This article originally appeared in Environmental Science and Technology, December 1, 2003.

Doing the right things right. It's not as easy as it sounds. Working smart may be easy, but working smart without perspective or guiding principles can ultimately become an efficient pursuit of the wrong goals. Consider historical approaches to industrial problem solving: Applying engineering strategies to make a wasteful or hazardous process more sustainable might seem like a beneficial course of action-there are many examples of this-but is fine-tuning a fundamentally flawed system actually the goal we want to pursue? Conversely, engineers can be headed toward positive ends yet be undermined by tools that will never get them where they want to go. This is the case of early approaches to the manufacture of photovoltaic cells, which often consumed more energy in their construction than could ever be recovered over the lifetime of the system.

So what are the right goals? The right tools? If we approach sustainability from a design perspective, we can see the need for a fundamental conceptual shift away from the design of the current industrial system, which generates toxic, one-way, "cradle-to-grave" material flows, toward a "cradle-to-cradle" system powered by renewable energy, in which materials flow in safe, regenerative, closed-loop cycles.

The Cradle-to-Cradle Framework [1] articulates this conceptual shift. Developed and successfully applied over the past decade, the Cradle-to-Cradle Framework is a science- and values-based vision of sustainability that enunciates a positive, long-term goal for engineers: the design of a commercially productive, socially beneficial and ecologically intelligent industrial system.

The Principles of Green Engineering [2] provide guidance for realizing this vision in practice, suggesting ways in which designers and engineers can pursue optimized, cradle-to-cradle products and systems. While Green Engineering addresses the issue at all levels of innovation, as illustrated in Figure 1, one sees that for a given investment of time, money or other resources, the greatest investments often come from redefining the problem.

In this article we will provide an overview of the Cradle-to-Cradle Framework and examples of design projects that have put the framework into practice. We will also address the Principles of Green Engineering and, following each example of cradle-to-cradle designs, suggest how engineers might apply the Principles to achieving the goals of the Cradle-to-Cradle Framework.

FIGURE 1: SCHEMATIC REPRESENTATION OF BENEFIT OF TIME, MONEY, AND RESOURCES FOR DECISIONS AT DIFFERENT LEVELS OF DESIGN.

Sustainablity: The Cradle-to-Cradle Perspective
The Cradle-to-Cradle Framework does not reach for sustainability as it is typically defined. Discussed at length in various papers, books and other venues [3-5], environmental sustainability in the industrial sector is popularly understood as a strategy of "doing more with less" or "reducing the human footprint" to minimize troubling symptoms of environmental decline. From an engineering perspective, conventional sustainability too often suggests retrofitting the machines of industry with cleaner, more efficient "engines" to secure ongoing economic growth. But this is not an adequate long-term goal. While being eco-efficient may indeed reduce resource consumption and pollution in the short-term, it does not address the deep design flaws of contemporary industry. Rather, it addresses problems without addressing their source, setting goals and employing practices that sustain a fundamentally flawed system.

The Cradle-to-Cradle Framework, on the other hand, posits a new way of designing human systems that ultimately can solve rather than alleviate the human-created conflicts between economic growth and environmental health that result from poor design and market structure. Within this principled framework, which is based on the manifested rules of nature and re-defines the problem at hand, eco-efficient strategies can serve a larger purpose.

The Foundations of Cradle-to-Cradle Design
The Cradle-to-Cradle Framework recognizes the operating system of the natural world as an unrivaled model for human designs. In essence, natural systems largely operate on the free energy of the sun, which interacts with the geochemistry of the earth's surface to sustain productive, regenerative biological systems. Human systems designed to operate by the same rules that govern the natural world can approach the effectiveness of the earth's diverse living systems, in which there is no waste at all.

Cradle to Cradle identifies three key design principles in the intelligence of natural systems, which can inform human design:

1. Waste Equals Food
2. Use Current Solar Income
3. Celebrate Diversity

Waste Equals Food. Waste does not exist in nature because the processes of each organism contribute to the health of the whole ecosystem. A fruit tree's blossoms fall to the ground and decompose into food for other living things. Bacteria and fungi feed on the organic waste of both the trees and the animals that eat its fruit, depositing nutrients in the soil in a form ready for the tree to use for growth. One organism's waste is food for another and nutrients flow indefinitely in cradle-to-cradle cycles of birth, decay and rebirth. In other words, waste equals food.

