Influence of Ancient Mining Settlements on Arsenic Pollution in the Southwest of Tuscany
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Influence of ancient mining settlements on Arsenic pollution in the southwest of Tuscany A. Donati1, G. Protano2, F. Riccobono2, L. Dallai3, R. Francovich3, F. Rossi1 & E . Tiezzi1 1Department of Chemical & Biosystem Science, University of Siena, Siena, Italy 2Department of Environmental Science, University of Siena, Siena, Italy 3Department of Archeology, University of Siena, Siena, Italy Abstract Italian law concerning the remediation of polluted areas forces the responsible party of the contamination to provide the complete characterization of the site, the project and the operative tasks for cleaning up soils and waters. In this context, determining the origin of pollution is mandatory for a correct approach to the whole remediation process. Our research group has been studying for two years the problem of Arsenic pollution in the area of an industrial plant for the production of sulphuric acid (SA) from pyrite roasting. The plant is located in a former wetland, in Scarlino, southwest of Tuscany. Horizontal distribution shows an almost regular decrease in the As concentration going far from the plant, but with the presence of “hot spots” ([As]> 600 ppm) at large distance. Other irregularities in the vertical distribution of As concentration in the clay-rich soil, were found. Several evidences identified the SA plant wastes as largely responsible for the high Arsenic levels of the soil, but other theories were suggested. One of the prominent explanations concerned the natural Arsenic anomaly of the area; this was proposed to explain the wide distribution of the element and its irregular trend. This hypothesis was supported by the fact that the site under study is relatively close (about 15 km south-west) to the “Colline Metallifere” mine field, from which pyrite and blended sulfides were extracted. In fact, As enriched sediments could be transported from the river and stream beds which originate in that area. Brownfield Sites II, A. Donati, C. Rossi & C. A. Brebbia (Editors) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-719-1 184 Brownfield Sites II In order to verify the basis of these theories and the mechanism of As diffusion in the environment, we started an extensive sampling of the stream sediments of several rivers which originate in the mining field area. Comparing all the data for Arsenic and other elements we were able to demonstrate that: i) the natural Arsenic levels were significantly lower than the values recorded in the site under study; ii) other wetlands with similar geo- mineralogical origin as the former Scarlino wetland did not present Arsenic and other metal anomalies; iii) all the high Arsenic values found in the stream sediments of the stream beds studied and in the soil were correlated with the presence of ancient mining sites or iron smelter. The results obtained are in favour of an anthropogenic source of the high Arsenic level in the site under study. 1 Introduction The redevelopment chances of a polluted area are related to the correctness of the whole remediation process. In particular, the accuracy of the early characterization of the site is fundamental for the two subsequent, “Preliminary” and “Operative” cleaning projects. The “Characterization” step, which is mandatory for law, is devoted to obtain an accurate knowledge of the geochemical and environmental features of the polluted site, as well as the sources, the diffusion routes and the risks for resident population. This preliminary analysis is essential to define the remediation goal (RG). The Italian law (but this is true also for other country) provided that RG can be modulated with respect to several scientific, technical and economic parameters. Consequently, a polluted area can be completely remedied for a full redevelopment or only partially cleaned without the possibility of a complete recover. Obviously, for the same site the costs of these two limit cases are very different, and the interest for environment preservation and restoration is often in contrast with the economic concerns of the subjects which are responsible for the pollution and the consequent remediation process. In the present work we report the case of a polluted area in the south-west of Tuscany which has been strongly impacted by the presence of a wide industrial plant since early 60th years [1-5]. The soil and the ground water of the area, which must be considered a partially refilled wetland, have been found polluted with high Arsenic levels. In several soil samples the element can reach more than 100 fold the limit and for ground water samples the concentration was found up to 200 fold the law limits. The main Companies in the area are Nuova Solmine s.p.a. and Huntsman Tioxide Europe, producing sulphuric acid from pyrite and titanium dioxide respectively. With respect to the Arsenic problem, attention is concentrated