Comparison of the Relative Efficacies of Granulated Activated Carbon and Biochar to Reduce Chlorpyrifos and Imidacloprid Loading and Toxicity Using Laboratory Bench Scale Experiments.

Pesticide loads and associated toxicity can be significantly reduced using integrated vegetated treatment systems, which remove moderately soluble and hydrophobic pesticides, but need a sorbent material to remove more soluble pesticides. Neonicotinoids such as imidacloprid are widely used insecticides, acutely toxic, and have been linked to a range of ecological effects. Laboratory experiments were conducted to test the sorptive capacity of granulated activated carbon and biochar for removing imidacloprid and the organophosphate insecticide chlorpyrifos in a scaled-down treatment system. Simulated irrigation water spiked with individual pesticides was treated with a bench-top system designed to mimic a 600 L carbon installation receiving 108,000 L of flow per day for sixteen days. Biochar reduced insecticides to less than detectable and non-toxic levels. Granulated activated carbon similarly reduced chlorpyrifos, but allowed increasing concentrations of imidacloprid to break through. Both media treated environmentally relevant concentrations, and would be effective if used under conditions with reduced particle loads.

Carbon Treatment as a Method to Remove Imidacloprid from Agriculture Runoff.

Use of neonicotinoid pesticides is increasing worldwide and there is growing evidence of surface water contamination from this class of insecticide. Due to their high solubility, traditional mitigation practices may be less effective at reducing neonicotinoid concentrations in agricultural runoff. In the current study, laboratory experiments were conducted to determine if granulated activated carbon (GAC) reduces concentrations of the neonicotinoid imidacloprid in water under simulated flow conditions. Imidacloprid was pumped through columns packed with GAC using flow rates scaled to mimic previously reported field studies. Treatments were tested at two different flow rates and samples were collected after 200 and 2500 mL of treated water were pumped through the column. Chemical analysis of the post-column effluent showed the GAC removed all detectable imidacloprid from solution at both flow rates and at both sample times. These results demonstrate the efficacy of GAC for treating neonicotinoids and the results are discussed in the context of incorporating this treatment into integrated vegetated treatment systems for mitigating pesticides in agricultural runoff. Future studies are being designed to evaluate this technology in full scale field trials.