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Influence of Aging and the Presence of Dissolved Organic Matter on Caffeine Adsorption onto Microplastics in Aquatic Environments
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Researchers studied how aged polyethylene microplastics adsorb caffeine in water containing dissolved organic matter. They found that aged microplastics adsorbed significantly more caffeine than pristine ones, and that higher concentrations of humic acid enhanced adsorption further. The study suggests that as microplastics weather in the environment, they become more effective carriers of pharmaceutical contaminants, particularly in organic matter-rich waters.
Polyethylene (PE) microplastics and caffeine (CFN) are ubiquitous in water and wastewater systems; however, PE microplastic’s ability to adsorb CFN in organic matter-rich waters and their interaction mechanisms are poorly understood. This study assessed the performance of aged PE microplastics for CFN adsorption in humic acid (HA)-mixed water compared to that of pristine PE microplastics. The effects of solution pH (pH 2–9), contact time (up to 72 h), and initial CFN concentration (1–30 mg/L) on the sorption performances of PE microplastics at different HA concentrations (0.5–2.5 mg/L) were assessed. A PE film was aged in sunshine for three months to obtain aged microplastics. Aged PE microplastics demonstrated the highest CFN adsorption (3.62 mg/g) compared to pristine PE microplastics (2.37 mg/g) at pH 6.0–7.0. The water mixed with the highest concentration of HA (2.5 mg/L) was found to be the most effective medium for sorption, suggesting that CFN adsorption onto PE microplastics is likely favorable in water enriched with HA. The cooperation of nucleophilic attractions, intermolecular hydrogen bonds, and van der Waals and π–π interactions would be prominent in CFN adsorption onto HA-bound PE microplastics. The adsorption results collectively suggested a multifaceted sorption mechanism for CFN adsorption onto PE microplastics through either chemisorption or physisorption. The poor desorption ability on slight changes in the pH further evidenced the existence of chemisorption of CFN and the minimal chance of bioavailability in bodily fluids after exposure. The results of this study indicate that the sorption dynamics within the CFN-microplastic-HA system could potentially impact the transport of CFN in aquatic environments. Further, aging of PE microplastics and HA concentration govern the vector potential of microplastics, which would have the most negative end-to-end impact on human health.
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Researchers investigated how humic acid and microplastic-derived dissolved organic matter (MP-DOM) influence tetracycline adsorption onto UV-aged polyethylene and polystyrene microplastics, finding that UV aging increased surface area and functional groups on the plastics while dissolved organic matter altered adsorption capacity through competitive and facilitative mechanisms.
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Researchers found that polyethylene microplastics adsorb pharmaceutical compounds including an antibiotic, a beta-blocker, and an antidepressant, with sorption capacity influenced by pH, aging of the plastic, and competition between compounds — raising concern about microplastics as carriers of pharmaceuticals in aquatic environments.
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Researchers tested how environmental aging changes the ability of three types of microplastics (LDPE, PET, and uPVC) to absorb ten different organic contaminants from water, including pharmaceuticals and pesticides. Aged microplastics showed different sorption behavior compared to new plastics, which has important implications for how weathered plastic particles in wastewater or the environment carry and transport toxic chemicals.
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Laboratory experiments showed that common plastic types — polyvinyl chloride and polypropylene — readily adsorb the heart medication metoprolol from water, and that this adsorption increases at higher pH and in the presence of dissolved organic matter (humic acids). These findings raise concern that microplastics in aquatic environments could act as transport vectors for pharmaceutical drugs, potentially delivering them to fish and other organisms in concentrated doses.
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