Anthropogenic arsenic - Workplan
Arsenic is released in the environment through a large variety of natural and anthropogenic sources. It is mobilized in aquifers, runs off from wastes left by the mining of sulphide metallic ores, and is released to the environment in the production of ceramics, application of wood preservatives and from landfills. In some countries drinking water forms an important source of arsenic, but in many other countries food, mining and industrial related exposure routes are posing important health risks.The safety limit for arsenic in soil is 50 mg/kg.Information on the contaminated sites at Pirkanmaa region has been collected into the the Register of Contaminated Land Areas which is maintained by the Regional Environmental Centers of Finland. This information is readily applicable for risk area definition, for selection of the test sites for detailed investigations (ecotoxicology, As transport etc.) and for risk assessment. For example, there are 14 wood preservative treatment plants in the research area, two of which are located within sensitive groundwater formation areas.
Additional information will be obtained from the municipalities which have carried out investigations on contaminated areas within their own territory. The collected data mainly describes the arsenic (and heavy metal) concentrations in soils, but some information is available on surface waters and on monitoring wells around sites under special supervision or remediation actions.
At the Cu-W-As mine site effluents have been monitored during operation and after closing the mine in 1966. An investigation of the present state of the mine site was carried out in 2001-2002. Geophysical, geochemical, mineralogical and peat investigations were carried out.
Some samplings will be conducted in the mine site in order to complement the existing data with peat and water samples. Selected soil will be sampled for ecotoxicological tests and leaching experiments from the vicinity of the mine waste area and also from selected wood preservative treatment plants. Mapping of vegetation and sampling of the dominant plant species will be done from the mine site and from selected wood preservative treatment plants to demonstrate the bioaccumulation of arsenic by plants.
The geochemical information from contaminated sites will be collected in a databases and risk area maps are compiled in the same way as is done for the natural source areas.
Summary of Results
Data was acquired about chemicals (wood impregnates, pesticides), products (ammunition, fertilizers, fodder), and industrial activities e.g. mining and waste treatment sites. RAMAS project also studied the possible role of landfill leachates in mobilizing the naturally occurring arsenic from the surrounding till. The most relevant arsenic sources at Tampere region turned out to be the wood preservative plants and the old mine sites (Parviainen et al. 2006).
Altogether 14 wood treatment plants were identified from the study area, two of which were in operation until late 2006, when the use of chromated copper arsenate (CCA) -based wood treatment was banned. The negligent use of CCA products, inappropriate storage of CCA-treated wood and the use of the impregnated wood in the past have caused soil, surface water and groundwater contamination. Concentrations of arsenic in the contaminated soils at CCA plants in the study area range from 3 up to 12000 mg/kg. The majority of harmful elements from the CCA-contaminated soils have already leached and migrated over time and at present the leaching is slow but continuous. The ecotoxicological tests carried out within the RAMAS project showed that the soils heavily contaminated by CCA appeared to be toxic to some organisms. There were also indications that copper rather than arsenic might be the cause of environmental hazards.
Mining of sulphide ores leaves behind waste rock and tailings areas giving rise to acid mine drainage and consequent release of harmful elements. There are five mine sites in the study area two of which, the Haveri Cu-Au mine and the Ylöjärvi Cu-W-As mine, were studied in RAMAS Project. The ore in Ylöjärvi contained 1200-4600 mg/kg of arsenic, while at Haveri the arsenic concentrations were well below 100 mg/kg.
The Ylöjärvi mining area has been identified as a potential source for arsenic contamination already years ago and, therefore, the nearby surface waters have been monitored since early 1970. The tailings area has an impact on the quality of surface waters and the active period of the mine can be traced from the lake sediment layers of nearby lakes and streams. The tailings area contains high concentration of arsenic ranging from 1000 to 2200 mg/kg resulting to run-off, which contains up to 250 ug/l of arsenic. The arsenic concentrations in surface water decline gradually downstream so that after seven kilometers, the load to Lake Näsijärvi is 3-14 ug/l. It is evident from the lake sediment profiles that during the mining period much more arsenic has been available along the route. At Lake Näsijärvi the sediment layers accumulated during mining contain 235 mg/kg of arsenic, whereas the natural background level was 17 mg/kg. The recent sediments still contain arsenic twice the amount of the natural background indicating that the tailings area is continuously stressing the environment.
References:
Bilaletdin, Ä., Kaipainen, H., Parviainen, A., Kauppila, T. & Ruskeeniemi, T. 2007. A transport model of arsenic for surface waters - An application in Finland Geological Survey of Finland, Miscellaneous Publications, 33 p.
Parviainen, A., Vaajasaari, K., Loukola-Ruskeeniemi, K., Kauppila, T., Bilaletdin, Ä., Kaipainen, H., Tammenmaa, J. & Hokkanen, T. 2006. Anthropogenic Arsenic Sources in the Pirkanmaa Region in Finland. Geological Survey of Finland, Miscellaneous Publications, 72 p.
