The effect of cyclic aerobic-anoxic conditions on biodegradation of benzoate.

The response of a mixed microbial culture to cyclic aerobic and anoxic (denitrifying) conditions was studied in a chemostat with a 48-hour hydraulic residence time receiving a feed containing benzoate and pyruvate. When the cyclic conditions were 3-hour aerobic and 9-hour anoxic, the bacteria-degraded benzoate aerobically via the catechol 2,3-dioxygenase (C23DO) pathway. The quantity of C23DO remained constant throughout the anoxic period but decreased during the initial portion of the aerobic period before returning to the level present in the anoxic period. Anoxic biodegradation of benzoate was via benzoyl-CoA reductase, which remained constant regardless of the redox condition. The aerobic benzoate uptake capability (AeBUC) of the culture increased during the aerobic period but decreased during the anoxic period. The anoxic benzoate uptake capability (AnBUC) exhibited the opposite response. When the cycle was 6-hour aerobic and 6-hour anoxic, aerobic biodegradation of benzoate proceeded via the protocatechuate 4,5-dioxygenase (P45DO) pathway. The P45DO activity decreased early in the aerobic period, but then increased to the level present during the anoxic period. The level of benzoyl-CoA reductase was constant throughout the cycle. Furthermore, AeBUC and AnBUC responded in much the same way as in the 3/9-hour chemostat. During a 9-hour aerobic and 3-hour anoxic cycle, the culture synthesized both P45DO and C23DO, with the former having significantly higher activity. Unlike the other two cycles, AeBUC changed little during the aerobic period, although AnBUC decreased. The culture was well-adapted to the cyclic conditions as evidenced by the lack of accumulation of either substrate during any cycle tested. This suggests that cyclic aerobic-anoxic processes can be used in industrial wastewater-treatment facilities receiving significant quantities of simple aromatic compounds like benzoate. However, the results showed that the kinetics of benzoate degradation were different under aerobic and anoxic conditions, a situation that must be considered when modeling cyclic bioreactors receiving aromatic compounds.     

Surfactant solubilization of hydrophobic compounds in soil and water

The soil/water partition coefficient (K_d) of hexachlorobenzene (HCB) ranged from 220 1/kg to 1800 1/kg for eight soils having a wide range of physico-chemical properties. K_d normalised to soil organic carbon (K_oc) was found to be 28000 ± 4800 1/kg. Anionic surfactant dodecylsulphate (DS) present at concentrations above the critical micellar concentration (CMC) caused reductions in the apparent soil/water partition coefficient (K_d ^*) in the range of 3–26 times for most soils and up to 36–91 times for sandy soils. Below CMC, at environmentally relevant surfactant concentrations, K_d ^* was reduced by a factor of 1–13. For clay and calcareous soils significant adsorption/complexation/precipitation of DS occurred. At the lowest DS concentration this produced a two-fold increase in K_d ^*. At increasing DS concentrations this effect was shielded by the solubihzing effect from DS. Monomer (K_mn) and micellar (K_mc) surfactant/water partition coefficients for HCB were determined to be, 980 ± 190 1/kg and 21000 ± 1600 1/kg, respectively.     

Influence of air pollution on the incidence of respiratory tract neoplasm

To evaluate the possible influence of air pollutants on the incidence of respiratory tract neoplasm we studied 12 S?o Paulo City districts where air pollution is observed. We collected data on pollutants from 1981-1990 and correlated it with the incidence of larynx and lung neoplasms in 1997. Ozone was the pollutant that best correlated with the incidence of neoplasm. The correlation coefficients were 0.7234 (p=0.277) and 0.9929 (p=0.007) for lung and larynx cancer, respectively. There may be a relationship between air pollution and the incidence of respiratory tract neoplasm. This study, however, does not allow us to conclude that there is a causal relationship.     

