Biodegradable plastics are designed to biodegrade in soil, not in water and especially not in our oceans.
The most effective way of addressing plastic litter and in fact any litter that ends up in the ocean, is to stop it at source, prevent it from getting there in the first place. This can be achieved by education to change the behaviour of people, perhaps engineering remedies like filtration and screening, formulation of products, but these are not matters that we are qualified to address.
Plastics marked as ‘biodegradable’ do not degrade rapidly in the ocean. National and international standards have been developed to define terms such as ‘compostable’ and ‘biodegradable’ which refer exclusively to terrestrial systems, most typically to industrial composting. The Australian Standard AS4736 defines biodegradable bioplastics that are suitable for industrial composting, but makes no claims about other environments, including marine environment.
Biodegradation occurs when microorganisms consume the material as feed and in the process generate CO2, water and leave some harmless residual biomass. The rate and extent of biodegradation is dependent on a number of variables, mostly the immediate microorganic population. A compostable bioplastic will completely biodegrade within a composting cycle, which is about three months. Composting conditions include a very healthy population of microorganisms, plenty of oxygen and water and elevated temperatures. When the conditions are less than ideal, the process is much slower or may not occur.
Conditions in the world’s oceans and seas varies in oxygen level, temperature, microorganism levels, action of tides and waves, so there is no single environment in which a microfibre might be found, but one common condition is that the level of microorganic activity is much lower than in a compost heap. Therefore the rate of biodegradation will be much slower and as a result, the microfibre will be present in the marine environment for some months, perhaps longer, before it completely biodegrades.
There are performance standards covering the compostability of plastics, like Australian Standard AS4736, but to date there have been no internationally recognised standards covering biodegradability in the sea, partly because the conditions vary so much. This is now changing with performance standards addressing biodegradability in the sea currently being developed in Europe and North America.
Plastics, whether plant-based, fossil-based, degradable or non-degradable, should never be allowed to end up as waste in the ocean, unless specifically engineered to decompose rapidly in marine environments. Further research and the design of products that biodegrade in marine environment can only help to reduce the impacts of marine litter in the future where efficient waste management is not sufficient enough. The main solution to plastics in the ocean is better waste collection and recycling.
For more information see – Are biodegradable bioplastics a solution for the problem of marine litter?