Atmospheric movements of lindane (gamma-hexachlorocyclohexane) from canola fields planted with treated seed

Lindane (gamma-hexachlorocyclohexane [gamma-HCH]) is used as an insecticide in many countries. Concentrations of gamma-HCH have been found in air, water, soil, snow, and tissue samples throughout the world and concerns have been raised for its potential effects on human and ecosystem health. In Canada, gamma-HCH is primarily used as a treatment on canola (Brassica napus L) seed with an estimated 455.3 Mg applied in 1997 and 510.4 Mg in 1998. The purpose of this study was to measure gamma-HCH volatilization from fields planted with treated canola seed. Atmospheric dry and wet deposition and soil samples were collected for two growing seasons (1997 and 1998) from a canola field planted with treated seed. Atmospheric concentrations as high as 16.1 and 7.4 ng m(-3) were measured at 1 m above the canola field compared with maximum concentrations of 2.9 and 2.7 ng m(-3) measured above a grass field located 2 km away (1997 and 1998, respectively). On the basis of measurements made in this study it was estimated that between 12 and 30% of the gamma-HCH applied as canola seed treatment may volatilize and be released to the atmosphere. This would create an atmospheric loading of 66.4 to 188.8 Mg for the 6-wk period following planting, estimated from the quantity of seed sown on the Canadian prairies in 1998. Dry deposition rates and rain concentrations as high as 2,203 ng m(-2) d(-1) and 170 ng L(-1) were measured adjacent to the canola field.     

Atmospheric concentrations and dry and wet deposits of some herbicides currently used on the Canadian Prairies

High volume air sampling in the Canadian Prairies was used to characterize atmospheric concentrations for 10 herbicides (alachlor, atrazine, ethalfluralin, metolachlor, 2,4-D, dicamba, bromoxynil, MCPA, trifluralin, and triallate) along a 500-km north-south transect. Atmospheric concentration measurements at various altitudes identified that of the six herbicides present in the highest concentrations, triallate was strongly influenced by local sources, while 2,4-D, dicamba, bromoxynil, MCPA and trifluralin were dominated by regional atmospheric transport. Concentrations of the herbicides measured at various altitudes were compared with dry deposition rates measured using a dry/wet deposition sampler and used to calculate deposition velocities V(d). The primary atmospheric transport mechanism for MCPA and bromoxynil was shown to be adsorption to particles dispersed in the atmosphere, with the same mechanism also confirmed for 2,4-D and dicamba, while trifluralin was shown to be transported mainly in the gas phase. This method of calculation indicated that transportation of triallate was influenced by particle adsorption. Weekly maximum atmospheric loadings of the major herbicides present in the Prairies were estimated to range from 73 kg for trifluralin to 541 kg for 2,4-D.     

Laboratory Wind Tunnel and Model Studies to Improve Gas Velocity Distribution in Cottrell Precipitators

Corrosion of flue gas desulfurization (FGD) scrubbing equipment is one of several critical problems facing both the power industry operating these units and the engineering firms that have to select materials of construction for the specific processes. The various processes and the status of flue-gas desulfurization technology were discussed at the 68th annual meeting of the Air Pollution Control Association.¹     

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 g 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 g 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.     

Cross-sectional biomonitoring study of pesticide exposures in Queensland,Australia, using pooled urine samples

A range of pesticides are available in Australia for use in agricultural and domestic settings to control pests, including organophosphate and pyrethroid insecticides, herbicides, and insect repellents, such as N,N-diethyl-meta-toluamide (DEET). The aim of this study was to provide a cost-effective preliminary assessment of background exposure to a range of pesticides among a convenience sample of Australian residents. De-identified urine specimens stratified by age and sex were obtained from a community-based pathology laboratory and pooled (n = 24 pools of 100 specimens). Concentrations of urinary pesticide biomarkers were quantified using solid-phase extraction coupled with isotope dilution high-performance liquid chromatography–tandem mass spectrometry. Geometric mean biomarker concentrations ranged from <0.1 to 36.8 ng/mL for organophosphate insecticides, <0.1 to 5.5 ng/mL for pyrethroid insecticides, and <0.1 to 8.51 ng/mL for all other biomarkers with the exception of the DEET metabolite 3-diethylcarbamoyl benzoic acid (4.23 to 850 ng/mL). We observed no association between age and concentration for most biomarkers measured but noted a “U-shaped” trend for five organophosphate metabolites, with the highest concentrations observed in the youngest and oldest age strata, perhaps related to age-specific differences in behavior or physiology. The fact that concentrations of specific and non-specific metabolites of the organophosphate insecticide chlorpyrifos were higher than reported in USA and Canada may relate to differences in registered applications among countries. Additional biomonitoring programs of the general population and focusing on vulnerable populations would improve the exposure assessment and the monitoring of temporal exposure trends as usage patterns of pesticide products in Australia change over time.     

A comparison of flux chambers and ambient air sampling to measure gamma-hexachlorocyclohexane volatilisation from canola (Brassica napus) fields

The insecticide gamma-hexachlorocyclohexane (gamma-HCH) is primarily used in Canada in treatments of canola (Brassica napus) seed. It has been shown that gamma-HCH so applied will volatilise with 12-30% entering the atmosphere within 6 wk after the seed is planted. Both flux chambers and high-volume air samplers were used to measure gamma-HCH volatilisation from a canola field and the results from each method compared. Daily samples were collected from three flux chambers located on the field. gamma-HCH was found in the air of the chambers on the first day after planting. Volatilisation rates were low for the first 7d (40.0 mg ha(-1) wk(-1)) but increased during the second week (143.8 mg ha(-1) wk(-1)). This was consistent with previous studies. Weekly composite air samples, from three heights above the canola field, were used to calculate volatilisation rates from the field. These were 190 mg ha(-1) wk(-1) (week 1) and 420 mg ha(-1) wk(-1) (week 2). Soil temperatures in the open field were warmer than those under the flux chambers and this may have contributed to the higher ambient air measurements.     

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.     

Effect of Dust Concentration Upon the Gas-Flow Capacity of a Cyclonic Collector

The flow rate through an industrial gas-cleaning cyclone at a fixed pressure drop is greater when the incoming gas is dusty than when it is clean. This observation by Briggs for a single cyclone tube was extended to multiple tubes, and ike results compared to observations by Soo and Trezek that the fraction factor for turbulent flow in a pipe is less for dusty gas than for clean. Empirical considerations indicated tJtat both of these observations should be connected with a rather large reduction in gas viscosity due to the dust. This predicted viscosity decrease was later observed. A physical theory accounting for viscosity reduction by a dust cloud is proposed. This effect also offers a means for increasing the heat, transfer coefficient in gas heat exchangers.     

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 chemical’s 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.