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Ecotoxicology, Recent projects

• Analysis of toxicology of food flavouring
• Copper-based fungicide
• OECD/FAO zoning project
• MRLs in grapes

Analysis of toxicology of food flavouring

This analysis concerned the toxic effects on mice of a food flavouring additive. Quantics was asked to consider the proposed procedure of Hayashi. Some amendments were necessary; in particular Quantics suggests that:

1. Using extra historical controls for comparisons with current data may provide more power for the statistical comparisons but has the potential for bias.
2. The use of the trend test at step 3 is inappropriate if there are no significant results in the initial comparison at step 2. This can affect the overall p values (for example if the trend test was positive but the tests in step 2 were negative.).
3. The suggested Cochran-Armitage test is for comparing trends in proportions. The experimental design must be carefully considered to ensure that this is the appropriate test. In many instances of this type of trial, this is not strictly the case as at each dose there are a number of separate, independent animals, each of which contributes a proportion. If the numbers of cells examined for toxic effects are pooled and the proportion treated as if it were binomial, the variance may be wrongly estimated by the Cochran-Armitage test because it ignores the animal-to-animal variation.

The effect of a copper-based fungicide on invertebrate populations

Quantics was asked to analyse data from a multi-dose multi-site longitudinal study (several years) to determine the effect of a copper fungicide on invertebrate populations.

A previous analysis by others had failed to make the best use of the data by considering changes at specific time points only, and failing to take into account interactions between populations and underlying changes in populations over time. Quantics re-analysed the data using Repeated Measures Analysis and was able to provide the client with a robust description of the effects of the treatments.

OECD/FAO zoning project

Quantics provided statistical analysis of various aspects of pesticide residue data for the OECD pesticide zoning study. The aim of the study was to examine the possibility of identifying geographic zones (rather than zones defined by national boundaries) for the testing of pesticide residues in agricultural crops.

Quantics provided 3 statistical discussion papers:

1. The Contribution of Zero-day Residue Values to the Variability of Residues Measured at Harvest: A Gould, 7 March 2002 (Revised 16 August 2002)
2. Statistical Analysis of the Relationship between Climate Factors and Pesticide Residues: Analysis of Data from the USA: A Gould, 5 February 2002 (Revised 16 August 2002)
3. The Relationship between Application Parameters and Residues Measured at Harvest - Analysis of Selected Crop/Pesticide Combinations: A Gould, 21 June 2002.

See: Report of the OECD/FAO Zoning Project (PDF document, 380KB)

Work by Quantics resulted in the following findings:

1. The differences in residue behaviour between the proposed residue zones were inconsistent and that the use of a residue zoning scheme based on refinements of existing climate maps could not be validated using the available data.
2. A general lack of significant correlation between the pre-harvest climatic conditions and residues at harvest reported in comparable residue trials. In the few cases where significant effects were observed, these effects were inconsistent.
3. Application factors such as spray concentration, treatment rate, the number of sprays and pre-harvest intervals explain a large proportion of the variation in residues at harvest; the additional effect of pre-harvest climate is relatively small, and 'other factors' are likely to be of more importance.

MRLs in Grapes

Quantics was asked to examine maximum residue limits (MRLs) in grapes across a number of different countries. In particular, a higher than expected MRL had been found in one country and Quantics was asked to explore the possible reasons for this and discuss how these results should be handled in relation to regulatory submissions.