Current US legislation on the environmental, health and safety impact of nanomaterials in coating products

Table of Contents

Abstract

List of Tables

List of Figures

List of Abbreviations

Acknowledgements

Dedications

1. Introduction
1.1 Background of the study
1.1.1 Nanotechnology
1.1.2 Coatings
1.1.3 Risk Regulations & Nanotechnology
1.2 Aim & Objectives of the Study
1.3 Boundaries of the study

2. Nanomaterials in Coatings in the USA Market
2.1 Nanomaterial Types Used in Coatings
2.2 Functional Benefits of Nanotechnology-based Coatings

3. Risks Posed by Coatings containing Nanomaterials
3.1 Hazards of Nanomaterials used in Coatings
3.2 Potential Releases
3.2.1 Potential Releases from the Nanomaterial Manufacturing Stage
3.2.2 Potential releases during the Material Processing Stage & NM-Coating Manufacturing
3.2.3 Potential Release of NMs from Coating Applications during Use Stage
3.2.4 Potential Release during the Incineration, Land-filling & Waste Water Treatment Stage

4. Life Cycle Regulations of Nanocoatings
4.1 Horizontal Issues across all Regulations
4.1.1 Absence of Nano-Definition
4.1.2 Failure of Reporting of Nanomaterials in Commercial Use and Fuzzy Commercialization Paths
4.1.3 No Standardized Methods
4.1.4 Poor Risk Communication
4.2 Pre-market Stage Regulations
4.2.1 TSCA Regulatory Issues
4.2.2 Ineffective Characterization at Different Life Cycle Stages
4.2.3 Federal Insecticide, Fungicide, and Rodenticide Regulatory Issues
4.3 Use Stage Regulations
4.3.1 Consumer Product Safety Act Issues
4.4 End of Life Regulations
4.4.1 Resource Conservation and Recovery Act Issues
4.4.2 The Comprehensive Environmental Response, Compensation, and Liability Act Regulatory Issues
4.5 Regulations along Lifecycle
4.5.1 OSHAct Issues
4.5.2 Clean Air Act & Clean Water Act Issues

5. Analysis & Discussion
5.1 Analysis
5.2 Discussion

6. Conclusions

7. References

Abstract

This study represents an analysis of the ability of current US environmental, health and safety regulations at a federal level to manage the risk posed by nanomaterials in coating products. Alongside the functional benefits from the use of nanomaterials in coating applications (e.g. antimicrobial, UV protection, anticorrosive, anti-scratch properties, etc.), there are concerns regarding the exposure of humans and the environment during the manufacture, processing, development, use and end of life stage of these materials. A life cycle paradigm is used, examining all regulations relevant to coating applications, identifying the issues in each regulatory framework but also, horizontal issues that govern all of them. This thesis makes an important contribution to the identification of which regulatory frameworks are the least effective and whether any changes are required.

Chapter 2 presents a list of nanomaterials which are used in coatings and the functional benefits that derive from their use. In Chapter 3, nanomaterial release from coating applications during the whole lifecycle are analyzed to evaluate potential exposure scenarios. This analysis aims to reveal the mechanisms of release and the possible exposure routes in each lifecycle stage. The released nanomaterials are likely to behave differently compared to the pristine (as produced) nanomaterials and more studies should investigate in more detail the potential hazards of nanomaterials at different stages of their lifecycle.

In Chapter 4, the US regulatory map relevant to coating applications is presented, and the specific issues in each statute discussed but also, cross-cutting issues across all lifecycle stages. The regulatory review draws out a number of issues regarding nanomaterials that need to be addressed towards a comprehensive regulatory scheme. Moreover, issues have been detected in the new proposed rule under Toxic Substances Control Act, the most relevant regulation to supervise coating products, which need to be addressed before the final promulgation.

Finally, in Chapter 5, the effectiveness of each regulatory framework based on simplistic method is assessed, by applying specific criteria appropriate to nanomaterials such as if nanomaterials are covered, if risk review is triggered, the availability and sufficiency of toxicological and exposure data, and risk communication effectiveness. According to these criteria, the preliminary regulatory screening show RCRA and CPSA are the most problematic regulations, followed by the CAA, CWA and CERCLA, the TSCA and at the end OSHAct. FIFRA has been found the most adequate regulatory framework. This analysis concludes that the capacity of the existing US regulatory system to address potential nanomaterial risk in coating applications is poorly able to do so. It also prioritizes the different statutes that need to be amended first, in the case of an incremental regulatory approach to ensure a better oversight. Prior to any regulatory change, regulators should focus to resolve the horizontal problems. But adequate regulatory authority is not the only requirement for a successful regulatory program. Sufficient resources of personnel and money and the will to use the resources and authority also are necessary.

