Publish date: January 7, 2009

The description of the health and environmental effects of deltamethrin is based on information presented by the manufacturer Alpharma. As part of the product approval process, the manufacturer obtained documentation that was submitted to the authorities for evaluation. This documentation has not been made public. Alpharma’s justification for not making the documentation public is its desire to protect its investment and prevent competitors from copying their documentation and getting an easier toehold in the market.


Therefore, Bellona has no independent sources beyond the Norwegian Pollution Control Authority’s remarks on Alpharma’s documentation (Brendgren and Vike, 2001). Bellona is not comfortable with using information from the manufacturer only, but has no reason to believe that the manufacturer is withholding data.



Alpha Max is a bath treatment for combating salmon lice. The active ingredient is deltamethrin, an insecticide in the pyrethroid group. The chemical formula for deltamethrin is C22H19Br2NO3.


Treatment with Alpha Max involves reducing the volume in the sea cage by pulling up the netting walls or "sewing them up". The cage is wrapped up, either in a skirt with an open bottom or a completely closed tarpaulin. Alpha Max is added, and the treatment ends after 30-40 minutes by removing the tarpaulin so that the water is replaced. In this way the substance is dispersed to the marine environment.



Deltamethrin kills salmon lice by blocking the transmission of impulses on its neural pathways.



The biodegradation time for deltamethrin has been studied in a laboratory at a temperature of 10 C, which is a relevant temperature for the environment in Norwegian fjords. For sea water, the tests showed that less than 10% of the quantity added persisted after 10 days and less than 2% after 181 days. For sediment taken from the seabed under a fish farm, a half-life was discovered of 140 days. 90% had biodegraded after less than one year. For sediment taken from another location, the biodegradation time was faster, with a half-life of 90 days. The reason for this difference is probably the unique composition of the sediment, for instance a higher percentage of organic material from feed spills and faeces under the fish farm. The biodegradation time is so long that there may be a risk of accumulation in the sediment from frequent treatments. However, this is hardly likely, due to the fact that the discharges will be diluted and distributed over large areas of the seabed by being dispersed in the water (effects of currents and waves). It is unlikely that differing current speeds and directions in connection with subsequent treatments will result in exposure to the same sediment. The biodegradation of deltamethrin forms substances that are less toxic and the substance degrades all the way to CO2.


Deltamethrin has little potential for bioaccumulation in fish. Experiments performed on the American catfish (Ictalurus punctatus) show that for fish continually exposed to deltamethrin, the substance bioaccumulates for 10-15 days. That is, the quantity in the fish increases day by day. After 10-15 days, the substance is converted in the fish, and the amounts of deltamethrin residues fall, despite continued exposure. When the test fish is transferred to clean water, deltamethrin will be excreted quickly.


When fish are exposed to deltamethrin for a brief period, which is the most comparable with the effects of salmon lice treatment, experiments on American catfish (Ictalurus punctatus) and salmon (Salmo salar) show no signs of bioaccumulation.



Tests conducted by SINTEF have shown that the substance does not sink to the bottom after treatment, but is dispersed out and down the water column. It is not until the properties of Alpha Max that enable it to be mixed with water stop working that deltamethrin precipitates. The dispersion of Alpha Max from the fish farm means that treatment should be avoided if the direction of the current carries the substance in towards the littoral zone, where various species of crustaceans thrive.



• Acutely toxic to crustaceans (salmon lice, copepods, shrimp, crab)

• Less toxic to fish and invertebrates (except for crustaceans)

• Non-toxic to microorganisms, birds and mammals.


Field studies

Alpharma has conducted field studies to compare observed effects with model estimates. Laboratory tests showed that deltamethrin is acutely toxic to prawns (Palaemon elegans).Then prawns were placed in cages in and around a fish farm in the county of Rogaland. After treatment with Alpha Max at twice the recommended dose, 100% mortality was seen in the prawns in or right up against the cages containing the fish. Prawns placed at a distance of 5 metres from the cages had 70% mortality at a depth of 1 metre and 50% mortality at depths of 3-5 metres. A distance of 30 metres yielded 5% mortality at a depth of 1 metre, 40% mortality at depths of 2-3 metres and no mortality 2 metres from the bottom. 50 metres away an average mortality of 8.6% was found, which does not deviate significantly from the control location, where the average mortality was 5-6%.


Human health

Deltamethrin has a NOEL (No Effect Level) of 1 mg deltamethrin per kilogram of body weight per day. This value is based on toxicological tests of blood chemistry, hematology, organ weight, histopathology, tumour development and reproductive health studies over several generations. The tests were performed on mice, rats, dogs and rabbits.


Based on NOEL, a threshold has been set for the acceptable daily intake (ADI). In calculating ADI a high safety factor is used, which for deltamethrin is set at 100. This means that the ADI is one-one-hundredth of NOEL, which is the highest intake that did not show signs of toxic effects in chronic animal tests. The ADI for deltamethrin is thus 0.01 mg per kilogram of body weight per day (10 μg/kg body weight/day).


Deltamethrin is also used as an agricultural insecticide. The breakdown of the intake of deltamethrin residues between veterinary medicinal use and pest control is crucial for determining the magnitude of the residues of the substance that can be approved in fish, the maximum residue limit (MRL).The breakdown of the ADI on which the MRL is based, is as follows: Pest control: 85% of ADI Veterinary medicine: 15% of ADI = 1,5 μg/kg/day


Thus, a person weighing 60 kilograms may ingest 1.5 μg x 60 = 90 μg of deltamethrin from veterinary medicinal use per day. Based on these calculations, the EU has set an MRL value for fish at 10 μg deltamethrin/kg of fish (EMEA, 2001). To prevent fish to be slaughtered from having deltamethrin residues exceeding the MRL, there is a retention period of three days. Residue concentration tests show that two hours after treatment there are no deltamethrin residues of the MRL (10 μg deltamethrin/kg fish). In other words, the Norwegian authorities have used an extra margin of safety when setting the retention period for deltamethrin in fish at three days after treatment.