The government agency, which published results of a preliminary environmental study, however stressed that there was currently no risk of drinking water becoming contaminated.
“Substances from buried minks have been found under the mink graves… The first steps are now being taken to collect and clean up the pollution,” the agency said in a statement.
Water from underneath the graves would be pumped up and sanitised, the agency said.
Denmark was the world’s largest exporter of mink fur, but culled all 15 million of its mink population last year after some were found to be carrying a mutated virus variant, and later banned mink breeding until 1 January 2022.
Fearing pollution due to the decomposition of the dead animals’ bodies in the areas where they had been hastily buried, the government decided in December to unearth the four million carcasses as soon as the risk of contagion had subsided and incinerate them instead.
The two burial sites are located in the western part of the Nordic country of 5.8 million inhabitants.
In one, signs of pollution have been detected in three of the 32 boreholes drilled and in one out of 26 on the other site. The main pollutants were ammonia and excess amounts of nitrogren.
In November, Denmark said the “Cluster 5” mutation carried by mink had been wiped out, and they were the only animal confirmed to be able to contract it and pass it to humans.
The process, however, was mired in scandal from the start.
Once culling had begun, questions arose over whether the government had the right to kill the animals elsewhere than where the mutated strain had been detected.
The country’s agriculture minister resigned as a result.