List of Tables

Table 1: Coatings using nanotechnology

Table 2: Nanomaterials used in the coating industry according to the literature

Table 3: Potential release scenarios for MWCNTs during the material processing relevant to coatings production

Table 4: Potential release scenario for MWCNT during the coating manufacturing

Table 5: Causes of potential releases for coating and paints during their use stage

Table 6: Release Scenarios found in the literature for machining and usage phase of NMs in coatings

Table 7: Assessment criteria for all the regulatory frameworks along lifecycle of NMs. Red indicates that the issue is significant impact in the effectiveness of the regulation, yellow indicates that the issue is of moderate significance and green of low or no significance

Table 8: Rating ranges for all criteria

Table 9: Scoring ranges for all criteria

Table 10: Risk communication scorings

Table 11: Total scorings for each regulatory framework

List of Figures

Figure 1: Diagram of NRC risk assessment/risk management paradigm

Figure 2: Number of NMs by Use Category

Figure 3: NM stages incorporated in paint

Figure 4: Additional points where the human toxicological and environmental effects need to be investigated for NMs incorporated into coatings

Figure 5: Life cycle of nano-enabled coatings and paints

Figure 6: Federal regulation over the NM life cycle incorporated in coating products

Figure 7: Regulatory approach across the US EHS legislation

Figure 8: The adequacy of the current regulatory frameworks to effectively manage the safety of nanomaterials in coating products. Red indicates that significant challenges render the regulation the less effective and in practice ineffective for managing potential health and safety risks compared to the others. Yellow indicates that regulatory frameworks provide a basis for managing the risks but there are a number of issues that limit their effectiveness. FIFRA is considered as the regulation which provides an effective basis to manage the risks as only a few issues were found

List of Abbreviations

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Acknowledgements

I would first and foremost like to thank my supervisors Professor Teresa Fernandes and Helinor Johnston for their guidance and mentorship throughout my master’s thesis. I have learned much about interdisciplinary thinking, chemical legislation, and have expanded my horizons well beyond those defined by my engineering studies. I am thankful to Professor Isabel Cavaco for her invaluable role as a coordinator throughout my two years as a master’s student. In addition, I want to thank Professor Paolo Ricci with whom I have had the opportunity to work with and learn from. Lastly, I am also grateful to the European Commission for the scholarship funded within the Erasmus+ KA1 Programme, ref. 2013-0241 - Erasmus Mundus Joint Master Degree in Chemical Innovation and Regulation.

Dedications

To my parents, and my grandmother Panagiota Kostea

1 Introduction

1.1 Background of the study

1.1.1 Nanotechnology

Nanotechnology is science, engineering, and technology conducted at the nanoscale, which is between 1 and 100 nanometers[1]. Nanoscience is the study of extremely small things and can be used across all the other science fields like natural and life sciences and engineering[1]. Nanoscience and nanotechnology spreads not only the scientific literature, but also policy statements and includes the development of products with new and exciting properties[2]. Nanomaterials (NMs) are a diverse class of small-scale substances that are of size 1-100 nanometres (nm) in at least one dimension[3]. NMs include nanoparticles (NPs), which are particles with at least two dimensions between 1 and 100 nm in diameter [4, 3]. The area of the dot of this “ i ” alone can encompass 1 million NPs[5]. NMs are a broader category than NPs since NMs include NPs. NMs can be categorized in three types, natural, incidental and engineered[6]. Engineered NMs are designed to have specific properties and produced intentionally. Because of their nanoscale size, NMs may possess unique physicochemical and biological properties compared with larger particles of the same material that allow them to be used for different applications including for instance environmental remediation, batteries, fuel and solar cells, food taste and drug delivery[3]. These same properties also make their health and environmental effects difficult to predict. Assessment of NM safety is being conducted in parallel to their efficacy, but there are still many unknown regarding the risks posed by NMs to human health and the environment. Due to this scientific uncertainty, it is essential to consider whether existing regulations are adequate to address the potential health and safety risks associated with the increased production and use of NMs and NM-enabled products. This study will focus on engineered NMs, particularly the ones used in the coating industry. The use of NMs in this industry has the potential to offer many benefits to society. However, the risks associated with NM exploitation for this purpose must be assessed in parallel.

