Deciding at just what level arsenic is harmful, and when regulators should take action to lower levels, is tremendously difficult.
The team set out to get a comprehensive picture of arsenic levels across the state, studying samples from areas with minimal human activity. For example, arsenic has been used for decades as a wood preservative and in pesticides and herbicides, so soil samples near fence posts and orchards were avoided.
The team analyzed samples from soil and stream sediments from across the nearly 45,000 square miles of land that make up Ohio. They included soil samples that the U.S. Geological Survey collected as part of the National Geochemical Survey and from a previous study related to uranium exploration. The analysis included two soil samples each from 348 sites throughout Ohio (one sample taken from 6-12 inches below the surface and another from 12-24 inches deep) and 144 sediment samples from streams.
Overall, arsenic in samples ranged from 2 to 45.6 parts per million by weight, with an average of 9.69 parts per million, compared to the U.S. EPA's screening standard of 0.39 parts per million. Very few samples had less arsenic than 3 parts per million; samples more than 10 parts per million were very common; and levels of more than 20 parts per million were common for central Ohio.
"When every soil sample has more arsenic than the recommended screening level, it may be time to re-evaluate those regulatory levels and to think about how best to interpret the data," said co-author Nicholas Basta, professor of Soil and Environmental Chemistry at Ohio State.
Yesterday's rocks, today's soil
The study found that bedrock created
|Contact: Tom Rickey|
DOE/Pacific Northwest National Laboratory