Generation and stability of bentonite colloids at the bentonite/granite interface of a deep geological radioactive waste repository

The possible mechanisms of colloid generation at the near field/far field interface of a radioactive repository have been investigated by means of novel column experiments simulating the granite/bentonite boundary, both in dynamic and in quasi-static water flow conditions. It has been shown that solid particles and colloids can be detached from the bulk and mobilised by the water flow. The higher the flow rate, the higher the concentration of particles found in the water, according to an erosion process. However, the gel formation and the intrinsic tactoid structure of the clay play an important role in the submicron particle generation even in the compacted clay and in a confined system. In fact, once a bentonite gel is formed, in the regions where the clay is contacted with water, clay colloids can be formed even in quasi-static flow conditions. The potential relevance of these colloids in radionuclide transport has been studied by evaluating their stability in different chemical environments. The coagulation kinetics of natural bentonite colloids was experimentally studied as a function of the ionic strength and pH, by means of time-resolved light scattering techniques. It has been shown that these colloids are very stable in low saline (approximately 1 x 10(-3) M) and alkaline (pH > or = 8) waters.     

Anaerobic digestion of thermo-oxidized excess municipal sludge.

The effect of a thermo-oxidative co-treatment placed between the two reactors of two-stage anaerobic digestion of excess municipal sludge was studied. The oxidant used was hydrogen peroxide (H2O2), and moderate temperatures below the boiling point of water were considered. The first experiment was to elucidate the effect of two different temperatures (65 and 90 degrees C) of oxidation using a constant oxidant dose of 1.0 g H2O2/g influent volatile suspended solids (VSSinfluent). The use of thermo-oxidative co-treatment increased overall solids destruction by 24.9 and 33.5%, respectively, when operating at 65 and 90 degrees C, respectively. Because of this significant effect of temperature on the performance of the process, a second experiment was conducted using the higher temperature of 90 degrees C while decreasing the hydrogen peroxide dosage to 0.5, 0.25, and 0.1 g H2O2/g VSSinfluent. An increase in solids destruction of 13.9, 18.9, and 25.6% was observed when the thermo-oxidative co-treatment was used using oxidant dosages of 0.1, 0.25, and 0.5 g H2O2/g VSSinfluent, respectively.     

Organochlorine and butyltin residues in walleye pollock (Theragra chalcogramma) from Bering Sea, Gulf of Alaska and Japan Sea

Persistent organochlorine (OC) and toxic butyltin compounds (BTs) were determined in walleye pollock (Theragra chalcogramma) collected from Gulf of Alaska, Bering Sea and Japan Sea, during 1991 and 1992. Polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDTs) and its metabolites were the most abundant compounds ranging up to 3200 and 2500 ng/g on lipid weight, respectively, followed by chlordane compounds (CHLs), hexachlorocyclohexane isomers (HCHs) and hexachlorobenzene (HCB) in the liver of walleye pollock. Concentrations of HCHs and HCB in walleye pollock from these remote areas were higher than those in fishes from the western North Pacific and Japanese coastal waters, indicating atmospheric transport of these compounds to higher latitude regions such as Bering Sea and Gulf of Alaska and/or local input around northern Japan Sea. The concentrations of other OCs were generally comparable to those in fishes from North Pacific Ocean and Japanese waters but significantly lower than in cod-like fishes from North Atlantic and European countries. Among sampling locations, walleye pollock from Japan Sea showed higher concentrations of DDTs and HCHs compared to fishes from Bering Sea and Gulf of Alaska, suggesting greater input of these compounds around Japan Sea. Slower declining trend of DDTs and CHLs and an increasing pattern of PCBs concentrations were found in walleye pollock from Bering Sea during 1982-1992. This may imply a continuous input of these compounds by long-range transport and/or long-term persistency in these cold regions. Compared to the fishes from Japan Sea, walleye pollock from Bering Sea and Gulf of Alaska showed higher proportions of alpha-HCH and p,p'-DDE in the composition of HCH isomers and DDT compounds, respectively. This suggests selective transportability of these compounds during long-range transport to higher latitude remote areas. Concentrations of tributyltin (TBT) in the muscle of walleye pollock ranged from 1.1 to 5.5 ng/g on wet weight. Concentrations of TBT in deep-sea walleye pollock from Gulf of Alaska and Bering Sea were lower than those in Japan Sea.     

