Eco-terms: Biodegradable and Compostable
Biodegradable and compostable are two important terms to understand when you’re trying to shop green, and knowing the difference can help ensure not only that you’re buying eco-friendly products but also that you’re disposing of them properly.
In simple terms, biodegradation is the name for the process by which biological organisms break down substances into basic compounds like CO2, water, and biomass (a mix of carbon, oxygen, hydrogen). There are a number of organisms, including bacteria, fungi, worms, and insects, that play a part in biodegradation, and most work best in warm, wet environments.
Technically speaking, everything is biodegradable: given enough time, all matter will break down into its component parts. However, the timeline for biodegradation varies widely. For natural, unprocessed items like fruits and vegetables, leaves, paper, and cotton fibers this process can take as little as a week to a few months. Other man-made products can take so long to degrade that for all practical purposes they are considered non-biodegradable. For example, aluminum cans take several hundred years to decompose, while it’s estimated that plastics will take up to 5000 years to decompose.
In general, biodegradable is used to mean that an item decomposes in a reasonably short amount of time under typical conditions. However, there is currently very little regulation of the use of the term biodegradable on packaging and in advertising, so products that require long periods of time to decompose may still advertise themselves as biodegradable.
It’s also good to keep in mind that even the most easily biodegradable items take a very long time to decompose in a landfill, where they are deprived of the oxygen, water, and microorganisms necessary for biodegradation. Even lawn clippings and table scraps that end up in a landfill won’t be breaking down anytime soon, so be sure to compost biodegradable items to keep them out of the waste stream.
Composting is a way to speed up the process of biodegradation. A properly maintained compost pile creates the ideal set of conditions for the microorganisms responsible for decomposition. Anything that is biodegradable will be compostable – composting speeds up the breakdown of materials but does not change the basic process. However, not everything that is advertised as compostable is will biodegrade under normal conditions. For example, the bioplastic PLA is compostable: under industrial compost conditions it will easily break down into CO2 and biomass. But in non-compost conditions PLA acts like any other plastic and takes just as long to decompose.
In general, products advertised as compostable will not biodegrade in the environment (on the side of the road or in the ocean, for example) but many will be compostable in a home compost bin. Others will need to be put into an industrial compost site, which achieves a much higher temperature than home compost bins and can maintain a more precise balance of microorganisms and nutrients. Again, remember that landfills slow decomposition considerably, so you can do the most good by ensuring compostable goods are actually composted and not just thrown away.
Plastics: Biodegradable or Compostable?
Plastic is usually considered non-biodegradable, however new technologies have led to the development of several biodegradable plastics. These come in two main varieties. The first is oxo-degradable plastics, which are manufactured the same way as regular, petroleum-derived plastics but have added metal compounds that aid in decomposition. These products are supposed to break down on their own in any environment, but there is some concern that the biodegradation is not complete. Instead, some oxo-degradable products only break down into smaller particles that may or may not be further broken down by microorganisms. There is also concern that the metal additives in oxo-biodegradable plastic may leach into the environment. Oxo-degradable plastics can be recycled alongside regular plastics.
The second type of biodegradable plastic is manufactured from natural sources such as vegetable starches or sugarcane. These include polylactic acid (PLA) as well as many plastics used in commercial products like soda bottles and chips bags. These plastics are compostable but do not biodegradable under normal conditions. PLA in particular requires high temperatures to decompose, so make sure any bioplastics you use make their way to a compost pile. Also be sure to keep them out of the recycling stream: bioplastics cannot be recycled with traditional plastics, and it can be difficult for recycling centers to identify and dispose of them.
Paper: Biodegradable or Compostable?
Because they’re made from wood pulp, almost all paper products will be biodegradable. There are exceptions, however. Some paper products like plates and cups are coated with a layer of plastic designed to make them waterproof, but that coating will also prevent or slow down decomposition. Glossy paper like wrapping paper or products coated with a glue or sealant are also less likely to be easily biodegradable. Another problem with composting paper is the ink: products like magazines and wrapping paper sometimes use inks with metals or other dangerous substances in them which will stick around when they’re composted. In general, though, paper products can easily be thrown into a home compost bin.
Several organization offer biodegradable certification for a range of products, including paper, soaps, and fibers, so look for these seals to ensure the products you purchase live up to their claims. The most recognizable of these comes from the Biodegradable Products Institute, which rates plastic products as either ASTM-D6400 (for plastic products) or ASTM-D6868 (for plastic coating and parts on other compostable products). Both designations mean the product is compostable, but not biodegradable.