科学观察, 2016, 11(6): 1-19
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摘要:
纳米材料越来越多地出现在各种广泛使用的产品中,如防晒霜、化妆品、抗菌纺织品、锂离子电池、玻璃涂层和网球拍。纳米材料——因其纳米尺寸所赋予的优异性能——在一系列应用中得以发挥作用。然而,这些特殊的化学和物理性质同样意味着潜在的与环境健康和安全相关的风险。在废弃物管理领域存在科学认识中的盲点。由于缺乏对相关风险及可能的环境危害的足够认知,含有纳米材料的废弃物被不加以区别的与传统废弃物同样处理。
序 言
在制定策略以阻止对环境修复力的持续损害时,加强材料管理和大幅降低废弃物的影响都是至关重要的因素。这也就意味着今后制定的政策或有关办法应能够支持对材料的可持续利用,从而确保人类健康和自然环境不受侵害。所制定的相关政策都需要适应因技术和工艺创新而快速变化的制造环境。其中的创新之一即是人工纳米材料的广泛使用。
纳米材料越来越多地出现在各种广泛使用的产品中,如防晒霜、化妆品、抗菌纺织品、锂离子电池、玻璃涂层和网球拍。纳米材料——因其纳米尺寸所赋予的优异性能——在一系列应用中得以发挥作用。然而,这些特殊的化学和物理性质同样意味着潜在的与环境健康和安全相关的风险。在废弃物管理领域存在科学认识中的盲点。由于缺乏对相关风险及可能的环境危害的足够认知,含有纳米材料的废弃物被不加以区别的与传统废弃物同样处理。
该报告旨在对该领域当前的科学认知状况及知识空白进行概述。报告所调查的文献涉及废弃物处理过程中纳米材料的结局及潜在影响,包括回收、焚烧、填埋和污水处理等过程。同时报告也着重给出了支持纳米材料可持续有效管理的关键信息、未来研究领域以及潜在方法。
该报告参考了OECD内外部相关文献, 由资源生产率与消耗工作组(Working Party on Resource Productivity and Waste, WPRPW)主导,纳米材料制造工作组(the Working Party on Manufactured Nanomaterials, WPMN)密切协作。鉴于这一科学领域的迅猛发展,OECD计划在该领域继续展开研究,并与其他包括政府、研究机构及学术界的各级国际和国家组织进行紧密合作。
Simon Upton
OECD环境理事会董事
1 引言
本报告由OECD环境政策委员会的WPRPW完成。回收、焚烧、填埋和污水处理等独立章节的撰写由来自瑞士、德国、加拿大及法国的技术专家承担。项目协调由OECD秘书处的Peter Börkey和Shunta Yamaguchi承担并由环境与经济一体化司主管Shardul Agrawala监督完成。
这项工作旨在引起人们对潜在风险的关注,即由于纳米材料的存在而导致的废弃物处理过程中可能产生的潜在危险。2012年5月Jeremy Allan发表了《纳米废弃物研究概述》,同年5月9日至11日“纳米废弃物安全管理”研讨会在慕尼黑举办。该研讨会揭示了纳米废弃物领域的研究现状,并延伸出本报告中包括回收、焚烧、填埋和污水处理等4篇废弃物特殊处理工艺的相关研究。
人工纳米材料工作组(WPMN)自2006年开始一直致力于研究纳米材料对健康和环境可能造成的影响。2013年9月,OECD发表了一项委员会建议,表明现有的监管框架基本适用于纳米材料的安全性评估,但需要做一些合理调整以应对纳米材料的特殊性。然而,该OECD委员会建议并未表明目前的废弃物管理工艺及技术对于解决纳米材料的潜在影响普遍适用。当前的废弃物处理设施一般并非为处理含纳米材料废弃物(WCNMs)而设计,这就导致了污染物的暴露及其与人体的接触。因此本报告的目的在于明晰当前该领域的知识认知现状、知识空白以及未来的首要工作重点。
鉴于纳米材料研究发展迅速,本报告旨在对纳米材料进入废弃物流所产生的风险及影响的现有科学认知进行概述。目前的研究结果仅仅是对当前一些中间结果的汇编,而随着科学发展这些结论可能会进一步演变。
本报告由WPRPW成员国合作完成。OECD秘书处负责报告的最终定稿,并负责起草评估及建议、执行摘要两个章节。独立章节由以下作者完成。
评估及建议：由OECD秘书处Peter Börkey及Shunta Yamaguchi完成;
含有纳米材料废弃物的回收：由瑞士伯尔尼Terra咨询公司的Mathias Tellenbach 完成;
含有纳米材料废弃物的焚烧：由德国联邦环境局(UBA)的Julia Vogel和Benjamin Wiechmann完成,Susann Krause提供了帮助;
含有纳米材料废弃物的填埋：由来自加拿大环境署的Martha King、Jacinthe Séguin以及Ashley Hui起草;
污水处理厂及农业应用中ENMs之命运：由位于法国的国家科学研究中心研究室主任Jean-Yves Bottero起草。
本报告还征求了OECD资源生产率和浪费工作组及人工纳米材料工作组的意见,也采纳了由OECD工商咨询委员会代表的各国及各行业代表团的建议。OECD秘书处要特别感谢瑞士、德国、加拿大和法国对这项工作在人力和物力方面的支持。
2 执行摘要
22人工纳米材料(Engineered Nanomaterials,ENMs)——其尺度界定为1nm~100nm——越来越多地在工业、商业和医学范畴加以应用,为医疗卫生、服装、建材、电子、运动器材等领域带来了诸多福音。包含人工纳米材料的产品有防晒霜、除臭剂、防水抗菌纺织品、锂离子电池、玻璃涂层和网球拍。
然而人工纳米材料给人类和环境带来的潜在风险和可能造成的影响目前还未得到充分的认识。由于它们的大小、形状、结构以及独特的性质,一些具有潜在危险性的ENMs可能成为困扰人类、生物体乃至环境的问题。虽然ENMs种类繁多,且并非所有种类都具有潜在毒性,但最近的研究表明某些纳米材料可能导致肺癌,或绕过重要生物保护机制如血脑屏障,或因某些材料的抗菌性能而对环境产生负面影响。此外,在某些情况下ENMs可以提高生物利用度,即吸收或吸附其他有毒物质造成可能污染物的生化输入。
2006至2011年间,全球范围内含有纳米材料的产品数量增长了4倍,超过1 300项产品被确定包含纳米材料。2012年全球纳米材料市场预计可达1 100万吨,市场价值200亿欧元。相应地纳米科技相关产品的销售额预计由2009年的2 000亿欧元增长到2015年的2万亿欧元。伴随如此迅猛的发展速度,环境风险应运而生。目前人们将含有纳米材料的废弃物(waste containing nanomaterials,WCNMs)与传统垃圾一同处理,并未采取任何特别措施。问题是,现有的废弃物处理工艺能否有效地减少ENMs可能带来的风险呢?
本报告对大量关于回收、焚烧、填埋和污水处理等4个特殊废弃物处理工艺方面的文献资料进行了研究,从而了解当前人们对ENMs在现有处理工艺条件下的最终结果及可能造成的环境影响。
2.1 关键信息
虽然先进的废弃物处理设施在某些情况下可以在废弃物中保留或去除ENMs,但因ENMs种类众多、废弃物处理设施的多样化以及废弃物实际组分的不确定性等原因,在诸多领域依然有待进一步的研究。这是从下面4篇研究报告中得出的主要结论。
(1)缺乏废弃物处理流程中ENMs的类型与数量信息。
即使人们对产品中人工纳米材料的含量及数量知之甚少,但对于进入不同类型废弃物处理设施的ENMs的来源还是比较好确认的。从生活垃圾中可以收集人工纳米材料并在材料回收设备中进行回收,或以固体生活垃圾或废水污泥的形式进入焚烧工厂。ENMs同样可通过家用、商用及工业污水排放或垃圾渗出液进入废水处理装置。最终,ENMs作为家用及商用废弃污染物连同焚烧炉中的灰渣或废水处理工厂排出的生物固体一起进行填埋。但由于缺少进入废弃物处理流程中的ENMs的类型和数量信息,所以存在重要的知识空白。
(2)尽管先进的废弃物处理工艺可处理大部分ENMs,但仍会有相当一部分被排放出来。
初步研究表明先进的废弃物处理装置可将大部分ENMs俘获、转移或排除,但这伴随着不同程度的不确定性。尽管先进的废弃物处理技术可控制大部分ENMs并将其排除,但相当份额的ENMs还是会以排放物的形式排放于装置之外,这便是值得关注的问题。实验废水处理装置可俘获超过80%的人工纳米材料并转化为固体污泥,其余则以原有状态冲洗至地表水体。同样地,配备有效废气处理系统(如排气过滤器)的焚烧炉可捕捉大部分ENMs并将其转化为如飞尘、底灰类的固体残余物。但这些结论目前并未得到完全证实,因为不同研究所显示的脱除效率大相径庭。关于填埋及回收操作方面的信息相当少,而且初期研究所得出的结论仅限于每项废弃物处理工艺中的某些ENMs,不仅如此,上述结论很多出自实验室测试或建模。因此我们可以说在这些废弃物处理装置中的ENMs的结局始终具有一定程度的不确定性。
(3)目前最佳可行技术的最有效之处表现为可以最小化风险。
在ENMs所带来的影响和危害都相对不确定的情况下,废弃物处理(可能并非专门用于处理ENMs)所采用的最佳可行技术(best available technologies,BAT)应为可有效降低废弃物流中ENMs风险的实用技术。
因此,需要重点关注那些不规范的废弃物处理工艺,如未配置充分废气处理系统的焚烧炉、不受控制的填埋等。如今这样的技术在世界上诸多地区仍在广泛使用,而对于它们制约ENMs的有效性我们却所知为零,因此可以断定采用这些技术对于潜在风险的控制非常有限。
