油田污染土壤残油组成与特征参数分析

为揭示石油在土壤中的降解规律、残油组分特征,筛选土壤残油的生物降解性评价参数,选取大庆、胜利、百色3个油田区共18个深度降解的石油污染土样,利用气相色谱-质谱联用仪(GC-MS)分析了土壤残油中链烷烃(正烷烃+姥鲛烷+植烷)、多环芳烃(PAHs)、萜烷、甾烷及三芳甾烃等5类超过100种石油烃单体.结果表明,经长期降解后残留在土壤残油中总烷烃残留率低于10%,总PAHs残留率低于30%,而萜烷、甾烷及三芳甾烃等生物标志物较难降解.正烷烃降解性随碳数增加有下降的趋势,但碳数<37的正烷烃降解率平均值>80%;PAHs中2～4环PAHs降解率平均值>70%,5～6环PAHs较难生物降解;萘系列、菲系列、系列及苯并e]芘系列中随烷基取代数增多而残留率增高.残油中可被GC-MS识别的组分<3%,主要为碳数高于20的正烷烃、烷基取代萘和菲、萜烷、甾烷及三芳甾烃等生物标志物.基于烷烃及多环芳烃组成特征,筛选出6个由易降解组分含量与总油或难降解组分含量的比值构成的标准残油的特征参数,可用于判断污染土壤中石油污染物的生物降解性.

Compositions and Diagnostic Ratios of Heavily Degraded Crude Oil Residues in Contaminated Soil in Oilfields

The aims of this study were to determine the rate of degradation of crude oil in soil, to reveal the fingerprints of residual oil after long-term biodegradation, and to screen parameters for evaluation of the biodegradability residual oil. A total of 18 contaminated soil samples containing heavily degraded crude oil residuals from Daqing, Shengli and Baise oilfields were analyzed. More than 100 individual target compounds including straight-and branched-chain alkanes (n-alkanes, pristane and phytane), polycyclic aromatic hydrocarbons (PAHs), terpanes, steranes and triaromatic steranes (TAS) in residual oil were determined by gas chromatography-mass spectrometry (GC-MS). For all the soil samples, less than 10% and 30% of alkanes and PAHs remained in the residual oils relative to crude oils. Terpanes, steranes and TAS were found to be less biodegradable. Depletions decreased with increasing carbon number of n-alkanes. However, average depletions>80% were found in n-alkanes with carbon numbers<37. Average depletions were>70% for 2-4 ring PAHs, while 5-6 ring PAHs were more resistant. Increase in alkylation level decreased depletion within homologues of naphthalene, phenanthrene, chrysene and Benzoe]pyrene. GC-MS could only reveal less than 3% of the compounds of residual oils, which were mainly comprised of n-alkanes with carbon number>20, alkylated naphthalenes and phenanthrenes, terpanes, steranes and TAS. Based on compositional characteristics of alkanes and PAHs in residual oils, 6 diagnostic ratios, which were ratios of susceptible compounds to resistant compounds or to the amounts residual oil, were proposed as the parameters for characterization of residual oils and determining the biodegradability of oils contaminated soils.