Aerobic biodegradation of bio-based plastics in the seawater/sediment interface (sublittoral) marine environment of the coastal zone - Test method under controlled laboratory conditions

Abstract

Pollution of the seas due to plastic litter is a rapidly growing environmental problem. Among several actions, legal and technological, undertaken to alleviate this problem, included are the control of single use conventional plastics and the replacement of conventional non-biodegradable plastics with innovative biodegradable-in-the-sea polymers, both aiming at the mitigation of marine litter accumulation. Laboratory tests have been used to characterize plastics regarding their biodegradation in various environments. Biodegradation of plastics depends on the inherent characteristics of the polymer and the particular marine habitat conditions. In the present work, the international standard test method ISO 19679 (2016) for determining the aerobic biodegradation of non-floating plastic materials in a seawater-sediment interface of the coastal marine zone under laboratory simulated conditions is evaluated. Modifications are proposed to improve the reliability of this test method in some aspects. Agitation of the seawater surface in the bioreactor was found to enhance the continuous availability of oxygen at the seawater-sediment interface, thus assuring aerobic biodegradation conditions throughout the test simulating real sublittoral conditions. Additional recommended improvements include the use of larger samples and supplementary nutrients to optimise biodegradation conditions. The laboratory measurements were validated by field experiments. The proposed modifications and refinements optimise the robustness and reliability of the test method for determining aerobic biodegradation of plastic materials in a simulated seawater-sediment interface of the coastal zone.

TSC Opinion

Voici une étude qui était attendue depuis longtemps : comment les plastiques se dégradent t’ils en conditions réelles in situ ? Elle est limitée au LDPE et à quelques plastiques biosourcés, mais son approche a l’avantage d’être simple : des films de plastique de chaque matière fixés entre deux grilles à mailles larges qui permettent leur maintient mais aussi un contact permanent avec le milieu. Les échantillons sont immergés en zone côtière à faible profondeur juste au-dessus d’un sédiment sablo-vaseux, ce qui est un point important car le sédiment est riche en bactéries très efficaces pour dégrader la matière organique. Les résultats montrent que le LDPE ne s’est quasiment pas dégradé en 1 an de séjour au fond de l’eau alors que les PHB et autres plastiques biosourcés sont se sont dégradés à 60% et plus.