Excess Cr and Ni in top soil: Comparing the effect of geology, diffuse contamination, and biogenic influence

Chromium (Cr) and nickel (Ni) are among the elements that are most mined, processed and used in modern industry and society. A realistic estimate of the diffuse contamination that has left a footprint on soil during the last 200 years by worldwide industrialization requires recognition and assessment of the dominant natural and anthropogenic sources. The relations between geogenic, anthropogenic, and biogenic Cr and Ni sources are estimated from eight large-scale geochemical surveys, by comparing the cumulative distribution functions (CDF) of the elements in top-and sub soil using cumulative probability (CP) diagrams. This method makes it possible to estimate the effect of long-term diffuse contamination on soil without monitoring. The method offers a cheaper and more reliable method for estimating dif-fuse contamination at the continental to regional scale than classical monitoring methods. The impact of diffuse con-tamination can be recognized at the low-concentration end while strong local contamination is shown as a distort at the high-concentration end of the distribution. Chromium, due to its structural similarities with essential nutrients, shows a clear biological signal in the CP-diagram. The bio-adjustment of Cr and Ni limits the accuracy of the diffuse contamination estimates. Combining CDF analysis with spatial mapping provides insight into the dominant contami-nation processes that distort the top soil CDF relative to the sub soil CDF. For both elements, a diffuse contamination signal of <1 mg/kg is obtained for soils at the European scale. Agricultural soil is affected by contamination from farm-ing practices and shows higher excess Cr and Ni in top soil than forest soil. Although the world has faced several cen-turies of industrial development and Cr and Ni are used everywhere, this is not reflected in surface soil at the continental to regional scale. The regional distribution of both elements is dominated by natural sources and processes.

Automated summary

Chromium and nickel are widely used elements in modern industry and society. It is important to recognize and assess the sources of diffuse contamination in soil caused by global industrialization. A method comparing the distribution of chromium and nickel in topsoil and subsoil allows for estimation of their sources and effects. This method is cheaper and more reliable than traditional monitoring methods. Chromium shows a clear biological signal in the analysis. Agricultural soil is more contaminated due to farming practices.