First limnological records of highly threatened tropical high-mountain crater lakes in Ethiopia

Lakes Dendi, Wonchi and Ziqualla are among the few remnants of undisturbed crater lakes in the central highlands of Ethiopia, and have never been investigated reliably owing to seclusion and inaccessibility. As the lakes offer a pristine environment in a beautiful landscape and are located in the vicinity of the capital city Addis Ababa, they are highly threatened by unsustainable tourism, shoreline and crater rim modifications, water abstraction and land grabbing. We provide a first limnological description to establish baseline data against which future environmental and biological changes can be monitored. The lakes are located above 2,800 m elevation with no surface outflow and generally show low concentrations of ions, displaying an equal distribution of readily soluble components like Na or K throughout the water column, but distinct oxygen depletion in greater depths linked to rising concentrations of Fe and Mn, which indicates subterranean springs. Based on nutrients, chlorophyll a, and water transparency, lakes Dendi and Wonchi are classified as oligotrophic and Ziqualla as oligo-mesotrophic. The phytoplankton community is dominated by coccal green algae, desmids and dinoflagellates in lakes Dendi and Wonchi, typical for unpolluted dilute waterbodies; whereas chlorococcales, in particular Botryococcus braunii and benthic diatoms, prevail in Ziqualla. The zooplankton fauna is depauperate, comprising a total of 11 rotifer taxa and 13 crustaceans. Copepods were the most abundant group and contributed over 60% to the total zooplankton abundance in all three lakes, followed by rotifers and cladocerans. The conservation significance of these lakes lies predominantly in their representation of dilute, nutrient–poor highland lake systems that support diverse biota assemblages like desmids and daphnids, which are highly sensitive to eutrophication

Heavy Metal Extraction under Environmentally Relevant Conditions Using 3-Hydroxy-2-Naphthoate- Based Ionic Liquids: Extraction Capabilities vs. Acute Algal Toxicity

We investigated the applicability of three task-specific ionic liquids (ILs) as heavy metal extracting agents by contrasting extraction capabilities with algal toxicity. The compounds tested were trihexyltetradecylphosphonium-, methyltrioctylphosphonium- and methyltrioctylammonium 3-hydroxy-2-naphthoates. Experiments were performed to assess if these ILs can provide environmentally safe residual concentrations of the target metals after extraction. Both pure water and natural mineral water samples were spiked with 20 mu g L-1 of Cu, Ag, Cd, Hg and Pb, respectively. Quantitative extraction (> 99%) of Hg and Ag was achieved. Cu and Hg were below the respective no-observed-effect-concentrations (NOECs) after extraction and Ag below 0.03 mu g L-1. Acute toxicity assays were conducted using two freshwater green algae Raphidocelis subcapitata and Tetradesmus obliquus. Growth inhibition and maximum photochemical quantum yield of photosystem II after 72 h were assessed. ILs were less toxic than similar compounds, but still must be classified as acute toxicants for algae. An inhibiting effect on both growth and chlorophyll fluorescence was observed. The leaching of the ILs into the samples remains a limitation regarding their environmental-friendly applicability. Nonetheless, the extremely efficient removal of Cu, Ag and Hg under environmentally relevant conditions calls for further research, which should focus on the immobilization of the ILs

Novel 3-Hydroxy-2-Naphthoate-Based Task-Specific Ionic Liquids for an Efficient Extraction of Heavy Metals

