Environmental assessment of the impact of agricultural activities on the concentration of potentially toxic elements in surface soils of Ashkezar greenhouses in Yazd

The particle diameter in the studied soils is 12-28% sand, 31-40% silt and 32-48% clay and there is no significant difference in the grain size composition of agricultural and non-agricultural soils. The study of the concentration of potentially toxic elements (Cd, Co, Cr, Cu, Ni, Pb and Zn) in soils contaminated and uncontaminated with agricultural fertilizers in greenhouses in Ashkzar County shows that agricultural activities have increased the concentration of these elements in soils, so that the permissible level of most elements is higher than the optimal level and the country's environmental organization, and its increase in contaminated soils has increased pollution measurement criteria such as the land accumulation index. The bioavailability of potentially toxic elements by the DTPA method for all elements in contaminated soils is significantly higher than in uncontaminated soils (samples ASH-2 and ASH-10). The changes in the increase in the bioavailability of these elements in different samples are also different. The highest bioavailability of Cd, Co and Zn elements is observed in sample ASH-1, while sample ASH-8 has the highest bioavailability of heavy metals Cr, Cu, Ni and Pb. TOC and pH of the environment are considered to be one of the basic factors in speciation, mobility, reactivity and bioavailability of heavy metals. All soils in the region have a pH above seven (7.15 to 8.74, slightly alkaline) and the pH in contaminated (agricultural) soils gradually decreases until it reaches the lowest value (7.15) in sample ASH-8. The range of TOC changes is limited and the trend of pH and TOC changes in the studied samples is almost opposite to each other, so that with increasing TOC, pH decreases relatively; and there is a significant relationship between pH and heavy metal concentration.