Sometimes known as mermaid tears or nurdles, the pellets are used to produce everyday items from water bottles to shopping bags and are known to add to the problem of plastic making its way into the world's oceans and rivers.
The millions washed up in Spain came from at least one container that fell from the Toconao - a Liberia-registered vessel chartered by shipping giant Maersk - off the coast of neighbouring Portugal last month, the pellets' manufacturer Bedeko Europe said in a statement.
Deputy Prime Minister Maria Jesus Montero told state broadcaster TVE the government was worried of possibly "serious repercussions" but did not yet know the exact impact and whether it would affect fishing.
The scenes of residents using household items to help clean up the beaches revived memories of Galicia's worst environmental catastrophe, the 2002 spill of 63,000 tonnes of fuel oil that forced the closure of Spain's richest fishing grounds.
"Unfortunately, we are all reminded of images from the past that we would like to erase," Montero said.
An estimated 10 trillion plastic pellets contaminate marine ecosystems every year, a 2020 report by the Pew Charitable Trusts found.
Environmentalist group Ecologistas en Accion denounced the regional government's "inaction two weeks after detecting the spill" and in a statement on Friday said it would file an environmental crime complaint against Toucan Maritime, the Dutch owner of the vessel.
Galicia's regional leader Alfonso Rueda, of Spain's conservative opposition People's Party, said the central government had known about the pellets being scattered for over two weeks but only informed his administration on Jan. 4.
Madrid's representative in Galicia said the maritime rescue service had first informed regional coast guards about the incident on Dec. 20.
(Reporting by Miguel Vidal and Emma Pinedo; writing by David Latona; Editing by Andrei Khalip and Barbara Lewis)
