Don T. Waite

Duplicate sampling reproducibility of atmospheric residues of herbicides for paired pan and high-volume air samplers.

The reproducibility of collection of atmospheric residues of the herbicides 2,4-D and triallate as bulk (wet plus dry) deposition samples by paired pan samplers and as particulate (filter) and vapour (PUF/XAD-2 resin cartridge) samples by paired high-volume air samplers was determined. Variability of herbicide concentrations in paired bulk deposition samples was within 25% for 65 and 80% of the samples for 2,4-D and triallate, respectively, with approximately 90% of the paired samples being within a factor of 2 for both herbicides. The vapour samples of 2,4-D and triallate showed similar reproducibilities. The highest reproducibility was observed for the filter samples with 92% of the paired data sets for 2,4-D being within 25% variability. No triallate was detected in the filter samples.

Influence of usage and chemical–physical properties on the atmospheric transport and deposition of pesticides to agricultural regions of Manitoba, Canada

This study quantified the masses of 14 pesticides deposited as wet (precipitation) versus dry (gaseous and particle) atmospheric deposition at a research farm in southwestern Manitoba, Canada. The concentration in air of these pesticides was also measured. Total bulk deposition amounts (wet+dry) ranged from 0.009 to 2.3 μg m(-2) for the 12 pesticides detected, and for the six pesticides with both wet and dry deposition detections, dry deposition contributed 12-51% of the total deposition over the crop growing season. Although not applied at the site, eight herbicides registered for use in Canada, as well as lindane (γ-HCH), were all frequently detected (92-100%) in the 12 air samples analyzed during the crop growing season, with by-product isomer α-HCH (75%), clopyralid (50%) and atrazine (8%) detected to a lesser extent. The chemicals physicochemical properties and the relative mean mass of each agricultural pesticide applied in the province of Manitoba and in a 13 km radius were significant parameters in explaining the trends in the concentrations of pesticides detected in our samples. The important contribution of dry deposition to total pesticide deposition warrants greater attention in arid and semi-arid areas such as the Prairie Region of Canada, also because under a changing climate this region is estimated to experience more severe droughts while the more favorable conditions predicted for pest infestations could lead to increased pesticide applications in agricultural and urban areas.

Dry atmospheric deposition and deposition velocities of dicamba, 2,4-dichlorophenoxyacetic acid and γ-1,2,3,4,5,6-hexachlorocyclohexane

This study documents the measurement of atmospheric concentrations and dry deposition rates of three agricultural pesticides currently used in the Canadian prairies: dicamba (2-methoxy-3,6-dichlorobenzoic acid); 2,4-D (2,4-dichlorophenoxyacetic acid); and γ-HCH (γ-1,2,3,4,5,6-hexachlorocyclohexane). Dry atmospheric deposition was measured using a unique new sampler. Deposition velocities were calculated from these data. Dicamba and 2,4-D had, generally higher dry deposition velocities (ranges 0.57–1.50 and 0.29–4.89 cm s−1, respectively) than did γ-HCH (range 0.07–1.0 cm s−1). The possible reasons for this variability are discussed.

Atmospheric pentachlorophenol concentrations in relation to air temperature at five Canadian locations

Pentachlorophenol (PCP), used as a wood preservative and as a disinfectant, has been found in human urine samples from Saskatchewan and in air samples from three Canadian sites. To confirm the presence of atmospheric PCP residues and to explore seasonality, weekly samples were collected at five Canadian sites for three consecutive weeks, in the months of July and October, 1995 and January, April and May, 1996, using a high volume sampler equipped with polyurethane foam (PUF) plugs. PCP was present in all samples collected adjacent to a utility pole storage site with concentrations ranging from 0.7 to 1233.0 ng m-3. There was a very strong correlation between average weekly air temperature, measured over a range of -29.3 to +20.0 degrees C, and the log10 of the average weekly concentration of PCP at this site. PCP was measured in 7 of 11 air samples from each of two small cities (concentrations ranging from 0.2 to 6.8 ng m-3) and the correlation between temperature and PCP concentration, for these two city sites, was similar to that for the utility pole storage site. Concentrations of PCP at two rural sites were lower (0.1-1.5 ng m-3) and detected less frequently. As a consequence, the correlation between air temperature and PCP concentration was more variable.

