Introduction and Project Definition

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

2. 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.

3. 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.

4. 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.

5. 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.

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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.