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Green Chemistry

Green chemistry is the science and practice of designing chemicals, products and processes in order to reduce or eliminate the generation and use of hazardous substances. Like the related field of green engineering, green chemistry seeks to protect human health and the environment by applying sustainability principles at the design phase of a process or a product, where they can have the greatest impact and be most cost-effective.[175]

Green chemistry is a transdisciplinary field encompassing elements of chemistry, engineering, biology, toxicology and environmental science. This nexus across disciplines is essential for focusing on the complex questions associated with sustainability and for providing the tools needed to answer those questions. Green chemistry is guided by a set of principles that encourage the creation of safer, more efficient, and more sustainable designs for chemical products, feedstocks, and processes.[176]

Inherent Property Analysis

Inherent property analysis is an emerging tool used to support green chemistry. It focuses on the “inherent” properties of chemicals, materials, products, processes, or systems that are relevant to sustainability. The information gained through an inherent property analysis may help maximize positive characteristics (e.g., recyclability) or reduce or eliminate undesired characteristics (e.g., toxicity) during the design phase.[177-179] For example, certain materials and substances are inherently benign (under normal exposure scenarios) because they pose no known acute or chronic risks to humans or other organisms. Other materials (e.g., metals) are inherently recyclable because they can be reduced to their elemental form.[180]

In the context of green chemistry, inherent property analysis facilitates incorporating inherent chemical properties into integrated testing, assessment, and management approaches. Such properties include structure, composition, size, and solubility, in the case of chemical compounds, or surface area, surface charge, and aspect ratio, in the case of particles. These properties may determine a chemical’s mobility, persistence, and bioavailability, thus influencing exposure and uptake of the chemical by humans or other species. They also may influence the degree to which chemicals or particles interact with biological processes in ways that can lead to human disease or adverse effects in wildlife species.[181] While inherent property analysis is still an emerging method, it can contribute to developing chemical products that have inherently lower risks of adverse human or environmental impacts. Beyond its use in green chemistry, inherent property analysis can also be used as a screening tool to determine if environmental challenges require the application of additional assessment tools.

Green Chemistry

How can Green Chemistry contribute to Sustainability?

The principles of green chemistry can be applied across the entirety of a chemical product’s life-cycle, including the product’s design, manufacture, use, reuse, and ultimate disposal. This approach reduces the potential for chemical products to manifest hazard, including physical, toxicological and global endpoints.

What are the main steps in Green Chemistry?

A variety of methods have been developed to advance green chemistry, including decision support tools, assessments, and complementary databases. These tools support the green chemistry philosophy of “benign by design” by characterizing the structure-hazard relationship in chemicals, products, and processes. Although no standard green chemistry methods have been established, the Center for Green Chemistry and Green Engineering at Yale University has proposed Twelve Principles of Green Chemistry.[182] These principles provide a framework for implementing green chemistry in research and product development.

Twelve principles of green chemistry.


Principle

Description

Prevention

It’s better to prevent waste than to treat or clean up waste afterwards.

Atom Economy

Design synthetic methods to maximize the incorporation of all materials used in the process into the final product.

Less Hazardous Chemical Syntheses

Design synthetic methods to use and generate substances that minimize toxicity to human health and the environment.

Designing Safer Chemicals

Design chemical products to accomplish their desired function while minimizing their toxicity.

Safer Solvents and Auxiliaries

Minimize the use of auxiliary substances wherever possible and make them innocuous when used.

Design for Energy Efficiency

Minimize the energy requirements of chemical processes and conduct synthetic methods at ambient temperature and pressure if possible.

Use of Renewable Feedstocks

Use renewable raw material or feedstock whenever practicable.

Reduce Derivatives

Minimize or avoid unnecessary derivatization if possible, which requires additional reagents and generates waste.

Catalysis

Catalytic reagents are superior to stoichiometric reagents.

Design for Degradation

Design chemical products so they break down into innocuous products that do not persist in the environment.

Real-time Analysis for Pollution Prevention

Develop analytical methodologies needed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.

Inherently Safer Chemistry for Accident Prevention

Choose substances and the form of a substance used in a chemical process to minimize the potential for chemical accidents, including releases, explosions, and fires.

 

Applying the principles of green chemistry across the entire life-cycle of a chemical, product or process can reduce reliance on post priori risk assessment or management approaches. The goal of green chemistry is to produce a chemical that does not manifest hazard under normal and expected exposure scenarios and, thus, contributes to sustainability.

