Nearly two tonnes of metal - including jewellery, gold teeth and fillings - have been collected from the ashes of cremated bodies in Northern Ireland.
The materials were shipped to the Netherlands where some were used to construct objects such as road signs and aircraft engines.
However, bereaved families were not told about the recycling scheme, which has been operating for the last four years.
It found more than 11,000 cremations have taken place since the scheme started in 2010.
Yet Belfast City Council, which is responsible for Roselawn Crematorium, said it had not notified relatives.
Industry guidelines recommend bereaved families are made aware of the recycling scheme.
The scheme's aim is to protect the environment by recycling the metals, with profits going to charity.
There is no suggestion of illegal or untoward conduct by Belfast City Council.
Metals found in ashes following cremation are removed with tongs and a magnet and placed into a recycling container.
The vast majority originate from metal hips, as well as nails, screws and ornaments from coffins, plus gold, silver and palladium, which is found in dental fillings.
The recycling container is collected by Orthometals, the Dutch company behind the scheme, and transported to the Netherlands where it is sorted and sold on to be melted.
Some material is sold for casting pieces in the aircraft, car and household industries.
Once costs for processing have been accounted for, proceeds are donated to charity.
Since 2010, two tonnes of metal has been collected from Roselawn Crematorium, including 1,069g of palladium valued at £16,920 and 446g of gold, worth £10,595.
The total worth of metal collected from Belfast was £31,337.
Dr Heather Conway from Queen's University, who is an expert on body disposal law and funeral disputes, said the council's failure to inform families of the recycling scheme raised a number of ethical concerns.
"Because of the symbolic and emotional attachment that we have to our loved ones' remains, this has the potential to be hugely upsetting for people," she said.
"Industry practice guidelines state that people should be informed and there are clear ethical issues if bereaved relatives are not made aware that their loved ones' remains may be subject to this process."
Belfast City Council said: "It is not deemed necessary to provide this information and no family has ever requested it.
"However, we keep this under review."
Orthometals said the scheme's main aim was promoting recycling in the interests of environmental protection.
Metal recovered from Belfast crematorium includes:
1,069g of Palladium worth £16,920
446g of gold worth £10,595
170kg of cobalt/chromium worth £1,480
38g worth of platinum worth £1,030
248kg of stainless steel worth £295
837g of silver worth £291