Introduction and Project Definition
Russell L. Jones
January 30, 2006
Introduction
 FOCUS
has spent a great deal of effort developing
and standardizing procedures for assessing
concentrations in surface and ground water.
 One
goal of this effort has been to remove the
influence of the modeler so that similar results are
obtained by anyone following the procedures.
 Some
of the most important input variables in
these assessment procedures are the degradation
rates of parent and metabolites.
January 30, 2006
2
Current Status
 Study
procedures are specified in guidelines but
calculation of degradation rates are not
standardized.
 Calculation
of first-order kinetics for parent
compounds is relatively straightforward.
 However,
assumptions about transformation of
data, treatment of values below the LOQ, etc. can
affect the resulting degradation rate.
January 30, 2006
3
Current Status
 Less
straightforward (especially from a regulatory
perspective):
 Procedures
when degradation kinetics are not first-
order.
 Obtaining degradation rates for metabolites.
 Obtaining degradation rates from water-sediment
studies
 How information from field studies should be used.
January 30, 2006
4
Current Status
 Most
registration authorities re-calculate
degradation rates from studies.
 Requires
additional time for dossier review
 Different rates can be obtained when different
assumptions/procedures are used
 Such re-calculations can negate increasingly
complex risk assessments.
January 30, 2006
5
Current Status
 Commonly
used software packages can give
different results.
 Some
organizations have issued guidelines but a
more comprehensive document is needed.
 the
EU in the soil persistence paper
 the U.S. EPA (draft)
 a joint working group of the IVA, BVL, and UBA for
calculating degradation rates of metabolites
January 30, 2006
6
Work Group Tasks
 Prepare
a report providing guidance on calculation
of degradation rates of parent and metabolites
from laboratory and field studies
 Areas
to address were specified in a project
definition document from the FOCUS Steering
Committee
 Propose
a revision to the EU Guidance Document
on Persistence in Soil
January 30, 2006
7
General Issues and Parent Kinetics
 Data
handling (for example, replicates,
transformation, outliers, values below LOQ)
 Endpoints for various regulatory uses
 First-order versus bi-phasic kinetics
 Statistical tests for goodness of fit
 Dealing with time zero samples
 Correcting field data to standard conditions
 Dealing with uncertainty (model and data)
 Procedures for calculating parent degradation
rates
January 30, 2006
8
Special Considerations for Metabolites
 Definition
and quantification of the degradation
pathway
 Need
for good fit for parent
 Starting
values for optimization
 Stepwise
versus simultaneous regression
 Accuracy
when several degradation rates are
determined
January 30, 2006
9
Other Tasks
 Kinetics
from water sediment studies
 Review
of software packages
 Reporting
of kinetic analyses
 Application
to regulatory assessments
 Averaging
multiple values for use in PEC
calculations
 Expansion of PECsoil calculations to bi-phasic
kinetics
January 30, 2006
10
Work Group Accomplishments
 The
work group meetings have provided a forum
for extensive discussion of the various viewpoints.
 The
report provides guidance on the topics
requested by the FOCUS Steering Group.
 Hopefully
the report provides a regulatory
framework for consistently conducting high quality
kinetic assessments, which will benefit both
regulators and industry.
January 30, 2006
11