Bioaccumulation of trace elements and ecological risks induced by petroleum extraction in Shengli oilfield, China

Oil extraction activities generate both organic and metal pollution, however, trace elements in oilfield areas have received less attention in terms of investigation and risk assessment. This study investigated the accumulation levels of eight trace elements (Cd, Mn, Ni, Cu, Pb, Zn, Cr, and Hg) in soils, plants, and animals from three sampling lines using ICP-MS. Potential ecological risks of these elements were assessed based on the local geochemical background of soils and the hazardous concentration for 5% species (HC₅) derived from the Species Sensitivity Distribution Curves of plant and animals. Biomagnification of these elements was characterized with the Biomagnification Factor (BMF). The results indicated potential soil contamination with Pb (19.8 ± 5.2 mg/kg) and Hg (0.023 ± 0.012 mg/kg), exceeding local environmental background values by 1.02 and 1.04 times, respectively. High accumulation of Mn, Zn, and Cu was observed in plants and animals, with concentrations ranging from 21.2 to 153, 20.4-335, and 12.7-143 mg/kg, respectively. Higher elemental concentrations were observed in Goosegrass (Mn: 93.5 ± 15.3 mg/kg, Zn: 32.2 ± 7.9 mg/kg, Cu: 9.1 ± 1.0 mg/kg) and grubs (Mn: 152 ± 38.1 mg/kg, Zn: 202 ± 45.3 mg/kg, Cu: 118 ± 8.1 mg/kg), demonstrating a stronger capacity for accumulating these elements. Mn, Cu, and Zn posed relatively high risks to the investigated organisms especially for insects, with Hazard Quotient (HQ) value high to 12,059, 25,191 and 9017, respectively. Biomagnification was evident for Zn, Hg, Cd, and Cu through the food chain transfer, with BMF high to 6.1, 26.1, 15.2, and 12.1, respectively. These findings highlight that less-regulated trace elements like Mn, Cu, and Zn, often perceived as less hazardous, can present ecological risks in oilfields via high bioaccumulation and trophic transfer, warranting greater attention in oilfield management.