Pitfalls of distinguishing anthropogenic and geogenic reasons for risk elements in soils around coal-fired power plants: from a case study in the Northwestern Czech Republic to general recommendations

Purpose Many historical industrial activities, including coal mining and burning, have started near geogenic anomalies. It resulted in spatial overlap of anthropogenic and natural causes of elevated soil risk element contents. Here, distinguishing between anthropogenic and geogenic contributions cannot be achieved by conventional geochemical soil mapping, in particular, when only pseudo-total contents of risk elements were obtained, soil depth profiles were not acquired, and geological maps were not implemented. Methods The local geology, topography and anthropogenic activities were taken into account when planning the soil sampling. Soil profiles were obtained using an auger sampler. Total contents of risk and lithogenic elements were obtained by X-ray fluorescence. Aqua regia extraction and inductively coupled plasma mass spectrometry (ICP-MS) were also used for analyses. Results Coal use in the study area increased the soil contents of Cd, Hg, and Zn in 7 km circle east of the major power plant, typically to 2 × local background in topsoils. In the profiles closest to that plant, Cd emissions have already been translocated to soils below ploughed horizons that weaken the contamination signal in topsoils. The highest As and Pb contents in the Most Basin soils originated from a local geogenic anomaly and not coal burning. Conclusion Common soil mapping projects and data mining routines cannot decipher anthropogenic contribution to the soil risk elements unequivocally, as it is demonstrated in this paper. When working in geogenically anomalous areas, a fundamental knowledge of the mechanisms controlling the content of risk elements in soils is required.