Transport of particulate material and dissolved tracer in a highly permeable porous medium: comparison of the transfer parameters

We are experimentally studying, by means of short-pulse injection, the transport and deposition kinetics of suspended particles (silts of the order of 10 microm) in a highly permeable medium consisting of a column of gravel. In our experiments, the breakthrough curves (BTCs) are well described by analytical solutions of a convection/dispersion model with first-order deposition kinetics. All the transport parameters calculated by the model for both particles and dissolved tracer depend on the flow rate. We demonstrate the existence of a critical flow rate, determined experimentally, beyond which the transfer time for the particles is longer than that for the tracer. This phenomenon is unusual in comparison with the results available in the literature. The increase in transfer time of particles in comparison to tracer leads us to assume a purely mechanical phenomenon, that is, collision between particles and grains of the medium with instantaneous reset in motion when the flow rate is sufficient to avoid settling. Thanks to the polydispersivity of the injected suspension and the control of grain size at the outlet, it can also be determined that the coarser particles are recovered before the finer particles, as expected when one considers the size-exclusion effect.     

Seasonal abundance and toxicity of the dinoflagellate Gambierdiscus spp. (Dinophyceae), the causative agent of ciguatera in Tahiti, French Polynesia

The benthic dinoflagellate Gambierdiscus spp. is the primary causative agent of ciguatera fish poisoning in French Polynesia. However, the initiation of ciguatera outbreaks and the factors that control ciguatoxin production in this dinoflagellate are still poorly understood. In this paper, we present some original data concerning the seasonal abundance and toxicity of natural populations of Gambierdiscus spp. based on a long-term survey in a ciguateric site of the island of Tahiti. From February 1993 to December 1997, Gambierdiscus spp. population densities were monitored weekly in the Atimaono barrier reef of Papara in relation to temperature and salinity. Densities peaked at 4992 cells g⁻¹ in October 1994 and constituted ≥1000 cells g⁻¹ on several occasions. A total of 58 blooms were recorded in the area, of which 65% occurred in 1995 and 1996 alone. Our data confirmed the high endemicity of Gambierdiscus spp. in the Papara area. Refined analysis of our raw data by a principal-component analysis of processes (PCAP) revealed a seasonality in cell densities from February 1993 to May 1995. During this period, Gambierdiscus spp. populations tended to reach maximum abundance at the beginning and end of the hot season. In contrast, salinity did not appear to be a determining factor in the seasonal abundance of this dinoflagellate. The noticeable increase in both peak densities and frequency of blooms further noticed in 1995 and 1996 was preceded by unusually high water temperatures in January to April 1994, concomitant with a severe coral-bleaching episode. During the course of the study, a total of 303 × 10⁶ cells obtained from 48 successive blooms was harvested. Toxicity screening revealed that toxin production was maximum from October 1994 through December 1996. No correlation was found between toxicity of these blooms and their biomass nor the seasonal pattern of temperatures. It is suggested that the toxicity of naturally-occurring blooms of Gambierdiscus spp. and, consequently, the severity of ciguatera incidents in a given area, is mainly dependent on the clonal nature of cells which coexist within local populations of this dinoflagellate. Received: 12 October 1998 / Accepted: 15 June 1999     

Critical review for the quantification of leachate production: Evaluation example for the “Oum Azza” public landfill in Rabat city,Morocco

The estimation of leachate quantities produced in landfills is necessary to dimension the treatment plants allowing to reduce the polluting load of these effluents and consequently avoid their negative impacts on the environment. Different leachate quantification methods were used in this study to assess the leachate volume produced at the Oum Azza landfill. The water balance method give comparable estimations of leachate production to the Ouled Berjal landfill ratio. The first method showed average values between 487 and 495 m³/day for 2015, 2018, and 2019, and at the same time, the second method gave values between 470 and 477 m³/day for the same years. In contrast, the World Bank ratio showed high values that vary between 2260 and 2295 m³/day for 2015, 2018, and 2019. The on-site data and the statistical analysis showed us that the World Bank ratio is not adapted for the estimation of the leachates produced in Oum Azza landfill, while the water balance and the ratio of Ouled Berjal landfill allowed to give comparable results to reality.     

Sorption of Isoproturon and Dimetomorph on lignocellulose from wheat

The adsorption of toxic chemicals on solid substates is a potential means to clean polluted waters. Here, the adsorption of two pesticides, isoproturon and dimetomorph, on lignocellulose extracted from wheat straw is investigated at 20 °C using batch adsorption experiments. Here, we show that the sorption of both pesticides is independent of pH. The sorption capacity of lignocellulose is evaluated. We show that the presence of metallic cations has no influence on the retention capacity of lignocellulose towards pesticides.     

Characterization of phosphate rock and phosphogypsum from Gabes phosphate fertilizer factories (SE Tunisia): high mining potential and implications for environmental protection

Environmental Science and Pollution Research - Since the establishment of the coastal industrial complex in Gabes city (Gulf of Gabes, SE Tunisia), hundred million tons of untreated phosphogypsum...     

Habitat, Landscape and Bird Composition in Mountain Forest Fragments

The study attempts to separate the effects of forest fragmentation related to landscape (patch area, isolation) and habitat (altitude, vegetation structure) on bird community composition in a mountain pine forest. Bird composition was related, using a multivariate approach (canonical correspondence analyses), to either habitat or to landscape, eliminating the effect of habitat statistically. Bird composition and species richness varied with patch area and isolation from large pine stands, but this effect could be assigned principally to variation in vegetation structure and altitude. Another effect, that of increasing occurrence and numbers of Anthus trivialis with decreasing distance to nearest low-altitude forest, could be assigned to both habitat (grass cover) and landscape (connectivity effects). Management implications are drawn from the results.     

Characterisation of particulate exposure during fireworks displays

Little is known about the level and content of exposure to fine particles (PM_2.5) among persons who attend fireworks displays and those who live nearby. An evaluation of the levels of PM_2.5 and their elemental content was carried out during the nine launches of the 2007 Montréal International Fireworks Competition. For each event, a prediction of the location of the firework plume was obtained from the Canadian Meteorological Centre (CMC) of the Meteorological Service of Canada. PM_2.5 was measured continuously with a photometer (Sidepak?, TSI) within the predicted plume location (“predicted sites”), and integrated samples were collected using portable personal samplers. An additional sampler was located on a nearby roof (“fixed site”). The elemental composition of the collected PM_2.5 samples from the “predicted sites” was determined using both a non-destructive energy dispersive ED-XRF method and an ICP-MS method with a near-total microwave-assisted acid digestion. The elemental composition of the “fixed site” samples was determined by the ICP-MS with the near-total digestion method. The highest PM_2.5 levels reached nearly 10 000 μg m^?3, roughly 1000 times background levels. Elements such as K, Cl, Al, Mg and Ti were markedly higher in plume-exposed filters. This study shows that 1) persons in the plume and in close proximity to the launch site may be exposed to extremely high levels of PM_2.5 for the duration of the display and, 2) that the plume contains specific elements for which little is known of their acute cardio-respiratory toxicity.