Céline Boutin

Aquatic phyto-toxicity of 23 pesticides applied at expected environmental concentrations

Abstract Environment Canada uses an Expected Environmental Concentration (EEC) in evaluating the hazard of pesticides to nontarget aquatic organisms. This concentration is calculated by assuming an overspray of a 15 cm deep waterbody at the label application rate. The EEC of pesticides is then related to the EC50 (concentration causing a 50% reduction in a chosen toxicity endpoint) for a given aquatic test organism. At present, the use of an uncertainty factor is suggested in the literature if only a few species are tested because of important interspecific differences in pesticide sensitivity. The phytotoxicity of the EEC of 23 different pesticides to ten algae (24 h inhibition of 14C uptake) and one vascular plant (7-day growth inhibition) was determined in an effort to examine the question of interspecific sensitivity and its relation to the development of pesticide registration guidelines. Chemicals included five triazine herbicides (atrazine, cyanazine, hexazinone, metribuzin, and simazine), four sulfonylurea herbicides (chlorsulfuron, metsulfuron-methyl, ethametsulfuron-methyl, triasulfuron), two phenoxyalkane herbicides (2,4-D and MCPA), two pyridine herbicides (picloram and triclopyr), a substituted urea, an amine derivative, and an imidazolinone herbicide (tebuthiuron, glyphosate and imazethapyr, respectively), a bipyridylium (diquat), a hydroxybenxonitrile (bromoxynil), an aldehyde (acrolein) and an acetanilide (metolachlor) herbicide, as well as two carbamate insecticides (carbofuran and carbaryl) and a triazole derivative fungicide (propiconazole). Test organisms were selected based on ecological relevance and present use in test protocols. Organisms included green algae (Scenedesmus quadricauda and Selenastrum capricornutum), diatoms (Nitzschia sp. and Cyclotella meneghiana), cyanobacteria (Microcystis aeruginosa, Oscillatoria sp., Pseudoanabaena sp., Anabaena inaequalis and Aphanizomenon flos-aquae) and a floating vascular plant, duckweed (Lemna minor). The five triazine herbicides, acrolein and diquat inhibited the carbon uptake of all algae, diatoms and cyanobacteria by more than 50%. Two other pesticides, carbaryl and tebuthiuron, caused more than 50% inhibition in 90% of the algae tested. Nine of the 23 pesticides, five of which were triazine herbicides, were therefore highly phytotoxic to algae. Twelve pesticides inhibited growth of duckweed by more than 50%. Once again, all five of the triazine herbicides were among this group, as well as three sulfonylurea herbicides and acrolein, diquat, metolachlor and tebuthiuron. Duckweed was the most sensitive organism tested, being equally affected by all pesticides causing algal phytotoxicity (with the exception of carbaryl), as well as being acutely affected by sulfonylurea herbicides. Green algae were least sensitive to diquat; diatoms and one cyanobacterium were the only organisms that showed sensitivity to glyphosate. Through testing the phytotoxicity of a variety of agricultural pesticides to a wide range of algal taxa, it is evident that there are considerable differences in sensitivity among species and that the use of an uncertainty factor is necessary to provide an acceptable margin of safety in evaluating the hazard presented by these chemicals to the aquatic environment.

Impacts of agricultural herbicide use on terrestrial wildlife in temperate landscapes: A review with special reference to North America

