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

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.