Prohibit importing non-compliant goods. Do compliance checking in ports and punish local importers, both companies and their owners/executives, for noncompliance.
I don't think the political will to do this exists. From the perspective of the state we care way more about drugs than we do about plastics, but people have been ordering asthma drugs, psychedelics, stimulants, steroids, and retinoids from Indian pharmacies successfully for at least a decade now, which makes me think that it's a hard problem to solve at scale.
I don't think the political will exists do much of anything which is hard, definitely not to coördinate laws on plastics. But to compare import of stimulants to plastics... I don't think it's the same thing. Nobody is going to gray import a plastic toothbrush from China just to get that extra cadmium.
