Labour AMs have voted down a call to stop ‘nuclear’ mud being dumped near Cardiff, by 26 votes to 22.
Every opposition AMs present voted for a suspension to the licence that allowed the dumping.
A second vote, calling for more to be done to reassure residents, was supported by 38 AMs to 10.
Contractors NNB Genco, responsible for building and operating the new Hinkley Point C nuclear power station in Somerset, are disposing of 300,000 tonnes of mud a mile off Cardiff Bay.
Natural Resource Wales has said that the chemical and radiological results from samples taken of the mud were within “acceptable, safe limits”.
However, campaigners, including Greenpeace, have called for more testing of the mud.
Independent AM Neil McEvoy, who had led the campaign against the nuclear dumping, said that the Welsh Government had failed to “stand up” for Wales.
“Many of us campaigned for years for this institution, because at times like this, we expected a Welsh Government to stand up for us,” he said.
“But what has Labour done? Want to dump your waste on us—no problem, fine,” he said.
“They’ve welcomed it. Let’s for the moment forget about the potential health concerns and the lack of an environmental impact assessment.
“Why would you accept 320,000 tonnes of waste being dumped on your doorstep by your neighbour? Why would you do that?”
Environment Secretary Lesley Griffiths however accused the campaign against dumping the mud of “ongoing scaremongering and lies”.
‘Out of touch’
Welsh Conservative Shadow Cabinet Secretary for the Environment and South Wales Central AM, Andrew RT Davies, also expressed anger at the decision to allow the dumping to continue.
“Tonight’s debate on nuclear mud dumping shows how shockingly out of touch the Welsh Labour Government is with the concerns of the general public,” he said.
“Welsh Labour Government ministers have the power to intervene and stop the mud-dumping – but instead have scandalously turned their backs on my constituents.
“From the very beginning, Natural Resources Wales has been at the heart of this fiasco, demonstrating that it is no longer fit for purpose with yet more staggering mismanagement and incompetence.
“This is a sad day for Welsh democracy and the views of people along the South Wales coastline, and I’m sure this will live long in the memory of the electorate.”