Spatial heterogeneity of chemistry of the Small Aral Sea and the Syr Darya River and its impact on plankton communities.

The shrinking of the Aral Sea represents one of the greatest ecological disasters of modern time. The data on the surviving northern part (Small Aral) is scarce and requires an update. This study aimed to analyze the chemistry, phyto- and zooplankton composition, and their relation in the waters of the Small Aral and its tributary, Syr Darya River. The chemistry of both ecosystems was significantly different. Small Aral was characterized by higher ionic concentrations, salinity, and electric conductivity and more significant spatial variation of chemical properties. The area near the river mouth was more pristine, while the ions concentration and salinity in the distant bays were much higher (>10‰). The highest concentrations of nitrates and total phosphorus in the Syr Darya were observed near Kyzylorda, indicating urban pollution. Overall, 109 phytoplankton taxa were identified in both ecosystems, with diatoms, green algae, and cyanobacteria being most abundantly represented. Oligohalobes dominated, but no polyhalobes and euhalobes algal species were identified. In total, 27 taxa of zooplankton were identified in both studied ecosystems, with the domination of rotifers over microcrustaceans. An exceptionally high level of dominance (65-91%) of rotifer Keratella cochlearis in the Syr Darya was found. The phyto- and zooplankton species richness was higher in the Syr Darya. Plankton communities of the Small Aral reflected horizontal variability of chemical properties. The total phosphorus promoted the prevalence of diatoms, rotifers, and crustaceans. Increased nitrogen concentration promoted cyanobacteria, chlorophytes, cryptophytes and chrysophytes, and rotifers Keratella cochlearis and K. quadrata. The abundance of dinophytes, diatoms Navicula cryptotenella and Cocconeis placentula, green algae Mychonastes jurisii and rotifer Keratella tecta was driven by the higher alkalinity and conductivity/salinity levels. The results represent a reference point for future monitoring of the area and add to understanding the complexity of biological transformations in the Aral Sea and its tributary.

Pollution with trace elements and rare-earth metals in the lower course of Syr Darya River and Small Aral Sea, Kazakhstan.

Over recent decades the Aral Sea has faced a major human-driven regression leading to environmental, economic and health impacts. Previous research has indicated that its region may be highly polluted yet there is little recent data to assess the scale or nature of the pollution. The present study investigated the concentration of elements for which the World Health Organization (WHO) has established guideline levels (Al, As, B, Ba, Cd, Cr, Cu, Ni, Pb, Sb) as well as 16 rare-earth elements (Ce, Eu, Er, Gd, La, Nd, Pr, Sc, Sm, Dy, Ho, Lu, Tb, Tm, Y, Yb) in the Small Aral Sea (SAS) and its inflow, the Syr Darya River (SDR). The latter displayed increased levels of Al (mean 851 µg L-1), As (35.8 µg L-1), Cd (2.8 µg L-1), Pb (10.1 µg L-1) and U (4.9 µg L-1), exceeding the guideline limits at selected sites. In the SAS these limits were exceeded at certain locations in the case of As and U. The total mean concentration of REEs in the SDR and SAS amounted to 22.6 and 61.7 µg L-1, respectively, with Pr, Ce and Nd constituting the greatest share. The concentrations of B, Ba Cr, Cu, Se and Ni were below the WHO guideline levels at all studied sites while Sb and Hg were always below detection limits. This research provides an updated status on the levels of contamination of the surface waters in the ecological disaster zone of the Aral Sea in Kazakhstan.

Correction to: The chemistry and toxicity of discharge waters from copper mine tailing impoundment in the valley of the Apuseni Mountains in Romania.

The authors would like to correct the error in the "Abstract" section of original publication. The correct sentence should read "The sampled waters were highly acidic (pH 2.1-4.9) and had high electrical conductivity (2.80-15.61 mS cm-1).

The chemistry and toxicity of discharge waters from copper mine tailing impoundment in the valley of the Apuseni Mountains in Romania.

Copper mining generates large quantities of waste, tailings, and acid outflows causing long-term environmental impacts and potential threats to human health. Valea Sesei is the largest tailing impoundment in Romania, created by flooding the valley (known as Valea Sesei) of the Metalliferous Mountains (a division of the Apuseni Mountains) with copper mining waste. The present study (i) estimated the total volume of tailings in this area; (ii) screened the concentration of 65 elements (rare earth and platinum group elements, alkali metals and alkali earth metals, transition and post-transition metals and metalloids) and cyanide concentrations in wastewater samples collected from tailing impoundment; (iii) evaluated the toxicity of these water samples using five in vitro bioassays employing human cells isolated from healthy donors and a short-term (1 h) exposure model. The sampled waters were highly acidic (pH 2.1-4.9) and had high electrical conductivity (2.80-15.61 mS cm-1). No cyanides were detected in any sample. Water samples collected from the stream (AMD) inflowing to the tailing impoundment were characterized by the greatest concentrations of alkali metals, alkaline earth metals, transition and post-transition metals, metalloids, rare earth elements, and noble metal group. At other sites, the elemental concentrations were lower but remained high enough to pose a relevant risk. The greatest magnitude of in vitro toxic effects was induced by AMD. Observed alterations included redox imbalance in human neutrophils followed by lipid peroxidation and decreased cell survival, significant aggregation of red blood cells, and increased prothrombin time. The study highlights that Valea Sesei is a large sink for toxic elements, posing environmental and health risks, and requiring action to prevent further release of chemicals and to initiate restoration of the area.