Auxin Herbicides and Pesticide Mixtures in Groundwater of a Canadian Prairie Province
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Published September 6, 2018 Journal of Environmental Quality TECHNICAL REPORTS GROUNDWATER QUALITY Auxin Herbicides and Pesticide Mixtures in Groundwater of a Canadian Prairie Province Sirajum Munira, Annemieke Farenhorst, Kamala Sapkota, Denise Nilsson, and Claudia Sheedy* bout 83% of Canada’s cropland is located in the prairies Abstract spanning the provinces of Alberta, Saskatchewan, and Groundwater samples were collected from piezometers and water Manitoba (Statistics Canada, 2016). Auxin herbicides are table wells in both dryland and irrigated agricultural regions of Awidely used in Canadian Prairie agriculture to control broadleaf Alberta, Canada, to examine the occurrence of pesticide mixtures. weeds in cereal crops and have been the focus of studies that previ- Fourteen current-use pesticides and two historical compounds were detected over a 3-yr sampling period. Pesticide mixtures ously examined the occurrence of pesticides in Canadian Prairie were detected in ?3% of the groundwater samples, and the groundwater (Miller et al., 1995a, 1995b; Hill et al., 1996). The frequency of detection increased from spring (1.5%) to summer auxin herbicides (2,4-dichlorophenoxyacetic acid [2,4-D], bro- (3.8%) and fall (4.8%). Pesticide mixtures always consisted of at moxynil, dicamba, diclofop, 2-methyl-4-chlorophenoxyacetic acid least one of two auxin herbicides: 2,4-dichlorophenoxyacetic [MCPA], and mecoprop) examined in the latter studies were all acid (2,4-D) or 2-methyl-4-chlorophenoxyacetic acid (MCPA). 19% of all samples contained a single pesticide, with auxin herbicides detected, with bromoxynil sometimes present at levels exceeding 2,4-D (7.3%), MCPA (4.4%), and clopyralid (3.9%) being most its guideline for Canadian Drinking Water Quality (Miller et al., prevalent. We detected 2,4-D predominantly in the fall (72% 1995a, 1995b). When the source of drinking water consisted of of 2,4-D detections) and less in spring and summer (28%). We surface water reservoirs integrated in Canadian Prairie agricultural detected MCPA mostly in summer (85% of MCPA detections) and landscapes, auxin herbicides were detected in both the source and less in spring and fall (15%). Clopyralid was more evenly detected across spring (30%), summer (25%), and fall (45%). Since the treated drinking water (Donald et al., 2007). auxin herbicides above are typically applied in summer, results In Alberta, >14 million kg of pesticide active ingredients suggest that each herbicide may have different mobility and are annually applied on ?10 million ha of cropland, with her- persistence characteristics in prairie soils. Guidelines for Canadian bicides accounting for 82% of such applications (AEP, 2015). Drinking Water Quality have been set for a range of individual About 90% of Alberta’s rural population relies on groundwa- pesticides, but not for pesticide mixtures. If Canada is to establish such guidelines, this study demonstrates that auxin herbicides ter for their potable water supply (AWA, 2015). Guidelines for should be prioritized. In addition, only 7 of the 16 compounds Canadian Drinking Water Quality have been set for a range of detected in this study have established maximum acceptable individual pesticides, but not for pesticide mixtures. However, concentrations (MACs), excluding clopyralid, which was detected it is well known that groundwater samples can contain more in all three sampling years. than one pesticide: a study conducted across the United States (?5000 samples collected) revealed that >50% of sampled shal- Core Ideas low groundwater wells contained pesticide mixtures (Gilliom, 2007). In Portugal, groundwater collected from 18 wells in an • Sixteen pesticides were detected in groundwater, most frequently agricultural region showed that samples collected in spring were auxin herbicides. more likely to contain pesticides mixtures, whereas samples col- • Detection of pesticide mixtures increased from spring (1.5%) to fall (4.8%). lected in summer and fall mostly contained an individual pesti- • Samples with pesticide mixtures always contained at least one cide (Silva et al., 2012). auxin herbicide. While the European Drinking Water Directive is using a cau- • In establishing water quality guidelines for mixtures, Canada tionary approach and has set the maximum total concentration must prioritize auxins. of pesticides in water at 500 ng L−1, the Canadian Drinking Water Quality guidelines are based on the potential for an individual pesticide to cause adverse health effects. Should Canada estab- lish guidelines for pesticide mixtures, it is important to know Copyright © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. S. Munira, A. Farenhorst, and K. Sapkota, Dep. of Soil Science, Faculty of J. Environ. Qual. 47:1462–1467 (2018) Agricultural & Food Sciences, Univ. of Manitoba, 362 Ellis Building, Winnipeg, MB, doi:10.2134/jeq2018.05.0202 Canada, R3T 2N2; D. Nilsson and C. Sheedy, Agriculture and Agri-Food Canada, This is an open access article distributed under the terms of the CC BY-NC-ND Lethbridge Research and Development Centre, 5403 1st Ave. South, Lethbridge, license (http://creativecommons.org/licenses/by-nc-nd/4.0/). AB, Canada, T1J 4B1. Assigned to Associate Editor Qingli Ma. Supplemental material is available online for this article. Received 23 May 2018. Abbreviations: b-HCH, b-hexachlorocyclohexane; MAC, maximum Accepted 7 Aug. 2018. acceptable concentration; MCPA, 2-methyl-4-chlorophenoxyacetic acid; 2,4-D, *Corresponding author ([email protected]). 