Environmental Engineering Reference
In-Depth Information
Fig. 2
Use of chlorpyrifos by crop (2007) (data from Gomez
2009
)
or dormant trees (Solomon et al.
2014
). Application can occur pre-plant, at-plant,
post-plant or during the dormant season using aerial equipment, chemigation, ground
boom or air-blast sprayers, tractor-drawn spreaders, or hand-held equipment.
1.2
Environmental Fate Properties
CPY has short to moderate persistence in the environment as a result of several
pathways of dissipation, including volatilization, photolysis, abiotic hydrolysis and
microbial degradation that can occur concurrently. Dissipation by volatilization
from foliage, as controlled by the physical and chemical properties of CPY (Tables
1
and
2
) is the dominant process during the first 12 h after application, but decreases
as the formulation adsorbs to foliage or soil (Mackay et al.
2014
). During the days
following application, CPY strongly adsorbs to soil and penetrates the soil profile to
become less available for volatilization, and consequently other degradation pro-
cesses become important. The magnitude of CPY adsorption varies substantially
between different soils, with a spread of two orders of magnitude in calculated Kd
coefficients (SI Table A4).
Key factors affecting degradation of CPY in soil have been reviewed previously
(Racke 1993) and these factors have been substantiated by additional recent research
cited herein. CPY can be degraded by UV radiation, dechlorination, hydrolysis, and
microbial processes. However, hydrolysis of CPY is the primary mechanism and
results in formation of 3,5,6-trichloropyridinol (TCP). This step can be either abi-
otic or biotic, and the rate is 1.7- to 2-fold faster in biologically active soils. The rate
of abiotic hydrolysis is pH-dependent and occurs more rapidly under alkaline con-
ditions. It is also faster in the presence of catalysts such as certain types of clay
(Racke
1993
). Degradation of TCP is dependent on biological activity, and leads to
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