1.1.2 Coatings

According to the ISO 4618:2014; 2.50.1^[1], a coating is a layer formed by a single or multiple types of coating material(s) products; the term “coating materials” includes varnishes, paints and similar products. In to a substrate. From to the same standard (ISO 4618:2014; 2.50.1) “a coating material is a product in liquid, paste or powder form which, when applied, to a substrate, forms a layer possessing protective, decorative and/or other specific properties”. Coating materials are complex chemicals and in most cases, coatings consist of the following four types of ingredients [7]:

- Binders - They ensure that during the drying and hardening of the lacquer a coherent film is formed;
- Pigments and extenders - They are used as colorant. Extenders are used to create or modify certain physical properties;
- Solvents - Solvents are single liquids or blends of liquids that dissolve other substances to form solutions without reacting with these substances (except reactive solvents);
- Additives - They are used to modify a large variety of properties, for instance, its flow behaviour, surface tension, gloss, structure, UV and weather resistance;

The above are referred to ISO definitions, however, they are generally accepted by the U.S. authorities. Paint and coating products are commonly grouped into four categories according to the US Environmental Protection Agency (EPA)[8]:

- Architectural coatings include interior and exterior paints, primers, sealers, varnishes and stains that are applied on-site to new and existing residential, commercial, institutional, and industrial buildings;
- Industrial coatings are those that are factory-applied to manufactured goods as part of the production process. They are used to decorate and protect a wide variety of products, including motor vehicles, appliances, beverage cans, furniture, machinery and electrical equipment;
- Special-purpose coatings include marine paints, high-performance maintenance coatings, automotive refinish paints, transportation markings and aerosol paints. Such coatings are generally used where durability is a key objective;
- Allied paint products include putties, paint and varnish removers, paint thinners, pigment dispersions, paintbrush cleaners, and frit (ground glass or glaze).

1.1.2.1 History of coatings

Coatings and paints have been used for centuries in numerous fields of society. In a review of the history of paints provided by Gooch[9], it was claimed that the earliest reported paints originated in Europe and Australia approximately 20 millennia ago. More advanced coating technology based on polymeric coatings and paints was developed in ancient Egypt, and later in Greece, Rome and China. Ancient Egyptians used natural resins and wax to form coatings, and artists employed lacquers based on dried oils to protect their paintings. Ancient Egyptian scientists developed a very fine coating technology that showed similarities with nanotechnology. Contemporary industrial nano-based applications had their origins in the 1930s, in operations used to develop Ag coatings for photographic film[5].

Nowadays, there are probably a few thousand coatings, ranging from sim ple structures based on one or two coating steps to sophisticated structures based on multilayers and complicated instruments. However, some of these coatings may have an adverse effect on the environment and humans [10, pp. 3-4].

1.1.2.2 Nanocoating

Nanocoatings or “smart coatings” are tailor-made coatings that use NMs. Coatings are used in a large number of products; automobiles, ships, planes, façades, machinery, interior buildings, household appliances and furniture are a few examples of products and applications, showing their importance in society. The global paints and coatings industry generates upwards of $100bn in annual revenue by some estimates[11]. In terms of production, the US is the global leader, with five of the world’s top ten manufacturers based there according to coatingsworld.com [11], and these include: PPG Industries, Sherwin-Williams, DuPont, RPM International, and Valspar. To meet the ever-growing demands of modern coatings, the paint industry continuously strives to improve their products. As a result, nanotechnology will play an important role in the development of coatings.

Nanocoatings such as paints and lacquers, specifically, are the interface between the product and the external environment and consequently determine not only aesthetic features of goods, but moreover, other properties such as anti-corrosion, self-cleaning, chemical and anti-scratch, etc. [10]. The term “nanocoatings” is used when the coatings are nanostructured (containing NMs) or its thickness is in the nanoscale. Nanostructuring is generally applied because of its ability to enhance hydrophobicity and radiation hardness, but also because it makes materials more flexible[10].

1.1.3 Risk Regulations & Nanotechnology

The intense industrial activity in the USA in the 1960s raised concerns about environmental and health effects. As a result, the US Congress passed the first environmental laws authorizing science-based regulatory action to ensure the protection of public health and the environment [12]. In the following years, risk assessment has been developed as a concept to address potential human and environmental hazards, and has been instrumental to many federal agencies in investigating public health and environmental concerns[13]. Risk assessment determines the likelihood/probability of a substance causing harm following exposure. The risk assessment and risk management paradigm in Figure 1 (hazard identification, dose-response assessment, exposure assessment, and risk characterization) is recommended by the National Academy of Sciences have been used mainly by the Environmental Protection Agency, the Food and Drug Administration and the Occupational Safety, Health Administration[14].

