Scientists from the University of Hull and Hull York Medical School, working with researchers from the Hull University Teaching Hospitals NHS Trust, analysed human saphenous vein tissue taken from patients undergoing heart bypass surgery in a small pilot study. Saphenous veins are blood vessels in the legs that help send blood from the legs and feet back to the heart. The veins consist of three layers of tissue. They are widely used in Coronary Artery Bypass Graft (CABG) procedures aimed at diverting, or bypassing, blood around narrowed or blocked coronary arteries to restore blood supply to the heart in patients with coronary heart disease.

Before this, no published studies have examined whether microplastics can infiltrate or cross any biological barrier, including blood vessels, or viewed any potential link between environmental microplastic exposure and CABG outcomes. Therefore, the aim of this study was to identify if any microplastic particles were present in human saphenous vein tissue samples.

The scientists discovered 15 microplastic particles per gram of vein tissue through this study. “We were surprised to find them”, said Professor Jeanette Rotchell, an environmental toxicologist at the University of Hull who led the research. “We already know microplastics are in blood from a study by Dutch colleagues last year. But it was unclear whether they could cross blood vessels into vascular tissue, and this work would suggest they can do just that. Whilst we don’t yet know the implications of this on human health, we can say that from studies using cells grown in dishes, they cause inflammation and stress-responses”.

The levels of microplastics observed were similar to, or higher than, those reported for colon and lung tissues. However, although the size ranges are similar, the shape characteristics and polymer types differ from other human tissue types analysed to date.

Scientists found five different polymer types in the tissue. The most prominent included:

• Alkyd resin: found in synthetic paint, varnishes and enamels used for furniture and architectural coatings, product finishes, special-purpose coatings and car refinishing primers as well as others.
• Polyvinyl acetate (PVAC): an adhesive found in food packaging, shipping boxes/bags and binders for paper, plastics and foils. It is one of the main ingredients of wood glue but has a recent biomedical use in DNA/drug delivery.
• Nylon and EVOH-EVA: used to bond plastic polymers to create flexible packaging materials, with blends optimised to improve their characteristics, such as helping to prevent moisture intrusion or tensile qualities. Applications include many uses, from food packaging and lamination to multi-layer pipe, wire and cable.

Professor Rotchell believed that these first human tissue analysis suggest that the distribution of the microplastics’ predominant types may be tissue specific. “The characterisation of types and levels of microplastics can now inform experiments to determine vascular health impacts, including any potential link between environmental microplastic exposure and CABG outcomes.”

Professor Mahmoud Loubani, a co-author and Honorary Professor of Cardiothoracic Surgery, said: “Failure of saphenous vein grafts has been a long-standing issue following coronary artery bypass surgery. It is an effective treatment, but longevity is limited by deterioration in the patency of the veins. The presence of these microplastics in the veins may well play a role in damaging the inside of the vein leading to it becoming blocked over time. We do need to identify if there is any correlation and figure out ways of maybe removing the microplastics.”