It’s not what marketers would like you to think. The problem is that plastics do not break down to organic or innocuous parts in the ocean — no matter how they are labelled — but they do have a serious impact on marine life.  If the final resting place is on land, the environmental impact is much less, but the label is still misleading – much, if not most, of the plastics labelled biodegradable may not fully break down.

Plastic waste has been accumulating in the oceans for some time. According to a study published in the journal Science, an estimated 4-12 million tons of plastics are dumped into the oceans each year. Apart from whatever environmental damage that causes, ridiculously large patches of plastic garbage are floating around the Atlantic and Pacific, as told here and elsewhere.

The environmental damage is serious. Plastic debris injures and kills fish, seabirds and marine mammals through suffocation, infection, drowning and entanglement. Plastic pollution of the oceans has impacted at least 267 species in this way, according to Clean Water Action.  Beyond this, steady ingestion of the substance continues all the while, some of it in the form insidious micro plastic particles, and the underlying consequences are not known. Whereas oil-soaked gulls never comprise more than a fraction of the total gull population, birds are ingesting so much that 99% of all sea birds, according to one projection, will have ingested significant plastic by 2050.

Some hoped that the problem could be solved by the advent of biodegradable plastics. But as explained in a recent UN report, claims about ocean biodegradability are simply not supported.

It is against international law to dump plastic waste into the sea. Plastics reach the ocean largely through the process of municipal waste collection, according Science article. In many countries, economic growth has run ahead of municipal infrastructure, creating shortfalls in the trash collection process. This results in plastic waste being blown into rivers and estuaries or getting to the oceans from coastal areas or in other ways. (After all, the stuff hangs around so long, it can take its time getting to the water, and it never leaves when it does.) While plastics find their way to the ocean more readily in developing countries, Science includes a list of top polluters in its study and the US is number 20 worldwide. Large coastal populations and “high per capita waste generation” are the primary factors.

In the US, a “biodegradable” label means that the product has passed tests performed by any one of numerous certification companies. These companies follow a complicated system involving FTC Green Guides and a standards body called the ASTM. At the end of the day, a product labelled in this manner is one that can, according to the certification, be biologically broken down, e.g. by microbes. Incorrect labelling can result in lawsuits or penalties, one way or another.

And yet, despite all the careful attention, most biodegradable plastics are not typically broken down even if they never reach the ocean. Most reach a landfill, and many if not most landfills are designed to suppress biodegradation because that process creates methane gas. Methane must be captured or burned off because it is explosive and also a greenhouse gas.  (Some landfills do degradation and treat the methane in that manner.) Plastic waste is less likely to reach a recycling plant, because recycling of plastics is relatively difficult and cost-inefficient. And finally, biodegradable plastics can actually interfere with recycling of plastics not specially designed to degrade.

Plastics labelled “biodegradable” might ease consumer conscience, but they don’t alleviate the plastic problem.