Abstract The existing literature was examined to assess the extent to which wildlife (plants, soil organisms, above-ground insects/arthropods, mammals, birds) living in terrestrial habitats has been affected by use of agricultural herbicides in temperate landscapes. Although North America was of special interest for regulatory reasons, the review was extended to western Europe because the most extensive and intensive work has been done there. The half-life of herbicides in the environment ranges from less than 1 month to more than 1 year. Wildlife within fields is most likely to be exposed to herbicides, particularly when fields are planted with crops (e.g. corn, soybean, wheat, cotton) which are routinely sprayed. Wildlife is also likely to be exposed in non-crop habitats adjoining croplands, primarily from direct overspray (especially during aerial application), and drift during and/or volatilisation after application. The most conclusive scientific evidence for direct effects of herbicides on arable weeds, and associated indirect effects on insects and birds exists in the United Kingdom. Evidence for similar effects in North America is primarily circumstantial at present. Little work has been done anywhere on impacts of herbicides on plants and their associated fauna in non-crop habitats adjoining treated fields. Chemical farming (in particular, the use of herbicides) has dramatically altered the habitat pattern of temperate landscapes in North America and western Europe. Strong evidence exists for adverse effects of changes in habitat pattern on beneficial insects and arthropods in the United Kingdom, and on birds in North America and western Europe. Toxicity testing guidelines for non-target plant protection need to be developed and enforced to support pesticide registration. In addition, research is needed to include more ecologically relevant plant species in laboratory tests, to develop multi-species tests (particularly in the field), to improve methods for risk assessment, and to develop options for mitigating risks. Large scale, long-term trans-disciplinary research of different farming systems is needed, particularly in North America, to integrate and better evaluate ecological, agronomic, and socio-economic costs and benefits of agricultural herbicide use in temperate landscapes.

Intensity of agricultural practices and effects on adjacent habitats

In intensive agricultural areas small woodlots and woody hedgerows constitute the only remnant of natural forested habitats. Because they are reduced in size and are surrounded by farmlands, remnant habitats may be impacted by several abiotic factors. The conservation value of these habitats, however, cannot be fully ascertained while plant species richness and composition remain unknown. We describe the vegetation composition of woodlot edges and hedgerows associated with agricultural fields of different farming intensities. We inventoried thirteen woodlot edges and hedgerows in each of three types of farming systems characterized mainly by different frequency of tillage and by different levels of herbicide and fertilizer use. The number and percentage cover of species present did not differ greatly between farming regimes whereas the species composition varied considerably. In habitats adjacent to intensively farmed fields, we found more short-lived grassy-type plants that were largely of introduced ori...

Toxicity of hexazinone and diquat to green algae, diatoms, cyanobacteria and duckweed

Abstract Hexazinone and diquat are two broad-spectrum contact herbicides used in a variety of crop and non-crop applications. Both pesticides are highly water soluble and persistent in the aquatic system. Hexazinone is mobile in soil and, thus, the potential for leaching into ground water and for overland runoff into surface water is high; diquat, however, is rapidly bound by soil and sediment to a biologically inactive form, at least temporarily. Toxicity to green algae (two species), diatoms (two species) and cyanobacteria (five species) was determined using inhibition of 14 C uptake. Toxicity to the floating vascular plant, duckweed, was tested by measuring seven-day growth inhibition. Test organisms exhibited large differences in sensitivity to both herbicides. The green algae, diatoms, and duckweed (all eukaryotes) were more sensitive to hexazinone than were cyanobacteria (prokaryotes). Mean concentrations at which 50% inhibition occurred in these groups were 0.01 (green algae), 0.05 (diatoms), 0.07 (duckweed), and 0.6 (cyanobacteria) mg hexazinone per litre, respectively. In contrast, green algae were comparatively tolerant of diquat (EC 50 values approximately 0.6 mg l −1 ), while the cyanobacteria and diatoms were much more sensitive (mean EC 50 values of 0.074 and 0.079 mg diquat per litre). Duckweed showed the greatest sensitivity to diquat, with 50% inhibition of growth occurring at 0.004 mg l −1 . That some non-target aquatic plants are susceptible to diquat toxicity at less than 0.01 mg l −1 is significant, as most methods of diquat analysis have minimum detection limits of 0.01 to 0.05 mg l −1 . Therefore, algae and vascular aquatic plants may suffer phytotoxic effects in a contaminated water body even when diquat is undetectable chemically. Differential sensitivity to herbicide contaminants among taxonomic groups of plants may have ecological consequences. Cyanobacteria may produce neuro- and hepato-toxins and constitute a poor food resource for higher trophic levels relative to the other organisms tested. Contamination of surface water with hexazinone may degrade water quality for wildlife, both by causing food reduction and habitat loss through inhibition of green algae, diatoms and macrophytes, and by allowing the proliferation of cyanobacteria. Varying responses among the different test algae to the two herbicides under study indicated that a wide taxonomic range of test species is necessary in evaluating the impacts of contaminants in aquatic systems.

