Chemical structure of tralopyril and of the transformation products CL 322,250, CL325,195, CL 322,248 and trifluoroacetic acid (TFA), contained in the IMR report.

Norway fisheries directorate warns against flushing impregnated nets

New assessments from Institute of Marine Research (IMR) show that cleaning nets impregnated with anti-biofouling chemical tralopyril can lead to short-term emissions of high concentrations of the substance.

Pål Mugaas Jensen editor-in-chief
Published

"We have received a new scientific assessment from the Institute of Marine Research on the environmental effects of tralopyril. The substance is used to impregnate nets in fish farms to prevent fouling," said Britt Leikvoll, section manager for the strategic aquaculture section at Norway's Directorate of Fisheries in an anouncement.

Key takeaways from the report

  • The use of tralopyril has increased rapidly since 2017.

  • Tralopyril works by inhibiting energy production in cells, which can lead to death in organisms. The substance has a short half-life in water (9-16 hours), but may be more persistent in sediments and when bound to particles, and several transformation products have been identified.

  • Toxicological data show that tralopyril is highly toxic to marine organisms, particularly in early life stages.

  • The no-effect threshold (PNEC) is very low (in the range of 1.7-8 ng/L), and many species show mortality at concentrations in micrograms per litre.

  • Compared to copper, tralopyril is toxic at lower concentrations.

  • Modelling of dispersion from fish farms shows that tralopyril leaks continuously from impregnated nets.

  • Passive leaching results in low, relatively stable background levels, mainly below threshold values.

  • In contrast, flushing of nets or initial release results in short but distinct emissions (pulses) that can lead to concentrations above threshold values.

  • Such pulses can last from hours to several days and spread over larger areas, depending on current conditions.

  • The substance has been detected in sediments up to 1,000 m from the facility.

  • It has also been detected in benthic organisms, fish, shrimp, and mussels, which shows that the substance is absorbed into the food chain.

  • Laboratory experiments show low but measurable uptake in salmon and mussels, as well as harmful effects upon exposure.

  • There have also been recorded cases of dead krill where tralopyril has been detected in the organisms, but there is insufficient knowledge to determine a causal relationship.

  • The knowledge base is still limited, especially when it comes to long-term effects, transformation products and effects at the ecosystem level.

  • Other new impregnating agents, such as zinc and copper pyrithione, are also considered hazardous and may enhance the effects when used in combination with tralopyril, but have not yet been fully risk-assessed.

Can cause emission pulses when flushing

According to the IMR, tralopyril - has been increasingly used in recent years as an alternative to copper-containing impregnation agents - continuously leaks from impregnated nets, but normally in low concentrations. The situation may be different when the nets are cleaned.

"The use of tralopyril results in continuous emissions to the environment, and flushing of impregnated nets can lead to short-term, high concentrations that can be harmful to marine organisms," IMR writes in the report.

"We recommend that the industry try to find biocide-free solutions to combat fouling. If biocide is used as an impregnation agent, we recommend that flushing is not used. We need more knowledge about how pulses of the size shown in the modelling can affect vulnerable organisms over time," IMR continues.

'Farmers are responsible for limiting emissions'

The Directorate of Fisheries refers to the professional assessment and at the same time issues a reminder of the environmental requirements that apply in Norway when cleaning nets.

According to Section 46a of the Aquaculture Regulations, aquaculture operations must take measures to minimise the release of environmentally hazardous chemicals when cleaning impregnated nets on site.

“The requirement applies to all chemicals that can cause acute harm or long-term effects if released into the environment,” said Leikvoll. 

The new knowledge from IMR makes emissions in connection with net cleaning an important point of attention.

To be used in further management

The Directorate of Fisheries says it will base its further follow-up of the environmental impact of the aquaculture industry on the IMR's professional assessments.

“The knowledge base will also be used to guide the industry on how to comply with the requirements for cleaning impregnated nets and how emissions of environmentally hazardous chemicals can be limited,” emphasised Leikvoll. 

Read the report (translation required) here.

directorate of fisheries fish farm nets tralopyril institute of marine research news environmental emissions