Biocides in aquaculture
Safe use of antifouling and clean net strategies for marine fish farms.
---a brief introduction
---a brief introduction
Abstract
Knowledge and product stewardship is important when choosing a strategy for keeping nets free of biofouling. Considerations for HSE, food safety and fish health must be made before utilizing active ingredients or in-situ cleaning in aquaculture.
What is a biocide?
A biocide is an active component added to a paint or substrate to achieve an antifouling effect. European legislation defines it as follows: “a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism by chemical or biological means.”
This implies that all substances claiming to have an antifouling effect must be considered a biocide. It is important to consider this when choosing antifouling as most countries have strict regulations with regards to the use of biocides. Even “harmless” ingredients such as enzymes or alloys will in this setting fall under biocide legislation.
Copper as antifoulant
Copper has been used as an antifoulant for centuries. It is a naturally occurring material and an essential element for normal growth of most plants and animals. Its excellent properties of generic biofouling protection and low environmental impact has made it the number one choice for aquaculture. The most common form of copper used as antifouling is cuprous oxide. (Cu2O) This is made from recycled pipes, wires, fridges etc.
Cuprous oxide is effective against both algae and animal biofouling; its effect can be seen over the timeframe where a sufficient concentration is leeched from the paint. Fouling pressure is very high in fish farms; with nets forming a near perfect growth surface and waters being saturated with nutrition. The protection level will eventually be overcome and the nets starts to foul. On rare occasions copper tolerant monocultures can form on the net, but the occurrence of resistance development is low with copper. Its efficacy limitations combined with various restrictions in copper usage has prompted the industry to search for alternatives. Safe use of boosters or biodegradable biocides might enhance the functionality of antifouling for aquaculture applications.
There is a risk of copper accumulation in sediments under fish farms. Copper is released to the environment by leeching into the water or by physical abrasion during in-situ cleaning operations. Toxic effects can occur where copper is accumulated in biologically available forms. (Bioavailable) The anaerobic sediment conditions will significantly reduce the bioavailability of accumulated copper through the formation of insoluble sulphide compounds. Most copper found in sediments is therefore harmless to the environment and for normal fish farms copper pose no significant ecological implications. It is important to distinguish between total and bioavailable copper levels when reviewing sediment concentrations.
The main source of copper for farmed fish is via its feed, typical concentrations around 10mg per kg feed. Few metals accumulate in the edible portions of aquatic organisms, moreover, most metals when ingested orally have a relatively low toxicity to humans. From the standpoint of human health copper toxicity is very low compared to metals like mercury or cadmium. Several studies demonstrate poor copper retention and no accumulation in edible fish tissue. Risks related to copper bioaccumulation in fish is therefore consider negligible in relation to human consumption.
Active ingredient alternatives
The selection of active ingredients for aquaculture is derived from the much larger shipping antifouling industry. Over time some substances such as TBT has been removed from the market due to negative environmental effects. Others, like Econea® and Zineb® have emerged as promising candidates. When evaluated for the application as a ship hull protection the criteria for HSE is significantly different than what should be the case for aquaculture. Special considerations must therefore be made before transcending a biocide into the aquaculture industry.
The US Environmental Protection Agency (EPA) has categorized antifouling products used on aquaculture nets as an indirect food contact application. Under the US Food Quality Protection Act (FQPA), any residue of biocides incorporated into fish tissue is considered unsafe unless it falls within an exemption or residue tolerance (MRL) set by US EPA. Use of antifouling products in fish farms without such settings induces a risk of illegal import of fish into the US.
Workers safety must also be given attention in relation to antifouling. The human interaction with a ship hull is relatively small compared to regular farming operations and net handling. The painted, dried net should not introduce hazards that inhibits regular operations or require bulky personal protection equipment.
Products containing alternative biocides and enhanced effect in comparison with copper has been in development for some time. Undergoing meticulous testing to ensure safe use in Aquaculture these products might well provide new solutions for antifouling in the future.
Biocide legislation in the EU
The use of antifouling in EU is regulated under the European Chemicals Agency, ECHA. The classification of biocides under the Biocidal Products Regulation (BPR) is divided into product groups, antifouling being Group 4 Type 21. In order to reach approval as an active substance the biocide must undergo a significant approval process, typically involving scientific dossiers of more than 20 thousand pages of documentation. Hence the list of approved substances is short, as of January 2017 this (Article 95 list) includes only 10 products. Substances not found on this list will not be permitted for usage in antifouling.
