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Photolysis of Triclosan in the Presence of Polyethylene Plastic
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Triclosan, an antibacterial chemical once common in soaps, can stick to plastic bags floating in water — and this new study finds that sunlight converts it into a dioxin-like compound up to 290 times faster when it's on plastic than when it's dissolved in water alone. This matters because plastic pollution in lakes, rivers, and oceans could be quietly speeding up the formation of more toxic byproducts, which may then make their way into the food chain and eventually to humans who eat fish or seafood.
Plastic pollution represents one of the greatest anthropogenic threats to the environment. Plastic debris may absorb potentially toxic compounds of low water solubility in aqueous environments. Aquatic plastic pollution may transfer absorbed compounds to aquatic animals causing premature death. Here we examine how polyethylene (PE) plastic grocery bags affect the photolysis of triclosan (TCS, 5-chloro-2-(2,4-dichlorophenoxy) phenol) when it is absorbed on the surface of the PE in aqueous solution. The photolytic conversion of TCS to 2,8-dichlorodibenzodioxin (2,8-DCDD) is up to ten times faster on plastic than in solution when irradiated at 300 nm and 290 times faster when irradiated at 350 nm. Under these conditions, 2,8-DCDD is formed from the protonated form of TCS unlike in solution where 2,8-DCDD is formed from the deprotonated anion. Quantum mechanical calculations suggest the photolytic transformation of TCS to 2,8-DCDD is initiated by a decrease in phenol pka from 8.1 to -1.7 in the S1 excited state of TCS which initiates the cyclization reaction to form 2,8-DCDD on the surface of the PE. PE is the most abundant form of plastic found in the environment and the most common form of PE are grocery bags. TCS was chosen as a model compound for these studies given its widespread occurrence in the environment, its photolysis in solution has been studied extensively under a variety of conditions.
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This review examines how triclosan, an antibacterial chemical found in many personal care products, harms aquatic organisms both on its own and in combination with other pollutants including microplastics. When triclosan and microplastics are present together in water, they can produce combined toxic effects that are worse than either alone. Since triclosan is widely used and microplastics are everywhere, their interaction in the environment is an important consideration for both ecosystem and human health.
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Researchers investigated how polystyrene microplastics interact with the antimicrobial compound triclosan in simulated environmental and cellular conditions. They found that surface-functionalized microplastics adsorbed significantly more triclosan and released it under cellular conditions, with the combination producing greater toxicity to human intestinal cells than either contaminant alone. The study suggests that microplastics can amplify the harmful effects of co-occurring organic pollutants.
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When PVC plastic breaks down in water, it releases dissolved substances that can trap antibiotics or, under sunlight, break them apart into new byproducts—but these breakdown products can actually be more toxic to aquatic algae than the original antibiotics. This matters because it shows microplastics aren't just passive pollution; they actively change how antibiotics behave in the environment, potentially creating new toxic chemicals and influencing the spread of antibiotic-resistant bacteria that can affect drinking water and food sources.
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Researchers studied how polyethylene microplastics interact with river biofilms growing on natural stone surfaces and how this affects the uptake of the antimicrobial chemical triclosan. They found that the presence of microplastics altered how biofilm communities absorbed and processed triclosan, potentially changing the chemical's toxicity profile. The findings suggest that microplastics in freshwater environments can indirectly influence how other pollutants affect aquatic life.
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