Regulatory agencies require that the dissipation rates and mobility
profiles for agrochemicals be determined under actual use conditions in the
field.
 Experimental Study Descriptions
Residues of agrochemicals and their metabolites in
soils are generally measured by chromatographic and/or spectrometric techniques
in an effort to determine their persistence and mobility. These studies are
commonly conducted on bare ground at several geographic locations and the soils
are analyzed over a period of 18 months at various depths. PTRL West conducts
the analytical phase of these studies and can either collaborate with the Sponsor's
designated Field Investigator or coordinate the field phase of the study
independently.
A second type of dissipation study involves
radiolabeled test substance utilizing much smaller plots and carefully
controlled field conditions. This approach is particularly useful for active
ingredients used at very low application rates or which produce complex and/or
numerous metabolites. A variant of the small plot approach is the use of
"field lysimeters", although here the focus of the study is on
downward mobility rather than dissipation. PTRL West has successfully conducted the
field and analytical phases of dissipation studies utilizing radiolabels both in
small plots and lysimeters.
These studies measure the dissipation of
agrochemicals and biocides from aquatic systems. Soil, sediment and water are
analyzed generally without the use of radiolabels. Optionally, the design can
include aquatic species such as different varieties of fish to establish
bioaccumulation potential.
- Field Volatility and Flux Measurement:
In cases where the volatility of a chemical is considered
high, as with the various methyl bromide replacement candidates, the
concentrations in the air above treated soil must be monitored and the flux
rates determined. PTRL West has considerable experience in conducting these
determinations and has developed protocols in collaboration with regulatory
agencies for this purpose. Air samplers are placed at predetermined locations
within the treated field and along its perimeter. These are equipped with
suitable traps whose efficiency and recovery have been previously determined and
validated.
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PTRL West 