Understanding these regenerative systems allows engineers and designers to recognize that all materials can be designed as nutrients that flow through natural or designed metabolisms. While nature's nutrient cycles comprise the biological metabolism, the technical metabolism is designed to mirror them; it's a closed-loop system in which valuable, high-tech synthetics and mineral resources circulate in cycles of production, use, recovery and remanufacture.

Within this cradle-to-cradle framework, designers and engineers can use scientific assessments to select safe materials and optimize products and services, creating closed-loop material flows that are inherently benign and sustaining. Materials designed as biological nutrients, such as textiles and packaging made from natural fibers, can biodegrade safely and restore soil after use. Materials designed as technical nutrients, such as carpet yarns made from synthetics that can be repeatedly depolymerized and repolymerized , are providing high quality, high-tech ingredients for generation after generation of synthetic products.

Use Current Solar Income. Living things thrive on the energy of the sun. Trees and plants manufacture food from sunlight, an elegant, effective system that uses the earth's unrivalled and continuous source of energy income. Despite recent precedent, human energy systems can be nearly as effective. Cradle-to-cradle systems-from buildings to manufacturing processes-tap into current solar income using direct solar energy collection or passive solar processes, such as daylighting, which makes effective use of natural light. Wind power-thermal flows fueled by sunlight-can also be tapped.

This is already beginning to change the energy marketplace. The City of Chicago, for example, has committed to buying 20 percent of its electricity from renewable sources by 2006, which is spurring the local development of renewable energy technology. Indeed, the City recently opened the Chicago Center for Green Technology, an ecologically intelligent facility on a restored industrial site that houses companies involved in developing the local capacity to tap wind and solar power. Germany, meanwhile, has already harnessed wind power equivalent to 20 coal-fired power plants and the European Union plans to generate 22 percent of its electricity from renewable sources by 2010.

Celebrate Diversity. From a holistic perspective, natural systems thrive on diversity. Healthy ecosystems are complex communities of living things, each of which has developed a unique response to its surroundings that works in concert with other organisms to sustain the system. Each organism fits in its place and in each system the fittingest thrive. Needless to say, long term perspective is needed since even the introduction of an invasive species can enhance diversity for the immediate term while virtually destroying that diversity over time.

Nature's diversity provides many models for human designs. When designers celebrate diversity, they tailor designs to maximize their positive effects on the particular niche in which they will be implemented. Engineers might profit from this principle by considering the cradle-to-cradle maxim, "all sustainability is local." In other words, optimal sustainable design solutions draw information from and ultimately "fit" within local natural systems. They express an understanding of ecological relationships and enhance the local landscape where possible. They draw on local energy and material flows. They take into account both the distant effects of local actions and the local effects of distant actions. The point is this: Rather than offering the one-size-fits-all solutions of conventional engineering, designs that celebrate and support diversity and locality grow ever more effective and sustaining as they engage natural systems.

Consider the building systems for the 901 Cherry, Offices for Gap Inc. in San Bruno, California. Aiming to enhance energy effectiveness and the qualities of the local landscape, William McDonough + Partners designed the building with an undulating roof blanketed in soil, flowers and grasses that mirrors the local terrain, re-establishing several acres of the coastal savannah ecosystem that had been destroyed by human intervention. The living roof also effectively absorbs storm water and provides thermal insulation, making the landscape an integral part of the building's energy systems.

In addition, a raised floor cooling system allows evening breezes to flush the building while concrete slabs beneath the floor remain cool and provide a cooling effect during the day. Windows are operable, the delivery of fresh air is under individual control, and daylighting provides natural illumination. By celebrating diversity-tapping local energy flows, integrating landscape and system design, maximizing positive effects rather than minimizing negative ones-the design contrasts starkly with typical, tightly-sealed, energy efficient buildings. Yet the Gap offices' advanced, integrated systems are so effective the building was recognized as one of the most energy efficient buildings in California by the regional utility company, Pacific Gas and Electric.

In short, by modeling human designs on nature's operating system-generating materials that are "food" for biological or industrial systems, tapping the energy of sun, celebrating diversity-cradle-to-cradle design creates a new paradigm for industry, one in which human activity generates a wide spectrum of ecological, social and economic value.

