Pesticides in fluvial wetlands catchments under intensive agricultural activities

A survey on pesticides (73 compounds) in the Bay St. Fran?ois wetland and its catchment (part of the wetlands of Lake St. Pierre area [St. Lawrence River, Québec]) was achieved in 2006. The metabolites as well as the active ingredients of pesticides (11 compounds) were detected in the wetland and its catchment. This wetland ecosystem was active in the degradation of agricultural pesticides (e.g., atrazine). The measured pesticides were individually below the criteria for aquatic species in natural water, except chlorpyrifos. Overall, the pesticides lost from agricultural field towards the streams were <1% of the quantity applied. The environmental fates of the pesticides were found to vary according to the size of the watershed. Over large catchments, half-life times were important in terms of global loss from the agricultural lands to wetlands whereas over small catchments, soil organic carbon/water distribution coefficient (Koc) was an important term for pesticides losses to water system since half-life times were not limiting factors.     

Two classes of anionic surfactants and their significance in hot water processing of oil sands

In hot water flotation of bitumen from Athabasca oil sands, two types of primary oil recovery response to sodium hydroxide addition are identified. Natural carboxylate surfactants can promote bitumen separation and flotation under certain process conditions, while a second, more polar, class of natural anionic surfactants can promote separation and flotation under different process conditions. As a result, some oil sands exhibit two recovery peaks as a function of sodium hydroxide addition. The phenomena are explained in terms of different sodium hydroxide additions required to reach critical surfactant concentrations specific to each surfactant class. The concept provides a means for interpreting a wide range of processibility phenomena.     

Spatial insolation models for photovoltaic energy in Canada

Spatial models of global insolation and photovoltaic electricity generation potential for Canada were developed. The main objective was to provide Canadians with an easily accessible, reliable tool for rapidly estimating the monthly and yearly electricity production potential of grid-connected photovoltaic systems anywhere in the country, and for assessing the dependence of production on location, time of year and array orientation. Monthly mean daily insolation data from 144 meteorological stations across Canada were used, along with data from an additional eight stations in Alaska to improve the models in that region. Several photovoltaic array orientations were considered, including South-facing arrays with latitude and vertical tilts and a sun-tracking orientation. Partial thin plate smoothing splines as implemented in ANUSPLIN were used to generate the spatial insolation models. The models were based on geographic position and a transform of monthly mean precipitation, the latter variable being a surrogate for cloudiness which affects surface insolation. Photovoltaic electricity generation (in kW h per kilowatt of photovoltaic installed power capacity) was estimated for each month and for the entire year from the insolation models by assuming international standard values for the performance ratio of photovoltaic systems. The yearly average root mean square predictive error (RTGCV) on the mean daily global insolation ranges between 0.75 (vertical tilt) and 1.43 MJ/m² (sun-tracking orientation) (or about 4.7–9.0 kW h/kW in terms of PV potential), or from 5.6% to 6.9% of the mean. Ultimately insolation and photovoltaic potential were mapped over the country at a 300 arc seconds (～10 km) resolution. The maps are available on a Natural Resources Canada Website. This is an important new tool to help Canadians gain an overall perspective of Canada’s photovoltaic potential, and allow estimation of potential photovoltaic system electricity production at any chosen location.     

Continuous analysis of dissolved gaseous mercury and mercury volatilization in the upper St. Lawrence River: exploring temporal relationships and UV attenuation

The formation and volatilization of dissolved gaseous mercury (DGM) is an important mechanism by which freshwaters may naturally reduce their mercury burden. Continuous analysis of surface water for diurnal trends in DGM concentration (ranging from 0 to 60.4 pg L(-1); n=613), mercury volatilization (ranging from 0.2 to 1.1 ng m(-2) h(-1); n=584), and a suite of physical and chemical measurements were performed during a 68 h period in the St. Lawrence River near Cornwall (Ontario, Canada) to examine the temporal relationships governing mercury volatilization. No lag-time was observed between net radiation and OGM concentrations (highest cross-correlation of 0.817), thus supporting previous research indicating faster photoreduction kinetics in rivers as compared to lakes. A significant lag-time (55-145 min; maximum correlation = 0.625) was observed between DGM formation and mercury volatilization, which is similar to surface water Eddy diffusion times of 42-132 min previously measured in the St. Lawrence River. A depth-integrated DGM model was developed using the diffuse integrated vertical attenuation coefficients for UVA and UVB (K(dI UVA) = 1.45 m(-1) K(dI UVB)= 3.20 m(-1)) Low attenuation of solar radiation was attributed to low concentrations of dissolved organic carbon (mean = 2.58 mg L(-1) and particulate organic carbon (mean = 0.58 mg L(-1) in the St. Lawrence River. The depth-integrated DGM model developed found that the top 0.3 m of the water column accounted for only 26% of the total depth-integrated DGM. A comparison with volatilization data indicated that a large portion (76% or 10.5 ng m(-2) of the maximum depth-integrated DGM (13.8 ng m(-2))is volatilized over a 24 h period. Therefore, at least 50% of all DGM volatilized was produced at depths below 0.3 m. These results highlight the importance of solar attenuation in regulating DGM formation with depth. The results also demonstrate both the fast formation of DGM in rivers and the importance of understanding DGM dynamics with depth as opposed to surface waters.     

The effect of shear and oil/water ratio on the required hydrophile-lipophile balance for emulsification

Required hydrophile-lipophile balance (HLB) values were examined in terms of the nature of kerosene-water, both oil-in-water (O/W) and water-in-oil (W/O), emulsions formed using Span 80/Tween 80 surfactant blends. Both the nature of the emulsification method and the oil/water ratio were critical in determining the resulting emulsion type. Both high- and low-shear conditions were investigated. Under high shear, low internal phase emulsions formed using the surfactant mixtures that corresponded to the required HLB values for emulsification involving kerosene (6 for W/O and 14 for O/W). However, at low shear, high internal phase (concentrated) emulsions resulted. Furthermore, depending on the oil/water ratio, some of the high internal phase emulsions were opposite to the type expected, given the HLB of the surfactant blend used. From these results, it appears that the emulsification technique (applied shear and oil/water ratio) used can be of greater importance in determining the final emulsion type than the HLB values of the surfactants themselves.