Plastic Pollution: How Biofilms Boost Cadmium Adsorption

Did you know that some plastics can soak up heavy metals like a sponge? Biodegradable polylactic acid (PLA) mulch is designed to replace conventional polyethylene (PE) mulch in farming. The goal? To cut down on plastic waste and microplastics in soil. But it turns out, these tiny plastic bits can also grab onto something nasty: cadmium (Cd), a big problem in soil contamination. Scientists left PLA and PE mulches outside for 16 months to see what happens. After that time, they made microplastics (MPs) from both the fresh and weathered mulches. Guess what? Biofilms, like tiny layers of living goop, grew on the older plastics. These biofilms can change how well MPs grab onto cadmium. When they looked closely, they found that weathered plastics had more oxygen-containing groups. These groups help to grab onto cadmium better. Even after scrubbing off the biofilms, these groups were still there. This means the weathering process changes the plastic in a way that helps it grab onto cadmium. In experiments, PLA MPs grabbed onto more cadmium than PE MPs, even though PE has a bigger surface area. This shows that the type of plastic matters a lot in how well it can grab onto cadmium. Weathered plastics could grab onto even more cadmium. But here’s the surprise: once the biofilms were gone, the weathered MPs didn’t grab onto any more cadmium than the fresh ones. This means that those tiny biofilms are a big reason why weathered plastics can grab onto so much cadmium.