Diel cycles of arsenic speciation due to photooxidation in acid mine drainage from the Iberian Pyrite Belt (Sw Spain)

Twenty four hours diel cycles of arsenic speciation in Acid Mine Drainage (AMD) due to photooxidation have been reported for the first time. AMD samples were taken during 48 h (31st March and 1st April, 2005) at 6 h intervals from the effluent of a massive abandoned polymetallic sulphide mine of the Iberian Pyrite Belt (Sw Spain). Samples were preserved in situ using cationic exchange prior to analysis by coupled high performance liquid chromatography, hydride generation and atomic fluorescence spectrometry (HPLC-HG-AFS) for arsenic speciation. The results indicated the presence of inorganic arsenic species with daily means of 262mugl(-1) for As(V) and 107 microg l(-1) for As(III). No marked diel trend was observed for As(V). However, a marked diel trend was observed for As(III) in the two studied days, with maximum concentrations during nighttime (141-143 microg l(-1)) and minimum concentrations at daytime (72-77 microg l(-1)). This difference in concentration during daytime and nighttime is ca. 100%. A similar diel cycle was observed for iron. An explanation for the arsenic diel cycles observed is the light induced photooxidation of As(III) and the elimination of As(V) due to its adsorption onto Fe precipitates during the daytime. Furthermore, the diel changes in arsenic speciation emphasize the importance of designing suitable sampling strategies in AMD systems.     

Do differences between metal body residues reflect the differences between effects for Chironomus riparius exposed to different sediments?

Sediment characteristics are well known to interfere with toxicity, mainly through differences in terms of bioaccumulation. Here, with chironomids exposed to zinc in an artificial and a field sediment, we investigated the differences of zinc accumulation and of effects on the life cycle, at individual and population level. We used biology and energy-based modeling to analyze the data at all the levels of biological organization. This permits a reliable estimation of thresholds values for tissue residues. Differences in zinc tissue residues accounted for most of the differences between the results for both sediments (a factor of 11 for differences from 20 to 100 depending on the parameter which is considered). Taking into account accumulation and background variability, the differences relative to thresholds could be accounted for. However, it appeared that, once the threshold was passed, effects were much more pronounced for organisms exposed to artificial sediment compared to field sediment. We concluded that some sediment characteristics can enhance toxicity, in addition to their influence on the compound accumulation, even if the latter was the major source of differences in our study.     

Cellular evaluation of the toxicity of combustion derived particulate matter: influence of particle grinding and washing on cellular response

There is increasing interest in continual monitoring of air for the presence of inhalation health hazards, such as particulate matter, produced through combustion of fossil fuels. Currently there are no means to rapidly evaluate the relative toxicity of materials or to reliably predict potential health impact due to the complexity of the composition, size, and physical properties of particulate matter. This research evaluates the feasibility of utilizing cell cultures as the biological recognition element of an inhalation health monitoring system. The response of rat lung type II epithelial (RLE-6TN) cells to a variety of combustion derived particulates and their components has been evaluated. The focus of the current work is an evaluation of how particles are delivered to a cellular sensing array and to what degree does washing or grinding of the particles impacts the cellular response. There were significant differences in the response of these lung cells to PM's of varying sources. Mechanical grinding or washing was found to alter the toxicity of some of these particulates; however these effects were strongly dependent on the fuel source. Washing reduced toxicity of oil PM's, but had little effect on those from diesel or coal. Mechanical grinding could significantly increase the toxicity of coal PM's, but not for oil or diesel.     

