Like the Czech Republic, Slovakia has had its air contaminated by sulfur dioxide emissions resulting from the use of lignite as an energy source by the former Czechoslovakia, which had the highest levels of sulfur dioxide emissions in Europe. Slovakia instituted a program to reduce pollution in the late 1980s. Air pollution by metallurgical plants endangers human health as well as the environment, and lung cancer is prevalent in areas with the highest pollution levels.
Airborne emissions in the form of acid rain, combined with air pollution from Poland and the former German Democratic Republic, have damaged Slovakia's forests. Land erosion caused by agricultural and mining practices is also a significant problem.
As of 2001, 22.1% of Slovakia's total land area is protected. In 2001, 8 mammal species, 4 types of birds, and 11 plant species were endangered. Threatened species include the Danube salmon, marsh snail, and false ringlet butterfly.