
Log K ow
5.0
Mackay et al. ( 2014 )
Table 2 Key environmental fate properties of chlorpyrifos
Parameter
Value
Source
Hydrolysis (t½)
pH 5: 73 d
USEPA ( 2011 )
pH 7: 72 d
pH 7: 81 d
pH 9: 16 d
Aqueous photolysis (t½)
29.6 d
USEPA ( 2011 )
Aerobic soil metabolism (t½) a
1.9-1576 d
See Table SI A1
Aerobic aquatic metabolism (t½)
22-51 d
See Table SI A5
Anaerobic soil metabolism (t½)
15 and 58 d
USEPA ( 2011 )
Anaerobic aquatic metabolism (t½)
39 and 51 d
USEPA ( 2011 )
Soil adsorption coefficient K OC
973-31,000 cm 3 g −1
See Table SI A4
Terrestrial field dissipation (t½)
1.3-120 d
See Table SI A3
t½ = half-life
a All values <335 d except one
formation of bound residues and reversible formation of 3,5,6-trichloro-2-me-
thoxypyridinol (TMP). Under aerobic conditions, the major terminal degradation
product of CPY is CO 2 . Since TCP and TMP are not considered to be residues of
concern (USEPA 2011 ), they were not included in the model simulations presented
below. Finally, while photolysis and oxidation are known to form the chlorpyrifos
oxon (CPYO) in air and on foliar surfaces (Mackay et al. 2014 ), this route is either
insignificant in soil or the oxon degrades as quickly as it is formed. CPYO has not
been reported in radiotracer soil degradation studies in the laboratory or field.
Concentrations of CPYO were not included in simulations because it has not been
observed in soils.
Under standardized laboratory conditions, rates of degradation of CPY in soil,
expressed as the half-life, have ranged from 1.3 to 1,575 d (all values except one are
<335 d; see SI, Table A1). Although half-lives of 7-120 d are considered typical,
this range narrows for medium textured soils across several states where reported
half-lives range from 33 to 56 d (USEPA 1999 ). This variability in reported
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