A zero-valent iron and organic matter mixture enhances herbicide and herbicide degradation product removal in subsurface waters

The pesticide atrazine, its degradation products, and 2,6-dichlorobenzamide (BAM) are persistent in groundwater environment. We studied whether their dissipation can be enhanced with a mixture of a complex carbon source and zero-valent iron (ZVI) called EHC®. The application rates were 1.0% and 2.0% (by weight) in subsurface sediments slurries (atrazine 30mg/L), and 2.0% in 1.5m pilot-scale sediment columns with groundwater flowing through (atrazine 0.08, desethylatrazine DEA 0.03, BAM 0.02μg/L). In the slurries under aerobic conditions, atrazine of 0.88±0.14mg/g of EHC® was dissipated chemically, as concentrations did not differ significantly between the slurries and their sterilized controls. No degradation occurred in the slurries under anaerobic conditions. In the pilot-scale columns under water-saturated conditions, atrazine, DEA and BAM were not detected in effluents during 33, 64 and 64days from the beginning of the water flow through EHC® columns, respectively, but thereafter traces of compounds could be detected. No atrazine or degradation products (BAM, DEA, deisopropylatrazine, desethyldeisopropylatrazine) could be extracted from the column sediments at the end of the experiment. As a result, the sum of dissipated pesticides was about 7.6μg/g of EHC® in columns under water-saturated conditions, and 0.88mg/g of EHC® in slurries under aerobic conditions. EHC® can be used to enhance the dissipation of studied pesticides in small quantities, preferentially under aerobic conditions.