In order to incorporate the active substance into a final paint solution this must also undergo an authorisation process. Although not as lengthy as for the active substances this authorisation process also includes a dossier documenting health risks, environmental impact, leeching rates etc. Antifouling paint without such authorisation is not permitted for sale in the EU.
Transitional arrangements have been made for active substances existing prior to the BPR regulations. This means that paint containing active substances under review or recently approved can be sold for a limited timeframe without BPR authorisation. National regulations will apply under such transitions.
In-situ cleaning
In-situ cleaning of the net is a possible alternative or supplement to antifouling and net change. This method commonly includes a hydraulic water jetting system blasting off the fouling organisms. Maintaining the clean net without adding chemicals or net replacements is a desirable feature. However, it is important to be aware of the environmental and fish welfare risks involved before using this method.
Without a closed cleaning loop the system will release a significant amount of particles into the water. These will most likely contain micro plastics, harmful nematocytes and pathogen carrying amoebae. Such a bloom of material in the water might harm the mucus and gill system of the fish; in addition to appetite loss triggering an increased risk of fish decease outbreak. Any applied antifouling will largely be lost in the cleaning process and a rapid recolonization of biofouling must be anticipated. Striving to achieve a “gentle cleaning cycle” will limit these effects.
References and resources
Sneddon R, Tremblay L 2011. Assessment of Environmental Effects - Copper and Zinc. Cawthron Report No. 1984.53 p.
Phillips G, Russo R 1978. Metal Bioaccumulation in Fishes and Aquatic Invertebrates: a Literature Review EPA-600/3-78-103
Isaksen TE, 2016. What type of infection risk do fouling organisms represent? RFFVEST project no. 252029
Monica S, 2015. Program for fish feed monitoring. NIFES ISBN 978-82-91065-27-4
ECHA biocidal products regulations, https://echa.europa.eu/regulations/biocidal-products-regulation
EPA Pesticide Registration, https://www.epa.gov/pesticide-registration
Knowledge and product stewardship is important when choosing a strategy for keeping nets free of biofouling. Considerations for HSE, food safety and fish health must be made before utilizing active ingredients or in-situ cleaning in aquaculture.
What is a biocide?
A biocide is an active component added to a paint or substrate to achieve an antifouling effect. European legislation defines it as follows: “a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism by chemical or biological means.”
This implies that all substances claiming to have an antifouling effect must be considered a biocide. It is important to consider this when choosing antifouling as most countries have strict regulations with regards to the use of biocides. Even “harmless” ingredients such as enzymes or alloys will in this setting fall under biocide legislation.
Copper as antifoulant
Copper has been used as an antifoulant for centuries. It is a naturally occurring material and an essential element for normal growth of most plants and animals. Its excellent properties of generic biofouling protection and low environmental impact has made it the number one choice for aquaculture. The most common form of copper used as antifouling is cuprous oxide. (Cu2O) This is made from recycled pipes, wires, fridges etc.
Cuprous oxide is effective against both algae and animal biofouling; its effect can be seen over the timeframe where a sufficient concentration is leeched from the paint. Fouling pressure is very high in fish farms; with nets forming a near perfect growth surface and waters being saturated with nutrition. The protection level will eventually be overcome and the nets starts to foul. On rare occasions copper tolerant monocultures can form on the net, but the occurrence of resistance development is low with copper. Its efficacy limitations combined with various restrictions in copper usage has prompted the industry to search for alternatives. Safe use of boosters or biodegradable biocides might enhance the functionality of antifouling for aquaculture applications.
There is a risk of copper accumulation in sediments under fish farms. Copper is released to the environment by leeching into the water or by physical abrasion during in-situ cleaning operations. Toxic effects can occur where copper is accumulated in biologically available forms. (Bioavailable) The anaerobic sediment conditions will significantly reduce the bioavailability of accumulated copper through the formation of insoluble sulphide compounds. Most copper found in sediments is therefore harmless to the environment and for normal fish farms copper pose no significant ecological implications. It is important to distinguish between total and bioavailable copper levels when reviewing sediment concentrations.
