Perfluoroalkyl substances, commonly known as PFAS, have been widely used since the 1950s as industrial surfactants in various processes, such as the production of fire-fighting foam, non-stick coatings, stain-resistant or waterproof fabrics. The industrial success of PFAS is due to their unique chemical characteristics of stability and amphiphilicity, given by a carbon chain completely replaced by fluorine atoms and a polar functional group in the terminal position. The same chemical characteristics that ensured their success proved to be extremely dangerous for the environment, as these molecules are resistant to degradation and tend to accumulate in various life forms and their habitat. Furthermore, epidemiological and toxicological studies have shown them to be harmful to human and animal health. Given the scarcity of information on these chemical compounds, it is necessary to investigate their distribution and their impact on ecosystems. There are more than 4,000 compounds on the market and more are under development. Older generation compounds (with a long carbon chain) are being replaced by newer generation compounds with a shorter carbon chain and lower environmental persistence. However, little is known about these new molecules from a toxicological point of view. Among the most commonly used new compounds is GenX (ammonium 2,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate). As a complete risk assessment data sheet for this substance is not yet available, the aim of this experimental thesis was to assess its potential toxic effects on the freshwater compartment, considering two distinct trophic levels. In particular, acute toxicity tests were performed on the green microalga Raphidocelis subcapitata (US-EPA 96h), and on the tiny crustacean Daphnia magna (OECD 202). In addition, at the end of the 48-hour exposure period, the daphnids were transferred to pure medium and any delayed toxic effects were assessed for the following ten days. The potential toxicity of GenX was then compared to that of PFOA (perfluorooctanoic acid) by repeating the same ecotoxicological assays with this well-known old molecule. The tests performed showed acute toxic effects in Daphnia magna after exposure to each of the two compounds; in addition, follow-up in pure medium revealed delayed toxicity in the crustacean. The alga Raphidocelis subcapitata was also sensitive to the toxicity of both PFOA and GenX. However, both compounds required very high concentrations (hundreds of mg/L), which are unlikely under 'normal' pollution conditions, to manifest an impact on the aquatic organisms. Lastly, it seems possible to conclude, from the comparison of EC50 values, that Genx is less toxic than its predecessor compound.
Le sostanze perfluoroalchiliche, comunemente note con l’acronimo PFAS, sono state largamente utilizzate dall’industria a partire dagli anni ’50 come surfattanti in diversi processi industriali: per la produzione di schiume antincendio, materiali antiaderenti, antimacchia e impermeabilizzanti. Il successo a livello industriale dei PFAS è dovuto alle peculiari caratteristiche chimiche di stabilità e anfifilicità, conferite dalla catena carboniosa completamente sostituita con atomi di fluoro e dal gruppo funzionale polare posto in posizione terminale della stessa. Le stesse caratteristiche chimiche che ne hanno assicurato il successo industriale si sono però rivelate pericolose per l’ambiente. Si tratta, infatti, di molecole refrattarie alla degradazione che tendono ad accumularsi nelle matrici ambientali e negli organismi viventi. Inoltre, studi epidemiologici e saggi tossicologici hanno evidenziato diversi effetti avversi sulla salute umana ed animale. Data la scarsa conoscenza di questi composti chimici, risulta necessario comprendere la loro distribuzione nell’ambiente e il loro potenziale impatto sui diversi ecosistemi. Sul mercato sono presenti più di 4000 composti ed altri sono ancora in fase di sviluppo. Le molecole di vecchia generazione (a lunga catena di carbonio) tendono ad essere rimpiazzate con molecole di nuova generazione (a catena più corta) che sono dotate di minore persistenza ambientale. Tuttavia, poco si sa riguardo queste nuove molecole dal punto di vista tossicologico. Tra i composti di nuova generazione più utilizzati troviamo il GenX (2,3,3,3-tetrafluoro-2-(eptafluoropropossi)-propanoato di ammonio). Non essendo ancora disponibile una scheda