Plastics are solids with an interior and a surface. Fragmentation of plastics in the environment, coupled with the release of chemical additives from these plastics, lead to a potential future peak release of toxic compounds (including chemical additives and nanoplastics). Humanity has produced a staggering volume and diversity of plastic materials. A significant proportion of this is accumulating as waste in a range of environmental compartments. The behavior and fate of plastics in the environment is a complex issue, strongly influenced by the unique properties of a given type of plastic, including shape and size, polymer type, the additives and impurities present in the plastic and the extent of prior environmental decay. The parameter space is so large that we may never know how all plastic types interact chemically and physically in every environmental situation or impact each unique ecosystem. Nevertheless, research in this area continues to make rapid and impressive progress, shedding light on many of these factors using short-term experiments. One key aspect of plastic pollution has been mostly overlooked, relating to longer-term consequences of plastic degradation and pollution release, and we call this the “toxicity debt” (Figure 1). In conservation biology, the number of species that are doomed to extinction because of habitat loss and fragmentation, but that have not yet gone extinct because of time lags to reach equilibrium conditions, are called extinction debt.(1) In analogy to this, we propose that there is a toxicity debt that we incur by having large amounts of plastic currently in the environment, exposed to degradation, but that has many more years of decay and release of toxic compounds to follow. This does not refer, therefore, to future pollution with plastic but to the current state of plastic pollution already present in the environment; but effects are of course compounded with any future pollution. Figure 1. Development of an environmental plastic toxicity debt. What are the underlying causes of this toxicity debt? This debt arises from a combination of three factors. First, plastics are fundamentally solids, with a surface area and polymeric molecular structure. Second, all plastics contain additional chemicals (additives), the purpose of which is to give certain properties to plastics during their useful life; plastics may also contain additional unintentional chemicals (impurities), such as catalyst residues, unreacted monomers or breakdown products.(2) Selected additives and impurities possess toxic properties, with implications for ecosystem and human health. Third, over time under environmental conditions, plastics fragment into smaller pieces, increasing the surface area of the solid plastic, further releasing trapped additives and impurities. The first two points, that plastics are solid bodies with additives and impurities “stored” within the structural volume of the plastic is a key property of this contaminant suite. These compounds are not immediately released into the environment, because this process is limited by slow rates of diffusion of the additive or impurity to the surface of the plastic item. Time scales over which additives and impurities are released from a plastic item vary extremely widely, from an estimated billions of years for brominated flame retardants to years for certain plasticizers, such as phthalates, adipates, and trimellitates. The third key point is that plastic items tend to fragment in the environment. Termed microplastics when fragments are below 5 mm in size, such fragments can degrade further to reach nanoparticle size.(3) Several crucial properties change along this pathway to smaller particle sizes: the interior volume becomes smaller, the surface area of the plastic fragment increases, with the increasing release of additives and impurities as the diffusion pathway to reach the fragment surface shortens. This means that we must expect larger amounts of potentially toxic compound cocktails to be released into the environment that exponentially increase with increasing time of environmental exposure of plastics. This time-delayed release of plastic additives and impurities forms a late pulse of potentially toxic compounds that contributes to the toxicity debt. In addition, multiple smaller nanoplastic fragments are created, which can themselves give rise to toxic effects. The toxicity of nanoplastic fragments in the environment is an area of active research, with detrimental impacts including oxidative stress, downregulated gene expression, and behavioral disorders in aquatic organisms.(4) This is a serious issue, since there are likely to be several orders of magnitude more nanoplastic particles in the environment than microplastic particles. This time-delayed appearance of nanoplastics and their toxic effects may be much more severe than effects related to the current levels of toxic chemicals released from micro- and nanoplastics. We, therefore, explicitly include this increased production of nanoplastics in the environment in our concept of toxicity debt. Plastics have been produced at an industrial scale since the 1950s. Given the production patterns, which have been steeply increasing, and the time scales of degradation with estimated half-lives ranging from less than a year to several thousand years depending on the plastic and its chemistry,(5) we very likely have not reached the peak of toxic release from the sum total of all environmentally available plastic on Earth. This is a sobering thought. There are some immediate research needs that arise from recognition of this impending plastic toxicity debt, as well as important consequences for policy. First, we need to understand how different plastics fragment in the environment and the time scales of fragmentation. This calls for innovative approaches that go beyond short-term laboratory incubations and involve longer-term approaches. Second, we need to study the release of additives, impurities, and other compounds from different plastic chemistries and piece sizes under environmentally relevant conditions, including in water, soil, or when ingested by organisms. We know comparatively little about the migration behavior of the various types of additives out of plastic pieces in the environment. This is because studies on migration behavior have typically addressed plastic materials during their useful life, for example when packing material is in contact with food.(6) On the policy side, this realization of a toxicity debt should become an additional, central argument in the discussion to curb single-used plastic use and to encourage the development of more intelligent polymers, designed for performance during their entire life cycle, including after end of life. Additionally, we need to include additives in policy considerations: behavior of additives should not only be appraised during the useful life of plastic but also in terms of their future release to the environment. The authors declare no competing financial interest. The authors declare no competing financial interest.
