Arsenic And Old Vats: UF Researchers Uncover Hidden Contamination Sites

November 9, 2004

GAINESVILLE, Fla. — It may be the nation’s biggest toxic mystery.

In the first half of the 20th century, farmers across the Sun Belt states dug thousands of pits in which they regularly dipped their cattle in arsenic-laden pesticide, to kill ticks that carry a dreaded cattle disease. Still contaminated with the cancer-causing metal, those pits now pose a threat to drinking water supplies, environmental officials say – but most of the pits are abandoned, their locations forgotten.

Now University of Florida researchers have developed a technique using aerial photography and computer technology that might make it possible to locate even the best-hidden vat sites.

“We need to know where all these sites are, if only to warn people who have wells or gardens on property with high levels of arsenic,” said Bill Todd, a graduate student at UF’s Institute of Food and Agricultural Sciences who conducted the research. “If we don’t find a faster, more reliable method for locating the vats, we’ll probably never find them all.”

UF researchers used aerial photographs and computerized maps to pinpoint the locations of 10 previously unlocated in-ground vats where Alachua County cattle ranchers once dipped cows in pesticide to kill cattle ticks. The research results were published earlier this year in the journal Applied Engineering in Agriculture.

The ticks were carriers of piroplasmosis, a disease that once plagued the cattle industry in the Southeastern U.S., killing large numbers of cattle and causing some northern states to halt shipment of cows from infected states. In the early 1900s, dipping vats were constructed by farmers and state agricultural agencies across the region. But nowhere was the practice more widespread than in Florida, where state law required farmers to dip their cattle twice a week.

“Not a lot of people remember it now, but at the time this was a huge undertaking for the state, and a lot of farmers resented it,” said Wayne Mishoe, a professor in the agricultural and biological engineering department and co-author of the study.

Well known as a poison, arsenic can be harmful even in trace amounts, causing cancer and other illnesses.

Abandoned vat sites are a matter of serious concern to environmental officials, who say that arsenic remaining in the ground under each vat could seep into the groundwater, contaminating wells. Cleaning up the contamination has been difficult, largely because after the dipping requirements ended, most farmers abandoned the vats without recording their locations.

“Usually we find out about an unknown vat site when arsenic begins to show up in someone’s well water, or when someone buys a property and the arsenic shows up in an environmental audit,” said Zoe Kulakowski, a geologist for the Florida Department of Environmental Protection who works on cattle-vat remediation projects.

Kulakowski said the state has assessment data on at least 100 known vat sites, the vast majority of which have been linked to some form of groundwater contamination. But many more sites remain unidentified. In Florida alone, state officials have found more than 3,000 vat sites mentioned by name in the minutes of state meetings on the cattle tick problem – but no directions to any of them.

“People just didn’t keep records of that kind of thing at the time,” Todd said. “This was a rural environment where people knew the local landmarks. If you said a vat was at Cooter Pond or the Adkins farm, there was no need for directions.”

The clues to vat sites were sketchy, but Todd saw a way to turn them into something more conclusive. He sorted through Alachua County tax records, matching the names of known vat sites to the names of businesses and landowners in the early 20th century. He created a computerized map of the county showing all those properties, plus the suspected sites of vats named after roads or other landmarks. Then he narrowed the field by searching for geographical features common to most dipping vats.

“Cattle were often dipped before they were shipped, so the vats were often not far from a railroad depot,” Todd said. “Some vats got a lot of traffic — hundreds of cows every week — so there’s usually an access road.”

Then Todd pored over old aerial photos of the suspected vat sites, looking for the T-shaped structures that housed the vats and corrals that surrounded them.

The process yielded the exact location of 10 previously unidentified vats throughout Alachua County. He has seven other “probable hits” – photos showing signs that seem to point to vats obscured by tree cover. And his mapping method uncovered the general locations of more than 80 other vats mentioned in historical records.

The researchers said ground-penetrating radar, or GPR, a technology often used by archaeologists to uncover underground structures, could be used to find vats on those 80 sites.

“A GPR system is usually towed behind a truck or a tractor, and you drive it across a piece of property in strips, like someone moving the lawn,” Todd said. “If you can narrow your search area down to a single property, and you know what sort of structures to look for, it becomes feasible to use GPR to find a buried vat.”

The technique could be applied in other areas with similar results, the researchers say. That information could prove valuable to environmental officials who hope to spot the worst sites before people are exposed to contamination.

“If someone could find an effective way to locate all the sites, that would help us select the sites most in need of remediation,” said Kulakowski.