Uticaj fizičko-hemijskih svojstava mikroplastike i odabranih perzistentnih organskih polutanata na interakcije u vodenom matriksu

Abstract

Mikroplastika je sveprisutna u vodenom ekosistemu pri čemu se često ističe značaj ispitivanja njihovog uticaja na ponašanje drugih jedinjenja u vodi. Pod pojmom mikroplastika podrazumevaju se plastične čestice manje od 5 mm. Imajući u vidu potrebu za unapređenjem znanja o štetnom uticaju mikroplastike u životnoj sredini u ovom radu sproveden je set eksperimenata u kom je ispitivan mehanizam interakcija koje se uspostavljaju prilikom adsorpcije hlorovanih fenola, derivata benzena i policikličnih aromatičnih ugljovodonika na mikroplastici u vodenom matriksu. Kako bi se što detaljnije razumeo uticaj mikroplastike i osobina vodenog matriksa na ponašanje organskih polutanata, laboratorijska ispitivanja su sprovedena u sintetičkom i realnom vodenommatriksu. Takođe je sprovedena optimizacija izolovanja i karakterizacije mikroplastike iz kozmetičkih sredstava u cilju procene uticaja osobina primarne mikroplastike na uspostavljanje interakcija sa organskim polutantima. Na osnovu dobijenih rezultata istraživanja može se zaključiti da se optimalna metoda izolovanja mikroplastike iz kozmetičkih sredstava zasniva na dodatnom tretiranju osušenog materijala 30% vodonik-peroksidom, nakon ekstrakcije sredstva u destilovanoj vodi, u cilju dobijanja čistijih uzoraka mikroplastike. Promena brzine mešanja ima znčajan uticaj na promenu stepena adsorpcije ispitivanih grupa organskih jedinjenja. Uticaj se ogleda u povećanju stepena adsorpcije sa porastom brzine mešanja, a maksimalni procenat adsorpcije postignut je pri brzini mešanja od 150 o/min. Dodatno, disperzija praškastih materijala u vodi nema značajan uticaj na promenu stepena adsorpcije hlorovanih fenola, derivata benzena i policikličnih aromatičnih ugljovodonika na mikroplastici.Ravnotežno stanje između koncentracije hlorovanih fenola, derivata benzena i policikličnih aromatičnih ugljovodonika u vodi i odabranih predstavnika mikroplastike (PEp, PE_PCPs_1, PE_PCPs_2, PEg, PET, PP i PLA) uspostavlja se nakon 24 i 48 h kontakta u zavisnosti od vrste jedinjenja. Na promenu adsorpcionog afiniteta hlorovanih fenola, derivata benzena i policikličnih aromatičnih ugljovodonika prema mikroplastici utiču kako fizičkohemijske osobine jedinjenja tako i karakteristike mikroplastike. Na osnovu kinetičkih eksperimenata, najveći adsorpcioni afinitet ka mikroplastici ispoljili su derivati benzena (qt=103-350 µg/g), dok je najmanji uočen kod hlorovanih fenola (qt=25-225 µg/g). Dobijeni rezultati adsorpcije derivata benzena na ispitivanim česticama mikroplastike takođe su ukazali na veći afinitet ovih jedinjenja ka mikroplastici, u poređenju sa jedinjenjima iz grupe policikličnih aromatičnih ugljovodonika i hlorovanih fenola sličnih logKow vrednosti. Dodatno, uticaj vodenog matriksa na adsorpciju hlorovanih fenola, derivata benzena i policikličnih aromatičnih ugljovodonika na mikroplastici zavisi od same grupe jedinjenja kao i od vrste mikroplastike pri čemu je najmanje izražen u slučaju ispitivanih policikličnih aromatičnih ugljovodonika, a najviše kod hlorovanih