Biofilm on the dome of the Jefferson Memorial National Park Service photo 
 
 August 10, 2016 
 
 Contact: Mike Litterst, 202-245-4676 
 
 
 
 
 
 "The increased presence of biofilm presents a new challenge in the care of memorials throughout the National Mall, particularly at the Thomas Jefferson Memorial," said Gay Vietzke, superintendent of National Mall and Memorial Parks. "We are continuing to study biofilm and research treatment methods, and look forward to restoring the dome to its original luster while ensuring its long-term preservation." 
 
 
 
 
 
 The blackening effects of biofilm are not a problem unique to the Jefferson Memorial. It can be found throughout Washington, from the Lincoln Memorial to tombstones at Congressional Cemetery, and around the world, from Hadrian's Villa in Italy to Angkor Wat in Cambodia and even on monuments in Egypt. It was successfully treated at the D.C. War Memorial in 2011. 
 
 
 
 
 
 While the study of the relationship of biofilms on buildings and the effects of cleaning them is still young, one of the common factors in the existence of many biofilms is the presence of nutrients and a place to grow, like stone. At the Jefferson Memorial, perhaps the most significant factor in its development is the erosion of the marble through natural weathering. The marble blocks that make up the Jefferson Memorial were smooth when they were originally hoisted into position, but over the years, rain has slowly eroded the marble, turning its once smooth surfaces into pitted surfaces –the perfect environment for a biofilm. 
 
 
 
 
 
 The black biofilm on the Jefferson Memorial first became noticeable in 2006 and has become increasingly more pronounced in recent years. A multi-disciplinary team of conservators, architects, and molecular biologists has been studying the growth on the Jefferson Memorial since 2014 as they prepare to test potential treatment options. 
 
 
 
 
 
 "Treatment of biofilm is difficult, as there is no known permanent method for removing it, and we have to ensure that any treatment must not do further damage to the soft marble of the memorial nor encourage further growth," said Catherine Dewey, chief of resource management for National Mall and Memorial Parks. "We are testing a variety of treatment techniques to find the option that is least damaging to the stone, safe for the environment and visitors, and cost effective." 
 
 
 
 
 
 National Park Service officials recently began testing ten different chemical biocides in small patches affected by biofilm at the base of the Jefferson Memorial and will monitor how effective each one is in the coming days and weeks. They will also experiment with more non-traditional treatment options, including ozonated water and irradiation with lasers. 
 
 
 
 
 
 There is no timeline for treatment of the dome and National Park Service officials stress that it's a deliberative process to ensure that whatever treatment is selected will do no further harm to the Jefferson Memorial. The treatment method ultimately chosen will help define the cost to restore the dome, which in turn drive the timeline for when the work will be scheduled. 
 
 
 
 
 
 NPS 
 
 
 
 
 
 
 
 
 
 About National Mall and Memorial Parks 
 
 The National Park Service's National Mall and Memorial Parks preserves, protects, and interprets the symbolic and monumental civic spaces and commemorative works in the center of the Nation's Capital that honor American ideals and values, distinguished public figures, and military and civilian sacrifices and contributions. On the National Mall these sites include the Washington Monument, Lincoln Memorial, Thomas Jefferson Memorial, Vietnam Veterans Memorial, Korean War Veterans Memorial, Franklin Delano Roosevelt Memorial, World War II Memorial, and Martin Luther King, Jr. Memorial. National Mall and Memorial Parks also serves as a public park and open space for active civic and cultural engagement, recreation, and public enjoyment. 
 
 WASHINGTON - The dome of the Thomas Jefferson Memorial is one of the iconic landmarks on the Washington, D.C. skyline. In recent years, however, the gleaming white rotunda has become increasingly darkened, but not by dirt or mold, as the casual eye might suspect. The culprit is a colony of microscopic organisms, called biofilm, which adheres to stone surfaces and is proving a challenge as the National Park Service investigates how to treat it. ||||| National Park Service officials are preparing to work on removing the black scum coating areas of the Jefferson Memorial in Washington. (Nikki Kahn/The Washington Post) 
 
 It’s black! It’s creepy! And it’s crawling over the Jefferson Memorial! 
 
 It’s biofilm — a microbial invasion of uncertain origin that has begrimed the stone surface of one of the nation’s most hallowed monuments. 
 
 Part algae, part bacteria, part fungi, the biofilm won’t eat your flesh, like the gooey Blob in the 1958 horror film, as a National Park Service spokesman remarked. 
 
 But it’s not clear if it’s munching on the stone. 
 
 And it can’t be killed. 
 
 A variety of samples are being tested to see which will work best and prove to be the least harmful as National Park Service officials get ready to work on removing the black scum coating areas of Jefferson Memorial in Washington. (Nikki Kahn/The Washington Post) 
 
 It has given the elegant white memorial on Washington’s Tidal Basin a dingy look, and, Blob-like, it is growing. 
 
 It is especially pronounced on the memorial’s dome, around its base, and on the triangular pediment that portrays Jefferson and four colleagues who helped draft the Declaration of Independence. 
 
 Concerned citizens have offered to try to clean it off. 
 
 And the Park Service is experimenting with several cleaning solutions to see what works best without harming the Vermont marble. 
 
 No damaging scrub brushes can be used, although some of the cleaning products leave a temporary orange tint. Officials have also discussed cleaning with lasers. 
 
