Superfund Research Program

September 2024

Hot Publication

Adding two widely available fertilizers can form minerals that may remove arsenic from underground water reservoirs, according to a study by researchers from Columbia University SRP Center. The method uses chemical reactions to filter out arsenic, a naturally occurring element that can leach into aquifers and contaminate groundwater.

Previous studies found that combining a solution of iron and nitrate – compounds commonly used as fertilizers – may react to form magnetite, a mineral that can adsorb arsenic. The researchers wanted to see if adding iron and nitrate could remove arsenic in the field. They used field push-pull tests – a method of groundwater research which involves injecting and extracting a test solution from an underground water source – to test the method on an arsenic-contaminated aquifer.

First, the team took samples of groundwater from the contaminated aquifer to measure pre-treatment levels of arsenic. Using an underground pump, the team then injected four cycles of iron and nitrate solution into the aquifer. After allowing the solution to sit for 25 days, the researchers extracted and analyzed samples of the groundwater for arsenic levels. They also analyzed aquifer sediment samples for their magnetite and arsenic content before and after the tests. The push-pull test was repeated after five months.

The scientists found that arsenic levels in the aquifer decreased significantly after injecting the iron and nitrate mixture into the water, before slowly returning to base levels as the solution reacted completely. Sediment samples taken after the tests contained more magnetite than sediment before the test, suggesting that the solution encouraged magnetite formation. Additionally, injecting the solution in the second test caused arsenic levels to decrease again, indicating that this method remains effective after repeated treatment.

According to the researchers, these findings suggest that iron and nitrate injections can be an effective way to remove arsenic from contaminated aquifers. This method could be scaled up to treat large volumes of groundwater at a relatively low cost, they added

To learn more, please refer to the following sources:

  • Sun J, Sun Y, Prommer H, Bostick BC, Liu Q, Ma M, Li Z, Liu S, Siade AJ, Li C, Han S, Zheng Y. 2024. Sustaining irrigation supplies through immobilization of groundwater arsenic in situ. Environ Sci Technol 58(28):12653-12663. doi:10.1021/acs.est.4c03225 PMID:38916402