Sustainability tools that complement green chemistry include risk assessment and chemical alternatives assessment. The first two elements of risk assessment, hazard identification and dose-response assessment are critical to identifying the intrinsic toxicity and potency of a molecule, information that informs implementation of the green chemistry principles listed above.

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What are the strengths and limits of Green Chemistry in a sustainability context?

As a non-regulatory approach to safer chemical design, green chemistry promotes innovation and accelerates adoption of new chemistries and new products. It puts into practice the ideas that prevention is better than later treatment, that products and processes can be designed to use fewer hazardous chemicals, that safer alternative chemicals should be used wherever possible, and that more efficient, more durable, and more renewable products and processes can be created.[183] In addition to contributing to sustainability, effective implementation of green chemistry can help practitioners realize economic efficiency gains.

As a developing tool, green chemistry does have some limitations. The technology needed to fully implement green chemistry in certain areas may remain out of reach for reasons of cost or other barriers.[184] Another challenge facing green chemistry is that comprehensive, effective metrics for assessing the relative hazard of chemicals are not yet universally applicable. [185] Finally, evaluating toxicological and other scientific data is a complex and time-intensive undertaking, requiring the input of highly skilled toxicologists and environmental health scientists. There currently is no robust process for translating the results of a toxicological evaluation into articulating design rules that can be applied by bench chemists. As a result, it can be difficult for practitioners of green chemistry to determine the appropriate levels of toxicity that are operationally acceptable to human and environmental health.[182] However, advances in mechanistic toxicology, the nexus between toxicology and green chemistry, promise to address this limitation.

Enabled by advances in toxicogenomics, computational chemistry, and improved computer capabilities, the National Toxicology Program, EPA, and the National Chemical Genomic Center have collaborated to form the Tox 21 project. This project aims to identify the molecular sequence of events that lead from chemical exposure to the manifestation of adverse effects, which will facilitate establishing rules for safer chemicals design. Improved mechanistic data has the potential to advance green chemistry more quickly and increase the likelihood that chemical products are designed with reduced toxicity.

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How is Green Chemistry being used to support EPA decision-making?

EPA promotes green chemistry through several programs, primarily the Presidential Green Chemistry Challenge Awards. Established in 1996, this incentive program encourages competition and innovation in academia, industry and government to demonstrate science and technology that embraces the principles of green chemistry.[186] EPA also supports green chemistry through projects, educational programs such as People, Prosperity and Planet (P3), and continued research and development.[187] In addition, EPA promotes green chemistry innovation through partnerships with states and universities as part of regional Pollution Prevention and Source Reduction Assistance grants.

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Where can I find more about Green Chemistry?

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Illustrative approaches applying Green Chemistry

  • Life-Cycle Assessment of Lithium Ion Battery Technologies 

    Source: EPA Office of Chemical Safety and Pollution Prevention[249]
    Suite of sustainability tools: life-cycle assessment; eco-efficiency analysis; green chemistry; collaborative-problem solving
    Use of lithium-ion batteries is growing in the US as the number of applications expands and as government programs encourage their use. Lithium-ion batteries are currently used in many products, including computers and cell phones. New technologies are under development that will allow for the use of lithium-ion batteries in electric cars. As electric vehicles become more prevalent in the United States, interest in developing these technologies grows. [250]

    With battery production on the rise, EPA’s DfE collaborated with EPA’s ORD to create the Lithium-ion Batteries and Nanotechnology Partnership in June 2009. The partnership is researching ways to produce batteries more efficiently and with fewer environmental impacts. DfE and ORD are conducting a quantitative environmental life-cycle assessment (LCA) of lithium-ion batteries used in electric drive vehicles, as well as of the nanomaterials and nanotechnology used to produce them.[251] Quantitative LCA is a technique for assessing potential environmental impacts associated with a product, process, or service. LCA helps battery manufacturers and suppliers to identify materials and processes that are associated with fewer environmental impacts and greater energy efficiency.

    In this case, the quantitative LCA assesses energy systems and environmental impacts at all stages of the batteries’ life: raw materials extraction and acquisition, materials processing, product manufacture, product use, and final disposition and end-of-life. The project is also assessing a nanotechnology application that has the potential to reduce environmental impacts. For example, this study is assessing battery anodes made from single walled carbon nanotubes. These anodes show promise for increased current capacity, extended electric vehicle range and battery life, and reduced recharge cycle time.