fenola.Visoke vrednosti koeficijenta determinacije kinetičkog modela pseudodrugog reda za adsorpciju hlorovanih fenola, derivata benzena i policikličnih aromatičnih ugljovodonika na čestice mikroplastike ukazjuju da je hemisorpcija mogući mehanizam. Pored visokih vrednosti koeficijenata determinacije u slučaju svih odabranih organskih jedninjenja dobijena konstanta brzine drugog reda bila je manja od po četne brzine adsorpcije što ukazuje na znatno brže odvijanje adsorpcije pri kraćim vremenima kontakta (12-24 h) nakon čega je dolazilo do usporavanja procesa adsorpcije.Mehanizam adsorpcije hlorovanih fenola, derivata benzena i policikličnih aromatičnih ugljovodonika ispitivan je primenom Freundlich-ovog, Langmuirovog, Redlich-Peterson-ovog i Dubinine-Radusckevich-evog adsorpcionog modela. Vrednosti Freundlich-ovog eksponenta za adsorpciju hlorovanih fenola, derivata benzena i policikličnih aromatičnih ugljovodonika bile su manje od 1, što ukazuje na to da je slobodna energije adsorpcije na mikroplastci opadala sa povećanjem inicijalne koncetracije ispitivanih polutanata. Vrednosti maksimalnog adsorpcionog kapaciteta dobijene za adsorpcione procese PAH na česticama mikroplastike bile su u opsegu od 29,7-2596,5 µg/g. Visoke vrednosti maksimalnih adsorpcionih kapaciteta dobijene su takođe za adsorpciju derivata benzena na ispitivanim vrstama mikroplastike 39,3-2010,1 µg/g. S druge strane, uočeno je različito adsorpciono ponšanje hlorovanih fenola u zavisnosti od vodenog metriksa u kom su eksperimenti sprovedeni pri čemu su qmax vrednosti iznosile 20,00-205,6 µg/g. Značajan uticaj pH vrednosti vodenog matriksa utvrđen je za adsorpciju hlorovanih fenola na mikroplastici, dok u slučaju derivata benzena i PAH promena pH vrednosti vodenog matriksa nije pokazala značajan uticaj. Rezultati dobijeni za adsorpciju hlorovanih fenola na mikroplastici ukazuju na nižu tendenciju ka formiranju interakcija hlorovanih fenola sa česticama mikroplastike pri pH 4 i pH 10, pri čemu se stepen adsorpcije kretao u opsegu od 8-35% i 15-35%, respektivno, u odnosu na pH 7 (55-65%). Najniži adsorpcioni afinitet uočava se pri adsorpciji ispitivanih grupa jedinjenja na PLA. Može se pretpostaviti da će se organski polutanti, ukoliko ova vrsta mikroplastike dospe u vodene sisteme, slabo vezivati na ovaj materijal pri čemu će značajno manje uticati na njihov trasport kroz životnu sredinu, u odnosu na druge ispitivane vrste mikroplastike. Na osnovu dobijenih rezultata istraživanja može se zaključiti da na adsorpciju ispitivanih grupa organskih jedinjenja i mikroplastike značajan uticaj imaju fizičko-hemijske osobine ispitivanih jedinjenja kao što su kiselinska konstanta, veličina molekula, hidrofobnost, stukturni raspored i dr. Pored toga, karakteristike vodenog matriksa, među kojima je najvažnija pH vrednost, imaju značajan uticaj na adsorpcioni afinitet jedinjenja ka mikroplastici. Dodatno, struktura i poreklo polimera ima veliki uticaj na formiranje interakcija sa ispitivanim grupama organskih polutanata. Dobijeni rezultati takođe ukazuju na nemogućnost određivanje unifomnog mehanizma adsorpcije organskih jedinjenja na česticama mikroplastike u vodi.

