Size-dependent distribution of metal(loid)s in recent marine sediments of the Adriatic sea

This paper investigates occurrence of metal(loid)s, and size-dependent changes in their concentration in recent marine sediments from coastal and open-sea environments in the eastern Adriatic. Size fractionation of sediments was performed after removal of organic matter (OM), and the individual fractions, comprising particles below 8 μm, 4 μm, 2 μm, 1 μm and 0.45 μm, were analysed using HR ICP-MS. The concentrations of most elements increased with decreasing particle size, as a result of accumulation of clay minerals and Fe and Mn (oxyhydr)oxides. A decrease in concentrations was observed for Ba, Sr, Ti and U, due to lowering of the carbonate content and presence in the coarse-grained and heavy mineral fraction. The highest element concentrations were determined in the fraction comprising particles below 1 μm. Occasionally, depending on the sedimentological environment and/or the element in question, the peak concentrations occurred in the <2 μm or <0.45 μm fraction. The lowest size-dependent enrichment was observed for elements associated with aluminosilicates (Al, Be, Cs, Co, Fe, K, Li, Rb). A different size-dependent behaviour of the elements was observed between deep-sea areas and shallow environments under greater coastal influence, mainly due to differences in sediment sorting, and between the northern and central vs. southern Adriatic due to the different catchment geologies. The Fe and Mn (oxyhydr)oxides, abundant in the deep-sea sediments, played an important role in the geochemical cycle of As, Cd, Co, Mo, Sb and V.

Differences in the behaviour of trace and rare-earth elements in oxidizing and reducing soil environments: Case study of Terra Rossa soils and Cretaceous palaeosols from the Istrian peninsula, Croatia

This study compares the differences between the distribution of trace elements and rare-earth elements (REEs) formed under reducing and oxidizing soil conditions during pedogenesis on carbonate bedrock. Terra rossa (TR) soils, representing pedogenesis under oxic conditions, and Cretaceous palaeosols (CP), representing pedogenesis under reducing conditions, were sampled on the Istrian peninsula. They were studied by ICP-MS, ICP-OES, XRF, XRD, sequential extraction and statistical analyses. The differences in trace-element behaviour between the TR and CP stem from different redox conditions, but the most remarkable difference was observed in the behaviour of the REEs. Statistical analyses revealed that in TR soils all the REEs showed a very positive correlation, while in CPs the light REEs and heavy REEs showed an internal, very positive correlation. TR soils have almost twice as much REEs as CPs. This difference is pedogenetic, as both materials have a very similar amount of REEs in the residual fraction. While TR soils have the same amount of REEs in fractions other than the residual fraction, CPs have almost no REEs in these fractions. Different REE patterns obtained from sequential extraction, such as a middle-REE enrichment and a positive Ce anomaly in TR soils and light-REE depletion, heavy-REE enrichment, positive Ce and Eu anomalies in CPs, contributed to an understanding of the redox and pedogenetic processes. This study successfully emphasized the influence of different redox conditions on the behaviour of trace and rare-earth elements during pedogenesis on a carbonate bedrock and the ability of the REEs to track pedogenetic processes.

Size-related mineralogical and surface physicochemical properties of the mineral particles from the recent sediments of the Eastern Adriatic Sea

The mineral composition and surface physico-chemical properties, i.e., specific surface area (SSA), cation exchange capacity (CEC), and surface charge of recent sediments and their submicron mineral fractions from different sedimentological environments of the Eastern Adriatic were investigated. The influence of organic matter on these properties was also investigated. It was shown that illite and mixed-layered clay minerals (MLCM) were ubiquitous and showed no size-related preferences while the occurrence of smectites, chlorites, and kaolinites varied. The smectites content increased and the chlorites decreased slightly with decreasing particle size. The sediments from the carbonate-rich environment contained no smectites or chlorites and had the highest kaolinite content. For the first time, in the recent sediments of the Adriatic Sea the poorly- and the well-crystallised kaolinite (Kl and Kl_D) were distinguished. While Kl predominates in the submicron-sized fraction, Kl_D occurred only in micron-sized fractions. Authigenic aragonite of submicron-sized was determined in a distinct environment of the semi-enclosed marine lake. The differences in mineral composition and particle size of sediments and their separated fractions were reflected in a wide range of the SSA and CEC values obtained. The highest values of SSA and CEC were determined in the phyllosilicates-rich submicron-sized fractions range, 109 m²g^-1 and 87.4 cmol₊kg^-1, respectively. The submicron-sized fraction from aragonite-rich marine lake showed the lowest values of SSA (56.4 m²g^-1) and CEC (38.8 cmol₊kg^-1), which are still unexpectedly high for carbonate-rich environments. The removal of organic matter resulted in a significant increase in SSA and CEC, up to 150% and 76%, respectively.

