Up to 20 firefighters, and two fire appliances are still at the scene of the blaze on Atlantic Way, between Newport and Cardiff.
Chief Fire Officer Huw Jakeway said they are trying to get to the seat of the refuse fire which is a "challenge". He said they we are working closely with on-site staff to achieve this.
The area is being monitored by Natural Resources Wales who will keep the public informed if the circumstances change.
Gareth O’Shea from Natural Resources Wales said their officers have stayed at the site over the weekend and have used mobile air monitoring equipment and this data has been shared with health professionals in Public Health Wales and Cardiff Council so they can monitor and advise on any risk to public health.”
Public Health Wales and Cardiff Council have confirmed that daily average air pollution levels are below health-based standards.
The cause of the fire is still under investigation.
Firefighters have cooled and removed 12 acetylene cylinders to a safe area and damping down operations are continuing.
FIREFIGHTERS must stay at a recycling site blaze between Newport and Cardiff "for the foreseeable future".
The fire at the Atlantic recycling site on Newton Road, Wentloog took hold on Friday morning.
Firefighters are having to keep 30-40 gas cylinders near the blaze cool to avoid them exploding.
Crews from Duffryn, Cwmbran, Malpas, Roath, Ely, Central Cardiff and Barry were called to the blaze at the site, which involves 2,000 tonnes of refuse and has spread to electric cables.