Understanding the degradation of plastics, some of the most widely used materials on Earth, is crucial in a broad range of fields from materials design to environmental monitoring. Many polymers yellow as they age, but there is no chemical explanation that can describe the origin of this yellowing for polyolefins specifically. Here, we show that irradiated blown polyethylene sheets preferentially scatter circularly polarized light. Because scattering of circularly polarized light only occurs in the presence of chiral structures, our findings provide evidence of formation of chiral supramolecular structures responsible for preferential light scattering that may be the underpinnings for the perceived yellow/ brown tint as polyethylene ages. Further, we demonstrate incident polarization-dependent detection of colored light scattering from irradiated polyethylene films and that the scattered light is distinctly different in color. Overall, these results provide evidence that the yellowing of polyethylene, previously assumed to be caused by polymer backbone rearrangements, is actually the product of chiral, optically active structures that form on the plastic's surface due to UV irradiation. To the best of our knowledge, this is the first explanation for polymer discoloring that provides evidence for the development of supramolecular structures of polymers during aging. Because of this, our findings provide an alternative direction in plastic degradation research for understanding the chemical and structural changes. Findings presented here shift our understanding about materials degradation and can inform our future materials designs and recovery.

Characterizing the impact of nanoplastics to organism health is important to understand the consequences of the environmental plastic waste problem. This article examines the impact of nano-polystyrene (nano-PS; 159 ± 0.9 nm diameter) to ecologically relevant bacteria Shewanella oneidensis. Bacterial viability was evaluated using a growth-based assay. Riboflavin secretion is a critical cell function of S. oneidensis, serving as an electron mediator in anaerobic respiration and/or as a signaling molecule when the bacteria are under stress. Thus, changes in cellular function were monitored through riboflavin secretion in order to evaluate toxic responses that may not result in cell death. Under aerobic and anaerobic exposures (4, 8, or 12 h), the viability of the S. oneidensis was minimally changed as compared to the control, while the concentration of riboflavin secreted varied with exposure dose. In order to determine if this was a specific response to nanoplastic particles, opposed to a response to either particles or plastic more generally, we exposed the system to colloidal TiO 2 nanoparticles and polystyrene and polyethylene thin films. We confirmed that riboflavin secretion trends were specific to nano-PS and not to these other materials, which showed no significant changes. We investigated the association of the nano-PS with ICP-MS using Pd that was chemically incorporated into the model nanoplastics. While 59.2% of the nano-PS were found in the non-cellular culture media, 7.0 and 6.6% was found associated with the loosely and tightly bound extracellular polymeric substance, respectively. There was significantly more nano-PS (10.9%) strongly associated with the cells. Taken together, we found that nano-PS had minimal impacts to viability but caused a significant change in the function of S. oneidensis that can be related to the nano-PS attached or in proximity to the bacterium. These trends are consistent between aerobic and anaerobic cultures, signifying that the stress response of S. oneidensis can be generalized between different environmental compartments. This work highlights that the association of nanoplastic materials with microorganisms may modify the cellular function that could ultimately be an impact to ecosystem health.

Plastic waste has the potential for significant consequences on various ecosystems; yet, there are gaps in our understanding of the interaction of bacteria with polymer additives. We studied the impact...