How do microplastic particle sizes influence bioaccumulation and toxicity in freshwater ecosystems?

Bioaccumulation of microplastics may be a result of their ingestion along with food or water by aquatic organisms.Then the smaller particles cross the epithelial layer into the blood stream, while the bigger particles are passed out into the water during egestion. This means that there is accumulation of these microplastic particles downstream, with an increasing concentration effect along the food chain.
The toxicity of these microplastic particles may be as a result of
-Some carcinogenic chemical         substances associated with their   manufacture
-These particles interfering with the   normal absorption process - over time   can 'clog' the epithelial layer
-These particles can also compete   with  the nutrients particles during   absorption, resulting in an organism   being deprived of essential nutrients
-The changing PH conditions in the   different parts of the GIT, probably   affect the physical and chemical   state.  of the microplastic particles,   which can translate into toxicity 

Larger microplastics tend to remain in the gut and mainly cause physical stress, such as blockage and reduced nutrition. Smaller microplastics can cross epithelial barriers, accumulate in organs and induce oxidative stress and inflammation. Whereas, nanoplastics penetrate cells, reach sensitive tissues such as the brain and gonads, alter gene expression and cause systemic toxicity.

Larger particles are less likely to be ingested, and if ingested are less likely to be absorbed into the tissues and more likely to work their way down the digestive tract and and be egested.