The Protocol on Heavy Metals, a protocol to the Convention on Long-Range Transboundary Air Pollution, was adopted in Aarhus, Denmark, in 1998. As of 2004, it had 36 signatories.^[1] As of 2016, it had 35 signatories and 33 parties, with no country having become a signatory since 1998.^[2] The protocol addresses the reduction of cadmium, lead and mercury emissions in the interests of environmental protection.^[3] Amendments to the Protocol were agreed in 2012^[4] to introduce more stringent emission limits^[5] but are not yet in force.