The main source of copper for farmed fish is via its feed, typical concentrations around 10mg per kg feed. Few metals accumulate in the edible portions of aquatic organisms, moreover, most metals when ingested orally have a relatively low toxicity to humans. From the standpoint of human health copper toxicity is very low compared to metals like mercury or cadmium. Several studies demonstrate poor copper retention and no accumulation in edible fish tissue. Risks related to copper bioaccumulation in fish is therefore consider negligible in relation to human consumption.
Active ingredient alternatives
The selection of active ingredients for aquaculture is derived from the much larger shipping antifouling industry. Over time some substances such as TBT has been removed from the market due to negative environmental effects. Others, like Econea® and Zineb® have emerged as promising candidates. When evaluated for the application as a ship hull protection the criteria for HSE is significantly different than what should be the case for aquaculture. Special considerations must therefore be made before transcending a biocide into the aquaculture industry.
The US Environmental Protection Agency (EPA) has categorized antifouling products used on aquaculture nets as an indirect food contact application. Under the US Food Quality Protection Act (FQPA), any residue of biocides incorporated into fish tissue is considered unsafe unless it falls within an exemption or residue tolerance (MRL) set by US EPA. Use of antifouling products in fish farms without such settings induces a risk of illegal import of fish into the US.
Workers safety must also be given attention in relation to antifouling. The human interaction with a ship hull is relatively small compared to regular farming operations and net handling. The painted, dried net should not introduce hazards that inhibits regular operations or require bulky personal protection equipment.
Products containing alternative biocides and enhanced effect in comparison with copper has been in development for some time. Undergoing meticulous testing to ensure safe use in Aquaculture these products might well provide new solutions for antifouling in the future.
Biocide legislation in the EU
The use of antifouling in EU is regulated under the European Chemicals Agency, ECHA. The classification of biocides under the Biocidal Products Regulation (BPR) is divided into product groups, antifouling being Group 4 Type 21. In order to reach approval as an active substance the biocide must undergo a significant approval process, typically involving scientific dossiers of more than 20 thousand pages of documentation. Hence the list of approved substances is short, as of January 2017 this (Article 95 list) includes only 10 products. Substances not found on this list will not be permitted for usage in antifouling.
In order to incorporate the active substance into a final paint solution this must also undergo an authorisation process. Although not as lengthy as for the active substances this authorisation process also includes a dossier documenting health risks, environmental impact, leeching rates etc. Antifouling paint without such authorisation is not permitted for sale in the EU.
Transitional arrangements have been made for active substances existing prior to the BPR regulations. This means that paint containing active substances under review or recently approved can be sold for a limited timeframe without BPR authorisation. National regulations will apply under such transitions.
In-situ cleaning
In-situ cleaning of the net is a possible alternative or supplement to antifouling and net change. This method commonly includes a hydraulic water jetting system blasting off the fouling organisms. Maintaining the clean net without adding chemicals or net replacements is a desirable feature. However, it is important to be aware of the environmental and fish welfare risks involved before using this method.
Without a closed cleaning loop the system will release a significant amount of particles into the water. These will most likely contain micro plastics, harmful nematocytes and pathogen carrying amoebae. Such a bloom of material in the water might harm the mucus and gill system of the fish; in addition to appetite loss triggering an increased risk of fish decease outbreak. Any applied antifouling will largely be lost in the cleaning process and a rapid recolonization of biofouling must be anticipated. Striving to achieve a “gentle cleaning cycle” will limit these effects.
References and resources
Sneddon R, Tremblay L 2011. Assessment of Environmental Effects - Copper and Zinc. Cawthron Report No. 1984.53 p.
Phillips G, Russo R 1978. Metal Bioaccumulation in Fishes and Aquatic Invertebrates: a Literature Review EPA-600/3-78-103
Isaksen TE, 2016. What type of infection risk do fouling organisms represent? RFFVEST project no. 252029
Monica S, 2015. Program for fish feed monitoring. NIFES ISBN 978-82-91065-27-4
ECHA biocidal products regulations, https://echa.europa.eu/regulations/biocidal-products-regulation
EPA Pesticide Registration, https://www.epa.gov/pesticide-registration