(4)由于知之甚少,所以对残余废弃物的处理特别关注
即便通过先进的废弃物处理工艺可以成功地捕捉ENMs并将其去除,人们依然担心下游的残余废弃物处理及材料循环回收工序可能会造成ENMs的排放。最令人担忧的情况也许是污水、污泥的农业应用。人们对于ENMs在土壤中如何变化、其与植物和细菌在根际的互动以及如何进入地表水系统等方面均未进行深度研究。另一个值得关注的问题是当ENMs以残余废弃物残渣(焚烧炉飞尘及底渣,废水处理装置产生的固体污泥)的形式被收集并最终以填埋的方式被处理时,对我们来说其结局依然是未知的。此外还存在这样的担忧,即通过循环工艺生产的再生材料可能受到ENMs的污染。
(5)ENMs可对某些废弃物处理流程本身产生副作用。
ENMs可对废弃物处理工艺带来不利影响。表面功能化纳米材料可能会减缓废水处理装置中纳米材料的相变动力,并对整个工艺造成不利影响。同理,填埋渗出液中的某些有机物质会对ENMs起到稳定作用,因而可能会降低渗出液处理效果。此外,ENMs可能会对废水处理装置中的某些用于防止污染物及富营养物质渗透至外界环境的工艺——即厌氧或脱氮工段——产生抑制作用从而最终影响装置的效能。
2.2 未来研究领域
鉴于重要性及相关文献的稀缺性,建议对如下领域进行深入研究。
(1)确认并量化废弃物处理流程中的人工纳米材料。
◆ 明晰进入废弃物处理工艺的ENMs类型与数量。
(2)废弃物处理工艺中纳米材料的状态和结局。
◆ 对配置完整废弃物处理系统且处理实际废弃产品的工业化工厂或中试装置的效能进行评估。
◆ 深入了解ENMs在废弃物处理工艺中的最终结果,特别关注以下领域：研究结论尚存在争议的领域(废水处理系统中的厌氧和脱氮工段,焚化炉的废气处理系统);参考资料不足的研究领域(循环回收设备,填埋)。
(3)来自残余废弃物及/或原料回收的潜在ENMs排放。
◆ 对农业中应用含有ENMs的污泥可能产生的影响进行研究。
◆ 考量使ENMs归于最终“栖息地”之填埋工艺的有效性。
◆ 研究含有ENMs的次生材料的潜在危险。
(4)对于排放的控制及最佳可用技术。
◆ 确定固定或去除ENMs并防止工人与ENMs接触的最佳可用废弃物处理技术的有效性。
◆ 评估不规范废弃物处理技术(如不具备完备废气处理系统的焚烧炉,黏土垫层填埋场或不受控填埋等)。
◆ 探究可从废弃物处理流程或残余废弃物中捕获、转化或清除ENMs的其他有效措施。
3 评估与建议
本章概括性展现了后续4章关于废弃物处理工艺的研究结果,这4个特殊工艺包括回收、焚烧、填埋和污水处理。本章阐述了现有的关于纳米材料在这些工艺中的结局及可能造成的影响等方面的认知水平,提供了可行的研究方向,明确了未来的研究领域及解决含有纳米材料废弃物可能带来问题的合理途径。纳米技术正越来越多地深入至工业、商业及医疗领域的高端应用,为人们的社会生活带来巨大的便利[1]。然而,它们对人类和环境可能造成的潜在风险和影响目前还未得到充分认知,研究人员也正在对此进行探究。纳米材料被定义为单一维度尺寸在1~100nm的材料,其独特的性能可用于医疗卫生、服装、电子设备、建筑材料和体育用品等诸多领域[2]。例如,某些纳米材料具有阻挡紫外线的性能,因此应用于防晒霜中,而另一些纳米材料具有抗菌功能,可用于除臭剂及各种纺织品。某些纳米材料可以用于锂离子电池从而延长产品使用寿命,而其他类型的纳米材料可以应用于建筑材料和玻璃涂层使其具备自清洁功能。纳米材料还可用于网球球拍,以满足质轻、性优、经久耐用的需求。
据威尔逊国际学者中心(the Woodrow Wilson International Centre for Scholars,WWICS)出具的纳米技术消费品清单[3]显示,2006至2011年间含有纳米材料的产品数量增加了521%,达到1 317种产品之多。2012年全球纳米材料市场预计可达1 100万吨,市场价值200亿欧元。相应纳米科技相关产品的销售额预计由2009年的2 000亿欧元增长到2015年的2万亿欧元[4,5]。
然而,近期的研究表明由于纳米材料的大小、形状、结构以及独特的性质,可能给人类、生物体乃至环境带来潜在的危险。例如,某些纳米材料可能导致肺癌,而一些具有抗菌特性的纳米材料可能在进入环境后对生态系统造成破坏[6]。不仅如此,一些纳米材料可以绕过重要生物保护机制如血脑屏障,进而产生神经毒副作用[7]。在某些情况下,由于纳米材料能吸收或吸附有毒颗粒,从而提高了污染物的生物利用度[8-12]。
纳米材料在环境中的暴露评估是一个重要问题[13],尽管有时很难将那些为特殊用途设计并制造的ENMs与那些天然存在的纳米材料加以区分,如由紫外线辐射生成的金属银纳米材料或在缺氧条件下自然形成的金属汞[14]。
本报告重点研究国际标准化组织(the International Organization for Standardization,ISO)定义的ENMs(见文本框3.1)以及其在不同废弃物处理流程中的情况,下文中被称为“含纳米材料废弃物”(WCNM)。本文中所提到的“纳米废弃物”特指纳米材料制造过程中产生的含有高水平纳米材料成分的废弃物。
3.1 废弃物管理与何相关?
随着纳米材料在工业及商业中的广泛应用,我们可以断定越来越多的纳米材料正在进入废弃物处理过程从而对报废产品处理过程造成影响[15]。
废弃物管理的目的一是回收废料用以生产再生原料,二是以填埋、焚烧或合理存储的方式处置废弃物。含有纳米材料的报废产品是城市固体垃圾的主要组成部分,可通过4种不同的途径进行处理。
文本框3.1 纳米材料定义
纳米级：大小约为1~100 nm
纳米材料：具有纳米级外形尺寸或内部结构或表面结构的材料。这个通用术语包含了纳米物体和纳米结构材料。
纳米物体：在一维、二维或三维上为纳米尺寸的材料。
纳米结构材料：具有内部纳米结构或表面纳米结构的材料
纳米结构：由相互关联的组成部分构成,其中一个或多个部分为纳米级
注：在研究文献中同时出现过Engineered nanomaterials(ENMs)及manufactured nanomaterials(MNMs),本报告我们统一为Engineered nanomaterials(ENMs)以保证与ISO标准的一致。
来源：ISO/TS 80004-1:2015和ISO/TS 12901-1:2012
(1)回收
回收过程一般有几个阶段。比如,为了使废弃物颗粒大小均匀或分离出多余材料,需要对合成材料和金属进行粉碎。在这个过程中,会排放颗粒并同时产生含有纳米粒子的灰尘。安全起见,处理需在特定工艺条件下进行以避免灰尘与人类或环境接触。
(2)焚烧
废弃物在焚烧装置中混合并做加热处理。可燃部分燃烧后剩下的残余物为炉渣或焚烧炉排放的废气。现代废气过滤器和清洗设备可将有害物质降至最低可检测浓度。然而,人们对纳米材料清除效率的信息知之甚少,最糟的情况就是很有可能这些微粒未被收集或销毁且未被过滤就直接通过烟囱进入环境。
(3)填埋
对未经处理(可生物降解及可燃垃圾)的废弃物进行填埋处理仍然是许多国家采用的主要废弃物管理技术。取决于填埋方式和地点,纳米材料可能从填埋地渗漏至土壤、水源以及空气当中。
(4)废水处理
含纳米材料的产品可以在其使用阶段或与水接触后释放纳米材料,例如带有表面涂层的纺织品在洗衣机中洗涤。因此,纳米材料可能在废水中出现,进而出现在污水处理厂排出的污泥中,而这些污泥将可能被送至焚烧装置进行焚烧或被用作农业肥料。然而在农业中使用这些污水、污泥对环境可能造成怎样的影响,目前人们却知之甚少。
废弃物处理过程中如此大量的ENMs通过不同的废弃物处理工艺处理后被保有或去除的程度如何?ENMs对这些工艺的效能有何影响?这是本研究所提出的主要问题。为此,本报告对四种特殊废弃物处理工艺：回收、焚烧、填埋以及废水处理等领域的文献进行了梳理和综述,旨在了解当前人们对于ENMs在这些工艺中的最终结果及可能造成的影响的认知水平。
基于后续4章的观点,本章首先总结了人们对于WCNMs在废弃物处理工艺中的结果的了解程度,然后提出了一些可行的推进方向。随后几章分别是：第4章——关于纳米材料在回收中的最终结果和可能造成的影响的研究;第5章——关于WCNMs在焚烧中之相关现状的研究;第6章——WCNMs在填埋中可能造成的影响之研究;第7章——废水处理中WCNMs之研究。
3.2 关于废弃物处理装置中WCNMs的结局我们了解多少?
即便通过现有的先进废弃物处理工艺可以成功捕捉大部分ENMs并将其加以转换或去除,但其最终的归宿依然具有较大不确定性,因此需要针对该领域进行进一步研究,这也是下文4个章节的研究结论。我们可以较准确地对WCNMs的来源以及这些废弃物处理工艺的相互联系予以确认,但是对于进入这些废弃物处理过程的ENMs的类型和数量却知之甚少。不仅如此,ENMs在废弃物处理工艺中的命运及其可能造成的影响的现有研究成果可谓喜忧参半,对于某些ENMs,如：纳米银(nAg)、纳米二氧化钛(nTiO2)、纳米氧化锌(ZnO)、纳米二氧化铈(nCeO2)以及碳纳米管(CNTs)的研究相对较多,而对于金属材料,如纳米铁(nFe)、纳米铝(nAl)、纳米铂(nPt)、纳米锆(nZr),金属氧化物,如纳米硅(nSiO2)或纳米黏土的信息却很少。总之,目前对该领域的研究尚未充分至得出明确结论的程度。
3.2.1 废弃物处理过程中ENMs的类型和数量如何?
