Microplastics are plastic fragments smaller than five millimetres. That is the entire definition. It says nothing about what the plastic was before, which is why the category covers things as different as a synthetic fibre shed by a fleece jacket and a shard of a bottle that has spent fifteen years in the surf.
Two ways they form
Primary microplastics were manufactured small. Plastic pellets used as industrial feedstock, microbeads in some cosmetic products, fibres released by synthetic textiles in the wash.
Secondary microplastics are the remains of larger items. A crate, a bag, a buoy, a length of rope — broken down by ultraviolet light, heat, salt and mechanical abrasion into fragments, then into fragments of fragments.
The second category is the larger one, and it is the one that grows every year regardless of what anyone buys, because it is fed by plastic that entered the environment decades ago and is still breaking down now.
Where they end up
In sediment on the seafloor. In the water column. In the tissue of filter-feeding shellfish, which pass water through their bodies for a living and cannot distinguish a fragment from a food particle. In fish that eat those shellfish. In salt harvested from seawater. In drinking water, bottled and tap alike.
Research on what this means for human health is active and, honestly, not settled. Anyone who tells you the effects are fully understood — in either direction — is ahead of the evidence.

What is not in dispute is the exposure itself. The fragments are measurably there.
Why "biodegradable" on a label often means very little
This is the part worth slowing down for.
Many products marketed as biodegradable will break down only under industrial composting conditions — sustained high temperature, controlled humidity, specific microbial activity. Put the same item in seawater or ordinary soil and it behaves much like conventional plastic, just with a better story on the packaging.
Others are conventional plastic with an additive that accelerates fragmentation. These do not biodegrade at all. They become microplastics faster. That is the opposite of the intended outcome.
A meaningful claim answers three questions: degrades in what environment, within what timeframe, and into what end products. If a supplier cannot answer all three, the label is marketing.
Where our work fits
We have developed a bioplastic formula from seaweed that degrades completely in soil, fresh water or seawater within three months, without leaving microplastic fragments behind. That result comes from our own testing, carried out with research partners at Universitas Padjadjaran, Politeknik Negeri Bali and Universitas Udayana.
We publish the conditions along with the claim, because a claim without conditions is exactly the problem described above.

At YAYASAN AKAR CINTA BUMI LESTARI, we believe that restoring our planet requires a collective heartbeat. We warmly invite conscious individuals, businesses, and organizations to join us in a powerful charitable partnership dedicated to cleaning and protecting Indonesia's magnificent oceans.