Category: Environment and Wildlife
Several published scientific reviews and risk analyses conclude that the risk of direct toxic effects to terrestrial wildlife species including small mammals, large mammals and birds which may be exposed both directly and indirectly through consumption of contaminated food or water is minimal. This conclusion is supported more specifically by a simple worst-case example comparing the maximal residues observed in berries from treated forest sites and no-observable effect thresholds in experimental mammals.
PMRA (Pest Management Regulatory Agency). Proposed re-evaluation decision – Glyphosate. PRCD2015-01. 13 April 2015. Available electronically at: email@example.com
Legris J, Couture G. Residues de glyphosate dans le sol forestier suite a des pulverizations terrestres en 1985 et 1986. Gouvernement du Quebec Ministere de l'Energie et des Ressources Direction de la Conservation. 1988:22p.
Legris J, Couture G. Residus de glyphosate dans un ecosysteme forestier suite a des pulverisations aeriennes au Quebec en 1987. Gouvernment du Quebec, Ministere de l'Energie et des Ressources, Direction de la conservation ER90-3085. 1990:35.
As noted in the review by Durkin (2003), terrestrial animals might be exposed to herbicides via direct spray, the ingestion of contaminated food or water, grooming activities or via contact with contaminated vegetation. In the risk assessment conducted by the latter author, all of these potential exposures were considered and compared to levels having no observable effects in experimental animals. Given an application rate equivalent to 2.1 Kg a.e./ha, which closely approximates the average use rate of glyphosate-based herbicides in Canadian forestry, risk quotients calculated for small mammals, large mammals and birds were all below levels of concern (Durkin et al. 2003). Parallel risk quotient analysis conducted by Giesy et al. (2000) and by PMRA (2015) drew the same general conclusion. In such analyses, small mammals are often considered because there is direct relevance to toxicity studies which are often conducted on mice, rats and rabbits. For acute toxicity the no observable effect threshold for small mammals exposed to glyphosate is 175 mg/kg of body weight based on rabbits exposed for a period of 21 days. The threshold level in this case is considered appropriate for risk assessment in large mammals as well (Durkin 2003).
The level of residues observed in berries depends largely upon the rate of herbicide applied, the method of application (e.g. ground based versus aerial) and how long after treatment that samples are taken. Following ground- based applications at a rate of 1.5 Kg a.e./Ha Legris and Couture (1989) observed maximal residues in raspberries of 36.5 ppm at 7 days post-spray, declining to 0.139 ppm by 27 days post treatment. In blueberries, residues were initially 7.90 ppm 1 day post spray and dropped to 2.09 mg/g after 22 days. Similarly Roy et al. (1989) reported maximal residues in raspberry and blueberry of 19.49 and 7.94 ppm respectively on the day glyphosate herbicide treatments were made with backpack sprayers at a rate of 2 kg a.e/ha, with slow decline of residue levels to values approximating 1.22 ppm by 33 days post-spray. Based on several worst-case assumptions, for example that wildlife consume only highly contaminated berries as a food source, that residue levels in the berries are constant for the entire time period which they might be available after the spray season, and that animals feed only in treated sites the toxicological risk from this source can be calculated. For example, using the maximal residue level observed in berries of 36.5 ppm (Legris and Couture 1989), food consumption rates per unit body weight for small mammals and large mammals of 15% (Durkin 2003) and 34% (Welch 1977) respectively, and a typical body mass of 0.02 Kg and 100 Kg for a typical rodent and bear, the calculated ingested dose rates would be 5.48 and 12.4 ppm body weight per day respectively, both values being far below the no observable toxic effects threshold of 175 mg/kg of body weight per day.
Durkin PR. Glyphosate - Human health and ecological risk assessment report. Syracuse Environmental Research Associates Inc, Fayetteville NY 2003.
Giesy JP, Dobson S, Solomon KR. Ecotoxicological risk assessment for Roundup® herbicide. Rev. Environ. Contam.Toxicol. 2000; (167):35-120.
Roy, D.N. et al. 1989. Uptake and persistence of the herbicide glyphosate (Vision) in fruit of wild blueberry and red raspberry. Can. J. For. Res. 19:842-847