A new test of random walks in heterogeneous environments

Environmental heterogeneities can change animal movement in two different manners. First, they can modify movement characteristics (move lengths or turning angles), in which case the movement remains of the diffusive kind. Second, they can bias displacement towards a particular direction in which case it becomes non-diffusive. We propose in this paper a simple method that only requires computing the mean length of a sample of trajectories in some bounded area to distinguish between these two kinds of movement. We show through simulations that the method allows to detect the presence of heterogeneities that orient animal movement. We apply it to experimental trajectories of Messor sancta ants engaged in corpse aggregation to show that their displacement is oriented at the contact of the formed corpse piles and that their trajectories become non-diffusive.     

Effects of a major municipal effluent on the St. Lawrence River: A case study

The St. Lawrence River (SLR) is the second largest waterway in North America. The discharge of the City of Montreal wastewater treatment plant (WWTP) represents the largest volume of treated wastewaters being released into the river. It also ranks as the largest sewage treatment plant of its kind in North America. Over the last decade, intensive multidisciplinary research has focused on assessing the impacts of Montreal wastewater effluents on the SLR. We describe the major findings of these investigations, including the determination of the fate of contaminants, bioaccumulation in fish and invertebrates, ecotoxicological measurements of aquatic animal health, evaluation of endocrine disruption, parasitism in fish, and combined effects of multiple stressors on the SLR. Impacts of the effluents from the WWTP on aquatic organisms from the SLR are both toxicological and ecological, demonstrating the need for an integrated view of the impacts of municipal effluents on aquatic ecosystems.     

Distribution of carbon 14 in the terrestrial environment close to French nuclear power plants

For 10 years, (14)C measurements have been performed around French nuclear power plant sites, both in zones influenced and zones not influenced by gaseous releases. Examining the results from these measurements in the terrestrial environment shows that the discharges have a very slight impact on the radiocarbon level (with a relative increase in the specific activity of the order of 3 Bqkg(-1)C in the influenced areas). In correlation, there is a near-negligible increase in dose, on average less than 0.1 microSvyr(-1), with reference to a dose from background radiation, which is of the order of 10 microSvyr(-1). The deltaC13 values are very similar between the influenced zone and the non-influenced zone, with a mean of -27 per thousand. The mean DeltaC14 varies from 101 per thousand in the non-influenced zone to 123 per thousand in the influenced zone. Moreover, a general reduction in (14)C concentration was found, with a time constant of the order of 95 years. The current level of (14)C specific activity in terrestrial environment is estimated to be 242+/-6 Bqkg(-1)C.     

Directionally drilled horizontal wells offer cost savings and technical advantages over alternative soil and groundwater remediation systems

Directionally drilled horizontal wells offer the opportunity for significant cost savings and technical advantages over alternative trenched well and vertical well soil and groundwater remediation systems in many cases. The magnitude of the cost savings is a function of the remediation technology deployed and the values placed on the reduction of site impacts, dramatic reduction in the time required to achieve site remediation goals and requirements, the ability of horizontal well remediation to easily treat normally recalcitrant contaminants such as MTBE, and the ability to drill under paved areas, operating plants, residential areas, landfills, lagoons, waterways, ponds, basins, and other areas that are normally difficult or impossible to access with conventional drilling or trenching methods. In addition to improvements in site access capabilities, horizontal wells have been found capable of addressing contaminants that vertical wells do not readily treat, even with the same remediation technology deployed, especially if air‐based remediation technologies are deployed. With biosparging, for example, greater treatment capabilities of horizontal wells over vertical wells are attributed to greater oxygen flux over a broader area, a larger treatment zone, and extremely prolonged residence of groundwater contaminants in the aerobic treatment area, typically months or years. This article describes the use of directionally drilled horizontal wells for application of a variety of treatment technologies and includes costs of various options with a detailed comparison of biosparging options. © 2002 Wiley Periodicals, Inc.     

Do the designated drivers of college students stay sober?