    To perform this analysis, DfE partnered with a number of battery manufacturing and recycling companies, research institutions, the Department of Energy’s Argonne National Laboratory, and non-governmental organizations.

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  • EPA Design for the Environment 

    Source: EPA Office of Chemical Safety and Pollution Prevention[257]
    Suite of sustainability tools: chemical alternative assessment; green chemistry; collaborative problem-solving; life-cycle assessment; risk assessment
    EPA’s Design for the Environment (DfE) Partnership Program helps consumers, businesses, and institutional buyers identify products that perform well and are cost-effective, but are safer for human health and the environment.[257] This program promotes sustainability by working with small businesses and consumers to identify risks involved with chemicals used in products or manufacturing processes. Chemical Alternatives Assessment is a key analytic tool for the implementation of DfE. It is a tool for evaluating chemicals of potential concern by comparing alternative chemicals within the same functional-use group across a consistent and comprehensive set of hazard endpoints. Other analytic tools that are instrumental for the conduct of this program include risk assessment and life-cycle assessment. Through the DfE, EPA collaborates with industry, environmental groups and universities to decrease health and environmental risk by encouraging green design and reformulation of a wide range of products while maintaining their effectiveness. As more consumers seek sustainable products that are designed to have minimal impact on the environment and their health, an environmental “seal of approval” could help consumers select products that match their values.[258

    DfE offers that “seal of approval” by awarding use of the logo on products that meet environmental design criteria. The logo assures consumers that the DfE scientific review team has screened each ingredient for potential human health and environmental effects and that—based on currently available information, EPA predictive models, and expert judgment—the product contains only those ingredients that pose the least concern among chemicals in their class. Products are also expected to meet effectiveness criteria, i.e., glass cleaners must meet criteria for effective glass cleaning. To obtain the DfE recognition, ingredients in the formulation must be publically disclosed (with the exception of specific allowances for trade secret ingredients). EPA also offers the DfE label to partnering companies that design or reformulate high-performance and cost-effective products using the safest ingredients.[258]

    The screening process (PDF) (43 pp, 726K) for the DfE logo is detailed and comprehensive. DfE scrutinizes ingredients, starting with known toxicity information and performing an inherent property analysis when toxicity information is not available. With inherent property analysis, scientists estimate toxicity for a chemical ingredient without toxicity information using available toxicity information for a chemical with similar structure. Strong structural similarities to a chemical with high environmental or health toxicity would be a flag for concern.

    DfE sets specific standards for chemicals of known toxicity. For example, DfE will not recognize products that contain any pollutants on the Hazardous Air Pollutants list. Furthermore, DfE will not recognize products that contain chemicals on the EPA Toxics Release Inventory chemical list unless they meet stringent DfE criteria.

    This program fosters sustainability in a cost-effective way that benefits companies, consumers, and environmental and public health. Through such partnerships and education, EPA is helping businesses and consumers select safer chemicals and technologies, thereby reducing the number of potentially hazardous chemicals in use.

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  • Sustainable Chemistry: An Even Darker Shade of Green  

    Source: EPA Office of Research and Development [265]
    Suite of sustainability tools: green chemistry; green engineering
    EPA researcher Dr. Rajender Varma has given new meaning to the phrase “reading the tea leaves” through his visionary development of new, green ways to synthesize chemicals and nanomaterials from things such as microwave ovens, magnets, and natural antioxidants found in coffee, vitamins, grape husks left over from winemaking operations, and, of course—tea.

    Varma and his team have developed dozens of new and patented methods for the chemical industry and others to make compounds in environmentally friendly ways.

    Working at an EPA research laboratory dedicated to tapping the principles of green chemistry and engineering to advance sustainability, Varma’s team is developing benign nanomaterials to replace conventional catalysts, substances that initiate or speed up chemical reactions but do not themselves change during the reaction. Catalysts can be expensive, dangerous if not handled properly, and may end up as waste products that must be treated and/or disposed of carefully. In contrast, Varma has created iron-based magnetic nanomaterial-based catalysts that are easily recycled.

    By building nanomaterial-based catalysts with a core of iron and coating them with other metals, the catalyst can be separated using a simple magnetic field and then re-used, avoiding the use of hazardous substances while creating virtually no waste. “I often feel these methods plagiarize Nature because our approaches mimic what nature does so elegantly in biological systems,” Varma says.

