Biodegradation of Polyethylene Terephthalate Microplastic in the Rumen of Cattle

Plastic pollution is a major environmental issue, with 91% of plastic not being effectively recycled and accumulating in the environment.1 Through physical biological and chemical processes, plastics degrade into microplastics (MPs, 5 mm-1 μm), which are widespread and pose significant ecological and health risks.2–4 Due to their small size, their properties and the interactions with the environment, MPs cannot currently be collected; consequently, no effective methods exist for their removal from the environment. However, ruminants may offer a potential opportunity for the environment. Cattle ingest MPs on a daily basis through contaminated feeds.5 Thanks to their specialized digestive system—which includes a large chamber called “rumen”, hosting a highly active microbial community—they may be capable of degrading MPs. In vitro studies have shown that the rumen microbiota can break down synthetic polyester MPs, such as polyethylene terephthalate (PET), as well as other biodegradable plastics.6–8 The complex microbial community in rumen fluid demonstrates higher degradation efficiency than isolated enzymes, with initial breakdown observed within 24 hours—highlighting the rumen’s promising role in mitigating MP pollution. The study aimed to investigate the promising yet insufficiently explored capacity of the rumen microbiota to degrade PET MPs. PET MPs (0.5 g, n=72) were incubated with buffered rumen fluid and total mixed ration, using the Ankom DaisyII system under anaerobic conditions at 39°C for 24 (n=18), 48 (n=18), and 72 (n=18) hours. For each incubation time, one jar was used, along with a control jar (n=18) that did not contain rumen fluid. Each jar also contained two blanks samples. The experiment was conducted in triplicate over three consecutive weeks. The MP degradability was assessed by measuring weight loss after incubation. Data were analyzed using the wilcox.test function from the stats package (version 4.2.2). Pairwise comparisons were adjusted using the Bonferroni correction to account for multiple testing. Results showed that PET MP degradability was significantly different from zero at all three incubation times (p<0.0001). Moreover, the degradability of PET MP at 72 h was significantly greater than at 24 hours, with values of 0.50±0.070%, 0.73±0.057%, and 0.96±0.082% at 24, 48, and 72 hours, respectively. This study provides the first evidence that ruminants, through their rumen microbiota, can partially degrade PET MPs. The presence of enzymes in the rumen, such as cutinases – typically involved in the hydrolysis of cutin contained in fibrous feeds – suggests a natural potential for biodegradation. Since certain polymers, such as PET, share structural similarities with natural fibers,6 it is hypothesized that the rumen microbiota may also be capable of breaking them down. These findings highlight the rumen as a promising biological system for MP reduction. Future research should investigate the rumen microbiota’s ability to degrade other types of polymers as well, enhancing this capacity. 1. Geyer et al., 2017 doi:10.1126/sciadv.1700782 2. Kimasz et al., 2024 ISBN 978-0-443-15397-6 3. Kumari et al., 2022 doi:10.3390/plants11030340 4. Corte et al., 2024 doi:10.3390/ani14020350 5. Glorio Patrucco et al., 2024 doi:10.1016/j.scitotenv.2024.174493 6. Quartinello et al., 2021 doi:10.3389/fbioe.2021.684459 7. Galyon et al., 2022 doi:10.3168/jdsc.2022-0319 8. Galyon et al., 2022 doi:10.3390/polym14102103