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.     

Does nitrogen deposition increase forest production? The role of phosphorus

Effects of elevated N deposition on forest aboveground biomass were evaluated using long-term data from N addition experiments and from forest observation plots in Switzerland. N addition experiments with saplings were established both on calcareous and on acidic soils, in 3 plots with Fagus sylvatica and in 4 plots with Picea abies. The treatments were conducted during 15 years and consisted of additions of dry NH₄NO₃ at rates of 0, 10, 20, 40, 80, and 160 kg N ha⁻¹ yr⁻¹. The same tree species were observed in permanent forest observation plots covering the time span between 1984 and 2007, at modeled N deposition rates of 12-46 kg N ha⁻¹ yr⁻¹. Experimental N addition resulted in either no change or in a decreased shoot growth and in a reduced phosphorus concentration in the foliage in all experimental plots. In the forest, a decrease of foliar P concentration was observed between 1984 and 2007, resulting in insufficient concentrations in 71% and 67% of the Fagus and Picea plots, respectively, and in an increasing N:P ratio in Fagus. Stem increment decreased during the observation period even if corrected for age. Forest observations suggest an increasing P limitation in Swiss forests especially in Fagus which is accompanied by a growth decrease whereas the N addition experiments support the hypothesis that elevated N deposition is an important cause for this development.     

The cost of being an omnivore: mandible wear from plant feeding in a true bug

Evolutionary and ecological transitions from carnivorous to omnivorous feeding may be constrained by the ability of the animal to cope with disparate types of foods, even if preadaptations for such behaviour exist. The omnivorous true bug, Dicyphus hesperus (Hemiptera: Miridae) requires both animals (small, soft-bodied insects) and plants in its diet and obtains the majority of its dietary and metabolic water from plant feeding. Serrations on the lateral margins of the mandibular stylets wear with age, and this wear is exacerbated when the insects feed on plants compared to those provided free water and no plants. D. hesperus that feed on plants attack fewer prey but consumed similar amounts of prey tissue compared to individuals that were provided free water. Although others have shown mandible wear for plant-chewing animals we show for the first time that plant feeding can impose similar wear on plant-piercing animals as well.