Risk analyses - Workplan
This task will focus on the health risks and ecological risks due to arsenic in the environment. All useful data will be collected, and complemented by new results from chemical and ecotoxicological analyses.Human health risk analysis comprises risk identification, dose response assessment and risk charac-terization. Preliminary assessment will be based on As-concentrations in well waters in Pirkanmaa area. Data will be complemented by demographic data and other risk factors. In addition to the well water data, arsenic content and accumulation to crops will be taken into account when assessing the exposure. We will use both national statistics and regional data. Our aim is to describe the possible risk to human health by elevated levels of arsenic in the environment, and also, to provide the un-certainty of the assessment.
Biological effects caused by arsenic and As-concentrations in different environmental compartments are the basis for ecological risk assessment. Because there are only limited measurements of effects on soil animals and plants by Finnish arsenic-rich soils, we will complement the existing data by ecotoxicological tests using samples from appropriate areas in Pirkanmaa region.
It is possible that biological effects of anthropogenic arsenic differ, either qualitatively or quantitatively, from those caused by naturally high concentrations. We will examine these differences by combining chemical and ecotoxicological methods. In the laboratory tests adverse effects are observed during exposure of the test species to the soil samples. We will use germination tests as well survival and reproduction with earthworms (Eisenia fetida) and enchytraeids (Enchytraeus albidus).
Leaching potential of arsenic and metals from contaminated soils over time will be demonstrated by leaching tests, and the potential hazard will be assessed by analyses of the eluates obtained. Leaching tests eluates will be analyzed chemically for arsenic and metal contents as well as ecotoxicological effects on aquatic species. A high priority will be given to the ecological risk assessment of the water courses adjacent to the mining area at the study site. A transport model will be built after analyses of leaching test eluates, measurements of surface runoff and observations of the catchment area.
Summary of Results
To assess the risks of environmental arsenic to human beings and biota, case-specific, quantitative human health risk assessments (HRA) and ecological risk assessments (ERA) were carried out. These risk assessments were focused on the specific site types previously identified in RAMAS -project. In the study area such site types included former wood treatment plants, which had used the CCA chemical, mine sites and areas with high level of natural arsenic in soil or groundwater (Sorvari et al. 2007).
The ecological risk assessment followed a tiered approach recommended on international and national levels (Fig. 5). In tier 0, the environmental concentrations of arsenic were compared with various ecological benchmark values, i.e. risk-based concentration limits. Exceeding of the benchmarks normally indicates the need for a more detailed i.e., baseline assessment (tier 1). Some uptake and intake models were used to derive risk estimates for the identified key species. In tiers 0 and 1, all available concentration data of arsenic in different media (soil, water, air, sediment) was used. In tier 2 we amended the data with the results of ecotoxicity test (Schultz & Joutti 2007) which measure harmful effects on test species at controlled standard conditions. As test species we used aquatic and terrestrial microbes and plants and soil animals. Besides toxicity of contaminants their environmental fate is of concern when assessing the factual risks. Hence, the combination of leaching tests, measuring the potentially available fraction of a compound, and ecotoxicity test with soil samples allowed the derivation of some estimates of possible environmental risks in the future.
The assessment of human health risks (HRA) was based on exposure modelling, human biomonitoring and epidemiological studies. In exposure modelling all the potential intake routes (food consumption, direct contact with soil and consumption of drinking water) were taken into account. Statistical estimates of intake from drinking water were calculated using Monte Carlo simulation based on the results from analyses of arsenic in well water samples. Exposure from other than site-specific sources was estimated from national level data. The potential exposure arising from the key anthropogenic hot spot areas i.e., mine sites and CCA wood impregnation plants was also considered. In case of anthropogenic sources, the primary calculations were based on the highest arsenic levels in order to cover the "worst case" exposure scenarios. The results from the biomonitoring study (urine analyses) and the epidemiological study (number of the incidences of several cancer types) were used to verify potential human exposure and risks on population scale.
The ecological risk assessment based on chemical data and exposure uptake modelling using conservative assumptions resulted in very high risk estimates, i.e hazard quotients (HQs) in the case of the former wood impregnation plant and the mine site. Judged by these results all study sites pose ecological risks varying from moderate to high. However, the ecotoxicological studies produced slightly different results showing high risk only in the case of the CCA plant and low risks in the case of the mine site and areas with high natural arsenic in till. When the results from different study methods were combined, the mine site appeared to pose the highest ecological risks compared with other study sites.
The ERA showed that even naturally occurring arsenic may pose adverse effects to the most sensitive species. Hence, we can expect that some selection of species has occurred at areas with high concentrations of naturally occurring arsenic in soil. The highest natural concentrations in soil are found in the deeper layers which limits the exposure of biota whereas the risks to groundwater quality may be high. In the case of excavations, such material can be brought in to surface layers where it can pose significant risks to biota. Due to the toxicity and steep dose-response effects of arsenic, safety margins need special attention in areas with elevated background levels. The risks to aquatic ecosystem adjacent to the mine site are not expected to decrease with time considering the vast amount of arsenic stored in the tailings area.
The health risk assessment indicated that the arsenic content in the dug well waters, typically below 1 ug/l, apparently do not pose any significant health risk to consumers. The average total arsenic intake within drilled well water users was estimated to be 0.56 ug/kg/d. The probability of exceeding the safe exposure level was estimated to be 5.9 - 46 % depending on the applied regulatory value. However, differences between the arsenic intake estimates in the different parts of the study area are considerable. The biomonitoring study verified exposure from drinking water, i.e., the concentrations of arsenic excreted in the urine were the highest among the users of water containing elevated concentrations of arsenic. However, in few cases high urinary concentrations were detected even though people were not exposed through drinking water. These elevated concentrations might be associated with occupational exposure or exposure, for example, in hobbies. Some evidence for the increased cancer incidence within Tampere region was obtained, although the results need to be interpreted with caution due to several sources of uncertainty that may bias the results. Nevertheless, this is a clear signal that underlines the need for further studies of the health impacts and preventive actions to reduce the exposure.
References:
Schultz, E. & Joutti, A., 2007. Arsenic ecotoxicity in soils. Geological Survey of Finland, Miscellaneous Publications, 53 p.
Sorvari, J., Schultz, E., Rossi, E., Lehtinen, H., Joutti, A., Vaajasaari, K. & Kauppila, T. 2007. Risk Assessment of Natural and Anthropogenic Arsenic in Pirkanmaa Region, Finland. Geological Survey of Finland, Miscellaneous Publications, 126 p.
