Polymer leachates emulate naturally derived fluorescent dissolved organic matter: Understanding and managing sample container interferences

Natural light driven plastic leaching effects on carbon chemistry in the tropical coastal waters of eastern Arabian sea: An experimental study

This study examined the effects of solar light driven plastic degradation on carbon chemistry in the coastal waters of eastern Arabian Sea along the west coast of India. The research was conducted through experimental incubations exposed to natural sunlight at multiple locations between December 2023-February 2024. Photodegradation induced a significant pH decrease (up to 0.38 ± 0.02) between controls and plastic incubations ranging from 8.17 ± 0.01 to 7.54 ± 0.02 with the highest variation in the Mumbai coast ranging from 8.13 ± 0.01 to 7.75 ± 0.03. pH variations are primarily caused by the leaching of organic acids and CO2 release during solar irradiated incubation. Plastic leaching due to natural light irradiation and subsequent changes in the water chemistry is of prime significance with dissolved organic carbon (DOC) leaching of 0.002-0.03% of plastic weight into the coastal waters. Our estimations suggest 15-75 metric tonnes (MT) of DOC release per year by plastic pollution in the eastern Arabian Sea coastal waters. Further, the fluorescent dissolved organic matter (FDOM) fragmentation, a part of DOC, may act as an organic source of synthetic contaminants and would promote heterotrophic microbial action in the coastal waters. Photodegradation of plastic and the interaction of natural DOC and plastic-derived DOC resulted in longer wavelengths FDOM, which may affect the penetration of photosynthetically active radiation in the water column, thereby impacting primary production. Finally, future research work focussing on the role of plastic pollution in coastal ocean acidification and vice-versa is essential and will be increasingly intense in the upcoming decades.

Leaching and bioavailability of dissolved organic matter from petrol-based and biodegradable plastics

Petrol-based plastic debris reaching the ocean releases dissolved organic carbon (DOC) and it can also leach fluorescent dissolved organic matter (FDOM). DOC is available to microbial uptake but the FDOM bioavailability has been scarcely studied. Although the most common plastic found in the ocean is petrol-based, the use of biodegradable plastic has increased substantially over the last years. Here we analysed the DOC and FDOM released by three petrol-based (LDPE, PS and EPS) and one biodegradable plastic (PLA) in seawater and examined their bioavailability. We found that the three petro-based plastics released FDOM in the protein-like region while the biodegradable PLA did not. FDOM released by EPS was available to microbial uptake while in the LDPE and PS treatments an increase of FDOM was observed, likely because the FDOM production by bacteria was higher than the consumption in those treatments. Biodegradable PLA leached similar amounts of DOC with comparable microbial bioavailability than petrol-based plastics indicating that, in seawater, it was not degraded faster than petro-based plastics. Especial care should be taken with biodegradable plastic since not all the types degrade in the ocean.