PROBLEM: By numerous accounts, alcohol abuse is considered the number one drug problem facing young people today. Alcohol consumption and its negative consequences, especially those due to drinking and driving, continue to have devastating effects on the college student population. METHOD: This field study examined the blood alcohol concentration (BAC) levels of male and female designated drivers (DD), non-DD, and their respective passengers as they were leaving drinking establishments in a university town. Also investigated were the effects of group size and gender on DD use. RESULTS: A 2 Gender x 2 Driver type (DD vs. non-DD) analysis of variance (ANOVA) for BAC indicated significant main effects for Gender and Driver type, with higher BAC for men and non-DD (p's<.001). A significant Gender x Driver type interaction (p<.05) was primarily due to female DD having lower BAC than male DD. In addition, larger groups were more likely to have a DD. IMPACT ON INDUSTRY: Results indicate that the success of DD programs may be influenced by group size and a DD's gender. While larger groups are more likely to have a DD, students riding home with a male DD may still be at risk for the negative consequences of drunk driving.     

Site-selection bias and apparent population declines in long-term studies

Detecting population declines is a critical task for conservation biology. Logistical difficulties and the spatiotemporal variability of populations make estimation of population declines difficult. For statistical reasons, estimates of population decline may be biased when study sites are chosen based on abundance of the focal species. In this situation, apparent population declines are likely to be detected even if there is no decline. This site-selection bias is mentioned in the literature but is not well known. We used simulations and real population data to examine the effects of site-selection biases on inferences about population trends. We used a left-censoring method to detect population-size patterns consistent with site-selection bias. The site-selection bias is an important consideration for conservation biologists, and we offer suggestions for minimizing or mitigating it in study design and analysis. Article impact statement: Estimates of population declines are biased if studies begin in large populations, and time-series data show a signature of such an effect.     

Environmental impact of sunscreen nanomaterials: ecotoxicity and genotoxicity of altered TiO2 nanocomposites on Vicia faba

Mineral sunscreen nanocomposites, based on a nano-TiO₂ core, coated with aluminium hydroxide and dimethicone films, were submitted to an artificial ageing process. The resulting Altered TiO₂ Nanocomposites (ATN) were then tested in the liquid phase on the plant model Vicia faba, which was exposed 48 h to three nominal concentrations: 5, 25 and 50 mg ATN/L. Plant growth, photosystem II maximum quantum yield, genotoxicity (micronucleus test) and phytochelatins levels showed no change compared to controls. Oxidative stress biomarkers remained unchanged in shoots while in roots, glutathione reductase activity decreased at 50 mg ATN/L and ascorbate peroxidase activity decreased for 5 and 25 mg ATN/L. Nevertheless, despite the weak response of biological endpoints, ICP-MS measurements revealed high Ti and Al concentrations in roots, and X-ray fluorescence micro-spectroscopy revealed titanium internalization in superficial root tissues. Eventual long-term effects on plants may occur.     

Coping with job insecurity: How does personality make a difference?

Reversing a long-standing tradition of neglect, occupational stress researchers have recently rediscovered the importance of personality disposition in understanding the transformation of stresses into strains and strains into symptoms. Two recent studies of job insecurity in our laboratory provided a fortuitous opportunity to explore the extent of this influence and the mechanisms by which it operates. The most important of our findings is that positive personality attributes impact as strongly on mental health as does negative personality disposition, albeit in the opposite direction. Thus, personality can cushion, as well as aggravate, the impact of occupational stress.     

Condition of larval cod (Gadus morhua) off southwest Nova Scotia in 1983 in relation to plankton abundance and temperature

In our study of the condition of larval cod (Gadus morhua) collected off southwest Nova Scotia in winter-spring, 1983, we (1) examined relationships between larval condition and ambient environmental conditions, and (2) compared the use of simple morphometric indices of larval condition and of multivariate statistics to obtain information relevant to larval condition. Twelve indices of relative condition were obtained, based upon seven measurements made on each larva, and a principal component (PC) analysis was performed on these condition indices. Most condition indices and the first PC were significantly correlated with numbers of nauplii and of zooplankters per m³ in the water column, which are direct measures of food available to the larvae, but not to less direct measures of environmental quality for the larvae, such as plankton displacement volume or chlorophyll concentration. Conventional indices based upon relations of dry weight or body height at the anus to length were most sensitive to environmental conditions. There was no apparent advantage in performing a multivariate analysis based upon a larger series of measurements.