Environmental Engineering Reference
In-Depth Information
half-lives has been attributed to differences in soil organic carbon and moisture
contents, prior CPY application rate, and microbial activity at the time of sampling,
but no quantitative relationships have been reported (Racke
1993
). Rates of degra-
dation are inversely proportional to rates of application, possibly because concen-
trations in soil water reach the solubility limit of approximately 1 μg CPY L
−1
.
Generally, when applied as a granular product, CPY dissipation is slower than when
applied as a liquid (Racke
1993
). Dissipation under field conditions is also variable,
with half-lives ranging from 1.3 to 120 d (SI, Table A2).
Results of laboratory aerobic degradation studies with CPY exhibit bi-phasic
behavior in some soils. Initial rates of degradation are greater than overall rates by
factors of 1.1 to 2.9 (Racke
1993
). This behavior of CPY is not as apparent for some
soils for which half-lives were calculated by use of simple, first-order kinetics (de
Vette and Schoonmade
2001
). Some half-lives reported in the literature (SI Table
A1) have been derived by assuming first-order kinetics for degradation, which can
overestimate the environmental persistence of CPY. This artifact is discussed in
greater detail in the second paper of this series (Solomon et al.
2013
).
CPY rapidly dissipates from plant surfaces, primarily from volatility and second-
arily from photolysis, with most reported dissipation half-lives being on the order of
several days (SI, Table A3). In a field study of CPY loss to air conducted in California,
maximum fluxes via volatilization occurred in the first 8 h after application to recently
cut alfalfa (Rotondaro and Havens
2012
). The total loss of mass was calculated from
fluxes determined by the Aerodynamic (AD) and Integrated Horizontal Flux (IHF)
methodologies and ranged from 15.8 to 16.5% of the applied mass of CPY.
Based on reported water-sediment adsorption coefficients normalized to fraction
of organic carbon in sediments (K
OC
) of 973-31,000 cm
3
g
−1
(mean 8216 cm
3
g
−1
, SI
Appendix X, Table A4), CPY has moderate to high potential to adsorb to soil.
Uptake by roots, translocation, and metabolism of CPY in plants are negligible and
thus CPY is non-systemic, although metabolism of foliar-applied CPY does occur
(Racke
1993
).
In aquatic systems, abiotic degradation from aqueous hydrolysis of CPY has
been reported to occur with half-lives of 73, 72, and 16 d at pH 5, 7, and 9, respec-
tively at 25 °C (Racke
1993
). An aqueous hydrolysis half-life of 81 d at pH 7 has
been reported (USEPA
2011
). Half-lives of 22-51 d have been reported from stud-
ies of aerobic metabolism in aquatic systems (SI Table A5, Kennard
1996
; Reeves
and Mackie
1993
). A half-life of 29.6 d was observed in a aqueous photolysis study
performed with CPY under sterile conditions at pH 7 in phosphate-buffered solution
under natural sunlight (Batzer et al.
1990
).
Transport of CPY off-site following application has been extensively examined
across a range of field conditions as affected by several factors: antecedent soil
moisture, soil physical and chemical properties, soil erosion, plant canopy cover-
age, plant development stage, time intervals of 2-h to 7-d between application and
rainfall events, and a range of rainfall events with return frequencies as little as 1-in-
833 yr (Cryer and Dixon-White
1995
; McCall et al.
1984
; Poletika and Robb
1994
;
Racke
1993
). CPY mass in runoff ranged from 0.003 (McCall et al.
1984
; Poletika
and Robb
1994
)) to 4.4% (McCall et al.
1984
; Poletika and Robb
1994
) of applied
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