Tackling Colorants Sustainability Combining Disruptive Science and Sustainable Leadership: A Review Article

: Many pigments and dyes are not only valuable molecules in manufacturing, but also environmental pollutants. Stemming from the observation of the slow pace of change taking place to counter the ‘fast fashion’ phenomenon and its environmental consequences, this critical review highlights the importance not only of biotechnological approaches but also of a sustainable leadership to achieve a future-proof fashion industry. Science has been producing sustainable alternatives to counter the issue of dyes, but this is not enough. A change in the business attitude and leadership approach of the organizations that operate in the industry is needed. Only through the successful combination of new technologies and forward-looking decision-making will it be possible to alter the status quo and deal with the multiple environmental challenges that businesses are and will be facing.


Introduction
Colors play a key role in our lives: our clothes, our cars, and the furniture in our houses come with a wide range of choices when it comes to hues, inks, and paints.Since the accidental synthesis of the first synthetic aniline dye, mauveine, by William Perkin in 1856 [1], the range of dye molecules available has widened and entered not only the textile, food, and cosmetic fields but also the pharmaceutical, plastics, ink, and packaging industries.As consumers, we mainly see them as a way of expressing our personal taste, mood, or personality and usually pay little attention to their origin and production process.As scientists, we are fascinated by the chemical processes behind them and, at the same time, mindful of the hazards they pose to the environment.Outside the lab, the colorants market has been steadily growing for decades, and it was estimated at 31.2 billion USD in 2020; it is now expected to reach 86.9 billion USD by 2030 [2].As a note, the terms colorant, dye, and pigment are used as synonyms in this article.
The use of colorants by the fashion industry impacts the environment, and its 'fast fashion' phenomenon in the last decades has led to an increased production, manufacturing, and discard of textile garments, irrespective of population growth.At the same time, the use of composite fibers, such as those containing elastane and colorants, complicates the already unprepared recycling phase [3].In March 2020, the European Commission launched a new circular economy action plan that is affecting multiple sectors dealing with material use, such as textiles [4].If we consider the fashion industry, finishing processes such as dyeing are energy-intensive steps requiring large amounts of energy and water, namely up to 150 L/kg of fabric, and taking a high toll on the environment [5].The dyeing of textiles is the second largest polluter of water at a global level, and a single pair of jeans can require up to 9000 L of water for its production [6].It might also be worth remembering that the textile industry is the only one of the many sectors that relies heavily on colored molecules.On the other hand, their use is highly restricted in the production of cosmetics, where colored natural ingredients usually provide a valid alternative [7].
Our relationship with clothes has been, and still is, full of contradictions, and colors have certainly fueled many controversial debates.The industry relied on only natural colorants until the middle of the 20th century, and this sometimes posed considerable risks.One striking example is that consumers wore arsenic dresses, mercury hats, and flammable clothing [8].Arsenic was widespread during the Victorian time because it represented a cheap way to color in bright green many everyday objects like candles, curtains, wallpaper, dresses, hair decorations, and shoes.Thanks to the introduction of synthetic dyes, it was eventually possible to find less-risky alternatives for producers and wearers.Discovered by accident, the synthesis of the first green dye was patented by Cherpin in 1862.Biotechnology has also now identified the synthesis of green pigments in many microorganisms (an early example is [9]).This is just one of many examples of how technological advances and scientific innovation have improved the nature and production processes of colorants in sectors like fashion, which has also resulted in higher safety for end-consumers, manufacturers, and the surrounding environment, thus improving sustainability.
Many studies indicate how sustainability, which entails an environmental, social, and economic dimension, provides a competitive advantage for companies by contributing to a positive reputation, improved customer satisfaction, and organizational commitment [10,11].Future-conscious leaders of all organizations should see sustainability as an opportunity to develop a competitive advantage and be at the forefront of their industry by combining their experience and influence with a typical start-up mindset.
Stemming from the observation of the slow changes taking place in the textile sector to counter its environmental consequences, for example due to the 'fast fashion' phenomenon, this critical review article will reflect on the importance of not only biotechnological approaches but also of sustainable leadership to achieve a future-proof fashion industry.Science is actively providing technical solutions, but adopting a suitable leadership style is crucial for the effective implementation of sustainable strategies and to continue to foster innovation (Figure 1).
heavily on colored molecules.On the other hand, their use is highly restricted in the production of cosmetics, where colored natural ingredients usually provide a valid alternative [7].
Our relationship with clothes has been, and still is, full of contradictions, and colors have certainly fueled many controversial debates.The industry relied on only natural colorants until the middle of the 20th century, and this sometimes posed considerable risks.One striking example is that consumers wore arsenic dresses, mercury hats, and flammable clothing [8].Arsenic was widespread during the Victorian time because it represented a cheap way to color in bright green many everyday objects like candles, curtains, wallpaper, dresses, hair decorations, and shoes.Thanks to the introduction of synthetic dyes, it was eventually possible to find less-risky alternatives for producers and wearers.Discovered by accident, the synthesis of the first green dye was patented by Cherpin in 1862.Biotechnology has also now identified the synthesis of green pigments in many microorganisms (an early example is [9]).This is just one of many examples of how technological advances and scientific innovation have improved the nature and production processes of colorants in sectors like fashion, which has also resulted in higher safety for end-consumers, manufacturers, and the surrounding environment, thus improving sustainability.
Many studies indicate how sustainability, which entails an environmental, social, and economic dimension, provides a competitive advantage for companies by contributing to a positive reputation, improved customer satisfaction, and organizational commitment [10,11].Future-conscious leaders of all organizations should see sustainability as an opportunity to develop a competitive advantage and be at the forefront of their industry by combining their experience and influence with a typical start-up mindset.
Stemming from the observation of the slow changes taking place in the textile sector to counter its environmental consequences, for example due to the 'fast fashion' phenomenon, this critical review article will reflect on the importance of not only biotechnological approaches but also of sustainable leadership to achieve a future-proof fashion industry.Science is actively providing technical solutions, but adopting a suitable leadership style is crucial for the effective implementation of sustainable strategies and to continue to foster innovation (Figure 1).

