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Data handling Sabine Beulke, CSL, York, UK FOCUS Work Group on Degradation Kinetics Estimating Persistence and Degradation Kinetics from Environmental Fate Studies in EU Registration Brussels, 26-27 January 2005

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Outline Data quality Replicates Concentrations below LOD or LOQ Experimental artefacts Outliers Time zero samples Data weighting For more information see Chapter 6.1 of the FOCUS report

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Data quality Dissipation pattern and - for metabolites and sediment data - the increase, plateau and decline phase must be clearly established No. of data points (n) >> no. of parameters (p) (theoretical minimum n = p+1, but this is often not sufficient) The better the quality the smaller the no. of datapoints needed

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Replicates Use true replicates individually in the optimisation Average replicate analytical results from same sample prior to curve fitting Average all replicates prior to calculating 2 statistics

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Concentrations below LOD or LOQ Parent in soil, total water-sediment system, water column Set all concentrations between LOD and LOQ to measured value or 0.5 x (LOD+LOQ) Set first sample < LOD to 0.5 x LOD Omit samples after first non-detect unless later samples > LOQ Set to measured value Set to 0.5 x LOD Omit

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Concentrations below LOD or LOQ Metabolite in soil and parent and metabolite in sediment Set time zero samples < LOD to 0 Set concentrations between LOD and LOQ to measured value or 0.5 x (LOD+LOQ) Set sample

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Experimental artefacts Discard results clearly arising from analytical or procedural errors before analysis If microbial activity declined significantly during study: Include all data initially, then exclude later sampling points and repeat fitting

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DT50 42 daysDT50 34 days Outliers Include all data in curve fitting as a first step Omit outliers based on expert judgement Statistical outlier test where possible

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Time zero samples Include initial amount of parent (soil, total w/s system and water column) in parameter estimation as a first step M0 variable: DT50 = 68 days M0 fixed: DT50 = 48 days Note: This hypothetical dataset is not described well by SFO kinetics and is only used to illustrate the effect of fixing or estimating the initial concentration.

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Time zero samples Add time-zero concentrations of metabolites > 0 to parent unless due to impurity in application solution Add time-zero concentrations > 0 of parent or metabolite in sediment to water M0 variable: DT50 = 68 days M0 fixed: DT50 = 48 days Note: This hypothetical dataset is not described well by SFO kinetics and is only used to illustrate the effect of fixing or estimating the initial concentration.

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Data weighting Always use unweighted data as a first step! No transformation: DT50 = 51 days Log transformed: DT50 = 57 days No transformation: DT50 = 54 days Log transformed: DT50 = 108 days Note: This hypothetical dataset is not described well by SFO kinetics and is only used to illustrate the effect of log-transformation.

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