accumulate synonyms:
verb
accrue, agglomerate, aggregate, amass, assemble, bring together, build up, collect, come together, gather, grow, heap up, hoard, increase, mass, multi ply, pile up, stack up, inf stash away, stockpile, store up.
Opp DISPERSE.
Example:
These marine pollutants are locked in the ecosystem and accumulate in mother seals from eating fish.