Maximum species richness at intermediate frequencies of disturbance: consistency among levels of productivity

Development of a mechanistic understanding and predictions of patterns of biodiversity is a central theme in ecology. One of the most influential theories, the intermediate disturbance hypothesis (IDH), predicts maximum diversity at intermediate levels of disturbance frequency. The dynamic equilibrium model (DEM), an extension of the IDH, predicts that the level of productivity determines at what frequency of disturbance maximum diversity occurs. To test, and contrast, the predictions of these two models, a field experiment on marine hard-substratum assemblages was conducted with seven levels of disturbance frequency and three levels of nutrient availability. Consistent with the IDH, maximum diversity, measured as species richness, was observed at an intermediate frequency of disturbance. Despite documented effects on productivity, the relationship between disturbance and diversity was not altered by the nutrient treatments. Thus, in this system the DEM did not improve the understanding of patterns of diversity compared to the IDH. Furthermore, it is suggested that careful consideration of measurements and practical definitions of productivity in natural assemblages is necessary for a rigorous test of the DEM.     

Selenium speciation in acidic environmental samples: application to acid rain-soil interaction at Mount Etna volcano

Speciation plays a crucial role in elemental mobility. However, trace level selenium (Se) speciation analyses in aqueous samples from acidic environments are hampered due to adsorption of the analytes (i.e. selenate, selenite) on precipitates. Such solid phases can form during pH adaptation up till now necessary for chromatographic separation. Thermodynamic calculations in this study predicted that a pH < 4 is needed to prevent precipitation of Al and Fe phases. Therefore, a speciation method with a low pH eluent that matches the natural sample pH of acid rain-soil interaction samples from Etna volcano was developed. With a mobile phase containing 20 mM ammonium citrate at pH 3, selenate and selenite could be separated in different acidic media (spiked water, rain, soil leachates) in <10 min with a LOQ of 0.2 μg L⁻¹ using ⁷⁸Se for detection. Applying this speciation analysis to study acid rain-soil interaction using synthetic rain based on H₂SO₄ and soil samples collected at the flanks of Etna volcano demonstrated the dominance of selenate over selenite in leachates from samples collected close to the volcanic craters. This suggests that competitive behavior with sulfate present in acid rain might be a key factor in Se mobilization. The developed speciation method can significantly contribute to understand Se cycling in acidic, Al/Fe rich environments.     

Fate of 5-fluorouracil, doxorubicin, epirubicin, and daunorubicin in hospital wastewater and their elimination by activated sludge and treatment in a membrane-bio-reactor system

Antineoplastic agents are applied in cancer therapy and end up in hospital wastewater by human excretions. In this study, the raw wastewater of the sewer of the oncologic in-patient treatment ward of the Vienna University Hospital was monitored for 98 d over 2 years for the cytostatics 5-fluorouracil (5-FU), doxorubicin (DOX), epirubicin, and daunorubicin. In a next step, the elimination of the drugs by a membrane-bio-reactor system was investigated. In addition, their fate in wastewater and elimination by activated sludge was investigated with radio-labelled substances. During the monitoring periods, concentration levels ranging from <8.6 to 124 microgl(-1) for 5-FU and from <0.26 to 1.35 microgl(-1) for DOX were determined. The concentrations analysed fitted the lower ranges calculated by an input-output model. Treatment of oncologic wastewater in the membrane bio-reactor as well as the analysis of the effluents of the Vienna University Hospital resulted in concentrations below the limit of detection. Investigations with radio-labelled compounds showed that 5-FU is eliminated from the liquid phase below the limit of detection. But, up to 25% of radio-labelled equivalents of the drug's amount were found in the gaseous phase and only a marginal part in the solid phase, this indicates that at least one part of the drug is biodegraded. For the anthracyclines more than 90% was eliminated from the liquid phase. In this case, adsorption to suspended solids seems to be the major elimination pathway, as up to 30% of the radio-labelled equivalents of the drug's amount was detected in the solid phase. Our results indicate that the investigated anticancer drugs are eliminated by sewage treatment plants, either by biodegradation or adsorption.