Plastics on your plate

Amritanshu Shriwastav is in a bind: he finds that the more he studies, the more he worries. Since he started examining microplastics in 2016, the engineer-environmental scientist has been trying to answer questions on their genesis, presence, and impact on the ecosystem. And the outcome of his research has been alarming.

His initial work demonstrated the presence of microplastics in salt and seawater. The study prompted him to assess human exposure to microplastics in a single day by sampling drinking water, cooked food, and breathable air. The result, showing high concentrations of microplastics, was startling. Now, as seen in his recently published work, he has explored how microplastics that enter people's bodies through the mouth interact with their digestive systems.

Given the difficulties in studying a living person's digestive system, he and his team at the Indian Institute of Technology (IIT) Bombay devised a way to perform experiments in a simulated in vitro system. For this, gastric juices were sequentially added to microplastics, mimicking the way enzymes act on various digestive system organs. The researchers took four common food-borne microplastics — polystyrene, polypropylene, low-density polyethylene and nylon — which were acted upon by digestive enzymes and bile juice. They found that ingested microplastics undergo fragmentation and become rough while passing through the human gastrointestinal tract because of their interaction with digestive enzymes. The team did not observe any drastic change in the chemical structure of these particles, which more or less established their inert nature, but found biomolecules sticking to the particles because of the microplastic's rough surface. The study also showed that different, and possibly toxic, monomers and plasticisers may leach out of microplastics. The study was recently published in the journal Science of The Total Environment (bit.ly/ingested-microplastics).

Over the years, the scientific community has been studying the occurrence of microplastics in various systems and human body parts to understand their impact on the health of humans and other organisms. Shriwastav believes that studies that examine the interaction of microplastics with human body parts are important as they are expected to guide future policies. "What is toxicity? What is the eventual risk? For regulations to come in place, we need solid evidence to show that this is harmful," says Shriwastav, an Associate Professor at IIT Bombay.