Microplastics are ubiquitous in aquatic ecosystems, so it is essential to study their impact on the behaviour of other compounds which are commonly present in water. The term microplastics refers to all plastic particles smaller than 5 mm. In order to address knowledge gaps relating to the potential harmful effects of microplastics in the environment, the experiments conducted during this thesis were designed to investigate the adsorption mechanism of chlorinated phenols, benzene derivatives, and polycyclic aromatic hydrocarbons on microplastics in water. To provide a more detailed understanding of the influence of different water matrices on adsorption properties of microplastics, experiments were conducted in both synthetic and real water matrices. In the course of this work, methods were optimised for the isolation and characterization of microplastifrom personal care products, in order to allow investigation of the influence of the properties of primary microplastics on their interactions with organic pollutants.Base on the obtained results, it can be concluded that the optimal method of isolating microplastics from personal care products is based on treating already dried material with 30% hydrogen peroxide, after extraction of the agent in distilled water, in order to obtain cleaner microplastic samples. The mixing rate was found to have a significant effect on the degree of adsorption of the investigated organic compounds. Increasing the mixing speed led to a higher degree of adsorption, with the maximum adsorption percentage reached at a mixing speed of 150 rpm. In addition, the dispersion of powdered materials in the water had no significant effect on the degree of adsorption of chlorinated phenols, benzene derivatives, and polycyclic aromatic hydrocarbons on microplastics. The adsorption equilibrium between the concentration of chlorinated phenols, benzene derivatives and polycyclic aromatic hydrocarbons in water and selected types of microplastics (PEp, PE_PCPs_1, PE_PCPs_2, PEg, PET, PP, and PLA) was established after 24 and 48 h of contact time, depending on the selected group of organic pollutants. The adsorption affinity of chlorinated phenols, benzene derivatives, and polycyclic aromatic hydrocarbons towards microplastics was influenced by both the physicochemical properties of the compounds and the characteristics of the microplastics. Based on the kinetic experiments, the highest adsorption affinity for microplastics was shown by benzene derivatives (qt=103-350 µg/g), while the lowest was observed during the adsorption of chlorinated phenols (qt=25-225 µg/g). Benzene derivatives showed higher adsorption affinities for the selected microplastic particles than the polycyclic aromatic hydrocarbons and chlorinated phenols which had similar logKow values. The influence of the water matrix on adsorption of chlorinated phenols, benzene derivatives, and polycyclic aromatic hydrocarbons on microplastics depended on the specific functional groups of the investigated compounds as well as on the type of microplastics. Water matrix had little impact on the adsorption of polycyclic aromatic hydrocarbons on microplastics but greatly impacted the adsorption of chlorinated phenols. Fitting the pseudo-second order kinetic model to the adsorption data of chlorinated phenols, benzene derivatives, and polycyclic aromatic hydrocarbons on microplastic particles resulted in high correlation coefficients, indicating that chemisorption is the likely adsorption mechanism. In addition to the high correlation coefficients obtained for all the organic pollutants investigated, the pseudo-second order rate constants obtained were lower than the initiaadsorption rate, indicating significantly faster adsorption at shorter contact times (12-24 h), with adsorption slowing down as equilibrium was reached.The adsorption mechanism of chlorinated phenols, benzene derivatives, and polycyclic aromatic hydrocarbons was investigated using Freundlich,Langmuir, Redlich-Peterson, Dubinine-Radusckevich, and Temkin adsorption models. The Freundlich exponent values for the adsorption of chlorinated phenols, benzene derivatives, and polycyclic aromatic hydrocarbons were less than 1 which indicates that the free energy of adsorption of these compounds on microplastics decreases as the initial concentration increases. The maximum adsorption capacities of PAHs on microplastic particles were in the range of 29.7-2596.5 µg/g. High maximum adsorption capacities were also obtained for the adsorption of benzene derivatives on the tested types of microplastics: 39.3-2010.1 µg/g. The chlorinated phenols behaved differently, and were more effected by the water matrix, with qmax values in the range 20.00-205.6 µg/g. The pH of the water matrix was found to have a significant effect on the adsorption of chlorinated phenols on microplastics, whereas in the case of benzene derivatives and polycyclic aromatic hydrocarbons, the degree of adsorption was largely independent of the water pH. For the adsorption of chlorinated phenols on microplastics, neutral pH conditions resulted in the greatest degrees of adsorption (55-65% at pH 7), while adsorption was inhibited under acidic (8-35% at pH 4) and basic (15-35% at pH 10) conditions. The microplastic type with the lowest observed adsorption affinities was PLA. It can be thus be assumed that in the event that this type of microplastic enters water systems, organic pollutants will only adsorb weakly to this material, such that it will have significantly less impact on the transport of the se compounds through the environment, than the other tested types of microplastics. The results obtained in this research demonstrate that the adsorption of the selected groups of organic pollutants on the microplastics investigated is significantly controlled by the physicochemical properties of the tested compounds, such as the dissociation constant, molecule size, hydrophobicity, structural properties, etc. In addition, the characteristics of the water matrix play an important role in controlling adsorption of organic pollutants on microplastic, especially the water pH. In addition, the structure and aging of the polymers had a major influence on their interactions with the selected organic pollutants. The obtained results also demonstrate the difficulty in determining a uniform mechanism of adsorption between the various organic compounds and microplastic particles in water.