Microbial degradation of 2,4-dichlorophenoxyacetic acid on the Greenland Ice Sheet

The Greenland ice sheet (GrIS) receives organic carbon (OC) of anthropogenic origin, including pesticides, from the atmosphere and/or local sources, and the fate of these compounds in the ice is currently unknown. The ability of supraglacial heterotrophic microbes to mineralize different types of OC is likely a significant factor determining the fate of anthropogenic OC on the ice sheet. Here we determine the potential of the microbial community from the surface of the GrIS to mineralize the widely used herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Surface ice cores were collected and incubated for up to 529 days in microcosms simulating in situ conditions. Mineralization of side chain- and ring-labeled [ ¹⁴C]2,4-D was measured in the samples, and quantitative PCR targeting the tfdA genes in total DNA extracted from the ice after theexperiment was performed. We show that the supraglacial microbial community on the GrIS contains microbes that are capableof degrading 2,4-D andthat they are likely present in very low numbers. They can mineralize 2,4-D at a rate of up to 1 nmol per m ² per day, equivalent to~26 ng Cm ^-2 day ^-1. Thus, the GrIS should not be considered a mere reservoir of all atmospheric contaminants, as itis likely that some deposited compounds will be removed from the system via biodegradation processesbefore their potential release due to the accelerated melting of the ice sheet.