Lead concentration and composition of organic compounds in settled particles in road tunnels from the Caracas Valley-Venezuela

Settled particulate matter was collected in three heavily travelled roadway tunnels (Trinidad, Paraiso and El Valle) to be characterised in terms of l ead concentration and composition of organic compounds. Atomic Emission Spe ctrometry with Inductively Coupled Plasma and Gas Chromatography-Mass Spect rometry (GC-MS) were employed to isolate and identify Pb in acid extracts, and organic compounds in hexane and hexane-dichloromethane extracts. The re sults for lead analysis reveal that the total concentration present in each tunnel ranges from 5500 to 1260 mug g(-1). This figure indicates a relativ ely low concentration of lead for settled particles, compared with those re ported for suspended particles in this kind of environment, which suggests the lead fractionating between settled and suspended particles in the Carac as Valley area. Thermogravimetric analysis shows the presence of total carb on (total organic carbon + carbonate), to be between 10% and 20% of the tot al sample. Of this total carbon, 55% is under carbonate (calcite) form and 45% as organic carbon, mostly in the form of tire residues. A fraction of t his organic carbon (1%) is soluble in organic solvent (hexane-dichlorometha ne). The analysis of saturated hydrocarbons showed a similar distribution p attern for each sample. The n-alkane, terpane and sterane compounds, closel y resemble those present in gasoline and lubricant additives. The aromatic fraction also displays very similar patterns for polycyclic aromatic hydroc arbons constituted by alkyl dibenzothiophene, phenanthrene, pyrene and chry sene. The distribution of polyaromatic hydrocarbons (PAHs) in the samples w as found to be very similar to those in the diesel fuel used by heavy truck vehicles.