Traditional Knowledge and Modern Biotechnologies
Since ancient times, the fascination with colors has led people to explore natural sources from plants, lichens, and animals for personal decoration and eventually textile dyeing.Colorants were extracted and processed from lichens such as Letharia vulpina or wolf lichen, mushrooms, plants such as madder (Rubia tinctorum) or henna (Lawsonia inermis), and insects such as the kermes family (Coccus ilicis) [12].While our ancestors proceeded by trial and error, our efforts are nowadays supported by modern technologies in the form of analytics, in vitro cultivation, and genetic engineering.
Plant-based dyeing is based on a large amount of traditional knowledge that provides insights on optimal processing conditions [13].Multiple ethnological studies report that the use of plants for dyeing is rooted in the context of the territory and the tribal population in which the knowledge has developed [14,15].However, this knowledge and the application of the process are currently under threat due to the easy accessibility of synthetic dyes and acculturation [15].While these traditional processes might be in danger in developing countries, scientists are looking at them as ways to improve the sustainability of industrial processes.Traditional knowledge and vegetal materials are gaining more attention, and new sources of dyes are being investigated.For example, the inflorescence of munj sweet cane (Saccharum bengalense Retz.) has proven effective in various processes, including the creation of mordants and the use of high temperatures and natural agents such as moringa and turmeric [16].Similarly, polyphenol-enriched banana and watermelon biowaste has been tested as a pre-treatment for cotton fibers, as it provided protection from fading from UV exposure [17].
Modern analytics based on chromatography can assist us in identifying and separating all the colored molecules present in a plant extract.In addition, surface-enhanced Raman spectroscopy (SERS) and high-pressure liquid chromatography (HPLC) have allowed the separation and identification of colorful molecules from the plants at the core of the Chinese tradition, such as Chinese mulberry (Cudrania tricuspidata), gromwell (Lithospermum erythrorhizon), Chinese rhubarb (Rheum palmatum), tangerine (Citrus reticulata), and Morinda [17].In an attempt to discriminate dyes with different chemical properties based on polarity, size, and chirality, the use of supercritical CO 2 has proven valuable and a sustainable alternative to organic solvents [18].At the same time, non-invasive techniques such as UV-Vis-NIR reflectance spectroscopy have been explored to rediscover natural dyes from ancient textiles and rugs in a non-destructive way [19].
Taking one step forward while leveraging current practices, upcycling provides a great strategy.Already applied to food waste, upcycling has also been explored for both textiles and colors.In general, this does not require novel processing methodologies, and even just wet spinning can be applied [20].For example, wood waste such as sawdust from the Pterocarpus indicus tree has been successfully applied to colored cotton and silk fabrics [21].Plants of current low economical value can also provide hidden valuable molecules.As a study reports, the use of prickly pear peels of Opuntia ficus-indica (L.Miller) can be a source of colored molecules suitable for the dying of vegetal and animal fibers [22].Onion and pomegranate peel extracts can be used to deliver a yellow and an orange color (400 to 500 nm absorbance) to cellulose-based fibers [23].Color fixation can often proceed successfully through physical treatment such as drying and heating or by using natural mordants such as lemon juice, gallnut, pomegranate rind, and gooseberry that can compete with metallic alternatives [21].It is therefore reasonable to think that, in order to respond to the different manufacturing needs while adapting to local environments and resources, it will be necessary to identify multiple solutions.

