The Hamburg Institute of Ecology and Politics, conducting the research on behalf of the opposition Green Party, found that Germany - a country heavily promoting clean energy - is emitting about two tons more mercury than previously thought.

Mercury, which, when released into the world's atmosphere eventually makes its way into the food chain, has been shown to cause neurological damage and some cancers.

IQ loss and delayed speech, particularly among children and adolescents, have also been associated with mercury vapor exposure.

More than forty percent of Germany's energy needs come from coal-fired power.

Oliver Krischer, deputy head of the Greens Party, appealed to Angela Merkel's coalition government to follow the lead of the US, which has recently significantly cut the limit for acceptable mercury emissions.

Berlin has tried to lower the limit of mercury emissions, and has committed to allowing a maximum of one microgram of mercury per cubic meter a day from 2019.

Responding to the criticism, German Environment Minister Barbara Hendricks defended Berlin's existing policy, adding that further measures were not necessary.

Speaking to German newspaper "Welt am Sonntag," Hendricks called, in principle, for coal to be phased out: "If we are to meet our long-term climate objectives, we must give up coal-fired power."

In the lead up to the signing of the Paris climate deal in December, pressure was placed on the world's biggest consumers of energy to nut out a pact which would encourage companies to invest in clean energy and reduce air pollution.

jlw/rc (dpa, AFP)