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Figure 1: Diagram of NRC risk assessment/risk management paradigm[15]

To perform risk assessment under this paradigm, there are three sources where the authorities can obtain risk data: (1) government laboratories, (2) academic institutions and (3) industry. These risk data could be a result of toxicological (hazard) and exposure measurement tests. In addition, when data are scarce, alternative data generation methods are employed such as computer models[16] and Bayesian methods[17]. Conducting risk assessments is often associated with controversy and is a very complex task as authorities have to ensure they use appropriate scientific evidence to support certain assumptions[14]. The finding of such risk assessments (like acceptable risk doses, virtual safety, no observed effect level) which are based on actual or predicted toxicological and exposure data, leave ample room for discretionary choices and rules of thumb and are based on the agencies’ expertise[18]. However, when rigorous quantitative risk assessment is not possible using these tools, qualitative risk (quantification of the estimated likelihood in a risk characterization) screening may be performed as an alternative using available data and decision-analytic approaches[19].

While the industry is taking the advantage of the new opportunities offered by nanotechnology and developing new nano-enabled products, it is of vital importance that such products are developed in a safe and sustainable manner[20]. In the USA, the Nanotechnology Environmental Health Implications (NEHI) Working Group provides a forum for the National Nanotechnology Initiative (NNI) regulatory agencies^[2] to coordinate the agencies’ activities related to understanding the potential risks of NMs[21]. Despite the significant efforts made by the US authorities, legislators encounter a substantial challenge when dealing with nanotechnology. Pursuing regulatory oversight on nanotechnology products faces multiple hurdles due to various reasons. Three main reasons are: (1) the high scientific uncertainty over potential risks posed along product life cycle, (2) the “newness” regarding their environmental behavior as a result of size[22] and (3) the information gap on what NMs are being produced, in what quantities and how they are being handled, used and disposed of different applications[23]. The development of appropriate regulation demands a thorough understanding of the science of nanotechnology in regards to the impacts on human and environmental health and comprehensive overview of the commercial use of NMs[24].

1.2 Aim & Objectives of the Study

The rapid development of nanotechnology application in the coating industry, despite the new and innovative opportunities, raises concerns about the potential risks to human health and the environment. There is a broad range of regulations governing novel substances and chemical products introducing into the market and throughout their lifecycle so as to manage safely these types of risk. Nevertheless, none of these regulations specifically address the exploitation of NMs. As a result, there are regulatory challenges to assess and manage the implications of nanotechnology.

This project will analyse the suitability of the existing US regulatory system to manage the safety of NMs in coatings over their life cycle as well as will prioritize the regulatory frameworks which need to be amended in the future. Specifically, each relevant regulatory framework is reviewed to assess any shortcomings and how new challenges posed by NMs may create issues within each regulation and collectively over the entire set of regulations. The examination involved an evaluation of relevant federal regulations and governmental, non-governmental, and academic studies that investigate federal Environmental, Health and Safety (EHS) regulations and their applicability to NMs in coatings and paints. Mapping of the regulatory issues is then used to identify the gaps that occur as NMs move along their life cycle from the cradle to the grave.

Broadly stated, the main aim of the project is to examine whether the US existing regulatory regime is adequate to address any potential risks arising from the use of NMs in coatings. There are three specific objectives:

1. To identify the important issues and regulatory fault-lines that the application of NMs in coatings pose for US federal EHS regulations;
2. To recognise the most inter-dependant and cross-cutting issues across different regulations;
3. To examine the adequacy of each regulatory framework to manage the EHS of NMs in coating products along their lifecycle.

As such, this study will make an important contribution towards the identification of “which regulatory framework is the least effective, and whether any changes are required”, however it does not purport to provide exhaustive coverage of the sort of details and evidence that should inform such changes.

1.3 Boundaries of the study

Nanotechnology has quickly promoted the development of intelligent and innovative products that are nano-enabled, and have created an enormous growth potential for a significant number of industrial sectors[25]. Based on the application, different regulations are applied. Within this study, it is considered appropriate to focus on one application of NMs (i.e. coatings) and the relevant regulatory frameworks across product/NM lifecycle whenever the term coating is too broad and involve particular legislation items. However, it is difficult to distinguish between coatings and paints, thus a coating is considered as a broader term, with paints coming under the umbrella of coatings. Coating and more specifically paints applications were selected for two reasons. The first reason is the high exposure potential of the paint applications because of the large quantities in the market[26] and second the width of which nanotechnology is being used in coatings creating novel nano-enabled products.

As discussed above, coatings have a broad range of applications. The industry of coating is regulated by a myriad of regulations and laws[27] including the different laws in different US states which operate in conjunction with a number of other statutes and associated regulatory requirements. More specifically, nano-enabled paint applications which fall under the umbrella of nanocoatings will be examined in regards to the major federal regulations when the term “coating” is considered too broad. A discussion of individual state laws is beyond the scope of this study. There are also a number of different international chemical management agreements that impose obligations that might impact on NMs; these are generally reflected in the US regulations and it is not considered appropriate to be covered here as a separate topic. It is also important to mention that the application of ISO safety guidelines on NMs and other voluntary schemes are out of the scope of this study.

