Three fields used to grow onions in Baarle-Nassau in Brabant have been found to be polluted with chemical waste, left after the production of the drug crystal meth, local broadcaster Omroep Brabant reported on Thursday.

Police were tipped off a year ago about the possible contamination and tested a total of 20 fields. Of them three had been polluted by drugs waste which had been mixed in with manure and sprayed on the fields as fertilizer.

Three men, who own the fields, have been questioned and are considered suspects, police said. All three, aged 48, 49 and 72, are farmers.

Left-over chemicals from drugs labs where amphetamines, ecstasy and crystal meth are made are often dumped in rural areas, posing a health risk and clean-up headache for local authorities.

It is the first time drugs waste has been found disguised as manure, the broadcaster said.

The food safety board is monitoring the situation to make sure there is no risk to health, the police said. It is unclear from the report if any onions from the fields have entered the food chain.