di rischio completa per quanto riguarda questa sostanza, la presente tesi sperimentale ha avuto lo scopo di valutarne i potenziali effetti tossici sul comparto dulciacquicolo, considerando due distinti livelli trofici. In particolare, sono stati effettuati test di tossicità acuta sulla microalga verde Raphidocelis Subcapitata (US-EPA 96h), e sul minuscolo crostaceo Daphnia magna (OECD 202). Inoltre, al termine delle 48 ore di esposizione le dafnie sono state trasferite in medium puro e per i successivi dieci giorni sono stati valutati eventuali effetti tossici ritardati. La potenziale tossicità di GenX è stata quindi comparata a quella di PFOA (acido perfluoroottanoico), andando a ripetere i medesimi saggi ecotossicologici con questa ben nota molecola di vecchia generazione. I test svolti hanno evidenziato effetti tossici acuti in Daphnia magna dopo esposizione a ciascuno dei due composti; inoltre, il follow-up in medium puro ha fatto rilevare nel crostaceo fenomeni di tossicità ritardata. Anche l’alga Raphidocelis Subcapitata è risultata sensibile alla tossicità sia di PFOA che di GenX. Tuttavia, entrambi i composti richiedono concentrazioni molto elevate (centinaia di mg/L), inverosimili in condizioni di ‘normale’ inquinamento, per manifestare un impatto su questi organismi acquatici. Infine, dalla comparazione dei valori di EC50 sembra di poter concludere che il Genx sia meno tossico del composto predecessore.
Valutazione comparativa preliminare della tossicità acquatica dell’Acido Perfluoroottanoico e di un suo sostituto di nuova generazione, il GenX.
ZANONI, VALENTINA
2022/2023
Abstract
Perfluoroalkyl substances, commonly known as PFAS, have been widely used since the 1950s as industrial surfactants in various processes, such as the production of fire-fighting foam, non-stick coatings, stain-resistant or waterproof fabrics. The industrial success of PFAS is due to their unique chemical characteristics of stability and amphiphilicity, given by a carbon chain completely replaced by fluorine atoms and a polar functional group in the terminal position. The same chemical characteristics that ensured their success proved to be extremely dangerous for the environment, as these molecules are resistant to degradation and tend to accumulate in various life forms and their habitat. Furthermore, epidemiological and toxicological studies have shown them to be harmful to human and animal health. Given the scarcity of information on these chemical compounds, it is necessary to investigate their distribution and their impact on ecosystems. There are more than 4,000 compounds on the market and more are under development. Older generation compounds (with a long carbon chain) are being replaced by newer generation compounds with a shorter carbon chain and lower environmental persistence. However, little is known about these new molecules from a toxicological point of view. Among the most commonly used new compounds is GenX (ammonium 2,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate). As a complete risk assessment data sheet for this substance is not yet available, the aim of this experimental thesis was to assess its potential toxic effects on the freshwater compartment, considering two distinct trophic levels. In particular, acute toxicity tests were performed on the green microalga Raphidocelis subcapitata (US-EPA 96h), and on the tiny crustacean Daphnia magna (OECD 202). In addition, at the end of the 48-hour exposure period, the daphnids were transferred to pure medium and any delayed toxic effects were assessed for the following ten days. The potential toxicity of GenX was then compared to that of PFOA (perfluorooctanoic acid) by repeating the same ecotoxicological assays with this well-known old molecule. The tests performed showed acute toxic effects in Daphnia magna after exposure to each of the two compounds; in addition, follow-up in pure medium revealed delayed toxicity in the crustacean. The alga Raphidocelis subcapitata was also sensitive to the toxicity of both PFOA and GenX. However, both compounds required very high concentrations (hundreds of mg/L), which are unlikely under 'normal' pollution conditions, to manifest an impact on the aquatic organisms. Lastly, it seems possible to conclude, from the comparison of EC50 values, that Genx is less toxic than its predecessor compound.File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.12608/59159