13 March 2024

Alaska researchers use biochar to decontaminate soil from copper


Researchers want to exploit biochar’s ability to absorb heavy metals. U.S. Environmental Protection Agency is currently at work on the soils of a former mine

by Matteo Cavallito


Biochar can be a crucial resource for decontaminating polluted mining soils, according to researchers from the U.S. Environmental Protection Agency (EPA), who have been working on the soils of the Salt Chuck Mine,y a former gold, silver, copper and palladium mine located on Prince of Wales Island in southeast Alaska.

Here, a statement from the agency explains, copper is the main contaminant in marine sediments. Its presence has affected adjacent mudflats by also impacting the invertebrate community.

The role of biochar

The researchers therefore aim to exploit the special characteristics of biochar, which is produced through the thermochemical decomposition (pyrolysis) of organic matter consisting mainly of cellulose, hemicellulose and lignin. Its properties, experts explain, are determined by the nature of the raw material (crop residues, waste wood, agribusiness waste, recovered biomass) and the duration and temperatures of the production process.

While this substance cannot be regarded as a silver bullet, it can be used to improve doil chemical, physical and biological characteristics, especially when integrated with the traditional composting process. Incorporating biochar into the soil makes it possible to increase organic carbon content and fertility. And in some cases, to reduce the availability of heavy metals.

The trial

This last issue is obviously the focus of U.S. scientists. Lab studies, the EPA points out, show, for example, that biochar is effective precisely in absorbing copper contamination in this type of environment. Before working in Alaska, researchers tested the substance elsewhere and found that it was able to compact into sediments, remaining in place even after they were submerged by the sea.

Later, the EPA notes, “Bioassay tests in the lab using a small marine worm and different biochar concentrations mixed with contaminated sediment from the Salt Chuck Mine site helped determine how much biochar would be required to improve habitat conditions for marine invertebrates.”

The results “showed that the 2.5% biochar treatment increased worm survival by over 90% and that the 5% treatment increased survival by even more, compared to near 0% survival in the untreated contaminated sediment collected from the flat closest to the mine.”

The tests in Alaska

EPA researchers are now working on the contaminated area in Alaska using one and a half tons of material. Operations, at the moment, are taking place on twelve two-meter by two-meter test plots in the intertidal mudflats. That is the area between low and high tide levels.

Here, the scientists mixed biochar with soil to a 2.5 percent mixture by weight in the top six inches of the polluted sections. By drawing water from the interstitial spaces between the contaminated sediments after a tidal cycle, it then becomes possible to measure the effect of decontamination. By comparing copper concentrations in the porous water of biochar-modified plots with those of unmodified plots, the EPA concludes, researchers will be able to assess the substance’s effectiveness in reducing the presence of the element.