Q&A on copper and biocides

Copper, whether as a metal or as a copper compound, has no significant effect at preventing fouling. Effect is only achieved when copper exists in ion form (Cu+ or Cu2+). This can be done in several ways depending on the desired result. To achieve anti-fouling effect at sea, you need compounds that slowly and in a controlled way release copper ions. For this purpose copper thiocyanate, copper metal and copper(I) oxide are used. The latter is the most commonly used and is found in more than 95% of all anti-fouling products worldwide.

Copper oxide Cu₂O is very poorly soluble in water. This property means the compound releases copper ions slowly over a long time.

NetKem advises against washing all biocide-containing net impregnations, regardless of whether the active biocide is dicopper oxide, tralopyril (Econea), CopperPyrithione and/or ZincPyrithione. If you must clean the nets, it should be done gently, without flaking off impregnation particles which would then be released into the environment.

NetKem has developed and declared in Norway several products based on other biocides, but these are not yet available on the market. We are working on risk assessments for environment, HSE and fish health, including large and time-consuming toxicity studies, and will only launch the products when we can be sure they can be used safely.

Copper in ion form is highly reactive — that's why it works against fouling. This same property means the ions are quickly, and within a fraction of a millimetre from the netting, transferred to other non-active compounds after being released from the net. Copper binds to dissolved organic carbon (DOC), to particles (Suspended Particulate Matter, SPM), and to inorganic compounds (Cu-OH).

In practice this can be observed on boats and pens treated with copper-containing compounds. The impregnation only works where applied, while "holidays" and untreated rope nearby become heavily fouled.

Copper occurs naturally in seawater: leached copper takes the same form, making it nearly impossible to measure what has leached from net impregnation versus what is natural.

Copper ions' ability to react with other compounds also applies in sediments. Copper binds quickly and strongly to organic material, which is often abundant under aquaculture facilities. Even stronger is the binding to sulphur compounds. In oxygen-poor sediments, i.e. the lower layer, sulphur compounds form which react strongly with copper to form insoluble copper sulphide. The copper has then been transformed into a mineral, an ore, which is no longer toxic to the environment.

Copper is an essential element that we need a daily intake of through the food we eat. Content in food varies greatly; from e.g. mussels and liver pâté with high copper content, to bread with smaller amounts. The body is able to handle this variation through homeostatic balance — it only takes up what it needs.

Using the word "heavy metal" as a negative environmental argument is based on lack of knowledge or other agendas.

In Norway the term "heavy metal" is often used as an umbrella term for the elements arsenic (As), mercury (Hg), lead (Pb) and cadmium (Cd), which are grouped together due to their toxicity. As a result the term is often wrongly associated with toxicity.

However, the definition of "heavy metal" is simply that it is an element with a density above 5 kg/dm³ (saying nothing about the substance's toxicity). By this definition, around 60 of the naturally occurring elements are heavy metals — including copper, iron, bismuth and gold.

Used as a biocide, the same applies to copper as to all other biocides: it must be handled correctly, since point pollution of soil and sediment can pose an environmental problem.

Copper is of low toxicity to fish. In fact, fish are among the organisms with the highest tolerance for copper. Again it is the ions that may have a toxic effect by binding to the gills, but this requires ion concentrations far above what is found in and around an aquaculture facility.

Copper is of low toxicity to shellfish, krill and shrimp. Mussels filter large volumes of water to extract plankton. In doing so they can also accumulate elevated copper levels if they grow e.g. inside a marina, but even this is not unambiguous.

Some seem to be of the view that copper oxide is no longer used in boat antifouling. This is wrong. On the contrary, copper oxide is the most-used biocide in antifouling, and proud boat owners will discover within a few years that only copper-based antifouling products are offered on the market.

A large share of agricultural products you find in the store have been protected with copper-based fungicides. This applies to olives, coffee, cocoa, oranges, avocado, canned field tomatoes, grapes, organic apples, beer (hops) etc. In addition copper is used as a feed additive for pigs, chicken and salmon — often in exactly the same form as found in net impregnation.

Kobber er godkjent som biocid i begroingshindrende midler i henhold til biocidregulativet i EU. For å bli godkjent der kreves det innlevering av en svært omfattende dokumentasjonspakke. Pakken for kobber ble vurdert av Frankrike, som med utgangspunkt i denne pakken leverte sin egen vurdering av de innleverte dataene. De innhentet også annen dokumentasjon. Vurderingen utarbeidet av Frankrike er tilgjengelig her hos ECHA.

Copper is due for renewed assessment in 2-3 years. No change in approval is expected.