The toxicity of herbicides to non‐target aquatic plants and algae: assessment of predictive factors and hazard

Abstract

Widely used herbicides sometimes inadvertently contaminate surface waters. In this study we evaluate the toxicity of herbicides to aquatic plants and algae and relate it to environmental herbicide concentrations and exposure scenarios, herbicide formulation and mode of action. This was done experimentally for ten herbicides, using the aquatic macrophyte Lemna minor L. and the green alga Pseudokirchneriella subcapitata (Korshikov) Hindak, supplemented with a database study comprising algae toxicity data for 146 herbicides. The laboratory study showed that herbicide formulations in general did not enhance herbicide efficacy in the aquatic environment. The Roundup formulation of glyphosate proved to be the only exception, decreasing the EC(50) of the technical product for both L. minor and P. subcapitata approximately fourfold. Comparison of the sensitivity of L. minor and P. subcapitata revealed up to 1000-fold higher sensitivity of L. minor for the herbicides categorized as weak acids (pK(a) < 5), emphasizing the importance of higher plants in hazard assessment. Database analyses showed that no herbicide group, categorized by site of action, was significantly more toxic than another. Synthetic auxins were the exception as they are virtually non-toxic to unicellular algae. There was no strong correlation between toxicity to algae and K(ow) of the herbicides, not even within groups having the same site of action. Evaluating all data, few herbicides were toxic at concentrations below 1 microg l(-1), which is the 99.9th percentile of the herbicide concentrations measured in the Danish surveillance programme. Joint action of several herbicides cannot however be excluded.

Biomedicine in the environment: Cyclotides constitute potent natural toxins in plants and soil bacteria

“…The variation between the controls expressed as the coefficient of variation (CV) of the controls was 8.3% for algae, 9.7% for duckweed, and 48.9% for lettuce. These variations are within the range reported in the literature [4,28,34]. The EC10 and EC50 values are listed in Table 1.…”

“…The effect of cyclotides on duckweed (L. minor) growth was conducted following the procedure described by Cedergreen and Streibig [28]. The concentrations and number of replicates were similar to the algae setup, apart from using 12 rather than eight replicates for the control treatment.…”

Assessment of the potential toxicity of herbicides and their degradation products to nontarget cells using two microorganisms, the bacteria Vibrio fischeri and the ciliate Tetrahymena pyriformis

“…Microalgae and crustaceans were four to five-fold more sensitive to Roundup than bacteria and protozoa. Effects of glyphosate and commercial formulations on plants and algae have been reported in the literature (Sáenz et al, 1997;Ma et al, 2002;Cedergreen and Streibig, 2005;Agritox, 2006;Ma et al, 2006;Pettersson and Ekelund, 2006;Toxnet, 2006). The toxicity of glyphosate has also been studied in a range of organisms including fish (salmon, trout, catfish), aquatic invertebrates (daphnids, midge's larvae) and ciliated protozoa (T. thermophila, Ichthyophthirius multililiis) (Folmar et al, 1979;Servizi et al, 1987;Mann and Bidwell, 1999;Everett and Dickerson, 2003;Agritox, 2006).…”

Effects of Herbicide Glyphosate and Glyphosate-Based Formulations on Aquatic Ecosystems

“…Some works showed that 10 % of reduction (EC 10 ) could be reached between 3 to 16 folds lower concentrations than EC 50 . For instance, 10% growth inhibition in the green algae Scenedesmus subpicatus was observed in treatments with 1.6 mg/L of glyphosate acid (Vedrell et al, 2009 (Cedergreen & Streibig, 2005). Lower differences in toxicity were registered by other authors (e.g.…”

“…Numerous contributions have demonstrated that inert ingredients in glyphosate formulations have several folds higher toxicity on non-target organisms than glyphosate alone (e.g. Folmar et al 1979;Wan et al 1989;Cedergreen & Streibig, 2005; among others). Therefore, glyphosate formulations are chemical mixtures and must be considered as mixtures in toxicity assessments.…”