Degradation of perfluoroalkyl acids by enzyme catalyzed oxidative humification reactions
MetadataShow full item record
The historical mass production, long term utilization and direct disposal of perfluoroalkyl acids (PFAAs) resulted in the wide distribution of such chemicals in the environment. Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) are two predominant environmental PFAAs which could induce adverse effects in humans and the environment. However, this group of chemicals is extremely persistent and resistant to traditional degradation technologies. Thus developing a cost-effective and eco-friendly remediation technique is needed to resolve the concerns of PFAAs contamination. Our data showed that an enhanced natural process called enzyme catalyzed oxidative humification reactions (ECOHRs) is effective in transforming both PFOA and PFOS in the aqueous phase at environmentally relevant conditions. The decomposition of PFOA and PFOS with the addition of 1-hydroxybenzotriazole as the model mediator and laccase as the model enzyme both followed a pseudo-first order reaction. Understanding the mechanisms of PFOA and PFOS transformation are critical in identifying optimal degradation conditions. High-resolution mass spectrometry results revealed that the primary degradation products were partially fluorinated shorter-chain alcohols and aldehydes. The proposed reaction mechanism involved the dissociation of COO− and SO3− from the PFCAs and PFASs respectively to form corresponding perfluoralkyl radicals, such radicals could further went through rearrangement or cross-coupling with the non-fluorinated compounds in the reaction solution. Additionally, we investigated the PFOA degradation efficiency by ECOHRs in soil. In the system without addition of any mediator, the degradation of PFOA up to 24% over 12 weeks of reaction was observed indicating that soil organic matter could serve as mediator. Such process could further enhanced by supplying extra natural organic matters into the system to sustain the ECOHRs. We identified a natural organic matter, i.e. soybean meal as a great mediator which could convert 36% of PFOA after 20 weeks of incubation. The data collected in our experiments suggested that both PFOA and PFOS could be effectively degraded into environmentally benign products during ECOHRs under mild reaction conditions. Therefore, ECOHRs has a promising future in the remediation of PFOA and PFOS.