Influence of land use in small karst watersheds on the chemical status of peloid sediments on the eastern Adriatic coast

Background, Aim and Scope Most of the cathment areas supplying water and mineral matter to the Adriatic bays with healing mud/peloids are affected by various degrees of human impact, i.e. activity that is introducing various types of contaminants to environment. The bays represent shallow marine depositional environments where organic-rich sediments accumulate. Investigations for balneological characterization of several localities along the Croatian coast have shown that these organic-rich sediments may be classified as healing mud, i.e. peloids. Healing mud due to its balneologic features is in treatment of various diseases and in improvement of the overall health conditions and general well-being. Various components of mud, particularly trace elements, could be absorbed through dermal contact. Therefore, the study of the abundance of such potentially toxic elements as As, Pb, Hg, Cd, Se, Sb, Cu, Zn in marine sediments used as healing mud is necessary in order to know their mobility and to avoid possible intoxications. Methodology In order to assess the most recent record of lithogenic and anthropogenic inputs to the Morinje Bay and Makirina Bay sediments (peloids) on the central Dalmatian coast, concentrations of both lithogenic and potentially toxic element (Cu, Pb, Zn and Mo) concentrations were analysed cores and surface sediments, as well as watershed topsoil. For characterizing the probable anthropogenic effects, the inputs of heavy metals was evaluated by calculation of enrichment factors (EF) for these elements, using Sc as the conservative element. Mobility of metals was assessed by application of the first step (0.11 mol dm −3 CH 3 COOH) of the harmonized BCR three-step sequential extraction procedure. Results Analysis of ten composite toposil samples from the vineyards (5 sampling sites) and uncultivated slopes (5 sampling sites) were used to determine concentrations of metals in soils from the watershed. The Cu concentrations in the vineyard soils ranged from 105 to 553 mg/kg. Analyses of soils with visible traces of the Bordeaux mixture showed that Pb (Pb/Sc 5.6) and Zn (Zn/Sc 21.5) were also being added to the soil. The amount of Cu bound to the carbonate phase of composite vineyard soil was 53.6 mg/kg or 22% of total Cu, while soil containing the Bordeaux mixture contained 2,827 mg/kg of extractable Cu (70% of total Cu), thus indicating that copper is probably supplied to the bay not only with eroded soil but also in runoff solution. Morinje Bay sediments have a higher mean Cu concentration (71.4 mg/kg) than the surrounding soils on limestone (which are not arable) and lower than the soils developed on flysch bedrock (arable soils). In the sediment cores from Morinje Bay, Mo increased (from 4.5 to 43 mg/kg) with increasing depth. The Cu EF in the surface sediments of Makirina Bay fluctuates around 2.5 in the offshore direction and drops to below 2 in the most distant profile. Discussion The calculated enrichment factors or Cu and Pb in sediments of the two bays show that lead is accumulating in the smaller Makirina Bay as a consequence of road runoff which drained into the bay. Copper, on the other hand, is the major indicator of anthropogenic load in the larger Morinje Bay watershed with extensive vineyard activity. Comparisons of total concentrations of the Zn, Pb, and Cu in sediments from both bays shows that they are below PEL for these elements. However, the high accumulation rate of sediment with bio-available Cu could reach levels in Morinje Bay which could cause toxic effects. High amounts of extractable Cu (11–13%) are present in the top 20 cm of the sediment core, which corresponds to the highest Cu enrichment factors (from 2.3 to 4.3). The sediment from the deeper part of the core (75–80 cm) contains only 2.8% of extractable Cu. The anomalous accumulation of Mo in deeper parts of the cores is probably a result of a natural process caused by resolubilization of Mo under aerobic conditions, i.e. upon air-drying of the sediments due to tidal conditions in Morinje Bay. Conclusions The geochemical analyses were performed to evaluate the extent of the anthropogenic contribution from the two major sources of potentially toxic elements to their lithogenic fraction in the sediments. The results for Cu, Pb Zn imply that they have distinct distributions, which imply anthropogenic burdening of the sediments/peloids while Mo is enriched due to natural processes. Since the analysed sediments are topically used as healing mud for various rheumatic diseases, the contents of bioavailable metals is important since heavy metals act directly or indirectly on intercellular proteins in the skin. The results of chemical characterization of heavy metals show that both the calculation of enrichment factors and extraction analysis can identify anthropogenic contribution of heavy metals to the sediment. Contaminants released into coastal environments can limit the use of these sediments for therapeutic purposes and as indicator thresholds. Recommendations and Perspectives Along the eastern Adriatic coast, sediments deposited in shallow bays have frequently been used for balneotherapy, a procedure dating back to Roman times. Due to the high expansion of wellness tourism in Croatia, a demand for healing mud has risen dramatically, leading to both uncontrolled exploitation of sediments and unsupervised application by individuals. Therefore, the results of this study, are intended to be used as an argument for local environmental authorities to plan use of sediments for healing/wellness purposes from bays with watersheds without anthropogenic influence. Also, there is a necessity to determine probable effects levels for bioavailable (mobile) metals and other potentially toxic substances that can enter the human body through the skin. The levels should be defined for both total and extractable levels of elements if the sediments are to be used as healing mud.