Marine biodegradable polymer particle groups and production method for same

A method for producing marine biodegradable polymer particles, comprising the step of crosslinking water-soluble polymeric polyvalent anions derived from a water-soluble anionic polymer containing at least a monovalent salt of alginic acid and having monovalent anionic substituents within:

• (A) a medium in which particles of the water-soluble anionic polymer have been dispersed to a concentration of at least 5 wt %,
• (B) a medium in which, using water and an oily medium, the water-soluble anionic polymer has been suspended or emulsified in water to a concentration of at least 5 wt %, or
• (C) a medium in which the water-soluble anionic polymer has been hydrophilized or dissolved to a concentration of at least 5 wt %
• by using as crosslinking agents two or more salt compounds containing at least divalent metal cations;
• wherein the crosslinking reaction is carried out by adding the two or more salt compounds a plurality of times in divided portions, such that the difference between the largest and smallest atomic radii of the metal elements making up the at least divalent metal cations included in the salt compound is 15 Å or more, and the content of the at least divalent metal cations derived from metal elements having an atomic radius of 150 Å or more is at least 25 wt % of all the at least divalent metal cations.