Comprehensive Analysis of the Value of Single Versus Multiple Year

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Comprehensive analysis of the value of single vs multiple year (season) crop residue data for establishment of Maximum Residue Levels (MRLs) Carrie R Fleming, Val Gartner, Pablo Valverde-Garcia, Pieter W Geurs, and Carmen Tiu J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b05106 • Publication Date (Web): 03 Jan 2017 Downloaded from http://pubs.acs.org on January 5, 2017

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Journal of Agricultural and Food Chemistry

TITLE: Comprehensive analysis of the value of single vs multiple year (season) crop residue data for establishment of Maximum Residue Levels (MRLs) AUTHORSHIP: Carrie R Fleming, Val Gartner, Pablo Valverde-Garcia, Pieter Geurs, Carmen Tiu* Dow AgroSciences, 9330 Zionsville Road, Indianapolis, IN 46268 *317-337-4041, [email protected] KEYWORDS: pesticides, residues, seasonality, homogeneity, variability, maximum residue levels, proportionality.

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ABSTRACT:

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Disharmony currently exists in regulatory requirements regarding whether multiple seasons of

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field residue trials are necessary. This analysis used historical residue data to evaluate whether

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the year in which trials are conducted is a significant contributor to the overall variability in field

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residue data. It was concluded that residue behavior is highly variable in nature, regardless of

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the season, that variation of residue data compiled from multiple years is not statistically greater

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than data resulting from trials conducted within any one year, and that variation across years

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does not result in large systematic differences in residue values or resulting Maximum Residue

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Limits compared to trials conducted in any single year. Field trials conducted at a variety of

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locations across geographical regions will capture variability due to different environmental

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conditions and agricultural practices and provide a robust estimate of the spread of residues

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expected due to labeled use of a pesticide.

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INTRODUCTION:

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The purpose of the research presented here is to determine if there is a need for pesticide residue

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data to be collected over more than one growing season. OECD and several regulatory agencies

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allow pesticide residue data to be collected in a single year1-6; however, some other regulatory

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agencies require residue data to be collected over more than one year or growing season7-11.

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This research assessed 97 sets of residue data that have been generated on 20 active ingredients,

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across four global regions, with pesticide residue trials (within same region) conducted over two

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or three years. Statistical analysis was conducted to assess whether pesticide residues differ

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between years and to determine the contribution of the year in which trials were conducted to the

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overall variability in field trial residue data.

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Pesticide residue field trials are conducted to determine the magnitude of the pesticide residues

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in or on raw agricultural commodities (RACs), for the purposes of registration of a pesticide,

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setting tolerances, or maximum residue levels (MRL) for the pesticide on RACs, and evaluating

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the consumer risk related to consumption of foods derived from treated crops. Depending on the

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crop and country, regulatory guidelines require 4-20 field residue trials to be conducted per

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representative crop under a diverse range of climates and growing practices. The trials are

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conducted under the Good Agricultural Practices (GAP) according to pesticide label instructions

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that are expected to produce the highest residues (i.e., maximum application rate, maximum

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number of applications, minimum re-treatment interval, and minimum period between treatment

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and harvest of samples or pre-harvest interval).

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A wide variety of factors can influence the magnitude of pesticide residue concentrations in

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agricultural commodities and can contribute to the variability observed within and across residue

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field trials12. A number of factors can affect the final amount of pesticide residue on the day of

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application to crops, even when the same GAP is followed, resulting in large variability between

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trials. These include differences in the spray equipment used, calibration of that equipment, tank

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mixing partners used (e.g, adjuvants), the crop growth stage at the time of application, etc.

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Differences in crop variety, horticultural practices (e.g., differences in planting density or

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pruning practices), and weather conditions can also lead to variability between trials.

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Furthermore, variability in pesticide residues within the field may occur due to differences in

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spray deposition (e.g., resulting from overlapping spray swaths or gusty winds) or crop growth

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and maturation (e.g, due to gradients in soil quality within a field). Together, these factors can

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lead to differences in the magnitude of pesticide residues from different trial sites, or even in

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multiple samples taken from the same trial site.

