La Prospección de placeres del oro y otros minerales densos

[eng] Alluvial prospecting is the most widely used method in heavy mineral exploration. Heavy minerals are resistant to meteoric agents. Economically, the most important heavy minerals are: precious metals (gold, silver and platinum group minerals), gems (diamonds, rubies, sapphires, emeralds, etc), the tin base metal group (cassiterite), technologic metals such as titanium (ilmenite and rutile), tungsten (wolframite and scheelite), zirconium (zircon) and the rare earths. The most usual techniques used in alluvial prospecting and the different criteria employed in exploration, mineral benefit and evaluation of alluvial ore deposits known as placers are presented.[cat] La prospecció al.luvionar es un mètode excepcional per la recerca de minerals de interès econòmic, com los minerals densos d'elevada resistència física i química. Entre ells son d' interès els metalls preciosos (or, plata i platí), gemmes (diamant, rubí, zèfirs, maragdes, aigua-marina, etc.), metalls de base com l'estany (cassiterites), minerals tecnològics com el titani (ilmenites i rutils), wolfram (volframita i scheelita), zirconi (zircó), de terres rares (monacites), etc.. En aquest text, és presenten las tècniques mas usuals en Prospecció al.luvionar com la batea, així com els distints criteris a seguir per dur a termini una prospecció, un benefici i una avaluació dels seus jaciments que es coneixen com ¿placeres¿.[spa] La prospección aluvionar es un método excepcional para la búsqueda de minerales de interés económico, como los minerales densos de elevada resistencia físico-química. Entre ellos son de interés los metales preciosos (oro, plata y platinoides), gemas (diamante, rubíes, zafiros, esmeraldas, aguamarinas, etc.), metales de base como el estaño (casiteritas), minerales tecnológicos como el titanio (ilmenitas y rutilos), wólfram (volframita y scheelita), circonio (circón), de tierras raras (monacitas), etc.. En este texto, se presentan las técnicas mas usuales en prospección aluvionar como la batea, así como los distintos criterios a seguir para llevar a cabo una prospección, un beneficio y una evaluación de sus yacimientos que se conocen como ¿placeres¿

Appendix A. Two tables containing the log10-transformed LC50 values of used in the study and the information about the the DNA sequences used to estimate phylogeny.

Two tables containing the log10-transformed LC50 values of used in the study and the information about the the DNA sequences used to estimate phylogeny

A new risk assessment approach for the prioritization of 500 classical and emerging organic microcontaminants as potential river basin specific pollutants under the European Water Framework Directive

Given the huge number of chemicals released into the environment and existing time and budget constraints, there is a need to prioritize chemicals for risk assessment and monitoring in the context of the European Union Water Framework Directive (EU WFD). This study is the first to assess the risk of 500 organic substances based on observations in the four European river basins of the Elbe, Scheldt, Danube and Llobregat. A decision tree is introduced that first classifies chemicals into six categories depending on the information available, which allows water managers to focus on the next steps (e.g. derivation of Environmental Quality Standards (EQS), improvement of analytical methods, etc.). The priority within each category is then evaluated based on two indicators, the Frequency of Exceedance and the Extent of Exceedance of Predicted No-Effect Concentrations (PNECs). These two indictors are based on maximum environmental concentrations (MEC), rather than the commonly used statistically based averages (Predicted Effect Concentration, PEC), and compared to the lowest acute-based (PNECacute) or chronic-based thresholds (PNECchronic). For 56% of the compounds, PNECs were available from existing risk assessments, and the majority of these PNECs were derived from chronic toxicity data or simulated ecosystem studies (mesocosm) with rather low assessment factors. The limitations of this concept for risk assessment purposes are discussed. For the remainder, provisional PNECs (P-PNECs) were established from read-across models for acute toxicity to the standard test organisms Daphnia magna, Pimephales promelas and Selenastrum capricornutum. On the one hand, the prioritization revealed that about three-quarter of the 44 substances with MEC/PNEC ratios above ten were pesticides. On the other hand, based on the monitoring data used in this study, no risk with regard to the water phase could be found for eight of the 41 priority substances, indicating a first success of the implementation of the WFD in the investigated river basins. © 2011 Elsevier B.V.The presented prioritization approach was developed within the NORMAN Association (No. W604002510) working group on prioritization of emerging substances (WG 1) and was approved by the WG members present at the WG meeting in Paris (22–23 November 2010). The work was supported by the European Commission through the Integrated Projects MODELKEY (Contract-No. 511237GOCE) and OSIRIS (contract No. 037017). Peter C. von der Ohe was financially supported through a Deutsche Forschungsgemeinschaft (DFG) postdoctoral fellowship (PAK 406/1). The authors would like to acknowledge the International Commission for the Protection of the Danube River and the team of experts and laboratories providing the data from the Joint Danube Survey 2 as well as the Landesbetriebes für Hochwasserschutz und Wasserwirtschaft Sachsen-Anhalt (Gen. LHW/5.4/003/2006), the Sächsisches Landesamt für Umwelt und Geologie (LfUG, Dresden, Germany), the Vlaamse Milieumaatschappij (VMM, Erembodegem, Aalst, Belgium) and the Agencia Catalana de l'Aigua (ACA, Barcelona, Spain) who kindly provided the monitoring data used for the application of the methodology. Emma L. Schymanski is thanked for valuable suggestions that improved the manuscript.Peer Reviewe