2 Nanomaterials in Coatings in the USA Market

The Woodrow Wilson Database is an inventory of nanotechnology-based consumer products in the United States. While it is not comprehensive, it is a “living” inventory that can be used as a resource in learning how nanotechnology is entering the marketplace. Currently^[3], the inventory contains 1,814 consumer products that have been introduced to the market with the large number of them originating from USA (746 products)[28]. According to the same Inventory, there are 47 NMs which are being used in the different consumer products in the US market. However, the data need to be used with caution, as the database suffers from the problem of insufficient available information[20]. Some of the products, claimed as nanotechnology products may not be derived by nanotechnology, whilst others may contain a nano-object, which is not declared as such[29] [30]. Currently, there is no compulsory labelling for products having nano- components.

Among the 1,814 nano-enabled products included in this database there are 114 coatings that are products of nanotechnology[28], which represents 6.2% of the total number of products. In reality most of the products in the Inventory can be readily purchased by consumers and are identified as nano-based by the manufacturer or other source, excluding a large number of other industrial nanocoating applications explaining the small total percentage. These coatings have various applications as can be seen in the Table 1. Thus, coatings are a cross-cutting category where different agencies with different regulatory frameworks are involved to address EHS requirements.

Table 1: Coatings using nanotechnology[28]

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In 2012, the largest markets for NMs were paints and coatings (19%), medical applications (14%), and electronics/optics (14%)[26]. Hence, it is clear the importance to investigate the adequacy of the regulations to manage the safety of the coatings and paints more profoundly regarding their environmental and human effects.

2.1 Nanomaterial Types Used in Coatings

There are a large number of NMs used in the coatings industry depending on the desired function and the final application. There are around 20 NMs used in coatings in the US-Canada market and 10 incorporated in paints (Figure 2, Table 2)[26]. Automobile, construction, consumer goods, glass, cosmetics, food contact, optic, wood preservatives, plastics are among the industries in which nanocoatings can be found. Many novel nano-coating applications might use NMs; however it is not possible to track all the types of NMs. A recent survey demonstrated that for nano-TiO2 about 10 to 30% of the global production are used in paints and coatings, for nano-zinc oxide 30%, for CeO2 5 to 10% and for nanosilver 10 to 30%[31].

Figure 2: Number of NMs by Use Category[26]

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Table 2: Nanomaterials used in the coating industry according to the literature ([32],[33],[34],[7],[28] )

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2.2 Functional Benefits of Nanotechnology-based Coatings

Nanocoatings have been introduced by various manufacturers, with the promise of addressing some of the functional and environmental challenges associated with conventional coatings. Sometimes the benefits resulting from the presence of NMs in the coating itself and other the actual size of coating structure is in nanoscale. But the former one is mainly used.

In general, nanocoatings offer better material and processing properties than conventional coatings[7] towards more cost effective, environmental friendly and sustainable solutions. There is a broad spectrum of functions in various industrial branches that can be improved by the use of nanocoatings. Below are presented some examples of the functional benefits of NMs in coating applications.

Multi Walled Carbon Nanotubes (MWCNTs) can be used as additives to improve the mechanical, electrical and thermal conductivity properties of the coating and contribute to significant weight reduction resulting in energy and resource savings[35]. The primary industry that employs MWCNT-enabled coatings is the automotive industry. MWCNTs can also be used as coating material itself[36]. When equipment is exposed to loading conditions, they need to be protected from permanent deformation. In these cases, the equipment could be coated with a material to provide protection from the external forces. The protective coating may shatter and it needs to be replaced with the base equipment to stay unaffected during the process. Nanocoating with enhanced mechanical properties such as coatings with MWCNTs as a component could be used without the need of replacement.

Graphene-nanosheets are used in paints and polishes[10]. Graphene nanosheets are utilized in many nano-films due to their unique thermoelectrical properties such as antistatic effects. They are also known for their structural properties, imparting superior mechanical properties such as the enhanced mechanical interlocking with polymer surfaces affording better interaction and adhesion with the host matrix[37].

Many coatings such as lacquers and other hygiene applications use NMs for their antimicrobial properties. NMs with such effects include biometals such as silver, copper and zinc but also metal oxides such as TiO2, ZrO2, SnO2, ZnO and SiO2. These nanoscale substances can also be functionalized by organic or organometallic molecular structures capable to connect ions of the transition biometals, such as silver and copper ions, offering new complex antibacterial nanosystems[38]. Particularly, TiO2 NPs are used in the manufacture of photocatalytic coatings. Adding anatase-TiO2 NPs to many materials creates highly reactive hydroxyl radicals (OH-) via photocatalysis, initiating the desired oxidation reactions. This results in products with self- cleaning and air purification effects[39].

