Smith P.G.,Stantec Consulting Ltd. |
Boutin C.,Environment Canada |
Knopper L.,Intrinsik Environmental Sciences Inc.
Archives of Environmental Contamination and Toxicology | Year: 2013
Vanadium concentrations in soil can be increased through anthropogenic inputs and can be harmful to plants. A Petri dish experiment was conducted to assess the effect of vanadium toxicity on the germination and survival of the garden lettuce, Lactuca sativa. A second study was conducted in a greenhouse to investigate the influence of species selection and nutrient concentration on the toxicity of vanadium pentoxide to plants. L. sativa and four non-crop native plant species, two grasses (Elymus virginicus and Panicum virgatum) and two broad-leaved species (Lycopus americanus and Prunella vulgaris) were selected. Artificial soil was used in both experiments, and a geometric progression of five vanadium concentrations plus controls was selected for the soil treatments. Results of the Petri dish experiment showed that seedling survival is a less sensitive end point than above-ground dry weight (DW) as measured in the greenhouse experiment. Nutrient level (100, 10, and 1 kg/ha) was found to strongly influence vanadium toxicity in the greenhouse study. At 100 kg/ha, plant tolerance to vanadium was greatest, as indicated by higher no-observed, lowest-observed, and percentage effect concentration values. Results showed that forbs (L. americanus and P. vulgaris) tended to be more sensitive than both the crop (L. sativa) and grasses (E. virginicus and P. virgatum) at high concentrations of vanadium. Soil concentrations resulting in a 25 % decrease in shoot DW were generally less than the Canadian soil quality guideline for vanadium, suggesting that 130 mg/kg may not be protective of the Canadian native plant species used in this study. © 2012 Her Majesty the Queen in Right of Canada. Source
Lade P.V.,George Mason University |
Karimpour H.,Stantec Consulting Ltd.
International Journal of Solids and Structures | Year: 2016
Time effects in granular materials relate to crushing of grains, which is a time dependent process. Depending on the proximity of the load applied to a grain relative to the instantaneous failure load of the grain, the time increases as the load is decreased below the failure load. A study of grain crushing associated with stress drop-creep and stress drop-stress relaxation experiments on dense Virginia Beach sand consisting mainly of quartz grains is presented. In these experiments the triaxial specimens are isotropically consolidated to 8000. kPa, sheared at a constant rate up to a given deviator stress followed by either creep or stress relaxation over a given time period. After dismantling the triaxial specimens, the grain size distributions are determined and their changes, as expressed through Hardin's relative breakage factor, are related to the amount of energy input. Results of the stress drop-creep tests and the stress drop-stress relaxation tests show that creep deformations and the amount of stress relaxation are considerably reduced with increasing amounts of stress drop. Depending on the amount of stress drop, a delay is detected before creep deformation or stress relaxation is initiated. Multiple stress drop-creep experiments are also performed. Structuration effects, which describe changes in yield surface location during creep or stress relaxation and are due to change in grain configuration and interlocking with time, are not observed in the specimens of Virginia Beach sand. © 2016 Elsevier Ltd. Source
Richardson G.M.,Stantec Consulting Ltd. |
Richardson G.M.,University of Saskatchewan
Human and Ecological Risk Assessment | Year: 2014
Dental amalgam is 50% metallic mercury (Hg0) by weight and causes Hg exposure. The first assessment of Hg exposure and risk from dental amalgam in Canada was published in 1996. Recent data provided the opportunity to update that assessment. During the Canadian Health Measures Survey (CHMS; 2007 to 2009) the number of tooth surfaces specifically restored with dental amalgam was recorded. Data were also collected on the concentration of Hg in urine of survey participants. These data were employed to determine Hg exposures in the Canadian population. Also determined was the number of amalgam-restored tooth surfaces that would not result in exposure exceeding the dose associated with Canada's reference exposure level (REL) for Hg0. Based on the CHMS data, 17.7 million Canadians aged ≥6 years collectively carry 191.1 million amalgam surfaces, representing 76.4 million amalgam-restored teeth. Average Hg exposures were: Children-0.065 μg Hg/kg-day; Teens-0.032 μg/kg-day; Adults-0.033 μg/kg-day; and Seniors-0.041 μg/kg-day. Of Canadians with dental amalgam restorations, 80.4% experience a daily dose of Hg that exceeds the Canadian REL-associated dose. The number of amalgam surfaces that will not result in exceeding the REL-associated dose varied from two amalgam surfaces (children, both sexes) to seven surfaces (adult males). © 2014 Copyright Taylor and Francis Group, LLC. Source
Hegmann G.,Stantec Consulting Ltd. |
Yarranton G.A.T.,121 Artists View Way
Environmental Impact Assessment Review | Year: 2011
Cumulative Effects Assessment (CEA) is a tool that can be useful in making decisions about natural resource management and allocation. The decisions to be made include those (i) necessary to construct planning and regulatory frameworks to control development activity so that societal goals will be achieved and (ii) whether or not to approve individual development projects, with or without conditions. The evolution of CEA into a more successful tool cannot occur independently of the evolution of decision making processes. Currently progress is painfully slow on both fronts. This paper explores some opportunities to accelerate improvements in decision making in natural resource management and in the utility of CEA as a tool to assist in making such decisions. The focus of the paper is on how to define the public interest by determining what is acceptable. © 2011 Elsevier Inc. Source
Simms E.L.,Memorial University of Newfoundland |
Ward H.,Stantec Consulting Ltd.
Remote Sensing | Year: 2013
The analysis of a series of five normalized difference vegetation index (NDVI) images produced information about a Labrador (Canada) portion of the tundra-taiga interface. The twenty-five year observation period ranges from 1983 to 2008. The series composed of Landsat, SPOT and ASTER images, provided insight into regional scale characteristics of the tundra-taiga interface that is usually monitored from coarse resolution images. The image set was analyzed by considering an ordinal classification of the NDVI to account for the cumulative effect of differences of near-infrared spectral resolutions, the temperature anomalies, and atmospheric conditions. An increasing trend of the median values in the low, intermediate and high NDVI classes is clearly marked while accounting for variations attributed to cross-sensor radiometry, phenology and atmospheric disturbances. An encroachment of the forest on the tundra for the whole study area was estimated at 0 to 60 m, depending on the period of observation, as calculated by the difference between the median retreat and advance of an estimated location of the tree line. In small sections, advances and retreats of up to 320 m are reported for the most recent four- and seven-year periods of observations. © 2013 by the authors; licensee MDPI, Basel, Switzerland. Source