Occurrence and sources of aliphatic hydrocarbons in surface soils from Riyadh city, Saudi Arabia

Soil particles contain a variety of anthropogenic and natural organic components derived from many sources such as industrial and traffic fossil fuel emissions and terrestrial biota. The organic contents of soil and sand from the Arabian region have not fully characterized. Thus, samples of fine soil particles (sieved to 125 μM) were collected from the Riyadh area in November 2006 (late summer) and February 2007 (late winter). The samples were extracted with a mixture of dichloromethane/hexane and analyzed by gas chromatography–mass spectroscopy (GCMS) in order to characterize the chemical composition and sources of aliphatic hydrocarbons. The results showed that both anthropogenic and natural biogenic inputs were the major sources of the aliphatic hydrocarbons in these extracts. Vehicular emission products and discarded plastics were the major anthropogenic sources in the fine particles of the soils and ranged from 64% to 96% in November 2006 and from 70% to 92% in February 2007. Their tracers were n-alkanes, hopanes, sterane, plasticizers and UCM. Vegetation was also a major natural source of hydrocarbon compounds in samples ranging from ~ 0% to18% in November 2006 and from 1% to 13% in February 2007 and included n-alkanes and triterpenoids.