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Wetlands are abundant throughout the agricultural landscape of central Saskatchewan, Canada, and the biota present in these wetlands may be vulnerable to the toxic effects of pesticides used on nearby crops. We hypothesized that herbicide concentrations would be higher in wetlands on minimum-tillage farms than on organic (no herbicide use) farms, and that the principal transport mechanisms of runoff versus atmospheric deposition could be identified based on the concentrations in these two wetland types. To test these hypotheses, 29 herbicides were monitored for 5 yr in 16 wetlands on minimum-tillage farms and in seven wetlands on organic farms. Twenty herbicides were detected in wetlands on minimum-tillage farms versus 12 in wetlands on organic farms. Clopyralid, MCPA, 2,4-D, bromoxynil, dichlorprop, and dicamba were detected at a >50% frequency in wetlands on both minimum-tillage and organic farms. Concentrations of clopyralid were significantly higher in wetlands on minimumtillage farms than in those on organic farms, whereas no significant difference was observed for any of the other five herbicides. Glyphosate, including its degradation product AMPA, was detected in >50% frequency only in wetlands on minimumtillage farms where the mean concentration (1278 ng L-1) was higher than the concentration of other herbicides. Mass applied, vapor pressure, and water solubility were important determinants of herbicide concentrations and detections in wetlands. Herbicide concentrations in all but two samples were less than their respective Canadian guideline for protection of aquatic life, suggesting that, overall, individual herbicide concentrations in the wetlands were not toxic to biota. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Sorption parameters (such as Kd values) are among the most sensitive input parameters in pesticide fate models. This study demonstrates that near-infrared spectroscopy (NIRS), in combination with batch equilibrium techniques, can be used to estimate Kd values, thereby increasing throughput of the many samples required to characterize spatial variability of pesticide sorption within fields. The Pesticide Root Zone Model version 3.12.2 (PRZM- 3) was used to compare scenarios that used NIRS spectral data, pedotransfer functions and batch equilibrium methods as inputs for the calculation of 2,4-dichlorophenoxyacetic acid (2,4-D) and atrazine leaching in 591 soil horizons. Based on the 3564 simulation runs conducted, we concluded that the added benefit of NIRS is most useful when the pesticides under study have small sorption potentials and short half-lives in soil. The 2,4-D and atrazine sorption by soil was highly correlated to soil organic C (SOC) content in the fields under study. The feasibility of using NIRS to predict pesticide Kd values largely relies on the sorption of the pesticide being significantly correlated to SOC. In addition, successful regional approaches to predicting Kd values from NIRS spectral data can also be developed when the calibration model is derived by combining a set of fields where each has a similar statistical population characteristic in Kd values. [ABSTRACT FROM AUTHOR]

ABSTRACT Periodic assessments of the risk of water contamination by pesticides help decision makers improve the sustainability of agricultural management practices. In Canada, when evaluating the risk of water contamination by pesticides, 2 main constraints arise. First, because the area of interest is large, a pesticide transport model with low computational running time is mandatory. Second, some relevant input data for simulations are not known, and most are known only at coarse scale. This study aims to develop a robust methodology to estimate the evolution of the risk of water contamination by pesticides across Canada. To circumvent the 2 aforementioned issues, we constructed a stochastic model and coupled it to the 1-dimensional pesticide fate model Pesticide Root Zone Model (PRZM). To account for input data uncertainty, the stochastic model uses a Monte Carlo approach to generate several pesticide application scenarios and to randomly select PRZM parameter values. One hundred different scenarios were simulated for each of over 2000 regions (Soil Landscapes of Canada [SLC] polygons) for the years 1981 and 2006. Overall, the results indicated that in those regions in which the risk increased from 1981 to 2006, the increase in risk was mainly attributable to the increased area treated by pesticides or an increase in the number of days with runoff. More specifically, this work identifies the areas at higher risk, where further analyses with finer-scale input data should be performed. The model is specific for Canadian data, but the framework could be adapted for other large countries. Integr Environ Assess Manag 2014;10:429-436. © 2014 SETAC [ABSTRACT FROM AUTHOR]

