Polychlorinated biphenyl is an organic industrial chemical whose discovery and usage is traced to have been since 1929. It has a Chemical Abstract Service number Aroclor 1242, CAS No: 53469-21-9. Its water solubility is 0.01-0.0001 Î¼g/L at 25Â°C, octanol-water partition coefficient of 4.3-8.26 and vapour pressure of 1.6-0.003 x 10-6 mm Hg at 20Â°C (UNEP, 2002). These physic-chemical properties confer on it the potential for atmospheric long range transport, long half-life thus making it characteristically persistent and toxic. It was used as heat exchange fluid, as transformer and capacitor oil, paint additives and plastics. Though its production and usage was banned in 1979 (USEPA, 2012) it is still found in the environment and most astonishingly in pristine locations such as the arctic.
In setting out for a field research such as the arctic, the experimental design and protocol is largely determined by the objective of the research, such as monitoring, trend detection etc. The fundamental questions that are needed prior to sampling are encapsulated in the sampling and analysis plan which addresses the data quality objective (Zhang, 2007).
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The climatic condition of the arctic makes it predominantly icy and snowy. Because of the variability of in its physical state; variety of methods exists for water sampling in the Arctic Ocean. This could be achieved by sampling snow, ice or dissolved water. In water, snow and air sampling, a fundamental factor that has to be taken into consideration includes, the representativeness of samples to be collected, also for air sample collection should be done giving consideration to meteorological and topographic factors.
Snow has been demonstrated to be a good scavenger for semi-volatile organic compounds and persistent organic pollutants such as PCBs (Wania et al., 1999). The snow surface area existing with standing snow pack or falling snow tends to control the quantity of chemical sorbed and also heterogeneous reactions for compound that are quite reactive (Sumner and Shepson, 1999). This implies that snow could act as a temporary storage for contaminants.
Organic contaminants in the arctic are usually low, so there is need to sample high volumes that will be representative of the environment and also enable contaminants to be detected (Franz and Eisenreich, 1998). In snow sampling, different samplers have been used such as Teflon-bags, metal canisters, low density polyethylene bottles (LDPE), Snow-cans and snow-tubes. Other materials needed include gloves, steel shovels and special sampling outfits.
An air tight 50L snow-can or a 7.5L snow-tube can be employed. These samplers are unique because they are sealed after sample collection and allows for the analysis of head space (Herbert et al. 2004). The 50L allows for sampling of low density snow and equally creates room for higher snow volume that is required to obtain enough melt-water needed to achieve measureable concentrations. Besides, it permits snow sample to be split into headspace, melt water and particulate matter. An upper and lower tap for the lid and base of the snow-can allows for emptying of headspace and drainage of melt-water respectively. The snow tube allows for sampling higher density snow and for collection of snow from defined layers due to its narrow diameter (Herbert et al. 2004).
Figure I: Specially designed 50L snow sampling can and 7.5L snow sampling tube for Arctic field work.
Adapted from Herbert et al. 2004
Before setting out for sampling, the snow-can, tube and shovel should be decontaminated by rinsing with acetone, dichloromethane and hexane and kept in baked aluminium foil until sampling (Quiroz et al., 2008). Trip or travel blanks are prepared prior to leaving for the field and kept together with sample containers. The reason for this is to assess error associated with shipping and handling. At the field, the operator should be well kitted in field attire inclusive of gloves. Sampling is conducted several meters away from the snow vehicle (100m) citation and from upwind side. Prior to snow collection, equipment blank or rinsate blanks are taken by using the pre-cleaned equipment to collect and fill the appropriate container with analyte free water. Snow blanks are to be prepared by rinsing a pre-cleaned sampler in the field with 250 mL Milli-Q water and subsequently extracted and treated like a snow meltwater. Snow samples are then collected using the shovel and transferred to the snow-can and spiked with a surrogate recovery standard containing PCB congeners before sealing off the container. Field replicate samples are also collected to determine sampling precision, assess intrinsic sample variability and sampling point representativeness (Popek, 2003). As part of quality control measure, field blanks are prepared in the field and undergoes simultaneously full handling and shipping process of an actual sample. It is aimed at detecting sample contamination that can occur during field operation or shipment. (Zhang, 2007).
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In the laboratory, samples are treated in batches. Snow samples are allowed to melt at room temperature; the head space is purged through a glass cartridge and evacuated with a vacuum pump (Herbert et al. 2004). Solid phase extraction of melt-water is carried out for about 12 hours. Interferences from water are removed by eluting with methanol, while the analytes are eluted with hexane and dichloromethane. The solvent fractions are collected, soxhlet extracted for 16hrs, evaporated and finally reduced in stream of nitrogen. The analyte are passed through alumina-silica and gel permeation chromatographic clean up processes and further reduced in a stream of nitrogen. After which it is transferred into dodecane (25 ul) with the addition of PCB internal standards and fixed for measurement using the gas chromatography-mass spectrometry. Afterwards, the percentage recoveries should be calculated for both recovery and internal standards to check if they are within acceptable range and subsequent correction or normalization made.
