Ambient geochemical baselines for trace elements in Chernozems—approximation of geochemical soil transformation in an agricultural area

Abstract

The legal regulatory/action levels of trace elements in soils are established at high concentrations, at which the crucial functions of soil are at risk or are eliminated. However, concentrations below these action levels, but above presumed natural levels, may also limit particular ecosystem services, including organic food production. Thus, defining the (ambient) background concentrations is an essential part of environmental or health risk assessment, e.g., on Chernozems, which are considered to be the most productive soils and ones that should be protected against all forms of contamination. Based on 28 profiles of chernozemic soils developed from loess in an agricultural region of SW Poland presumed to be free of industrial contamination, ambient geochemical baselines have been derived for Fe and six trace metals for four standardized soil layers, including the topsoil (plow layer) and parent material layers. The median values for the plow layer (1.89% for Fe, and 537, 49, 17, 14, and 26 mg kg−1 for Mn, Zn, Pb, Cu, and Ni, respectively) are lower than the values reported for other Chernozems in SE Poland/Europe/the world, and thus may serve as a general geochemical baseline for chernozemic soils developed from loess. The concentration of Cd, although lower than in other Chernozems around the world, is higher than in Ukrainian Chernozems and thus may serve as a local (or Central European) baseline only. The median concentrations of Fe, Cu, Mn, and Zn are very close to their concentrations in the Chernozem buried under the Neolithic kurgan. However, Pb and Cd concentrations are two times higher than in the buried soil, indicating the scale of general contamination of the topsoil horizons of arable soils. Concentrations of the elements under study, excluding Fe, in both the buried and surface soils are significantly higher in the topsoil layer compared to parent material (loess), and this justifies the separate baseline values for topsoil horizons, instead of background values derived universally for parent rock types. This is essential, in particular in soils texturally differentiated within profiles, where the subsoil material has a different origin and cannot be considered the parent material for topsoil horizons. Underlying or locally outcropped bedrock (e.g., serpentinite rocks) may naturally enhance the total concentration of trace elements in the entire soil profile by the addition of metal-rich regolith particles during the formation of surface covers, e.g., by eolian processes under periglacial conditions (Late Pleistocene). Such soils are naturally enriched with metals (with nickel in the case of serpentinite bedrock), cannot be considered contaminated, and thus require a separate legal treatment, including separate (or individually suited) background baselines for health risk assessments.

Geochemical Baseline Values Determination and Evaluation of Heavy Metal Contamination in Soils of Lanping Mining Valley (Yunnan Province, China)

“…In the case of soils of the upstream area, concentrations of heavy metals from all the horizons were used to calculate the baseline, which was conducted by adding the geometric mean to twice the standard deviation [3,38,39] (Table 3). The proposed baseline values of Pb, Cu, Zn and Cd were 169.93, 31.81, 569.06 and 4.13 mg·kg −1 , respectively.…”

“…The application of the regional geochemical baseline values proposed in this study will allow the rapid identification of sites that could be affected by pollution processes due to current mining exploitation in the area [3]. In addition, this information will also be very useful for a restoration plan to try to reproduce the environmental conditions that existed prior to mining [39,42].…”

“…Soil heavy metal pollution is a common environmental problem of global concern [1,2,3]. The main causes of soil pollution include human activities such as industry, mining, agriculture and high background values of soil.…”

“…The determination of environmental geochemical baselines, which should be different for each heavy metal in geologically different regions, is necessary to understand the situation of the environment and to provide soil quality standard values in the evaluation of contaminated soils and environmental risk [13,14]. The value of the geochemical baseline could be calculated with the addition of the arithmetic or geometric mean at twice the value of the standard deviation, considering the diffuse entry of these elements into soils [3,15,16]. Many studies on soil heavy metal contamination have been carried out in the Pb and Zn mine area in China, and the environmental geochemical baseline, which could be an important aid to the location of contaminated areas and to the recognition of anthropogenic inputs, is still lacking.…”

Chemometric Assessment of Soil Pollution and Pollution Source Apportionment for an Industrially Impacted Region around a Non-Ferrous Metal Smelter in Bulgaria

“…Chemometric methods for data mining and modeling, such as principal components analysis (PCA) or principal components regression (PCR) are often used for the identification of factors influencing the soil pollution and the bioavailability of heavy metals [ 9 , 10 , 11 , 16 ]. Some useful chemometric methods for source apportionment include [ 11 , 17 , 18 ].…”