title: Measuring variability in phytotoxicity testing using crop and wild plant species.
abstract: A series of experiments was conducted to assess the level of variability in phytotoxicity testing and to investigate factors that may explain some of the observed uncertainties and inconsistencies. The work was conducted in greenhouse or growth chamber environments with plants growing individually in pots and harvested 28 d after spraying with two herbicides, glyphosate and atrazine, as formulated products. Between six and 10 doses were used on five or six replicates, necessitating over 4,500 individually growing plants. In the first set of experiments, several ecotypes (originating from different areas of the world) of eight wild plant species were tested. Significant differences in sensitivity to atrazine and glyphosate were found among ecotypes of most species tested. In the second suite of experiments, the reproducibility of results during different seasons (when growing conditions vary) was investigated using three crops and four wild plant species. Results showed that seasonal variability elicited a pronounced discrepancy in response between plants tested at different times of the year. It was found that no consistent effects could be attributed to the biotic or abiotic factors investigated. Several ecotypes of the same species differed in their seed size, percentage germination, or germination requirements, as well as in growth patterns, but these differences could not explain differences in herbicide sensitivity. Likewise, differences in phytotoxicity could not be attributed to factors such as temperature, light intensity, and sunlight duration. The present study supports the inclusion of an uncertainty factor in risk assessments to account for the intrinsic variability in plant sensitivity to herbicides.
authors.affiliation: Science and Technology, Environment Canada, 1125 Colonel By Drive (Raven Road), Carleton University Campus, Ottawa, Ontario, K1A 0H3, Canada.
authors.forename: Céline
authors.initials: C
authors.lastname: Boutin
authors.affiliation: Environment and Biodiversity Science, Fisheries and Oceans Canada, 200 Kent Street (Stn. 12S049), Ottawa, Ontario, K1A 0E6, Canada.
authors.forename: Andrea L
authors.initials: AL
authors.lastname: White
authors.affiliation: Science and Technology, Environment Canada, 1125 Colonel By Drive (Raven Road), Carleton University Campus, Ottawa, Ontario, K1A 0H3, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Carpenter
mesh_terms: D018556:Crops, Agricultural / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D006540:Herbicides / Q000633:toxicity*; D008027:Light; D010944:Plants / Q000187:drug effects*; D018570:Risk Assessment
chemical_list: D006540:Herbicides
references.citation: U.S. Environmental Protection Agency. 1996. Ecological effects test guidelines: Terrestrial plant toxicity-vegetative vigor. EPA 712-C-96-163. U.S. Environmental Protection Agency, Washington, DC.
references.citation: Organization for Economic Co-operation and Development. 2006. Terrestrial Plants, Growth Test 208 and 227. In OECD Guidelines for Testing Chemicals. Paris, France.
references.citation: White AL, Boutin C. 2007. Herbicidal effects on nontarget vegetation: investigating the limitations of current pesticide registration guidelines. Environ Toxicol Chem 26: 2634-2643.
references.citation: Aude E, Tybirk K, Pedersen MB. 2003. Vegetation diversity of conventional and organic hedgerows in Denmark. Agric Ecosyst Environ 99: 135-147.
references.citation: Bleeker W, Schmitz U, Ristow M. 2007. Interspecific hybridisation between alien and native plant species in Germany and its consequences for native biodiversity. Biol Conserv 137: 248-253.
references.citation: Brown RA, Farmer D. 1991. Track-sprayer and glasshouse techniques for terrestrial plant bioassays with pesticides. In Gorsuch JW, Lower WR, Wang W, Lewis MA, eds, Plants for Toxicity Assessment: Second Volume. STP 1115. American Society for Testing and Materials, West Conshohocken, PA, pp 197-208.
references.citation: Cole JFH, Canning L, Brown RA. 1993. Rationale for the choice of species in the regulatory testing of the effects of pesticides on terrestrial non-target plants. Proceedings, Brighton Crop Protection Conference, Weeds, Brighton, UK, November 22-25, pp 151-156.
references.citation: Kjaer C. 1994. Sublethal effects of chlorsulfuron on black bindweed (Polygonum convolvulus L.). Weed Res 34: 453-459.
references.citation: Breeze VG, Marshall EJP, Hart A, Vickery JA, Crocker J, Walters K, Packer J, Kendall D, Fowbert J, Hodkinson D. 1999. Assessing pesticide risks to non-target terrestrial plants. Pesticides Safety Directorate, Commission No. PN0923. Ministry of Agriculture, Fisheries and Food, London, UK.
references.citation: Boutin C, Lee H-B, Peart ET, Batchelor SP, Maguire RJ. 2000. Effects of the sulfonylurea herbicide metsulfuron methyl on growth and reproduction of five wetland and terrestrial plant species. Environ Toxicol Chem 19: 2532-2541.
references.citation: Blackburn LG, Boutin C. 2003. Subtle effects of herbicide use in the context of genetically modified crops: a case study with glyphosate. Ecotoxicology 12: 271-285.
references.citation: Riemens MM, Dueck T, Kempenaar C. 2008. Predicting sublethal effects of herbicides on terrestrial non-crop plant species in the field from greenhouse data. Environ Pollut 155: 141-149.
