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The Vrana Basin, located in the central part of Croatian Adriatic Sea coast, is a typical cryptodepression formed by tectonic activities, with agricultural land and Lake Vrana situated in the very basin. The area is ecologically highly sensitive and it is characterised by intensive vegetable production in a karst environment where, due to geological and climatic conditions as well as anthropogenic influence, it is easy for harmful substances to enter the food chain or penetrate ground water or open watercourses. This threatens the largest Croatian lake, Lake Vrana, as well, which is a large potential source of water for agriculture, possibly also drinking water, as well as for tourism and leisure activities. Because it is one of the rare natural habitats of waterbirds as well as because of its fresh water springs and biodiversity, the Vrana Lake and its surroundings have been declared a nature park. To evaluate the impact of natural processes and agricultural practice on trace metals accumulation and behaviour in soils a multi-element geochemical survey was carried out. The main objective of this study was to identify the main factors that control the spatial distribution of soil trace elements (TEs) in topsoil from the Mediterranean agricultural karst catchment by using multivariate statistics and geostatistics. Topsoil (0-30 cm) samples were taken from 75 locations within the 6830 ha of pastures and agricultural fields in the Vrana Lake Basin applying a stratified random sampling scheme, based on regular 500x500 m grid, with exceptions of inability to access certain sampling points. Core samples were bulked to obtain a composite sample from each location. The observation sites were spatially referenced using GPS and data were stored in different GIS layers. Main soil physico-chemical characteristics were determined along with the TEs contents (Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Ni, P, Pb, Zn) after aqua regia extraction. Reactive pools of Cd, Cu, Pb and Zn were assessed as well using 0.43 M HNO3 extraction. The resulting data were examined through principal component analysis (PCA) that is the multivariate technique most extensively used for processing the results of TEs concentrations in soils. PCA enables the interpretation of the mutual influence or the presence some common or opposite characteristics, such as soil and landscape properties or source of the elements. The analysis of large number of variables (pH, organic matter, calcium carbonate, available K2O and P2O5, trace element contents, particle-size distribution: sand, silt and clay) proved that the main factors controlling TEs distribution are soil texture and variations in parent material and weathering. Land use and agricultural practices have been identified as secondary factors affecting topsoil TEs distribution relating mostly to pH and organic carbon variations. A geochemical baseline model is used to quantify metal enrichments (Cd, Cu, Pb and Zn) in the topsoil and separate them from natural metal concentrations in soils (using Fe2O3). Regression analyses showed very meaningful relationship in which topsoil samples are enriched, to varying extents, as compared to subsoil samples. Also, there is a linear relationship between total metal concentrations and enrichments. Geostatistical interpolation using co-kriging method was applied to map topsoil TEs distribution over the study area. This method included Gaussian anamorphosis modelling for TEs which did not have normal distribution and variogram fitting for selected TEs. Both the results of PCA and co-kriging method provided evidence of strong spatial structures attributed to different natural processes. The methodology used has proved to be a useful tool to separate geological and anthropogenic causes of variation in soil heavy metal content and to identify common pollution sources.

Beside anthropogenic sources, trace metals can be found in the parent material from which the soils develop. Whether these inputs will become toxic and to what degree mobile depends on a number of factors: specific chemical and physical trace metal characteristics, soil type, land use, geomorphological characteristics within the soil type and exposure to emission sources. Processes that control the mobility, transformation and toxicity of metals in soil are of special importance in the soil root developing zone – the rhizosphere. For this reason, there is a considerable interest in understanding trace metals behaviour in soil, with special emphasis on the way they enter the soil and on processes by which plants take them up. Full understanding and prediction of chemical behaviour of an element in the environment is possible only by identification of all forms in which that element can be found under different environmental conditions. Various chemical methods, geochemical models and biotests are used for assessment of the bioavailable metal fraction in soil. However, these methods are not universally applicable for all elements and different soil characteristics. Chemical methods for assessment of metal bioavailability are commonly grouped within methods for identification of total metal content in soil, methods for assessment of currently available and potentially available fractions, as well as methods for prediction of metal speciation in soil solution. This article offers a critical review of methodologies available for assessing metal speciation in solid and liquid phases in soils taking into consideration the array of parameters that might influence uptake and effects upon the plant., European Chemical Bulletin, Vol 1, No 11 (2012): European Chemical Bulletin

Soil degradation under excessive salinity and pollution by potentially toxic metals are increasing rapidly in agricultural areas, representing a serious threat to food production and human food security. A factorial combination of four salt concentrations (0, 20, 40 and 60 mM NaCl) and three cadmium (Cd) levels (0.3, 2.5 and 5 mg kg-1) in peat soil on mineral uptake/distribution in radish plants (Raphanus sativus L. var. sativus) was studied under the greenhouse conditions. After 34 days of exposure to increasing NaCl concentrations, plants proportionally increased Na and Cl accumulation in leaf and hypocotyl tissues. Salinity significantly increased accumulation of Cd (up to 20%), Cu (up to 11%) and Zn (up to 7%) in leaves. In contrast, raising salinity levels did not affect Cd and Cu translocation from leaves and deposition into the edible hypocotyls, which may indicate that the phloem mobility of those elements in radish plants is relatively poor and unaffected by NaCl exposure. Increasing salinity improved Zn accumulation in the hypocotyl tissue up to 27%. Soil contamination by Cd resulted in 10-fold increases of Cd content in leaf and hypocotyl tissues, and significant decreases of Zn and Cu content in leaves. Cu and Zn deposition in radish hypocotyls was unaffected under saline conditions. Leaf accumulation of all observed metals (Na, Cd, Zn and Cu) exceeded their accumulation in edible tissues, suggesting that the apoplast and the vacuoles of leaf cells may be the sites of preferential deposition of these metals.

Human-induced salinization and trace element contamination are widespread and increasing rapidly, but their interactions and environmental consequences are poorly understood. Phytoaccumulation, as the crucial entry pathway for biotoxic Cd into the human foodstuffs, correlates positively with rhizosphere salinity. Hypothesising that organic matter decreases the bioavailable Cd2+ pool and therefore restricts its phytoextraction, we assessed the effects of four salinity levels (0, 20, 40 and 60 mM NaCl) and three Cd levels (0.3, 5.5 and 10.4 mg kg− 1) in peat soil on mineral accumulation/distribution as well as vegetative growth and fruit yield parameters of muskmelon (Cucumis melo L.) in a greenhouse. Salt stress reduced shoot biomass and fruit production, accompanied by increased Na and Cl and decreased K concentration in above-ground tissues. A 25- and 50-day exposure to salinity increased Cd accumulation in leaves up to 87% and 46%, respectively. Accumulation of Cd in the fruits was up to 43 times lower than in leaves and remained unaltered by salinity. Soil contamination by Cd enhanced its accumulation in muskmelon tissues by an order of magnitude compared with non-contaminated control. In the drainage solution, concentrations of Na and Cl slightly exceeded those in the irrigation solution, whereas Cd concentration in drainage solution was lower by 2–3 orders of magnitude than the total amount added. Chemical speciation and distribution modelling (NICA-Donnan) using Visual MINTEQ showed predominance of dissolved organic ligands in Cd chemisorption and complexation in all treatments; however, an increase in salt addition caused a decrease in organic Cd complexes from 99 to 71%, with free Cd2+ increasing up to 6% and Cd-chlorocomplexes up to 23%. This work highlights the importance of soil organic reactive surfaces in reducing trace element bioavailability and phytoaccumulation. Chloride salinity increased Cd accumulation in leaves but not in fruit peel and pulp.