The Principles of Green Engineering
While the Cradle-to-Cradle vision sets a course and answers "What do I do?" the Twelve Principles of Green Engineering can answer "How?" Shown in Figure 2, they can be viewed as a toolbox of approaches to be used systematically to optimize a system or its components. This approach builds on the technical excellence, scientific rigor and systems thinking that has addressed the issue of science and technology for sustainability and sustainable development in recent years [6-23]. As is the case in any complex multi-parameter system, there will be the need to contextually understand when to balance one principle or collection of principles versus another. Often an understanding of this type is not obvious or transparent and requires asking questions that apply locally and across the life-cycle. Applied thoughtfully, however, these principles can be useful tools for turning vision into reality.

FIGURE 2: THE TWELVE PRINCIPLES OF GREEN ENGINEERING [2]

The Principles of Green Engineering can be used to provide guidance to engineers working to develop a practical methodology for implementing cradle-to-cradle goals.

Consider Principle 1: "Designers need to strive to ensure that all material and energy inputs and outputs are as inherently non-hazardous as possible." From a cradle-to-cradle perspective, human systems approach optimal effectiveness when inputs and outputs are as safe and beneficial as those generated by natural systems, which effectively uses energy and generates materials while producing no waste. With this in mind, designers working on cradle-to-cradle products and systems begin the design process by analyzing the chemistry of materials to determine which ones are inherently safe and non-hazardous and which should be avoided. When a cradle-to-cradle material is optimized it is not only non-hazardous but also provides nourishment for something new after its useful life-either "food" for biological systems or high-quality materials for subsequent generations of high-tech products. Approaching product and system design from an engineering perspective, designers following Principle 1 would be moving toward this entry point to Cradle-to-Cradle systems.

Principle 2 is complementary, and follows from the Waste Equals Food aspect of nature's design. Principle 2 says: "It is better to prevent waste than to treat or clean up waste after it is formed." By designing safe, healthful materials that can flow in closed-loop cycles, cradle-to-cradle designers are eliminating waste by putting filters in their heads instead of on the end of pipes. That is, rather than managing the costly liabilities or potential liabilities of flawed designs, cradle-to-cradle designers conceive products and materials that generate assets at every step of their life-cycle. Engineers striving to meet Principle 2 would be laying the groundwork for systems that sustain cradle-to-cradle material flows.

An old adage suggests the importance of making the elimination of waste an upfront engineering priority:

What do you have when you put a drop of chardonnay in a barrel of hazardous waste? A barrel of hazardous waste. What do have when you put a drop of hazardous waste in a barrel of chardonnay? A barrel of hazardous waste.

Clearly, managing waste is a limited goal. And each Principle of Green Engineering, in its own way, offers to engineers a way to go beyond it, to move from managing liabilities and hazards toward designing effective, ecologically intelligent materials, products and systems. The brief case studies that follow show some of the ways in which designers and engineers have already begun to apply the Principles of Green Engineering in developing models for cradle-to-cradle industry.

Designing Biological and Technical Nutrients
As we have seen, cradle-to-cradle materials and products are conceived as either biological nutrients or technical nutrients-food for nature or industry. Their design and manufacture has been going on for nearly a decade. The examples that follow were designed using a cradle-to-cradle approach, and utilizing the methods and tools that have been developed for cradle-to-cradle design. They also illustrate the applicability of the Principles of Green Engineering, many of which they exemplify.

Biological Nutrients
By 1995, the Swiss firm Rohner and the textile design company DesignTex, working with McDonough Braungart Design Chemistry (MBDC), had already developed examples of a textile that is a biological nutrient, a product so benign it could be assimilated by natural systems without any toxicity [24].

To ensure that the fabric would safely biodegrade, the design team worked with the chemical company CibaGeigy to select only the most inherently benign chemicals and materials used in the textile industry to finish and dye natural fabrics. The team eliminated from consideration chemicals containing any form of mutagen, carcinogen, heavy metal, endocrine disruptor, or bio-accumulative substance. Applying these criteria, the team identified 38 chemicals suitable for a material destined to be food for the soil, enough to produce a textile meeting all quality standards.
Going into the project, the mill chosen to produce the fabric had an interesting problem: although the mill's director had been diligent about reducing levels of dangerous emissions, government regulators had recently defined the trimmings of his fabric as hazardous waste. In stark contrast, the trimmings of the new biological nutrient fabric serve as mulch for the local garden club. At the end of its useful life, the fabric itself can be safely composted to build healthy soil.