references.citation: Zhou J, Tao B, Messersmith CG, Nalewaja JD. 2007. Glyphosate efficacy on velvetleaf (Abutilon theophrasti) is affected by stress. Weed Sci 55: 240-244.
references.citation: Environment Canada. 2005. Guidance document on application and interpretation of single-species tests in environmental toxicology. Report EPS 1/RM/46. Methods Development and Application Section, Environmental Technology Centre, Ottawa, ON.
references.citation: Norberg-King TJ. 1993. A linear interpolation method for sublethal toxicity: the inhibition concentration (ICp) approach (version 2.0). Technical Report 03-93. U. S. Environmental Protection Agency, Environmental Research Laboratory, Duluth, MN.
references.citation: Aldenberg T, Slob W. 1993. Confidence limits for hazardous concentrations based on logistically distributed NOEC toxicity data. Ecotoxicol Environ Saf 25: 48-63.
references.citation: van Straalen NM, van Leeuwen CJ. 2002. European history of species sensitivity distribution. In Posthuma L, Suter GW, II, Traas TP, eds, Species Sensitivity Distributions in Ecotoxicology. Lewis, Boca Raton, FL, USA, pp 19-34.
references.citation: Baskin CC, Baskin JM. 1998. Seeds-Ecology Biogeography and Evolution of Dormancy and Germination. Academic, San Diego CA, USA.
references.citation: White AL, Boutin C, Dalton RL, Henkelman B, Carpenter D. 2009. Germination requirements for 29 terrestrial and wetland wild plant species appropriate for phytotoxicity testing. Pest Manag Sci 65: 19-26.
references.citation: Systat 11. 2004. Systat for Windows, Version 11. Evanston, IL, USA.
references.citation: StatSoft. 2005. Statistica Data Analysis Software System, Version 7.1. Tulsa, OK, USA.
references.citation: Boutin C, Freemark KE, Keddy CJ. 1995. Overview and rationale for developing regulatory guidelines for nontarget plant testing with chemical pesticides. Environ Toxicol Chem 14: 1465-1475.
references.citation: Kapustka LA. 1997. Selection of phytotoxicity tests for use in ecological risk assessments. In Wang W, Gorsuch JW, Hughes JS, eds, Plants for Environmental Studies. CRC, New York, NY, USA, pp 516-537.
references.citation: Davy M, Petrie R, Smrchek J, Kuchnicki T, François D. 2001. Proposal to update non-target plant toxicity testing under NAFTA. Scientific Advisory Panel, U.S, Environmental, Protection Agency, Washington, DC.
references.citation: DeGennaro F, Weller SC. 1984. Differential susceptibility of field bindweed (Convolvulus arvensis) biotypes to glyphosate. Weed Sci 32: 472-476.
references.citation: Klingaman TE, Oliver LR. 1996. Existence of ecotypes among populations of entireleaf morningglory (Ipomoea hederacea var. integriuscula). Weed Sci 44: 540-544.
references.citation: Noldin JA, Chandler JM, Ketchersid ML, McCauley GN. 1999. Red rice (Oryza sativa) biology. II. Ecotype sensitivity to herbicides. Weed Technol 13: 19-24.
references.citation: Warwick SI. 1991. The influence of intraspecific variation on the biology and control of agricultural weeds. Proceedings, Brighton Crop Protection Conference, Weeds, Brighton, UK, November 15-18, pp 997-1006.
references.citation: Price SC, Hill JE, Allard RW. 1983. Genetic variability for herbicide reaction in plant populations. Weed Sci 31: 652-657.
references.citation: Gasquez J, Darmency H. 1991. Variability in herbicide response within weed species. Proceedings, Brighton Crop Protection Conference, Weeds, Brighton, UK, November 15-18, pp 1023-1032.
references.citation: Baril A, Whiteside M, Boutin C. 2005. Analysis of a database of pesticide residues on plants for wildlife risk assessment. Environ Toxicol Chem 24: 360-371.
references.citation: Whitworth JW, Muzik TJ. 1967. Differential response of selected clones of bindweed to 2,4-D. Weeds 15: 275-280.
references.citation: Wilkinson RE. 1980. Ecotypic variation of Tamarix pentandra epicuticular wax and possible relationship with herbicide sensitivity. Weed Sci 28: 110-113.
references.citation: Anderson DM, Swanton CJ, Hall JC, Mersey BG. 1993. The influence of temperature and relative humidity on the efficacy of glufosinate ammonium. Weed Res 33: 139-148.
references.citation: Petersen J, Hurle K. 2001. Influence of climatic conditions and plant physiology on glufosinate ammonium efficacy. Weed Res 41: 31-39.
references.citation: Kleijn D, Snoeijing GIJ. 1997. Field boundary vegetation and the effects of agrochemical drift: botanical change caused by low levels of herbicide and fertilizer. J Appl Ecol 34: 1413-1425.
references.citation: Clark J, Ortego LS, Fairbrother A. 2004. Sources of variability in plant toxicity testing. Chemosphere 57: 1599-1612.