    Varma’s group has also pioneered a new method of synthesizing nanoparticles. Instead of using a typical “top-down” approach that relies on large energy inputs and toxic solvents to break down larger materials, Varma and his colleagues employ a simple “bottom-up” method that assembles nanomaterials at the molecular level. This novel approach avoids the use of hazardous reducing agents, and instead employs benign metallic salts (such as iron salts), water, and polyphenols from plant materials (tea, coffee, and red grapes) to act as reducing or capping agents to prevent nanomaterials from aggregating into larger clumps during the production process.

    Varma’s innovative methods for coating iron nanomaterials are earth-friendly in both their production and degradation processes, allowing them to be used for environmental remediation operations, even to clean up pesticides from soils near crops.

    Working with the Connecticut-based firm VeruTEK, Varma and his EPA colleagues have played an important role in developing and commercializing green remediation technologies. VeruTEK has used this approach for degradation of pollutants in water. The technology can also be applied directly to soil, where it forms nanomaterials that breakdown organic toxicants. The iron-based, phenolic-coated nanomaterials naturally degrade, so they can be left in place once applied, offering an attractive alternative to standard cleanup methods of extracting and hauling away contaminated soils for offsite cleaning before they are trucked back in and replaced.

    Not surprisingly, Varma’s work has attracted significant attention from the scientific community and beyond. He has briefed US Congressional staff and the President of India in addition to lecturing in Chile, China, India, Peru, and Venezuela. He pointed out that developing countries are immensely interested in methods that allow them to “leapfrog” by circumventing older technologies and embracing more efficient ones, such as when governments encourage the establishment of cell phone networks, allowing them to skip costly and disruptive installations of telephone poles and overhead wires in areas that previously had no telecommunications technology.

    The nanocatalysts that Varma’s team produces can be safely recycled and may be used over and over, and can even be utilized for clean-up operations using visible light from the sun. According to Varma, “this process allows for a little darker shade of green” as we transition to practices for more sustainable chemical manufacturing and use. “In addition to its monitoring and compliance efforts, hopefully EPA can be a beacon to others in developing sustainable methods going forward,” Varma says.

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  • Next Generation of Risk Assessment (NexGen)

    Source: EPA Office of Research and Development [269]
    Suite of sustainability tools: risk assessment; green chemistry
    EPA’s ORD is heading a multi-Agency program to bring the new biological testing described in the 2007 NRC report Toxicity Testing in the 21st Century: A Vision and a Strategy to EPA’s risk assessment program. The results of this effort will not only benefit EPA and partnering agencies’ risk assessors to incorporate molecular systems biology data into risk assessments, but also support industrial green chemistry efforts by providing a rapid way to make more sustainable choices in selecting industrial chemicals and evaluating their life-cycle.

    The program, called NexGen (for Next Generation of Risk Assessment), began in early 2008 as an effort to modernize the risk assessments being done by the Agency for IRIS and other purposes. A multi- Agency work group was established to analyze the vast quantity of molecular biology data being generated on various chemicals and discover ways to incorporate this new knowledge into the risk assessment process. The work group focused on three representative cases as proof of concept. They selected three well-studied cases for which there was not only an abundance of new molecular biology data, but also existing conventional risk assessments: benzene, ozone, and polycyclic aromatic hydrocarbons. In each case study, the work group attempted to “reverse-engineer” the processes described by the molecular biology results to discover if they might produce similar results to those seen in conventional risk assessment. After developing these three draft prototype cases, a group of experts from both inside and outside government was established to discuss the prototypes at a workshop held in November 2010. Experts from that workshop presented the concepts and the case studies at a Public Dialogue Conference in February 2011 to explain the program to a wide audience drawn from industry/trade associations, environmental/public health organizations, academia, media, citizens, international agencies, and other government agencies.

    The NexGen framework projects that, in the future, there will be three tiers of assessment. The first tier, which will be used for screening and ranking, will use high-throughput molecular biology methods as well as structure-activity analysis to examine tens of thousands of chemicals with potential exposure to seek information on hazards. (This approach can also be used in industrial green chemical selection). The second tier will focus on thousands of potential problem chemicals identified in tier 1 and include limited risk assessments based on science-based defaults and upper confidence limits. This may lead to hundreds of chemicals entering tier 3, where extensive analysis and risk assessment may lead to major regulatory decision-making.

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