Methods for assessing the toxicity of herbicides to submersed aquatic plants

Abstract

A new test design for the non-axenic submergent aquatic macrophytes Elodea canadensis Michx. and Myriophyllum spicatum L. has been developed for potential use in herbicide toxicity testing. For the non-axenic cultures, the best growth conditions were observed in the Elendt-M4 medium in which no growth of algae or bacteria was observed. Cuttings were placed in beakers containing only the artificial M4 medium or were planted in small beakers containing OECD (Organisation for Economic Cooperation and Development) sediment (5% peat, 75% sand, 20% kaolinite), which were then placed in larger vessels with the M4 medium. The plants were observed for main and secondary shoot length, biomass and root formation within 2-3 weeks of planting. Growth rates were calculated for total plant length and biomass. The variance between the replicates was low throughout the experiment [coefficient of variation (CV) < 26% for total plant length, and between 16 and 40% for biomass]. Relative growth rates based on total plant length were determined as 0.028 and 0.050 per day for M. spicatum in the systems containing M4 medium only and medium plus sediment respectively. Similar results were observed for E. canadensis, with relative growth rates of 0.26 and 0.073 per day in the two test systems. The root-shoot ratio at harvest was greater by a factor of 2-3 for E. canadensis in the M4 medium than in the system containing sediment. However, comparable ratios were observed for M. spicatum in the two test systems. Both growth in total plant length and growth in biomass of the two species have potential as measures of toxicity.

Comparing growth development of Myriophyllum spp. in laboratory and field experiments for ecotoxicological testing

“…Non-axenic cultures of M. spicatum were supplied as 10 to 15 cm long cuttings by the company Van der Valk Knauer et al (2006). The outdoor mesocosm experiment (experiment 6) was performed at the mesocosm test site of Syngenta Crop Protection in Stein, Switzerland.…”

“…For the determination of phytotoxic effects in pure bulk sediments, a new sediment contact test with M. aquaticum was developed by Feiler et al (2004). Various endpoints have been discussed for assessing toxic effects to freshwater plants, such as chlorophyll fluorescence, biomass and length of shoots and roots (Getsinger et al 1982;Hanson et al 2001;Feiler et al 2004;Knauer et al 2006;Arts et al 2007;Küster et al 2007).…”

Variability in Nontarget Terrestrial Plant Studies Should Inform Endpoint Selection

“…However, it is important that the selected endpoint is statistically reliable (Green 2015(Green , 2016. Previous evaluations of variability and statistical detectability in toxicity tests have been conducted for aquatic plant species (Brain et al 2004(Brain et al , 2005Hanson et al 2003;Sanderson et al 2009;Knauer et al 2006) and for mesocosms (Kraufvelin 1998) but have not been explored to such a degree for terrestrial plants. Previous evaluations of variability and statistical detectability in toxicity tests have been conducted for aquatic plant species (Brain et al 2004(Brain et al , 2005Hanson et al 2003;Sanderson et al 2009;Knauer et al 2006) and for mesocosms (Kraufvelin 1998) but have not been explored to such a degree for terrestrial plants.…”

Essai n° 239 : Essai de Toxicité sur Myriophyllum Spicatum dans un Système Eau-Sédiment

“…Selon un document d'orientation récemment publié à l'issue d'un atelier de la Society of Environmental Toxicology and Chemistry (SETAC) sur l'évaluation des risques liés aux pesticides pour les macrophytes aquatiques (Aquatic Macrophyte Risk Assessment for Pesticides, AMRAP), il est parfois nécessaire de disposer de données concernant les effets sur une espèce de macrophyte enracinée d'un produit chimique d'essai dont on sait que son mode d'action n'affecte pas les espèces Lemna et les algues, ou dont le coefficient de partage dans le sédiment laisse craindre une exposition par les racines (3). D'après les connaissances actuelles et l'expérience acquise à ce jour, ce sont les végétaux appartenant au genre des Myriophylles qui ont été choisis comme spécimens privilégiés lorsque des données supplémentaires sur une espèce dicotylédone immergée et enracinée sont requises (4) (5) (6). Cet essai ne supplante pas les autres essais de toxicité aquatique, mais doit les compléter de manière à permettre une évaluation plus complète des dangers et des risques pour la flore aquatique.…”