Oxide NPs such as SiO2, ZrO2, and TiO2 can be used for improved scratch and abrasion resistance of coatings [40, 41]. Other metal oxides’ functional benefits include surface conductivity, supermagnetism, superhard properties of metal alloys, superhydrophobic and size- dependent electrical properties [42, 37]. Due to the superhard properties, silicon nitrite (Si3N4) nanocomposites can find many industrial applications as coatings on metal working and cutting tools too[43].

Functional benefits also achieved sometimes as a result of the manufacturing method, producing the coatings in nanosize. In some studies[37],[44], it was found that the scratch hardness increase with an increase in a silica NP composite coating thickness.

Moreover, the fact that some NMs have size below the critical wavelength of light renders them transparent, a property that can be exploited in coatings[5]. The transparency of these NMs such as TiO2 results in the development of additives with new properties to otherwise non-transparent coatings[7].

Coating and paints belong in the first generation of nanotechnology development, the so-called passive nanostructures[45]. According to the US EPA[46], it is the end of the basic research and the development of this first generation of materials. Thus, most of these applications are already commercialized[47] or will be commercialized in the near future. However, in terms of efficacy and safety there is still ample room for research in the development of passive nanostructures. Apart from the functional benefits from the use of NMs, there many other commercial factors that are critical to market success such as safety, cost and reliability.

3 Risks Posed by Coatings containing Nanomaterials

Understanding NM source emission and identifying the potential hazards from the released NMs is a key point for making safer^[4] coating products. Various studies are examined in this chapter in order to identify all the possible release sources and mechanisms during the production, use phase, post application/service life and final disposal of nano-based coatings. Studying the mechanisms of release and the inherent characteristics of each NM is essential for assessing their risks to the environment and human health. However, to assess the risk of every NM with different physicochemical properties on a case-by-case basis examining all human and environmental exposure scenarios is impracticable[48]. Source emission is a key point of the NM release for the regulatory approach, the market and generally the social acceptance of nano products[49].

3.1 Hazards of Nanomaterials used in Coatings

The Renaissance scientist Paracelsus (credited for founding the discipline of toxicology) explained that “the dose makes the poison”[50]. Alcohol or even simple water can kill people if ingested in excessive amounts[51]. All substances can cause toxic effects, but some cause toxic effects at much lower exposure levels than others. The same is true for NMs. NMs are similar to conventional chemicals in that some may be toxic and some may not[52]. Hence, the term “nano” itself does not represent an intrinsic hazard characteristic.

The human health and environmental hazards have been demonstrated for a variety of manufactured NMs in laboratory tests. For instance, laboratory studies using simulated solar radiation show that photo-catalytically active TiO2 NM has some toxic effects on aquatic organisms such as daphnia magna and Japanese medaka due to the production of free oxygen radicals[53]. Carbon nanotubes present some toxicological properties in common with asbestos and thus, concerns exist regarding that human exposure may lead to some of the same diseases associated with exposure to asbestos[54]. Moreover, the toxicity from carbon nanotubes exposure has been reported in many aquatic species[55] and numerous studies have shown aquatic toxic effects of nanosilver[56] [57]. Ecotoxicological data are also available for other NMs that may be contained in coatings, for example, nanoscale zinc oxide, iron oxide, other metal oxides, carbon black, and nanoclays[7]. Regarding human health, the toxicity of certain metal oxides in nanoscale size that could be used in coatings has been demonstrated to have inflammogenic, oxidative, and genotoxic effects[58]. In the scientific literature, there are plenty of studies regarding the toxicity of NMs and many more studies are ongoing, investigating their physico-chemical properties which drive their toxicity and the mechanism of NM toxicity. Whether the obtained data are appropriate and what existing data can be used are questions that remain open[59]. In most cases there is insufficient information regarding possible adverse effects to come to a final conclusion, in particular with regard to long-term exposure[7].

The vast body of experimental work with NMs has been conducted mostly with pristine NMs, the as-manufactured form[60]. However, a study[61] showed that the released NMs from paint products were mainly identified as paint-matrix fragments, which are different to the pristine particles and hazard studies for nano-SiO2 need to take this into account as modifications to the NMs are likely to influence the biological response. Similarly, the NanoHouse Project[62] states that the released NM behaviour from paints during weathering is observed to be different compared to the pristine NM and may not necessarily be predicted by studying the pristine materials[63]. As a result, hazard studies based on the pristine material cannot necessarily be used directly to assess the risks associated with the release of NM in the coating and paint products, and more research need to be conducted.

