Integration of toxicological and chemical tools to assess the bioavailability of metals and energetic compounds in contaminated soils

Bioavailability is critical for understanding effects that might result from exposure of biota to contaminated soils. Soils from military range and training areas (RTAs) are contaminated principally by energetic materials (EM) and metals. Their chemical characteristics are relatively well known and toxicity assessment of soils from RTAs are in some cases available. However, bioavailability on these sites needs to be comprehensively characterized. A holistic approach to bioavailability, incorporating both chemical and earthworm toxicological indicators, was applied to soils from an anti-tank firing range at a Canadian Forces Base. Results showed that HMX and the metals Zn, Pb, Bi and Cd, though not consistently the prevailing toxicants, were the most accessible to earthworms. Some metals (notably Cu, Zn, Cr and Bi) were also accumulated in earthworm tissue but those were not necessarily expected given their bioaccessibility (i.e., the chemical availability of contaminants in the environment for the organisms) at the beginning of the exposure. The tested soils impaired earthworm reproduction and reduced adult growth. Measurement of selected sublethal parameters indicated that lysosomal integrity (determined as the neutral red retention time--NRRT) was decreased, while elevated superoxide dismutase (SOD) activity suggested that earthworms experienced oxidative stress. The correspondence between the NRRT and metal contamination pattern suggested that metals may be the main cause of lysosomal disruption in EM-contaminated soils. The approach to bioavailability appraisal adopted in this case appears to be a promising practice for site-specific assessment of contaminated land.     

A New Test Method for Determining Biodegradation of Plastic Material Under Controlled Aerobic Conditions in a Soil-Simulation Solid Environment

A new test method is described for assessing biodegradation of plastic material under simulated soil conditions. An inert substrate can be activated with soil extract and nutrient and used in place of soil in biodegradation tests. The biodegradation level is evaluated by determining the carbon dioxide (CO₂) production released by the test reactors. Effects of substrate nature, solution pH, nutrient composition, soil extract concentration, and activation duration on CO₂ production were investigated, and the experimental conditions were optimized. Results obtained with cellulose showed a biodegradation rate of 80% within 28 days. Moreover, with this kind of substrate, reaction products and residues can be easily extracted and analysed.     

Modelling Easily Biodegradability of Materials in Liquid Medium-Relationship Between Structure and Biodegradability

In the present project, twenty materials (e.g., polyhydroxybutyrate-hydroxyvalerate, polycaprolactone, cellulose acetate, polyacticacid, polyethylene), representing varied biodegradability levels were studied. An aerobic respirometric test, based on the CEN Draft, was setup. The biodegradability of each plastic film was evaluated by measuring the percentage of carbon converted into CO₂ during 35 days. The values of the CO₂ production were plotted versus days as a cumulative function. In order to reduce its number of points, the cumulative curve was modeled using a sigmoïd function (Hill sigmoïd). This model was compared to one found in the literature. A _i ² test showed that the biodegradation curve was more accurately fitted with the model than the previous one. Three kinetic parameters were determined by this Hill model: one represents the maximal percentage of carbon converted into CO₂, the second the half-life time in days of the degrading part of the material and the third one the curve radius.In addition, the following analyses were carried out on each sample: elemental analysis, thickness, hydrophobicity and surface free energy measurements. In order to compress the information and to keep only relevant pieces, these parameters were submitted to a Principal Component Analysis. PCA found linear combinations of variables that describe major trends in the data. The two principal components which separate groups of materials were closely related to a chemical and a physical axis respectively. Materials showing a high biodegradability were related to high oxygen (and nitrogen) contents and low hydrophobicity: Material thickness did not influence the likeliness to biodegradability described by the maximum biodegradation rate. Finally, this study established the correlation between the biodegradation and the structure of biopolymers.     