 The film is also on the memorial amphitheater at Arlington National Cemetery, the Washington Monument and the Lincoln Memorial, the Park Service said. 
 
 [Nearing 100, Lincoln Memorial to get a facelift] 
 
 A variety of samples are being tested to see which will work best and prove to be the least harmful as National Park Service officials get ready to work on removing the black scum coating areas of Jefferson Memorial in Washington. (Nikki Kahn/The Washington Post) 
 
 It was on the D.C. War Memorial on the Mall, the District’s tribute to its World War I dead, before that monument was refurbished in 2011. And it may be coming back there, too. 
 
 [Refurbished DC War Memorial, a tribute to city’s WWI dead, reopens] 
 
 It’s somewhat akin to other biofilms, like dental plaque, the Park Service said. 
 
 But what, exactly, is it? 
 
 “We don’t even know the who, what, when, where, why,” said Judy Jacob, senior conservator with the Park Service’s Historic Architecture, Conservation, and Engineering Center in New York. 
 
 “We’re just starting to understand what it is, and its relationship to stone,” she said in an interview Monday. 
 
 “We can remove a good amount of it,” she said. “But it doesn’t mean we kill it. We can’t do that. . . . And it doesn’t mean that it won’t come back.” 
 
 The film is actually a “multicultural” community of organisms living in the relatively harsh environment of the sun-blasted stone, said Federica Villa, a Milan-based microbiologist who has been studying the memorial’s surface. 
 
 The black pigment is produced by the organisms to protect themselves from solar radiation, she said in an interview Tuesday. 
 
 But does the biofilm damage stone? 
 
 “We don’t know,” Villa said from Montana State University’s Center for Biofilm Engineering. “If you read the scientific literature, most of the scientists correlate the presence of a biofilm with deterioration.” 
 
 But she said her experiments have shown that biofilm may have a protective impact on stone. 
 
 “To be honest, we have a lot of work to do,” she said. 
 
 The memorial was dedicated in 1943. The biofilm became noticeable less than a decade ago, the Park Service said. 
 
 The reason may be that air pollution, which can inhibit the growth of such organisms, has decreased, the Park Service said. 
 
 Or it may have something to do with the microclimate near the memorial. 
 
 There’s a small weather station on top of the memorial, and data is collected monthly, said Catherine Dewey, chief of resource management for the National Mall and Memorial Parks. 
 
 “Because we have this huge body of water,” she said, referring to the Tidal Basin, “is that tiny little bit of extra humidity . . . a factor?” 
 
 “We have some photographs from . . . 2009 where there’s very, very little growth,” she said. “In 2012, you see a little bit more. In 2014, it’s even worse. It’s grown immensely over the last few years.” 
 
 One day last week, Dewey tested cleaning fluids on small strips at the base of the memorial’s east side. 
 
 “It’s particularly bad on this memorial, for whatever reason,” she said as she sponged on the cleaning fluids. 
 
 “It’s really deep into the stone, so it will take some time,” she said. “What we’re finding is it may not be clean immediately. But give it six months, and it will be much lighter.” 
 
 Some repair work is planned for the memorial in 2018, and the grit on the dome could be addressed then, she said. 
 
 The 32,000-ton memorial, which honors the nation’s third president and main author of the Declaration of Independence, rests on 634 pilings and caissons sunk down to bedrock on the south side of the basin. 
 
 During the annual Cherry Blossom Festival, it is a prime backdrop for photographers. 
 
 Six years ago, a $12.4 million repair project shored up its poorly supported seawall, which had been sinking into the basin. 
 
 And in 2014, a large chunk of limestone fell from the ceiling. The ceiling was stabilized, and netting was installed in case anything else came loose, Park Service spokesman Mike Litterst said. A full repair has not yet been done. 
 
 [Jefferson Memorial seawall sinking into the Tidal Basin] 
 
 The memorial turns 75 in two years.
– It sounds like the stuff of horror films: a creeping black slime that can't be killed. But experts say a real-life microbial invasion is coating some of the nation's most important monuments in black. The National Park Service earlier this month reported the "biofilm" has befouled the Jefferson Memorial, particularly its "gleaming white rotunda," and appears on the Washington and Lincoln Memorials and on tombstones in the Congressional Cemetery. But the mysterious substance—"part algae, part bacteria, part fungi," the Washington Post reports—isn’t unique to the Washington, DC, area. Biofilm has slimed sites around the globe, from Egypt to Italy to the Angkor Wat temples in Cambodia, per the NPS. Scientists are only now "starting to understand what it is, and its relationship to stone," a senior conservator with the NPS tells the Post. The NPS reports it has uncovered a "common factor" related to the establishment of various biofilms: the somewhat vague "presence of nutrients and a place to grow, like stone." It suspects that in the case of the Jefferson Memorial, the dimples and holes that have formed in the eroding marble may create an environment ripe for biofilm. That soft marble poses an additional challenge, notes the NPS, as any treatment needs to be tested to make sure it won't actually inflict harm on the stone. While there's no known permanent removal method, the NPS is evaluating 10 chemicals as potential cleaners and intends to also review options like ozonated water and lasers. The Jefferson Memorial's biofilm first became readily visible in 2006, and there's currently no timeline for treatment.