进入回收、焚烧、填埋以及废水处理四类典型废弃物处理工艺的ENMs来源相对好确认,即便人们并不知道哪种产品含有何种ENMs。ENMs的形式可以为纯纳米材料、携带或沾染纳米材料的物质、含有纳米材料的悬浮液或固体物质[16]。这些材料可能通过ENMs的生产、含有纳米材料产品的分销和使用以及对最终产品的处理等环节排放[15]。它们可能以城市固体垃圾或报废产品的形式被收集并送至循环回收装置,同样也可能以城市固体垃圾或废水污泥的形式进入焚烧装置[17-22],或者通过家用排污系统、商业及工业化废水排放以及填埋渗出液等方式进入废水处理装置[23-27]。最终,作为工业和生活垃圾中的污染物与焚烧炉产生的炉渣或废水处理装置产生的污泥一起进入填埋环节[28,29]。
表3.1
WCNMs的可能来源
然而,至今我们仍无法对进入废弃物流中的ENMs类型和数量进行确认[30]。由于含有ENMs的产品数量急剧增长,最终需要处理的产品也在增加,因此可以断定进入这些废弃物流中的人工纳米材料将会越来越多。由于人工纳米材料的类型和数量不同,这些废弃物处理工艺也会受到不同程度的影响;因此,确定废弃物流中人工纳米材料的类型和数量是后续关于回收、焚烧、填埋及废水处理4个章节需要面对的首要问题。
3.2.2 这些废弃物处理工艺可以捕获ENMs吗?
初步研究表明先进的废弃物处理装置可将大部分ENMs俘获或去除,但这伴随着不同程度的不确定性。尽管先进的废弃物处理技术可控制大部分ENMs并将其排除,但相当份额的ENMs还是会以排放物的形式排放于装置之外,这是值得关注的问题。
研究人员针对城市废水处理系统中的某些纳米材料,如纳米二氧化钛(nTiO2)、纳米银(nAg)、纳米二氧化铈(nCeO2)或纳米铜(nCu)进行过分析。中试废水处理工厂通过有氧工艺中的反应、细菌聚集、生物聚合物吸附以及沉积等过程可以捕获并将超过80%(以重量计)的人工纳米材料转化为固体污泥[26,31-35]。而剩余部分则仍以人工纳米材料的形式存在于地表水中[36,37]。
针对废弃物焚烧炉的研究表明,先进的废气处理系统可将相当部分的人工纳米材料捕获并将其转化为飞灰或炉底渣。但是不同的文献中阐述的人工纳米材料脱除效率却不尽相同。一些研究提出就纳米二氧化铈(nCeO2)来说,采用静电除尘以及湿法废气净化系统可有效脱除排放物中的ENMs成分[38]。而另一些研究却得出了这样的结论：高达20%的成分可能排放于系统之外,因此仍需额外装置对该类材料进行防控[39]。
有关填埋操作方面的相关信息就要少得多。根据对城市废水处理系统的研究结果,研究人员推测处理系统通过有机物与细菌参与下的聚结与团聚反应对填埋渗出液进行处理也可达到同等的ENMs捕获水平[27,32,40]。然而由于渗出液是与城市废水大不相同的液体污染物,研究人员还需对该领域进行研究分析以证实上面的推测。当前针对填埋隔离层阻止人工纳米材料向环境渗漏有效性的研究相当有限,并且初步的研究结果是相互矛盾的[41-43]。不仅如此,ENMs从填埋表面或通过填埋产生的气体而进入环境的程度至今仍未有深入研究。
最后,因为在实际工作环境下对ENMs的排放测量依然是个难题,所以纳米材料在包括分解、粉碎及加热等回收过程中的结局还未可知[13]。因此,这方面的研究在很大程度上依赖于模拟结果。
综上所述,最初的研究结论仅仅针对某些种类的ENMs,并且依赖于实验室模拟或建模的结果,而非针对实际现有设施的研究。因此不同废弃物处理工艺中ENMs的处理结果还存在一定程度的不确定性,需要进一步调查。
3.2.3 ENMs会对渗出液及废水处理造成负面影响吗?
除了担忧废弃物处理装置脱除ENMs的能力,人们不禁要问ENMs是否会对废弃物处理工艺本身造成不良影响。例如表面功能化纳米材料——由于其在好氧反应中相对稳定,聚合及沉降程度有限——可能减缓废水处理装置中纳米材料的相变动力学,进而对整个工艺造成不良影响[23,31,44]。
不仅如此,研究表明某些ENMs可能对废水处理装置中的厌氧和脱氮环节产生抑制作用。据报道高浓度金属性ENMs可能影响细菌群落,抑制厌氧及脱氮工艺并最终使得装置污泥毒性清除性能降低[31,45-49]。因此,更好地了解进入这些处理装置的ENMs的类型和数量可以帮助研究人员对潜在风险进行评估。
3.2.4 废弃物处理工艺与残留物的关系会引发哪些问题呢?
尽管有证据表明先进的废弃物处理工艺可成功捕获ENMs并通过将其转化为固体污泥或飞灰及炉渣的形式令其脱除,但是人们对于后续处理这些残留物及/或材料回收环节还是有所担忧,担心在此环节存在ENMs排放至环境的可能。
最令人担忧的情况也许是污泥的农业应用。法国的一项研究表明,该国一半以上的污泥用于农业土壤肥料[53]。鉴于越来越多的ENMs进入废水处理环节,那么可能将会有更多的ENMs进入污泥。而关于这些材料在土壤中的变化、在根际环境中与植物及微生物之间的相互作用,以及向表面水体的转移等领域均未有过深入研究,因此通过该处理方式的ENMs的最终归宿依然具有很大的不确定性。
同样,对ENMs在填埋场中的归宿的了解的有限性使人们对该问题又产生了更多的担忧,因为填埋基本上是处置来自焚烧及废水处理工艺残余物的最后一环。垃圾焚烧厂通过过滤器将ENMs收集于飞灰及炉渣中,然后被发送到垃圾填埋场进行最终处置[54]。同样,来自废水处理的污泥也可能会被送至垃圾填埋场进行填埋[27,28,55]。
由于从废弃物中回收生成的再生材料可能被所含的ENMs污染,而其潜在风险却几乎不为人所知,因此当这些次生材料被用于其他方面时,新的问题就随之而来[56]。焚烧炉飞灰及炉渣工业化应用于道路建设即是这样的实例。废弃物处理工艺中可能产生的泄漏途径详见表3.2。
表3.2
废弃物处理中存在的ENMs排放之可能途径
3.3 对于已知风险的最佳管理方法我们了解多少?
在ENMs的影响、危害及归宿尚无定论的情况下,一些相关研究提出采用最优实用技术可能是应对这些潜在风险及相关不确定性的务实方法[6,15,57-59]。尽管最优实用技术并非专门为处理ENMs所设计[60,61],但通过它可有效地降低排放。以欧洲废气处理为例,采用最优实用技术的焚烧废气处理被认为比传统的淋洗法去除废气中的ENMs的方式更有效。同样,研究认为现代工程化填埋在防止ENMs排放方面优于非工程化填埋。
在循环回收装置中,工人可能在粉碎、装卸及热处理工段接触到ENMs,因此应有相应的保护措施。
(1)技术措施(通过密封、提炼、过滤、分离及通风工艺以及擦拭而非吹扫的方式减少粉尘);
(2)行政措施(减少人员与材料接触时间、减低接触人数,限制进出以及对员工进行危险及防范措施的指导);
(3)个人防护措施(配备颗粒过滤器的呼吸防护系统、防护手套、封闭护目镜、防护服等)[6]。
因此,废弃物处理中由ENMs带来的潜在风险更多地产生于不规范的操作,而很多不规范操作依然在全球范围内进行着,在一些欠发达地区问题尤为突出。这正是当前亟待深入研究的领域。
废弃物处理工艺中关于ENMs最终结果的知识现状及空白在表3.3中列出。
表3.3
废弃物处理工艺中关于ENMs最终结果的知识现状及空白
3.4 敢问路在何方?