Ionic liquids (ILs) are per definition salts with melting points below 100°C and might be green alternatives for the extraction of heavy metals from aqueous solutions due to their favorable environmental and physico-chemical properties. Partial solution during extraction, so-called leaching, however, limits their applicability. The present study synthesizes three novel ammonium and phosphonium ILs based on 3-hydroxy-2-naphthoic acid—trihexyltetradecylphosphonium—([P66614]), methyltrioctylphosphonium—([P1888]), and methyltrioctylammonium 3-hydroxy-2-naphthoate ([N1888][HNA])—by a deprotonation-metathesis route. The aims were to improve stability during extraction while still achieving high selectivity toward heavy metal ions, as well as to study the impact of different alkyl chains and the central atom of the cation on physico-chemical properties, extraction efficacy, and leaching. Extraction capabilities for the seven heavy metals Ag, Cd, Co, Cu, Mn, Ni, and Pb were studied in pure water at pH 8.0. Further experiments were conducted in water containing 30 g L−1 NaCl to simulate a seawater matrix and/or 30 mg L−1 humic acids, as well as metal-spiked natural water samples. All three ILs showed extraction efficacies ≥90% for Cu and Pb after 24 h. Overall, extraction efficacies for Ag, Cd, Cu, and Pb were highest for drinking water samples. Ag and Cd extraction was increased by up to 41% in (hyper-) saline samples using IL [P66614][HNA] compared with pure water samples. Leaching values were reduced down to 0.07% loss of the applied IL, which can be attributed to the hydrophobic character of 3-hydroxy-2-naphthoate. Our results represent a positive development toward a greener extraction of heavy metals from natural waters

Evaluation of Trace Element and Metal Accumulation and Edibility Risk Associated with Consumption of Labeo umbratus from the Vaal Dam, South Africa

With the occurrence of recreational and small scale subsistence fishing activities at the Vaal Dam, South Africa, consumption of fish from this dam may result in health risks associated with trace elements and metals. The Vaal Dam is one of the largest dams in South Africa, located between the Gauteng Province and Orange Free State, and supplies water to approximately 11.6 million people. A total of 38 specimens of the benthic cyprinid fish Labeo umbratus were collected from the Vaal Dam during two surveys, in 2011 and 2016. Samples of muscle, liver, kidney, gill and spinal cord were analysed, along with sediment samples collected during the same surveys. Thirteen trace elements were analysed in the samples by Inductively Coupled Plasma–Optical Emission Spectrometry, Inductively Coupled Plasma–Mass Spectrometry, Atomic Absorption Spectroscopy and Total Reflection X-ray Fluorescence spectroscopy. This is the first survey on trace element and Hg accumulation in this fish species from the Vaal Dam and target hazard quotients (THQ) indicated that there is a risk for consumers of fish for As and Hg (THQ = 1.43 and 1.14 respectively). Although levels of trace elements in this impoundment have shown little change for a number of years and are lower than global background levels, studies detailing the accumulation of metals by fish inhabiting the Vaal Dam have indicated that trace elements in muscle tissue are above food safety guidelines. Trace element levels in L. umbratus are lower compared to other species inhabiting the Vaal Dam and further indicate that risks for consumers can be decreased if humans relying on fish from the Vaal Dam preferentially consume this species over others

Heavy Metals in Sediments and Greater Flamingo Tissues from a Protected Saline Wetland in Central Spain

Aquatic ecosystems often act as sinks for agricultural, industrial, and urban wastes. Among potential pollutants, heavy metals can modify major biogeochemical cycles by affecting microorganisms and other biota. This study assessed the distribution and concentration of heavy metals (Cd, Hg, Cu, Pb, and Zn) in Pétrola Lake, a heavily impacted area in central Spain where the greater flamingo Phoenicopterus roseus breeds. This study was designed to determine the concentration and identify the potential sources of heavy metals in Pétrola Lake protected area, including sediments, agricultural soils, and tissues of the greater flamingo. A six-step sequential extraction was performed to fractionate Cu, Pb, and Zn from lake sediments and agricultural soil samples to gain insight into different levels of their bioavailability. Our results showed that Pb and Cd accumulated in lake sediments and agricultural soils, respectively, most likely derived from anthropogenic sources. Multivariate analysis revealed differences between these (Pb and Cd) and the remaining studied elements (Cu, Hg, and Zn), whose concentrations were all below the pollution threshold. Lead pollution in sediments was apparently dominated by organic matter binding, with fractions up to 34.6% in lake sediments. Cadmium slightly accumulated in agricultural soils, possibly associated with the use of fertilizers, but still below the pollution thresholds. In the flamingo samples, low bioaccumulation was observed for all the studied elements. Our study suggests that human activities have an impact on heavy metal accumulation in sediments and soils, despite being below the pollution levels