Uptake of atmospheric mercury by deionized water and aqueous solutions of inorganic salts at acidic, neutral and alkaline pH

Mercury (Hg) is well known as a toxic environmental pollutant that is among the most highly bioconcentrated trace metals in the human food chain. The atmosphere is one of the most important media for the environmental cycling of mercury, since it not only receives mercury emitted from natural sources such as volcanoes and soil and water surfaces but also from anthropogenic sources such as fossil fuel combustion, mining and metal smelting. Although atmospheric mercury exists in different physical and chemical forms, as much as 90% can occur as elemental vapour Hg0, depending on the geographic location and time of year. Atmospheric mercury can be deposited to aquatic ecosystems through both wet (rain or snow) and dry (vapour adsorption and particulate deposition) processes. The purpose of the present study was to measure, under laboratory conditions, the rate of deposition of gaseous, elemental mercury (Hg0) to deionized water and to solutions of inorganic salt species of varying ionic strengths with a pH range of 2-12. In deionized water the highest deposition rates occurred at both low (pH 2) and high (pH 12). The addition of different species of salt of various concentrations for the most part had only slight effects on the absorption and retention of atmospheric Hg0. The low pH solutions of various salt concentrations and the high pH solutions of high salt concentrations tested in this study generally showed a greater tendency to absorb and retain atmospheric Hg0 than those at a pH closer to neutral.

Toxicity of a Complex Mixture of Atmospherically Transported Pesticides to Ceriodaphnia Dubia

The presence of several anthropogenic chemicals has been documented in the atmosphere of the Canadian prairies. The deposition of these chemicals as a mixture is of importancesince little is known of the combined effects of these chemicalson aquatic organisms. This study was designed to evaluate theacute and chronic toxicity of a complex mixture of nineatmospherically transported pesticides to Ceriodaphniadubia. The nine selected pesticides (bromoxynil, dicamba, 2,4-D,MCPA, triallate, trifluralin, pentachlorophenol, lindane, and4,4′-DDT) were detected in appreciable quantities in dryatmospheric deposits. The concentration of each pesticide in themixture was based on maximum measured daily dry deposition ratesfor central Canada, except for pentachlorophenol, which wasestimated based on atmospheric concentrations. The 48-h LC50estimate for C. dubia exposed to the pesticide mixture was174.60 μg L-1 (340 times the measured total dry deposition concentration). The estimated NOEC and LOEC for bothsurvival and reproduction, as determined in the 7-d chronic toxicity test, were 51.3 (100 times) and 154 μg L-1 (300 times), respectively. A basic risk assessment, using the toxic unit approach, suggested that the toxicity of the pesticide mixture was mainly due to 4,4′-DDT. Overall, this atmospherically transported complex mixture of pesticides appearsto pose a negligible toxicological risk to non-target aquatic invertebrates such as zooplankton.

Environmental Fate of Triclopyr

Triclopyr is nonpersistent in surface water. It has limited mobility and low to medium persistence in soil. Considering its adsorptive characteristics and that it dissipates via multiple pathways, such as photolysis, plant metabolism, and microbial degradation, its potential to leach to depth in soil and to contaminate groundwater is low. This conclusion is corroborated by field leaching and groundwater monitoring data, both derived from use areas in several states in the U.S. and sites directly near handling/mixing facilities. Even when detected in the groundwater, e.g., five reported detections in two states in the U.S., the highest concentration was well below the estimated HAL of the USEPA.

