Microplastics are tiny pieces of plastics less than 5 mm in length. They mainly come from larger pieces of plastic that have broken down as well as microbeeds that are used in cleansers and some toothpaste.
The use of microbeads was banned in the US in 2015 but microplastics are still fairly ubiquitious in our environment and food supply and frequently end up in us, creating immune issues.
The most common sources of ingested microplastics are in plastic bottled water, sea salt and some sources of shellfish. Awareness of how to reduce exposure and improve detoxification (which you are already doing in Stage 1), can help to minimize the negative impact for you and help you to cultivate an effective and accurate immune system.