Degradation of Plastics in Simulated Landfill Conditions.

Different degradable plastics have been promoted as a solution for the accumulation of waste in landfills and the natural environment; in Mexico, the most popular options are oxo-degradable, which degrade in a sequential abiotic-biotic process, and compostable plastics. In this research, high-density polyethylene, oxo-degradable high-density polyethylene, and certified compostable plastic were exposed to simulated landfill conditions in an 854-day-long experiment to assess their degradation. High-density polyethylene showed limited degradation, due mainly to surface erosion, evidenced by a 13% decrease in elongation at break. The pro-oxidant additive in the oxo-degradable plastic increased this loss of mechanical properties to 27%. However, both plastic films kept their physical integrity and high molecular weight by the end of the experiment, evidencing degradation but no biodegradation. While the compostable film fragmented, had a lower molecular weight at the end of the experiment, and decreased the presence of C=O bonds, this degradation took place remarkably slower than expected from a composting process. Results show that oxo-degradable and compostable plastics will not biodegrade readily in landfills. This fact should be known and understood for decision-makers to match the characteristics of the materials to the features of the waste management systems.

Identification and characterization of single use oxo/biodegradable plastics from Mexico City, Mexico: Is the advertised labeling useful?

The compositional characterization of single-use plastics (SUPs), often advertised as biodegradable (B) and oxo-biodegradable (OB), is an important step towards plastic pollution mitigation through the formulation of appropriate (re) use and disposal strategies. We present here the very first study to screen daily SUPs in Mexico through comprehensive characterizations of 33 randomly collected samples (B and OB) of high consumption, with or without food contact, from the markets (n = 80), bakeries (n = 5), pharmacies (n = 5) and near public transportation systems (n = 2) across 16 municipalities of Mexico City, using the polymer composition, metal contents and thermal properties. These SUPs are composed of 85% high-density polyethylene and 15% low-density polyethylene, with significant inorganic additives, and all of them show variable thermal degradation behavior. Among the twenty five different metals identified, most of the SUPs exceed the standard international norms (94/62/EC; EN 13432; 2016/1416; ASTM D6400-04) for Cu, Cr, Mo, Zn, Fe and Pb with the maximum concentrations of 1898 mg/kg, 1586 mg/kg, 95 mg/kg, 1492 mg/kg, 1900 mg/kg and 7528 mg/kg, respectively. Our findings uncovered that the collected SUPs from Mexico City did not have the suitable physicochemical characteristics and they might end up adding to the exponentially growing solid waste in the immediate future. Hence, we recommend the implementation of strict norms to certify the SUPs.