Colorants and Biotech-Assisted Sustainability
The diversity in chemical structure and origin of colorants (Figure 2) is one of the reasons why making them sustainable across both phases of production and later remediation presents multiple difficulties.Biotechnological studies have addressed the issue by looking at the single-molecule level and by using complex microbial communities (Figure 2).Non-biobased but physical pre-treatments of textiles to promote dyeability have also been developed using high-energy radiation such as UV, plasma, and gamma rays that prove cost-effective and environmentally friendly as no by-product is produced [24][25][26].Production processes with a reduced environmental impact have also been reported to use continuous reaction conditions to decrease the water requirement by some 40% and the footprint by even a 4-fold [27].

Colorants and Biotech-Assisted Sustainability
The diversity in chemical structure and origin of colorants (Figure 2) is one of the reasons why making them sustainable across both phases of production and later remediation presents multiple difficulties.Biotechnological studies have addressed the issue by looking at the single-molecule level and by using complex microbial communities (Figure 2).Nonbiobased but physical pre-treatments of textiles to promote dyeability have also been developed using high-energy radiation such as UV, plasma, and gamma rays that prove cost-effective and environmentally friendly as no by-product is produced [24][25][26].Production processes with a reduced environmental impact have also been reported to use continuous reaction conditions to decrease the water requirement by some 40% and the footprint by even a 4-fold [27].
Figure 2. Multi-scale dimension of the biotech-based solutions to improve the sustainability of colorants.Biotechnological solutions encompass a wide range of dimensions, from the nanometer-scale of single proteins, e.g., laccase (PDB ID: 1KYA), to the millimeter-size of complex microbial communities that provide a whole enzymatic toolbox for bioremediation.(Lower panel) Representative colorants used on the industrial scale.(A) Trypan Blue is an example of azo dyes, organic molecules characterized by the functional group R-N=N-R′, currently applied to cotton coloration on a large scale but also applied to laboratory analytics.(B) Rubixanthin is a carotenoid, and carotenoids from waste from tomato processing are being tested for dyeing silk, wool, and polyamide [28] to provide a yellow coloration.(C) Disperse violet 27, or 1-anilino-4-hydroxyanthraquinone belongs to the aniline group of colorants and has been tested with polylactide fabrics.It is used in cosmetics but not allowed for products in contact with mucous membranes.(D) Methyl violet is a family of dyes that has been the subject of extensive studies focusing on adsorption and bioremediation [29].(E) Malachite green is a chemically formed triarylmethane dye that is recognized by laccase.
Fungi, bacteria, even algae and plants have proven effective in dye degradation of colorants of synthetic nature.Remediation can additionally be obtained using microbial approaches based on single-bacterial or fungal strains with adapted metabolism [30]; similarly, consortia can also be applied [31,32] Fungi, bacteria, even algae and plants have proven effective in dye degradation of colorants of synthetic nature.Remediation can additionally be obtained using microbial approaches based on single-bacterial or fungal strains with adapted metabolism [30]; similarly, consortia can also be applied [31,32].Their intracellular and extracellular enzymes are produced in response to the environment of growth, and, upon growth in polluted settings, the enzymatic activity can be tuned to recognize the contaminants and transform them.At the molecular level, multiple enzymes have been explored to catalytically convert dye molecules into less toxic compounds of less color.Major enzymes with potential in this respect are derived from the laccase (benzenediol-oxygen oxidoreductase, EC 1.10.3.2),high redox potential peroxidases (EC 1.11.1.X), polyphenol oxidases (EC 1.14.18.1), and azoreductases (azobenzene reductases, EC 1.7.1.6)classes [33,34].Catalases are versatile enzymes catalyzing an oxidative reaction using hydrogen peroxide or an organic peroxide.As an example sourced from the food industry, waste products (soybean and potato) peroxidases in an immobilized or free form led to the