7.4 Microbes Involved in the Degradation of Plastic and Related Polymers

99

esophageal papillae inhibits regurgitation and may end up in its accumulation.

An increased concentration of microplastics in the vicinity may cause cyto-

toxicity, decreased feeding, and decreased phagocytic and increased lysozyme

activity in lower marine invertebrates.

b) The ingested microplastics accumulating inside the body may block fluid pas-

sage across the body, thus rendering internal organs inflamed and damaged.

The long-term accumulation of microplastics may start leaching of additives,

plasticizers, flame retardants, which may be fatally toxic.

7.3.2

Nanoplastics

Nanoplastics exhibit enhanced toxicity in comparison with microplastics. Even

the short-term exposure of nanoplastics has been reported to cause assimilation

and deposition inside the body. Polystyrene nanoplastics cause embryotoxicity and

abnormal gene expression in the sea urchin Paracentrotus lividus [5]. Carboxy-

lated and amino-modified nanoplastics adversely affect feeding, motility, and cell

viability.

Various studies have shown that the trophic transfer of nanoplastics is one of the

major routes of pollutant exposure. It has also been concluded to confer behavioral

modifications and metabolic issues in large marine animals. The behavioral changes

are the result of the invasion of the brain by nanoplastics.

7.4

Microbes Involved in the Degradation of Plastic

and Related Polymers

Plastic degradation in the marine environment can occur in multiple ways like abi-

otic and biotic processes or biological processes like microbial degradation using

various microbial entities. The natural phenomenon of degradation is a prolonged

process. The natural weathering effects here account for the degradation of plastic.

Microbes, on the other hand, aid in the biodegradation of plastic polymer in a speedy

and environment-friendly manner. The basic principle behind this process is that

the microorganisms directly utilize plastic as a source of carbon and energy for their

growth and multiplication, consuming it in the process. The degradation of plas-

tic occurs by an enormous genus of bacteria by both aerobic and anaerobic modes,

and fungi by anaerobic mode only. Aerobic bacteria utilize as a terminal electron

acceptor and mineralize plastics and other polymers to CO2 and H2O. Anaerobic

microorganisms (including bacteria and fungi) may use iron, sulfate manganese,

and nitrate as a terminal electron acceptor to degrade organic hydrocarbons into

simpler molecules like methane, for example (Table 7.1).

7.4.1

Biodegradation of Plastic

Different microbial entities employ a specific mechanism by which they can degrade

various forms of plastic. Recent studies revealed that polyethylene (PE), polyethy-

lene terephthalate (PET), and polystyrene (PS), along with polypropylene (PP) con-

stitute a significant portion of plastic debris in the marine system.