A team of researchers at the University of Bayreuth in Germany has found that microplastics that make their way into biowaste can show up in organic composts and fertilizers. In their paper published on the open access site Science Advances, the group describes their results when testing organic composts and fertilizers from several processing plants.
Microplastics have been in the news a lot of late, due mainly to their presence in water, but they may be causing unknown problems on land, as well. In this new effort, the researchers wondered if microplastic bits that make their way into uneaten food or farmer plant waste could also make their way into fertilizers that are made using organic waste. To find out, they tested samples from a wide variety of commercially available organic fertilizers.
Organic fertilizer is made the old-fashioned way—by letting microorganisms break down organic material. It is made via aerobic and anaerobic processes. Aerobic composting plants create fertilizer by mixing organic matter with soil and allowing microbes to break it down into material suitable for feeding to plants. An anaerobic biowaste digester, on the other hand, is a facility where organic material is thrown into a sealed vat where it is “digested” to produce both fertilizer and biogas.
The testing by the researchers was done on fertilizers made in facilities in Germany, which is unique, because Germany is a country that is serious about dealing with organic waste such as table scraps or food that has gone bad in the fridge. Thus, in addition to paper bins, most Germans also have bins for disposing of such materials. Those materials are sent to processing plants where it is cleaned and combed before conversion into fertilizer. Such facilities also collect plant waste from farms.
In their study, the researchers tested samples from both aerobic and anaerobic facilities, and also from a control facility that used only plant waste from a farm They found some amount of microplastics in all of the samples they tested except those from the control farm. They further found that the amount of microplastics depended on the process used at a given plant and that there tended to be more in the fertilizer from the aerobic facilities. They suggest microplastics wind up in biowaste due to their presence in foods, and also from being collected or stored in plastic containers.