Effects of a Pulsed Treatment With the Herbicide Afalon (Active Ingredient Linuron) on Macrophyte-Dominated Mesocosms. Ii. Structural Responses

Abstract

Outdoor mesocosms (experimental drainage ditches) were treated repeatedly with linuron at nominal concentrations of 0, 0.5, 5, 15, and 50 g/L. After each of three treatments (with 4-week intervals), the systems were kept static for 1 week. Subsequently, they were flushed with nonpolluted surface water with a residence time of 5 d until the next treatment. Species composition and abundance of macrophytes, periphyton, phytoplankton, zooplankton, and macroinvertebrates were examined at prefixed time intervals. During the treatment periods, significant decreases in oxygen concentration and pH were observed, whereas the systems recovered during the flushing periods. The effects of the pulsed treatments on the structural endpoints (biota) were rarely significant and consistently were difficult to interpret. We conclude that under these experimental conditions, pulsed treatment with linuron causes only minor and negligible effects on the abundance of organisms in mesocosms, even when maximum permissible concentrations are exceeded by about 80 times. Risk assessment based on the more sensitive physiologic and functional endpoints suggested that the safety factor of 0.1 times the acute EC50 of the most sensitive standard alga (Scenedesmus acutus), as adopted in the Uniform Principles of the European Union, is sufficient to protect the community of the mesocosms in an exposure regime that was realistic for Dutch drainage ditches, using a photosynthesis inhibitor as the benchmark compound. Keywords-MesocosmsEcosystem structure Linuron Risk assessment Effect of linuron on ecosystem structure

An assessment of direct and indirect effects of two herbicides on aquatic communities

“…decreased at various sampling time points. [43]. have been reported to be far greater than the concentrations used in the present study (48-h EC50 D. magna ¼ 8.6 mg/L diuron [40]).…”

Higher‐tier laboratory methods for assessing the aquatic toxicity of pesticides

“…A number of approaches have been used to address concerns arising from the preliminary assessments, including the use of pond mesocosms,2 artificial streams,3, 4 field monitoring studies3 and experimental ditches 5. These approaches have been applied to pesticides and surfactants, and have a number of advantages over single‐species investigations, including the ability to assess: (1) endpoints at higher levels of biological organisation, (2) species interactions and (3) indirect effects.…”

Effects of a pulsed treatment with the herbicide afalon (active ingredient linuron) on macrophyte-dominated mesocosms. I. Responses of ecosystem metabolism

“…However, the plant materials might, have changed in such a way that the same photosynthetic efficiency yielded a higher production. Indications exist that the chlorophyll‐ a content of Elodea is higher after linuron incubation [14]. This could mean that a higher production is achieved with the same photosynthetic efficiency.…”

“…This article is the first of two dealing with the impact of a repeated application of linuron at the ecosystem level. The present paper reports on the effect of the herbicide on the ecosystem metabolism, whereas the second paper deals with the effect on the structure [14]. The fate of linuron [15], and the herbicide's effect on the photosynthetic efficiency of isolated parts of the ecosystem (macrophyte shoots, periphyton, and phytoplankton) will be reported elsewhere (J. Snel, personal communication).…”