Institute for Environmental Research and Education

The biogeochemical cycle of copper (Cu) is mediated by its complexation with organic ligands. An emerging strategy for Cu uptake by marine and freshwater phytoplankton involves organic molecules of biological origin, such as cysteine (Cys), indicating an important role for Cys in controlling the redox state and uptake of Cu in surface waters. In this study, Cys-like compounds were detected in the surface layer of the Krka River estuary by cathodic stripping voltammetry (CSV), while high fractions of Cu(I) were simultaneously determined using an adapted solid phase extraction method. The affinity of Cys for associated redox reactions and for Cu(I) stabilisation depends on its complexation affinity towards Cu(I), which remains controversial in the literature, as values of reported stability constants for Cu(I)-Cys are inconsistent. Spectrophotometric and electrochemical approaches were used to determine the conditional stability constant of the Cu(I)-Cys complex (K″CuL), which refers to the equilibrium constant conditional with respect to both Cu and the ligand. Spectrophotometric reverse titration against a known Cu(I) probe, bathocuproine disulfonate (BCS), under seawater conditions (0.55 mol/L NaCl) revealed a previously unrecognised effect of chloride (Cl−) on the stability of the [CuBCS2]3− complex due to the possible formation of ternary complexes involving Cu(I), BCS, and Cl−, which calls for caution when determining the stability of Cu(I) complexes this way. The results of the electrochemical reverse titration of the Cu(I)-Cys complex with BCS in Cl−-containing medium are consistent with the spectrophotometric results. The logarithm of the derived K″CuL for the Cu(I)-Cys complex is 15.35 ± 0.11, corresponding to the conditional stability constants of the strong Cu-binding ligand class (L1) in seawater, which further supports the importance of Cys for Cu uptake and redox cycling in seawater and estuarine water. By elucidating the stability of the Cu-Cys complex, this study provides insight into how biologically produced and naturally occurring thiol-like ligands influence Cu redox speciation in marine and estuarine waters, which can affect Cu transport and uptake and is therefore essential for accurately representing the Cu biogeochemical cycle.

The current study investigated the long-term effects of CO2 enrichment on cambial activity and wood tracheid traits of Pinus densiflora grown in Open Top Chambers (OTCs). We monitored the cambial activity and analyzed quantitative and qualitative variations in the tracheid at different CO2 enrichments. The cambial activity in the trees was found to begin in mid-to-late March and end in late October to early November. So, the growing season was a little longer than the monitoring period. The time of maximum growth rate was delayed as CO2 enrichment increased, thereby suggesting that rising CO2 concentration may affect intra-annual cambial activity. The quantitative growth (number of cells) increased with higher concentrations of CO2 in the early years of the CO2 exposure. However, a decline in growth was observed from the 8th year after exposure. Qualitatively, cell wall thickness was found to be the largest for the highest CO2 treatment, which was in contrast to previously reported pot experimental results obtained over a couple of growing seasons. The observed quantitative growth increase coupled with the qualitative variations (increased cell wall thickness) may influence the physical properties of wood and carbon storage capacity, and such knowledge is important for forest resource utilization and management planning.

This research is focused on the assessment of the pollution status of river and lake sediments near Pb, Zn, and Cu mines and tailings in the southeastern part of Serbia—Krajište area. The study is based on hypothesis that investigated rivers and lakes in the Krajište area could be polluted by potentially toxic elements (PTEs) and that these elements could pose considerable ecological risk to the studied surface water environment. High PTE contents are detected in studied river sediments (up to 7892 mg kg −1 for Zn, 3224 mg kg −1 for Cu, 36,790 mg kg −1 for Pb, 64.2 mg kg −1 for Cd, and 1444 mg kg −1 for As). Given that the contents of the studied elements in most of the river sediments exceeded the background values, values prescribed by regulations of the Republic of Serbia, as well as probable effect concentration (PEL), it is possible to conclude that sediments were heavily polluted and that detrimental effects can be expected. Contamination indices including the enrichment factor (EF), contamination factor (CF), index of geoaccumulation (Igeo), potential ecological risk index (Eri), ecological risk index (RI), pollution load index (PLI), and aggregative toxicity index (ATI) were used to assess the degree of pollution by PTEs. The ecological risk assessment revealed that there is a significant risk observed for toxic elements (primarily Pb, Cu, Cd, and As) at this moment. The highest contamination indices (EF, Igeo, CF, PLI, and ATI) are mainly associated with historical and current mining activities. The Monte Carlo analysis based on the risk assessment indices was used to evaluate the uncertainty. The most pronounced toxic risk is found for the Pb, Cu, Cd, and As which assessment was in the range of high and extremely high-risk probabilities. The obtained results suggest that levels of toxic elements pose a significant ecological risk to the surface water environment near Pb, Zn, and Cu mines in the Krajište area. The methodology applied in this paper could be very useful for other researchers dealing with the problem of environmental pollution by toxic elements.

We present the results of the charge ratio ($R$) and polarization ($P^{\mu}_{0}$) measurements using the decay electron events collected from 2008 September to 2022 June by the Super-Kamiokande detector. Because of its underground location and long operation, we performed high precision measurements by accumulating cosmic-ray muons. We measured the muon charge ratio to be $R=1.32 \pm 0.02$ $(\mathrm{stat.}{+}\mathrm{syst.})$ at $E_{\mu}\cos \theta_{\mathrm{Zenith}}=0.7^{+0.3}_{-0.2}$ $\mathrm{TeV}$, where $E_{\mu}$ is the muon energy and $\theta_{\mathrm{Zenith}}$ is the zenith angle of incoming cosmic-ray muons. This result is consistent with the Honda flux model while this suggests a tension with the $\pi K$ model of $1.9\sigma$. We also measured the muon polarization at the production location to be $P^{\mu}_{0}=0.52 \pm 0.02$ $(\mathrm{stat.}{+}\mathrm{syst.})$ at the muon momentum of $0.9^{+0.6}_{-0.1}$ $\mathrm{TeV}/c$ at the surface of the mountain; this also suggests a tension with the Honda flux model of $1.5\sigma$. This is the most precise measurement ever to experimentally determine the cosmic-ray muon polarization near $1~\mathrm{TeV}/c$. These measurement results are useful to improve the atmospheric neutrino simulations.

Historical changes of sediment characteristics and levels of inorganic and organic contaminants were studied in dated sediment cores from the Visovac Lake, situated in the Krka National Park, Croatia, to identify the main sources of anthropogenic pressures on this highly protected system. Depth distributions of lithogenic elements showed a steady decrease of terrigenous inputs due to the reduction in agricultural activities in the area, which was particularly pronounced during the 1991-1995 war in Croatia. Vertical and longitudinal distributions of Cd and Zn indicated that they are predominately of anthropogenic origin. The historical profiles of these toxic metals coincide well with the recorded production of metal industry in the upper reach of the Krka River with a sharp decrease reflecting the interruption by the war and slow recovery afterwards. By contrast, the recovery of the tourist industry in Krka NP after the war was accompanied by increasing contamination by elements characteristic of boat and car traffic (Sn, Cu, Pb) as well as oil pollution. The contamination with polycyclic aromatic hydrocarbons and polychlorinated biphenyls was only moderate. Although levels of metallic and organic contamination can be considered relatively low, the observed shift from industrial to tourism-related sources indicated that touristic activities should also be regarded as a possible threat for this vulnerable karst aquatic ecosystem.