二次塑料是由較大的塑料廢棄物分解而成的小片塑料。在時間演進之中,歷經物理、生物和化學光降解(包括由陽光照射引起的光氧化(英語:Photo-oxidation of polymers)),這些碎片的結構最終降低到肉眼無法察覺到的大小。 [30]這種過程稱為破碎化(fragmentation)。[28]微塑料被認為會再進一步降解成尺寸更小的程度,但據報導,目前在海洋中檢測到最小微塑料的直徑為1.6微米(6.3×10−5英寸)。[31]破碎化持續進行是導致各處普遍均有各式形狀微塑料的原因。 [14]據觀察,無論在海水或是淡水中,由可生物降解聚合物所形成的微塑料數目,遠高於由不可生物降解聚合物所形成的。[32]
航運是造成海洋污染的重要原因。一些統計數據顯示在1970年,世界各地的商業船隊向海洋環境傾棄超過23,000噸塑料垃圾。在1988年簽訂的《防止船舶污染國際公約(MARPOL 73/78,附 V)禁止船舶把廢棄物傾倒進入海洋環境。美國在1987年通過的海洋塑料污染研究和控制法案( Marine Plastic Pollution Research and Control Act of 1987)禁止船舶(包括海軍艦艇)在海中排放塑料。 [72][73]但航運業仍是塑料污染的主要來源,在1990年代初期即傾棄約650萬噸塑料進入海洋。[74][75]研究顯示在夏威夷海灘上發現的塑料中約有10%是塑料顆粒。[76]在2012年7月24日,香港經歷一場大風暴後,有150噸塑料顆粒和其他塑料原料從附近海岸的船上溢出。據報導,這批來自中國石化公司的塑膠廢棄物大量堆積在海灘上。[34]這事件是一起大型洩漏事件,研究人員推測還有更小的事故發生,而進一步加劇海洋微塑料污染。[34]
2008年在華盛頓大學塔科馬校區舉行名為微塑料海洋垃圾的發生、影響和歸宿國際研究研討會(International Research Workshop on the Occurrence, Effects and Fate of Microplastic Marine Debris),參與者[97]的結論認為微塑料是海洋環境中的一個問題,原因為:
研究人員凱利等人(Kelly et al)在2009年從南極洲東部取樣的冰芯中發現有96種微塑料顆粒,屬於14種不同的聚合物 。[153]在此之前,南極洲的地表水和沈積物以及北極海冰中都有塑料污染的記錄,但這次被認為是首次在南極海冰中發現有塑料污染。這些相對較大的顆粒顯示是來自當地的局部污染源。[153]
此外,某些微生物(參見塑料生物圈(英語:plastisphere)#Degradation by microorganisms)已適應食用塑料,一些細菌物種經過基因改造後可食用某些類型的塑料。 [179]微生物除用於降解微塑料外,還可從受污染的樣品中捕獲其上的生物薄膜基質中的微塑料,以更容易的方式去除此類污染物。[180]還有生物薄膜中的微塑料可利用加工後的「釋放」機制,從薄膜擴散而釋放,促進微塑料的回收。[181]
隨着人們越來越警覺到微塑料對環境的不利影響,相關團體也提倡從各種產品中去除和禁用微塑料。[191]其中一項活動是「打敗柔珠」,重點是從個人護理用品中去除塑料。[61]倡議組織Adventurers and Scientists for Conservation開展全球微塑料倡議,目的為收集水樣,提供更好的證據給科學家,以了解微塑料在環境中擴散的的狀況。[192]UNESCO贊助研究和進行全球評估計劃,以處理會跨境影響的微塑料問題。[193]這些環保組織將持續向製造商施壓,要求他們從產品中去除塑料,以維持健康的生態系統。[194]
歐盟執行委員會已注意到人們越來越關注微塑料對環境的影響。[204]2018年4月,歐盟委員會的首席科學顧問小組通過歐盟的科學建議機制委託,對微塑料污染的科學證據進行全面審查。[204]審查由歐洲學術機構提名的工作組進行,並於2019年1月交付結果。[205]一份基於SAPEA報告(SCIENCE ADVICE FOR POLICY
BY EUROPEAN ACADEMIES Report)的科學意見向執行委員會提出,委員會將根據資料決定是否應在歐盟層面上提出政策變化,以遏制微塑料污染。 [206]
執行委員會的循環經濟行動計劃對關鍵產品(即塑料包裝)的回收和減廢提出強制性要求。行動計劃啟動限制在產品中添加微塑料。規定在產品生命週期各階段捕獲更多微塑料的措施。例如該計劃將審查目的在減少輪胎和紡織品釋放二次微塑料的各項政策。[208]委員會計劃更新《城市污水處理指令(英語:Urban Waste Water Treatment Directive)》,以進一步解決微塑料廢棄物和其他污染問題,用以保護環境,免受工業和城市廢水排放之害。又臨時批准對歐盟飲用水指令的修訂,以確保定期監測飲用水中的微塑料。如果發現問題,指令要求各國必須提出解決方案。[10]
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