目前,虽然已有一些针对WCNMs相关内容的研究,但尚不充分,未来依然需要大量的研究工作。而现阶段该领域相关知识及数据的缺乏是因为这是一个新兴的、活跃的研究领域,新的文章正在不断发表。不过基于当前的研究资料,研究人员还是可以窥见未来研究的首要任务。其中有些建议相对明确且适用于化学品的评估,如关注高容量、高风险的ENMs。OECD的ENMs工作组目前正在对不同类型ENMs的排放及危害进行调查和评估,随后将会提出重要指导意见。同样,未来的研究首先应关注气体和液体中的ENMs,因为比起固体材料它们更容易传播,可通过呼吸和接触影响人体。
由于当前的研究大多基于实验室数据而非来自处理含ENMs产品的真实废弃物处理工厂,对现行处理装置的能效的评估仍需要深入的调查,这也包括那些在不发达国家盛行的未按标准规范运行的废弃物装置。
研究表明,基于当前不同废弃物处理工艺之间的联系,人们应当对残留物处理技术予以特别的关注。由于来自焚烧的飞灰及炉渣以及来自废水处理的污泥通常会被填埋处置,因此填埋场可能会聚集最大密度的ENMs。将含有ENMs的污泥应用于农业肥料以及使用含ENMs再生材料的风险方面目前受到的关注较少。
最后,有些领域的科学证据是相互矛盾的,如废水处理中的厌氧及脱氮工艺,还有一些领域的研究不够充分,如填埋工艺及一些急需深入研究的领域。
3.5 对WCNMs未来研究方向的建议
综合文献分析,推荐如下未来研究方向。
(1)确认并量化废弃物流中的人工纳米材料
◆ 明晰进入废弃物处理工艺的ENMs类型与数量。
(2)废弃物处理工艺中纳米材料的状态和结局
◆ 对配置完整废弃物处理系统且处理实际废弃产品的实际工业化工厂或中试装置进行绩效评估。
◆ 深入了解ENMs在废弃物处理工艺中的最终结果,特别关注以下领域：当前研究结论存在争议的领域(废水处理系统中的厌氧和脱氮工段,焚化炉的废气处理系统);参考资料不足的研究领域(循环回收设备,填埋)。
(3)通过残留物及/或原料回收导致的潜在ENMs排放
◆ 对在农业上应用含有ENMs的污泥可能产生的影响进行研究。
◆ 考察填埋工艺的有效性。
◆ 研究含有ENMs的次生材料的潜在危险。
(4)对于排放的控制及最优实用技术
◆ 确定最优实用废弃物处理技术控制或去除ENMs、防止工人与ENMs接触的有效性。
◆ 评估不规范废弃物处理技术(如不具备完备废气处理系统的焚烧炉,黏土垫层填埋场或不受控填埋等)。
◆ 探究可从废弃物流或残余废弃物中捕获、转化或清除ENMs的有效措施。
4 WCNMs的回收
本章节对回收工艺中纳米材料的归宿的认知现状进行了综述,明确了未来为实现环境无害化管理WCNMs所需要努力的方向,并就纳米废弃物所引发的相关风险、最优实用技术的有效性以及不规范废弃物处理所带来的后果等问题进行研究,明确当前主要知识空白以及未来可做进一步研究的领域。
今天,含纳米材料的商品正在不断增多[62],特别是在个人护理/化妆品/防晒类产品中屡见不鲜。这些未用完的产品及其包装以及其他含有纳米材料的产品,如电子设备、纺织品或复合塑料,最终都会成为城市或工业垃圾,再通过回收利用、能量回收、废弃物焚烧或填埋等方式进行处理。一般而言,回收优先于焚烧及/或填埋[63,64]。
当前含有纳米材料的产品与不含纳米材料的类似产品被一同回收,人们不会仅仅因为某种产品含有纳米材料而将其分离或单独回收。而且就目前的回收技术而言,消除WCNMs可能带来的潜在风险还未纳入考虑范围。
回收所采用的技术不能满足无害化环境管理的标准要求,回收的产品中含有纳米材料,这些不可避免地会引发涉及人体健康和环境安全问题的潜在风险。如果操作过程中缺乏环保标准,将会引发诸多问题。
本文旨在对纳米材料在回收中的归宿的认知现状进行回顾,对含纳米废弃物环境无害化管理的未来工作重点予以明确。
本章首先对回收在废弃物管理中的重要性进行解释,并确定主要的纳米材料;进而对纳米材料的归宿展开调查,分析WCNMs可能引发的问题,并对最优实用技术以及不规范废弃物处理带来的问题等方面进行阐述;最后确定知识空白以及未来潜在研究领域。
4.1 废弃物管理中回收的重要性
废弃物回收是实现废弃物产量最小化、废弃物污染防治[65]以及可持续性材料管理的重要举措[66]。世界各国及国际组织都在制定相关计划并采取相应对策确保实施。欧洲制定了相应法律[63],规定其成员国均有对其城市垃圾进行回收的义务。美国环保局则通过美国资源保护和恢复法对城市、工业、制造业、商业及危险品废弃物进行管理。实现对固体废弃物的有效管理需要国家、政府、地区以及地方实体的共同努力。
2011年OECD成员国城市垃圾平均回收率预估为33%(其中包括废弃物制堆肥份额),各国从不到10%至63%不等(OECD 统计数据1(1 http://stats.oecd.org/Index.aspx?DataSetCode=WASTE))。欧盟的总体材料回收率高达42%,各国水平从2%到70%不等[67]。
根据来源的不同,从城市和工业废弃物中回收的主要废弃物包括以下几类[68-70](另外,当前回收行业对从城市固体废弃物焚烧炉炉渣中回收金属及次生矿物质原料越来越感兴趣[71],它作为其中一项也被列出)。
◆生物垃圾
◆食物垃圾
◆玻璃制品(玻璃瓶)
◆金属
◆纸张及硬纸板
◆塑料(聚酯及其他塑料)
◆皮革及纺织品
◆废旧电子及电气设备
◆电池
◆木制品
◆建筑垃圾
◆报废车辆
◆轮胎
◆废弃物焚烧工厂的残余物(通过炉渣机械分离或酸洗飞灰的方式回收金属)
与纳米材料相关的废弃物可通过生产、分配、处理(使用)以及废弃物处理等渠道产生[72]。由于纳米材料应用的日益广泛,产品数量的逐渐增多,预计未来会出现越来越多的WCNMs,除了自然界中的纳米材料,工业纳米材料可能会越来越广泛地分布在我们周围。因此,如果对废弃物处理中排放的纳米材料的未来去向及可能产生的潜在风险没有充分的认知,将会导致管理上的缺陷。
4.2 产品中的主要纳米材料
在讨论纳米材料废弃物回收问题之前,有必要先将产品的类别及其所含的ENMs种类梳理清楚,因为最终成为纳米材料废弃物的正是这些物质。按照来源的不同,含纳米材料产品及其纳米材料类型汇总在表4.1,参考文献包括：消费类产品[62,73];建筑材料[74,75];纳米材料在复合塑料中的应用(纳米复合材料)[72]。
表4.1
纳米材料废弃物中的已知纳米成分
表4.1提供了消费产品中可能含有的纳米材料清单及产品实例。
4.3 纳米材料在回收中的归宿及潜在的泄漏问题
废物回收涵盖很多方面,可回收的材料种类繁多,回收方式多种多样,特殊废弃物及/或次生材料的回收技术不尽相同。本章后的附表说明了含有纳米废弃物的废弃物处理流,并对回收工艺以及所含纳米材料进行了简要描述。
附表1
废弃物处理过程中可能含有的纳米材料
4.4 废弃物中纳米材料的相关风险
WCNMs所携带的人工纳米粒子在回收反应过程中可能保持独立,也可能形成更大的聚集物。而与“纳米”相关的排放主要涉及二维或三维游离态纳米级物质(纳米粒、纳米纤维、纳米棒)。
◆ 纳米粒子可能穿过生物屏障
◆ 对于有毒物质,其毒性可能被增强
◆ 生物利用度增强
◆ 可能与“母体”材料具有不同的物理和化学性质
◆ 一些碳纳米管及纳米线可能与石棉纤维一样对肺部功能产生影响
◆ 必须对粉尘爆炸的危险予以关注(易燃粉尘)
在管理WCNMs时对可能发生的排放必须予以足够重视,特别是对那些在回收过程中易于排放的纳米物质。对于纳米材料废弃物的安全回收及处理指导意见在VCI (2012)中有所说明。
目前的大量研究工作还仅限于纳米材料对人类健康和环境的影响以及材料的毒性和生态毒性等领域[80,81]。“一些ENMs被证实确实会对健康和环境造成威胁,但是并非所有纳米材料都具有毒性。一些ENMs已经投入使用了很长时间(如炭黑、二氧化钛),事实证明其毒性很低。因此,颗粒越小越活跃毒性越强的假设并未得到数据支持。其实纳米材料与常规的化学品/材料一样,一些有毒一些无毒。只是现在对于纳米材料危害的鉴定还没有一个普遍适用的标准,因此建议逐一对纳米材料的危害进行评估” [82]。
由于纳米消费品种类繁多,很难设计并验证一个通用的风险评估及管理标准[80]。有研究显示消费品进入回收环节后可能会造成潜在危险[73,83,84]。对纳米材料的实例研究包括纳米银[85]、氧化锌及纳米纤维素(Nanosustain2(2 http://www.nanosustain.eu/component/content/article/1-latest-news/128-nanosustain-factsheet-and-case-studies))、二氧化钛[81]、二氧化铈、富勒烯、银、零价铁、二氧化硅及纳米黏土等。
由于相关研究较少,ENMs在纳米废弃物回收中引发的潜在风险依然充满诸多不确定性。最好的情况是利用数据做出初步评估[73]。相关研究中有一些关于潜在风险实例的报道,如碳纳米管——因其特殊的结构而可能导致肺癌的发生,用于纺织品及其他产品的纳米银——如果其以游离态进入自然界其抗菌特性可能对环境带来潜在影响。
废弃物中的ENMs之所以存在风险不仅仅源于纳米材料的毒性或生态毒性,也源于回收过程中的其他因素,未来需针对以下问题进行探究。
◆ 产品或废弃物流中ENMs的数量及密度。
◆ ENMs在产品中的结合模式：游离态?与其他材料相关联?被化学键固定?
◆ 在特定的回收操作下ENMs会不会被释放?
◆ “自由态”ENMs将保持单一纳米粒或纳米棒形态还是聚集成更大的单元?
◆ WCNMs通过回收工艺生成的次生材料(塑料或建筑材料)会否因其原料中携带的ENMs而被污染?
4.5 回收程序及最佳可行技术
依据最佳可行技术(Best Available Techniques, BAT)及最佳环境实践(Best Environmental Practices, BEP)[63,64,88],回收操作不应对环境造成不利影响。欧盟提倡在技术生命周期的所有阶段(包括概念的提出、研发、生产、分配、使用及最终的处理)对人类健康、环境、消费者、生产者可能面临的危害进行综合评估[89]。鉴于回收环节纳米材料的诸多不确定性,作为防范措施,这种评估可以降低暴露在ENMs中的可能性。
在回收操作中,人员与纳米材料接触的主要环节可能包括[73]：
◆ 与含有“自由”纳米物质的尘埃接触,其可能来自输送、筛选、粉碎、研磨及倾倒纳米材料废弃物过程。
◆ 清洗产品时通过液体媒介(水、溶剂)与纳米物质的接触;维修或清理设备时与纳米物质的接触。
◆ 未采取严格的职业防控时,与废气中的纳米物质或与通过热反应(加热、焊接、高温分级)排放至空气中的纳米物质的接触。
(1)源头处的技术措施。如：采用密封设备;减少粉尘及气溶胶的生成;直接在源头处提取粉尘埃及气溶胶;如果工作区域需要隔离、室内通风需要改造,可以对空气进行抽取过滤;回收设施的清洗可以采用合理设备进行吸尘处理或湿布擦拭而非吹扫清理。
(2)行政措施。如：缩短接触时间;降低接触人数;限制进入;对相关人员进行危险注意事项及防范措施的指导。
(3)个人防护措施。配备颗粒过滤器(P3)的呼吸防护装置;防护手套;封闭护目镜;防护服(无纺布)。
4.6 非标准处理废弃物的问题
Struwe等人将WCNMs分为两类[73]。
(1)异质成分WCNMs,即废弃物中包括不同的产品,产品中所含的纳米材料也不尽相同,有些成分甚至无从知晓。这类物质包括电子废弃物、报废车辆、纸张及塑料废弃物。
(2)成分相对均匀的WCNMs,其所含纳米材料可知且种类很少,如聚酯瓶、旧轮胎、锂电池。
可以看出由于第一类WCNMs的成分及所选用的回收技术比较复杂,因此对其排放的控制更困难(如电子废弃物、报废车辆、建筑及拆除废物)。
在废弃物处理3过程中采用最佳可用技术通常可降低污染的排放,从而降低人员与ENMs接触的可能。文献中所提及的在处理废弃物过程中最佳可用技术应具备的基本点列举如下。
◆ 建立环境保护体系以了解整个处理工艺,了解废物、一般废物以及经过处理设备后的次生产品。
◆ 保证存储装置规划于合理地理位置,配备适当的排放系统。
◆ 在封闭区域进行固体及污泥的卸载。
◆ 对可能产生排放物(臭气、灰尘、挥发性有机物)的原料实行粉碎、过筛等处理的区域应配备与去除设备相连接的抽取排放系统。
◆ 对来自污水净化厂的废水的合理管理。
◆ 空气排放的治理。
◆ 处理过程中产生的残余物的管理。
◆ 避免土壤污染。
这是由英国卫生与安全管理局提出的适用于电子废弃物回收的最佳可用技术及最佳环境操作规范,针对的是类似汞及铅类的物质而非WCNMs,但是该准则稍加修改同样可用于指导纳米材料废弃物回收工艺。
“多种产品混合后所包含的物质及材料众多,其中会含有一些危险物质(包括砷、镉、铅、汞及阻燃成分),这些电子废弃物的回收过程会导致一些威胁人类健康的问题,因此需要特别关注并妥善管理。危险之一即是人员与回收过程中排放的某些物质的接触(从荧光灯中排放出的汞,阴极射线管破裂后排放的铅及五氯化磷)。值得重点强调的是,如果采用的措施得力可有效防控与汞和铅的接触,那么对其他危险物质的防控也应如法炮制”4(4 英国卫生与安全管理局网站www.hse.gov.uk/waste/waste-electrical.htm.)。
纳米材料的回收可能存在同样的排放问题,因此也应采取充分的防控措施。
4.7 知识空白及可能的研究活动
建立安全环保的WCNMs回收工艺的主要挑战包括以下几点。
(1)对WCNMs源自回收过程的卫生、安全和环境问题的控制;
(2)对来自上游废物流可能携带ENM的次生材料的技术指标及环境质量的控制;
(3)鉴于ENMs的数量、经济价值及受关注度,对回收产品中的ENM进行技术开发。
表4.2
WCNMs回收领域存在的关键知识空白及相应对策
(未完，待续)
翻译：朱海峰 审校：马建华
The authors have declared that no competing interests exist.