Thresholds for the Effects of Pesticides on Invertebrate Communities and Leaf Breakdown in Stream Ecosystems

We compiled data from eight field studies conducted between 1998 and 2010 in Europe, Siberia, and Australia to derive thresholds for the effects of pesticides on macroinvertebrate communities and the ecosystem function leaf breakdown. Dose–response models for the relationship of pesticide toxicity with the abundance of sensitive macroinvertebrate taxa showed significant differences to reference sites at 1/1000 to 1/10 000 of the median acute effect concentration (EC50) for <i>Daphnia magna</i>, depending on the model specification and whether forested upstream sections were present. Hence, the analysis revealed effects well below the threshold of 1/100 of the EC50 for <i>D. magna</i> incorporated in the European Union Uniform Principles (UP) for registration of single pesticides. Moreover, the abundances of sensitive macroinvertebrates in the communities were reduced by 27% to 61% at concentrations related to 1/100 of the EC50 for <i>D. magna</i>. The invertebrate leaf breakdown rate was positively linearly related to the abundance of pesticide-sensitive macroinvertebrate species in the communities, though only for two of the three countries examined. We argue that the low effect thresholds observed were not mainly because of an underestimation of field exposure or confounding factors. From the results gathered we derive that the UP threshold for single pesticides based on <i>D. magna</i> is not protective for field communities subject to multiple stressors, pesticide mixtures, and repeated exposures and that risk mitigation measures, such as forested landscape patches, can alleviate effects of pesticides

Occurrence and risk assessment of an azo dye - The case of Disperse Red 1

Made available in DSpace on 2018-12-11T17:28:06Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-08-01Water quality criteria to protect aquatic life are not available for most disperse dyes which are often used as commercial mixtures in textile coloration. In this study, the acute and chronic toxicity of the commercial dye Disperse Red 1 (DR1) to eight aquatic organisms from four trophic levels was evaluated. A safety threshold, i.e. Predicted No-Effect Concentration (PNEC), was derived based on the toxicity information of the commercial product and the purified dye. This approach was possible because the toxicity of DR1 was accounting for most of the toxicity of the commercial mixture. A long-term PNEC of 60 ng L-1 was proposed, based on the most sensitive chronic endpoint for Daphnia similis. A short-term PNEC of 1800 ng L-1 was proposed based on the most sensitive acute endpoint also for Daphnia similis. Both key studies have been evaluated with the new Criteria for Reporting and Evaluating ecotoxicity Data (CRED) methodology, applying more objective criteria to assess the quality of toxicity tests, resulting in two reliable and relevant endpoints with only minor restrictions. HPLC-MS/MS was used to quantify the occurrence of DR1 in river waters of three sites, influenced by textile industry discharges, resulting in a concentration range of 50-500 ng L-1. The risk quotients for DR1 obtained in this work suggest that this dye can pose a potential risk to freshwater biota. To reduce uncertainty of the derived PNEC, a fish partial or full lifecycle study should be performed.Faculty of Pharmaceutical Sciences University of São Paulo USPSchool of Technology State University of Campinas UNICAMPAmalex Environmental SolutionsChemical Institute State University of São Paulo UNESPSchool of Life Sciences Heriot-Watt UniversityDepartment of Biology and CESAM University of AveiroChemical Institute State University of São Paulo UNES

Impacts of multiple stressors on freshwater biota across spatial scales and ecosystems

Climate and land-use change drive a suite of stressors that shape ecosystems and interact to yield complex ecological responses (that is, additive, antagonistic and synergistic effects). We know little about the spatial scales relevant for the outcomes of such interactions and little about effect sizes. These knowledge gaps need to be filled to underpin future land management decisions or climate mitigation interventions for protecting and restoring freshwater ecosystems. This study combines data across scales from 33 mesocosm experiments with those from 14 river basins and 22 cross-basin studies in Europe, producing 174 combinations of paired-stressor effects on a biological response variable. Generalized linear models showed that only one of the two stressors had a significant effect in 39% of the analysed cases, 28% of the paired-stressor combinations resulted in additive effects and 33% resulted in interactive (antagonistic, synergistic, opposing or reversal) effects. For lakes, the frequencies of additive and interactive effects were similar for all spatial scales addressed, while for rivers these frequencies increased with scale. Nutrient enrichment was the overriding stressor for lakes, with effects generally exceeding those of secondary stressors. For rivers, the effects of nutrient enrichment were dependent on the specific stressor combination and biological response variable. These results vindicate the traditional focus of lake restoration and management on nutrient stress, while highlighting that river management requires more bespoke management solutions