Aliphatic and cyclic hydrocarbons in urban street dust from Riyadh city, Saudi Arabia: Levels, distribution, and sources

Abstract

Dust particles contain diverse natural and anthropogenic organic compounds and act as local collectors of pollutants, particularly in urban settings. Samples of street dust were collected from various sites in Riyadh city in 2023. These samples were extracted using a dichloromethane–methanol mixture, and the resulting extracts were subjected to analysis through gas chromatography–mass spectrometry (GC–MS). The primary compounds identified included n-alkanes, methyl n-alkanoates (FAMEs), hopanes, steranes, polycyclic aromatic hydrocarbons (PAHs), plasticizers, tobacco miscellanies, and an unresolved complex mixture (UCM). Vegetation detritus constituted the primary natural source of organic compounds, ranging from 7.4 ± 3.5% to 15.0 ± 4.0%, and included fractional n-alkanes and FAMEs. Petroleum-related products from vehicular emissions, oil combustion, and spills were predominant, accounting for 73.3 ± 5.1% to 87.5 ± 4.8%, and included partial n-alkanes, hopanes, steranes, PAHs, and UCMs. Litterings from discarded plastics and tobacco smoking varied from 5.2 ± 1.3% to 12.0 ± 5.3%, and included phthalates, nicotine, and cotinine, as well as recreational drinks (coffee and tea beverages containing caffeine). The occurrence and distribution of natural and anthropogenic extractable organic matter in this arid urban area were influenced by local vegetation and human activities. The prevalence of anthropogenic organic compounds in Riyadh city's street dust depended on the location and type of urban activity, with elevated levels observed in high-traffic and industrial zones. Consequently, further investigations are necessary to understand the potential health effects of anthropogenic organic matter on city residents.