Another fantastic question came from a steward-in-training aboard our ship last week. “How do scientists know how long it takes for different items of trash to decompose?”
This is an excellent question! We often talk about how certain types of waste decompose or biodegrade quickly, such as food scraps, and how others, such as plastic, degrade very slowly. This is why we have all learned to reduce, reuse and recycle! But, when we consider that plastic became more popularly used in consumer goods only recently (1950’s), it is fair to question how the estimates ranging from 500 – millions of years to decompose came about. It is also important to understand more generally how our landfills work, and how waste of any sort breaks down.
Decomposition occurs at different rates depending on the conditions. For bacteria to break down waste, such as leafs and twigs, it needs to be warm, moist, and well-oxygenated. Under these conditions, food scraps, for example, will break down fairly quickly. To measure exactly how long, scientists use respirometry tests. As bacteria work to break down waste, they use up oxygen and release gases—they respire. In a respirometry test, ideal conditions (moist, warm, oxygenated) are created and the amount of carbon dioxide released by the bacteria over a certain amount of time, to break down a known amount of trash, is measured. The more the bacteria respires, the more it is working! From this, scientists are able to estimate how quickly certain types of trash will be degraded.
Some things don’t biodegrade, even in these bacteria-friendly conditions. Plastic, for example, will show no degradation in a respirometry test—bacteria doesn’t break it down. Instead, plastic is photodegraded by sunlight. The energy from the sun causes the material to break down. This process is very, very slow.
Most garbage doesn’t make it to a perfect, bacteria-friendly environment to break down. Trash that is not composted or recycled ends up in landfills. Modern landfills are not designed to rot trash, only to cover it up. The conditions in landfills are ultra-hot, dry, and low-oxygen—not good for bacteria. Trash that would otherwise degrade in a little amount of time, such a newspapers and even food scraps has been excavated from old landfills perfectly in-tact, decades later.
Check out this video to learn more about how the landfills work, and definitely stay tuned to hear about “trash-hole explosions”!
So what can a steward do? Simple! Reduce what you put into those landfills by reducing, reusing and recycling. Check out some trash-free experts: