Acute toxicity of commonly used forestry herbicide mixtures to Ceriodaphnia dubia and Pimephales promelas

• Published in: Environmental toxicology 2012-12, Vol.27 (12), p.671-684
• Main Authors: Tatum, Vickie L., Borton, Dennis L., Streblow, William R., Louch, Jeffrey, Shepard, James P.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Applied ecology; aquatic toxicity; Biological and medical sciences; Ceriodaphnia; Cladocera - drug effects; Cyprinidae; Ecosystem; Ecotoxicology, biological effects of pollution; fathead minnow; Forestry; Fresh water ecosystems; Fundamental and applied biological sciences. Psychology; General aspects; glyphosate; herbicide mixtures; Herbicides - toxicity; hexazinone; imazapyr; metsulfuron methyl; sulfometuron methyl; Surface-Active Agents - toxicity; Synecology; Toxicity Tests, Acute; triclopyr; Water Pollutants, Chemical - toxicity
• ISSN: 1520-4081; 1522-7278
• DOI: 10.1002/tox.20686

Because many herbicides selectively control specific species or types of vegetation, they are often applied as mixtures to achieve better control over undesirable vegetation. When herbicides are applied in forest ecosystems, streams, ponds, and other bodies of water are typically protected by buffer zones in which no herbicide is applied. However, in some landscapes, small wetlands and streams are difficult to see and avoid, thus the potential acute toxicity of herbicide mixtures to aquatic organisms is of interest, yet it has not been well‐studied. We examined the acute toxicity of 23 different herbicide mixtures to Ceriodaphnia dubia and fathead minnows (Pimephales promelas) at environmentally relevant concentrations, and, where possible, characterized mixture interactions using Marking's Additive Index. Maximum exposure concentrations were equivalent to applying the maximum allowable rate for each component directly to the surface of a 6‐in. deep pond with no dissipation following application. Under the conditions of this study, herbicide formulations containing Accord Concentrate (glyphosate), Arsenal AC (imazapyr), Chopper (imazapyr), Escort (metsulfuron methyl), Oust XP (sulfometuron methyl), and Velpar L (hexazinone) were not associated with appreciable acute toxicity to fathead minnows or C. dubia when used alone or in mixtures with each other and various surfactants and adjuvants. Herbicide mixtures for which Additive Indexes could be calculated exhibited primarily antagonistic or simple additive toxicity. In the few cases where synergistic toxicity was observed, the degree of synergism was slight, never exceeding approximately twice the effect estimated based on additive toxicity. Based on the results of this study, neither acute toxicity nor enhanced acute aquatic toxicity due to synergistic mixture effects appears to be a significant concern for applications of the herbicide mixtures most commonly used in forestry. © 2011 Wiley Periodicals, Inc. Environ Toxicol 2012.