QUALITY CONTROL PROTOCOLS.
A range of quality control measures incorporated both in the field and laboratory to check for errors that could arise in the analytical processes includes.
Travel or trip blanks are usually designed for sampling events involving volatile organic compounds (VOCs). It is prepared prior to field work and kept closed, transported to the field and back to the laboratory the same way other samples are handled. Its use is to evaluate errors that may arise from shipping, handling and analytical procedures.
Field blanks samples are prepared in the field for detection of sample contamination that could arise during field operation and shipment.
The surrogates or a recovery spike is an organic compound similar to the analyte of interest added to the analytical sample during sample preparation. It is spiked in all blanks and samples and used to assess percentage recovery and performance method.
Reagent blanks are employed to detect contaminants that may be introduced into the sample during preparation and analysis. It is usually analyte-free water analysed with the samples of interest.
Instrument blanks is a clean sample such as distilled water or another solvent injected and processed through the measuring instrument to determine instrument contamination or carry over sample. This done during the gas chromatography mass spectrometry measurement.
The matrix spike and it is aimed at determining the effect of matrix on analyte recovery. The samples are spiked with known amount of analyte and subjected to all preparatory and analytical procedures.
Laboratory duplicates are also incorporated as a quality control measure during analysis to detect poor analytical reproducibility or poor homogenization in the field. This is an aliquot of the same sample that are prepared and analysed at the same time but usually submitted and analysed as separate samples.
Calibration standards are standard solutions used to obtain calibration curves. The standard solutions often range from lower to higher concentrations.
Internal standards are chemically similar to the analyte but are not expected to be present in the sample and should not also interfere in the analysis. The reason for using this is to refine the calibration process and compare analytical signals for calibration to those of internal standard (Popek, 2003; Zhang, 2007).
This whole range of range of quality control measures are aimed at arriving at robust and convincible results (data).
To achieve a high quality and robust result, an ultra-clean room is designed in the sampling vehicle (ship) for storing of samples until arrival to the laboratory. The ultra-clean room is designed to prevent any background contamination arising from the ship. The ship is anchored within an ice floe and engine switched off. Special field apparel is worn so as to prevent contamination. Both ice blocks and ice cores are to be collected using stainless steel ice-core drills which have no greased part and operated on electricity to prevent contamination. The chain of the drill is to be thoroughly washed and solvent rinsed. Ice samples are collected several meters away from the ship and transferred into double large volume stainless steel ice melters of about 370L each so as to obtain enough samples that will enable detection of the organic compound (PCB). The transfer of samples into the melter should be rapid so as to reduce exposure time. The two ice melters should be labelled in order to keep track of cross contamination between subsequent ice samples (Gustafsson et al., 2005).
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Figure 2: Specially designed large-volume ice-melting equipment developed for dedicated ultra-clean sampling and handling of trace organic substances from Arctic ice.
Full-size image (68 K)
Adapted from Gustafsson et al., 2005
Use is made of polyurethane foam (PUF) which should be cleaned thoroughly prior to field expedition to minimize blank. The cleaning process is achieved by washing with detergent for 1hr at 90oC (Sobek and Gustafsson, 2004) and drying at 50oC for 24hrs followed by soxhlet extraction in toluene for 24hrs and acetone for 24hrs. Then it's finally dried in desiccator with a PUF scrubber at the gas jet or inlet. Glass-fibre filters (GFF) or borosilicate filters are to be cleaned by baking at 450oC for 12hrs in a muffle furnace then removed, wrapped in aluminium foil that has been baked at 450oC and stored at -18oC until usage. Large volume of seawater (1000L) should be collected so as to exceed the method detection limit (PCB concentration in the arctic is expected to be very low). This is achieved using a stainless steel pipe at depth of 8m through the ship's intake system located in the keel or prow and directly deposited in the ultra-clean room designed for the expedition. The flow rate should be monitored and taken note of while the pressure over the GFF (constantly monitored using a pressure indicator so that it does not exceed 1bar in order to reduce cell lyzing (Sobek and Gustafsson, 2004). The pre-combusted fibre filter is used in collection of particle-associated PCBs and subsequently through polyurethane foam adsorbents or XAD cartridge to collect dissolved chemical of interest (PCBs). Collected samples are kept in baked aluminium foil envelopes and stored in plastic bags that is double sealed and kept in freezer at a temperature of (-18 to -20oC) until analysis.
