Microplastics particles are pollutants of increasing concern in marine environments worldwide. A significant fraction is formed through the degradation and fragmentation of larger plastic debris. Their formation mechanisms likely depend on both their chemical nature and environmental conditions. Numerous studies have mimicked the effect of temperature and solar radiation through accelerated weathering in the laboratory. However, it is often unclear how well artificial weathering conditions model the actual fate of plastics over extended timescales in natural environments. Few studies have deliberately placed plastics of well-defined composition into marine environments and analysed them before and after recovery, and the majority of these focused on a single type of material.
We present a study of five polymer/additive formulations with known compositions that were deployed at three marine locations across Aotearoa / New Zealand. Their mechanical and thermal properties and surface topologies were investigated as a function of deployment location and time (up to one year). Accelerated weathering was also used as a pre-treatment before deployment in the marine environment. Across different plastic types, we observed significant differences in the affected characteristics and the extent of the measured changes. While PET remained largely inert, LLDPE, PA6 and PLA underwent moderate changes. The strongest effects were observed in artificially aged LLDPE: increased crystallinity, intense surface cracking and massive deterioration of its mechanical properties. By contrast, marine deployment had lesser effects. With few exceptions, no differences between the three locations were identified. Generally speaking, accelerated weathering did not accurately model the changes undergone by marine deployed plastics over one year. This finding has implications for the use of results from laboratory studies for simulating and extrapolating aging in natural conditions. Our findings also shed light on the initial phases of the degradation and eventual fragmentation of larger pieces of plastic debris into microplastics particles.