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Understanding environmental impacts of nanomaterials necessitates analyzing the life cycle profile. The initial emphasis of nanomaterial life cycle studies has been on the environmental and health effects of nanoproducts during the production and usage stages. Analyzing the end-of-life (eol) stage of nanomaterials is also critical because significant impacts or benefits for the environment may arise at that particular stage. In this article, the Woodrow Wilson Center's Project on Emerging Nanotechnologies (PEN) Consumer Products Inventory (CPI) model was used, which contains a relatively large and complete nanoproduct list (1,014) as of 2010. The consumer products have wide range of applications, such as clothing, sports goods, personal care products, medicine, as well as contributing to faster cars and planes, more powerful computers and satellites, better micro and nanochips, and long-lasting batteries. In order to understand the eol cycle concept, we allocated 1,014 nanoproducts into the nine end-of-life categories (e.g., recyclability, ingestion, absorption by skin/public sewer, public sewer, burning/landfill, landfill, air release, air release/public sewer, and other) based on probable final destinations of the nanoproducts. This article highlights the results of this preliminary assessment of end-of-life stage of nanoproducts. The largest potential eol fate was found to be recyclability, however little literature appears to have evolved around nanoproduct recycling. At lower frequency is dermal and ingestion human uptake and then landfill. Release to water and air are much lower potential eol fates for current nanoproducts. In addition, an analysis of nano-product categories with the largest number of products listed indicated that clothes, followed by dermal-related products and then sports equipment were the most represented in the PEN CPI (http://www.nanotechproject.org/inventories/consumer/browse/categories/http://www.nanotechproject.org/inventories/consumer/browse/categories/ 2010).
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| [18] |
DOI:10.1007/s11051-014-2394-2
PMID:24944519
URL
Abstract Information related to the potential environmental exposure of engineered nanomaterials (ENMs) in the solid waste management phase is extremely scarce. In this paper, we define nanowaste as separately collected or collectable waste materials which are or contain ENMs, and we present a five-step framework for the systematic assessment of ENM exposure during nanowaste management. The framework includes deriving EOL nanoproducts and evaluating the physicochemical properties of the nanostructure, matrix properties and nanowaste treatment processes as well as transformation processes and environment releases, eventually leading to a final assessment of potential ENM exposure. The proposed framework was applied to three selected nanoproducts: nanosilver polyester textile, nanoTiO 2 sunscreen lotion and carbon nanotube tennis racquets. We found that the potential global environmental exposure of ENMs associated with these three products was an estimated 0.5-143 Mg/year, which can also be characterised qualitatively as medium, medium, low, respectively. Specific challenges remain and should be subject to further research: (1) analytical techniques for the characterisation of nanowaste and its transformation during waste treatment processes, (2) mechanisms for the release of ENMs, (3) the quantification of nanowaste amounts at the regional scale, (4) a definition of acceptable limit values for exposure to ENMs from nanowaste and (5) the reporting of nanowaste generation data.
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| [19] |
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| [20] |
DOI:10.1007/s11051-013-1692-4
URL
Engineered nanomaterials (ENMs) are now becoming a significant fraction of the material flows in the global economy. We are already reaping the benefits of improved energy efficiency, material use reduction, and better performance in many existing and new applications that have been enabled by these technological advances. As ENMs pervade the global economy, however, it becomes important to understand their environmental implications. As a first step, we combined ENM market information and material flow modeling to produce the first global assessment of the likely ENM emissions to the environment and landfills. The top ten most produced ENMs by mass were analyzed in a dozen major applications. Emissions during the manufacturing, use, and disposal stages were estimated, including intermediate steps through wastewater treatment plants and waste incineration plants. In 2010, silica, titania, alumina, and iron and zinc oxides dominate the ENM market in terms of mass flow through the global economy, used mostly in coatings/paints/pigments, electronics and optics, cosmetics, energy and environmental applications, and as catalysts. We estimate that 63–9102% of over 260,000–309,000 metric tons of global ENM production in 2010 ended up in landfills, with the balance released into soils (8–2802%), water bodies (0.4–702%), and atmosphere (0.1–1.502%). While there are considerable uncertainties in the estimates, the framework for estimating emissions can be easily improved as better data become available. The material flow estimates can be used to quantify emissions at the local level, as inputs for fate and transport models to estimate concentrations in different environmental compartments.
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| [21] |
DOI:10.1016/j.wasman.2010.08.004
PMID:20797842
Magsci
URL
Reinhart DR, Berge ND, Santra S, Bolyard SC.
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| [22] |
DOI:10.1016/j.envint.2013.04.003
PMID:23708563
URL
[Cite within: 1]
It can be concluded that in general, significant release of CNTs from products and articles is unlikely except in manufacturing and subsequent processing, tires, recycling, and potentially in textiles. However except for high energy machining processes, most likely the resulting exposure for these scenarios will be low and to a non-pristine form of CNTs. Actual exposure studies, which quantify the amount of material released should be conducted to provide further evidence for this conclusion.
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| [23] |
DOI:10.2217/nnm.10.61
PMID:20735233
URL
[Cite within: 2]
Among all environmental contaminants, those emerging from nanotechnologies constitute one of the most critical challenges for the coming years. The new properties of nanoparticles are at the heart of current scientific advances and the growing interest in harnessing them brings awareness of potential impacts that we cannot ignore. To date, scientists and industrialists have focused on the manufacture of nanomaterials more than on the assessment of the risks for humans and ecosystems. Few databases exist regarding the amounts released within ecosystems and no specific procedure of recycling has yet been established. However, nanoparticles cannot be considered as molecular pollutants or larger particles, and careful consideration is needed to establish a legal system that is specific. Their novel properties, surface energy and reactivity make it impossible to simply transfer our physicochemical, thermodynamic and toxicological knowledge from the micronscale to the nanoscale. This article highlights, nonexhaustively, the strong relationship existing between the unique properties of metallic and metal oxide nanoparticles and their biological effects on aquatic organisms.
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| [24] |
DOI:10.1021/es903757q
PMID:20222656
URL
A number of commercialized nanomaterials incorporate TiO(2) nanoparticles. Studying their structural stability in media mimicking the environment or the conditions of use is crucial in understanding their potential eco-toxicological effects. We focused here on a hydrophobic TiO(2) nanoparticle-based formulation used in cosmetics: T-Lite SF. It is composed of a TiO(2) core, coated with two successive protective layers of Al(OH)(3), and polydimethylsiloxane. Soon after contact with water (pH = 5, low ionic strength), the T-Lite SF becomes hydrophilic and form aggregates. During this aging, 90%wt of the total Si of the organic layer is desorbed, and the PDMS remaining at the surface is oxidized. The Al(OH)(3) layer is also affected but remains sorbed at the surface. This remaining Al-based layer still protects from the production of superoxide ions from the photoactive/phototoxic TiO(2) core in our experimental conditions.
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| [25] |
DOI:10.1016/j.envint.2010.08.005
PMID:20832119
Magsci
URL
Recent exponential growth in the development of nanomaterials (NMs) and nanoproducts is premised on the provision of novel benefits to the society-through the exploitation of their unique industrial and biomedical applications like medical imaging, fabrics in textiles, tissue engineering, nanocomposites, bioremediation, and biomedicine. These NMs and nanoproducts have increased in quantity and volume from few kilograms to thousands of tonnes over the last fifteen to twenty years, and their uncontrolled release into the environment is anticipated to grow dramatically in future. However, their potential impacts to the biological systems are unknown. Among the key present challenges in the waste management sector include the emergence of nanowastes; however, the effectiveness and the capability of the current systems to handle them are yet to be established. Because of limited studies on nanowastes management, in this paper, three-fold objectives are pursued, namely; (i) to raise concerns related to the alarming increases of uncontrolled releases of NMs into the environment through nanowastes, (ii) examine the unique challenges nanowastes pose to the waste management systems-both from technological and legislative perspectives, and (iii) summarize results of the first nanowastes classification formalism in order to elucidate the potential challenges of waste streams containing nanoscale dimension materials to the present waste management paradigm. Finally, the article closes by summarizing several proactive steps of enhancing effective long-term and responsible management of nanowastes.