This example of cradle-to-cradle design benefits from many of the tools that the principles of Green Engineering supply. By using Principle 1, engineers can not only choose the most suitable chemicals from those available, but molecular designers can also make new chemicals that have environmental and health benefits built in as a performance criterion. Ciba Geigy embraced targeted durability (Principle 7) in recognizing that the performance in commercial after-life (Principle 11) must be a design goal.

Technical Nutrients
In a paper in this issue (page XX), Bradfield et. al. describe how Shaw Carpet has accomplished significant, quantifiable benefits by working within the Cradle-to-Cradle Design Framework in ways that are compatible with the Principles of Green Engineering. Shaw's approach involves scientific assessments of the material chemistry of its carpet fibers and backing, using MBDC's material assessment protocol as shown in Table 1 and Figure 3. Throughout the design process, dyes, pigments, finishes, auxiliaries-everything that goes into carpet-are examined and each ingredient selected meets rigorous environmental health criteria of the protocol. Out of this process has come the promise of a fully optimized carpet tile-a completely safe, continuously recyclable technical nutrient. This new design for carpet tiles has earned Shaw carpet the 1999 Georgia Governor's Pollution Prevention Award and the 2003 Presidential Green Chemistry Challenge Award [25].

Carpet is made from two primary elements, a face fiber and a backing. Shaw's face fiber is made from nylon 6, which has a demonstrated ability to be easily depolymerized into its monomer, caprolactam, and repolymerized repeatedly to make high quality carpet fiber. The main competing face fiber, nylon 6,6 cannot be depolymerized effectively for recycling. As for carpet backing, PVC has dominated the industry for 30 years.

PVC, commonly known as vinyl, is a cheap, durable material widely used in building construction and a variety of consumer products, including toys, apparel and sporting goods. The vinyl chloride monomer used to make PVC is a human carcinogen (IARC), while incineration of PVC can result in dioxin emissions. There are also concerns about the health effects of many additives commonly used in PVC. Responding to widespread scientific, consumer and public concern for PVC, Shaw developed a polyolefin-based backing system with all the performance benefits of PVC which it guarantees it will take back (along with its nylon 6 face fiber) and recycle into new backing.

In effect, the new carpet tile eliminates the very concept of waste. The material that goes into the carpet will continually circulate in technical nutrient cycles. Given the hundreds of millions of pounds of carpet fiber and backing that each year are not recycled and instead are sent to landfills or incinerated or are recycled into products of lesser value, the impact of this new design on the carpet market will be very significant.

Shaw's accomplishments exemplify a number of the Principles of Green Engineering. The company's product development process illustrates how Principles 6 (complexity viewed as an investment) can be put into practice through the technical skills and engineering rigor needed to invent a new approach to carpeting. By upfront design for commercial after-life (Principle 11) the people at Shaw both prevented waste (Principle 2), and designed the separation and purification processes, in this case depolymerization, to be less material and energy consumptive (Principle 3)

A Material Assessment Protocol
The application of the Cradle-to-Cradle Design Framework has yielded a rigorous materials assessment protocol that can be applied in a wide range of industries. Working with MBDC, the footwear manufacturer Nike employed the MBDC protocol to determine the chemical composition and environmental effects of the materials used to produce its line of athletic shoes [26]. Focusing primarily on Nike's global footwear operations, the effort began with factory visits in China, where teams collected samples of rubber, leather, nylon, polyester, and foams, and information on their chemical formulations, to begin assessing their chemistry.

TABLE 1: HUMAN AND ECOLOGICAL HEALTH CRITERIA FOR MBDC'S MATERIALS ASSESSMENT PROTOCOL.

FIGURE 3: PRELIMINARY CHEMICAL ASSESSMENT STEPS FROM MBDC'S MATERIALS ASSESSMENT PROTOCOL.

