Pedro Rafael de Pena de La Cruz, 52, of The Dominican Republic, was held overnight in a federal detention centre and was to appear in court on the charge of transportation of hazardous materials, FBI spokesman Harry Rodriguez said.

If convicted, he faces fines and a possible prison sentence of up to five years.

The spill Tuesday morning delayed more than a dozen flights as the Luis Munoz Marin International Airport closed three terminals out of concern for dangerous vapours.

De La Cruz told Puerto Rican authorities he was bringing the mercury to a dentist in the Dominican Republic.

Toxic metal

He was carrying about 20 pounds (nine kilogrammes) of the toxic metal and only a small amount spilled inside the suitcase, police said.

While too much mercury can damage the brain and nervous system, it is widely used as an ingredient in dental fillings.

The US Food and Drug Administration says silver fillings contain too little of the substance to harm people.

- AP