Field and mesocosm methods to test biodegradable plastic film under marine conditions

Abstract

The pollution of the natural environment, especially the world's oceans, with conventional plastic is of major concern. Biodegradable plastics are an emerging market bringing along potential chances and risks. The fate of these materials in the environment and their possible effects on organisms and ecosystems has rarely been studied systematically and is not well understood. For the marine environment, reliable field test methods and standards for assessing and certifying biodegradation to bridge laboratory respirometric data are lacking. In this work we present newly developed field tests to assess the performance of (biodegradable) plastics under natural marine conditions. These methods were successfully applied and validated in three coastal habitats (eulittoral, benthic and pelagic) and two climate zones (Mediterranean Sea and tropical Southeast Asia). Additionally, a stand-alone mesocosm test system which integrated all three habitats in one technical system at 400-L scale independent from running seawater is presented as a methodological bridge. Films of polyhydroxyalkanoate copolymer (PHA) and low density polyethylene (LD-PE) were used to validate the tests. While LD-PE remained intact, PHA disintegrated to a varying degree depending on the habitat and the climate zone. Together with the existing laboratory standard test methods, the field and mesocosm test systems presented in this work provide a 3tier testing scheme for the reliable assessment of the biodegradation of (biodegradable) plastic in the marine environment. This toolset of tests can be adapted to other aquatic ecosystems.

Not Only Diamonds Are Forever: Degradation of Plastic Films in a Simulated Marine Environment

“…Bagheri et al (2017) executed a laboratory experiment exposing PLA and PHA films to seawater, under fluorescent light, at 25°C, for a period of 12 months: PLA films showed no significant degradation, and PHA films lost a mere 8.5% of their initial mass. One recently published work compared LDPE and PHA (Mirel P5001) film degradation after exposure to a temperate versus a tropical marine environment: films submerged for 22 months in a pelagic setting in the Mediterranean Sea (Elba Island, Italy) showed no surface loss, while films placed for the same amount of time in the Indonesian sea experienced a ∼90% surface loss (Lott et al, 2020). Overall, these studies seem to demonstrate a proportional relationship between degradation rate and temperature and irradiance.…”

“…In further experiments, it will be fundamental to characterize the microbiota, and add to the seawater an inoculum supplemented with appropriate medium for growth (as in i.e. Lott et al, 2020), to reach conditions overlapping with those of real seawater surface.…”

“…Although laboratory tests maintain their informational value within a comprehensive assessment strategy, field tests are of utter importance. However, the latter type of experiment does not come without disadvantages: they are liable to tampering by macrofauna and humans alike, difficult to check upon, and biofouling can disrupt the exposure of the plastic samples (Lott et al, 2020). A balanced solution could be found in hybrid test systems, allowing exposure to natural sunlight, and incorporating stirring/movement, with natural or inoculated seawater -but contained vessels to avoid tampering, and easier accessibility to the experiment, for control purposes.…”

Disintegration half-life of biodegradable plastic films on different marine beach sediments

“…Disintegration was determined photogrammetrically as described before (Lott et al, 2020). The remaining plastic was marked on the photos and the area loss of the total exposed area was measured using ImageJ (Abramoff, Magalhaes & Ram, 2004).…”

Ecological Effects of Benzyl Chloride on Different Korean Aquatic Indigenous Species Using an Artificial Stream Mesocosm Simulating a Chemical Spill

“…Besides pesticide studies, most mesocosm research related to chemical spills has focused on oil spills in marine ecosystems [21][22][23]. Moreover, recently, an increased number of mesocosm studies have been conducted to evaluate the impacts of microplastics on aquatic organisms [24,25].…”