While there is a lot of information on the hazard of free NMs, only a minor number of studies have investigated the adverse impacts of NMs when part of a matrix, their release and their environmentally transformed phase. However, a study[64] focusing on TiO2, Ag and SiO2 NPs embedded in a complex paint matrix observed no significant toxicological change compared to the pristine NPs. More information is needed towards a clear conclusion.

The purpose of NanoKem^[5], a Danish project for the safety of coatings, was to investigate how the incorporation of NMs of the same larger particle chemical in paints and lacquers and fillers affects risk of exposure and adverse health effects. The impacts of sanding dust from a number of identical paints with and without incorporated NMs were tested in the project. The tested products were eight different NMs and thirteen samples of dust acquired by sanding different boards, painted with five conventional products without NMs and eight versions with NMs[65]. Sanding dust from paints for both, NMs and NMs-free samples, were tested in order to compare any effects associated with the possible release of NM[66]. Results showed that some of the paints with nano-components had an increased formation of particles in nanoscale size compared to the reference paint[66]. Sanding dust from nanotechnology-based paints or lacquers did not result in significant increased inflammation or DNA damage in comparison to dust from conventional samples, even though some of the added NMs induced inflammatory responses in mice when dosed as pristine NM and some induced DNA damage[67]. Nonetheless, when comparing diverse paint and lacquer matrices, the genotoxic effects differed between the paint and lacquer types. Dusts from both lacquers (with and without nano-SiO2) and the acrylic-based reference paint had increased level of DNA damage in mice (24 hours after intratracheal instillation of a single dose of 54 μg), while dust from polyvinyl acetate-based paint did not demonstrate increased level of DNA damage compared to vehicle exposed mice[66].

Based on the preliminary screening in another study[68], TiO2 NPs and sanding dusts from the corresponding paints with and without nano-TiO2 were tested for dose-response relationship because TiO2 NPs were found to be inflammogenic and genotoxic in a mice model. TiO2 NPs have been observed to induce DNA and chromosomal damage in mouse liver following exposure via oral route[69] [70]. The result was that there was no different effect of adding TiO2 NPs to the paint in comparison to the reference paint for any of the measured toxicological endpoints [68].

In another similar study[71] the sanding dusts with and without NMs had similar toxicity. The same outcome was reached in another recent study on the toxicity of NPs embedded in a paint matrix[72]. The few toxicity data of sanding dust from paints and lacquers is in good agreement with each other. No additional toxicity has been detected for any of the nano-paints compared to the corresponding products without NMs.

The key issue is whether the dust released from the paints has an increased or decreased reactivity or toxicity relative to the pristine material, and if any differences are due to their NM content. However, four different stages exist of NMs incorporated in paints, as outlined in Figure

3 Figure 3below that could reflect diversified properties and thus diversified hazards. In most cases, at the material processing stage, the pristine NMs are modified before they are embedded in the final product[73]. For instance, MWCNTs undergo physical and chemical processing before they are incorporated into flame retardant coating applications. Commercial MWCNTs that have not been purified can contain large amounts of impurities, such as amorphous carbon, graphite, and encapsulated metallic particles[74]. Moreover, before application MWCNTs generally require surface functionalization[75]. Functionalization, the modification of materials by covalently or non-covalently attaching new molecular components to the surface, can alter the physicochemical properties of MWCNTs dramatically and thus their behaviour[76] [77] [78]. It is understood that the physical, chemical and biological properties of NMs in the products differ from those NMs from which they are made[60]. The same stands for the release phase in the environment where several alteration and transformation processes can act. The environmental behavior of released NMs has been investigated in one study[62] in order to assess the reactions in water and soil-plant system. The results showed that the released NMs in paints behave differently compared to the pristine particles in natural waters. Hence, toxicity studies should investigate profoundly the hazards posed by the NMs in paints based on the different phases in order to reach the right conclusions. The points with the higher safety concerns are presented in the Figure 4.

Figure 3: NM stages incorporated in paint[60]

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Figure 4: Additional points where the human toxicological and environmental effects need to be investigated for NMs incorporated into coatings[60]

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3.2 Potential Releases

Release of NMs from coatings and paints might take place throughout the coating life-cycle, depending on the manufacturing, use of the product in specific environments, and its disposal off at the end of life[79]. It is necessary to consider all the continuum of activities involved in the production of coatings and paints containing NMs, but also, the use and discard so as to inform the consideration of potential release scenarios.

3.2.1 Potential Releases from the Nanomaterial Manufacturing Stage

This is the first stage where possible release and hence exposure to the workers can take place. Release and consequently exposure to NMs is related to the mechanical and chemical process undergone by the material and the type of the material. NMs are either produced top-down by milling and grinding of bulk material or bottom-up starting from nucleation with subsequent particle growth by condensation and/or coagulation[80]. Generally, two parameters influence the release[81]:

- Production via the gas or liquid phase;
- Production in an open or closed process.