biodegradation of an anthraquinone dye with efficiency levels above 70% [35].This is a great example of upcycling.Used mainly for wool, tartrazine is a synthetic yellow azo dye used in printing and food coloring (E102) and has been degraded using bacteria Pseudomonas aeruginosa reaching 72.65% removal in 5 h [36].Similarly, Pseudomonas strains isolated from industrial water streams have delivered positive results in the remediation of methyl violet [37].The multi-purpose azo colorant trypan blue has proven useful in the industrial production of garments, cosmetics, laboratory analytics, and materials but poses an environmental concern for both the product and its degradation [27,38].Immobilized bacterial consortia [39] achieved the decolorization of wastewater in 24 h, i.e., a 50 mg•L −1 dye concentration, but produced fewer toxic derivatives.This reduced toxicity is however not an automatic outcome, and a case-by-case assessment is needed, e.g., Congo red in vitro degradation products by peroxidase fungal enzymes led to an increased in vitro toxicity whereas an equal treatment of methyl green reduced toxicity [40].
Removal of dyes from wastewater can also be achieved via physical methods, such as adsorption.This physical approach not always requires specialized active materials but can be performed with a sustainable perspective in mind by using waste-products from other industries such as Indian Rosewood sawdust, a timber industry waste for the adsorption of methylene blue [41] or sunflower (Helianthus annuus L.) seed hull for methyl violet removal [42].

Entrepreneurial Future
In view of a circular economy, the use of waste products or by-products is advisable.The ecological impact of the dyes and chemicals used by the textile industry is critical, and international organizations are responding with limitations and bans, giving companies only a few years to adapt [43].Several publicly funded projects have tackled the production of dyes in a biotech-based manner without relying on fossil sources.As an example, the BioNaD project, which ended in 2016 [44], addressed both new biosynthetic dyes and their biodegradation to create an environmentally friendly leather dyeing process.To reduce the land-use of the textile industry, even bacterial fibers such as bacterial nanocellulose has been suggested as textile material that can be dyed with natural extracts of natural dyes based on eucalyptus (Eucalyptus globulus L.) and onion (Allium cepa L.) [45].At the end of the supply chain, bioremediation is crucial to repairing the danger posed by the disposal of colorants in the environment.Biotechnology and an increased attention to sustainability can positively affect most of the supply chain for colorants (Table 1).
Natural dyes provide a sustainable, renewable source with high biodegradability and low toxicity for people and the environment as they are produced following green chemistry principles.The use of natural sources such as plant extracts offers the advantage of providing a complex mixture with possible additional bioactivities to the mere colorant action, e.g., antioxidant, antimicrobial, flavor, and medicinal action, due to the presence of metabolites such as flavonoids, carotenoids, tannins, and even alkaloids [46,47].Applied to leather dyeing, chitosan combined with caffeine, nettle extract, or shellac has proven effective in delivering a brown color and an environmentally friendly process [48].Plants certainly have a long history of use, but they require considerable time to grow, and they heavily depend on the surrounding environment and climate.Bacteria and fungi, on the other hand, allow easier and faster growth in vitro [49].Biotechnology has targeted the biosynthesis of more sustainable dyes using the tools of genetic engineering or by exploiting the enzymatic machinery already present in organisms such as fungi [49,50].Fungal species are specifically rich in oxidative enzymes such as laccase.Laccases have a wide substrate range and can thus accept different molecules as substrates to produce a plethora of colored products; moreover, results can be obtained only after a few days of cultivation.Fungal species are also a natural source of pigments; these are often produced as a mixture whose composition and resulting color can be tuned by tailoring the cultivation conditions [50].
Table 1.Examples of how biotechnology has tackled the sustainability of the extended supply chain of the textile industry.

