Abstract: A process for the treatment of solid waste material which is or is suspected to be contaminated with plutonium or compounds thereof with or without other hazardous contaminants, which process includes: contacting the said material with and thereby dissolving contaminants as complexes by a liquid medium which comprises Solution X which comprises an aqueous solution which is free of ingredients which are naturally degradable to non-toxic products with or without mild physical assistance such as heat or ultra-violet radiation, said solution comprising:(a) carbonated water;(b) a conditioning agent; and(c) a complexing agent which comprises the anion of a single or multiple carboxylic acid species having from 2 to 6 carbon atoms in each carboxylic acid species;and separating the liquid medium from the waste material and recovering the dissolved contaminants from the liquid medium and wherein the step of contacting the waste material with the said liquid medium is preceded by a step of contacting the waste material