The liquid phase process which does not involve airborne NMs is the safer option as it was less likely that the NM would be inhaled during the manufacture. The physical state of the NM, in suspension or powder, was an important determinant of exposure with the former significantly decreasing the potential for release[82]. Various studies have indicated that workers are most likely to be exposed to free NMs during the production of dry powders[81]. Potential exposure routes are dermal, inhalation and ingestion (e.g. hand to mouth contact).

In addition, wastes containing NMs are generated from the production of NMs. As a result indirect exposure may occur to the general population, not only the workers, since NMs can be found in different environmental compartments. Particularly, inhalation exposure is one the most important routes of entrance into the human body because these nanosized particles suspended in the air can spread over long distances from their release, resulting uncontrollable human exposure[83].

3.2.2 Potential releases during the Material Processing Stage & NM-Coating Manufacturing

The manufacture of paints and other coatings includes a series of operations. There are few or no chemical reactions; the operations are mostly mechanical. Typically, the manufacture involves the assembling of raw materials, mixing, dispersing, thinning and adjusting, filling of containers and warehousing[84].

During the recovery, processing, handling, and packaging stages, NMs are more likely to be released. For example, potential release scenarios for MWCNT prior to incorporation in a coating during the material processing stage are outlined in Table 3. The most critical phase for air and water releases during the formulation stage is the discharging and the cleaning of the mixing chamber[42].

Table 3: Potential release scenarios for MWCNTs during the material processing relevant to coatings production ([74], [85],[86],[87],[88] )

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Few data are available that describe NM releases from the commercial-scale manufacture of nanocoatings. To estimate environmental emissions of NMs, worker exposure measurements per se are not relevant. Such measurements are not utilizable since any data about the NM volume or flow into at least one environmental compartment is considered. Hence, the mass flow per unit time of the pollutant reaching an environmental compartment is needed. Environmental releases during nano-coating manufacturing can occur a result of the following activities: weighting, mixing, handling/packaging, cleaning, the same as during the material processing stage.

Application of nano-coatings to surfaces also could lead to air or water releases. Once the NMs are released e.g. to indoor air such substances is likely to enter eventually the environment[89]. Any spray application could lead to the potential airborne releases of matrix-bound NMs if the application does not occur in a closed environment. For example, one study observed airborne release of both NMs and fine particles when spraying an MWCNT suspension onto wafers as a coating[86]. If the coating is applied by soaking the surface, water release of matrix-bound NMs could occur when the surface is rinsed[90]. Additional cutting, shaping, stapling, and other finishing processes could result in the airborne release of free or matrix-bound NMs through abrasion. Similar to the above, Table 4 outlines potential release scenarios from a MWCNTcoating manufacturing stage used as a flame retardant.

Table 4: Potential release scenario for MWCNT during the coating manufacturing[90]

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3.2.3 Potential Release of NMs from Coating Applications during Use Stage

The possible release of NMs from coatings and paints has been subject to various studies. Simulation of real conditions and the evaluation of nano-object release into different compartments were the common basis in all the studies [91, 92]. During abrasion, sanding and aging processes particles smaller than 100 nm were released in most of the cases. Different surfaces like wood, plastic, bricks and different types of stress were tested. Results showed a considerable generation of NMs during the sanding processes[91]. However, some other studies indicate that no significant difference could be observed between coatings containing and not containing NM additives[80].

The identification of the causes of potential release is a crucial point for these studies. The type and the amount of NMs, binder and pigments affect the NM release. The binder is one the most important factors that influence the release of NMs[93]. Table 5 presents some other potential causes of NM release from coating and paints. NM behaviour is another important factor in their release to the environment which highlights that proper characterization of the NM is vital. Specifically, in the[92] study for which different pigment materials and different NMs were used, showed that the sample material, the sample composition, the sample condition (e.g. weathering state) and the type of mechanical treatment have also a strong effect on the particle release. Despite occasional high numbers of released NMs, no free NMs were observed in the study.

In another study[94] the release of NMs during operations related to the handling of and processing of nano-coated automobile part were investigated. The results found that the release of NMs increased with the wear energy applied on the surface. The particles emitted by scratching were mainly in the size range of 10-500nm with total number concentration of approximately 10 particles per cm[3]. Peak concentrations during sawing reached 1,000 particles / cm[3] and 900 particles /cm[3] during sanding[94].

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^[1] Available at: https://www.iso.org/

^[2] The NNI is comprised of 26 federal agencies

^[3] Day accessed: 20/03/15

^[4] “Safe” is defined as a level of acceptable risk

^[5] More information at: http://www.arbejdsmiljoforskning.dk/