Copper and cadmium content in Polish soil: Analysis of 25‐year monitoring study

Abstract Metals can accumulate in agricultural soils, presenting a serious threat to human health; therefore, it is important to analyze the quality of these soils to avoid possible harm related to their contamination in the future. Despite the importance of monitoring arable soil quality, few studies have examined the current state of Cu and Cd soil contamination through analysis of historical data and temporal trends in heavy metal content. Therefore, this study was aimed at analyzing the spatial variability of Cu and Cd content (expressed by toxicity indices) and assessing the level of contamination of arable soils in Poland over the last 25 years (1995–2020). The average Cu content in soil throughout the duration of the study was ~10 mg/kg. The average Cd content increased from 0.7 mg/kg (in 1995) to 3.4 mg/kg (in 2020). The evaluation of Cu and Cd soil contamination showed that soils contaminated with Cd and Cu constituted 1.4% and 2.3% of the total monitoring points, respectively. The geoaccumulation index and pollution index ranged for Cu from −5.23 to 3.09 (mean: −2.50) and from 0.02 to 6.40 (mean: 0.20), and for Cd from −5.23 to 6.92 (mean: −1.67) and from 0.01 to 60.58 (mean: 0.44). The soil was practically uncontaminated with Cu and Cd in 98.77%/98.92% and 93.44%/97.92% of cases, respectively. On a national scale, the contents of Cu and Cd in soils depend on soil properties (pH, C, OM, ST, and CM) to a very small extent. An assessment of the spatial distribution of Cu and Cd concentrations in Polish arable soils indicated regional differences related to the degree of industrialization/urbanization. The obtained results show the impact of human activity on the level of heavy metals present in soils.