Three hundred million tons of plastic are used each year. Over time the plastic breaks down into microplastics which range from sizes 1 um to 999 um. Their miniscule size allows them to be readily transported and consequently they make their way into terrestrial and aquatic environments. This experiment specifically focuses on microplastics in agroecosystems. As microplastics pass through water treatment plants, they accumulate into biosolids that are applied as fertilizers, or remain in the water used for irrigation, inevitably making their way into farmlands.

The purpose of this research study is to examine the effects of microplastics in the soil on plant health, as well as on the properties of the soil. Whether microplastics have an effect on plant or soil properties is important for the agriculture business, for animals and humans, and for terrestrial ecosystems.

In this study, a control group of lettuce was grown in plain soil and an experimental group of lettuce was grown in soil with a 10% concentration of microplastics, which were about 100 micrometers in size. After 49 days, the plant height, biomass, and root length were taken as measures of the overall health of the plants. In another group fluorescent polyethylene beads were added to the soil in order to track if the microplastics were taken in by the plants. After 19 days of growing, the lettuce were extracted from the soil, thoroughly cleaned, mashed up, and then observed with a black light for the fluorescent beads. The water holding capacity of the soils with and without microplastics was also measured.

monstrated that microplastics in the soil increase the water holding capacity by 29%, that plants growing in soil with microplastics added grew 17.9% taller than the control plants, and that the differences in dry biomass and root length between the two groups were not statistically significant. The processing of the lettuce grown with fluorescent microplastics demonstrates that microplastics are carried along with the plant matter even after rinsing thoroughly with water as people regularly do with their food. This means that when plants are grown with plastic in the soil, it is likely that people will be ingesting plastic as well.

Future studies could be conducted on the effects of microplastic ingestion on humans and animals. The amount of microplastics in agriculture soils could be quantified and the microplastic tendency to degrade in the soil could be tested as well. The effects of microplastics on other soil biota could also be tested.