The discovery of dangerously high levels of arsenic that prompted the closure of a popular park in Washington last week came as a shock to families who enjoy the green space for soccer games and picnics.
One possible source of the poison is especially disturbing -- it could stem from mortician practices during the Civil War.
During the conflict, Fort Reno Park was a military outpost for soldiers protecting the capital from Confederate invasion. Because arsenic was a common ingredient in embalming fluid, one theory is that it seeped into the ground during the preparation of soldiers' remains for burial elsewhere.
"It was common for the Civil War, especially on the Union side, for the dead to be embalmed with arsenic, but whether the arsenic that is being detected now goes back that far, I cannot say," National Park Service spokesman Bill Line said.
While tourists flock to Washington for its monuments and museums, the city rests on ruins from a bygone era. Fort Reno was part of a circle of defensive positions that included at least a dozen forts protecting the capital during the war.
Tests indicate arsenic levels in some places are as high as 25 times the level deemed safe by federal standards.
"If morticians were there, that would make perfect sense," said George Wunderlich, executive director of the National Museum of Civil War Medicine in Frederick, Md., which has a permanent exhibit on embalming.
Arsenic was inexpensive, easy to come by and the most effective product to prevent a corpse from stinking.
"It basically petrifies you," Wunderlich said.
Formaldehyde replaced arsenic at the beginning of the 20th century after groundwater near cemeteries became poisoned.
The 33-acre park, in a suburban northwest corner of the city, is next to a reservoir and two schools.
In light of its indefinite closure, the fates of a summer concert series and a community garden on the federally managed land are unknown.
On Thursday, the Environmental Protection Agency took about two dozen soil samples at the park. Results are expected as soon as this week; only a few spots may have abnormal levels. Other sources -- fertilizers, pesticides, treated lumber -- could be to blame for the arsenic levels, experts said.
Trish Taylor, community involvement coordinator for the EPA, said investigators might be dispatched to study historical records and review old maps to get to solve the mystery. She said she considered it premature to speculate on the Civil War link as the source of the contamination.
The discovery was made when Terry Slonecker, a geographer with the U.S. Geological Survey, was looking for arsenic in a nearby area where the Army had conducted chemical warfare research and had buried hazardous explosives during World War I. He detected unusual readings on the far edge of his study site, which turned out to be Fort Reno.
Since 2002, the Army Corps of Engineers has been removing arsenic-laced soil from residential yards in Spring Valley, home to American University, which also has been affected by the World War I research.
Slonecker said there was no evidence to connect the World War I contamination in Spring Valley to the arsenic discovery in Fort Reno.
Using computer software to analyze patterns in aerial photographs, he detected arsenic in the ground based on the coloring of trees and grass, which show stress and stunted growth when the chemical is present at high levels. When soil analysis validated what the images were telling him, Slonecker alerted the Park Service, which shut Fort Reno within 12 hours.
The geographer said the Civil War embalming theory was "as good as any that I've got right now."
City officials have urged residents not to panic, saying the arsenic might be several feet deep in the soil and that someone would need to have repeated direct contact with the chemical to suffer serious health effects.
Still, the Park Service decided to err on the side of caution in shutting down Fort Reno.
On Friday, commuters and students who are used to cutting through the park on their way to work and school were forced to take a longer route to the local subway stop.
Larissa Jackson, 24, who works for an after-school program, said she has seen increased police patrols as children hop the fence to try and play in Fort Reno. "The kids are curious," she said.