Residents want the air quality in their village to be closely monitored following the approval of a waste recycling plant.
The site at Cwmfelinfach, Caerphilly county, would turn thousands of tonnes of waste, that would normally go into landfill, into fuel.
Natural Resources Wales (NRW) insisted “robust” evidence showed there would not be “significant” harm to residents’ health.
But many still believe nitrogen dioxide levels will be too high.
Hazrem Environmental is behind the venture at Nine Mile Point. It was originally refused a permit by NRW, but it later dropped its opposition after new technical information came to light.
John Wheadon, Permitting Service Manager from NRW, said: “The planning inspector found that our evidence was both robust and reliable and convincingly demonstrated that the facility can operate without significant harm to the health of people in the area.”
However, some residents are still not satisfied, and campaigners want AMs to monitor possible incidents of air pollution.
Campaigner Alan Sharpe, from Lower Sirhowy Valley Residents Group, said: “It’s been a mining community for many years and we still suffer from a considerable amount of chest conditions.
“There are many ex-miners now to this day who are suffering from shortness of breath.”
Philippa Marsden, Labour councillor for Ynysddu, said: “It’s our health. It’s us that are going to be impacted and our future generations in terms of health.”
Chris Evans, Labour MP for Islwyn, said: “We don’t want these waste transfer stations coming into our valleys. I’m deeply concerned that nitrous gases will be pumped into the area and I’m deeply concerned.”
Hazrem Environmental was unavailable for comment.