Category: Environment and Wildlife
In forestry scenarios, the risk to most aquatic organisms, including aquatic plants, is strongly mitigated by the use of protective buffer zones which are designed to minimize potential exposure levels. Risk analyses show that aquatic plants and algae are relatively more sensitive to glyphosate herbicides than aquatic animals. Among aquatic animals, fish and larval amphibians (tadpoles) are particularly sensitive to products containing POEA (a surfactant mixture used in some glyphosate based herbicides). Amphibians associated with small, shallow wetlands within targeted spray site are considered to be at relatively great risk. However, several field studies examining the effects of glyphosate and POEA demonstrate no significant effects on amphibians under realistic exposure levels and environmental conditions.
Small, shallow wetlands which are not mapped or easily observed from the air present a special case of potentially higher risk, particularly to amphibians which frequent these habitats. Although laboratory studies clearly demonstrate that fish and amphibian larvae (i.e. tadpoles) are quite sensitive to formulated glyphosate products containing the POEA surfactant, several field studies show no significant effects under realistic exposure scenarios. Some species of algae and aquatic plants are also very sensitive to glyphosate-based herbicides. Field study results support the conclusions drawn by several independent reviews which suggest that the use of glyphosate-based herbicides in accordance with product labels and as typically used in Canadian forest vegetation management do not pose a significant risk to aquatic organisms. This is particularly true given the routine application of buffers specifically designed to protect sensitive aquatic systems.
An extensive number of studies have focused on the potential effects of glyphosate-based herbicides to aquatic organisms including zooplankton, fish and amphibians and these studies have been reviewed by several authors (Giesy et al 2000, Solomon and Thompson 2003, Durkin et al. 2003; Tatum 2004) all of whom conclude that he likelihood of direct acute toxic effects to aquatic organisms are unlikely. Fish and amphibian larvae (tadpoles) are known to be highly sensitive to glyphosate-based herbicide formulations, particularly those containing the polyethoxylated tallow amine (POEA) surfactant when exposed under laboratory conditions (e.g. Folmar et al. 1979; Wan et al. 1989; Howe et al. 2004; Edginton et al. 2004). As part of a watershed level investigation on the effects of a glyphosate-based herbicide applied to a western Canadian coastal forest system (Holtby and Bailey 1989) , temporary stress effects and minor mortality (2.6%) were observed in caged coho salmon fingerlings held in an experimentally over-sprayed tributary and the main stream below the sprayed area. However, no acute mortality, changes in over-winter mortality, growth rate or probability of using the tributary were observed for resident fingerlings. Similarly, several subsequent studies confirm the general sensitivity of amphibian larvae to these herbicide products when exposed under laboratory or mesocososm conditions (e.g. Chen et al. 2004; Relyea et al. 2005; Williams and Semlitsch 2009).In general, the lowest reported concentrations resulting in 50% or greater mortality in amphibian larvae after 96 hrs exposure under lab conditions approximates 0.8 mg a.e./L (Edginton et al. 2004; Relyea and Jones 2099), although Williams and Semlitsch have reported >80% mortality in 1 of 3 amphibian larval species following exposure to the Roundup WeatherMax formulation at an equivalent of 0.6 mg a.e./L. Coincidentally, the 0.8 mg a.e./L value is also considered to be threshold concentration below which all aquatic organisms would be protected irrespective of exposure period (CCME 2012). Given the demonstrated sensitivity of amphibian larvae and the potential for direct overspray or off-target drift inputs to small ephemeral wetlands under typical forest-use scenarios, raised legitimate questions with respect to potential risk to amphibians under typical forest-use scenarios (Thompson et al. 2004; Govindarajulu 2008). To address this issue directly an extensive hierarchical program of research was conducted including laboratory, in-situ mesocosm, whole wetland and operational monitoring. Based on operational monitoring studies of typical aerial spray programs in Ontario (Thompson et al. 2004), the maximum concentration expected in such wetlands would be less than 0.55 mg/L (ppm) 99 times out of 100 (i.e. below the threshold concentration for significant acute effects). No significant differences were observed in mortality of two different amphibian species that were variously exposed in buffered, adjacent and oversprayed wetlands. Several other field studies have confirmed no significant acute effects of formulated glyphosate herbicide products on larval amphibian survival, growth or development even at levels considered to represent a maximum worst case in small wetlands (Wojtaszek et al. 2004; Edge et al. 2014; Edge et al. 2012). Similarly, in situ enclosure studies conducted in naturalized wetlands showed no significant effects on juvenile frogs directly exposed to a formulated glyphosate-based herbicide even following direct exposure at the maximum permissible label rates (Edge et al. 2011; Edge et al. 2013). The differences between laboratory and field study results can be generally explained by sediment sorption and degradation process that are active in natural shallow wetland ecosystems and which limit exposure magnitude and duration to both glyphosate and the POEA surfactant (Wojtasek et al. 2004; Edge et al. 2012; Wang et al. 2005; Rodriguez Gil 2015 Personal communication) as compared to laboratory studies where these factor are either not included or minimized in standardized testing protocols. Overall, results of these field studies confirm that the use of glyphosate-based herbicides in accordance with product labels and as typically employed in Canadian forest vegetation management do not pose a significant risk to amphibians or other aquatic organisms.
Giesy JP, Dobson S, Solomon KR. Ecotoxicological risk assessment for Roundup® herbicide. Rev. Environ. Contam.Toxicol. 2000; (167):35-120.
