Properties and Uses of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 18

Table 3 Half-lives of chlorpyrifos in selected soils recalculated using a two-compartment model

Reported
T½ a

Calculated T½ 1 from
t wo-compartment model b Soil Group Reference

Commerce, MI 11 11 2 Bidlack ( 1979 )

Barnes, ND 22 22 2 Bidlack ( 1979 )

Miami, IN 24 18 2 Bidlack ( 1979 )

Caitlin, IL 34 28 2 Bidlack ( 1979 )

Marcham, UK 43 9 2 de Vette and Schoonmade

( 2001 )

Thessaloniki, GR 46 31 1 de Vette and Schoonmade

( 2001 )

Charentilly, FR 95 93 1 de Vette and Schoonmade

( 2001 )

Norfolk, VA 102 57 1 Bidlack ( 1979 )

Stockton, CA 107 96 1 Bidlack ( 1979 )

Cuckney, UK 111 84 1 de Vette and Schoonmade

( 2001 )

German 2:3 141 99 1 Bidlack ( 1979 )

a Rounded to nearest day
b For detailed derivation of the data, see SI Appendix B in (Williams et al. 2014 )

Adsorption to soil. Based on reported water-soil adsorption coefficients (K OC ) of
973 to 31,000 mL g −1 ; mean 8,216 mL g −1 (SI Table A-3), CPY has a large potential
to adsorb to soil and would not likely be biologically available for uptake by roots
of plants. Possible uptake by roots, translocation, and metabolism of CPY in plants
also has been investigated (summarized in Racke 1993 ). In general, negligible
amounts enter the plant via the roots. Thus, CPY is not systemic and this pathway
of exposure need not be considered in exposure assessments for CPY.

Dissipation from plants. CPY rapidly dissipates from foliar surfaces of plants,
primarily due to volatility and secondarily due to photolysis, with most reported
dissipation half-lives on the order of several days (Racke 1993 ). In a field study
performed in California that examined mass loss of CPY to air, maximum vola-
tility fluxes occurred in the first 8 h after application to recently cut alfalfa
(Rotondaro and Havens 2012 ). Total mass loss of CPY, based on the calculated
fluxes, ranged between 15.8 and 16.5% of applied mass, as determined by the
Aerodynamic (AD) and Integrated Horizontal Flux (IHF) methodologies,
respectively. Data on dissipation of CPY from various crops are provided in SI
Table A-4.

Dissipation in aquatic systems. In aquatic systems, abiotic degradation of CPY due
to aqueous hydrolysis has been reported to occur with half-lives at 25 °C of 73, 72,
and 16 d at pH 5, 7, and 9, respectively (summarized in Racke 1993 ). The U.S. EPA
( 2011a ) used an aqueous hydrolysis half-life of 81 d at pH 7 in modeling to esti-
mate concentrations of CPY in drinking water. Half-lives of 22-51 d have been