In this ongoing partnership, when Nike and MBDC identify materials that meet or exceed the company's emerging criteria for sustainable design, those components are added to a growing palette of materials (a 'Positive List') that Nike will increasingly use in its products. These ingredients are designed to either be safely metabolized by nature's biological systems at the end of a product's useful life (Principle 11), or be repeatedly recovered and reutilized for new products (Principle 10). [this last one seems to me to fit better with Principle 11 than with 10]

Nike's systematic effort to develop a positive materials palette has begun to produce tangible results, such as the phasing out of polyvinyl chloride (PVC). After two years of scientific review, Nike set its sites on the elimination of PVC from footwear and non-screenprint apparel by the end of 2002. In Spring 2002 Nike highlighted two of the company's PVC-free products, Keystone Cleats and Swoosh Slides, as a way to begin a dialogue with consumers about its PVC-free commitment.

Green Engineering can be driven even further by companies like Nike when they place environmental and health criteria as specifications for the suppliers of basic feedstocks that enter their products. Through the use of Principle 1, large and influential companies can cause their vendors to design next generation materials to be intrinsically less hazardous and more sustainable. The new materials also eliminate the need for the other additive substances required by PVC and accomplish Principle 9 in allowing for greater ease of disassembly and value retention.

Integrating Design Strategies
The furniture company Herman Miller has gone a long way toward integrating cradle-to-cradle principles into its product development process. Herman Miller has developed an interdisciplinary Design for Environment team that implements materials assessments based on MBDC's protocol, translates design goals throughout the company, measures environmental performance and engages its supply chain in implementing design criteria [27].

Working closely with MBDC, the DFE team built a chemical and material assessment methodology that could be used by the firm's designers and engineers as shown in Table 2. Throughout the design process, the multi-faceted assessment analyzes materials for their human health and eco-toxicological effects, recycleability, recycled content and/or use of renewable resources, and product design for disassembly.

TABLE 2: HERMAN MILLER DESIGN FOR ENVIRONMENT ASSESSMENT CRITERIA
(WITHOUT SCORING LEGEND AND WEIGHTING).

Human Health and Eco-Toxicological Assessment
1. No problems identified or expected, or extremely low risk.
2. Low to moderate risk
3. Lacking sufficient data to make a determination.
4. Severe problems or high risks identified or expected.

Recyclability
1. Material is a technical or biological nutrient and a commercial infrastructure exists.
2. Material can be down-cycled and a commercial infrastructure exists.
3. Material can be incinerated for energy recovery.
4. Material is normally land filled.

Recycled / Renewable Content
Percentage of total product weight:
Post Industrial Recycled Content
Post Consumer Recycled Content
Renewable Content

Disassembly
Can the component be separated with no dissimilar materials attached?
Can common disassembly tools be used (pry-bar, hammer, drivers, utility knife, pliers)?
Can one person disassemble the component in 30 seconds or less?
Can the material type be identified through markings, magnets, etc?

The DFE team includes a chemical engineer who incorporates findings from assessments into an evolving materials data base, and a purchasing agent who acts as a conduit and data source between the supply chain and Herman Miller's purchasing team. This strategy engages both groups as partners in implementing new design criteria, thereby ensuring the consistent procurement of safe materials. As one Herman Miller engineer has said, "getting a handle on supply chain issues from an environmental standpoint has also helped us get a handle on the organization and prioritization of materials." Now, for example, Herman Miller can use the new database to record the volume and content of the raw materials it uses and distributes, figures it had not previously tracked.

Clearly, the Herman Miller assessment criteria have large commonalities with the goals of the Green Engineering Principles such as intrinsic hazards elimination (Principle 1), renewability (Principle 12), design for commercial after-life (Principle 11) and design for disassembly (Principle 3).

Sustainable Facilities
Cradle-to-Cradle Design can also be applied to the restoration of industrial landscapes, as Ford Motor Company is doing at its historic Rouge River manufacturing complex in Dearborn, Michigan [28]. There, the automaker has built an automotive assembly plant with a 10-acre green roof that cost-effectively filters storm water run-off, which is typically managed with expensive technical controls.

Rather than approaching anticipated environmental requirements from the common industrial perspective, Ford opted for a Cradle-to-Cradle approach: a manufacturing facility that would connect employees to their surroundings, create habitat, make oxygen, restore the landscape and invite the return of native species. The result is a daylit factory with a 450,000 square-foot roof blanketed with topsoil and growing plants-a "living" roof.

