Occurrence, Fate, and Disinfection Byproduct Formation Potential of Selected Plastics in Aqueous Environment

Abstract

Plastics have been detected in all environmental compartments, owing to their diverse applications and exceptional durability. Plastic particles in natural environments undergo natural weathering processes and can fragment into smaller particles, referred to as microplastics (MPs) when their size becomes smaller than 5 mm. Coastal environments are significant endpoints for MPs, with stormwater being a potential transport pathway. However, there is a significant research gap regarding the quantification and characterization of MPs in beach sediment, coastal waters, and sediment near stormwater drainage systems (SDS). This study addressed this gap by monitoring the nine most common plastics in beach sediment, SDS sediment, and seawater in Auckland, New Zealand, using laser direct infrared imaging to identify, quantify, and assess the size distribution of MPs. The results demonstrated the widespread occurrence of MPs and the dominance of polyethylene terephthalate, confirming the important contribution of stormwater to MP pollution in marine ecosystems. Our investigations through the characterization of naturally weathered high-density polyethylene (HDPE) pile sleeves and controlled UV irradiation experiments in the laboratory, offered novel insights into the primary contributors to MP pollution, specifically for HDPE utilized in marine settings. Our laboratory results challenged the often-assumed dominance of photodegradation as the primary plastic degradation pathway and demonstrated the importance of non-UV mechanisms. However, UVB irradiation was found to release dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) from HDPE pile sleeves, with potential detrimental consequences not previously studied, including the formation of disinfection byproducts (DBPs). Hence, the last set of experiments investigated the potential role of dissolved organic and inorganic matters leached from MPs as precursors of DBPs. Despite high levels of DOC and TDN leached from MPs, specifically polyamide 6 and polyurethane, no N-nitrosamines formed under chloramination. Nonetheless, the chloramination of DOC and TDN leaching produced butanedinitrile and diacetamide, which are considered potentially toxic non-halogenated DBPs. Furthermore, chlorination of leachate yielded unregulated DBPs, such as chloral hydrate and propanenitrile. Overall, our research reveals MPs as sources of potentially toxic chemicals, including precursors of DBPs. This calls for a better consideration of the potential indirect effects of MPs, going beyond ecotoxicity testing of MPs themselves and implementing stricter controls to protect our aquatic ecosystems. Insights from this research can inform effective strategies for mitigating MPs' adverse environmental effects, impacting stakeholders, policymakers, and water treatment facilities.