Photographs showing bags of clinical waste piled at three health centres in North Lanarkshire have been posted on social media.
The images - from Coatbridge, Kilsyth and Cumbernauld - showed bags of waste on top of large waste containers.
It comes after the collapse of the firm Healthcare Environmental Services (HES), which had previously processed clinical waste across Scotland.
NHS Lanarkshire said the waste had since been removed and posed no risk.
Following the collapse of HES in December, the Scottish government said contingency plans would ensure clinical waste continued to be disposed of safely.
'Waste backed up'
NHS National Services Scotland also said "appropriate contingency measures" were in place to process clinical waste after HES lost its service contract.
However, one former HES worker, who asked not be named, said: "The firms who have taken over the collections are working flat out, but there is weeks and weeks of waste backed up."
The pictures of the three Lanarkshire sites, reportedly taken this week, appeared on a Facebook page set up by those who said they were concerned about the HES situation. The images have since been removed.
John Paterson, director of property and support services at NHS Lanarkshire, said. "The waste at Coatbridge, Kilsyth and Central (in Cumbernauld) Health Centres was uplifted between 9 and 11 January.
"We have an agreed interim process in place to ensure that clinical waste is uplifted as and when required, while the national contract is resolved.
"There was a delay in uplifts being requested with these three centres, but we have taken steps to avoid this in future. This was low level clinical waste that was bagged in accordance with procedures and held in closed-off areas. There was no risk to public health."
Appropriate protective equipment
A spokesman for the health board was unable to confirm exactly how long the waste had been lying at the sites.
Shotts-based HES lost its contract to provide waste processing services with NHS England after reports emerged in October last year that human body parts and other clinical waste was piling up after the company struggled to incinerate it.
In December, NHS Scotland announced that the firm would not have its contract continued north of the border when it came up for renewal in April.
Since then the company has served hundreds of redundancy notices and failed to pay the salaries of 350 staff for December.
In Inverness, four porters at Raigmore Hospital were injured carrying out work involving clinical waste.
It is understood porters at the site have had a greater role in dealing with the material following the collapse of HES.
A Scottish government spokesman said: "We regard the safety of all NHS employees as paramount.
"The clinical waste contingency arrangements recently introduced across the country, have been risk assessed and safe systems of work identified, with appropriate protective equipment issued and made available to all staff."