Clay minerals and their interactions with heavy metals and microbes of soils irrigated by various water resources at Assiut, Egypt

الملخص EN

Soil samples were collected from four soil profiles at Assiut city, Egypt, that they have been irrigated by fresh and contaminated (sewage and agricultural drainage) Nile waters as well as artesian water for more than 40 years, in order to study the clay minerals and their interactions with heavy metals and microbes of these soils.

X-ray diffraction analysis of the clay fraction of the different irrigated soil samples revealed that spectates occurred as major clay minerals in all studied soil samples, and tended to increase with depth.

Kaolinite was the second abundant clay mineral, followed by mica-smectite mixed layers, vermiculite, and mica-vermiculite mixed layers, mica, sepiolite and palygorskite that are arranged in a decreasing order of abundance.

The source of these clay minerals in the studied soils is largely due to the detrital materials from the Ethiopian Plateau that is mixed with the detrital materials from the sandstones and limestone's plateaus surrounding the Nile river course.

Concerning the interaction between clay minerals and heavy metals, the significant relations between smectite and Fe or Cu, kaolinite and Pb, mica-smectite mixed layers and Mn, mica-vermiculite mixed layers and Zn, Cu or Ni, vermiculite and Cu, sepiolite and Fe or Pb, and palygorskite and Mn or Cu may be mainly attributed to the adsorption of these heavy metals on these clay minerals.

Regarding the interaction between clay minerals and microbes, the examination of the soil surface samples using the scanning electron microscope (SEM) pointed out that the bacillus and coccus bacteria were observed in all investigated samples, but they were found as colonies in the soils irrigated by sewage contaminated Nile water.

Fungi were shown in all examined samples, but they were in smaller amounts than bacteria that were probably associated with smectite.

Some of fungi types were characterized to specific soils, such as Triscelophoius monosporous Ingold in the soil irrigated by artesian water, and Pilobolus (Zygomycota) in the soil irrigated by sewage contaminated Nile water.

However, actinomycetes appeared in the soil irrigated by fresh Nile water.

These reflected the influence of irrigation water source, which led to the diversity of bacteria, fungi and actinomycetes in these different soil samples.