CAB Publication date
Certificate holder Date of submission
Unit of certification Species
Country Reference to other Q&As
Document reference Version
Salmon 1.1
Indicator Other relevant indicator/clause
Background info
Interpretation request (PTI for new sea lice medicine that is not released into the environment). Mowi Norway AS and Benchmark
Rationale for PTI calculation – Ectosan (Imidacloprid): The ASC standard includes a number of indicators aimed at promoting the responsible use of therapeutic treatments. The environmental risks linked with using chemical therapeutants are linked with the release of such chemicals into a wild environment where non-target organisms may be affected. Therefore, the development of new medicinal treatments that avoid the release of active therapeutants into the environment is in alignment with the ASC aim of environmental stewardship. Ectosan is a new therapeutic treatment against sea lice which fulfills this intention. Ectosan is administered as a bath treatment in wellboats or other closed contained treatment vessels only. This allows for accurate dosing of the medicine, control of water quality parameters, monitoring of fish welfare and the capture and retention of all treatment water. The fish are pumped into the wellboats with the medicine administered after all fish are onboard. Once the exposure period is completed, the fish are pumped out of the wellboat over a dewatering system fitted with a rinse bar to both separate fish from treatment water and ensure no residues of treatment water remain on the exterior of the fish. All water, including all rinse water, is collected and returned to the wells. Once all fish have been discharged over this system the treatment water is then transferred through CleanTreat, Benchmark’s novel water purification system, whereby the medicine is removed from the water prior to the water being discharged back to the environment. The purified water is measured continuously using onboard equipment to ensure levels remain below quantifiable limits. The Parasiticide Treatment Index (requirement 3.1.7) has been developed during the Aquaculture Salmon Dialogues (ASD) with the aim of “The ultimate goal would be that farms could meet the ASC Salmon Standard without using therapeutants or without the risk of those therapeutants negatively impacting the environment.” (page 47 of the ASC salmon standard v1.1). As mentioned earlier the use of Ectosan does not lead to any release of chemical therapeutants into the environment. In addition, the toxicity factor of the active ingredient used in Ectosan (Imidacloprid) has already been established as 85 mg/l (LC 50 for Daphnia, Fossen, 2016) which is higher compared with H2O2 (7.7 mg/l, which is given a toxicity factor of 0 in the ASC-PTI calculation). Therefore, the therapeutant factor for Ectosan will be zero and as a result so will the PTI. DNV GL response to ASC: DNV GL can not find PTI calculation values for the therapeutant Ectosan (Imidacloprid) in the ASC Salmon Standard v1.1 – April 2017, Appendix VII: Parasiticide Treatment Index and therefore needs clarification and determination from ASC related to which values shall be used when PTI is calculated. The text below is from page 95 in the ASC Salmon Standard v1.1 – April 2017, Appendix VII: Parasiticide Treatment.
DNV GL interpretation of this text is that it is ASC and the Technical Advisory Groups responsibility to determine which values shall be used when PTI is calculated for use of therapeutant Ectosan (Imidacloprid). DNV GL can not approve the given values from the user or producer of the therapeutant Ectosan (Imidacloprid) without a clarification and determination with acceptance of the given values from ASC. (page 95 in the ASC Salmon Standard v1.1 – April 2017)
Supporting evidence
(page 95 in the ASC Salmon Standard v1.1 – April 2017) Updating PTI with new information: If new therapeutants become available for sea lice treatment, or if new treatment method are developed, the Technical Advisory Group of the ASC may be asked to determine a therapeutic factor or treatment factor for that new parasiticide or new method, following guidelines for assignment of factors left by the SAD SC.
Effective date
March 15, 2019
The PTI-index is calculated using the following formula: PTIi= [(therapeutant factor) * (treatment factor) * (resistance factor) * (sensitive time factor)] Within this formula, the therapeutant factor and treatment factor vary per used active ingredient. The resistance factor and sensitive time factor are based on other variables (i.e. number of treatments applied and lobster presence). For the therapeutant factor, a classification of the parasiticides used at the time of the Aquaculture Dialogues is given in the table on page 93 (v1.1). This table does not include Imidacloprid (Ectosan). For this susbstance to qualify, the parameters that contribute to the toxicity factor need to be determined. These are:
  1. Treatment mechanism (bath or oral)
  2. Toxicity factor (0-2)
  3. Daphnia LC50 (μg/L)
  4. Persistence factor (0-3)
  5. Dosage factor (0-3)
The final therapeutant factor is calculated as following: Therapeutant factor = [(Toxicity factor) * (Persistence factor) * (Dosage factor)]
Treatment mechanism Ectosan is applied through a bath treatment. It is noted that the treatment is applied within a well boat and treatment water is purified before released back into the environment. The table on page 93 (v1.1) does not reference the sources from which the Daphnia LC50-scores are derived. In order to find consistency in toxicity scoring, the Pesticide Properties Database (PPDB – was consulted to verify the referenced values in the ASC Standard. The majority of listed LC50-scores where confirmed by this database and as such this database is used as a proxy to derive ecotoxicity values from. The toxicity factor of the active ingredient used in Ectosan (imidacloprid) has been established as 85 mg/L (Fossen, 2016). This score was confirmed by the PPDB-database ( As this score is 11 times less toxic as the stated value for H2O2 (7.7 mg/L), a similar rating as H2O2 for toxicity should be given as well (i.e. toxicity factor “0”). 4. Persistence factor (0-3) According to the PPDB-database, imidacloprid has a water-sediment and water phase only DT50-score (“half-life time”) of 129 and 30 days, respectively.
Compared to the other parasiticides listed in the table on page 93, these values are considered high (i.e. slow breakdown). For this reason a persistence factor of 3 is given. 5. Dosage factor (0-3) As there is no information available on the dosage applied – a (maximum) score of 3 is given from a precautionairy approach. Summary: For the application of Ectosan (imidacloprid) via the described process, the following values for the toxicity factor in the overall PTI-calculation need to be used: Therapeutant factor = [(Toxicity factor) * (Persistence factor) * (Dosage factor)] – Toxicity factor = 0 – Persistence factor = 3 – Dosage factor = 3 Therapeutant factor = [(0)* (3) * (3)] = 0 Please note that the use needs to be registered through Appendix VI of the ASC Salmon Standard v1.1.
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