Marine pollution /
Marine pollution / Marine degradation Designing for biodegradability in ocean environment A solution or exacerbating the solution? The Problem The issue of plastics and microplastics leaking into the oceans is the subject of much discussion and concern [1]. Articles in print and electronic media document not only the unmanaged plastic waste entering the oceans but the negative impacts on the marine ecosystem as a whole [2 – 4]. United Nations (UN) estimates suggest that 80 % of ocean plastic comes from land based sources, and the actual number is probably higher [1]. These estimates are based on the fact that most plastic waste is typically buoyant and that much of it could be found floating across the ocean in the large gyres. The remaining 20 % of ocean plastic is believed to originate from marine-based sources, such as oil rigs, fishing vessels, piers, and boats transporting freight or passengers. In a recent paper published in the high impact peer reviewed journal Science [5], we reported that in 2012, 4.8 to 12.7 million tons of plastics leaked into oceans from land based mismanaged wastes in 192 countries located within 50 km of a coast – primarily from the developing countries of Asia. This is shown in detail in figure 1. The mismanaged plastic waste shown as blue bars goes from 31.9 million tons in 2010 to 69.9 million tons in 2025 without any intervention and business as usual. The red, green, and orange bars represent three different scenarios of mismanaged waste leakage into the oceans – 15 %, 25 %, and 40 % for each of the years. Therefore, without any intervention, 10.4 to 27.7 million tons of mismanaged plastic waste in these costal countries will leak into the oceans by 2025. These are conservative figures and other literature papers put this number much higher. Is marine biodegradability a solution or problem? In response, scientists and technologists in academe and industry are developing and introducing plastics for biodegradability in the marine environment as a solution to the problem of plastic pollution of the oceans. There are ASTM standards for determining the percent biodegradability in marine environment – ASTM D6691 is Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials in the Marine Environment by a Defined Microbial Consortium or Natural Sea Water Inoculum; ASTM D7473-12 Standard Test Method for Weight Attrition of Plastic Materials in the Marine Environment by Open System Aquarium Incubations; a new Standard Test Method for Determining Aerobic Biodegradation of Plastics Buried in Sandy Marine Sediment under Controlled Laboratory Conditions. The operating temperatures for these laboratory scale test methods are around 23 to 28 °C. Certain PHA (polyhydroxyalkanoates) films show 80 %+ biodegradability in river water at 25 °C as shown in figure 2. Synthetic polyesters – polyethylene succinate, polyethylene adipate, and polybutylene adipate are biodegradable in river water at 25 °C as shown in figure 3. Fig. 1: Land based mismanaged plastic waste from 192 countries located within 50 km of a coast – primarily from the developing countries of Asia [5] 80 70 60 Mismanaged plastic waste (MMT/year) 15% leakage to ocean 25% leakage to ocean 40% leakage to ocean 50 MMT 40 30 20 10 0 2010 2015 2020 2025 Year 18 bioplastics MAGAZINE [02/16] Vol. 11
Marine pollution / Marine degradation By: Ramani Narayan Distinguished Professor, and Sayli Bote Research Assistant at Biobased Materials Research Group Michigan State University East Lansing, Michigan, USA However, the ocean (marine) environment is NOT a managed disposal environment like composting or anaerobic digestion which are sound end-of-life options for food and biowaste components of the solid waste stream along with truly and completely biodegradablecompostable plastics. Furthermore, ocean temperatures drop precipitously as you go down in depth (4 ° C on reaching 2,000 m) and the ocean environment can be much different and less active than the lab test environment. So these marine biodegradable plastics (which show complete biodegradability in a lab test method) could remain in ocean environments for very long period of time and cause serious environmental impacts that have been recorded for ocean microplastic wastes. Therefore, designing for marine biodegradability is NOT A SOLUTION to plastics pollution in the ocean environment. The goal should be to prevent these plastics from entering the ocean environment in the first place. For products used in the marine environment like fishing nets, lobster pots, biodegradability may provide a value attribute so that if it is inadvertently lost and enter into the ocean environment they are utilizable as food by the microbial populations over a period of time. However, this cannot and should not be used for making marketing claims especially in Business to Consumer (B2C) communication. The marine biodegradability test method Standards are useful in evaluating the persistence, fate, and impact of plastics in the ocean environment but not to be used in marketing claims. Solution for microplastics in ocean environment and the role for biodegradability. Another major finding of the Science paper (5) is that reducing the amount of land based mismanaged wastes generated in these developing Asian countries would significantly reduce plastics waste entering into the oceans. For example: • Reducing mismanaged waste by 50 % in the Top 5 countries corresponds to a 26 % reduction. • Reducing mismanaged waste by 50 % in Top 10 countries corresponds to a 34 % reduction. • Reducing mismanaged waste by 50 % in Top 20 countries corresponds to 45 % reduction. • Reducing mismanaged waste by 50 % in Top 35 countries corresponds to 75 % reduction. Figure 4 schematically shows the effect of this reduction on the overall land based mismanaged waste generation (blue bar) – from 69.1million tons with zero intervention BOD-biodegradability (%) 100 80 60 40 20 P(3HB-co-36 % 3HP) P(3HB) P(3HP) 0 0 7 14 21 28 Time (day) Fig. 2: Biodegradability of PHA (polyhydroxyalkanoates) films in river water at 250 °C Fig. 3: Biodegradability of synthetic polyesters in river water at 25 °C [5] BOD-biodegradability (%) 100 80 60 40 20 Poly(ethyelene succinate) Poly(ethylene adipate) Poly(butylene adipate) Poly(butylene sebacate) 0 0 7 14 21 28 Time (day) bioplastics MAGAZINE [02/16] Vol. 11 19