2,4-dichlorophenoxyacetic acid. 1462 the types of pesticide mixtures present in Canadian groundwa- and 2010 and situated in an area with fine- to coarse-textured ter. Current use pesticides such as auxins and chloroacetamide soils. Twenty-one wells and 11 piezometers were sampled in this herbicides have reported half-lives (days to 50% degradation) of region ranging in depth from 4.8 to 19.5 m. The mean depth of 0.5 to 5 yr in groundwater (Cavalier et al., 1991). Some histori- groundwater wells was 7 ± 0.8 m, and that of piezometers was cal pesticides that were used in agricultural production decades 15 ± 3.5 m. Groundwater samples were collected in the spring, ago have been detected in drinking water wells long after these summer, and fall periods of 2013, 2014, and 2015, except that pesticides were banned (Burow et al., 2008). In this study, we central Alberta was not sampled in spring 2013. The spring sam- screened groundwater samples from Alberta for 42 active ingre- pling period from late April to early June corresponded to the dients of pesticide products currently registered for agricultural period when preplant and preemergent herbicides are typically use in Canada, and for 63 compounds that were active ingredi- applied in Alberta. The summer sampling in August reflected ents, metabolites, or byproducts of pesticide products no longer the timing of preharvest applications in Alberta, with other in- registered or currently not registered (Supplemental Table S1). crop applications having been completed in June and July. The The objective of the study was to examine the detection fre- fall sampling period from late September to late October corre- quency, types, and concentrations of pesticide mixtures occur- sponded to the preharvest period to initial soil freeze up during ring in samples collected from piezometers and wells in both which preharvest and burn-off herbicides are applied. dryland and irrigated agricultural regions of Alberta. Sample Analysis Materials and Methods The analytical suite included 42 active ingredients that are in Site Locations and Sampling Times pesticide products registered for agricultural use in Canada and 63 other compounds that were active ingredients, metabolites, A total of 436 groundwater samples were collected from or byproducts in pesticide products no longer registered or cur- piezometers and wells in two representative agricultural regions rently not registered (Supplemental Table S1). These compounds of Alberta. The region in southern Alberta is the Battersea drain- were herbicides (44.8%), insecticides (42.9%), fungicides (7.6%), age basin near Lethbridge (49°52¢ N, 112°46¢ W; population and others such as nematicides and algicides (4.7%) and included ? 93,000), located in the moist mixed grassland ecoregion and all pesticides previously detected in surface drinking water and dominated by dark brown Chernozemic soils. The southern groundwater in Alberta such as 2,4-D, MCPA, bromoxynil, clopy- Alberta region has a mean (1981–2010) annual precipitation of ralid, and dicamba (Hill et al., 1996; Donald et al., 2007). 380 mm and a mean annual temperature of 5.9 ± 1.1°C (ECCC, Water samples were analyzed within 3 (minimum) to 7 d 2018). This region includes? 6% of the crop land in Alberta that (maximum), including collection in the field, transportation to receives irrigation ranging from 300 to 450 mm yr−1 and contrib- the laboratory, extraction, and analysis. Water samples were col- uting to >19% of the net worth of primary agricultural produc- lected in an amber glass bottle (1 L) using a polyethylene bailing tion in the province (AAF, 2015a). The region in central Alberta tube and transported to the laboratory in ice-packed coolers for near Red Deer (52°28¢ N, 113°44¢ W; population ? 100,000) storage in the fridge (4°C) prior to extractions. Water samples is located in the aspen parkland ecoregion, dominated by black were filtered through glass wool, acidified with concentrated Chernozemic soils and dryland farming (no irrigation). The H SO (pH 2), and extracted by liquid–liquid partitioning using region has a mean (1981–2010) annual precipitation of 486 mm 2 4 CH Cl . After phase separation, CH Cl extracts were dried and a mean annual temperature of 3.7 ± 1.1°C (ECCC, 2018). 2 2 2 2 with acidified Na SO , methylated using CH Cl , and added to Cereal, oilseed, and forage crops dominate crop production in 2 4 2 2 hexane (40 mL). Nitrogen gas was used to remove the remain- the two regions, with potatoes (Solanum tuberosum L.) also ing CH Cl and adjust the final volume to 10 mL.