Plastics are the most relevant type of ocean, lake or stream debris, which come in all shapes and sizes, but those which are less than 5mm in size are called "microplastics".
Micro plastics are very slow-degrading contaminants in water, having long residence time and easily to transfer along food chains to cause physical damages to our living organism.
Although no solid evidence has been found that microplastics pose a health risk to human beings, small particles are far riskier because they can enter the bloodstream, the lymphatic system, and reach the liver.
Microplastics might act as irritants, in much the same way asbestos fibers are now known to inflame the lungs and cause cancer. Microplastics are also thought to act as vectors for microorganisms and toxic chemicals, thus posing further health risks.