Investigation on the Experimental Determination of Crude Oil in the Faeces from the Marine Copepod Calanus finmarchicus.
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- Institutt for kjemi 
Oil spilled into the ocean is subjected to weathering processes which alter the spilled or discharged oil. Natural dispersion is a weathering process which removes oil from the sea surface by breaking the oil into droplets. The copepod Calanus finmarchicus is shown to actively filter and ingest oil droplets from water, and it is believed that active grazing by zooplankton may result in significant transport of oil to the bentic environment in faecal pellets. It is hypothesised that these ingested oil droplets could be biodegraded more rapidly than oil droplets which remain in the seawater column. The main aim of this study was to establish a suitable method to determine the amount of crude oil in C. finmarchicus faeces. Several experiments were performed in order to achieve this. Uncontaminated C. finmarchisus faeces were spiked with a known amount of Troll oil to evaluate if ‘Alkaline saponification in reaction vials’ is a suitable extraction method for crude oil in faeces. Following this extraction, two different clean-up methods were tested: 1) silica and alumina clean-up in pasteur pipettes, and 2) SPE clean-up (silica). Alkaline saponification with SPE clean-up was deemed the better of the two clean-up methods, and was therefore used in the main experiments. This method reclaimed approximately 40-50% of the crude oil (70% for the ‘low oil’ sample) analysed on GC-FID, and had a higher and more stable recovery of the internal standards used (67-85%). However, this clean-up procedure was characterized by a high ‘blank’ sample, indicating that contamination was introduced to the samples. After the extraction and clean-up method was established, an experimental set-up for the main experiments was determined. This set-up consisted of a flow through system made up of 6 x 20 L glass tanks, each contained 400 stage five C. finmarchicus. The copepods were given a diet of the micro algae Rhonomodas baltica. The oil dispersion was generated by a dispersion generator developed at NTNU and SINTEF Sealab which generate oil dispersions with defined droplet size distribution. The estimated amount of crude oil in C. finmarchicus faeces exposed to 1ppm Troll crude oil was also determined. It was decided, based on the low amount of oil estimated, to collect faeces from the individual exposure tanks once every day, and to combine the collected faeces from three days into composite samples. Two experiments (experiment 1 and 2) were performed using this set-up. During experiment 1, the C. finmarchicus started egg production. Observations made during the development of the extraction and clean-up method indicate that C. finmarchicus in the egg laying phase has reduced faeces production. This may strongly affect the amount of oil detected from the faeces. The experiment was therefore repeated (experiment 2), with care being taken to avoid egg laying animals. The samples in this experiment were analysed on GC-FID to determine the total hydrocarbon concentration (THC). Oil was not detected in any of the samples at concentrations above the blank levels (6.5±0.7 µg/mg dry weight). The samples were also analysed on GC-MS SIM for selected aromatic compounds, however, no compound was detected above the blank levels. The high concentrations detected in the ‘blank’ samples are believed to have been introduced by the use of the commercial SPE columns during the clean-up step. Other possible sources of contamination are the filter papers used, or cross-contamination from the other samples and from the laboratory in general. This high ‘blank’ sample makes it clear that more work is needed in order to develop a suitable clean-up method for the determination of crude oil in C. finmarchicus faeces.