Do biodegradable bags decompose in sea water?

Plastic in the sea is a real problem for the environment. On land, compostable bags are the best alternative to plastic bags. But what happens in water? Do bags made of biodegradable materials decompose there - and if so, how long does it take?

What are biodegradable bags

Biodegradable bags are made from bioplastics. At Naturabiomat® we use the bioplastic Mater-Bi from Novamont. This contains renewable raw materials such as vegetable oils and corn starch. However, bioplastics of this type do not compete with food.

Biodegradable bags must comply with the EN 13432 standard to be listed as such. This standard states that the bags have to be converted into carbon dioxide to a level of 90% during composting. The carbon dioxide produced during the composting process can be measured. The remaining 10%, however, cannot be measured, as it is used by the bacteria and fungi involved in the composting process as building materials for their own growth and reproduction.

Bioabfallbeutel im Meer

Do bags for compostable waste decompose completely in the sea?

Scientific studies have been carried out to test whether Mater-Bi films made from bioplastics are completely broken down in the sea. Samples of the bioplastics were exposed to marine sediments from the intertidal zone. Metabolic monitoring of the bacteria that "digest" the bioplastics was used to monitor the biodegradation.

High biodegradation rates were achieved in a relatively short time - less than one year. The samples therefore did not disappear immediately, but due to a much shorter residence time they pose a lower ecological risk than products made of other substances.

So if biodegradable bags end up in the sea, that’s OK, isnt it?

No, even if the biodegradable bags decompose in the sea more quickly than other types of waste, it will still take months before there is nothing left. Careless disposal in the environment, regardless of whether the waste eventually ends up in the water or not, is a social problem that has to be solved not with biodegradable bags but with an overall social focus on environmentally conscious behaviour. Biodegradable bags are developed for organic recycling, not as an excuse to treat waste carelessly.

Unfortunately, however, despite our ingenious miller collection and recycling system, plastic bags and packaging are still found in soil and water. There they slowly decompose into microplastics. This is also the reason why it is better to use quickly and completely biodegradable materials for such products - as Austria is now demonstrating.

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