The Arsenic–Antimony Creek at Sauerbrunn/Burgenland, Austria: A Toxic Habitat for Amphibians

(1) Background: All Austrian amphibians are affected by the degradation of habitats. Mining contributes to habitat destruction by the formation of spoil heaps and mine drainage waters. In Stadtschlaining/Burgenland, antimony mining led to increased arsenic (As) and antimony (Sb) concentrations in soil and water. This study investigates a contaminated creek, still inhabited by amphibians. (2) Methods: Water and soil were analyzed along the creek and correlated with the occurrence of amphibians. (3) Results: As and Sb were increased, with up to 49,000 mg/kg As and 2446 mg/kg Sb in the soil. Up to 317 mg/kg As and 156 mg/kg Sb became bioavailable under gastric, and up to 298 mg/kg As and 30 mg/kg Sb under intestinal conditions, and were absorbed upon ingestion of soil. Larvae of Salamandra salamandra were found throughout the creek; survival rates were low. Rana temporaria occurs in the most contaminated sections but does not propagate here. Bombina variegata appears occasionally. Amphibians seem not to be able to detect and avoid metal or metalloid contamination. (4) Conclusion: Survival of larvae is dubious, but adult amphibians survive without apparent damage under severe metalloid contamination

Novel thiosalicylate-based ionic liquids for heavy metal extractions

AbstractThis study aims to develop novel ammonium and phosphonium ionic liquids (ILs) with thiosalicylate (TS) derivatives as anions and evaluate their extracting efficiencies towards heavy metals in aqueous solutions. Six ILs were synthesized, characterized, and investigated for their extracting efficacies for cadmium, copper, and zinc. Liquid-liquid extractions of Cu, Zn, or Cd with ILs after 1–24h using model solutions (pH 7; 0.1M CaCl2) were assessed using flame atomic absorption spectroscopy (F-AAS). Phosphonium-based ILs trihexyltetradecylphosphonium 2-(propylthio)benzoate [P66614][PTB] and 2-(benzylthio)benzoate [P66614][BTB] showed best extraction efficiency for copper and cadmium, respectively and zinc was extracted to a high degree by [P66614][BTB] exclusively

Oxygen and light determine the pathways of nitrate reduction in a highly saline lake

International audienceNitrate (NO3 −) removal from aquatic ecosystems involves several microbially mediated processes including denitrification, dissimilatory nitrate reduction to ammonium (DNRA), and anaerobic ammonium oxidation (anammox) regulated by slight changes in environmental gradients. Saline lakes are prone to the accumulation of anthropogenic contaminants, making them highly vulnerable environments to NO3 − pollution. We investigated nitrate removal pathways in mesocosm experiments using lacustrine, undisturbed, organic-rich sediments from Pétrola Lake (Spain), a highly saline waterbody subject to anthropogenic NO3 − pollution. We used the revised 15 N-isotope pairing technique (15 N-IPT) to determine NO3 − sink processes. Our results demonstrate the coexistence of denitrification, DNRA, and anammox processes, and their contribution was determined by environmental conditions (oxygen and light). DNRA and N2O-denitrification were the dominant nitrogen (N) removal pathways when oxygen and/or light were present (up to 82%). In contrast, anoxia and darkness promoted NO3 − reduction by DNRA (52%) and N loss by anammox (28%). Our results highlight the role of coupled DNRA-anammox, as yet has never been investigated in hypersaline lake ecosystems. We conclude that anoxia and darkness favored DNRA and anammox processes over denitrification and therefore reduce N2O emissions to the atmosphere