Historical data to design and optimize the plant testing

Depending on the regulatory objective, these studies often require defining a no observed effect rate or various effective concentration (ECx) values and may include testing up to 10 species of common plants. The inherent variability in this testing coupled with other challenges (hormesis, frequent shallow dose responses, lack of standardization for replication, or planting density) presents significant issues in conducting this testing and interpreting the data. In NTTP, inherent variability can be defined as differences in measured parameters (emergence, growth, etc.) as a function of biological variability rather than true toxicity effects. While increasing replication or testing additional application rates can increase the statistical power of these tests, this is often not feasible due to the resources required to conduct larger studies. The sensitivity analysis was conducted by harvesting relevant information from our extensive historical database for seedling emergence and vegetative vigor studies. Tomato most frequently generated the lowest reported endpoint for studies while incidences in which no effects were observed represented 84% of the ANOVA comparisons. The percent minimum significant difference (PMSD) was not a clear indicator of sensitivity with regards to toxic effects and no clear trends were observed across compound classes or modes of action.

Accessing historical data

Since Smithers typically conducts standard studies according to specific guidelines and under confidentiality agreements with our clients, we rarely have the opportunity to publish the results of individual studies. However, from our robust set of historical testing data related to several test types, we are often able to perform retrospective queries, extract the data, and interpret that information to guide the optimization of existing test methods.

In this instance, we compiled endpoint data from 32 seedling emergence and 25 vegetative vigor studies, surveyed species sensitivity by the lowest reported endpoint for each test type, across compound class, and by mode of action. Finally, we assessed the sublethal endpoint Percent Minimum Significant Difference (PMSD) for each species across test types. 

How the tests were performed

The studies included testing up to 10 species of common plants, measuring both lethal and non-lethal endpoints to generate dose-response data with EC25, noobserved?effect concentration (NOEC), and lowest-observed-effect concentration (LOEC). Studies were conducted in accordance with the relevant EPA and OECD guidance.

Interpreting the results

Data mining consisted of assessing our most recent plant testing data. A database was designed to include some of the following components: test material, compound class, test type, species tested, units for application rate, and the various endpoints required for testing. The relevant data was then extracted from study reports and added to the database for assessment. The following figure summarizes the completed database as it relates to the statistical endpoints.

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Authors: C. Picard, A. Kirkwood and J. Schwalbe, Smithers -Wareham, Massachusetts

Photo created by standret - freepik

Source: Ag News