Supply Chain Part
Example Reference

Disposal
Use of renewable materials for the adsorption of colorant molecules from effluents [65-69] Biotechnological removal of colorants using microorganisms such as mesophilic bacteria, fungi, algae, and others

The Leadership Perspective
Today more than ever, organizations are interconnected and exercise a reciprocal influence in a constant process of exchange and cross-pollination.The advances in biotech and science are therefore only one of many factors that should be considered when addressing sustainability issues.Novel technological solutions and processes cannot be effective without the engagement of all the people involved and an overarching change in strategy that is consistent and supported by all stakeholders.Over the last few decades, many industries, like the fashion and furniture sectors, have pursued growth strategies aimed at achieving high financial returns by producing significant volumes of products and attracting a wider customer base.Unfortunately, this often resulted in high-volume, low-quality products that come with a significant negative impact on the environment [6].
The ongoing COVID-19 pandemic and conflict in the Ukraine have also exacerbated a few of the already-existing issues related to supply chain and raw material sourcing, highlighting the importance of developing reliable and efficient relationships with all parties involved in the production process [70,71].This is also an increasingly important factor in the ability to attract new customers and retain existing ones.Consumers from newer generations are much more aware than in the past of the use of natural products and compliance with environmental protection regulations when it comes to choosing a product based on factors like carbon footprint [72,73].
Thanks to documentaries like The River Blue that drew the public's attention to phenomena such as the disposal of chemical waste in 2017, the mindset of consumers' has been shifting towards a focus on quality rather than quantity [74].In other words, organizations are under a significantly higher level of scrutiny and need to respond to a demand for change and the adoption of an ethical approach throughout the manufacturing process [73].The alternative is losing part of the consumer base and damaging, often irreversibly, a brand's reputation.

A Paradigm Shift: Sustainable Leadership
Pressure is built on organizations to show that they are genuinely adapting their strategies to the changing times and requirements of consumers and society.This is made even more difficult by phenomena like greenwashing in the fashion industry, which is the use of misleading claims on the environmentally friendly nature of their products and production methods and results in consumers being particularly skeptical when choosing to buy a specific product [75].To build a trust-based relationship with savvy customers, it is not enough for organizations to invest in biotech to find new, better solutions; it is also necessary to show how the whole business supports the change and has a forwardlooking strategy.In other words, it is essential that they find a balance between science and leadership.So, when it comes to leaders, how can they make sure that they do that?A successful approach can be summarized by three key points: 1.
Full commitment.Environmental, social, and governance (ESG) criteria have been increasingly part of companies' agendas, but policies and strategies are often fragmented and only focus on limited aspects of an organization.To adopt processes and techniques that are less harmful for the environment, the consumer, and the wider society, it is essential for leaders to encourage a full commitment of financial, human, and cultural resources across all business units and functions, from procurement and production to finance and reporting.

2.
A clear strategy and actionable plans.It is equally important that there be clarity on short-and long-term objectives, as well as the action plans necessary to implement them successfully within an organization.This requires the engagement of employees at all company levels, and leaders play a key role in fostering the right mindset and level of commitment to combine the change process with a culture shift.

3.
Communication.Both within and outside an organization, it is critical to devise an effective communication strategy.Employees and customers demand high levels of transparency when it comes to the nature of the raw materials used as well as their sourcing and manufacturing.It is therefore key for leaders to manage expectations and provide a consistent, clear message on the strategy adopted and how it will impact customers and products.
When discussing this topic, many experts speak about sustainable leadership, a concept that refers to an approach that focuses on creating benefits for all stakeholders in both the long-and short-term but also aims at improving the lives of those affected by, or involved in, its work as well as the product end users [73,74].An often-cited example is that of Swedish organizations that make sustainability a central point in the way they operate across all business units, including, for example, procurement, marketing, and communication [75][76][77][78].As a result, they enjoy high levels of trust both in the domestic market and worldwide, which often encourages the creation of a stronger brand image and higher levels of customer brand loyalty.

