Distribution And Ecological Risk Assessment Of PAHs In Oily Sludges, Soils And Plants From Zhongyuan Oilfield

Polycyclic aromatic hydrocarbons (PAHs), ubiquitous in the environment are one kind of semi-volatile persistent organic pollutants, which can be formed by human activities such as oil-leak and incompletely burning of organic matter. PAHs have already found to be a serious threat against human health due to their cancerogenic, teratogenic and mutagenic efects, persistence and bioaccumulations. To protect human health against noxious environmental pollution, it is very important to understand the characteristics of level, sources and transport of PAHs in the environment.This study taking oily sludges, soils and corns in Zhongyuan Oilfield as cases, firstly investigated the distribution characteristics of the sixteen US EPA prefered controled PAHs in oily sludges, soils and corns in both winter and summer, and the risks of PAHs in those had been assessed.The oily sludges, soils and corns samples were treated in ultrasonic washing machine with dichlormethane as the extract. The determination of PAHs in oily sludges, soils and corns samples was carried out by high performance liquid chromatograph (HPLC) equipped with ultraviolet (UV) absorption detector and the mobile phase consist of acetonitrile and water. PH value in oily sludges and soils samples were determined by acidimeter. Determination of TOC in oily sludges and soils samples by Potassium Dichromate Method.The results of the study show that the sixteen PAHs concentrations of fresh and dried oily sludges in Zhongyuan Oilfield in winter are 3183.5-4112.0μg/g and 1953.8-2449.1μg/g, respectively. The contents of PAHs of three different oily sludges from high to low present that the third Wenming plant of the oily sludge (3W)>the third Mazhai plant of the oily sludge (3M)>the fourth Wener plant of the oily sludge (4W). The PAHs contents in soil samples adjacent to oily sludges vary widely from 434.49 to 2408.8 ng/g. The order of pollution degree in soils near the three plants is as follows: 3W>3M>4W, which is consistent with the order of the contents of PAHs of oily sludges in three plants. In summer, the sixteen PAHs concentrations of fresh and dried oily sludges in Zhongyuan Oilfield are 3369.3-4488.8μg/g and 2068.5-2676.3μg/g, respectively. The contents of PAHs of three different oily sludges from high to low present that 3W>3M>4W. The PAHs contents in soil samples adjacent to three different oily sludges is 215.1-2047.5ng/g. The order of pollution degree in soil near the three plants is as follows: 3W>3M>4W. The PAHs contents of corn root samples from soils around oily sludges from high to low are 3W > 3M> 4W, which is consistent with the order of the contents of PAHs of soil samples in three plants, and 2-4 rings PAHs are still the most predominant components of PAHs in corn root samples. The PAHs contents of corn leaf samples from high to low are 3W> 4W > 3M, which is not consistent with the order of the contents of PAHs of soil samples and corn root samples in three plants. And 5-6 rings PAHs are the most predominant components of PAHs in corn leaf samples.In winter, The BaP equivalent consistence ranging from 9.58-75.83 ng/g in soil somples have potential health risks. According to nemero index P, soil samples present 66.7% of those as'heavily contaminated', 16.7% as'medium contaminated', and 16.7% as'light contaminated'. The result of the risk assessment show that all points are polluted badly and have high ecological risks. In summer, The BaP equivalent consistence rang from 4.67-67.50ng/g in soils adjacent to oil sludges. According to nemero index P, soil samples presents 33.3% of those as'heavily contaminated', 5.6% as'medium contaminated', 44.4% as'light contaminated', 11.1% as'warning', 5.6% as'not contaminated'.