Persistent organic pollutants in Scottish freshwater biota

Persistent organic pollutants (POPs) are potentially harmful chemicals that stay in the environment for a long time. Their concentrations in water can be minute – often below what can be detected by analysing water – but over time these tiny amounts can be absorbed into the fatty tissues of living things, where they can build up to measurable amounts.

To get a better understanding of the levels of these POPs in Scotland’s freshwater environments, in 2004 SEPA began monitoring contaminant concentrations in the tissues of eels (Anguilla anguilla). We chose eels as the ‘biomonitor’ species because of their high fat content and long lifespan, which make them ideal for measuring long-term POP accumulation.   

However, the eel population of Europe is in decline so we wanted to find potential alternative species. A research project was therefore run in parallel with our existing eel monitoring efforts to do just that. Our new report Persistent organic pollutants in Scottish freshwater biota: monitoring options, current levels and the way forward (pdf link 3.6mb) describes the research project and its findings as well as the results and future direction of the eel monitoring programme.

 

Species options

Scientists from our Chemistry and Ecology units evaluated several species and organism types:

  • brown trout (Salmo trutta);
  • minnows (Phoxinus phoxinus);
  • Atlantic salmon (Salmo salar);
  • 3-spined stickleback (Gasterosteus aculeatus);
  • brook lamprey (Lampetra planeri);
  • pike (Esox lucius);
  • molluscs (Radix balthica);
  • plants.

Brown trout were the only species found to be suited to wide-scale biomonitoring of POPs in the Scottish freshwater environment, but they cannot fully replace eels as biomonitors because of issues such as natural gaps in their distribution. Brown trout were therefore caught and analysed for POPs in parallel with our eel monitoring.

 

Biomonitoring with eels and trout

The results revealed that both eels and trout can be valuable biomonitor species when present in an aquatic system, with each providing environmental information from differing perspectives: trout provide information on very recent (i.e. 1 to 2 year) exposure to contaminants, while eels show an integrated picture of longer term exposures.

Eel results showed DDT (the infamous insecticide used widely in the 1940s and 1950s, considered to be a major reason for the decline in peregrine falcon and osprey numbers) and its derivatives are still readily detectable in Scottish rivers, but that concentrations are lower than they were in the 1980s and 1990s. Reductions in the concentrations of Lindane, a known neurotoxin that affects the nervous system in humans, are even more distinct, and eels from many sites do not have any detectable concentrations. Polychlorinated biphenyls (PCBs), a group of plasticisers with varying toxic effects, were detected at various sites around the country, though most commonly at low levels that pose no immediate cause for concern. Some of the more modern chemicals, including brominated flame retardants (BDEs), were noteworthy contaminants in some areas.

The trout data generally indicated very low or non-detectable contaminant levels, with concentrations much lower than those observed in eels. This reflects the lower fat content and shorter life-spans of trout compared to eels, but probably also reflects the smaller number of sites from which trout were collected during the research project. However, BDE concentrations in trout were noteworthy in some areas, mirroring the increased observance of these contaminants in other environmental settings across Europe (e.g. dolphins, seals and other organisms in the marine environment).

Both the eel and trout results demonstrate the value of long-term monitoring and the benefits to our understanding of environmental status that can be gained by monitoring contaminants in biota rather than in water alone.     

 

Next steps

The results from the monitoring and research project are helping to shape SEPA’s future freshwater monitoring programmes under the Water Framework Directive (WFD). The results will also contribute to the work of important partner organisations such as Marine Scotland, who are responsible for Scotland’s eel management plan and other related activities. Continued interaction between all agencies involved in environmental monitoring and management will help to build a holistic view of Scotland’s environment and maximise the effectiveness of our environmental programmes. 

 

More information

The full report: Persistent organic pollutants in Scottish freshwater biota: monitoring options, current levels and the way forward (pdf link 3.6mb).

A feature article on biomonitoring is on page 2 of SEPA View 50 (pdf link 5.6mb).

 

External links

European Commission Water Framework Directive (WFD)

United Kingdom Technical Advisory Group (UKTAG) WFD information

Eel conservation in Scotland and Europe

European Commission Eel Recovery Plan (Council Regulation No 1100/2007)