Solid Phases of Zn in Some Contaminated Soils in Sohag, Egypt.

Abstract

Almost all human activities have contaminated or polluted vast soil tracts. Measuring the total metal concentration needs to provide more information on the bioavailability or toxicity of metals. Therefore, it has been established that the free metal ion concentration (or activity) is crucial in determining metal bioavailability and toxicity in most circumstances. The present study aimed to:1-evaluate the effects of prolonged use of three types of irrigated water (sewage effluent-, industrial effluent-and Nile-water) on some soil properties, 2-determine the active portion of Zn 2+ , and 3-identify the possible solid phases (minerals), which govern the solubility of Zn2+ in some soil in Sohag Governorate, using stability mineral diagrams. The results revealed that clay content increased by 3.38 %, 9.2 %, and 14.64%) in industrial -, sewage -, and Nile-irrigated soil, respectively, over their corresponding values in the last layer of their profiles. Organic matter increased by 10 %, 30.9 %, and 8.69 % in industrial-, sewage-and Nileirrigated soil, respectively. While CaCO3 content decreased by 5.21%, 19.78 %, and 12.85% in industrial-, sewage-and Nileirrigated soil, respectively. Soil acidity (pH) increased in industrial effluent irrigated soil by (9.65%), while it decreased by (6%) in both Nile-and sewage-effluent irrigated soil. Soil salinity increased in industrial and sewage effluent irrigated soil by 38.51% and 40.58%, respectively. However, the continual use of Nile water declined EC by 6.77% over their corresponding values in the last layer of their profiles. Moreover, the data also manifest that the continuous use of sewage effluent water in irrigation increased Zn content in soil by 877%, followed by industrial effluent irrigated water (525.3%), while in the Nile irrigated water soil, zinc content only increased by 1.42 %, over their corresponding values in the last layer of their profiles. The measured Zn2+ activities in the tested soils varied widely among the tested soil. It could be arranged to ascend as follows; in uncontaminated soil (Sohag) (5.24552 E-10 Ml) followed by industrial effluent irrigated soil (Gerga) ( 2.05739E-09 Ml) and sewage effluent irrigated soil (Kola) (4.20663E-09 Ml). It is clear from these results that the continual use of industrial effluent water or sewage effluent water in irrigation has led to an increase in Zn activity by about (3.9 and 8) times, respectively, higher than its value in Nile irrigated soil. The established Znstability diagrams indicated that the estimated free Zn-ion (Zn2+) activities for all the tested soils were governed by the solubility line of franklinite mineral in equilibrium with soil-Fe, especially Nile irrigated soil (super saturated), and with increasing Zn activity and we found that the values of Zn activity shifted up near to Willemite (Zn2SiO4) mineral in equilibrium with quartz (undersaturated). The formation of highly soluble minerals, namely, willemite, indicates Zn's potential ecological risk in sewageand industrial-effluent irrigated soils...