Variability in Nontarget Terrestrial Plant Studies Should Inform Endpoint Selection

Abstract

Inherent variability in nontarget terrestrial plant (NTTP) testing of pesticides creates challenges for using and interpreting these data for risk assessment. Standardized NTTP testing protocols were initially designed to calculate the application rate causing a 25% effect (ER25, used in the United States) or a 50% effect (ER50, used in Europe) for various measures based on the observed dose-response. More recently, the requirement to generate a no-observed-effect rate (NOER), or, in the absence of an NOER, the rate causing a 5% effect (ER05), has raised questions about the inherent variability in, and statistical detectability of, these tests. Statistically significant differences observed between test and control groups may be a product of this inherent variability and may not represent biological relevance. Attempting to derive an ER05 and the associated risk-assessment conclusions drawn from these values can overestimate risk. To address these concerns, we evaluated historical data from approximately 100 seedling emergence and vegetative vigor guideline studies on pesticides to assess the variability of control results across studies for each plant species, examined potential causes for the variation in control results, and defined the minimum percent effect that can be reliably detected. The results indicate that with current test design and implementation, the ER05 cannot be reliably estimated. Integr Environ Assess Manag 2018;14:639-648. © 2018 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Comparative Assessment of Vegetative and Reproductive Terrestrial Plant Species Endpoints from Exposure to Herbicides and Potential Environmental Implications: A Review

“…The more complex a test system, the more processes lead to deviations from the average, which lead to less accurate predictions. This is in line with the relatively high MDDs that can be obtained in NTTP testing (often ranging between 20% and 35% 1‐sided, α = 5%; e.g., Staveley et al ). These are values from standard 21‐d testing of vegetative endpoints; regarding reproductive endpoints see further down.…”

“…He touched on at least 4 separate aspects that could possibly be more differentiated: 1) statistical feasibility (that depends on the nature of the data assessed), 2) different statistical methods (hypothesis testing vs alternatives), 3) a scientifically sound environmental protection goal, and 4) political thresholds. Staveley et al (2018) deal only with the first and second (and as do we in the present paper). Staveley et al (2018) give plenty of evidence that due to the nature of NTTP ecotoxicological data, low thresholds such as a 5% or 10% effect level cannot be handled statistically (and this affects any robust evaluation, not just hypothesis testing-of which Suter disapproves-but also all regression approaches).…”

“…Staveley et al (2018) deal only with the first and second (and as do we in the present paper). Staveley et al (2018) give plenty of evidence that due to the nature of NTTP ecotoxicological data, low thresholds such as a 5% or 10% effect level cannot be handled statistically (and this affects any robust evaluation, not just hypothesis testing-of which Suter disapproves-but also all regression approaches). However, Staveley et al (2018) do not claim that a 25% threshold (which would allow us to obtain unequivocal and statistically sound endpoints) defined any environmental protection goal; but this is what Suter is criticizing.…”

“…The sole existence of a (politically motivated) threshold (e.g., 5% in the Endangered Species Act; USEPA 2013) does not make it scientifically valid. And even if there were scientific evidence that <5% effect is exactly the threshold that ensures protectivity, it would not be expedient to force such a threshold directly on experimental data that are not suitable for it (due to their intrinsic variability, see Staveley et al 2018, and also the data of our database, e.g., Table 38 and Figure 50 in Christl 2017b). If the nature of NTTP ecotoxicological data were ignored and a 5% or 10% effect threshold directly imposed on them anyway, the applied science-which should inform the risk assessment-would turn into a game of chance.…”

Statistics Cannot Decide How Much to Protect the Environment

“…Glenn Suter* † †Cincinnati, Ohio, USA DEAR EDITOR: Staveley et al (2018) argue against the use of a 5% effects limit for assessing the effects of pesticides on endangered species because it is "undetectable" and recommend a 25% limit as "reliable," using herbicides and plants as a case. They base their recommendation on an analysis of minimum detectable differences (MDDs), which they define as "the likelihood of finding a specific size effect statistically significant from a hypothesis test."…”