Microbial Diversity and Activity During the Biodegradation in Seawater of Various Substitutes to Conventional Plastic Cotton Swab Sticks

Abstract

The European Parliament recently approved a new law banning single-use plastic items for 2021 such as plastic plates, cutlery, straws, cotton swabs, and balloon sticks. Transition to a bioeconomy involves the substitution of these banned products with biodegradable materials. Several materials such as polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), poly(butylene succinate) (PBS), polyhydroxybutyrate-valerate (PHBV), Bioplast, and Mater-Bi could be good candidates to substitute cotton swabs, but their biodegradability needs to be tested under marine conditions. In this study, we described the microbial life growing on these materials, and we evaluated their biodegradability in seawater, compared with controls made of non-biodegradable polypropylene (PP) or biodegradable cellulose. During the first 40 days in seawater, we detected clear changes in bacterial diversity (Illumina sequencing of 16S rRNA gene) and heterotrophic activity (incorporation of 3H-leucine) that coincided with the classic succession of initial colonization, growth, and maturation phases of a biofilm. Biodegradability of the cotton swab sticks was then tested during another 94 days under strict diet conditions with the different plastics as sole carbon source. The drastic decrease of the bacterial activity on PP, PLA, and PBS suggested no bacterial attack of these materials, whereas the bacterial activity in PBAT, Bioplast, Mater-Bi, and PHBV presented similar responses to the cellulose positive control. Interestingly, the different bacterial diversity trends observed for biodegradable vs. non-biodegradable plastics allowed to describe potential new candidates involved in the degradation of these materials under marine conditions. This better understanding of the bacterial diversity and activity dynamics during the colonization and biodegradation processes contributes to an expanding baseline to understand plastic biodegradation in marine conditions and provide a foundation for further decisions on the replacement of the banned single-used plastics.

Bacterial Abundance, Diversity and Activity During Long-Term Colonization of Non-biodegradable and Biodegradable Plastics in Seawater

“…The potential activity of plastic biodegradation in seawater is determined by several standard tests based on biomass and respirometric activity measurements (mainly CO 2 production) under laboratory conditions during 3 months (ASTM D6691-09), 6 months (ASTM D7473-12), or 24 months (ISO 18830, ISO 19679, ASTM D7991-15). Other activity tests can be considered as alternative methods, such as tests based on ATP measurements ( Fontanella et al, 2013 ) or bacterial heterotrophic production ( Jacquin et al, 2021 ). We are aware that intra- and extracellular bacterial activities under natural conditions may be related to processes other than plastic biodegradation (biodegradation of organic matter and cross-feeding in the biofilm) ( Pande et al, 2014 ), but this study provides a set of congruent results that, although not definitely compelling, gives concrete hints for effective biodegradability in seawater ( Jacquin et al, 2021 ).…”

“…Other activity tests can be considered as alternative methods, such as tests based on ATP measurements ( Fontanella et al, 2013 ) or bacterial heterotrophic production ( Jacquin et al, 2021 ). We are aware that intra- and extracellular bacterial activities under natural conditions may be related to processes other than plastic biodegradation (biodegradation of organic matter and cross-feeding in the biofilm) ( Pande et al, 2014 ), but this study provides a set of congruent results that, although not definitely compelling, gives concrete hints for effective biodegradability in seawater ( Jacquin et al, 2021 ).…”

Closing the Carbon Loop in the Circular Plastics Economy

“…A comparative study of cotton swabs made from the substituted bio‐based materials, such as PLA, PBAT, PBS, PHBV, and starch‐based plastics (, and Mater‐Bi ), using cellulose and non‐biodegradable PP as reference samples, revealed a massive decay of bacterial activity for PP, PLA, and PBS, all of which failed to serve as nutrients and did not biodegrade within a 40‐days period of immersion in seawater followed by 94 days of “ strict diet conditions with the different plastics as sole carbon source”. [ 434 ] In contrast, the positive responses of PBAT, Mater‐Bi , Bioplast , and PHBV were similar to that of cellulose. For plastics such as PHB, PBS, and polybutylene sebacate‐terephthalate (PBSeT), biodegradation strongly differs for each plastic type by orders of magnitude, depending on climate zones and local marine habitats.…”

“…[433] When PLA waste ends up in seawater, it does not seem to biodegrade at all. [353,432,434,435] In 2021, the European Parliament endorsed replacing singleuse plastics items, including cutlery, straws, plastic plates, and cotton swabs, with biodegradable plastics, in order to fight marine littering. A comparative study of cotton swabs made from the substituted bio-based materials, such as PLA, PBAT, PBS, PHBV, and starch-based plastics (, and Mater-Bi), using cellulose and non-biodegradable PP as reference samples, revealed a massive decay of bacterial activity for PP, PLA, and PBS, all of which failed to serve as nutrients and did not biodegrade within a 40-days period of immersion in seawater followed by 94 days of "strict diet conditions with the different plastics as sole carbon source".…”

Differences in the Plastispheres of Biodegradable and Non-biodegradable Plastics: A Mini Review

“…Biodegradable plastics that enter the environment tend to have rougher surfaces, which provide a larger specific surface area for microbial colonization. Purahong et al (2021) observed that on burying a poly(butylene succinate- co -adipate; PBSA) film in the soil, its smooth morphology got corroded and became rough after 180 d. Conversely, Jacquin et al (2021) found that there was no clear morphological change on the surface of PP after incubating it in seawater for 6 weeks. On the other hand, the surfaces of PHBV and PBAT got significantly corroded in seawater ( Jacquin et al, 2021 ).…”