Solomon KR, Thompson DG. Ecological Risk Assessment for Aqautic Organisms from Over-Water Uses of Glypohsate. Journal of Toxicology and Environmental Health, Part B. 2003;6:289-324.
Durkin PR. Glyphosate - Human health and ecological risk assessment report. Syracuse Environmental Research Associates Inc, Fayetteville NY 2003.
Tatum V. The toxicity of silvicutural herbicides to wildlife - volume two: Glyphosate and Imazapyr. NCASI Technical Bulletin. 2004(886):81.
Folmar LC, Sanders HO, Julin AM. Toxicity of the herbicide glyphosate and several of its formulations to fish and aquatic invertebrates. Archives of Environmental Contamination and Toxicology. 1979;8:269-78.
Wan MT; Watts RG; Moul DJ. 1989. Effects of different dilution water types on the acute toxicity to juvenile pacific salmonids and rainbow trout of glyphosate and its formulated products. Bull Environ Contam Toxicol. 43(3):378-85.
Howe CM, Berrill M, Pauli BD, Helbing CC, Werry K, Veldhoen N. Toxicity of Glyphosate-Based Pesticides to Four North American Frog Species. Environmental Toxicology and Chemistry. 2004;23(8):1928-38.
Edginton AN, Sheridan PM, Stephenson GR, Thompson DG, Boermans HJ. Comparative Effects of pH and Vision® Herbicide on Two Life Stages of Four Anuran Amphibian Species. Environmental Toxicology and Chemistry. 2004; 23(4):815-22.
Holtby, LB, Baillie, SJ. Effects of the herbicide Roundup (Glyphosate) on coho salmon fingerlings in an over-sprayed tributary of Carnation Creek, British Columbia. In: Proceedings of the Carnation Creek Herbicide Workshop. (ed. P.E. Reynolds), pp 273-85. Forest Pest Management Institute, Forestry Canada, Sault Ste. Marie, Ontario. 1989.
Chen CY, Hathaway KM, Folt CL. Multiple Stress Effects of Vision® Herbicide, pH, and Food on Zooplankton and Larval Amphibian Species from Forest Wetlands. Environmental Toxicology and Chemistry. 2004; 23(4):823-31.
Relyea RA, Jones DK. 2009. The toxicity of Roundup original max to 13 species of larval amphibians. Environ Toxicol Chem 28:2004–2009.
CCME (Canadian Council of Ministers of the Environment). Canadian water quality guidelines for the protection of aquatic life: Glyphosate. In: Canadian environmental quality guidelines. Canadian Council of Ministers of the Environment, Winnipeg. 2012.
Thompson DG, Wojtaszek BF, Staznik B, Chartrand DT, Stephenson GR. Chemical and Biomonitoring to Assess Potential Acute Effects of Vision® Herbicide on Native Amphibian Larvae in Forest Wetlands. Environmental Toxicology and Chemistry. 2004; 23(4):843-9.
Govindarajulu, PP. Literature review of impacts of glyphosate herbicide on amphibians: What risks can the silvicultural use of this herbicide pose for amphibians in B.C.?. B.C. Ministry of Environment, Victoria, BC. 2008. Wildlife Report No. R-28.
Wojtaszek BF, Staznik B, Chartrand DT, Stephenson GR, Thompson DG. Effects of Vision® Herbicide on Mortality, Avoidance Response, and Growth of Amphibian Larvae in Two Forest Wetlands. Environmental Toxicology and Chemistry. 2004; 23(4):832-42.
Edge C, Thompson D, Hao C, Houlahan J. The response of amphibian larvae to exposure to a glyphsate-based herbicide (RoundupWeatherMax) and nutrient enrichment in an ecosystem experiment. EcotoxicologyandEnvironmentalSafety. 2014; 109:124-32.
Edge CB, Thompson DG, Hao C, Houlahan JE. A silviculture application of the glyphosate-based herbicide VisionMax™ to wetlands has limited direct effects on amphibian larvae. Environmental Toxicology and Chemistry. 2012:32
Edge CB, Gahl MK, Pauli BD, Thompson DG, Houlahan JE. Exposure of juvenile green frogs (Lithobates clamitans) in littoral enclosures to a glyphosate-based herbicide. Ecotoxicology and Environmental Safety. 2011; 74:1363-9.
Edge CB, Gahl MK, Thompson DG, Houlahan JE. Laboratory and field exposure of two species of juvenile amphibians to a glyphosate-based herbicide and Batrachochytrium dendrobatidis. Science of the Total Environment. 2013; 444:145-52.
Wang N, Besser JM, Buckler DR, Honegger JL, Ingersoll CG, Johnson BT, et al. Influence of sediment on the fate and toxicity of a polyethoxylated tallowamine surfactant system (MON 0818) in aquatic microcosms. Chemosphere. 2005;59:545-51.
Rodriguez-Gil, JL. Dissipation of a commercial mixture of alkylamine ethoxylates in outdoor aquatic micorcosms: optimization of analytical methods and effect of water depth and sediment organic carbon. Personal communication based on draft thesis chapter. June 2015.
Williams BK, Semlitsch RD. Larval Responses of Three Midwestern Anurans to Chronic, Low-Dose Exposures of Four Herbicides. Archives of Environmental Contamination and Toxicology. 2009:9.