Fate in the Environment and Long-Range Atmospheric Transport of the Organophosphorus Insecticide, Chlorpyrifos and Its Oxon - Reviews of Environmental Contamination and Toxicology - page 63

outdoor mesocosms treated with 1 μg L −1 in Thailand (Daam et al. 2008 ). Using
small (70-L) open-air estuarine microcosms to investigate dissipation of 14- C CPY, a
DT 50dis of ~5 d was reported under tropical conditions with loss to air a major driver
of dissipation (Nhan et al. 2002 ). In studies conducted in flowing, outdoor meso-
cosms, a DT 50dis was reported to be <1 d, probably as a result of hydraulic dilution.
However, in still-water-only laboratory mesocosms, DT 50dis ranged from 10 to 18 d
(Pablo et al. 2008 ). Dissipation in small (2.4-L) laboratory microcosms with water
and gravel was biphasic with a phase-1 DT 50dis of 2.25-3 d and a phase-2 DT 50dis of
14-18 d (Pablo et al. 2008 ). DT 50dis of CPY in microcosms was reported to be ~5 d
from water (Bromilow et al. 2006 ). Overall, dissipation of CPY in natural waters
under field conditions was rapid with the range of DT 50dis s from 4 to 10 with a geo-
metric mean of 5 d (SI Table 1 ).

4 Fate in Soils and Sediments

Studies on the fate of CPY in soils and sediments were summarized in the review by
Racke ( 1993 ) and discussed in the context of adsorption and desorption in a detailed
review in 2012 (Gebremariam et al. 2012 ). Most of the half-lives in soil (DT 50dis and
DT 50deg ) summarized from laboratory studies in Racke ( 1993 ) were in the range of
1.9-120 d for rates of application associated with agricultural uses, with most in the
range of 7-30 d (Table 6 ). Longer half-lives (DT 50deg ) were reported for rates of
application for the now-cancelled use for control of termites in soil. Half-lives in
soil were dependent on temperature (a doubling in rate of degradation for a 10 °C
increase in temperature) and soil pH, with faster rates at greater pH (0.0025 d −1 at
pH 3.8 to 0.045 d −1 at pH 8) (Racke 1993 ). Mean and geometric mean values for all
data (SI Table 2 ) were 82 and 32 d, respectively.
Generally, dissipation (DT 50dis ) of CPY in soils under field conditions was reported
to be more rapid than in the laboratory. The DT 50dis was reported to range from <2 to
120, with mean and geometric means of 32 and 22 d, respectively (SI Table 3 ); most
values were in the range of 7-30 d (Table 6 ). Comparison of rates of dissipation of
CPY from soils from Brazil under laboratory conditions suggested a tenfold greater
rate of dissipation in the field than in the laboratory (Laabs et al. 2002 ).
Half-lives (DT 50deg ) in sediments were reported to range from 6 to 223 d (SI
Table 4 ), with longer times likely reflecting more anaerobic conditions. Some more
recent studies have reported dissipation of CPY from sediments in microcosms, a
more realistic scenario. The DT 50dis values for CPY were reported to range from 68
to 144 d in wetland sediments under flooded conditions (Budd et al. 2011 ).
Measurements of dissipation of CPY from sediments collected in San Diego and
Bonita Creeks (Orange County, CA, USA) gave DT 50dis values of 20 and 24 d under
aerobic and 223 and 58 d under anaerobic conditions, respectively (Bondarenko and
Gan 2004 ). DT 50dis of CPY in microcosms was reported to be 15-20 d from sedi-
ment (Bromilow et al. 2006 ). The DT 50dis value measured in sediment in a laboratory-
based marine microcosm study was approximately 6 d under tropical conditions