SUITMA 2005 Cairo - Mineralogical and chemical characteristics of aerial sediments in the greater Cairo area, Egypt
SUITMA 2005 Cairo
| This abstract is about one of the papers of the Properties of unconventional soils theme of the SUITMA 2005 symposium. |
| Salah Tahoun,i | Mohamed E. Abdel-Rahman.ii |
- i - Soil Science Department, University of El-Zagazig, El-Zagazig, Egypt
The Greater Cairo area is a collection of contrasting neighborhoods at the foot of the Eastern and Western Deserts. It extends over 510 square kilometers and hosts 15 million capita in daytime utilizing 2 million vehicles. Therefore, environmental pollution is generated by many natural and anthropogenic driving forces. This work was undertaken to investigate the mineralogical constituents and the active heavy metal contents of aerial sediments. Five samples were collected from sites along a north-south transect in the Greater Cairo area. The northern-most sample was taken from El-Khosous close to a municipal garbage dump with an incinerator, followed southward by samples from El-Mataria Square, Nasr City, Ramsis Square, and El-Giza Square. Furthermore, a sample was taken from El-Zagazig city, in the Eastern Delta region, and another from Shenbara, which is a small rural village about 20 km west of El-Zagazig. Specimens were mounted on x-ray holders and examined by a Philips x-ray diffractometer before and after treatment with diluted HCl. Moreover, the DTPA extracts of samples were analyzed by the ICP to determine their chemically active contents of Fe, Mn, Cu, Zn, Pb, Co, Cd, Ni, Cr, Mo, Sr, and V.
The x-ray diffraction patterns show that quartz and calcite are the dominant minerals. Complementary minerals include proportions of feldspars, dolomite, hematite, gypsum (in urban samples only), and a suite of clay minerals. Samples treated with HCl lost their calcite and gypsum, and the characteristic clay peaks were greatly enhanced in intensity especially in samples of rural connection. There is a great number of weak and very weak peaks. Whether or not these peaks are indicative of some pollutant phases could not be equivocally stated. The pattern of the sample from Ramsis Square indicates the absence of calcite, and shows a great hump in the 2θ region between 20 and 30º, indicating the presence of a considerable amount of amorphous materials. It is of a particular interest to note that the samples of El-Zagazig and rural Shenbara do not contain gypsum in contrast to samples from Cairo. We postulate here that gypsum is not an authentic mineral in urban samples, but rather it is a reaction product between air-born calcite and gaseous SOx emitted into air by fossil fuel combustion.
The active heavy metal fraction of the samples shows that Zn is most prevalent in almost all samples with an average of 106.76 mg kg–1. Its highest concentration at 206.20 mg kg–1 resides in the Khosous sample of the garbage dump. In contrast, Zn concentration is lowest at 42.34 mg kg–1 in rural Shenbara followed by El-Zagazig at 74.94 mg kg–1. Actually, these contrasting concentrations set a trend whereby heavy metals in urban samples are higher than those of the rural areas. There are few exceptions. The Shenbara sample is highest in both Mn and Mo, probably due to contamination by some agricultural chemicals added to cultivated land in the neighborhood. Furthermore, the El-Zagazig sample contains the highest concentrations of Pb at 69.64 mg kg–1 compared to an average of 40.10 mg kg–1 for all samples. This result could be interpreted on two bases. First, the El-Zagazig sampling site is confined between large buildings overlooking a narrow street carrying heavy traffic. Second, gasoline on the Cairo market contains smaller amount of Pb additives compared to other areas of the country.