Air concentrations of currently used herbicides and legacy compounds in the Canadian prairies, subarctic, and arctic

Passive air samplers were installed in the summers of 2005 and 2007 for 90 days at four locations in the agricultural region of the Canadian Prairies and at five locations in the Canadian Subarctic and Arctic. The presence and masses of ten currently used herbicides and three legacy compounds in the polyurethane foam disks were quantified. Herbicides 2,4-D, bromoxynil and MCPA were detected at all locations in the Canadian Prairies and in both years because these herbicides are widely applied to control broadleaf weeds in cereal crops that are an integral part of Prairie agricultural production systems. MCPA was also detected at one location in the Arctic in 2007. The detection of the other seven herbicides in the 2 years combined ranged from no detections (atrazine only) to five detections for the relatively volatile herbicides trifluralin and triallate. Triallate was the only other herbicide detected in the Arctic (2005). Legacy compounds were either not detected (alachlor) or at levels near their detection level (γ-HCH and α-HCH). γ-HCH and α-HCH were more frequently detected in 2005 than in 2007 indicating that their concentrations in Canadian air have decreased over time. γ-HCH, widely used as an insecticide in Prairie oilseed production until 2002, was detected at larger concentrations in the Canadian Prairies than in the Subarctic and Arctic. α-HCH, a manufacturing by-product in technical HCH prior to 1971 in Canada, was not detected in the Canadian Prairies but was at detectable levels in the Subarctic and Arctic as the Arctic Ocean is reported to be a major source of α-HCH to the atmosphere. We conclude that some of the most widely used herbicides in Canadian agriculture today are commonly present in the air in regions where they are applied and that a portion of these herbicides may be traveling as parent molecules to the Canadian Arctic. To the authors’ knowledge, this is the first evidence of the presence of MCPA and triallate in Arctic air samples, perhaps because previous research has seldomly monitored for currently used herbicides in this region.

Materials selection for a dry atmospheric mercury deposits sampler

In order to develop a sampler for measuring dry deposition rates for atmospheric mercury, suitable materials are needed that neither adsorb nor release mercury. In this paper, four materials (polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS), Teflon and glass) were tested. Each of the materials was placed in a beaker containing mercuric solution under varied conditions for pH, preservative concentration, initial mercuric concentration, temperature, acid type and contact time of the material. The concentrations of the mercuric solutions were determined using the cold-vapor atomic absorption (CVAA) technique. The experimental results show that glass has the lowest absolute net adsorption rates (NARs) of 0.026-1.13 pg/m2 among the materials tested. Teflon, PVC and ABS have NARs ranging from 0.54 to 10.4 microg/M2 over an adsorption duration of one or two weeks. ABS has significantly higher adsorption rates for mercury than PVC and Teflon, indicating its inappropriateness as the material for building the sampler. Teflon and PVC will be the materials of choice for the sampler. The experimental results can also be used in establishing appropriate sampling conditions in the field.

An Adsorption-Separation Process for Collecting and Analyzing Atmospheric Mercury Deposits—Development of a Chelex 100 Resin Column System

Abstract Many previous studies for detecting the atmospheric mercury from wet deposition have been reported. In comparison, little effort has been made in studying mercury from dry deposition. There is currently no sampler that collects atmospheric mercury dry deposits. A new mercury dry deposition sampler has been designed conceptually. It employs a moving sheet of water to passively collect dry deposits of mercury. The water will be drained into a reservoir and recirculated through a resin column that is capable of retaining the mercury deposits. In this article, an adsorption-separation process is proposed for collecting and analyzing dry atmospheric mercury deposits through development of a Chelex 100 resin column system. When the water flows continually through the resin column, the mercury deposits will be adsorbed by the resin. After the sampling process, the mercury can then be separated from the resin through application of an acidic solution. The extracted solution that contains the separated mercury is then analyzed through a cold-vapor mercury analyzer. In this study, hydrochloric acid, nitric acid and sulfuric acid were tested. Chelex 100 resin (Sigma Chemical Co., St. Louis) selected for this study was tested under laboratory conditions using solutions of known mercury concentration in order to determine its efficiency in adsorption and separation. The results indicate that Chelex 100 resin could adsorb more than 95% of the mercury in the test solutions with a pH range from 1.65 to 11.45. Sulfuric acid was found to have better overall performance than hydrochloric acid and nitric acid in extracting (desorbing) the mercury from the resin column. The highest desorption rate (95.2%) was achieved with 4 N H2SO4 for a mercury solution of pH 5.90. Development of the adsorption-separation process and identification of the optimal system conditions provides scientific bases for designing the sampler. The experimental results are also useful for other mercury-related studies.