Transformation And Mechanism Of Perfluorooctanoic Acid In Soil-plant System

Perfluorooctanoic acid?PFOA?is an anionic surfactant that have been mass-produced since the 1950s.Due to the extensive uses in consumer products and industrial applications,a huge amount of PFOA will inevitably be released into the subsurface environment.Part of the PFOA that enters the soil will continue to move down,affecting the quality of groundwater,and the other part may be absorbed by plants and used.Previous studies have shown that PFOA can cause a series of hazards such as neurotoxicity to animals and humans,and will gradually increase with the food chain.Thus,a good understanding of the fate of PFOA in subsurface system and how PFOA affects plant growth is of considerable interest for evaluating its potential risks to humans and ecosystems.Thus far,only a handful studies have yet addressed this issue.In this study,the key effects of environmental concentrations of PFOA migration in the soil-groundwater system were systematically studied using a combination of radioisotope tracer technology and laboratory column experiments,numerical simulations,and studies on cucumber physiological and biochemical parameters and leaf metabolism analysis.Factors and master control mechanisms,and potential mechanisms that plants use to respond to PFOA-induced stress.The main research results are as follows:1.The transport of PFOA in soil media is affected by organic matter content,mineral content,and ionic strength.The retention of PFOA in the soils under two solution ionic strengths conditions?1.0 m M and 10.0 m M Ca Cl₂?followed an order of red soil>black soil>desert soil?expect red soil in 10 m M Ca Cl₂?.PFOA retention in the black soil?soil organic carbon content:2.57%?was higher than that in the desert soil?soil organic carbon content:0.05%?.In addition,PFOA also showed higher mobility in treated black soils with lower organic carbon contents.These results suggest that the hydrophobic interaction is a key mechanism governing PFOA retention and transport in soils.Besides,more PFOA retention in the red soil?zeta potential:7.15 m V and 14.8 m V?than the desert soil?-15.6 m V and-9.15 m V?was observed,suggesting that electrostatic interaction may be another important mechanism for PFOA retention and transport in soils.Increasing ionic strength slightly increased the retention of PFOA in the desert and black soils,but significantly decreased the retention of PFOA in the red soil.Findings of this study point to the importance of soil physiochemical properties to the fate and transport of PFOA in natural soils.2.Hydroxide coatings and ionic strength of aluminum and iron have effects on the transport of PFOA in saturated porous media.Results showed a clear increase in PFOA retardation in Al/Fe oxyhydroxide coated sand?retardation factor:Al:1.87-5.58,Fe:1.28-4.05?than those in uncoated sand?1.00-1.05?,due to the stronger electrostatic attraction between anionic PFOA and Al/Fe oxyhydroxide coated sand surface.Notably,Al oxyhydroxide have a more profound effect on PFOA retention and retardation than Fe oxyhydroxide.Besides,higher ionic strength significantly inhabited PFOA retention and retardation in positively charged sand,and the considerable retention of PFOA??90%?in deionized water than those in 1.5 m M and 30.0 m M Na Cl?<10%?clearly proves the role of competitive adsorption of Cl^-on PFOA transport in positively charged sand.In contrast,higher ionic strength?0m M-30 m M Na Cl?slightly increased PFOA retardation in negatively charged sand,illustrating the dominance of electrostatic interaction.Findings advance current knowledge to understand PFOA transport in natural media with different surface charge property under environmental PFOA concentrations.3.Results showed that PFOA depressed cucumber biomass and accumulated highest in leaves.Photosynthesis analysis revealed that PFOA at both doses reduced the chlorophyll contents and net photosynthesis rate of cucumber leaves.Gas chromatography-mass spectrometry-based non-targeted metabolomics revealed that PFOA induced metabolic reprogramming in cucumber leaves,including up-regulation of phenols?at 0.2 and 5 mg/kg?and down-regulation of amino acids?at5 mg/kg?,indicating disrupted nitrogen and carbon metabolism.Results revealed how PFOA represses plant growth by down-regulating photosynthetic pigments and disturbing the metabolism of carbohydroxides,phenols and amino acids.These findings provide valuable information for understanding the molecular mechanisms involved in plant responses to PFOA-induced stress.