Biofilm threatens monuments in the US capital
In the latter 20th century, the disastrous effects of increasingly acidic content of rainwater became apparent to conservationists of historic structures and monuments. In the Washington DC area, federal regulations that limit pollutants allowed by industry have resulted in lowering the threat of acid rain to the white marble monuments that line the national mall. Today, a new threat can be found in the form of a black biofilm.
By Michael E. Ruane
The Washington Post
August 10, 2016