Organic certification, especially for smallholders, often uses group certification procedures. An internal control system (ICS) visits all farmers, and then the external certification body (CB) inspects a sample to assess the ICS' performance. Harmonised methods for measuring the ICS' reliability are missing so far. Here, we define criteria of "ICS performance", propose a new procedure for quantifying this performance and, based on this procedure, suggest that the sample size can be determined using classical statistical methods for survey sampling, instead of using the square root or a percentage of group size as in current practice.
Pesticide residues are much lower in organic than in conventional food. The article summarizes the available residue data from the EU and the U.S. organic market. Differences between samples from several sources suggest that organic products are declared conventional, when they have residues—but the origin of the residues is not always investigated. A large number of samples are being tested by organic certifiers, but the sampling methods often do not allow to determine if such residues stem from prohibited pesticide use by organic farmers, from mixing organic with conventional products, from short-range spray-drift from neighbour farms, from the ubiquitous presence of such substances due to long-distance drift, or from other sources of contamination. Eight case studies from different crops and countries are used to demonstrate that sampling at different distances from possible sources of short-distance drift in most cases allows differentiating deliberate pesticide application by the organic farmer from drift. Datasets from 67 banana farms in Ecuador, where aerial fungicide spraying leads to a heavy drift problem, were subjected to statistical analysis. A linear discriminant function including four variables was identified for distinguishing under these conditions application from drift, with an accuracy of 93.3%.
In Supplementary Information 5, in the legend of Table 3, "Comparability of the datasets from two laboratories used in Figure 1c for pesticide residues: (mostly) before release to the organic market (Eurofins) and on the (retail and wholesale) organic market (CVUA). " now reads:"Comparability of the datasets from two laboratories used in Figure 1d for pesticide residues: (mostly) before release to the organic market (Eurofins) and on the (retail and wholesale) organic market (CVUA). "
Residues of pesticides not allowed in organic farming are often found in organic food. A large number of samples are being tested by organic certifiers, but the sampling methods often do not allow to determine if such residues stem from prohibited pesticide use by organic farmers, from mixing organic with conventional products, from short-range spray-drift from neighbour farms, from the ubiquitous presence of such substances due to long-distance drift, or from other sources of contamination. Eight case studies from different crops and countries are used to demonstrate that sampling at different distances from possible sources of short distance drift allows in most cases to differentiate deliberate pesticide application by the organic farmer from drift. Datasets from 67 banana farms in Ecuador, where aerial fungicide spraying leads to a heavy drift problem, were subjected to statistical analysis. A linear discriminant function including four variables was identified for distinguishing under these conditions application from drift, with an accuracy of 93.3%.
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