Organic matter composition and pesticide residues found in soil and sand from Riyadh, Saudi Arabia

The main cities of Saudi Arabia receive source mixtures of organic matter from local activities and long range atmospheric transport. Determination of organic contents of aerosols, sand, soil and aquatic systems, which vary seasonally, is useful for environmental assessment processes. Therefore, soil and sand samples from Riyadh city areas were collected in winter (January 2002) and in summer (August 2003), extracted with a mixture of dichloromethane and methanol (3: 1, v:v) and analyzed by gas chromatography-mass spectrometry (GC-MS). The results of the chemical analysis showed that both anthropogenic and natural sources are apparent. The anthropogenic sources were mainly from fossil fuel combustion and activities related to agriculture and shopping. They consisted mainly of pesticide residues, plasticizers, and n-alkanes as well as hopane and sterane biomarkers. Pesticides were detected only in winter samples and mainly from market places. Plasticizers were major compounds in both winter and summer samples. Organic inputs from natural sources, which were significant in rural area included n-alkanes, methyl alkanoates, sterols, and terpenoids.