Pollutants in char

Method

The samples are processed in the laboratory using a variety of techniques to permit the analysis of several groups of pollutants. The following is performed to analyse organic, fat-soluble herbicides, PCBs and some brominated flame retardants (BFRs):

Muscle samples are homogenised, ca 3g are weighed and an internal standard is added. Sodium sulphate is used to remove water from the sample. Fat and fat-soluble substances are extracted from the sample using the solvents acetone and cyclohexane. The quantity of fat is determined in a small part of the extract by weighing. Fat must be removed from the extract prior to analysis. This is done using a GPC (Gel Permeation Chromatography) robot.

The sample is analysed with an interlinked, high-resolution, gas chromatograph (GC) and mass spectrometer (MS). The concentrations are calculated by quantifying internal standards with known concentration and comparing these with the response (chromatogram) from the samples.

As the data were collected every 10th year until 2016, the analysis will not supply information on year-to-year variations in the pollutant concentration. When the time series is analysed, allowance must therefore be made for the possibility that year-to-year variations are not detected.

Detection limits for the individual compounds are three times the noise level of the instrument. The detection limit varies between each analysis and different types of samples, but the typical detection limit is 1–500 pg/g wet weight (corresponding to 0.001–0.5 ng/g wet weight). The uncertainty is around 25–30 %. The detection limit in particular, but also the measurement uncertainty, has been improved in recent years. In all time series, there will therefore be increasing uncertainty attached to measurements earlier in the series.

Analysis of mercury (Hg)

Mercury was analysed using cold extraction and an MHS-15 (Mercury/Hydride System). Quality assurance and quality control for the mercury analyses included the analysis of blank samples and duplicates, and the use of reference materials and an internal standard. The detection limit was 0.005 mg/kg wet weight.

Quality

Fieldwork is carried out using the best available methods to avoid sample contamination. Samples from the Bjørnøya lakes, Øyangen and Laksvatn, are treated as coming from a single lake. Øyangen was originally chosen as a reference lake for far-transported pollutants, but Laksvatn had to take over because Øyangen had a small char stock. These lakes can be compared because they have the same qualities. Both are on the low plain on the northern part of Bjørnøya. Both are oligotrophic and there is no run-off to them from the settlement or former human activity, and unlike Ellasjøen they are not affected by seabirds.

The chemical analyses were performed by NILU-Tromsø, which is a research laboratory. It uses the same internationally published and approved techniques as the accredited NILU laboratory in Oslo. To avoid contamination, only superclean equipment is used. A blank sample and a standard reference sample are analysed for each tenth sample. In addition to the accreditation, the laboratory regularly takes part in international intercalibration tests. All the data used in the indicator are collected for research. They may therefore not be collected optimally with respect to monitoring. For this reason, all the data are assessed for comparability before being included in the indicator. The most important factors assessed for char are the time of year the samples were collected and that all the samples consist of muscle. Many data points presented in scientific publications will therefore not be included in the indicator.

Reference level and action level

Since persistent organic pollutants are anthropogenic pollutants which are not found in a natural state, the reference level for an unaffected state will be zero (in reality, the detection limit).

Serious efforts have been made to limit the spread of persistent organic pollutants. The Stockholm Convention regulates an international ban on the manufacture and use of PCBs, several herbicides, brominated flame retardants and some fluorine compounds.

Food safety and harmful effects

Since many organic pollutants are poorly degradable and fat-soluble, they may be accumulated and concentrated upwards in the food chain (biomagnification). Fish, birds and mammals – including people – will therefore be exposed to the highest concentrations. Dioxin and dioxin-like PCBs are found in fatty fish, meat, dairy products and eggs. In fatty fish, these substances are found in fillets and in lean fish in the liver.

Dioxin-like PCBs are carcinogenic and they can be transferred during pregnancy from the mother to the embryo.

The calculation of toxicity equivalents (TEQ) for dioxin-like PCBs in char fillets from Ellasjøen in 2010 shows an average TEQ value as high as 42.5ng/kg wet weight (min–max values: 1.93–81.3). There is no specific tolerance level for dioxin-like PCBs in fish, but the tolerance level for the sum of dioxins and dioxin-like PCBs in fish which can be sold as food for humans is 6.5 ng TEQ/kg. This means that it would not be permissible to sell (average) fish from Ellasjøen. However, if you are to eat a fish from Ellasjøen, it is the tolerable weekly intake of the sum of dioxins and dioxin-like PCBs that has significance. This tolerance level is 14 pg TEQ/kg body weight per week. This means that a 60kg person only needs to eat 20g of fish from Ellasjøen to consume the tolerable weekly intake of dioxins and dioxin-like PCBs.

Average TEQ levels for trout in mainland Norway are 0.36ng/kg. Levels of ΣPCB and toxicity equivalents (TEQ) for dioxin-like PCBs are presented in Akvaplan-niva report 4232 – Christensen and Evenset (2011) Pollutants in char from lakes in Svalbard (in Norwegian).