In concert with porous paving and a series of constructed wetlands and swales, the living roof effectively filters stormwater run-off for $35 million less than the typical stormwater management systems required to meet regulations. In addition to absorbing storm water, soil and vegetation on the roof:

• provide extra insulation
• protect the roof membrane from wear and thermal shock
• contribute to mediating the urban heat island effect
• capture harmful particulates

The roof and the swales also create new and revived habitats on the site for native birds, butterflies, insects and microorganisms, generating a larger biological order and encouraging diversity.

Phytoremediation, the process of using plants to absorb or neutralize toxins in the soil, is also being employed at the Rouge site [29, 30]. Ford has cultivated 20 native plants in contaminated soil and is monitoring them to test how well each breaks down and purifies polycyclic aromatic hydrocarbons (PAH), a prevalent on-site toxin. So far, big bluestem and green ash seem to have been the most effective for PAHs. With other native plants, which are being monitored by a group of scientists, big bluestem and green ash are being planted in phytoremediation gardens along the Rouge's main thoroughfare. The researchers will continue to systematically test which plants most effectively absorb toxins. Other scientists are doing research on plants they believe may sequester heavy metals and other compounds.

The Rouge River example is an excellent illustration of how to build in the integration and interconnectivity of available energy and materials flows, as called for in the Principles of Green Engineering. Rather than introduce synthetic materials or machinery to accomplish a goals, in this case remediation, the existing natural systems' processes and energy flows are used to accomplish these goals more effectively. In this example both Principle 10 (interconnectivity) and Principle 12 (renewable energy and materials) are utilized in the design of the restoration system.

Remaking an Industry
While the Cradle-to-Cradle Framework sees the transformation of a wide range of mobility systems as a key objective on the path to sustainability, it has to date been most effectively applied in the automobile industry. Given that long-range projections estimate that global vehicle registrations could reach 2 billion during the second half of this century, this appears to be a good place to start.

Building a truly sustainable automobile industry means developing closed-loop systems for the manufacturing and re-utilization of auto parts. In Europe, the End-of-Life Vehicle Directive, which makes manufacturers responsible for automotive materials, is encouraging companies to consider design for disassembly and effective resource recovery more seriously. Cradle-to-cradle systems, in which materials either go back to industry or safely back to the soil, are built for effective resource recovery. In such a system, each part of every car is either returned to the soil or recovered and reused in the assembly of new cars, generating extraordinary productivity and consistent employment.

These ideas are emerging in the American auto industry. Working with MBDC, Ford Motor Company has developed the Model U, the world's first automobile designed to explore the concept of inherently safe, beneficial cradle-to-cradle materials.

Environmentally benign materials used in the manufacture of the Model U include Milliken & Co. polyester upholstery fabric, a technical nutrient made from chemicals chosen for their human and environmental health qualities, and capable of continuous recycling. The car top is made from a potential biological nutrient, a corn-based biopolymer from Cargill Dow that can be composted after use. Both are examples of materials designed for cradle-to-cradle life cycles.

This first step toward the cradle-to-cradle vehicle lays the foundation for a clear, long-term vision that sees American automobiles as products of service-customers buy the service of mobility for a defined use period, not the car itself-designed for disassembly, their materials circulating in closed-loop cycles and providing "food" for nature and industry, generation after generation.

This strategy for the design of next generation automobiles incorporates several Principles of Green Engineering. This approach utilizes inherently benign chemicals and materials (Principle 1) that can be recovered at end of life (Principle 3) to cycle in closed-loop, integrated systems (Principles 2, 10). In addition, introducing the automobiles as a "product of service," the components designed to have a commercial afterlife in new automobiles (Principle 11).

The Foundation of Sustainability
Engineers across a wide spectrum of industry are already laying the foundation for green manufacturing. Throughout this issue of Environmental Science and Technology are examples that illustrate a variety of approaches to sustainability. When considered through the lens of the Principles of Green Engineering, we can see them as steps moving toward a larger transformation of industry.

From a Cradle-to-Cradle perspective, green engineering represents a practical approach to the transformation of industry. Applied to the goals of the Cradle-to-Cradle Framework, the Twelve Principles of Green Engineering can help achieve the long-term goal of designing a commercially productive[no example or principle has explicitly addressed social issues in this paper] and ecologically intelligent industrial system. Together, they create a useful framework for doing the right things right.

