Microplastics Generation: Onset of Fragmentation of Polyethylene Films in Marine Environment Mesocosms

Abstract

The fragmentation of high-density polyethylene (HDPE) films from single-use supermarket plastic bags to microplastics under laboratory-simulated onshore and nearshore conditions was investigated for a period of 6 months. The weathering process of the plastic strips either on beach sand or in seawater under direct natural sunlight was monitored by tensile strength, molecular weight measurements, FTIR, weight loss, and image processing of photographs of the plastic strips before and after mild mechanical stress was applied. The latter represents a novel method proposed for determining the onset of fragmentation through the application of mild mechanical stress on the weathered plastic samples emulating the action of sand and wind on a beach. It was found that 12 h of application of mild mechanical stress in rotating glass bottles filled partially with sand was sufficient time to reach the maximum degree of fragmentation that could occur for the weathered plastics samples being tested. For example, applied mechanical stress yielded an area loss of almost 14% for samples weathered for a period of 5 months and about 16.7% after 5.5 months. While tensile strength tests and molecular weight measurements were rather inconclusive till the very last month when the onset of fragmentation was identified; FTIR measurements revealed that samples under ultraviolet irradiation were gradually modified chemically until fragmentation commenced. After 6 months of weathering, molecular weight measurements showed a 60% reduction for sample SMB-1 whereas for sample SMB-2 the measurement was not possible due to extensive fragmentation. The onset of fragmentation for SMB-1 and SMB-2 samples occurred at a cumulative luminance of 5.3 × 10 6 lux•d and in the presence of atmospheric oxygen whereby the polymer films broke down partially to microplastics. When the UV exposure reached 7.2 × 10 6 lux•d the weathered plastic strips broke down fully to microplastics with the application of a mild mechanical stress. Samples placed in seawater proved to be resistant to fragmentation compared to those on sand over the 6-month period of the weathering experiment. The direct implication of this work is that beached macroplastic debris should be regularly collected from the seashore before they are weathered by sunlight and returned to the sea as microplastics by the action of high waves or strong winds.

Delineating and preventing plastic waste leakage in the marine and terrestrial environment

“…are just a few to mention. However, exact and reliable estimates on the quantities of the individual sources and/ or origins of the different types of plastics are hampered by the complexity of the sources of micro-and macroplastics; the lack of quantitative data on transport and fate in the environment; and the high geographic, hydrographic and geomorphologic variability of the relevance of different sources and introduction routes, which is caused by differences in the infrastructure, especially with regard to waste management (Kalogerakis et al 2017;Lambert et al 2014;Law and Thompson 2014).…”

“…The generation of MPs via the fragmentation of larger plastic particles is a complex and multifactorial process, depending on various parameters, such as luminance, temperature, and oxygen level, and characteristics inherent to the nature of the degrading material, e.g. its molecular weight distribution and presence of additives (Hahladakis et al 2018b;Kalogerakis et al 2017). Environments where plastics are exposed to mechanical stress or high oxidizing radiation will accelerate their deterioration; such environments may be a substantial source of MPs.…”

“…Nonetheless, due to various conditions and environments (e.g. weather, UV light, seawater), plastics can potentially be degraded and dissociated (fragmented) into smaller pieces, 50-5 mm, called "microplastics" (MPs) (Andrady 2011;Kalogerakis et al 2017;Wang et al 2016). Finally, the nanometre-sized plastic particles usually defined in < 100 nm of size constitute the "nanoplastics" group (Koelmans et al 2015).…”

Delineating the global plastic marine litter challenge: clarifying the misconceptions

“…Nonetheless, due to various conditions and environments (e.g., weather, UV light, seawater, etc. ), plastics can potentially be degraded and dissociated (fragmented) into smaller pieces, 50 μm-5 mm, called microplastics (MPs) (Andrady, 2011;Kalogerakis et al, 2017;Wang et al, 2016). Finally, the nanometer-sized plastic particles, usually defined in < 100 nm of size, constitute the "nanoplastics" group (Koelmans et al, 2015).…”

Novel trends in plastic waste management

“…The process of recycling plastics has been elucidated as involving scrap or plastics waste recovery and subsequent material reprocessing into viable products which entirely vary from their original status [23]. The end product derived from varying techniques of plastic recycling has enabled classification between various plastic recycling techniques [24]. This classification can be fundamentally elucidated in Fig.…”