Biomedical subjects

Réjean Samson

Publications and source records attributed to Réjean Samson.

8 recordsLinked to original sources

PubMed2006

Effect of 2,4-D contamination on soil functional stability evaluated using the relative soil stability index (RSSI).

Soil functional stability is the capacity of soil functions to resist and recover from an environmental perturbation and can be used to evaluate soil health. It can be influenced by the presence of xenobiotics such as herbicides. The impact of a fresh 2,4-D contamination (36 mg kg(-1) dry soil) on soil functional stability was evaluated by comparing the capacity of soil enzyme activities to resist and recover from a heat perturbation for both a clean and 2,4-D-contaminated soil. The functional stabilities of the soils (uniform sands, pH 6.9, 7% (w/w) organic matter) were calculated using the relative soil stability index (RSSI). The RSSI scores indicate the proportion of potential enzyme activity the soil retains after a perturbation compared to the potential activity of an unperturbed soil. Six extra-cellular enzyme activities (acid and alkaline phosphatases, arylsulfatase, urease, protease and beta-glucosidase) were monitored in soil microcosms during a 15-day period. During this period, a 60 degrees C heat perturbation was applied to the soil for 24 h. The activities of arylsulfatase and protease were found to be the most stable following heat perturbation obtaining the highest RSSI scores (87% and 77%, respectively). Urease activity showed the lowest RSSI score (38%). Although all enzyme activities were inhibited by the presence of 2,4-D, the RSSI results indicated that contamination lowered the stability of only three enzyme activities (arylsulfatase, beta-glucosidase and urease). The RSSI adequately described resistance, recovery and recovery rate parameters and enabled differentiation between functional stabilities of clean and contaminated soil and between different soil types.

2,4-Dichlorophenoxyacetic Acid↗

PubMed2006

Long-term persistence of a nutrient-starved biofilm in a limestone fracture.

The persistence of biofilms is a key element of the biobarrier concept applied to fractured rock. After a 43-day biostimulation with molasses for the biofilm growth (phase I), the effects of a 179-day starvation on the persistence of the biofilm (phase II) were investigated in a single-fractured limestone apparatus equipped to detect small changes in hydraulic conductivity (K) (cm min(-1)). The K in the central fracture section (Kf) decreased by 4.6 logs between days 0 and 167 and increased by 1.3 logs between days 167 and 222, leading to an overall 3.3-logs reduction for the 222-day experiment. Accumulation of rod- and filamentous-shaped bacteria and deposition of minerals were thought to account for the decrease in Kf. Even though the filamentous bacterial cells possibly enhanced the stability of the developing biofilm, increases in Kf became more frequent after 100 days of operation. This decrease in stability was presumably related to sloughing events, which were in turn attributed to a combination of processes, including nutrient deprivation, the release of deposited minerals, decreasing fluid flowrate, and endogenous decay as part of biofilm ageing. This study indicates that biofilms developed in fractures can persist for extended periods at reduced K when exposed to a long-term starvation.

Bacteria↗

PubMed2004

A proactive approach can make site remediation less expensive.

Without any incentive to clean up a contaminated site, remediation is often delayed until the site owner is compelled to act by regulatory agencies. In such a context, the selected technology is typically the one that will reach the remediation goals as quickly as possible. Unfortunately, this criterion is often met by overly expensive technologies, resulting in high and sometimes unaffordable total remediation costs, leading to a remediation with a negative net benefit. This study examines the effects of time constraint and benefit value on the optimal remediation strategy for a diesel-contaminated site. This strategy is developed using the technico-economic model METEORS, which takes into account the technology's effectiveness, the uncertainty of the level of contamination, and the possibility of reducing this uncertainty through either an additional characterization (before selecting and applying a technology) or the monitoring of the remediation technology (during its use). Results of simulations with both economic and temporal constraints support a proactive approach to site remediation.

Biodegradation, Environmental↗

PubMed2003

A technicoeconomic approach for the selection of a site remediation strategy--part B: model application.

Different tools, such as a screening matrix or decision framework, are available to select a remediation technology to treat a contaminated site. However, unless these methods can point out the appropriate technology in regards to the decision-maker's knowledge about the contaminated site, they are less useful to evaluate both the technical effectiveness and the cost of the remediation, and to assess different remediation strategies from either future data acquisition or the use of an irreversible remediation technology. A model developed to allow such evaluations has been used to simulate the remediation of a virtual contaminated site. From this, four remediation recommendations have been made. These recommendations are guidelines for the build up of a remediation strategy that would both maximize the effectiveness of the decontamination and minimize its total cost.

Cost-Benefit Analysis↗

PubMed2002

A technicoeconomic approach for the selection of a site remediation strategy--part A: theory.