The chemical species of mercury accumulated by Pseudomonas idrijaensis, a bacterium from a rock of the Idrija mercury mine, Slovenia

A mercury-resistant bacterial strain has been isolated from a rock of the Idrija mercury mine in Slovenia. The rock had 19 g carbon and 2952 mg mercury (Hg) per kg. Mass spectrometry and DNA sequencing showed that the bacterium belongs to the Pseudomonas genus. It is called Pseudomonas idrijaensis. This bacterial strain is sensitive to methylmercury (MeHg) like the reference P. aeruginosa strain PAO1, and is resistant to divalent mercury (Hg(II)) in contrast to PAO1. This difference could be attributed to the presence of the mer operon yet deprived of the merB gene encoding the organomercurial lyase, on the basis of whole genome sequencing. The P. idrijaensis mer operon displays the RTPCADE organization and is contained in the Tn5041 transposon. This transposon identified here occurs in other Gram-negative Hg-resistant strains isolated from mercury ores, aquatic systems and soils, including Pseudomonas strains from 15,000 to 40,000 years old Siberian permafrost. When P. idrijaensis was exposed to mercury chloride, two intracellular Hg species were identified by high energy-resolution XANES spectroscopy, a dithiolate Hg(SR)₂ and a tetrathiolate Hg(SR)₄ complex. P. idrijaensis had a much higher [Hg(SR)₂]/[Hg(SR)₄] molar ratio than bacteria lacking the mer operon when exposed to 4 μg Hg²⁺/L - resulting in an intracellular accumulation of 4.3 μg Hg/g dw. A higher amount of the Hg(SR)₂ complex provides a chemical signature for the expression of the dicysteinate Mer proteins in response to mercury toxicity.

Presence of carbapenem-resistant bacteria in soils affected by illegal waste dumps

The carbapenem-resistant bacteria (CRB) are currently at the top of the WHO priority list of bacteria that pose the greatest threat to human health. Considering that soil is one of the important environments for the emergence of antibiotic-resistant bacteria, we isolated and quantified cultivable CRB in soils across Croatia, including ones affected by illegal dumps.We cultivated CRB at two temperatures, distinguishing between the intrinsically resistant CRB (37°C, mostly Stenotrophomonas spp.) and the ones that are presumably human-associated and clinically relevant (42°C, Acinetobacter sp., Enterobacteriaceae, Burkholderia spp.). Our study demonstrated that distinguishing between the two offers a better insight into the diversity of CRB in the environment. The ones cultivated at 37°C were found in almost all soil samples, while the presumably clinically relevant ones were absent from uncontaminated pasture and grassland, indicating that human-associated CRB are unlikely to be found in soils spared from anthropogenic influence.

Extensively and multi drug-resistant Acinetobacter baumannii recovered from technosol at a dump site in Croatia

In a karst pit above City of Rijeka in Croatia the hazardous industrial waste was continuously disposed from 1955 to 1990, and later it was periodically used as an illegal dump site. The surface part of a technosol at the edge of dump was analysed mineralogically, geochemically and bacteriologically. From the technosol rich in petroleum hydrocarbons and heavy metals three isolates of Acinetobacter baumannii were recovered. Isolates from technosol shared many features that are previously described for clinically isolates: the affiliation to IC1 and 2, multi-drug resistant (MDR) or extensively drug-resistant (XDR) antibiotic resistance profile, carbapenem resistance mediated by bla_OXA72 and bla_OXA23 genes, and the expression of virulence factors. In in vitro conditions, isolates were able to survive in contact with technosol during 58days of monitoring. The most probable source of A. baumannii in technosol was the illegally disposed hospital waste. Proper management and disposal of human solid waste is mandatory to prevent the spread of clinically important A. baumannii in nature.