M.C.R. acknowledges funding from an ERC Advanced Grant (694368), from the Federal Ministry of Education and Research (BMBF; projects BIBS and μPlastic), and the Deutsche Forschungsgemeinschaft. S.W.K. acknowledges a postdoctoral grant from the National Research Foundation of Korea funded by the Ministry of Science, ICT, and Future Planning (2019R1A6A3A03031386). T.Y.K. acknowledges support from the National Research Foundation of Korea (2019R1A2C1007170). W.R.W. acknowledges a Capes-Humboldt Research Fellowship (1203128-BRA-HFSTCAPES-E-Finance code 001). This article references 6 other publications.

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全球塑料毒性债务

塑料是具有内部和表面的固体。塑料在环境中的破碎，再加上这些塑料中化学添加剂的释放，可能导致有毒化合物（包括化学添加剂和纳米塑料）在未来的潜在峰值释放。人类已经产生了惊人的数量和种类繁多的塑料材料。其中很大一部分作为废物堆积在一系列环境隔室中。塑料在环境中的行为和命运是一个复杂的问题，受给定类型的塑料的独特性能（包括形状和尺寸，聚合物类型，塑料中存在的添加剂和杂质以及先前环境恶化的程度）的强烈影响。参数空间是如此之大，以至于我们可能永远都不知道所有塑料类型在每种环境情况下如何发生化学和物理相互作用或影响每个独特的生态系统。尽管如此，该领域的研究仍在继续取得迅速而令人瞩目的进展，并通过短期实验揭示了其中许多因素。与塑料降解和污染释放的长期后果有关，塑料污染的一个主要方面已被普遍忽视，我们称其为“毒性债务”（图1）。在保护生物学中，由于栖息地丧失和破碎而注定要灭绝但由于达到平衡条件的时间差而尚未灭绝的物种的数量被称为灭绝债务。（1）类似地，我们建议，由于环境中目前存在大量塑料而容易遭受降解，因此会产生毒性债务，但随后会腐烂并释放出更多的有毒化合物。因此，这不是指未来的塑料污染，而是指环境中已经存在的塑料污染的当前状态；但是影响当然会与未来的任何污染加在一起。图1.环境可塑性毒性债务的发展。产生这种毒性债务的根本原因是什么？该债务来自三个因素的组合。首先，塑料基本上是固体，具有表面积和聚合分子结构。其次，所有塑料都包含其他化学物质（添加剂），其目的是在塑料的使用寿命内赋予某些特性；塑料还可能包含其他无意的化学物质（杂质），例如催化剂残留物，未反应的单体或分解产物。（2）选定的添加剂和杂质具有毒性，对生态系统和人类健康具有影响。第三，随着时间的流逝，在环境条件下，塑料会破碎成较小的碎片，从而增加固体塑料的表面积，从而进一步释放被困的添加剂和杂质。前两点是，塑料是带有添加剂和杂质的固体，这些杂质“存储”在塑料的结构体积内，这是该污染物套件的关键特性。这些化合物不会立即释放到环境中，因为此过程受到添加剂或杂质向塑料物品表面的缓慢扩散速度的限制。从塑料物品中释放出添加剂和杂质的时间范围差异很大，从溴化阻燃剂的估计数十亿年到某些增塑剂（例如邻苯二甲酸酯，己二酸酯和偏苯三酸酯）的年数。第三个关键点是塑料制品在环境中容易破碎。当碎片的尺寸小于5 mm时，称为微塑料，此类碎片会进一步降解以达到纳米粒子的尺寸。（3）一些关键特性沿此途径改变为较小的粒子尺寸：内部体积变小，塑料碎片的表面积增加，随着到达碎片表面的扩散途径的增加，添加剂和杂质的释放越来越短。这意味着我们必须期望大量潜在的有毒化合物混合物被释放到环境中，并且随着塑料在环境中暴露时间的增加呈指数增长。塑性添加剂和杂质的这种延时释放形成了潜在有毒化合物的延迟脉冲，从而加剧了毒性负担。