A technicoeconomic model is developed to select an optimal strategy for the remediation of a contaminated site and to determine the value of this remediation strategy. The model is an extension of actual cost-benefit analysis, with consideration of "irreversible" remediation technology choices, technology effectiveness, and uncertainty on the site's level of contamination. The model considers the possibility of reducing uncertainty by both acquiring more and better information on the level of contamination and by offering the decision-maker the opportunity to reevaluate his decision and switch to a more appropriate technology. It is believed that this model will help decision-makers in the selection of a remediation strategy by presenting all potentially feasible strategies, and how uncertainty on the site's level of contamination affects these strategies.

Decision Making↗

PubMed2002

Multiple factor design for reactive mixture selection for use in reactive walls in mine drainage treatment.

Sulfate-reducing reactive walls installed in situ in the path of acid mine drainage contaminated groundwater, present a promising passive treatment technology. However, a rigorous and methodical selection of the most appropriate reactive mixture composition still needs to be investigated. The aim of this study was the selection of the most reactive medium using a multiple factor design and the modeling of the sulfate-reduction rate. Reactivity of 17 mixtures was assessed in batch reactors (in duplicates) using a synthetic AMD. Results indicate that within 41 days, sulfate concentrations decreased from initial concentrations of 2,000-3,200 mg/l to final concentrations of <90 mg/l. Metal removal efficiencies ranged between 51-84% for Ni and 73-93% for Zn. Generated sulfate-reduction rate predictive models which had very satisfactory parameters (R2 = 0.86, F = 62.38 (p-level < 10(-13)) and R2 = 0.90. F = 62.30 (p-level < 10(-13))) identified poultry manure and two other carbon sources as the critical variables for sulfate-reduction rate.

Animals↗

PubMedDate not supplied

Modelling the dynamics of pentachlorophenol bioavailability in column experiments.

The aqueous-phase concentration of an organic pollutant found in a subsurface environment is often assumed to be its bioavailable concentration. However, the aqueous-phase concentration does not adequately reflect the dynamics of contaminant availability to microbes in flow-through systems. This paper assesses the effects of interacting processes such as sorption, biodegradation, and transport on contaminant bioavailability, and the fraction of the bioavailable contaminant that is taken up by microbes. The evolution of the bioavailable and uptake fractions is studied in two ways. Firstly, column experiments are conducted in which the introduced contaminant (pentachlorophenol, PCP) can flow through the columns, be consumed by microorganisms, or be sorbed by a solid matrix. Secondly, a phenomenological model (Flow/Sink/Reservoir model) that illustrates the dynamic nature of bioavailability and quantifies the uptake fraction is developed, based on a flow balance. Results show that after 60 h of sorption-limited bioavailability, the microorganisms induce desorption, so that the sorbed pool becomes bioavailable and bioavailability is limited by the PCP injection rate. A conclusion is drawn that the aqueous-phase concentration is a poor indicator of contaminant bioavailability to microbes.

Adsorption↗

PubMedDate not supplied

Occurrence of metals in soil and ground water near chromated copper arsenate-treated utility poles.

To thoroughly investigate the metal contamination around chromated copper arsenate (CCA)/polyethylene glycol (PEG)-treated utility poles, a total of 189 soil samples obtained from different depths and distances near six treated poles in the Montreal area (Canada) were analyzed for Cu, Cr, and As content. Various soil physicochemical properties were also determined. Ground water samples collected below the poles were analyzed for metals and bioassays with Daphnia magna were conducted. Generally, sandy soils had lower contaminant levels than clayey and organic soils. Copper concentrations in soil were highest followed by As and Cr. The highest Cu (1460 +/- 677 mg kg(-1)), As (410 +/- 150 mg kg(-1)), and Cr (287 +/- 32 mg kg(-1)) concentrations were found at the ground line and immediately adjacent to the pole. Contaminant levels then decreased with distance, approaching background levels within 0.1 m from the pole for Cr and 0.5 m for Cu and As. Chromium and Cu levels generally approached background levels at a depth of 0.5 m. Average As content near the pole on all study sites was three to eight times higher than Quebec's Level C criterion (50 mg kg(-1)), although it dropped to 31 mg kg(-1) at 0.1 m. Results also showed that As persisted up to 1 m in soil depth (17-54 mg kg(-1)). Copper and Cr concentrations in ground water samples were always <1.000 mg L(-1) and <0.05 mg L(-1), respectively and Cr(VI) was <0.02 mg L(-1). One sample contained an As concentration >0.025 mg L(-1) but bioassays showed that, overall, ground water had a low ecotoxic potential.

Aluminum Silicates↗