Apart from the quality control measure mentioned in the sampling process, some other measures taken include;
Parallel samples of the seawater could be taken with a Kiel in situ pump and analysed differently as a complementary quality control measure.
Field blanks and laboratory blanks are to be analysed in parallel with main samples to serve as control for anyÂ contamination arising from the described sampling and analytical processes.
Analytical blanks (procedural blanks) of PUF and GFF filters are to be arranged for and analysed during sample analysis.
A second filter should be placed behind the main filter and a separate analysis done to assess filter breakthrough and dissolved PCBs absorption to the filter surface.
For the ice and water samples, 13C12-labeled PCB congeners should be added as internal standards to each prior to soxhlet extraction with toluene which is operated for 24-hrs. The samples are to be cleaned up by eluting in open silica column and further cleaned up through HPLC separation on a column of amino acid. After the routine clean up procedures, samples are to measured using GC-MS operated in the electron impact mode. Added to the sample is 13C12-labeled recovery standard (PCB congener) before injection on the GC-MS for measurement. The internal and recovery standard are added as quality control measures to check for errors that may arise from the analytical process. The recoveries are to be calculated and possible corrections made for both recoveries and blanks for each of the samples.
Air sampling could be carried out using high volume air samplers with polyurethane foam plugs (PUFs) and glass fibre filter (GFF) as sampling media. The polyurethane foam plugs (PUFs) should be pre-extracted for 16hrs in dichloromethane (DCM) and dried in a desiccator while the GFF are pre-combusted at 450oC in the furnace before deployment (Hung et al., 2010). Field and travel blanks are to be provided consisting of three or more pre-cleaned PUFs which is to be exposed to the atmosphere all through the sampling period. The lower PUFs are to be tested for any potential breakthrough. Samplers are to be controlled by the use of wind sensor to ensure samples collected are flowing from the direction of the ship's bow in order to avoid sample contamination from air stack emissions arising from the ship. Air samples of (1200 m3Â air volume for 24hrs or weekly which amounts to aspiration of 11,400 m3Â of air.) are absorbed on board using the high volume air sampler in front of the upper deck of the ship (20m above sea level). The GFF traps the airborne particle while the PUF column traps the gaseous phase. Both the filters and air column are stored at -20oC until analysis (Cai at al., 2012).
The PUF plugs are to be pre-extracted with dichloromethane (DCM) while the GFF is to be pre-combusted at 450oC. Samples are to be spiked with a recovery standard of 13C12 -labelled PCB congeners. Samples are to be soxhlet extracted and the extract concentrated in a rotary evaporator and further reduced in a stream of hydrogen. The extract is to be cleaned up through alumina silica chromatography and gel permeation chromatography. The resulting solvent is to be exchanged with 25mL of dodecane containing PCB congeners as internal standards. Instruments blanks should be taken and samples can be analysed by GC-MS operated at selected ion mode (SIM).
QUALITY CONTROL AND ASSURANCE
Air columns should be pre-cleaned with organic solvents such as acetone, hexane and methanol.
The GFFs should be baked at 450oC for 12hrs prior to use while the PUF should be soxhlet extracted in hexane:acetone or dichloromethane.
Air columns should be given protection against UV- sunlight during sampling by use of aluminium foil in order to avoid degradation of target compounds.
Field blanks and laboratory blanks consisting of pre-extracted PUF should be simultaneously engaged during sampling and analysed during sample extraction and analysis.
The GFFs and the PUFs are to be analysed for all samples in order to calculate for any breakthrough of the analytes during sampling.
Passive air samplers should be kept in different parts of the ship and later analysed so as to establish if contamination was arising from the ship.
Field blanks should be used to calculate the method detection limits (MDLs) as 3times the standard deviation of the blank concentration.
Calibration standards should routinely processed with each batch of samples.
Peaks should be integrated when the signal to noise ratio is high.
Instruments performance should be checked using quality control standards after each batch analysed.
There should be an analysis of reference material.
Figure: 3 High Volume Air Sampler.
Adapted from Lear Siegler Australasia (http://www.learsiegler.com.au)
Figure: 4 Passive air sampling device
Adapted from Gevao et al.,2006.
AIR MASS BACK-TRAJECTORIES
The wind direction during the sampling period should be determined by analysing meteorological data. Individual air mas origins of samples collected during the cruise segments should be calculated using NOAA's HYSPLIT model. Different meteorological data (e.g., air temperature, wind direction, wind speed, visibility, and atmospheric pressure) should be measured and recorded.
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Popek, E.P., (2003) Sampling and analysis of environmental chemical pollutants: A complete guide. Academic Press. Amsterdam.
Quiroz, R., Popp, P., Barra, R. (2008) Analysis of PCB levels in snow from the Aconcagua Mountain (Southern Andes) using the stir bar sorptive extraction.Environ Chem Lett 7:283-288.
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