In the present study, an ephemeral (E) and a semipermanent (SP) wetland were divided into halves using a polyvinyl curtain and one-half of each wetland was treated with dicamba (3,6-dichloro- o-anisic acid), bromoxynil (3,5-dibromo-4-hydroxy-benzonitrile), MCPA [(4-chloro-2-methylphenoxy)acetic acid], 2,4-D [(2,4-dichlorophenoxy)acetic acid], mecoprop-P (R)-2-(4-chloro- o-tolyloxy)propionic acid], and dichlorprop [(RS)-2-(2,4-dichlorophenoxy)propionic acid] such that concentrations in the water simulated an overspraying event, thus representing a worst-case scenario for wetland contamination. Water and sediment samples were taken over the 77-d study period to monitor herbicide concentrations. The dissipation of all six herbicides could be described by first-order reaction kinetics. In water, the field half-life (DT50) values ranged from 2.3 d (bromoxynil) to 31 d (dichlorprop). All six herbicides were detected in sediment samples from both wetlands. Overall, the phenoxypropionic acids (mecoprop-P and dichlorprop) were more persistent than the phenoxyacetic acids (2,4-D and MCPA) in both sediment and water. Use of bromide ion as a conservative tracer indicated that infiltration through sediment was an important route of water loss in both wetlands, especially in wetland E. Because strong correlations were found between the mass of each herbicide and bromide ion mass in wetland SP ( r 2 = 0.59-0.76) and wetland E ( r 2 = 0.80-0.95), it is likely that herbicide dissipation was due, in part, to mass lost by way of infiltration through sediment. Environ. Toxicol. Chem. 2011;30:1982-1989. © 2011 SETAC [ABSTRACT FROM AUTHOR]

The article discusses research investigating the prairie wetland sediment properties and herbicide sorption coefficients as a result of land use and riparian effects. Sorption of herbicides by wetland sediments can provide researchers with important information for use in herbicide fate modeling. The team sampled bottom sediments from 17 wetlands consisting of five land use classes including ephemeral wetlands with no riparian vegetation in a cultivated catchment (ENCR) and ephemeral wetlands with riparian vegetation in a cultivated catchment (ECR). They examined the effects of land use on the physical and chemical properties of wetland sediments and their association with sediment properties and herbicide sorption. Results from the sediment analyses are presented.

The article discusses a study on sorption and degradation of 2,4-dichlotophenoxyacetic acid (2,4-D) in 123 surface soils in Alberta. Soil samples were collected in 2002 and 2004. Factors observed in the soils include soil organic carbon content (SOC), electrical conductivity, pH, cation exchange capacity and total soil microbial activity. According to the study, half-life of the herbicide was less than those reported in literature. It concluded the mineralization takes effect regardless of soil properties.

Tillage is a driving force of soil movement in cultivated fields. Soil constituents, together with the mass of soil, are redistributed across landscapes by tillage. The pattern of tillage-induced soil constituent redistribution is determined by the pattern of tillage erosion (tillage-induced soil mass loss or gain) and the dispersiviry of translocation. In this study, we used a convoluting procedure and developed a Tillage Translocation Model (TiIITM) to simulate the tillage translocation process and to demonstrate tillage-induced soil mass and soil organic carbon (OC) (as an example of soil constituents) redistributions across four hypothetical landscapes subjected to different tillage patterns (directions) and over different lengths of tillage period. We determined that the local tillage-erosion rate is mainly dependent on topography and that the effects of tillage pattern and the length of tillage period are relatively minor. The redistribution of OC content in the till layer is mainly determined by the number, location, and size of soil loss positions in the landscape, as well as the soil loss rates at these positions. Net loss of OC content occurs in the till layer and this loss increases with time. In contrast, an increase of OC content in the sublayer occurs at soil accumulation positions. The model was validated against field data collected at a site near Cyrus, MN. The patterns of OC and inorganic C redistribution can be adequately estimated by TillTM. There are discrepancies, however, between the model-estimated values and the field measurements due to the limitations and uncertainties associated with the model. The results clearly showed that tillage translocation causes the vertical redistribution of soil constituents across the landscape, which implies that tillage translocation is one of the driving forces behind the spatial variability of soil properties and properties that impact biophysical processes. [ABSTRACT FROM AUTHOR]

Agricultural policy frameworks aim to develop scientifically sound measures that can be used to assess the environmental performance and risks associated with agricultural systems. As part of this assessment, pesticide leaching models are applied at large scales to assess the risk of pesticide groundwater contamination across soil series, agricultural fields, watersheds, or regions. Measurements of pesticide sorption by soil are among the most sensitive input parameters in pesticide leaching models. Soil organic matter (SOM) is the single most important soil constituent influencing pesticide sorption in soils. The interaction of pesticides with SOM is often studied in the laboratory using batch-equilibrium experiments in combination with techniques that quantify chemical and structural characteristics of SOM. This paper reviews these laboratory studies and discusses their importance to the development of agricultural policy frameworks. This review paper was written as part of a symposium on "Meaningful pools in determining soil C and N dynamics" which was held by the SSSA and the Canadian Soil Science Society during the 2004 ASA-CSSA-SSSA International Annual Meetings in Seattle, WA. [ABSTRACT FROM AUTHOR]