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A couple of previous analyses have established precedents for statistical methods to determine

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the contribution of the different field related parameters into the typically high variability of crop

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residue data. Brief summaries are presented below, as important precedents to the analysis

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provided in this paper.

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Proportionality of Residue Data to Application Rate

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This was the first analysis using statistical means to compare residue data from different

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pesticides, crops and regions13 and provided proof of evidence for the hypothesis that there is a

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direct relationship between application rates and magnitude of residues. Based on this statistical Page 4


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procedure, more data was validated and published by the Food and Agriculture

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Organization/World Health Organization (FAO/WHO) Joint Meeting on Pesticide Residues

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(JMPR) to conclude that a proportional relationship between pesticide application rate and the

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resulting residues in harvested commodities exists within the range of 0.3 – 4 times the

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maximum labeled application rate14, 15.

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Homogeneity of Residue Data Across Regions

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Analysis of variability in residue data across climatic regions (zones) has shown that there are no

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systematic differences in pesticide residues from trials conducted at similar GAPs in different

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regions, and that zone is a minor contributor to the overall variability. A joint OECD/FAO

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project developed in 1999 through 2003 concluded that highest contributors to residue data

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variability seemed to be the agricultural practices, while climatic zones did not appear to be a

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significant contributor, though further analysis was considered necessary to confirm these

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results12. A subsequent analysis on a global residue program using data from four continents and

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five crops (apple, cabbage, grape, tomato, and wheat (grain, forage, hay, and straw)) concluded

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that data is homogeneous across regions, and variability between regions is smaller than the

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variability between trials within individual regions. This work was presented at the Global

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Minor Use Summit meeting in Rome 2012 and published in the report from this meeting 16. To

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further expand on and validate these conclusions, a joint effort was coordinated between the

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United States Environmental Protection Agency (US EPA), the Canadian Pest Management

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Regulatory Agency (PMRA) and Crop Life America (CLA) to evaluate more than 4,000 trials

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generated on more than 70 crops in at least two climatic zones. A draft technical document Page 5



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summarizing this work and supporting the global exchangeability of field trial residue data was

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appended to the OECD Crop Field Trials Guidance document17 and proceedings from the Codex

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Committee on Pesticide Residues (CCPR)-4818.

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Hypothesis for Homogeneity of Residue Data Across Seasons/Years

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There is currently a lack of harmonization in global regulations concerning the need to conduct

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residue trials in more than one year. OECD and several regulatory bodies consider residue data

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generated all in a single growing season to be acceptable, as long as there are a sufficient number

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of trial sites distributed across a wide enough geographical area to capture different climatic

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conditions (e.g.,1-6). However, for other regulatory bodies, residue trials are required to be

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distributed across more than one growing season7-11, leading to disharmonies in global data

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requirements for establishment of pesticide MRLs. As part of a sequence of initiatives aimed at

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harmonization of MRLs (e.g. comprehensive global programs – OECD 5093, exchangeability of

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data across regions – CCPR 48 item 0.81 19, several documents of crop groupings – CCPR 4820),

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harmonization of the requirement for trials from multiple growing seasons is the next step to

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further align regulatory requirements for residue trials to facilitate the establishment of globally

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harmonized MRLs, which are necessary for smooth global trade of food and feed commodities.

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The purpose of this research was to address the disparity in regulatory requirements for field trial

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data from either a single or multiple growing seasons by determining whether the growing

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season contributes significantly to the variability captured in the overall package of field trial

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data.

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MATERIALS AND METHODS: Page 6


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Selection of Data

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Pesticide residue data from existing regulatory studies were used to evaluate the homogeneity of

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the data over two or three years. Residue data from trials conducted according to a similar Good

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Agricultural Practices (GAP), and containing field trial data across more than one year, with at

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least four trial sites per year, and with quantified residue values (i.e. all residues cannot be non-

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detectable) were selected for inclusion in this analysis. The determination that trials were

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conducted at a similar GAP was made according to the following criteria:

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1.

