They will capture some, but they were not designed for microfiltration in the first place. Microplastics are defined as polymer particles that are less than 0.5 mm (500 microns) in diameter, but can be as small as 2.5 microns.
Brita filters are designed to remove odors from water, but they use a loose-packed granular carbon filter that is ineffective at capturing particles, lead, and other contaminants.
ALSO SEE: Can Brita Filter River Water?
Your best bet is to purchase either a solid block carbon filter (which filters down to 1 micron and is reasonably priced – under $50 on Amazon from a variety of manufacturers – just make sure it says solid block rather than granular or packed, and attaches directly to your faucet or countertop unit) or a reverse osmosis filter (which can go as low as 0.1 micron, will also remove bacteria and most chemicals, but are more expensive and require more upkeep).
There are some that are designed for refrigerator water feeds, but you must verify that they fit your model.
While anything less than 100 microns in capture size is beneficial, aiming for 2 microns or smaller is preferable.
Although there is no evidence that microplastics harm humans or animals, I prefer plastic-free water.
Microplastic is a synthetic material with a diameter of approximately 5000 microns. Water filters or purifiers can remove particles as small as 5 microns.
I have not used Brita, but have heard that it can remove particles as small as 1 micron.
Do not be alarmed by the presence of microplastic particles in tap water. Because surface tap water is filtered to remove the majority of particulates of all types, tap water is probably the least of the minute exposures that include foods.
Bottled water contains significantly more plastic particles than tap water, most likely due to the way caps are manufactured by routing a block of plastic. In any case, there is also no known risk.