另外，产生了多个较小的纳米塑料碎片，它们本身可引起毒性作用。纳米塑料碎片在环境中的毒性是一个活跃的研究领域，其有害影响包括氧化应激，基因表达下调和水生生物的行为失常。（4）这是一个严重的问题，因为可能有几个方面的问题。与微塑料颗粒相比，环境中的纳米塑料颗粒数量更多。纳米塑料的这种延迟出现的外观及其毒性作用可能比与目前从微塑料和纳米塑料释放的有毒化学物质水平有关的影响严重得多。因此，我们明确将这种增加的环境中纳米塑料的生产纳入我们的毒性债务概念。自1950年代以来，塑料一直以工业规模生产。鉴于生产模式一直在急剧增长，并且降解的时间范围取决于塑料及其化学性质，估计的半衰期从不到一年到几千年不等（5），我们很可能还没有达到地球上所有环保塑料的总和中毒释放的峰值。这是一个发人深省的想法。认识到这种即将到来的塑料毒性债务以及对政策的重要后果，引起了一些立即的研究需求。首先，我们需要了解环境中不同塑料的破碎方式以及破碎的时间尺度。这就要求创新的方法要超越短期的实验室孵化，而要涉及长期的方法。其次，我们需要研究在环境相关的条件下，包括在水，土壤中或被有机物摄入时，不同塑料化学和片大小的添加剂，杂质和其他化合物的释放。我们对环境中各种类型的添加剂从塑料碎片中迁移出来的行为知之甚少。这是因为有关迁移行为的研究通常针对塑料材料的使用寿命，例如包装材料与食物接触时的情况。（6）在政策方面，这种对毒性债务的认识应该成为塑料加工中的另一个核心论点。讨论旨在遏制一次性塑料的使用，并鼓励开发更智能的聚合物，这些聚合物旨在在其整个生命周期（包括使用寿命结束）中发挥作用。此外，我们需要在政策考虑因素中包括添加剂：不仅应在塑料的使用寿命期间评估添加剂的行为，而且还应评估其未来释放到环境中的行为。作者宣称没有竞争性的经济利益。作者宣称没有竞争性的经济利益。例如，当包装材料与食品接触时。（6）在政策方面，这种毒性债务的实现应成为讨论中的另一项中心论据，以遏制一次性塑料的使用并鼓励人们发展更智能的产品。聚合物，旨在在其整个生命周期内（包括寿命结束后）发挥作用。此外，我们需要将添加剂纳入政策考虑范围：不仅应在塑料的使用寿命期间评估添加剂的行为，而且还应评估其未来释放到环境中的行为。作者宣称没有竞争性的经济利益。作者宣称没有竞争性的经济利益。例如，当包装材料与食品接触时。（6）在政策方面，这种毒性债务的实现应成为讨论中的另一项中心论据，以遏制一次性塑料的使用并鼓励人们发展更智能的产品。聚合物，旨在在其整个生命周期内（包括寿命结束后）发挥作用。此外，我们需要将添加剂纳入政策考虑范围：不仅应在塑料的使用寿命期间评估添加剂的行为，而且还应评估其未来释放到环境中的行为。作者宣称没有竞争性的经济利益。作者宣称没有竞争性的经济利益。讨论中的中心论点是限制一次性塑料的使用，并鼓励开发更智能的聚合物，这些聚合物旨在在其整个生命周期（包括寿命结束）中发挥作用。此外，我们需要将添加剂纳入政策考虑范围：不仅应在塑料的使用寿命期间评估添加剂的行为，而且还应评估其未来释放到环境中的行为。作者宣称没有竞争性的经济利益。作者宣称没有竞争性的经济利益。讨论中的中心论点是限制一次性塑料的使用，并鼓励开发更智能的聚合物，这些聚合物旨在在其整个生命周期（包括寿命结束）中发挥作用。此外，我们需要将添加剂纳入政策考虑范围：不仅应在塑料的使用寿命期间评估添加剂的行为，而且还应评估其未来释放到环境中的行为。作者宣称没有竞争性的经济利益。作者宣称没有竞争性的经济利益。添加剂的行为不仅应在塑料的使用寿命内进行评估，而且还应根据它们将来向环境中释放的方式进行评估。作者宣称没有竞争性的经济利益。作者宣称没有竞争性的经济利益。添加剂的行为不仅应在塑料的使用寿命内进行评估，而且还应根据它们将来向环境中释放的方式进行评估。作者宣称没有竞争性的经济利益。作者宣称没有竞争性的经济利益。
MCR感谢联邦教育与研究部（BMBF； BIBS和μPlastic项目）的ERC高级拨款（694368）和Deutsche Forschungsgemeinschaft的资助。SWK承认由科学，信息与通信技术和未来规划部资助的韩国国家研究基金会的博士后资助（2019R1A6A3A03031386）。TYK感谢韩国国家研究基金会（2019R1A2C1007170）的支持。WRW感谢Capes-Humboldt研究奖学金（1203128-BRA-HFSTCAPES-E-财务代码001）。本文引用了其他6个出版物。