Effects of the phenylurea herbicide isoproturon on periphytic diatom communities in freshwater indoor microcosms

The toxic effects of the phenylurea herbicide Isoproturon -IPU: (3-(4-isopropylphenyl)-1, 1-dimethylurea)-were studied on the colonization of periphytic diatom communities, within indoor microcosms consisting of a mixed biotope (water column and natural sediment) and two biological species-rooted macrophyte cuttings (Elodea densa) and benthic bivalve molluscs (Corbicula fluminea). The periphyton, essentially composed of diatoms, was collected on artificial substrata (glass slides) in the upper layers of the water column, after two periods of exposure (34 and 71 days). IPU was initially added in the water or in the sediment compartment, at two nominal concentrations (L1 and L2 levels) for each contamination source-5 and 20 microg litre(-1) and 100 and 400 microg kg(-1) in sediment (w/w) respectively. The effects of IPU on the density and community structure of periphytic diatoms are described. A marked reduction in the diatom density was observed after 34 days exposure to the lower concentration of IPU in the water (5 microg litre(-1)). For the L2 levels, the very small number of live cells present did not permit quantification of the diatom density. After 71 days, recovery in community parameters occurred for the two contamination levels of the sediment and water column sources. Samples collected in the experimental units contaminated with the L2 levels were dominated by heterotrophic and smaller diatom species, such as Sellaphora seminulum. Data treatment based on factorial discriminant analysis enabled us to distinguish the different contamination conditions, with only 11 species from the 130 taxa identified.     

The ecological and economic potential of carbon sequestration in forests: examples from South America

Costs of reforestation projects determine their competitiveness with alternative measures to mitigate rising atmospheric CO2 concentrations. We quantify carbon sequestration in above-ground biomass and soils of plantation forests and secondary forests in two countries in South America-Ecuador and Argentina-and calculate costs of temporary carbon sequestration. Costs per temporary certified emission reduction unit vary between 0.1 and 2.7 USD Mg(-1) CO2 and mainly depend on opportunity costs, site suitability, discount rates, and certification costs. In Ecuador, secondary forests are a feasible and cost-efficient alternative, whereas in Argentina reforestation on highly suitable land is relatively cheap. Our results can be used to design cost-effective sink projects and to negotiate fair carbon prices for landowners.     

Detection,Quantification, and Microbial Risk Assessment of Group A Rotavirus in Rivers from Uruguay

Food and Environmental Virology - The aim of this study was to detect, quantify, and assess the risk of infection and illness for Group A Rotavirus (RVA) in the watersheds of the Santa Lucia and...     

Meta-networks for the study of biogeographical traits in ecological networks: the Mexican hummingbird-plant assemblage

Recent studies on ecological networks have quantified the contribution of ecological, historical, and evolutionary factors on the structure of local communities of interacting species. However, the influence of species’ biogeographical traits, such as migratory habits or phylogeographical history, on ecological networks is poorly understood. Meta-networks, i.e., networks that cover large spatial extensions and include species not co-occurring locally, enable us to investigate mechanisms that operate at larger spatial scales such as migratory patterns or phylogeographical distributions, as well as indirect relationships among species through shared partners. Using a meta-network of hummingbird-plant interaction across Mexico, we illustrate the usefulness of this approach by investigating (1) how biogeographical and morphological factors associate with observed interactions and (2) how species-specific biogeographical characteristics associate with species’ network roles. Our results show that all studied hummingbird and plant species in the meta-network were interrelated, either directly or through shared partners. The meta-network was structured into modules, resulting from hummingbirds and plants interacting preferentially with subsets of species, which differed in biogeographical, and, to a lesser extent, morphological traits. Furthermore, migrants and hummingbirds from Nearctic, Transition, and widespread regions had a higher topological importance in the meta-network. Our study illustrates how meta-networks may contribute to our current knowledge on species’ biogeographical traits and biotic interactions, providing a perspective complementary to local-scale networks.