Plant diversity in three types of hedgerows adjacent to cropfields

The farming landscape of eastern Canada is dotted with three main types of hedgerows: (1) natural woody, (2) planted woody and (3) herbaceous. The objective of this study was to compare the value of these habitats as a repository of plant biodiversity in agricultural areas of southern Quebec. The overall plant diversity was higher in natural hedgerows and they contained more plant species of conservation values than other hedgerow types. Plant species richness per quadrat was, however, higher in planted woody hedgerows, and together with the species composition, lead to the conclusion that planted hedgerows in their entirety consisted of an ecotone type of vegetation such as is found in field edges which usually support high plant diversity and productivity but where transient plant species predominate. Consequently, this study indicated that natural hedgerows fare better than planted hedgerows in terms of diversity of plants of conservation interest. In spite of that, planted woody hedgerows contained plant (and bird) species of some interest and should be favoured over more desolate herbaceous hedgerows. In areas where hedgerows were removed and are not re-establishing naturally, a mixture of deciduous trees and conifers should be encouraged in further windbreak planting programs so as to conciliate both the conservation and agronomic objectives. Furthermore, management practices should optimise the growth of establishing plants of conservation values.

Population trends in selected species of farmland birds in relation to recent developments in agriculture in the St. Lawrence Valley

Abstract Changes in the populations of 28 species of birds typical of farmland habitats were assessed using data from seven Breeding Bird Survey (BBS) routes surveyed in southern Quebec over the last 25 years. Aerial photographs taken in the 1960s and 1980s covering 82 stops along these routes were interpreted to evaluate changes in the rural landscape. Based on the crops grown at these stops in 1992, four types of agricultural landscapes were identified: cash crops, forage crops and pastureland, crops and livestock raising, and heterogeneous landscape. An intensive bird census of these stops in June 1992 showed that species richness and abundance are greater at stops with a heterogeneous landscape than at those characterized mainly by cash crops. Cash crops (corn, wheat, soybean) now cover more surface area than in the 1960s, whereas numerous dairy farms have disappeared over the past 25 years because of abandonment, urbanization and industrialization. These changes in the crops grown in the most productive agricultural regions of Quebec appear to be responsible for fluctuations in populations of a number of farmland species in the St. Lawrence Lowland. Many species associated with dairy farming, such as the Savannah Sparrow, Bobolink, Brown-headed Cowbird and Eastern Meadowlark, show decreasing population abundance, while other species such as the Ring-billed Gull and Rock Dove appear to be benefiting from the introduction of intensive agriculture.

Subtle Effects of Herbicide Use in the Context of Genetically Modified Crops: A Case Study with Glyphosate (Roundup®)

Research on the effects of glyphosate and seed germination spans 30 years. Despite several studies reporting detrimental effects of the herbicide on seedling germination and growth, glyphosate is still being registered for use as a weed killer and preharvest desiccant. Its nonselective nature and low chance of species developing resistance has lead to the development of genetically modified crops tolerant to the herbicide which also raises concerns about increased reliance on herbicide use, and subtle ecological impact.This paper presents the result of a literature review on past studies mostly, on crop species, and the results of a new experiment performed with emphasis on noncrop species. The new experimental part attempted to determine whether glyphosate (Roundup®) would have an effect on the germination and growth of the F1 generation of seeds produced by plants sprayed with the herbicide. It was designed to mirror spray drift which might affect noncrop plants in nontarget drift zones. Of the 11 species tested using treatments of 0% (control), 1%, 10% or 100% of a 890 g a.i./ha label rate solution sprayed near seed maturity, seven showed a significant effect of the glyphosate treatment on germination and/or growth characteristics.Results of this experiment together with several previous studies reviewed in this paper suggest that there are significant effects to keep in mind when using herbicides such as glyphosate as severe ecological changes could occur.

