Testing for Pesticide Toxicity to Aquatic Plants: Recommendations for Test Species

Abstract

A literature review of pesticide toxicity to aquatic plants was conducted in order to arrive at a set of species for use in preregistration testing. Criteria used in the selection process were: (1) existing database; (2) interspecies variability in response to pesticides; (3) availability of well-characterized plant cultures; and (4) ease of culture. Freshwater and marine algae and freshwater and estuarine macrophytes were included in the study. Results showed that the three practical criteria [1,3,4] all resulted in the selection of unicellular green algae (Chlorophyceae) for the freshwater algae tests. However, variability among freshwater species and classes was so great and so unpredictable that it became obvious that a species battery approach was required. The battery should consist of representatives of each of the major algal classes. Research into culture methods and alternative endpoints is required before species other than unicellular green algae can be routinely incorporated into species battery tests. The studies in the marine algal database had much more consistent methodology; therefore, it was possible to include relative sensitivity and variability as well as practical considerations in the selection of marine tests species. The golden-brown algae (Chrysophyceae) were generally the most sensitive. However, because variability in response was still high, we recommend a species battery for marine algae as well. Four species of golden brown alga, two diatoms (Bacillariophyceae) and two green algae, were chosen based on the four criteria. Macrophytes should be part of preregistration testing because they can be more sensitive than algae and because of their ecological importance. The database showed a great variety of test methods and very few laboratory methods. No species emerged as the most consistently sensitive among either freshwater or estuarine macrophytes. Lemna gibba and Lemna minor are fast growing, easy to culture, and available commercially; they are logical test species for effects of pesticide drift and surface films. However, they are not always very sensitive. Rooted macrophytes belong in a comprehensive test program; however, test methods have to be developed. One criterion not included in this study was ecological importance. We recommend that ecological importance become part of any selection process in order to facilitate extrapolation to the field during hazard assessments.

Application of a fluorometric microplate algal toxicity assay for riverine periphytic algal species

“…Thus, only a few data are available for the pesticide toxicity on riverine periphytic algal species (for example Larras et al, 2012). Moreover, it is well known that the sensitivity to pesticides differs markedly among species (van den Brink et al, 2006;Nagai et al, 2011), and a single specific indicator algal species cannot be representative of the whole algal assemblage (Freemark et al, 1990;Swanson et al, 1991). Therefore, toxicity data for multiple species should be obtained efficiently.…”

“…The effects of pesticides on algae are generally analyzed by standard test methods (OECD, 2006), which require considerable labor for testing multiple species and is not suitable for periphytic species because of algal attachment to the surface of Erlenmeyer flasks (Swanson et al, 1991). Instead, Ishiahara et al (2006) showed the use of a microplate assay in which periphytic algae are attached to the bottom of a microplate.…”

Uptake and Transformation of Pesticide Metabolites by Duckweed (Lemna gibba)

“…Members of the Lemnaceae family are ubiquitous, ecologically important, easily grown, and readily and reliably manipulated. Also, its value as a test species for toxicity assessment has been discussed worldwide, and it has been adopted as a test material in guidelines used for registration of agrochemicals (8). Given the wide distribution and ecological importance of duckweed, it is indispensable for aquatic risk assessment in determining its uptake and metabolic response to typical pesticide metabolites.…”

New Concept for Evaluating Toxicity of Herbicide for Ecological Risk Assessment

“…To improve this situation, a species battery approach needs to be used in laboratory phytotoxicity tests where several taxonomically different algae are exposed to the test substance. Swanson et al (1991) provide a list of possible species. Aquatic macrophytes are used less frequently than algae in the toxicity tests.…”