Assessment of heavy metal concentrations and behavior in cultivated soils under humid-subhumid environmental condition of the Black Sea region

Abstract

In present time, contamination of soils with heavy metals has become a serious problem for the ecosystem, which is caused not only by industrial wastes but also by natural reasons such as geological origin and other human impact e.g., agricultural activities. This study discussed the sources of heavy metals, their spatial distribution, and factors affecting mobilization or retention mechanisms in soils. Soil pH (soil acidity), clay content, and soil organic matter content were studied as the main properties affecting the behavior of heavy metals in soil formed under humid and subhumid coastal environmental conditions. For this purpose, 3395 soil samples were collected from agricultural lands in the central and eastern Black Sea Regions. The results show that agricultural soils in the region have medium texture, high organic matter content, and an acidic response. While the average concentration levels of total heavy metal contents were determined as Fe > Mn > Ni > Zn > Cr > Cu > Pb > Co > Cd, the average levels of available heavy metal contents were Fe > Mn > Cu > Zn > Ni > Co > Cd > Cr in soil samples. When enrichment factor (EF) values of the soils were examined, the values of Cd and Pb were above 2, while the EF values of the other heavy metal elements were below 2; that is, they were classified as deficiency to minimal enrichment. It was also found that the heavy metals Cu and Cd had the highest availability ratio values (AR). In addition, a path analysis was carried out to determine the effects of pH, clay content, and soil organic matter content on the behavior of heavy metals. Direct effects on extractable and total forms of heavy metals was ranked as pH > OM = Clay, while the impacts on EF and AR was ranked as OM > pH > Clay.