Are "biodegradable" plastics really biodegradable ? The case study of the marine environment.

Résumé fourni par la source

The "biodegradable" polymers have been proposed as one of the solutions to face plastic pollution. Nevertheless, biodegradability standard tests have been widely criticized by scientists for their lack of representativeness of natural conditions. Here, we studied the influence of experimental conditions on tests carried out for the marine environment, with particular emphasis on the choice of microbial inoculum (concentration and origin) and test medium (seawater or synthetic medium). Experimental conditions were miniaturized to enable a multiplication of the modalities and parameters analyzed (2043 tubes). Biodegradability tests were carried out for cellulose, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) and polyethylene (PE) by measuring diversity (16S rRNA sequencing), bacterial activity (O2 consumption, CO2 production and heterotrophic bacterial activity) and the presence of oligomers (1H NMR) for 90 days. The experimental conditions were validated by comparison with cultures on larger volumes. Our results support the use of mature biofilms grown in natural seawater as test inoculum, rather than the use of free bacteria in seawater. In addition, we encourage the use of a synthetic medium enriched with nutrients rather than natural seawater, particularly for oligotrophic conditions (offshore seawater). Finally, the analysis of microbial diversity underlines the limits of the representativeness of these tests, which reflect potential biodegradability and whose applications should be relativized according to variations in the conditions of the natural environment. Our results provide new insight into the biodegradability of polymers in the marine environment, and open up new routes for better design and testing of biodegradable plastics. Also see: https://micro2024.sciencesconf.org/558757/document

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