Introduction and Project Definition Russell L. Jones January 30, 2006

2 Introduction u FOCUS has spent a great deal of effort developing and standardizing procedures for assessing concentrations in surface and ground water. v 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. u Some of the most important input variables in these assessment procedures are the degradation rates of parent and metabolites.

3January 30, 2006 Current Status u Study procedures are specified in guidelines but calculation of degradation rates are not standardized. u Calculation of first-order kinetics for parent compounds is relatively straightforward. v However, assumptions about transformation of data, treatment of values below the LOQ, etc. can affect the resulting degradation rate.

4January 30, 2006 Current Status u Less straightforward (especially from a regulatory perspective): v Procedures when degradation kinetics are not first- order. v Obtaining degradation rates for metabolites. v Obtaining degradation rates from water-sediment studies v How information from field studies should be used.

5January 30, 2006 Current Status u Most registration authorities re-calculate degradation rates from studies. v Requires additional time for dossier review v Different rates can be obtained when different assumptions/procedures are used v Such re-calculations can negate increasingly complex risk assessments.

6January 30, 2006 Current Status u Commonly used software packages can give different results. u Some organizations have issued guidelines but a more comprehensive document is needed. v the EU in the soil persistence paper v the U.S. EPA (draft) v a joint working group of the IVA, BVL, and UBA for calculating degradation rates of metabolites

7January 30, 2006 Work Group Tasks u Prepare a report providing guidance on calculation of degradation rates of parent and metabolites from laboratory and field studies v Areas to address were specified in a project definition document from the FOCUS Steering Committee u Propose a revision to the EU Guidance Document on Persistence in Soil

8January 30, 2006 General Issues and Parent Kinetics u Data handling (for example, replicates, transformation, outliers, values below LOQ) u Endpoints for various regulatory uses u First-order versus bi-phasic kinetics u Statistical tests for goodness of fit u Dealing with time zero samples u Correcting field data to standard conditions u Dealing with uncertainty (model and data) u Procedures for calculating parent degradation rates

9January 30, 2006 Special Considerations for Metabolites u Definition and quantification of the degradation pathway u Need for good fit for parent u Starting values for optimization u Stepwise versus simultaneous regression u Accuracy when several degradation rates are determined

10January 30, 2006 Other Tasks u Kinetics from water sediment studies u Review of software packages u Reporting of kinetic analyses u Application to regulatory assessments v Averaging multiple values for use in PEC calculations v Expansion of PECsoil calculations to bi-phasic kinetics

11January 30, 2006 Work Group Accomplishments u The work group meetings have provided a forum for extensive discussion of the various viewpoints. u The report provides guidance on the topics requested by the FOCUS Steering Group. u Hopefully the report provides a regulatory framework for consistently conducting high quality kinetic assessments, which will benefit both regulators and industry.