Farmland birds in southern Ontario: field use, activity patterns and vulnerability to pesticide use

Abstract The use of cropfields by birds is largely unknown in southern Canada and consequently the risk incurred by pesticide use on bird populations cannot be adequately characterised. The activity patterns and relative interior to edge use of bird species were examined for four crops in southern Ontario to assess the susceptibility of different species to pesticide use. Altogether 138 species were identified in the four crops over the 2 year period but only 25 species were recorded during 50% of visits in at least 1 month: 14 in corn (Zea mays L.), 16 in soybean (Glycine max L. Merr.), 14 in apple (Malus spp.) orchards and eight in vineyards (Vitis spp.). Territorial behaviour was an important activity for several species from May through July in the four crops. Nesting was confirmed in May, June and July for most species, with the exception of American Goldfinch Carduelis tristis, Chipping Sparrow Spizella passerina and Cedar Waxwing Bombycilla cedrorum which nested in August/September. Foraging was the most important activity for most species in all months (7/10 species in May, 6/8 species in June, 4/8 species in July, 5/8 August/September). Few fledgling young were observed. Most species used field edges consistently more often than expected in corn and soybean fields, according to the edge/interior ratio, Yellow Warbler Dendroica petechia being the exception. In apple orchards, relatively few species differentiated between edge and interior. Based on their frequency of occurrence (>50%), behaviour and temporal coincidence with pesticide applications, 13 species were considered most at risk: Killdeer Charadrius vociferus, Horned Lark Eremophila alpestris, American Crow Corvus brachyrhynchos, American Robin Turdus migratorius, European Starling Sturnus vulgaris, Chipping Sparrow, Vesper Sparrow Pooecetes gramineus, Savannah Sparrow Passerculus sandwichensis, Song Sparrow Melospiza melodia, Red-winged Blackbird Agelaius phoeniceus, Common Grackle Quiscalus quiscala, Brown-headed Cowbird Molothrus ater and Barn Swallow Hirundo rustica. The latter species, because of its foraging habit, is less likely to be exposed to pesticides. This study was important to identify focal species that can be used for detailed investigations on exposure to pesticides.

Pattern of sensitivity of plant species to various herbicides - an analysis with two databases.

Two extensive databases were used to examine the pattern of species sensitivities to pesticides. The first database consisted of industry-sponsored data collated over several years by the Canadian regulatory authority (data on weed efficacy and crop margin of safety). The second dataset consisted of data submitted to the United States Environmental Protection Agency (U.S. EPA). On the whole we found that crop species were not consistently more, or less, sensitive to the herbicide tested than non-crop species. Within the Poaceae family (grasses), however, non-crop species exhibited higher sensitivity in 15 cases (out of 23), and only in five cases were crops more sensitive. The range of species sensitivity increases with an augmentation of numbers of species tested, suggesting that the number of species tested in current guidelines is insufficient. Principal Component Analyses showed that only two groups of species could be separated; in both databases, grass and broad-leaved species formed two distinct groups. Correlations between species demonstrated a relationship when comparing within genera or within families. The distribution-based method used with the Canadian database ascertained further the importance of testing more or other species than those recommended in the U.S. EPA guidelines. We concluded that, given the limitations of the current databases, further analyses could not be carried out. We suggest that an improved database on phytotoxicity is a prerequisite to refine the risk assessment of pesticide effects of non-target plants.

Nontarget-plant risk assessment for pesticide registration

The approach developed by Environment Canada to assess risk to aquatic and terrestrial plants in nontarget habitats potentially exposed to pesticides evaluated for registration is described. An anonymous sample of pesticide submissions is used to illustrate the approach and to examine its merits and limitations in relation to test species, response variability, testing protocols, ecological relevance, and comparability with other regulatory agencies. Future directions are identified, particularly in relation to impending nontarget-plant testing guidelines for pesticide registration in Canada. This approach incorporates some of the latest research and developments in the field of risk assessment for plants. The novelty of this approach also lies in the use of the plant screening data routinely generated by chemical pesticide companies, which is intended to provide a maximum amount of information to evaluators at minimal increment cost to registrants. The proposed approach can serve as a basis for guideline development and modernization for other jurisdictions.