A field trial for an ex-situ bioremediation of a drilling mud-polluted site

The remediation of drilling mud-polluted sites in the Southeast of Mexico is a top priority for Mexican oil industry. The objective of this work was to find a technology to remediate these sites. A field trial was performed by composting in biopiles, where four 1ton soil-biopiles were established, one treatment in triplicate and one unamended biopile. Amended biopiles were added with nutrients to get a C/N/P ratio of 100/3/0.5 plus a bulking agent (straw) at a soil/straw ratio of 97/3. Moisture content was maintained around 30-35%. Results showed that, after 180 d, total petroleum hydrocarbon (TPH) concentrations decreased from 99300+/-23000mgTPHkg(-1) soil to 5500+/-770mgTPHkg(-1) for amended biopiles and to 22900+/-7800mgTPHkg(-1) for unamended biopile. An undisturbed soil control showed no change in TPH concentrations. Gas chromatographic analysis showed residual alkyl dibenzothiophene type compounds. Highest bacterial counts were observed during the first 30 d which correlated with highest TPH removal, whereas fungal count increased at the end of the experimentation period. Results suggested an important role of the straw, nutrient addition and water content in stimulating aerobic microbial activity and thus hydrocarbon removal. This finding opens an opportunity to remediate old polluted sites with recalcitrant and high TPH concentration.     

Pteris umbrosa R. Br. as an arsenic hyperaccumulator: accumulation, partitioning and comparison with the established As hyperaccumulator Pteris vittata

The capacity of the Australian native fern Pteris umbrosa to function as an arsenic (As) hyperaccumulator (shoot:soil As concentration >1) was examined by growing plants under glasshouse conditions in an inert medium supplemented with As. Arsenic preferentially accumulated in the fronds, a trait of a hyperaccumulator. The As concentration of fronds decreased with age, being particularly high in the croziers and low in the senesced fronds. Below ground, rhizomes accumulated more As than adventitious roots. Uptake from a range of solution concentrations followed Michaelis Menten kinetics up to a soil solution As concentration of 400mgl(-1). The K(m) for As uptake by roots suggested the operation of a low-affinity carrier. The predicted Nernst membrane potential indicated that uptake was against the electrochemical gradient of As. At 600mgl(-1), the rate of As uptake increased and phytotoxic effects were indicated by a significant decline in biomass. Arsenic uptake and translocation in P. umbrosa and Pteris vittata were similar at low exposure to As. At higher exposure, As uptake and translocation by P. vittata increased more than in P. umbrosa. The growth rate of both ferns was similar, whereas the biomass distribution was not, with P. vittata having a much larger root mass. This suggests that As uptake by P. umbrosa roots was very efficient and may be improved by stimulating root growth to enhance its potential.     

The influence of radical architecture on cadmium bioaccumulation in the black mangrove, Avicennia germinans L

Two groups of Avicennia germinans plants with differences in the radical architecture were exposed under hydroponic conditions to 95ppm of cadmium (Cd) for a period of 24h. Later, Cd concentration in roots, stems and leaves was determined by graphite furnace atomic absorption spectrophotometry. Our results showed that, for both groups of plants, the roots accumulated higher concentration of Cd as compared to stems and leaves, though, the plants of group B displayed enhanced radical architecture, better growth performance, and lower Cd concentration as compared to plants of group A. In contrast, low values of leaves/roots Cd transportation index, and bioaccumulation factor were found in plants of group B. These results suggest that the higher radical architecture developed in plants of group B might better adjust the uptake of Cd as a result of an integrated network of multiple response processes for instances, production of organic acids, antioxidative replay, cell-wall lignification and/or suberization. Further studies will be focused in understanding the role of the radical system in mangrove plants with the rhizosphere activation and root adsorption to soil Cd under natural conditions.     

Bioconcentration, biomagnification and metabolism of 14C-terbutryn and 14C-benzo[a]pyrene in Gammarus fossarum and Asellus aquaticus

