Most plastic we use in our daily lives is not "micro" by any measure. Plastic waste has to be worn and broken up into much smaller pieces (less than 5 millimeters in diameter) to be considered a "microplastic."
The most common items that eventually become microplastics are marine litter, fishing gear, litter from dumping yards, laundry discharge, and packaging materials. (Tiwari et al. 2019).
These plastics are generally broken down in two different ways.
Photo-oxidation:
Environmental Weathering:
While both of these factors break down plastics, neither breaks them down completely. The removal of microplastics by natural breakdown, such as photo-oxidation and weathering, would take hundreds of years. (Thompson et al., 2004).
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无论如何，我们日常生活中使用的大多数塑料都不是“微型”的。塑料垃圾必须被磨碎成更小的碎片(直径小于5毫米)，才能被认为是“微塑料”。
最终成为微塑料的最常见的物品是海洋垃圾、渔具、来自垃圾场的垃圾、衣物排放和包装材料。(Tiwari等，2019)。
这些塑料通常有两种不同的分解方法。
光致氧化:
光氧化是指塑料在紫外线照射下的弱化作用。
紫外线破坏了构成塑料的分子(聚合物)之间的一些键。(Albertsson等，1987)
塑料内部的键断裂使其更容易断裂。
环境风化:
环境风化是指风、水等因素对塑料破碎成小块的影响。
光氧化有助于老化，使塑料更脆弱，更容易分解。(Cozar等，2014; Lambert and Wagner，2016)
虽然这两种因素都能分解塑料，但都不能完全分解。通过自然分解(如光氧化和风化)去除微塑料需要数百年的时间。(Thompson等，2004)。