Geological boundaries can’t prevent the spread of chemical pollution – it’s a global risk

Obviously, pollution did not respect geographical boundaries. Pollutants can transfer from one soil to another through wind blows or water runoff among other carriers. Soil pollution is associated mainly with human activities such as urbanization, agricultural, and industrial developments. For example, in the adjacent surrounding urban areas, continuous disposing of untreated wastewater into the soil is an obvious example of the accumulation of toxic chemical and biological contaminants in soil (Elbana et al. ). In the agricultural sector, the use of fertilizers causes the accumulation of some potentially toxic elements that adversely affect plants and soil biota in the long term. Polluted air, wastewater, and the applied agrochemicals in agriculture can be considered as sources of soil pollution. These different sources can carry numerous organic, inorganic, and biological pollutants. The fate of different pollutants in a soil depends on the physical, chemical, and biological characteristics of the soil as well as pollutant characteristics. Reactivity and mobility of chemical pollutants are controlled by many factors including soil reaction (pH), soil organic matter (OM), ion exchange capacity, and calcium carbonate contents, oxides and hydroxides among other (Han ; Shaheen et al. ; Kabata-Pendias ; Kodešová et al. ). Consequentially, the different soils exhibit varied potentiality to retain or release certain contaminant. Moreover, the retention and release of a specific contaminant are regulated by adding another reactive chemical into the soil. Elbana and Selim () showed that the release of Cd was influenced by introducing Cu into a soil column, whereas the release of Pb was not affected by introducing Cd or Cu into a soil that has 2.8% CaCO3.

Vulnerability of surface and ground waters for contamination is directly related to polluted soil. This vulnerability depends on soil properties that control contaminant sorption and mobility in soil. The contaminants are generally more mobile in sandy soils that have low CaCO3, OM, and amorphous oxides contents than its mobility in the clay soils that usually exhibit higher CEC. Under intensive agricultural system, Muhammetoğlu et al. () explained that in addition to soil properties, the depth of the groundwater and the quality of irrigation water are key factors for groundwater vulnerability. Ceplecha et al. () applied vulnerability matrix as a field assessment tool to evaluate the groundwater vulnerability to nitrate contamination. They considered soil texture, irrigation efficiency, nitrogen application rate/timing, and best management practices for quantifying vulnerability rating. Aquifer contamination with N and P due to chemical fertilization in the Nile valley, Egypt was explored by Shamrukh et al. (). They concluded the implementation of the best management practices to control nitrate leaching especially for the newly reclaimed areas where there is an absence of clay–silt cap. In addition, they related the contamination of shallow depth with nitrate because of the nearness to the agricultural regions. However, their study emphasized that P fertilization was not the source of groundwater contamination. Moreover, the pesticides vulnerability of the Quaternary aquifer in Sohag area, Upper Egypt, was high to very high because of the high hydraulic conductivity of this aquifer (Ahmed ).