The contribution of bioconcentration and biomagnification of 14C-terbutryn and 14C-benzo[a]pyrene via food and water to the bioaccumulation in Gammarus fossarum and Asellus aquaticus was investigated in single species-tests. In this investigation the uptake of 14C-terbutryn and 14C-benzo[a]pyrene via food and water by G. fossarum (L.) and A. aquaticus (L.) was examined. Bioconcentration factors (BCFs) and biomagnification factors (BMFs) were determined. Calculated BCFs were clearly higher than BMFs, indicating that water is the primary route of uptake. The uptake of terbutryn and benzo[a]pyren via water in G. fossarum and A. aquaticus is faster than uptake via food. The elimination and metabolism of the two chemicals by G. fossarum and A. aquaticus were studied. Terbutryn was eliminated almost completely in both species. In general, the elimination of terbutryn from G. fossarum and A. aquaticus was fast with half-life of 5 h. The elimination of terbutryn by G. fossarum after biomagnification is slower than after bioconcentration. No difference was found in elimination of terbutryn by A. aquaticus after biomagnification and after bioconcentration. Metabolites of terbutryn in G. fossarum and A. aquaticus were analyzed by HPLC. After the bioconcentration experiment a higher percentage of metabolites was found in G. fossarum than in A. aquaticus. This was confirmed for the experiment with uptake via food. The spectrum of metabolites was similar in both species, with hydroxyterbutryn being the major metabolism product in water. 14C-B[a]P could nearly completely be eliminated by G. fossarum (rest of activity 2%) after uptake via water. 14C-B[a]P could not be eliminated by G. fossarum and A. aquaticus after uptake via food. The metabolite could not be identified.     

Comparison of calculated and measured foliar O3 flux in crop and forest species

We designed a new gas exchange system that concurrently measures foliar H2O, O3, and CO2 flux (HOC flux system) while delivering known O3 concentrations. Stomatal responses of three species were tested: snapbean, and seedlings of California black oak (deciduous broadleaf) and blue oak (evergreen broadleaf). Acute O3 exposure (120-250 ppb over an hour) was applied under moderate light and low vapor pressure deficits during near steady state conditions. The rate of stomatal closure was measured when the whole plant was placed in the dark. An adjacent leaf on each plant was also concurrently measured in an O3-free cuvette. Under some conditions, direct measurements and calculated foliar O3 flux were within the same order of magnitude; however, endogenously low gs or O3 exposure-induced depression of gs resulted in an overestimation of calculated O3 fluxes compared with measured O3 fluxes. Sluggish stomata in response to light extinction with concurrent O3 exposure, and incomplete stomatal closure likewise underestimated measured O3 flux.     

Antimony distribution and mobility in topsoils and plants (Cytisus striatus, Cistus ladanifer and Dittrichia viscosa) from polluted Sb-mining areas in Extremadura (Spain)

A study about topsoil antimony distribution and mobility from the soils to the biomass has been afforded in three abandoned Sb mining areas located at Extremadura. Physico-chemical characteristics of the soils and total antimony levels were measured in soils and autochthonous plant species (Cytisus striatus, Cistus ladanifer and Dittrichia viscosa). Comparison with corresponding values in reference areas isolated from the mining activities is discussed. Antimony mobility in the soils was estimated by measuring the water extractable fraction; low results were obtained for the three soil areas, with no statistical differences. Plant ability to accumulate antimony was estimated by use of plant accumulation coefficients (PAC). Seasonal (spring vs. autumn) effects on the antimony content in the plant species. Cytisus striatus from Mari Rosa mine presented antimony excluder characteristics, whereas Dittrichia viscosa specimens growing in San Antonio mine showed a significant antimony bioaccumulation.     

Stomatal conductance of semi-natural Mediterranean grasslands: implications for the development of ozone critical levels

Intra-genus and intra-specific variation and the influence of nitrogen enrichment on net assimilation and stomatal conductance of some annual Trifolium species of Mediterranean dehesa grasslands were assessed under experimental conditions. Also gas exchange rates were compared between some Leguminosae and Poaceae species growing in the field in a dehesa ecosystem in central Spain. The results showed that the previously reported different O3 sensitivity of some Trifolium species growing in pots does not seem to be related to different maximum g(s) values. In addition, no clear differences on gas exchange rates could be attributed to Leguminosae and Poaceae families growing in the field, with intra-genus variation being more important than differences found between families. Further studies are needed to increase the database for developing a flux-based approach for setting O3 critical levels for semi-natural Mediterranean species.