Linking Herbicide Dissipation to Soil Ecological Risk along Transmission Rights‐of‐Way in the Yukon Territory, Canada

Abstract

In the Yukon Territory, transmission rights‐of‐way (ROWs) are managed using brushing and mowing techniques alone. When cut, target species such as Populus tremuloides Michx. and Salix spp. grow rapidly shortening maintenance cycles. Long‐term vegetation control may be improved by integrating herbicide application. However, prior to implementation, the dissipation and toxicity of herbicides in northern latitudes needed to be assessed. The dissipation of Garlon XRT (triclopyr) and Arsenal Powerline (imazapyr) in soils was assessed at five ROW locations representative of the main ecoregion types where ROWs occur within the Yukon Territory. Soils from four sites were collected at 1, 30, and 365 d after treatment to determine persistence of herbicides for each of three application methods (backpack spraying, cut stump, and point injection). Increased sampling intervals were added to better determine the dissipation rate of each herbicide in Yukon Territory soils. Soil dissipation data were linked to a series of standardized toxicity tests, including three soil invertebrates (Enchytreaus crypticus, Folsmia candida, and Oppia nitens). Additionally, the dissipation of both herbicides from the target species Salix glauca L. was assessed at one site. Herbicide residues persisted in soils for longer than 365 d after treatment and longer than 30 d after treatment in S. glauca. However, concentrations were below the concentration that would affect 25% of the invertebrate species tested. Weight of evidence and toxic exposure ratios were used to characterize the risks associated with herbicide application in northern latitudes and provided both qualitative and quantitative means to communicate the results to the public. Core Ideas Herbicide use may improve vegetation management along rights‐of‐way in the Yukon. Triclopyr is a good alternative due to a mobile‐phase DT50 of 1 d after treatment. Imazapyr presented no unacceptable risk to the soil invertebrates tested. Risk characterization indicated triclopyr and imazapyr are acceptable in northern latitudes. Triclopyr presents less risk due to fast dissipation and low risk to soil invertebrates.

Oppia nitensC.L. Koch, 1836 (Acari: Oribatida): Current Status of Its Bionomics and Relevance as a Model Invertebrate in Soil Ecotoxicology

“…Similarly, when O. nitens was exposed to the herbicides imazapyr and triclopyr, toxicity could not be determined at concentrations >4000 mg active ingredient kg/dry weight for imazapyr, whereas triclopyr only had an effect at the EC25 level when the concentration was 1500 mg/kg (Jimmo et al 2018).…”

“…All available studies on O. nitens ’ response to pesticides show the mite to be less sensitive to pesticides than other soil invertebrates (de Lima e Silva et al ; Jimmo et al ). In fact, for some neonicotinoid pesticides, O. nitens was less sensitive by several orders of magnitude (de Lima e Silva et al ).…”

“…For example, when O. nitens was exposed to the insecticide chlorantraniliprole (a ryanoid), no effect on survival and reproduction at concentrations >1000 mg/kg were noted (Lavtižar et al ). Similarly, when O. nitens was exposed to the herbicides imazapyr and triclopyr, toxicity could not be determined at concentrations >4000 mg active ingredient kg/dry weight for imazapyr, whereas triclopyr only had an effect at the EC25 level when the concentration was 1500 mg/kg (Jimmo et al ).…”

Soil Chemistry and the One Health Initiative: Introduction to the Special Section

“…Jimmo et al (2018) evaluated the risks associated with the use of two herbicides (triclopyr and imazapyr) for vegetation control in power transmission rights‐of‐way. Soils were sampled 1, 30, and 365 d after spraying at four sites, and, more intensively, after 0.1, 1, 3, 7, 14, 21, 30, and 365 d at a fifth site.…”

“…However, concern still exists that even at these low antibiotic concentrations, there may be chronic health effects for humans and animals, as well as the potential of the development of antibiotic resistance. Jimmo et al (2018) evaluated the risks associated with the use of two herbicides (triclopyr and imazapyr) for vegetation control in power transmission rights-of-way. Soils were sampled 1, 30, and 365 d after spraying at four sites, and, more intensively, after 0.1, 1, 3, 7, 14, 21, 30, and 365 d at a fifth site.…”