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Design and interpretation of NTA field studies - PS2363

Environmental risk assessments for pesticides under Directive 91/414/EEC (and it's revision) cover potential effects on non-target organisms. Ecotoxicological field studies may be conducted as part of a tiered testing programme. Typically, an ecological community is exposed to a chemical stressor in order to investigate direct and indirect effects on non-target organisms, thereby offering additional realism over single species studies.

The definition or scope of the subject community may differ between study types. Aquatic studies may assess effects on the entire community present including primary producers, higher plants, zooplankton and invertebrates. In contrast, terrestrial studies may be confined to the above ground arthropod community or aspects of the soil community. Beyond these wider definitions, however, are aspects of experimental design (replication, plot size, sampling technique, duration) which may affect the relevance of the study to the actual community of concern. Therefore, the complexities of the studies include both the community responses and aspects of study design. Careful interpretation is required in order to arrive at appropriate conclusions.

In terms of interpreting and analysing ecotoxicological community data, a range of approaches exist. Simply, abundance plots from treatment and control groups may be presented to illustrate trends over time in relation to application regime. Non-statistical, comparative measures include percent reduction in relation to control groups such as Abbott values (Abbott, 1925). These may provide relative measures but do not give an indication of statistical significance of differences between counts in control and treatment groups. Interpretation of percent reduction values based on count data can also be misleading when there is background variability in density of individuals between treatment groups.

Statistical approaches available include univariate methods (such as t-test, Wilcoxon test, ANOVA) and multivariate methods (latterly, for example, principal response curves; Van den Brink & Ter Braak, 1999). All of these approaches to interpretation of ecotoxicological field data are currently used to varying degrees by researchers reporting regulatory field studies.

The range of potential responses in community systems is, of course, vast. Therefore, and depending upon the aim of the study, it is necessary to consider not only the overall community response, but also taxa which may respond differently. Considerble skill is required in order to fully interpret the output for taxa which do not follow the overall community response. This may require reference to multivariate and univariate statistics and the raw data.Ecotoxicological field studies may be conceived by industry notifiers in association with external consultants and contract research organisations (CROs). The results may then be interpreted and summarised before inclusion in a regulatory submission in support of a product registration. The submission will be reviewed by representatives from Member State (MS) Competent Authorities, in terms of both study quality and meaning. Not all involved parties may be experts in the conduct and interpretation of such studies.

Whilst laboratory studies are typically conducted to familiar guidelines which stipulate experimental conditions as well as design, field studies are far less consistent. The conduct of studies may vary significantly between research institutes – this may include design of experimental facility (especially for mesocosms) and preferred approaches to statistical analyses. Interpretation by risk assessors, therefore, must be made on a case by case basis to account for effects of study design and prevailing test conditions.

There is a need, therefore, for guidance on both field study experimental set-up and statistical analysis of ecotoxicological community data. This would take the form of guidance and a checklist of issues for study design and various statistical analyses relevant to community data and would be a useful reference for researchers, consultants, notifiers and MS representatives. Indeed, van den Brink & Ter Braak (1999) highlighted the need for guidance on use of multivariate techniques in ecotoxicology – this work would extend to experimental design and community statistical analysis.

It is important to note that this project would not seek to critically assess different sampling methods or experimental systems (e.g. design of mesocosm facilities). Rather, it would provide an overview of issues to consider during experimental design which may affect statistical analysis (replication, plot size, study duration, randomisation, selection of species for inclusion in analysis - broad criteria which may depend on statistical method employed - and optimal study design for certain statistical analyses) and provide guidance on the statistical analysis of ecotoxicological community effect data.
a. Develop a guide to best practice for experimental design of ecotoxicological community studies (aquatic mesocosms, non-target arthropod field studies, soil mesofauna field studies).
b. Develop a guide to best practice for statistical analysis of ecotoxicological community data (aquatic mesocosms, non-target arthropod field studies, soil mesofauna field studies).
Project Documents
• FRP - Final Report : PS2363 Final report   (843k)
Time-Scale and Cost
From: 2011

To: 2012

Cost: £61,586
Contractor / Funded Organisations
Ecosystem Functioning              
Environmental Effects              
Pest and Weed Control              
Pesticide use              
Plants and Animals              
Fields of Study
Pesticide Safety