11 3.1. Fragmentation and degradation Several studies show PS foam can break up into microplastics more easily than other plastic types (Lee et al 2013, Biber et al 2019). While all plastics exposed to sun, wind, waves, ice and biota can eventually fragment, the breakdown of plastic depends on the environment and the type of plastic (Eubeler et al., 2010). Large plastic pieces often break apart (fragment) into smaller pieces due to physical abrasion. Due to its physical structure, polystyrene foam can easily fragment. In a recent study, Biber et al. (2019) found PS deteriorated more rapidly compared to PE, PET, and a biodegradable plastic. This showed that PS is expected to break up into microplastics more quickly in the environment than other polymers (Biber et al., 2019). A study by Leonas and Gorden (1993) investigated PS degradation and showed that the aquatic environment can slow polymer degradation. Other studies, however, show that aquatic environments can speed up degradation (Andrady and Pegram, 1991). Fragmentation varies by the polymer type and environmental conditions, and due to the wide range of plastic types and habitats where plastic pollution is found, this can be highly variable (Sivan 2011; Gewert et al. 2015; Andrady, 2015). PS foam in docks has been reported to fragment into macro- and micro-plastics due to abiotic and biotic factors such as water, ice, sunlight, and biota. Abiotic The breakup of PS foam floats and docks can be due to a number of abiotic factors, including water, ice, and sunlight. Fluctuating water levels can cause the breakup of PS foam docks (Figure 3). In the Lake of the Ozarks, for example, PS foam debris was created from seasonal water level changes (Missouri Department of Natural Resources, 2006). The amount of debris eventually prompted a lake-wide ban of PS docks and floats (Missouri Department of Natural Resources, 2006). Since PS foam is not perfectly waterproof, it can become waterlogged. In areas with cold winters, this waterlogging can cause fragmentation. EPS can be especially vulnerable to this fragmentation because of its open network of interstitial gaps between the expanded beads. When water is trapped in the interstitial gaps, ice can form inside the foam, causing material to break apart (Dunham and Finn, 1974). Sun exposure also deteriorates PS foam. UV can make PS brittle, and prone to fragmentation (Andrady and Pegram, 1991). When PS foam fragments enter the environment, these fragments can be further broken down by other abiotic and biotic factors. Degraded and fragmented pieces of PS foam litter Abiotic and biotic Abiotic factors are non-living physical and chemical elements in an ecosystem. Examples of abiotic factors are water, air, sunlight, and minerals. Biotic factors are living or once-living organisms in an ecosystem. Examples of biotic factors are animals, birds, plants, fungi, and other organisms. Figure 3: Shoreline cleanup from Lake of the Ozarks, Missouri in 2019 removing large PS debris. Lake of the Ozarks has banned PS foam docks because of debris caused by fluctuating water levels and boat traffic. Recent shoreline cleanups report less dock foam debris after the local ban (Miller, 2019). Photo used with permission from Mitch Prentice.