|
| [26] |
DOI:10.1021/es901102n
PMID:19764246
URL
[Cite within: 1]
Abstract Titanium (Ti) occurs naturally in soils and as highly purified titanium dioxide (Ti5O2) in many commercial products that have been used for decades. We report for the first time the occurrence, characterization, and removal of nano- and larger-sized Ti at wastewater treatment plants (WWTPs). At one WWTP studied in detail, raw sewage contained 100 to nearly 3000 microg TVL Ti larger than 0.7 microm accounted for the majority of the Ti in raw sewage, and this fraction was well removed by WWTP processes. Ti concentrations in effluents from this and several other WWTPs ranged from <5 to 15 microg/L and were nearly all present in the < 0.7 microm size fraction. As Ti was removed, it accumulated in settled solids at concentrations ranging from 1 to 6 microg Ti/mg. Ti-containing solids were imaged in sewage, biosolids, and liquid effluent as well as in commercial products containing engineered TiO2. Single nanoparticles plus spherical aggregates (50 nm to a few hundred nanometer in size) composed of sub-50 nm spheres of Ti and oxygen only (presumably TiO2) were observed in all samples. Significantly larger silicate particles containing a mixture of Ti and other metal atoms were also observed in the samples. To support the field work, laboratory adsorption batch and sequencing batch reactor experiments using TiO2 and activated sludge bacteria verified that adsorption of TiO2 onto activated sludge biomass occurs. Monitoring for TiO2 in the environment where WWTP liquid effluent is discharged (rivers, lakes, oceans) or biomass disposed (landfills, agriculture and soil amendments, incinerator off-gas or residuals) will increase our knowledge on the fate and transport of other nanomaterials in the environment
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| [27] |
DOI:10.1089/ees.2012.0340
Magsci
URL
[Cite within: 3]
Engineered nanomaterials (ENMs) already occur in sewage and wastewater biosolids due to their release from commercial products (e. g., nanoscale titanium dioxide). Increasing levels and diversity of nanomaterials may enter sewage and wastewater treatment plants (WWTPs) in the future as they are released from products containing nanomaterials (e. g., coatings) embedded in products, or from industrial processes that use nanomaterials (e. g., polishing). Some metallic nanomaterials may dissolve (e. g., silver-, zinc-, or copper-based) or biodegrade (e. g., fullerenes) in wastewater, and subsequently sorb to settable biomass, precipitate as inorganic solids, or form stable aqueous complexes. Nanomaterials themselves sorb onto bacterial biomass in WWTPs, leading to their removal from water, but accumulation in biosolids that are disposed to land surface spreading fields, landfills, or incineration where their fate needs to be further considered. Because of the dense biological communities in WWTP unit processes, under typical conditions, >90% of the nanomaterials may attach to biomass, which is removed within the WWTP. Inclusion of membrane filtration to augment gravity settling has the potential to increase nanoparticle removals. At expected production/use levels, the presence of nanomaterials in biomass appears unlikely to influence current biosolids treatment processes (e. g., anaerobic digestion) or landfill biogas production. Additional research is needed to be able to monitor the transformation and removal of nanomaterials throughout WWTPs and biosolids treatment to assure they are not released into the environment where they may pose human or ecological risks.
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| [28] |
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| [29] |
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| [30] |
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| [31] |
DOI:10.1016/j.watres.2010.05.036
PMID:20547403
Magsci
URL
[Cite within: 3]
Sorption to activated sludge is a major removal mechanism for pollutants, including manufactured nanoparticles (NPs), in conventional activated sludge wastewater treatment plants. The objectives of this work were to (1) image sorption of fluorescent NPs to wastewater biomass; (2) quantify and compare biosorption of different types of NPs exposed to wastewater biomass; (3) quantify the effects of natural organic matter (NOM), extracellular polymeric substances (EPS), surfactants, and salt on NP biosorption; and (4) explore how different surface functionalities for fullerenes affect biosorption. Batch sorption isotherm experiments were conducted with activated sludge as sorbent and a total of eight types of NPs as sorbates. Epifluorescence images clearly show the biosorption of fluorescent silica NPs; the greater the concentration of NPs exposed to biomass, the greater the quantity of NPs that biosorb. Furthermore, biosorption removes different types of NPs from water to different extents. Upon exposure to 400 mg/L total suspended solids (TSS) of wastewater biomass, 97% of silver nanoparticles were removed, probably in part by aggregation and sedimentation, whereas biosorption was predominantly responsible for the removal of 88% of aqueous fullerenes, 39% of functionalized silver NPs, 23% of nanoscale titanium dioxide, and 13% of fullerol NPs. Of the NP types investigated, only aq-Cshowed a change in the degree of removal when the NP suspension was equilibrated with NOM or when EPS was extracted from the biomass. Further study of carbonaceous NPs showed that different surface functionalities affect biosorption. Thus, the production and transformations in NP surface properties will be key factors in determining their fate in the environment.
|
| [32] |
DOI:10.1021/es1041892
PMID:21466186
URL
[Cite within: 1]
We investigated the behavior of metallic silver nanoparticles (Ag-NP) in a pilot wastewater treatment plant (WWTP) fed with municipal wastewater. The treatment plant consisted of a nonaerated and an aerated tank and a secondary clarifier. The average hydraulic retention time including the secondary clarifier was 1 day and the sludge age was 14 days. Ag-NP were spiked into the nonaerated tank and samples were collected from the aerated tank and from the effluent. Ag concentrations determined by inductively coupled plasma-mass spectrometry (ICP-MS) were in good agreement with predictions based on mass balance considerations. Transmission electron microscopy (TEM) analyses confirmed that nanoscale Ag particles were sorbed to wastewater biosolids, both in the sludge and in the effluent. Freely dispersed nanoscale Ag particles were only observed in the effluent during the initial pulse spike. X-ray absorption spectroscopy (XAS) measurements indicated that most Ag in the sludge and in the effluent was present as Ag(2)S. Results from batch experiments suggested that Ag-NP transformation to Ag(2)S occured in the nonaerated tank within less than 2 h. Physical and chemical transformations of Ag-NP in WWTPs control the fate, the transport and also the toxicity and the bioavailability of Ag-NP and therefore must be considered in future risk assessments.
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| [33] |
DOI:10.1021/es101355k
PMID:20853883
URL
Bench scale studies were performed to evaluate removal and toxicity of copper nanoparticles (CuNPs) and copper ions in activated sludge biomass. The data indicated that, under the test conditions, copper nanoparticles were removed more effectively (95%) than copper ions (30-70%) from the wastewater. Mechanisms of CuNP removal were further investigated by equilibrating CuNP and copper ion in activated sludge filtrate (0.45 m). The predominant mechanisms of copper removal appear to be aggregation and settling (CuNP) or precipitation (copper ion) rather than biosorption. Most probable number (MPN) test data indicated that addition of 10 mg/L of copper ion was toxic to both coliform and ammonia oxidizing bacteria in the wastewater while no inhibitory effects were observed with the addition of the same amount of copper nanoparticles. Respirometry data indicated a 55% decrease in respiration rate when 10 mg/L ionic copper was added. However, no significant decrease in respiration rate was observed in the presence of copper nanoparticles. The toxicity of copper to activated sludge microorganisms appears to be a function of the concentration and characteristics of copper remaining in solution/suspension.
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| [34] |
DOI:10.1016/j.jhazmat.2011.10.086
PMID:22154869
URL
As engineered nanomaterials (NMs) become used in industry and commerce their loading to sewage will increase. In this research, sequencing batch reactors (SBRs) were operated with hydraulic (HRT) and sludge (SRT) retention times representative of full-scale biological WWTPs for several weeks. Under environmentally relevant NM loadings and biomass concentrations, NMs had negligible effects on ability of the wastewater bacteria to biodegrade organic material, as measured by chemical oxygen demand (COD). Carboxy-terminated polymer coated silver nanoparticles ( fn -Ag) were removed less effectively (88% removal) than hydroxylated fullerenes (fullerols; >90% removal), nano TiO 2 (>95% removal) or aqueous fullerenes ( n C 60 ; >95% removal). Experiments conducted over 4 months with daily loadings of n C 60 showed that n C 60 removal from solution depends on the biomass concentration. Under conditions representative of most suspended growth biological WWTPs (e.g., activated sludge), most of the NMs will accumulate in biosolids rather than in liquid effluent discharged to surface waters. Significant fractions of fn -Ag were associated with colloidal material which suggests that efficient particle separation processes (sedimentation or filtration) could further improve removal of NM from effluent.
|
| [35] |
|
| [36] |
DOI:10.1039/b926029c
URL
[Cite within: 1]
Detection and characterisation are two of the major challenges in understanding the fate, behaviour and occurrence of engineered nanoparticles (ENPs) in the natural environment. In a previous paper we described the development of hydrodynamic chromatography coupled to plasma mass spectrometry (HDC-ICP-MS) for detecting and characterising ENPs in aqueous matrices. This paper describes the applicability of the approach, to study the behaviour of silver nanoparticles in a much more complex and relevant environmental systemi.e.sewage sludge supernatant. Batch sorption studies were performed at a range of nanosilver concentrations. Following completion, the sludge supernatant was characterised by ICP-MS, HDC-ICP-MS and transmission electron microscopy (TEM). It was found that, after a contact time of 6 h, most of the silver had partitioned to the sewage sludge (>90%). However, of the silver remaining in the supernatant, some of this was in the nanoparticle form, implying that closer consideration should be given to the longer-term impact of the release of silver ENPs into aquatic ecosystems. These preliminary data clearly show the utility of HDC-ICP-MS for studying the occurrence and behaviour of ENPs in complex natural environments.
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| [37] |
DOI:10.1021/es101565j
PMID:20839838
URL
[Cite within: 1]
Nanosized silver sulfide (-Ag(2)S) particles were identified in the final stage sewage sludge materials of a full-scale municipal wastewater treatment plant using analytical high-resolution transmission electron microscopy. The Ag(2)S nanocrystals are in the size range of 5-20 nm with ellipsoidal shape, and they form very small, loosely packed aggregates. Some of the Ag(2)S nanoparticles (NPs) have excess S on the surface of the sulfide minerals under S-rich environments, resulting in a ratio of Ag to S close to 1. Considering the current extensive production of Ag NPs and their widespread use in consumer products, it is likely that they are entering wastewater streams and the treatment facilities that process this water. This study suggests that in a reduced, S-rich environment, such as the sedimentation processes during wastewater treatment, nanosized silver sulfides are being formed. This field-scale study provides for the first time nanoparticle-level information of the Ag(2)S present in sewage sludge products, and further suggests the role of wastewater treatment processes on transformation of Ag nanoparticles and ionic Ag potentially released from them.
