Impact of oil excavation activities on soil metallic pollution, case study of an Iran southern oil field

The Ahvaz oil field located in southern Iran has been identified as a possible point of elemental pollution, since elevated levels of metallic pollution (As, Cd, Cr, Ni, Cu, Zn, Pb and V) have been introduced to the adjacent environment through the oil excavation activities. The concentration of metals Cr, Ni, Cu, Pb and Zn are far below all reference values while that of As, Cd and V are remarkably above limits. Enrichment factor (EF) reports the mean waste status to be enriched by all three elements As, Cd and V while the Igeo values manifest the strongly polluted condition for Cd and moderately polluted for As and V. In order to quantify the association of metal concentrations with various Acid soluble, reducible, oxidizable and pseudo-total phases and consequently to estimate the potential mobility of existent metallic pollution, the sequential chemical partitioning technique was used for the samples collected from clean soil, drilling mud and wastage pit. According to the results achieved by chemical partitioning analysis, Cd seems to be mobile. Similar conditions exist for V with relatively lower risk level. Regarding As, the potential mobility is estimated to be low as a remarkable portion of bulk concentration (more than 70 %) is accumulated in the pseudo-total phase. Paying attention to the bulk and partitioning concentrations of three enriched elements in the drilling mud, it is concluded that the main cause of wastage pit contamination may be attributed to the nature of drilling mud utilized in excavation activities. Additionally, the geological texture in different depths may also play a role in this scenario.