Auxin Herbicides and Pesticide Mixtures in Groundwater of a Canadian Prairie Province

Abstract

Groundwater samples were collected from piezometers and water table wells in both dryland and irrigated agricultural regions of Alberta, Canada, to examine the occurrence of pesticide mixtures. Fourteen current‐use pesticides and two historical compounds were detected over a 3‐yr sampling period. Pesticide mixtures were detected in ∼3% of the groundwater samples, and the frequency of detection increased from spring (1.5%) to summer (3.8%) and fall (4.8%). Pesticide mixtures always consisted of at least one of two auxin herbicides: 2,4‐dichlorophenoxyacetic acid (2,4‐D) or 2‐methyl‐4‐chlorophenoxyacetic acid (MCPA). 19% of all samples contained a single pesticide, with auxin herbicides 2,4‐D (7.3%), MCPA (4.4%), and clopyralid (3.9%) being most prevalent. We detected 2,4‐D predominantly in the fall (72% of 2,4‐D detections) and less in spring and summer (28%). We detected MCPA mostly in summer (85% of MCPA detections) and less in spring and fall (15%). Clopyralid was more evenly detected across spring (30%), summer (25%), and fall (45%). Since the auxin herbicides above are typically applied in summer, results suggest that each herbicide may have different mobility and persistence characteristics in prairie soils. Guidelines for Canadian Drinking Water Quality have been set for a range of individual pesticides, but not for pesticide mixtures. If Canada is to establish such guidelines, this study demonstrates that auxin herbicides should be prioritized. In addition, only 7 of the 16 compounds detected in this study have established maximum acceptable concentrations (MACs), excluding clopyralid, which was detected in all three sampling years. Core Ideas Sixteen pesticides were detected in groundwater, most frequently auxin herbicides. Detection of pesticide mixtures increased from spring (1.5%) to fall (4.8%). Samples with pesticide mixtures always contained at least one auxin herbicide. In establishing water quality guidelines for mixtures, Canada must prioritize auxins.

Algae biostimulants: A critical look at microalgal biostimulants for sustainable agricultural practices

“…When 24 algal strains were analysed, the higher intracellular auxin concentrations in faster-growing strains suggested that auxin is involved in cell growth and division in microalgae (Wendy A. . Auxins are also known for their use in agriculture due to herbicide and pesticide properties (Munira et al, 2018;Quareshy et al, 2018). Cyanobacteria excrete indole acetic acid, amino acids and other growth promoting compounds into their immediate environment, which can stimulate the growth of microbial populations in soil and thereby improve crop and soil quality due to interactions with bacteria (Karthikeyan et al, 2009).…”

Groundwater quality

“…The groundwater quality could be affected by chemicals of agricultural use, and the residual pesticides and herbicides are recognized as the primary contaminants. By analyzing 436 groundwater samples in Alberta, Canada, Munira, Farenhorst, Sapkota, Nilsson, and Sheedy (2018) discovered 14 types of current‐use pesticides. Moreover, these pesticides contained at least one auxin herbicide compound, while 2,4‐D, MCPA, and clopyralid were the most frequently detected as the auxin herbicide.…”

From peaks to prairies: a time-of-travel synoptic survey of pesticides in watersheds of southern Alberta, Canada

“…In addition, samples collected directly from rivers tended to have fewer pesticides than effluents and tributaries, especially upstream from urban centers. Finally, most studies of pesticides in surface waters tend to be conducted beginning in early spring (May-Jun), whereas the synoptic survey was conducted in summer when pesticides such as 2,4-D and MCPA are predominantly used (Munira et al 2018) but prior to pre-harvest pesticide applications. Pesticides most 5 (1.6 ± 0.4) bd 11 (4.6 ± 0.9) cd 9 (4.0 ± 0.4) bc 10 (4.0 ± 1.3) bcde 17 (3.0 ± 0.4) C Tributary 9 (0.9 ± 0.2) ace 7 (1.7 ± 0.4) cd 3 (0.4 ± 0.3) de 5 (3.0 ± 2.0) bcde 10 (1.1 ± 0.2) B Mainstem 1 (0.2 ± 0.1) ace 2 (0.6 ± 0.1) be 2 (0.1 ± 0.1) de 2 (1.3 ± 0.2) bcde 4 (0.4 ± 0.1) A frequently detected in the synoptic survey followed a similar pattern to that reported in Anderson (2005) for the period 1995-2002, with 2,4-D, mecoprop, dicamba, and clopyralid the most frequently detected pesticides.…”

“…Pesticides can persist and be detected in surface waters outside of their application period (Kimbrough and Litke 1996). More specifically, auxin herbicides such as 2,4-D and mecoprop have been detected in soil (Anesio et al 2018), groundwater (Munira et al 2018), and stormwater (Rippy et al 2017) during the off-season, likely a consequence of their physicochemical properties and those of the soils as well as pesticide usage (quantities and formulations applied in a region). Similar results were obtained in water across the Canadian prairies (Byrtus et al 2004, Donald et al 2007).…”

“…Several monitoring studies of pesticides in agricultural streams, irrigation water, and storm water conducted in Alberta have shown that surface water contamination is prevalent (Anderson 2005, Saffran 2005, Phelan 2012, Charest et al 2015, Basiuk et al 2017, but few studies have looked at pesticides in Alberta's groundwater (Munira et al 2018), urban storm water (Derksen et al 2015), and WWTP effluents (Kerr et al 2008). To our knowledge, none has looked at the occurrence of pesticides in all regions of Alberta at the watershed scale using a time-of-travel survey (in which sampling is performed as a conceptual parcel of the water flows from its headwaters to its confluence, and tributaries and effluents are sampled as they contribute to the parcel) to evaluate point-source pesticide contributions and to determine whether or not loads are cumulative with multiple input sources as the parcels flow downstream.…”