Iron Furnaces Left Behind Manganese-Contaminated Soils

According to a new scientific investigation published this week, it would appear that operating iron furnaces for decades at single locations left its marks on the soils of central Pennsylvania, which now exhibit higher-than-normal manganese concentrations. The findings may apply elsewhere too.

In a paper appearing in the latest issue of the esteemed journal Environmental Science & Technology (ES&T), experts argue that the chemical is toxic to sugar maple, as well as most other forms of vegetation.

The US National Science Foundation (NSF) provided the funds for this investigation, which was carried out by a team of experts at the Penn State University, led by geosciences graduate student Elizabeth Herndon.

She and her team looked at how much manganese was contained in soil core samples collected from one of the six NSF-supported Critical Zone Observatory (CZO) in the US, called Shale Hills.

“Critical Zone Observatories are natural laboratories for investigating the processes that occur at and near the Earth's surface, and that are affected by freshwater,” explains expert Enriqueta Barrera.

“These interconnected processes leave their mark on everything from the production of soil to the evolution of ecosystems,” she adds.

“This study, for example, reveals that a significant amount of manganese from human sources affected soils in Pennsylvania,” the official goes on to say.

Barrera holds an appointment as the program director of the NSF Division of Earth Sciences (DES), the organization in charge of providing sponsorship for CZO investigations.

“Our focus was to study the soil chemistry in Shales Hills. We saw excess manganese in the soil and decided that we needed to quantify the manganese and determine where it came from,” Herndon says.

The graduate student is also the lead author of the new ES&T paper. She explains that manganese also forms in soils naturally, following the disintegration of bedrocks when the soils first develop.

In the Shale Hills CZO, the average manganese concentration in the shale is about 800 parts per million. But sample analysis revealed concentrations of up to 14,000 parts per million in some areas.

“We needed to quantify how much extra manganese there was in the samples. While soil formation puts manganese into the soil, chemical weathering and physical erosion remove manganese from the soil, so we used a mass balance model to account for these inputs and outputs,” says the study author.

Her team determined that 53 percent of manganese in the samples came from anthropogenic sources, which means that they were produced by human activities.

“Because the amount of manganese in the soil was highest near the surface, the added manganese was very likely from industrial pollution,” Herndon concludes.