Microplastics, which can be found everywhere today, are at the heart of a new study, the results of which are very worrying. US researchers explain that those found in wastewater carry bacteria that are potentially increasingly resistant to antibiotics.
Real nests for germs
They come from our plastic waste, our clothes or our cosmetics and measure less than 5mm in length. Today, microplastics are everywhere, in oceans, rivers at the poles and even mountain peaks. They therefore represent a danger for the environment, but also for human health. In August 2020, microplastics (and nanoplastics) were detected in human tissue for the very first time. Each year, humans individually ingest up to 2,000 particles of microplastics per week, that is to say the weight of a credit card (5 g).
Humanity must now also deal with a new problem concerning microplastics. A team from the New Jersey Institute of Technology (USA) studied them as part of the wastewater treatment process. These works to appear in the Hazardous Materials Letter Journal have been detailed in a statement published on March 17, 2021.
Dung Ngoc Pham, lead author of the study, began by indicating that the vast majority of wastewater treatment plants were not not able to process microplastics. However, the fact is that these stations are points of convergence for a large quantity of microplastics. They are also important for certain chemicals and pathogens. Unfortunately, microplastics are real nests for germs.
Gene exchange between bacteria
As part of this work, scientists collected mud samples from three purification stations of the State of New Jersey. To these samples, the scientists voluntarily added microplastics of a common nature: polyethylene (PE) and polystyrene (PS). Using various techniques, including PCR (Polymerase Chain Reaction) genetic analysis, they were able to understand the development of bacteria on microplastics, as well as their genetic modifications.
Based on their results, the researchers observed the presence of sul1, sul2 and intl1 genes. However, their presence was up to thirty times more numerous in the biofilms formed by the microplastics than in other biofilms (sand). These genes are also known to promote resistance to antibiotics. The scientists therefore added an antibiotic to the samples and observed a multiplication by 4.5 of these famous genes.
On entering the treatment plants, the microplastics mix with the sludge and then bacteria attach themselves to it. These can then secrete extracellular substances similar to glue. Over time, other bacteria are added and in turn grow. By exchanging DNA with each other, bacteria spread antibiotic resistance genes.
Researchers are now continuing their investigation to find out how microplastics that carry bacteria can bypass the water treatment process.