Impact assessment following an oil spill near Yorkeys Knob, north Queensland

Surface sediments were collected in January 1994, after oil was dumped along a road adjacent to sugar cane fields and wetlands near Yorkys Knob, north Queensland. Samples were taken from a variety of visually oiled and unoiled wetland areas, the oiled road, and the stock pile of oiled sediments that had been scraped off the road during initial clean up efforts.Core samples were also collected using a hand coring device, made from 4 cm diameter aluminium pipe. Cores were taken by pounding the tube into the sediment and twisting it back up to the surface. Cores were removed, sliced with a steel knife and samples were taken from the centre of specific depth layers (0-2, 10-12, 16-18, 25-27 and 38-40 cm) and put into labelled jars. The soil samples were packed on ice and taken to a commercial laboratory in Cairns, which sent the samples to their Melbourne laboratory for analysis of total hydrocarbons by gas chromatography with flame ionisation detection (GC-FID).After evaluation of the first set of chemical data, three sites were selected for longer term impact assessment. Site 3 was in a Melaleuca forest and samples were collected in three areas: heavily oiled, 5 m from the road (3A); moderately oiled at 15 m from the road (3B); and unoiled at 30 m from the road (3C). Site 6 was located 5 m from the road in dense intertidal mangrove forest composed predominantly of Avicennia marina. Site 5 was a small tributary, which drained the most heavily oiled wetlands and flowed into Richters Creek. Sampling at these sites was conducted in January and June 1994, May and July 1995 and the samples sent to the commercial laboratory for analysis. The final samples were collected in December 1995 and were analysed at AIMS for individual components. Oil composition was determined by three independent methods of analysis: (1) scanning ultraviolet fluorescence (UVF), (2) GC-FID, and (3) Selected IonMonitoring GC/Mass Spectroscopy (GC/MS) for individual aromatic hydrocarbons and triterpane biomarkers.QDEH also sank 25 cm diameter aluminium tubes into the sediment at 5 monitoring sites, to a depth of around 3 m, to determine if oil was leaching from the contaminated sediments into ground water. Sampling was done with a stainless steel tube, after each bore was cleared of water and allowed to refill. Water was collected and 500 ml drained into 1 litre glass jars to ensure that no oil from previous accumulations of surface water contaminated the ground water samples. The samples were placed on ice and airfreighted along with the sediments for analysis.Additional sampling was done in May 1995 at six sites along the roads in the sugar cane farm. These sites were excavated with a shovel and each layer was examined for visual and olfactory presence of oil. Samples for chemical analysis were taken in layers likely to contain oil, if it had seeped through the road into subsurface layers, such as into clays at ground water level. These samples were analysed at AIMS.
An estimated 76,000 litres of a mixture of fuel and lubricating oils were dumped on a road, adjacent to sugar cane fields near Yorkys Knob, north Queensland in January 1994. The oil soaked into sediment and contaminated a band along the road 30m wide and 200m long. Mangroves and a Melaleuca forest were impacted.AIMS was contracted by the Queensland Department of Environment and Heritage (QDEH) to assist in producing an impact assessment. The specific tasks undertaken were:1. supervision and participation in sediment sampling2. an assessment of the analytical methods used by the contracting commercial laboratory3. interpretation of the analytical data in terms of oil composition, its probable toxicity, and the rate and patterns of dispersion and degradation of the contaminant hydrocarbons4. detailed chemical analysis of initial and final samples5. comparison of the results with data obtained from long term impact assessments of oil spills in other tropical wetlands.
At the time that the dumping occurred, the surface oiling of powdery dirt roads in sugar cane fields had been practiced for about 20 years in Queensland.

1994年1月，在北昆士兰州约基斯诺布（Yorkys Knob）附近毗邻甘蔗田与湿地的路段倾倒燃油后，研究人员采集了表层沉积物样本。样本采集自多个目视可见受油污染与未受污染的湿地区域、受油污染的路段，以及初期清理作业中从路面刮除的受油沉积物堆。
研究人员同时使用直径4厘米的铝制管材自制手动取芯装置采集岩芯样本：将管材锤入沉积物后扭转提至地表，取出岩芯后用钢刀切片，从特定深度层（0-2、10-12、16-18、25-27及38-40厘米）的中心部位取样，装入贴有标签的广口瓶。此类土壤样本置于冰上冷藏，送往凯恩斯的商业实验室，该实验室将样本送至墨尔本实验室，采用火焰离子化检测器气相色谱法（Gas Chromatography with Flame Ionization Detection, GC-FID）分析总烃含量。
在对首批化学数据进行评估后，研究人员选定3个点位开展长期影响评估：点位3位于千层木（Melaleuca）林内，在3个区域采集样本——距路面5米的重度污染区（3A）、距路面15米的中度污染区（3B），以及距路面30米的未污染区（3C）；点位6位于距路面5米的潮间带密生红树林中，该林分以白骨壤（Avicennia marina）为优势物种；点位5为一条小型支流，汇纳受污染最严重的湿地径流并注入里希特溪（Richters Creek）。上述点位的采样分别于1994年1月、6月，1995年5月、7月开展，样本送往商业实验室进行分析。最后一批样本采集于1995年12月，由澳大利亚海洋科学研究所（Australian Institute of Marine Science, AIMS）开展单体组分分析。
本次研究采用三种独立分析方法测定油类组成：（1）扫描紫外荧光法（UVF）；（2）火焰离子化检测器气相色谱法（GC-FID）；（3）针对单体芳烃与三萜类生物标志物的选择离子监测气相色谱/质谱法（Selected Ion Monitoring GC/Mass Spectroscopy, GC/MS）。
昆士兰环境与遗产部（Queensland Department of Environment and Heritage, QDEH）还在5个监测点位使用直径25厘米的铝制管材插入沉积物中，插入深度约3米，以研判受污染沉积物中的燃油是否会淋滤进入地下水。每次钻孔排尽积水并待其重新充水后，采用不锈钢管采集水样：收集500毫升水样至1升玻璃广口瓶中，避免先前地表积水残留的油污污染地下水样本。样本置于冰上冷藏，与沉积物样本一同空运至实验室开展分析。
1995年5月，研究人员还在甘蔗种植区沿线的6个路段点位开展补充采样：使用铁锹开挖剖面，逐层通过目视与嗅探检测是否存在燃油污染。若燃油已渗入路面下方的地下层（如地下水层的黏土层），则在疑似含油的层位采集样本用于化学分析，此类样本由AIMS完成分析。
据估算，1994年1月共有约76000升燃油与润滑油混合物被倾倒于北昆士兰州约基斯诺布附近毗邻甘蔗田的路段。燃油渗入沉积物，污染了沿路段宽30米、长200米的带状区域，红树林与千层木林均受其影响。
澳大利亚海洋科学研究所（AIMS）受昆士兰环境与遗产部（QDEH）委托，协助开展环境影响评估工作，具体任务包括：
1. 监督并参与沉积物采样工作
2. 评估签约商业实验室所采用的分析方法
3. 结合油类组成、潜在毒性以及污染物烃类的扩散与降解速率与模式，解读分析数据
4. 对首批与最终批次样本开展详细化学分析
5. 将本次研究结果与其他热带湿地溢油事故的长期影响评估数据进行对比
在此次燃油倾倒事件发生时，昆士兰州已在甘蔗田的粉状土路表面实施撒油防尘作业约20年。