Investigating the potential of Plantago major in the removal of PFAS from soils and surface waters

Abstract

The occurrence of per- and polyfluoroalkyl substances (PFAS) in environmental media, such as soils and surface waters, has led to a worldwide concern. This is because most PFAS have a tendency to accumulate in organisms, potentially leading to toxicity. Currently, conventional remediation techniques, such as sorption and chemical treatments, are costly, have adverse environmental effects, and are not viable for large-scale projects. Phytoremediation, or the use of plants for environmental cleanup, is a potentially low-cost and environmentally friendly technique that is suitable for large-scale PFAS remediation from soils and surface waters. This study aimed to investigate whether perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) can accumulate in plant tissues (leaves, stems, and roots) under UV light exposure, and whether subsequent degradation of these compounds occurs. Plants of the species Plantago major were grown for a maximum of 28 days in two separate fume hoods each with a different light regime. One fume hood was equipped with a UV-light (UV-A + UV-B) and a white growing light, while the other fume hood only contained a growing light. The plants were cultivated in nutrient solutions containing spiked 13C labelled PFOA and PFOS, at two concentrations of 2.5 µg/L and 25 µg/L. The effect of UV light and PFAS exposure on the health of plants was assessed visually and by determining the net biomass gain, i.e., the difference between the initial and final wet mass as a proxy for plant growth. The δ 13C (‰) value of the plants was determined using EA-IRMS as an indicator for the bio-accumulation of PFOA and PFOS in the tissues of Plantago major. NanoSIMS was used to determine the spatial distribution of accumulated PFAS in the plant tissues and to investigate whether PFAS degradation occurred in the plants. The majority of plants remained healthy throughout the study period. Visually, no significant difference was visible in color, morphology, and growth between exposed (UV and/or PFAS) and non-exposed plants. The net biomass gain did not significantly differ between UV treated and non UV treated plants. Additionally, no significant correlation was observed between the net biomass gain and the PFAS treatment the plants received. This indicates that the plant growth and health is not significantly affected by UV-light and the presence of PFOA and PFOS in the nutrient solution. Also no significant correlation between the δ 13C value and the treatment was found. The biological variability of this values [2] exceeded the potential increase in δ 13C due to PFAS, which made it impossible to differentiate between PFAS incorporation into the tissues and natural biological variability. Analysis of both 13C/12C ratios and 19F/(12C+13C) ratios in plant tissues, obtained via NanoSIMS analysis, revealed possible accumulation of both PFOA and PFOS in the leaves of several plants. Interestingly, elevated ratios were also detected in a leaf of a plant that did not receive UV or PFAS treatments. However, most samples did not exhibit enhanced 13C/12C ratios and/or 19F/(12C+13C). Therefore, the elevated ratios in some of the samples cannot solely be attributed to PFAS accumulation in plant tissues. Given the uncertainty surrounding the accumulation of PFAS in the plants, further interpretations concerning the potential degradation of PFAS within the plant tissues (leaves) were abstained from