A new study by The James Hutton Institute has revealed an increase of up to 1,450% in the level of microplastics found within soil samples after just four years of sewage sludge application. The study, which was carried out in collaboration with Robert Gordon University (RGU), also found that the number of microplastics in the soil remained relatively unchanged 22 years after application. Researchers drew their conclusions by looking at soil samples from a field in Hartwood, North Lanarkshire, which was included in a UKwide sewage sludge experiment between 1994 and 2019. Investigating the long-term impacts of sewage sludge application, scientists applied a variety of sludges to plots of land for four years and maintained the area as grassland. Soil samples were taken every two years over a 25-year period and archived in the National Soils Inventory for Scotland at the Hutton.
Microfilm in soil
These archived samples provided researchers with a unique opportunity to analyse the fate of microplastics in soils over an extended period, which they were able to do with funding from the Macaulay Development Trust. In addition to their discoveries around the quick increase in and longevity of microplastics, scientists found that degradation varied between different forms of plastic. Microfibres from clothing (the most common type of microplastic found) and microfilms from packaging both broke down in the soil, while other shapes – such as flakes from plastic containers and bottles – did not. Microplastics that did degrade formed smaller microplastics and nanoplastics, posing an additional hazard to the environment. Researchers were able to determine the potential sources of the sludges used on the soil samples by examining the types of microplastics present, such as uncommon materials only used in industrial locations. They also noticed that textile fibres found within the sewage sludge lost their colour over time, however the cause of this is still unknown. It may be that the dyes are degrading, causing the fibres to fade, however it is also possible that dyes are leaching into the environment, which could cause further toxic effects in the soil.