References

1. McDonough, W.; Braungart, M. Cradle to Cradle: Remaking the Way We Make Things. 2002, North Point Press, New York.
2. Anastas, P. and J. Zimmerman (2003). "Design through the Twelve Principles of Green Engineering." Environmental Science and Technology 37(5): 94A-101A.
3. The World Commission on Environment and Development (ed.), Our Common Future. 1987, Oxford University Press, New York.
4. NRC Board on Sustainable Development (ed.), Our Common Journey: A Transition Toward Sustainability. 2000, National Academy Press, Washington D.C.
5. Kates, W. K., et al. Science, 2001, 292(5517), 641.
6. Anastas, P. and J. Warner, Green Chemistry: Theory and Practice. 1998, London: Oxford University Press.
7. Benyus, J.M., Biomimicry: Innovation Inspired by Nature. 1997, New York, New York: William Morrow. 256.
8. Anderson, R., Mid-Course Correction: Toward a Sustainable Enterprise: The Interface Model. 1999, White River Junction: Chelsea Green.
9. Bishop, P., Pollution Prevention: Fundamentals and Practice. 2000, Boston: McGraw Hill. 620.
10. Congress, U.S., Green Products by Design: Choices for a Cleaner Environment. 1992, Office of Technology Assessment.
11. Desimone, L.D. and F. Popoff, Eco-Efficiency : The Business Link to Sustainable Development. 2000, Boston: MIT Press. 306.
12. Dodds, F. and T. Middleton, Earth Summit 2002: A New Deal. 2002, London: Earthscan Publications, Ltd. 364.
13. Ehrenfeld, J., Industrial ecology: a framework for product and process design. Journal of Cleaner Production, 1997. 5(1-2): p. 87-95.
14. Fiksel, J., Design for Environment: Creating Eco-Efficient Products and Processes. 1998, New York: McGraw-Hill.
15. Graedel, T.E. and B.R. Allenby, Industrial Ecology. 1995, Englewood Cliffs: Prentice Hill. 341.
16. Graedel, T.E. and B.R. Allenby, Design for Environment. 1997, New York: Prentice Hall College Division. 175.
17. Hawken, P., A. Lovins, and L.H. Lovins, Natural Capitalism: The Next Industrial Revolution. 1999, London: Earthscan.
18. Keoleian, G.A., Pollution Prevention through Life-Cycle Design, in Industrial Pollution Prevention Handbook, H.M. Freeman, Editor. 1995, McGraw Hill, Inc.: New York. p. 253-92.
19. Panjabi, R.K.L. and A.H. Campeau, The Earth Summit at Rio: Politics, Economics, and the Environment. 1997, Boston: Northeastern University Press. 432.
20. Rees, W.E., P. Testemale, and M. Wackernagel, Our Ecological Footprint. 1995, British Columbia, Canada: New Society Publisher. 176.
21. United Nations Environment Program, Global Environmental Outlook 2000. 1999, United Nations: New York.
22. Allen, D.T. and D.R. Shonnard, Green Engineering: Environmentally Conscious Design of Chemical Processes. 2001, New York: Prentice Hall. 574.
23. Anastas, P., L. Heine, and T. Williamson, Green Engineering. 2000, Washington, D.C.: American Chemical Society. 252.
24. Kaelin, A., "The development of Climatex Lifecycle," in Sustainable Solutions, pp 393-401, ed. M. Charter and U. Tischner, Sheffield, 2001.
25. Ritter, S., Chemical and Engineering News, 2003, 81(26), 30-35.
26. Nike Corporate Responsibility Report, 2001.
27. Herman Miller press release, "Design for the Environment Program Advances Herman Miller's Sustainability Protocol", April 2, 2002.
28. Ford Motor Company, Rouge Renovation (http://www.ford.com/en/goodWorks/environment/cleanerManufacturing/rougeRenovation.htm)
29. Bizily, S.J., C.L. Rugh and R.B. Meagher, 2000, Nature Biotechnology 18:213-217.
30. C. L. Rugh, "Design and Construction of Phytoremediation Demonstration Facility" (presentation poster for Society for Environmental Journalism Annual Meeting), October 2000.