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.

Pesticides in the atmosphere across Canadian agricultural regions.

The Canadian Atmospheric Network for Currently Used Pesticides (CANCUP) was the first comprehensive, nationwide air surveillance study of pesticides in Canada. This paper presentsthe atmospheric occurrence and distribution of pesticides including organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), acid herbicides (AHs), and neutral herbicides (NHs) during the spring to summer of 2004 and 2005 across agricultural regions in Canada. Atmospheric concentrations of pesticides varied within years and time periods, and regional characteristics were observed including the following: (i) highest air concentrations of several herbicides (e.g., mecoprop, triallate, and ethalfluralin) were found at Bratt's Lake, SK, a site in the Canadian Prairies; (ii) the west-coast site at Abbotsford, BC, had the maximum concentrations of diazinon; (iii) the fruit and vegetable growing region in Vineland, ON, showed highest levels for several insecticides including chlorpyrifos, endosulfan, and azinphos-methyl; (iv) high concentrations of atrazine and metolachlor were measured at St. Anicet, QC, a corn-growing region; (v) the Kensington site in PEI, Canada's largest potato-producing province, exhibited highest level of dimethoate. Analysis of particle- and gas-phase fractions of air samples revealed that most pesticides including OCPs, OPPs, and NHs exist mainly in the gas phase, while AHs exhibit more diversity in particle-gas partitioning behavior. This study also demonstrated that stirred up soil dust does not account for pesticides that are detected in the particle phase. The estimated dry and wet deposition fluxes indicate considerable atmospheric inputs for some current-use pesticides (CUPs). This data set represents the first measurements for many pesticides in the atmosphere, precipitation, and soil for given agricultural regions across Canada.

Impacts of lindane usage in the Canadian Prairies on the Great Lakes ecosystem. 2. Modeled fluxes and loadings to the Great Lakes.

Atmospheric loadings of gamma-hexachlorocyclohexane (gamma-HCH) from May 1, 1998, to April 30, 1999, to the Great Lakes simulated by a coupled soil-air and water-air atmospheric transport model are presented. Modeling results on an annual basis indicate that Lake Superior received the highest dry deposition load of 2.17 kg yr(-1). Dry deposition to the lower Great Lakes (Lakes Erie and Ontario) was 2-6 times lower as compared to the upper Great Lakes. Greater deposition in the upper Great Lakes is due mainly to their larger surface area and greater proximity to sources of gamma-HCH. Dry deposition fluxes (pg m(-2)) to lake surfaces were much lower than to land as a result of lower deposition velocities and lower air concentrations of gamma-HCH over the lakes. The highest gamma-HCH loading (kg yr(-1), in 1998-99) due to wet deposition occurred for Lake Ontario. This was mainly attributed to greater annual rainfall over Lake Ontario. An investigation of average seasonal fluxes predicted by the model shows that deposition fluxes to the Great Lakes are considerably higher in the summer than that in the autumn and winter seasons. The net direction of gas exchange also exhibits a seasonal dependence. Lakes Michigan, Huron, and Ontario show net absorption in the summer 1998 whereas at all other times net outgassing occurred at all of the lakes. Overall, gas exchange was the dominant process affecting loadings to the Great Lakes. Model-derived loadings and total deposition flows across the Great Lakes basin due to dry and wet depositions and net gas exchange agree reasonably well with the summer estimates compiled by the Integrated Atmospheric Deposition Network whereas autumn values show greater discrepancies. Better agreement was also observed for dry deposition as compared to wet deposition. Specifically, to improve short-term loading estimates (e.g., over days to months), the model results indicate the need for better spatially and temporally resolved information on concentrations in air and surface water and better estimates of precipitation and deposition velocities over the lakes.

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 importance since little is known of the combined effects of these chemicals on aquatic organisms. This study was designed to evaluate the acute and chronic toxicity of a complex mixture of nine atmospherically transported pesticides to Ceriodaphnia dubia. The nine selected pesticides (bromoxynil, dicamba, 2,4-D, MCPA, triallate, trifluralin, pentachlorophenol, lindane, and 4,4'-DDT) were detected in appreciable quantities in dry atmospheric deposits. The concentration of each pesticide in the mixture was based on maximum measured daily dry deposition rates for central Canada, except for pentachlorophenol, which was estimated based on atmospheric concentrations. The 48-h LC50 estimate for C. dubia exposed to the pesticide mixture was 174.60 microg L(-1) (340 times the measured total dry deposition concentration). The estimated NOEC and LOEC for both survival and reproduction, as determined in the 7-d chronic toxicity test, were 51.3 (100 times) and 154 microg/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 appears to 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.