Plastic pollution and beyond: do microbes hold the key towards a sustainable solution to this global crisis?

Abstract

Plastic is a wonder product, perhaps one of humanity's best innovations, and has become an indispensable part of our daily lives. Besides the indisputable benefits of plastic materials, significant concerns arise about plastic leakage to the environment. Tiny plastic particles, so-called microplastics (MP), have been detected ubiquitously in various ecosystems around the globe. They are bioavailable for many organisms and may negatively affect ecosystems and society, and the economy. The present study was conducted at first to understand the nature, behavior, and interactions of microscopic plastic waste in the marine environment.A preliminary study was conducted in the coastal environment from the Andaman Sea to map the current plastic pollution status and establish baseline data MPs in water, sediment, and marine food web. In this work, clear evidence of MP bioaccumulation was observed in the marine food-chain organisms like zooplankton, finfishes, and shellfishes. A high amount of MP retention was observed in the zooplankton community. Maximum MP ingestion was observed in adult carangid fish Carangoides malabaricus (up to 67 micro-particles/fish). FT-IR revealed many anthropogenic polymers like polyethylene, polypropylene, nylon, acrylic, and ionomer surlyn. These results depict that plastic pollution is ubiquitous and reached almost every compartment of the coastal environments.Further, to understand the plastic pollution hotspots in the Indian marine environments, a comparative study was carried out to assess the abundances and characteristics of MPs in the bottom sediments from the continental shelf zone of the Andaman Sea and the Arabian Sea. Surface sediments were collected onboard FORV Sagar Sampada from 14 locations of the Andaman Sea and 8 locations of the Arabian Sea with a depth varied from 76 to 264 m. Microplastics were isolated using density separation methods and were enumerated using light microscopy and epi-fluorescence microscopy. MP concentration ranged from not detected (ND) to 267 particles per kilogram. Mean MP concentration at the Arabian Sea was significantly higher (p < 0.001) than in the Andaman Sea. Among different types of MPs, fiber had the highest distribution, followed by fragment and pellet. The mean MP concentration at the Arabian Sea was significantly higher than the Andaman Sea, suggesting the Arabian Sea experiences more anthropogenic pressures than the former area.The present study revealed the widespread occurrence of MPs throughout the Indian seas. Further, to understand the ecological consequences of these microscopic litters, MP ingestion by oceanic zooplankton of the Arabian Sea was analyzed. Clear evidence of higher amounts of MP ingestion was observed in carnivorous zooplankton than in the herbivorous or omnivorous species. These results suggest that feeding habits play critical roles in the pollutants' availability in the marine environment. The plastic pollution problem is magnifying due to the long-term persistence and prolonged degradation of plastics in the environment. Omnipresent accumulation, persistence, and environmental toxicity of plastic waste warrant immediate action for developing efficient, eco-friendly, and sustainable technologies for their degradation. However, some of the microbes, including bacteria, are capable of synthetic polymer degradation.To understand whether microbes can play a critical role in solving the plastic pollution, 11 marine bacteria with plastic degradation potentials were isolated from the coastal environments of Andaman Island. Further, based on the preliminary screening, a bacterial consortium was prepared with four bacterial strains from the genus Vibrio (2 strains), Paenibacillus, and Bacillus. The bacterial consortium was incubated with low-density polyethylene (LDPE) sheets as sole carbon source and incubated for 120 days. After 120 days of incubation on average, nearly 47% LDPE degradation was observed. These observations were supported with FT-IR, SEM, AFM, NMR, and TG-DSC analysis. These results suggest that the bacterial consortia used in this work may have great potential to degrade plastics and solve the problem. However, further research is required to develop innovative, cutting-edge, and eco-friendly technology to solve plastic pollution.