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All trials conducted in the same geographical region (e.g., EU southern zone, or North America)

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All trials measured the same analyte(s)

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All trials sampled from the same crop and crop matrices (e.g., tomato fruit, or

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wheat straw)

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All trials had the same number of applications

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5.

Application rate and pre-harvest interval (PHI) did not differ between trials

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by more than a combined difference of 25%.

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According to OECD Test Guideline 509, “In the case of up to 25% increases or decreases of the

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active ingredient application rate, the number of applications, or the PHI, under otherwise

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identical conditions, the residue results can be assumed to be comparable” 3. Therefore, the

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selection criteria used in this analysis were conservative and would be considered to effectively

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identify trials that should be considered comparable. For each of the 97 data sets included in the

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analysis, the application rates at each trial site were within 17% of the mean application rate for Page 7



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their data set, with an average difference of 5%. The PHIs at each trial site were within 13% of

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the mean PHI for their data set, with an average difference of 1%. Furthermore, when the

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differences between the application rate and PHI for each trial site were compared to their data

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set’s averages, the total cumulative difference was within 17% of the mean, with an average

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difference of 3%.

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There were 91 sets of residue data over two years and 6 sets of data over three years giving a

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total of 97 sets of residue data included in the analysis. These data sets included residue results

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from 20 active ingredients (eight herbicides, six insecticides, and six fungicides), 31 crops, and

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four regions (Canada, European Northern Zone, European Southern Zone, and United States).

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Table 1 presents the pesticide mode of action/crop combinations included in the analysis.

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Of the 97 data sets available for analysis, 46 had replicate samples taken from each trial, i.e. two

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independently collected samples from one field trial location analyzed for residues. For these 46

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datasets, further evaluations were performed regarding the contribution of the trial site to the

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overall variability vs. within trial residual variability (as described further below).

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Assumptions for Data Analysis

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Residue results less than or equal to the limit of quantitation (LOQ) were assigned the LOQ

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value for analysis. For example, if the residue was reported as ND (non-detectable), and the

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LOQ was 0.01 ppm, the residue value was adjusted to 0.01 ppm for the analysis. This is

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consistent with the OECD guidance for MRL calculation, which requires the substitution of non-

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detected residues by the LOQ values. 21 Page 8


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Based on common global regulatory pesticide residue definitions, where appropriate, metabolite

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residue values were converted to stoichiometric active ingredient parent equivalents and added to

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parent residue values; this total residue value was used in subsequent analyses.

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Procedures and Methods for Data Analysis

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From the procedural perspective, four different steps have been conducted:

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1. Residue ratio comparison analysis,

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2. Non-parametric and parametric statistical analysis to identify any systematic differences,

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3. Variance components analysis,

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4. Regulatory impact of exceptions on MRL calculations.

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A brief description of the methods used for each of the 4 steps is described below. 1. Residue ratio comparison analysis

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Residue values were log10 transformed to satisfy linear model assumptions (normality and

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homogeneity of variance) for the parametric statistical analysis at step 2. The additional

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property of the log10 transformation is that the difference in residue levels between two

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years in the log10 scale is equivalent to the ratio of those residue levels in the physical

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scale. For each dataset, differences between any pair of years were calculated as absolute

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values, which provide ratios ≥ 1, and the maximum ratio between any pair of years was

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reported.

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2. Non-parametric and parametric statistical analysis to identify any systematic differences

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Yearly subsets of each data package for the same combination of active and crops were

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evaluated by non-parametric statistical tests. Non-parametric analyses used Wilcoxon

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test for datasets with two years and Kruskal-Wallis test for datasets with more than 2

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years (χ2 approximation, P

Comprehensive Analysis of the Value of Single Versus Multiple Year

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