only on the big plant for the production of sulfuric acid from pyrite combustion (SAP). In fact, it is well known that mining and processing of pyrite ores induces a rising of Arsenic levels in the impacted area. Moreover, here, for several decades, the Brownfield Sites II, A. Donati, C. Rossi & C. A. Brebbia (Editors) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-719-1 Brownfield Sites II 185 wastes of the milling, enrichment and combustion of pyrite, have been stored in the ground without any form of protection. The complete picture of the site is complicated by the fact that the pyrite ores were produced in a minefield (Colline Metallifere) which is geographically related to the Scarlino plan (about 15 km east of the site). This induces a high grade of uncertainty to clarify the origin of the Arsenic anomaly. The hypotheses oscillate between two limit cases: anthropogenic impact due to the SAP plant and natural effect due to the mineralized border area. This uncertainty induces a difficulty to define the RG. In this frame several authors attempted to clearly define the origin of pollution. In this paper we describe the results of an extensive sampling of fluvial sediments collected from two very similar rivers and their affluents, which flows almost parallel from the “Colline Metallifere” towards the coastal wetlands: the Pecora river, which flows in the Scarlino plan and the Bruna river which flows in the Castiglion della Pescaia wetland. Important is to point out that the two twin rivers source and flows through identical geological and mineralogical territories, and both, until the middle 19th century, had as terminal point two similar coastal lake. Both these coastal lagoons underwent to similar filling processes, but their final destinations have been completely different. In fact, as reported above the Scarlino site was strongly industrialized conversely the Castiglion della Pescaia wetland was preserved as natural reservoir. From a comparative study of these two environments we were able to establish the extent of Arsenic natural background. Moreover we accumulated strong evidences of the importance of ancient mining and smelter sites in the formation of the environmental geochemistry as it is now. The re-use of these polluted areas, both for industrial and residential scope is considered as a priority for the local administrations. Consequently, understanding and solving the problem of the wide Arsenic dispersion is fundamental for a correct and safe remediation. 2 Experimental Samples of sediment were collected along the course of the Pecora River together with samples of their affluent. The fraction of 150µm of the dried matter was homogenized and digested with a mix of fluoridric acid, percloric acid, nitric acid and cloridric acid in a microwave oven. Arsenic concentrations were determined by graphite furnace – atomic absorption spectroscopy (GF-AAS). 3 Results and discussion In Figure 1 are reported the sampling points of the fluvial sediments, over the map of the hydrographic basins of the PR of the Colline Metallifere district. The distribution of Arsenic concentration appears irregular and it was not easily interpretable only on geological basis. In fact, several points present completely different levels even if they are very close in space. One example of this fact was easily recognizable observing the small affluent of PR in the median-terminal Brownfield Sites II, A. Donati, C. Rossi & C. A. Brebbia (Editors) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-719-1 186 Brownfield Sites II tract of its course. In the whole run of the PR, we observed that in the initial tract Arsenic concentration was ranging from 40-70 ppm. These values can be considered relatively high with respect to the average Tuscan concentration (7 ppm), but normal for a mineralized area like the Colline Metallifere. The river rapidly (in three kilometers) approach to a sedimentary plan and from here it flows slowly until the mouth in the Scarlino pond. From geological maps we observed that the type of sediments in which did not vary appreciably through its path. After about 11 km the Arsenic concentration showed a peak of 185 ppm. Monte Arsenti 78 50 34 Pecora MASSA MARITTIMA Fosso Venelle 35 65 94 28 421 MARSILIANA 183 58 34 39 89 VALPIANA 42 199 Fosso Valmora 122 53 212 205 307 190 221 193 382 188 313 273 14 153 191 Gora delle Ferriere 188 183 140 SCARLINO SCALO 152 FOLLONICA 114 INDUSTRIAL AREA Figure 1: Position and Arsenic concentration for fluvial sediments samples of the Pecora river basin. The Scarlino industrial area and the major towns and villages are also reported. Pecora river is reported as bold line and bold figures are its Arsenic concentrations. Brownfield Sites II, A. Donati, C. Rossi & C. A. Brebbia (Editors) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-719-1 Brownfield Sites II 187 After that it returns to low values. After about 16km Arsenic level grown again and remained high until the mouth (Figure 2).