Boron and lithium behaviour in river waters under semiarid climatic conditions.

Boron (B) and Lithium (Li) concentrations were studied in the Platani river, one of the most important catchments of South-Central Sicily which is under semiarid climatic conditions for roughly eight months to a year. In this area, evaporites result in potential B and Li sources for surface waters. Results from river waters have measured ionic strength values between 0.1 and 4.54 M. B and Li distributions in these waters were studied in colloidal (CF, extracted by ultrafiltration from the 0.45 µm filtrate) and total dissolved (TDF) fractions and in fractions extracted from corresponding riverbed sediments, according to changes of the B/Li ratio. In river waters, CF and TDF showed very similar B/Li values, suggesting that only negligible fractionation occurs between Li and B in the aqueous phase. Similar evidence was observed between B/Li values in TDF and the labile sediment fraction, whereas an inverse relationship arose between B/Li values in TDF and in the easily reducible sediment fraction. This relationship indicates that Mn oxy-hydroxides preferentially react with aqueous B species relative to Li at the riverbed sediment interface. The extent of the B-Mn oxy-hydroxide reactions is influenced by the ionic strength, so that only B/Li values below 4 are measured in river waters with ionic strength values above 0.5 M. Comparing B/Li and ionic strength values measured in the Platani river with those from oxic brines worldwide, the same preferential B removal relative to Li is observed. This evidence suggests that B is removed as positively-charged borate ion-pairs, formed in the aqueous phase under higher ionic strength conditions, reacting with negatively charged surfaces of Mn oxy-hydroxides. The observed B reactivity relative to Li could be exploited to bring down the B excess from natural or waste waters, allowing the natural reactions with Mn oxy-hydroxides to take place under natural conditions.

Trace element fractionation through halite crystallisation: Geochemical mechanisms and environmental implications.

Halite is an important mineral for industry, agriculture and food production. It crystallises during water evaporation, and the progressive increase of dissolved metal ions in the brine occurs simultaneously. Thus, halite exploitation may deliver metal ions into the environment and the mechanism of this trace element accumulation has to be studied. In this work, we investigate the distribution of lanthanides and Y (hereafter called rare earth elements, REE), Zr and Hf between crystallising halite and brines in the Dead Sea as geochemical tools for recognising the mechanism of metal ion removal from brines and accumulation in halite. Halite forms cubic crystals where octahedral planes sometimes occur under particular thermal gradient conditions. Our findings indicate that crystal morphology influences the mechanism of metal ion removal from brines because octahedral surfaces are polar unlike those that are cubic. Accordingly, octahedra preferentially fractionate aqueous charged species such as [Hf(OH)5]-, compared to neutral species such as [Zr(OH)4]0. Cubic surfaces do not fractionate aqueous species. In crystal cores, positive Eu anomalies occur suggesting Eu substitution for Na in the lattice. This substitution is energetically justified by ab initio calculations. Hf enrichment relative to Zr also occurs in primary halite-rich evaporites. It is not found in cubic halite from saltworks. The results of this study suggest that primary halite kinetically crystallised from brines can concentrate dissolved metal ions onto crystal surfaces where dissolved charged species are adsorbed. Accordingly, the dissolution of halite due to human activity can release these metal ions to the environment.

Zr, Hf and REE distribution in river water under different ionic strength conditions.

The Platani River flowing in south-central Sicily, interacting with evaporite rocks, generates a wide range of ionic strength in the water catchment from 0.1 to 5.0molkg-1. We sampled 38 river sites and analysed the composition for the dissolved fraction filtered through 0.45µm, the truly dissolved fraction obtained through ultrafiltration (10kDa) and the relative included colloidal fraction. This study was focused on the recognition of Zr, Hf and REE behaviour under changing ionic strength conditions, since this is one of parameters responsible for colloid stability in natural waters. In turn, this phenomenon leads to REE release from the colloidal fraction and their scavenging onto surfaces of suspended particles or sediment, or their complexation with dissolved ligands. Our results indicated that in both dissolved and ultra-filtrated fractions REE increases either in the middle (Sm - Dy) or in the heavier (Ho - Lu) part of the PAAS-normalised distribution, while the Zr/Hf ratio value ranges from sub-chondritic to super-chondritic. Scanning Electron Microscopic and Energy Dispersive X-ray Spectrometric (SEM-EDS) analyses and dissolved Mg, Al and Fe concentrations suggested that the studied colloids consist of aggregations of Al-oxyhydroxides, carbonate nanoparticles and clays where organic traces were not found. The studied colloids showed greater affinity with dissolved Zr than Hf determining Zr/Hf values larger than the chondritic values. The largest Zr/Hf values were found in colloidal fractions from waters with ionic strength larger than 0.6molkg-1. These Zr/Hf values up to 280 (w/w) are provided by the faster removal of Hf relative to Zr from coagulating colloids and its preferential scavenging onto authigenic Fe-oxyhydroxides in bottom sediment. Further studies are needed to clarify is this suggested process can represent a suitable starting point for the Zr-Hf decoupling observed in seawater.

Trace elements in scalp hair of children chronically exposed to volcanic activity (Mt. Etna, Italy).

The aim of this survey was to use scalp hair as a biomonitor to evaluate the environmental exposure to metals and metalloids of schoolchildren living around the Mt. Etna area, and to verify whether the degree of human exposure to trace elements is subject to changes in local environmental factors. Twenty trace elements were determined in 376 samples of scalp hair from schoolboys (11-13 years old) of both genders, living in ten towns located around the volcanic area of Mt. Etna (Sicily). The results were compared with those (215 samples) from children living in areas of Sicily characterized by a different geological setting (reference site). As, U and V showed much higher concentrations at the volcanic site whereas Sr was particularly more abundant at the reference site. Linear Discriminant Analysis (LDA) indicated an Etna factor, made up of V, U and Mn, and a second factor, concerning the reference site, characterized by Ni and Sr, and to a lesser extent by Mo and Cd. Significant differences in element concentrations were also observed among three different sectors of Mt. Etna area. Young people living in the Mt. Etna area are naturally exposed to enhanced intakes of some metals (V, U, Mn) and non-metals (e.g., As) than individuals of the same age residing in other areas of Sicily, characterized by different lithologies and not influenced by volcanic activity. The petrographic nature of local rocks and the dispersion of the volcanic plume explain the differences, with ingestion of water and local food as the most probable exposure pathways.