Perfluoroalkyl substances (PFAS) are a group of synthetic organic compounds that have been developed since the mid-20th century. These are aliphatic molecules in which all the hydrogen atoms bonded to carbon are replaced by fluorine atoms, except for those in any functional groups that may be present. The strong carbon-fluorine bond imparts PFAS with unique technological properties, which underpin their widespread industrial use. However, this characteristic also makes these compounds highly resistant to degradation processes, leading to their persistence and accumulation in the environment. PFAS are found in a wide range of everyday products, including detergents, cosmetics, non-stick cookware, waterproofing agents for fabrics, and food packaging materials. Their extensive use has led to widespread environmental contamination, posing a significant threat to ecosystems worldwide. Once released into the environment, PFAS can be absorbed by plants intended for human and animal consumption, thereby entering the food chain. Numerous studies highlight the negative effects of their accumulation in blood and various organs, with serious human health implications. In this context, there is an urgent need to develop effective strategies to remediate contaminated agricultural soils, ensuring the protection of public health. Phytoremediation is an innovative and eco-friendly technique for soil recovery that leverages the ability of plants to absorb and accumulate pollutants. This approach could potentially be applied to perfluoroalkyl substances (PFAS), offering a cost-effective, natural, and low-impact environmental solution. However, further research is needed to assess its effectiveness. In this context, the present thesis aimed at assessing PFAS phytoextraction potential by three plant species in a greenhouse experiment using soil contaminated with perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) at a total concentration of 1 ppm (1 mg kg⁻¹ of soil). The main objectives were: i) to evaluate the potential of three high-biomass plant species: maize (Zea mays L.), sunflower (Helianthus annuus L.), and hemp (Cannabis sativa L.) to absorb PFOA and PFOS; ii) to analyse the effect of applying an organic amendment containing humic acids to enhance plant growth and their capacity to remove contaminants from the soil. The results revealed that none of the three species exhibited phytotoxicity symptoms in presence of the contaminant mixture, confirming their suitability for phytoremediation applications. Among the species analysed, Cannabis sativa demonstrated the best phytoextraction performance, followed by Helianthus annuus and a lower capacity in Zea mays. Notably, hemp excelled in its ability to accumulate PFOA in its foliage, with a bioconcentration factor (BCF) exceeding 10, allowing to classify it as a hyperaccumulator plant. The combined application of humic acids and PFAS did not result in a significant increase in phytoextraction efficiency, likely due to adsorption interactions between the humic acids and the contaminants. Further studies under field conditions will be necessary to validate the results obtained. Future research should also address various aspects, including PFAS-soil interactions, with particular focus on the role of organic matter and soil texture in contaminant retention and bioavailability. Additionally, it will be essential to deepen the understanding of PFAS uptake mechanisms in plants and their ability to translocate these compounds to aerial parts.
Le sostanze perfluoro alchiliche (PFAS) rappresentano una classe di composti organici sintetizzati a partire dalla metà del XX secolo. Si tratta di molecole alifatiche in cui tutti gli atomi di idrogeno legati al carbonio sono sostituiti da atomi di fluoro, ad eccezione degli idrogeni presenti nei gruppi funzionali. Il forte legame carbonio-fluoro conferisce ai PFAS proprietà tecnologiche uniche, alla base del loro ampio utilizzo industriale. Tuttavia, questa caratteristica rende tali composti estremamente resistenti ai processi degradativi, determinando una elevata persistenza e accumulo nell'ambiente. I PFAS sono diffusi in numerosi prodotti di uso quotidiano, tra cui detersivi, cosmetici, pentole antiaderenti, agenti impermeabilizzanti per tessuti e materiali per il confezionamento alimentare. Questa vasta applicazione ha causato una contaminazione ambientale globale, rappresentando una minaccia significativa per gli ecosistemi. Una volta rilasciati nell'ambiente, i PFAS possono essere assorbiti dalle piante destinate all'alimentazione umana e animale, entrando nella catena alimentare. Numerosi studi evidenziano effetti negativi del loro accumulo nel sangue e nei vari organi, con gravi implicazioni per la salute. In questo scenario, appare evidente l’urgenza di sviluppare strategie efficaci per bonificare i terreni agricoli inquinati, garantendo la tutela della salute pubblica. Il fitorimedio rappresenta una tecnica innovativa ed ecocompatibile per il recupero dei suoli, che sfrutta la capacità delle piante di assorbire e accumulare inquinanti. Questa tecnica potrebbe essere applicata anche alle sostanze perfluoro alchiliche, rappresentando così una soluzione economica, naturale e di basso impatto ambientale; tuttavia, sono necessari studi specifici per valutarne l’efficacia e l’applicabilità. In questo contesto, la presente tesi ha studiato la capacità fitoestrattiva di tre specie erbacee coltivate in condizioni controllate (serra) e su suolo contaminato da acido perfluoroottanoico (PFOA) e