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| [38] |
DOI:10.1038/nnano.2012.64
PMID:22609690
URL
[Cite within: 1]
More than 100 million tonnes of municipal solid waste are incinerated worldwide every year. However, little is known about the fate of nanomaterials during incineration, even though the presence of engineered nanoparticles in waste is expected to grow. Here, we show that cerium oxide nanoparticles introduced into a full-scale waste incineration plant bind loosely to solid residues from the combustion process and can be efficiently removed from flue gas using current filter technology. The nanoparticles were introduced either directly onto the waste before incineration or into the gas stream exiting the furnace of an incinerator that processes 200,000 tonnes of waste per year. Nanoparticles that attached to the surface of the solid residues did not become a fixed part of the residues and did not demonstrate any physical or chemical changes. Our observations show that although it is possible to incinerate waste without releasing nanoparticles into the atmosphere, the residues to which they bind eventually end up in landfills or recovered raw materials, confirming that there is a clear environmental need to develop degradable nanoparticles.
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| [39] |
DOI:10.1016/j.scitotenv.2011.12.030
PMID:22265599
URL
[Cite within: 1]
If nanotechnology proves to be successful for bulk applications, large quantities of nanocomposites are likely to end up in municipal solid waste incineration (MSWI) plants. Various studies indicate that nanoobjects might be harmful to human health and the environment. At this moment there is no evidence that all nanoobjects are safely removed from the off-gas when incinerating nanocomposites in MSWI plants. This paper presents a preliminary assessment of the fate of nanoobjects during waste incineration and the ability of MSWI plants to remove them. It appears that nanoobject emission levels will increase if bulk quantities of nanocomposites end up in municipal solid waste. Many primary and secondary nanoobjects arise from the incineration of nanocomposites and removal seems insufficient for objects that are smaller than 100nm. For the nanoobjects studied in this paper, risks occur for aluminum oxide, calcium carbonate, magnesium hydroxide, POSS, silica, titanium oxide, zinc oxide, zirconia, mica, montmorillonite, talc, cobalt, gold, silver, carbon black and fullerenes. Since this conclusion is based on a desktop study without accompanying experiments, further research is required to reveal which nanoobjects will actually be emitted to the environment and to determine their toxicity to human health.
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| [40] |
|
| [41] |
|
| [42] |
DOI:10.1016/j.wasman.2012.03.019
PMID:22608471
Magsci
URL
Escalating production and subsequent incorporation of engineered nanomaterials in consumer products increases the likelihood of nanomaterials being discarded in landfills. Although direct measurement of particle disposal has not yet occurred, life cycle assessments suggest that over 50% of nanomaterials produced will eventually reside in landfills. Laboratory-scale experiments were conducted to evaluate how organics (humic acid: 20-800 mg/L), ionic strength (100-400 mM NaCl), and pH (6-8) typical of mature leachates influence surface charge, relative stability, and mobility through representative solid waste environments. Results from the batch experiments suggest that the presence of high molecular weight organics, such as humic acid, acts to stabilize present in leachate, even at high ionic strengths (>100 mM NaCl). These results also suggest that in mature landfill leachate, as long as humic acid is present, ionic strength (when represented as NaCl) will be a dominant factor influencing nanomaterial stability. Column experiment results indicate the may be mobile through solid waste, suggesting particle placement within landfills needs to be examined more closely.
|
| [43] |
|
| [44] |
DOI:10.1021/es404946y
PMID:24870403
URL
[Cite within: 1]
Engineered nanomaterials (ENMs) are used to enhance the properties of many manufactured products and technologies. Increased use of ENMs will inevitably lead to their release into the environment. An important route of exposure is through the waste stream, where ENMs will enter wastewater treatment plants (WWTPs), undergo transformations, and be discharged with treated effluent or biosolids. To better understand the fate of a common ENM in WWTPs, experiments with laboratory-scale activated sludge reactors and pristine and citrate-functionalized CeO2 nanoparticles (NPs) were conducted. Greater than 90% of the CeO2 introduced was observed to associate with biosolids. This association was accompanied by reduction of the Ce(IV) NPs to Ce(III). After 5 weeks in the reactor, 44 卤 4% reduction was observed for the pristine NPs and 31 卤 3% for the citrate-functionalized NPs, illustrating surface functionality dependence. Thermodynamic arguments suggest that the likely Ce(III) phase generated would be Ce2S3. This study indicates that the majority of CeO2 NPs (>90% by mass) entering WWTPs will be associated with the solid phase, and a significant portion will be present as Ce(III). At maximum, 10% of the CeO2 will remain in the effluent and be discharged as a Ce(IV) phase, governed by cerianite (CeO2).
|
| [45] |
DOI:10.1021/es204540z
PMID:22533675
URL
[Cite within: 1]
Abstract Silver nanoparticles (AgNPs) are increasingly used as bacteriostatic agents to prevent microbial growth. AgNPs are manufactured with a variety of coatings, and their potential impacts on wastewater treatment in general are poorly understood. In the present study, Nitrosomonas europaea, a model ammonia oxidizing bacterium, was exposed to AgNPs with citrate, gum arabic (GA), and polyvinylpyrrolidone (PVP). GA and citrate AgNPs inhibited nitrification most strongly (67.9 3.6% and 91.4 0.2%, respectively at 2 ppm). Our data indicate that Ag(+) dissolution and colloid stability of AgNPs were the main factors in AgNP toxicity. In general, low amounts of dissolved Ag initially caused a post-transcriptional interruption of membrane-bound nitrifying enzyme function, reducing nitrification by 10% or more. A further increase in dissolved Ag resulted in heavy metal stress response (e.g., merA up-regulation) and ultimately led to membrane disruption. The highest effect on membrane disruption was observed for citrate AgNPs (64 11% membranes compromised at 2 ppm), which had high colloidal stability. This study demonstrates that coating plays a very important role in determining Ag dissolution and ultimately toxicity to nitrifiers. More research is needed to characterize these parameters in complex growth media such as wastewater.
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| [46] |
DOI:10.1016/j.copbio.2013.11.008
PMID:24863899
URL
Manufactured nanomaterials (MNMs) are increasingly incorporated into everyday products and thus are entering the environment via manufacturing, product use, and waste disposal. Still, understanding MNM environmental hazards and fates lags MNM industry growth. To catch up, keep pace, and influence future MNM safe design strategies, rapid safety assessments are needed. Bacteria are important ecological nanotoxicology targets to consider when assessing MNM safety: bacteria are exposed to MNMs in water, sewage, soils, and sediments, wherein they influence MNM fates; bacteria can also be impacted ith potential health and ecosystem consequences. Routinely using bacteria for assessing MNMs would promote effective management of the environmental risks of this rapidly growing industry, but appropriate protocols and policies for this assessment need to be instituted.
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| [47] |
DOI:10.1016/j.solmat.2006.12.009
PMID:19086204
URL
The recent advances in nanotechnology and the corresponding increase in the use of nanomaterials in products in every sector of society have resulted in uncertainties regarding environmental impacts. The objectives of this review are to introduce the key aspects pertaining to nanomaterials in the environment and to discuss what is known concerning their fate, behavior, disposition, and toxicity, with a particular focus on those that make up manufactured nanomaterials. This review critiques existing nanomaterial research in freshwater, marine, and soil environments. It illustrates the paucity of existing research and demonstrates the need for additional research. Environmental scientists are encouraged to base this research on existing studies on colloidal behavior and toxicology. The need for standard reference and testing materials as well as methodology for suspension preparation and testing is also discussed.
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| [48] |
|
| [49] |
DOI:10.1016/j.wasman.2012.01.009
PMID:22317796
URL
[Cite within: 1]
Abstract Silver nanoparticles (AgNPs, nanosilver) released from industrial activities and consumer products may be disposed directly or indirectly in sanitary landfills. To determine the impact of AgNPs on anaerobic digestion of landfill waste, municipal solid waste (MSW) was loaded in identical landfill bioreactors (9L volume each) and exposed to AgNPs (average particle size=21nm) at the final concentrations of 0, 1, and 10mgAg/kg solids. The landfill anaerobic digestion was carried out for more than 250 days, during which time the cumulative biogas production was recorded automatically and the chemical property changes of leachates were analyzed. There were no significant differences in the cumulative biogas volume or gas production rate between the groups of control and 1mgAg/kg. However, landfill solids exposed to AgNPs at 10mg/kg resulted in the reduced biogas production, the accumulation of volatile fatty acids (including acetic acid), and the prolonged period of low leachate pH (between 5 and 6). Quantitative PCR results after day 100 indicated that the total copy numbers of 16S rRNA gene of methanogens in the groups of control and 1mgAgNPs/kg were 1.97±0.21×10(7) and 0.90±0.03×10(7), respectively. These numbers were significantly reduced to 5.79±2.83×10(5)(copies/mL) in the bioreactor treated with 10mgAgNPs/kg. The results suggest that AgNPs at the concentration of 1mg/kg solids have minimal impact on landfill anaerobic digestion, but a concentration at 10mg/kg or higher inhibit methanogenesis and biogas production from MSW. Copyright 08 2012 Elsevier Ltd. All rights reserved.
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| [50] |
DOI:10.1021/es702916h
PMID:18605564
URL
[Cite within: 1]
Abstract The effect of natural organic matter (NOM) characteristics and water quality parameters on NOM adsorption to multiwalled carbon nanotubes (MWNT) was investigated. Isotherm experiment results were fitted well with a modified Freundlich isotherm model that took into account the heterogeneous nature of NOM. The preferential adsorption of the higher molecular weight fraction of NOM was observed by size exclusion chromatographic analysis. Experiments performed with various NOM samples suggested that the degree of NOM adsorption varied greatly depending on the type of NOM and was proportional to the aromatic carbon content of NOM. The NOM adsorption to MWNT was also dependent on water quality parameters: adsorption increased as pH decreased and ionic strength increased. As a result of NOM adsorption to MWNT, a fraction of MWNT formed a stable suspension in water and the concentration of MWNT suspension depended on the amount of NOM adsorbed per unit mass of MWNT. The amount of MWNT suspended in water was also affected by ionic strength and pH. The findings in this study suggested that the fate and transport of MWNT in natural systems would be largely influenced by NOM characteristics and water quality parameters.
