When first carried out in 1987, the original US EPA inventory of dioxin sources revealed that incineration represented more than 80% of known dioxin sources. As a result, US EPA implemented new emissions requirements. These regulations succeeded in reducing dioxin stack emissions from incinerators. Incineration of municipal solid waste, medical waste, sewage sludge, and hazardous waste together now produce less than 3% of all dioxin emissions. Since 1987, however, backyard barrel burning has showed almost no decrease, and is now the largest source of dioxin emissions, producing about one third of the total output.