Assessment of the Presence of Microplastics in Stabilized Sewage Sludge: Analysis Methods and Environmental Impact

Wastewater treatment processes can fragment microplastics (MPs), which may subsequently enter fertilizers applied in agricultural settings. This study aimed to quantify the occurrence of MPs in stabilized sewage sludge intended for fertilizer production. Matrix elimination was performed using an oxidative method to isolate MPs, followed by MPs separation with a saturated salt solution of appropriate density to enhance the accuracy of identification. The resulting samples were analyzed using spectroscopic and microscopic techniques to provide the detailed characterization of MPs content. The highest concentrations of MPs were recorded during the months of June, July, and May, with average values of 2942, 2341, and 1746 fragments per 100 g of dry weight, respectively. The analysis revealed that fragments were the dominant morphological form, and low-density polyethylene was the most common polymer type detected. These findings underscore a significant risk of MPs re-emission into the environment through the agricultural application of fertilizers derived from sewage sludge. Such practices may lead to the introduction of between 6110 and 13,889 MPs per square meter of soil, depending on the application rates, thereby posing potential risks to soil health and the broader ecosystem. This study highlights the importance of monitoring MPs content in fertilizers derived from wastewater treatment by-products.