There’s been a project around New York Harbor and surrounding waters for a while now, seeding oysters of a species that was known to flourish there in historic times, so that they will sequester pollutants. The oysters will be unfit for consumption, but their shells, when crushed, will be fine aggregate for paving material, and no worse for toxicity than the local limestone, which is made up of sea creatures that sequestered heavy transition elements in the Devonian period. The creatures themselves will be no worse to handle than other organic waste, since the transition metals will pretty much all be in the shells. (They’ll be unfit for consumption because of bacterial and algal contamination.) The shells will sequester some carbon, as well, but the quantities are minuscule.