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| [51] |
DOI:10.1021/es903059t
PMID:20184360
URL
The initial aggregation kinetics of single-walled carbon nanotubes (SWNTs) were studied using time-resolved dynamic light scattering. Aggregation of SWNTs was evaluated in the presence of natural organic matter [Suwannee River humic acid (SRHA)], polysaccharide (alginate), protein [bovine serum albumin (BSA)], and cell culture medium [Luria-Bertani (LB) broth] with varying solution concentrations of monovalent (NaCl) and divalent (CaCl(2)) salts. Increasing salt concentration and adding divalent calcium ions induced SWNT aggregation by screening electrostatic charge and thereby suppressing electrostatic repulsion, similar to observations with aquatic colloidal particles. The presence of biomacromolecules significantly retarded the SWNT aggregation rate. BSA protein molecules were most effective in reducing the rate of aggregation followed by SRHA, LB, and alginate. The slowing of the SWNT aggregation rate in the presence of the biomacromolecules and SRHA can be attributed to steric repulsion originating from the adsorbed macromolecular layer. The remarkably enhanced SWNT stability in the presence of BSA, compared to that with the other biomacromolecules and SRHA, is ascribed to the BSA globular molecular structure that enhances steric repulsion. The results have direct implications for the fate and behavior of SWNTs in aquatic environments and biological media.
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| [52] |
DOI:10.1021/es800329c
PMID:18767645
URL
[Cite within: 1]
Dissolved organic matter (DOM) has been reported to stabilize () suspensions, which increases concern over the subsequent and of . However, it is unknown exactly which compounds or functional groups cause the stabilization of in natural environments. Naturally occurring tannic acid (TA), which has a large number of aromatic functional groups, was used as a surrogate of DOM to investigate its interaction with . suspendability in TA solution increased with increasing diameter without the aid of sonication. Sorption affinity of for TA increased with decreasing diameter, positively related to their surface area. A two-stage sorption model was proposed to illustrate the interaction between and TA. TA molecules may be adsorbed first onto with aromatic rings to the surface carbon rings via -interactions, until forming a monolayer; the TA monolayer then further sorbed the dissolved TA by hydrogen bonds and other polar interactions. The sorbed TA increased the steric repulsion between individual , which might disperse the relatively loose aggregates and result in the stabilization of large-diameter in TA solution. The sorption and suspending processwere also examined bytransmission electron microscopy, providing further evidence for the above proposed -TA interactions. This study implies that widely distributed TA may promote the mobility and of in natural aqueous environments.
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| [53] |
|
| [54] |
|
| [55] |
DOI:10.1016/j.powtec.2013.08.025
URL
[Cite within: 1]
The increasing use of nanoparticles will inevitably result in their release into the aquatic environment and thereby cause the exposure of living organisms. Due to their larger surface area, high ratio of particle number to mass, enhanced chemical reactivity, and potential for easier penetration of cells, nanoparticles may be more toxic than larger particles of the same substance. Some researchers have been showing some relations between nanoparticles and certain diseases. However, the doses, surface shapes, material toxicity and persistence of nanoparticles may all be factors in determining harmful biological effects. In order to better evaluate their risks, potential exposure route of nanoparticles has to be taken into consideration as well. Finally, a brief summary of techniques for nanoparticle removal in waters and wastewaters is presented, but it seems that no treatment can absolutely protect the public from exposure to a large-scale dissemination of nanomaterials.
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| [56] |
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1)This study is aimed at analysing the likely route and extent of human exposure to carbon nanotubes (CNTs) via inhalation for a set of representative CNT-containing products in a lifecycle perspective. 2)The study has been conducted by the Safety of nanomaterial Interdisciplinary Research Centre (SnIRC), led for this study by the Food and Environment Research Agency, with participation of other Academic and Industrial Experts. 3)As part of the study, a review of all available CNT-containing products was carried out, and a representative subset of the products was identified for exposure analysis. The three CNT-containing products selected for the study included lithium-ion batteries, epoxy adhesive resins, and textiles. 4)The study assessed the suitability of current lifecycle assessment (LCA) protocols for assessing inhalation exposure from CNT and other nano-products. The relevance and adequacy of the relevant ISO protocols was assessed in relation to nanotechnology products (especially CNT-containing products), and any inadequacies have been highlighted. 5)The study also analysed the possibility of exposure to CNTs arising via inhalation during all stages of the life cycles of the selected study products. 6)The findings of the study indicate that: 6a)LCA is not a tool for exposure assessment. On the contrary, exposure assessments can provide information to LCA that is relevant for impact assessment of CNT releases. LCA is, however, useful in identifying the stages in the lifecycle during which exposure may be relevant. 6b)There is an almost complete lack of data to enable both a full-scale LCA, or a quantitative exposure assessment. Due to unavailability of the required data, a simplified LCA approach is adopted in this study, focusing on the potential inhalation exposure during the lifecycle of the selected CNT-containing products. Also, the exposure assessment is limited to qualitative analysis because of the lack of data necessary for a quantitative assessment. 7)Both LCA and exposure analysis have shown that the material synthesis stage (both for CNT materials, and CNT-containing products) is prone to giving rise to inhalation exposure to CNTs. However, the few studies carried out so far have generally shown that nanoparticle emissions during synthesis can be effectively controlled through appropriate engineering measures. Significant inhalation exposure to CNT material at this stage should be preventable provided such processes are carried out under appropriate emission control and waste management procedures. The main emphasis from the exposure point of view, therefore, needs to be on other stages/ processes in the lifecycle of products, where any sophisticated emission control measures are not likely to exist, e.g. during handling, transportation, accidental release, and use and disposal of the relevant materials and products. 8)Using the currently available level of scientific evidence, those stages in the lifecycle of each study product have been highlighted where inhalation exposure to CNT is possible. 9)In brief, the study has indicated that during post-production lifecycle stages: 9a)CNT-containing batteries will carry a risk of inhalation exposure during use only if the batteries are physically cut open. The main likelihood of exposure exists during accidental release (e.g. fire), and during recycling and disposal stages. People likely to be exposed will be those working at the recycling or waste disposal premises, or in the immediate vicinity. 9b)The use of the textiles, to which CNT is added on the outer surface of the yarn in a post-production coating process, is likely to pose a greater potential for exposure to CNT than any of the other processes studied. This is the only case where a significant consumer exposure during use stage seems plausible. Other lifecycle stages where there is a likelihood of exposure include recycling (shredding and milling of worn-out textiles), and disposal through incomplete incineration. Thus those likely to be exposed would include those working at the recycling or waste disposal premises, or in the immediate vicinity. 9c)CNT-containing epoxy adhesive resins may carry a risk of inhalation exposure during use only if there are conditions that lead to formation of aerosols. The main likelihood of exposure will be during disposal through incomplete incineration. It is also of note that epoxy resins generally have a relatively short shelf life (9 months in the case of the study product). There is therefore a need to develop a mechanism for appropriate disposal of the unused (unhardened, liquid) epoxy resin for appropriate disposal. 10)Common to all the three product types studied is the need for mechanisms for appropriate end-of-life treatments (e.g. separate collection of (spent) CNT-containing batteries, recycling of CNT-containing batteries and textiles under controlled conditions, and processes that ensure complete incineration of CNT in the disposed of products). 11)Urgent research is needed to address the almost total lack of exposure data for CNT-containing consumer products, and the appropriateness of end-of-life treatments. The findings of the research would also enable the manufacturers to develop safer products through better designs that are aimed at minimising the likelihood of exposure to CNTs (and/ or other nanomaterials) during subsequent stages in the lifecycle.
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DOI:10.1039/c0em00547a
PMID:21387066
URL
[Cite within: 2]
Abstract There is scientific agreement that engineered nanomaterial (ENM) production, use and disposal lead to environmental release of ENM. However, very little is known on emissions of ENM to the environment. Currently, techniques are lacking to quantitatively monitor ENM emissions to and concentrations in the environment, and hence data on emissions and environmental concentrations are scarce. One of the few available studies reports the detection of nano-TiO(2) in water leaching from exterior facades. Some experimental evidence is available on the release of nanosized materials from commercial textiles during washing. A handful of modeling studies have investigated ENM release to the environment. These studies modeled either the release of ENMs to the environment from ENM containing products during the consumer usage, or the release throughout the whole life cycle of ENM and ENM-containing products. Sewage sludge, wastewater, and waste incineration of products containing ENM were shown to be the major flows through which ENMs end up in the environment. However, reliable data are particularly lacking on release during ENM production and on the application amounts and empirical information on release coefficients for all life cycle stages and environmental compartments. Quantitative data linking occupational exposure measurements and ENM emission flows into the environment are almost completely missing. Besides knowing the amounts of ENM released into the environment, it is equally important to investigate in what form ENMs are released. First results show that much of the ENM released from products is present in matrix-bound form, but that also some fraction is released as single, dispersed nanoparticles.
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DOI:10.1177/0960327109105149
URL
[Cite within: 1]
Chances and risks of nanomaterials is a most fascinating challenge of future technologies. This new technology and their related materials are beneficial, for example, for energy reduction, lower emissions to the environment, and safe resources. However, there are concerns about health effects related to the very small dimensions of such materials. Because of our commitment to the principles of "Sustainable Chemistry" and "Responsible Care(R)," the chemical industry actively cooperates with all relevant stakeholders to assure a safe handling and use of nanomaterials. In this manner, the German chemical industry is committed to establish and disseminate best practices for a responsible production and use of nanomaterials. Protection of life and the environment is a fundamental principle for our industry. Even though in the European Union the existing legal framework for risk assessment for applies for nanomaterials, specific properties of nanomaterials may require amendments. The German Chemical Industry Association (Verband der Chemischen Industrie, VCI) has, therefore, issued guidance documents and recommendation papers to support companies in the sustainable and responsible development of nanotechnology-based applications. One of these guidance documents focused on ensuring the workplace safety of our employees. Background for this document was a joint survey on occupational health and safety in the handling and use of nanomaterials, which was conducted in spring 2006 from the German Federal Institute for Occupational Safety and Health (Bundesanstalt f r Arbeitsschutz und Arbeitsmedizin, BAuA) and VCI. The purpose of the survey was to obtain an overview of occupational health and safety methods currently applied in the chemical industry in activities involving nanomaterials. The questionnaire survey was evaluated by BAuA; the "Guidance for Handling and Use of Nanomaterials at the Workplace" was elaborated predominantly by VCI. This Guidance provides some orientation regarding measures in the production and use of nanomaterials at the workplace. The recommendations given there reflect the current state of science and technology.
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