Between introgression events and fragmentation, islands are the last refuge for the American crocodile in Caribbean Mexico

Habitat loss and degradation in the Mexican Caribbean, caused by the development of tourism, have decreased the potential nesting area for the American crocodile (Crocodylus acutus) and have fragmented the populations of the Yucatan peninsula. Our study investigated five populations (three continental: North, South, Sian Ka’an, and two insular: Cozumel, Banco Chinchorro) of C. acutus in the Mexican Caribbean using seven different inter simple sequence repeat (ISSR) markers as tools for genetic variability and population differentiation. Three classification methods were tested and compared: distance analysis, self-organizing map, and Bayesian methods, to evaluate the resolution of each method with ISSR markers. The 77 loci selected revealed a high variability between populations (polymorphism from 17% for Sian Ka’an to 75% for Banco Chinchorro) with a total polymorphism of 84% and a global coefficient of gene differentiation (G _ST ) of 0.296, but low values of Nei’s Gene diversity (from 0.065 for Sian Ka’an to 0.233 for Banco Chinchorro). Our results suggest elevated inbreeding in all local populations with higher indices for Banco Chinchorro and lower indices for Sian Ka’an. Three independent classification methods gave similar results, and suggested that most continental individuals are admixtures, with different levels of introgression, with the sympatric species Crocodylus moreletii. We propose that the islands/atolls remain the sole areas with genetically “pure” American crocodiles and we discuss these results for future conservation of this endangered crocodile species.     

Interaction of carbonaceous nanomaterials with wastewater biomass

Increasing production and use of carbonaceous nanomaterials (NMs) will increase their release to the sewer system and to municipal wastewater treatment plants. There is little quantitative knowledge on the removal of multi-walled carbon nanotubes (MWCNTs), graphene oxide (GO), or few-layer graphene (FLG) from wastewater into the wastewater biomass. As such, we investigated the quantification of GO and MWCNTs by UV-Vis spectrophotometry, and FLG using programmable thermal analysis (PTA), respectively. We further explored the removal of pristine and oxidized MWCNTs (O-MWCNTs), GO, and FLG in a biomass suspension. At least 96% of pristine and O-MWCNTs were removed from the water phase through aggregation and 30-min settling in presence or absence of biomass with an initial MWCNT concentration of 25 mg·L⁻¹. Only 65% of GO was removed with biomass concentration at or above 1,000 mg·L⁻¹ as total suspended solids (TSS) with the initial GO concentration of 25 mg·L⁻¹. As UV-Vis spectrophotometry does not work well on quantification of FLG, we studied the removal of FLG at a lower biomass concentration (50 mg TSS·L⁻¹) using PTA, which showed a 16% removal of FLG with an initial concentration of 1 mg·L⁻¹. The removal data for GO and FLG were fitted using the Freundlich equation (R² = 0.55, 0.94, respectively). The data presented in this study for carbonaceous NM removal from wastewater provides quantitative information for environmental exposure modeling and life cycle assessment.     

Looking for the clock mechanism responsible for circatidal behavior in the oyster Crassostrea gigas

Valve activity rhythm of the oyster Crassostrea gigas is mainly driven by tides in the field, but in the laboratory, only a circadian clock mechanism has been demonstrated. In an attempt to reconcile these results, the mechanisms underlying the circatidal rhythm were studied in the laboratory under different entrainment or free-running regimes and in the field at Arcachon (44°39′N/1°09′W) in February–April 2011). Results confirm the existence of a circadian clock in C. gigas. Under entrainment regimes (12-h dark/12-h light photoperiod and tidal cycles simulated by a reversing current flow), oysters exhibited both circadian and circatidal cycles. Under free-running conditions (e.g., continuous darkness), the endogenous rhythm appeared to be circadian. There was no experimental evidence for an endogenous circatidal rhythm, even in oysters just transferred from the field, where a clear tidal cycle was expressed. There are two possible mechanisms to explain tidal behavior in C. gigas: an exogenous tidal cue that drives tidal activity and masks the circadian rhythm and an endogenous circatidal clock that is sensitive to tidal zeitgebers and runs at tidal frequency.