Elsevier

Chemosphere

Volume 52, Issue 7, August 2003, Pages 1189-1197
Chemosphere

Aquatic toxicity of glyphosate-based formulations: comparison between different organisms and the effects of environmental factors

https://doi.org/10.1016/S0045-6535(03)00306-0Get rights and content

Abstract

Glyphosate-based herbicides (e.g. Roundup®) are extensively used in the aquatic environment, but there is a paucity of data on the toxicity of the formulated products and the influences by environmental factors. In this study, the acute toxicity of technical-grade glyphosate acid, isopropylamine (IPA) salt of glyphosate, Roundup® and its surfactant polyoxyethylene amine (POEA) to Microtox® bacterium (Vibrio fischeri), microalgae (Selenastrum capricornutum and Skeletonema costatum), protozoa (Tetrahymena pyriformis and Euplotes vannus) and crustaceans (Ceriodaphnia dubia and Acartia tonsa) was examined and the relative toxicity contributions of POEA to Roundup® were calculated. The effects of four environmental factors (temperature, pH, suspended sediment and algal food concentrations) on the acute toxicity of Roundup® to C. dubia were also examined. Generally, the toxicity order of the chemicals was: POEA > Roundup® > glyphosate acid > IPA salt of glyphosate, while the toxicity of glyphosate acid was mainly due to its high acidity. Microtox® bacterium and protozoa had similar sensitivities towards Roundup® toxicity (i.e. IC50 from 23.5 to 29.5 mg AE/l). In contrast, microalgae and crustaceans were 4–5 folds more sensitive to Roundup® toxicity than bacteria and protozoa. Except photosynthetic microalgae, POEA accounted for more than 86% of Roundup® toxicity and the toxicity contribution of POEA was shown to be species-dependent. Increase in pH (6–9) and increase of suspended sediment concentration (0–200 mg/l) significantly increased the toxicity of Roundup® to C. dubia, but there were no significant effects due to temperature change and food addition.

Introduction

Glyphosate (N-Phosphonomethylglycine) is a non-selective and post-emergent herbicide. The major formulation is Roundup® in which glyphosate is formulated as isopropylamine (IPA) salt and a surfactant, polyoxyethylene amine (POEA), is added to enhance the efficacy of the herbicide. Another formulation, Rodeo®, contains the IPA salt of glyphosate without the surfactant and is primarily used for controlling aquatic weeds in some countries (e.g. United States). Owing to their high water solubility and extensive usage in the environment (especially in shallow water systems), the exposure of non-target aquatic organisms to these herbicides is a concern of ecotoxicologists.

Although there has been documentation on the physical, chemical and toxicological properties of glyphosate (Malik et al., 1989; WHO, 1994), the aquatic toxicity data for glyphosate-based formulations are relatively sparse with most previous work focusing on freshwater invertebrates and fishes (Folmar et al., 1979; Wan et al., 1989) and recently on frogs (Mann and Bidwell, 1999; Perkins et al., 2000). Work by Folmar et al. (1979) remained one of the most comprehensive, which compared the acute toxicity of technical-grade glyphosate acid, Roundup®, IPA salt of glyphosate and POEA to several freshwater invertebrates and fishes, and concluded that POEA was mainly responsible for the relatively high toxicity of Roundup®. However, there is no similar study to examine whether POEA also accounts for the toxicity of Roundup® to microorganisms such as bacteria, microalgae and protozoa which were very different from invertebrates and vertebrates (e.g. fishes and amphibians) in terms of morphology, cytogenetics and physiology. Furthermore, the lack of toxicity data of many kinds of pesticides on aquatic bacteria and protozoa was highlighted in a recent review (DeLorenzo et al., 2001), and this is also the case for glyphosate-based herbicides.

Several environmental factors such as pH and temperature have been identified to modify the toxicity of pesticides (Sprague, 1985; Fisher, 1990; Howe et al., 1994). For glyphosate-based formulations, Wan et al. (1989) examined the effects of different dilution waters on the toxicity of Roundup®, while Folmar et al. (1979) investigated the effects of pH and temperature on Roundup® toxicity. Nevertheless, these studies employed different organisms and test conditions and therefore could not easily generalize the individual effects of different factors on Roundup® (and glyphosate) toxicity.

This study was therefore carried out to differentiate the relative toxicity contribution of IPA salt of glyphosate and POEA to Roundup® using different groups of organisms with emphasis on microorganisms to provide new toxicity data of glyphosate on these species, and to evaluate the effects of various environmental factors on modifying the toxicity of Roundup® employing standard 48 h Ceriodaphnia dubia acute toxicity test (USEPA, 1993). Using a single and standard toxicity test allows better comparison between the influences of different environmental factors, rather than using different toxicity tests to address their influences.

Section snippets

Test organisms

Seven organisms which represent four major taxonomic groups (viz. bacteria, algae, protozoa and crustaceans) were chosen, the selection of which was based on their frequent employment in toxicity tests, reported sensitivity to pollutants and wide occurrence in the environment. Except bacteria, all groups consisted of both a freshwater and a marine species. Freeze-dried bacterium (Vibrio fischeri) was purchased from Azur Environmental (Delaware, CA, USA). Algae, Selenastrum capricornutum (UTEX

Experiment I: comparison between different groups of organisms

Glyphosate acid caused the greatest decrease in pH, followed by IPA salt of glyphosate and Roundup® herbicide, while POEA slightly increased the pH of the test medium (Fig. 1). The dissolved oxygen contents of the water in the lethality tests were always greater than 90% of saturation at the beginning and above 70% at the end of the test.

The toxicity of glyphosate acid, Roundup®, IPA salt of glyphosate and POEA to the various test organisms are summarized in Table 2. Generally, Microtox®

Discussion

The sensitivities of aquatic microbes and crustaceans to glyphosate and its formulations were examined, and the effects of several important environmental parameters on the Roundup® toxicity were studied. In contrast to past studies (e.g. Folmar et al., 1979; Mann and Bidwell, 1999; Perkins et al., 2000), we found that the toxicity of Roundup® to aquatic organisms could be attributed to both the IPA salt of glyphosate and POEA, which depended on the group of organisms considered. Algae, which

Acknowledgements

We thank Mr. Raymond Wong and Ben Yeung for their technical assistance and Prof. Keith R. Solomon (University of Guelph, Canada) for his helpful comments and suggestions. The free supplies of Roundup® herbicide and isopropylamine salt of glyphosate solution by Monsanto Chemical Company were gratefully acknowledged. This work was partially supported by a UGC Direct Grant for Research, The Chinese University of Hong Kong.

Martin Tsui graduated from The Chinese University of Hong Kong. His master thesis was on the aquatic toxicology of glyphosate-based formulations.

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  • Cited by (0)

    Martin Tsui graduated from The Chinese University of Hong Kong. His master thesis was on the aquatic toxicology of glyphosate-based formulations.

    L.M. Chu received his Ph.D. from the University of Liverpool, UK. He joined The Chinese University of Hong Kong in 1992 and is currently an Associate Professor at the Department of Biology. He has published 27 peer-reviewed papers in international journals, one book chapter and co-edited one book. His research specializes in restoration ecology, soil and water pollution, and ecotoxicology.

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