Fate in the Environment and Long-Range Atmospheric Transport of the Organophosphorus Insecticide, Chlorpyrifos and Its Oxon - Reviews of Environmental Contamination and Toxicology - page 70

Detectable concentrations of the organophosphorus insecticide CPY in air, rain,
snow and other environmental media have been measured in North America and
other locations at considerable distances from likely agricultural sources, which
indicates the potential for long range transport (LRT) in the atmosphere. This issue
was addressed by first compiling monitoring results for CPY in all relevant envi-
ronmental media. As a contribution to the risk assessment of CPY in remote
regions, a simple mass balance model was developed to quantify likely concentra-
tions at locations ranging from local sites of application to more remote locations
up to hundreds of km distant. Physical-chemical properties of CPY were reviewed
and a set of consistent values for those properties that determine partitioning and
reactivity were compiled and evaluated for use in the model. The model quantifies
transformation and deposition processes and includes a tentative treatment of dis-
persion to lesser atmospheric concentrations. The model also addressed formation
and fate of CPYO, which is the major transformation product of CPY. The
Characteristic Travel Distance (CTD) at which 63% of the original mass of volatil-
izedCPYisdegradedordeposited-basedonaconservativeconcentrationof•OH
radicals of 0.7 × 10 6 molecules cm −3 and a half-life of 3 h, was estimated to be
62km.Atlesserconcentrationsof•OHradical,suchasoccursatnightandatlesser
temperatures, the CTD is proportionally greater. By including monitoring data
from a variety of media, including air, rain, snow and biota, all monitored concen-
trations can be converted to the equilibrium criterion of fugacity, thus providing a
synoptic assessment of concentrations of CPY and CPYO in multiple media. The
calculated fugacities of CPY in air and other media decrease proportionally with
increasing distance from sources, which can provide an approximate prediction of
downwind concentrations and fugacities in media and can contribute to improved
risk assessments for CPY and especially CPYO at locations remote from points of
application, but still subject to LRT. The model yielded estimated concentrations
that are generally consistent with concentrations measured, which suggests that the
canonical fate and transport processes were included in the simulation model. The
equations included in the model enable both masses and concentrations of CPY and
CPYO to be estimated as a function of distance downwind following application.
While the analysis provided here is useful and an improvement over previous esti-
mates of LRT of CPY and CPYO, there is still need for improved estimates of the
chemical-physical properties of CPYO.
Based on the persistence in water, soils, and sediments, its bioconcentration and
biomagnification in organisms, and its potential for long-range transport, CPY and
CPYO do not trigger the criteria for classification as a POP under the Stockholm
convention or a PB chemical under EC 1107/2009. Nonetheless, CPY is toxic at
concentrations less than the trigger for classification as T under EC1107/2009; how-
ever, this simple trigger needs to be placed in the context of low risks to non-target
organisms close to the areas of use. Overall, CPY and CPYO are judged to not trig-
ger the PBT criteria of EC 1107/2009.
Acknowledgements The authors wish to thank the anonymous reviewers of this paper for their
suggestions and constructive criticism. Prof. Giesy was supported by the Canada Research Chair
program, a Visiting Distinguished Professorship in the Department of Biology and Chemistry and