engleski

Influence of Land Use in Small Karst Watersheds on the Chemical Status of Peloidic Sediments on the Eastern Adriatic Coast

Background, Aim and Scope. The bays of the Adriatic represent shallow, marine depositional environments where organic-rich sediments accumulate. Investigations for balneological (medical treatment by bathing) characterization of several localities along the Croatian coast have shown that these organic-rich sediments may be classified as healing mud or peloidic sediment. Peloidic sediment is used in the treatment of various diseases and in the improvement of overall health conditions and general well being due to its balneologic features. Various components of peloidic sediment, particularly trace elements, can be absorbed through contact with skin. Most of the catchment areas supplying water and mineral matter to the Adriatic bays that contain peloidic sediment are affected by various degrees of human impact, i.e. activity that is introducing various types of contaminants to the environment. Therefore the study of the abundance of potentially toxic elements, such as As, Pb, Hg, Cd, Se, Sb, Cu and Zn, in marine sediments used as healing mud is necessary in order to know their mobility, so as to avoid possible toxic effects. 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 elements (Cu, Pb, Zn and Mo) were analysed in cores and surface sediments as well as topsoil from the contributing catchments. Probable anthropogenic inputs of heavy metals were 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 CH3COOH) of the harmonized BCR three-step sequential extraction procedure. Results. Analysis of 10 composite topsoil samples from the vineyards (5 sampling sites) and uncultivated slopes (5 sampling sites) were used to determine concentrations of metals in soils delivered from the catchment. The Cu concentrations in the vineyard soils ranged from 105 to 553 mg/kg. Analyses of soils with visible traces of the fungicide “ Bordeaux mixture” (1% mixture of copper sulphate and hydrated lime) 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 2827 mg/kg of extractable Cu (70% of total Cu) indicating that Cu is probably supplied to the bay with both eroded soil and 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 for Cu and Pb in sediments of the two bays show that Pb 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 catchment which has extensive vineyard activity. Comparisons of total concentrations of Zn, Pb and Cu in sediments from both bays shows that they are below probable effects levels (PEL) for these elements. However, the high accumulation rate of sediment with bioavailable 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 the deeper parts of the cores is probably a result of a natural process caused by the resolubilization of Mo under aerobic conditions (i.e. upon air-drying of the sediments due to tidal conditions in Morinje Bay). Conclusions Geochemical assessment was 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 and Zn imply that they have distinct distributions, which suggest anthropogenic contamination of the peolodic sediments while Mo is enriched due to natural processes. Since the analysed sediments are typically used as healing mud for various rheumatic diseases, the content 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 contributions of heavy metals to the sediment. Contaminants released into coastal environments can limit the use of these sediments for therapeutic purposes. Recommendations and Perspectives. Along the eastern Adriatic coast, sediments deposited in shallow bays are frequently used for balneotherapy dating back to the Roman times. Due to the high expansion of wellness tourism in Croatia, a demand for healing mud/sediment has risen dramatically leading to both uncontrolled exploitation of sediments and to unsupervised application by individuals. Therefore, the results of this study are intended to be used as an argument for local environmental authorities to use sediments for healing and wellness purposes from bays that contain catchments without significant anthropogenic influences. 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.

healing mud; peloidic sediment; clay; contaminated sediment; heavy metals; extraction; bioavailability; karst catchments; soil; normalization; enrichment factors

DOI: http://dx.doi.org/10.1065/jss2007.10.254