acido perfluoroottansolfonico (PFOS) ad una concentrazione complessiva elevata, 1 ppm (1 mg kg-1 suolo). Gli obiettivi principali sono stati: i) valutare il potenziale di assorbimento di PFOA e PFOS da parte di tre specie vegetali con elevata produzione di biomassa: mais (Zea mays L.), girasole (Helianthus annuus L.) e Cannabis sativa (L); ii) analizzare l'effetto dell'applicazione di un ammendante organico a base di acidi umici, per potenziare la crescita delle piante e la loro capacità di rimozione dei contaminanti dal suolo. I risultati hanno evidenziato che nessuna delle tre specie ha manifestato sintomi di fitotossicità in presenza della miscela contaminante, confermando la loro idoneità per applicazioni di fitorimedio. Tra le specie a confronto, Cannabis sativa ha mostrato le migliori performance fitoestrattive, seguita da Helianthus annuus e in minor misura Zea mays. In particolare, la canapa si è distinta per la capacità di accumulare PFOA a livello fogliare con un fattore di bioconcentrazione (BCF) superiore a 10, potendo considerarla pianta iperaccumulatrice. La somministrazione combinata di acidi umici e PFAS non ha determinato un aumento significativo dell’efficacia fitoestrattiva, probabilmente a causa di interazioni di adsorbimento tra acidi umici e contaminanti. Saranno necessari ulteriori studi in condizioni di pieno campo per confermare i risultati ottenuti. Le ricerche future dovranno, inoltre, chiarire diversi aspetti, tra cui l’interazione PFAS-suolo, con particolare riferimento al ruolo della sostanza organica e della tessitura nella ritenzione e biodisponibilità dei contaminanti. Parallelamente, sarà fondamentale approfondire i meccanismi di assorbimento dei PFAS da parte delle piante e la loro capacità di traslocarli alla parte epigea.
Risposta morfo-fisiologica e capacità fitoestrattiva di sostanze perfluoro alchiliche (PFAS) in specie erbacee coltivate
CHISINI GRANZOTTO, GILBERTO
2023/2024
Abstract
Perfluoroalkyl substances (PFAS) are a group of synthetic organic compounds that have been developed since the mid-20th century. These are aliphatic molecules in which all the hydrogen atoms bonded to carbon are replaced by fluorine atoms, except for those in any functional groups that may be present. The strong carbon-fluorine bond imparts PFAS with unique technological properties, which underpin their widespread industrial use. However, this characteristic also makes these compounds highly resistant to degradation processes, leading to their persistence and accumulation in the environment. PFAS are found in a wide range of everyday products, including detergents, cosmetics, non-stick cookware, waterproofing agents for fabrics, and food packaging materials. Their extensive use has led to widespread environmental contamination, posing a significant threat to ecosystems worldwide. Once released into the environment, PFAS can be absorbed by plants intended for human and animal consumption, thereby entering the food chain. Numerous studies highlight the negative effects of their accumulation in blood and various organs, with serious human health implications. In this context, there is an urgent need to develop effective strategies to remediate contaminated agricultural soils, ensuring the protection of public health. Phytoremediation is an innovative and eco-friendly technique for soil recovery that leverages the ability of plants to absorb and accumulate pollutants. This approach could potentially be applied to perfluoroalkyl substances (PFAS), offering a cost-effective, natural, and low-impact environmental solution. However, further research is needed to assess its effectiveness. In this context, the present thesis aimed at assessing PFAS phytoextraction potential by three plant species in a greenhouse experiment using soil contaminated with perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) at a total concentration of 1 ppm (1 mg kg⁻¹ of soil). The main objectives were: i) to evaluate the potential of three high-biomass plant species: maize (Zea mays L.), sunflower (Helianthus annuus L.), and hemp (Cannabis sativa L.) to absorb PFOA and PFOS; ii) to analyse the effect of applying an organic amendment containing humic acids to enhance plant growth and their capacity to remove contaminants from the soil. The results revealed that none of the three species exhibited phytotoxicity symptoms in presence of the contaminant mixture, confirming their suitability for phytoremediation applications. Among the species analysed, Cannabis sativa demonstrated the best phytoextraction performance, followed by Helianthus annuus and a lower capacity in Zea mays. Notably, hemp excelled in its ability to accumulate PFOA in its foliage, with a bioconcentration factor (BCF) exceeding 10, allowing to classify it as a hyperaccumulator plant. The combined application of humic acids and PFAS did not result in a significant increase in phytoextraction efficiency, likely due to adsorption interactions between the humic acids and the contaminants. Further studies under field conditions will be necessary to validate the results obtained. Future research should also address various aspects, including PFAS-soil interactions, with particular focus on the role of organic matter and soil texture in contaminant retention and bioavailability. Additionally, it will be essential to deepen the understanding of PFAS uptake mechanisms in plants and their ability to translocate these compounds to aerial parts.| File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.12608/77870