Can a Start-Up Mindset Offer an Effective Alternative?
Regardless of the type of innovation developed, it is important for businesses to adopt a new mindset and way of operating, in order to survive the competition [79].This radical change is often difficult to achieve because it entails a significant disruption in traditional business operations, something that proves particularly challenging for big corporations.On the other hand, publicly funded investigations have now reached the entrepreneurial scene, and many start-ups have emerged.A few notable examples are start-ups such as the French company, PILI, which received €3.6M in funding to develop a technology using microbes and renewable nutrient sources to produce dyed molecules in 2019 (https:// www.pili.bio/accessed on 23 November 2022).Similarly, the French company, Synovance (https://synovance.com/accessed on 23 November 2022) has the production of five colors ranging from blue to pink in the pipeline and has raised 50K euros through crowdfunding in 2022.UK-based Colorifix targets agricultural waste products as a source of energy for the conversion of dyes using microbes and, as of today, has developed 11 different tones and built collaborations with the major sector players (https://colorifix.com/accessed on 23 November 2022).Furthermore, the startup Allonia (https://allonnia.com/accessed on 23 November 2022) aims at extracting valuable compounds from wastewaters and has received a $20-million investment in 2021 [76].It could therefore be argued that sustainabilityfocused start-ups, play a key role in making the colorants industry greener and encourage a shift towards sustainable practices and production methods.In conclusion, what can bigger organizations learn from start-ups?Start-ups work as powerful idea incubators.Free from a few of the constraints typical of big corporations, they not only foster learning and knowledge sharing but also address issues from a different perspective and encourage the generation of disruptive solutions that often break existing knowledge boundaries.In addition, the agile business model typical of start-ups facilitates lean decision-making and enables this type of organizations to adapt quickly to the changing needs of the market and identify multidisciplinary approaches.On the other hand, what larger business entities have is accumulated knowledge and experience, as well as high levels of investment, power, and influence.This last point is key.Established businesses could play an instrumental role in leading institutional change and collaborative initiatives across sectors by teaming up with other companies, governments, suppliers, and stakeholders from the wider society.

Conclusions
The challenges posed by the fashion industry and its impact on the environment are urgent and need a collaborative effort to be tackled.Sustainable leadership might be the way to go, as it focuses on producing benefits for all stakeholders over time, especially for the lives of those directly involved in the supply chain.The scientific sector has been active in developing different tools to enable more sustainable sourcing and manufacturing across the entire supply chain; these are often adopted by small companies and first market-tested by start-up-like companies.The highly flexible and forward-looking approach of start-ups, as well as their innovation-oriented leadership style, can be a model for bigger companies to follow in order to shift away from inefficient supply chains and towards a more sustainable way to do business.

Figure 1 .Figure 1 .
Figure 1.The journey towards a sustainable future requires the combination of multiple aspects, with biotechnology and leadership playing an equally key role in the implementation of change to the textile industry and its environmentally hazardous use of synthetic colorants.

Figure 2 .
Figure 2.Multi-scale dimension of the biotech-based solutions to improve the sustainability of colorants.Biotechnological solutions encompass a wide range of dimensions, from the nanometer-scale of single proteins, e.g., laccase (PDB ID: 1KYA), to the millimeter-size of complex microbial communities that provide a whole enzymatic toolbox for bioremediation.(Lower panel) Representative colorants used on the industrial scale.(A) Trypan Blue is an example of azo dyes, organic molecules characterized by the functional group R-N=N-R , currently applied to cotton coloration on a large scale but also applied to laboratory analytics.(B) Rubixanthin is a carotenoid, and carotenoids from waste from tomato processing are being tested for dyeing silk, wool, and polyamide[28] to provide a yellow coloration.(C) Disperse violet 27, or 1-anilino-4-hydroxyanthraquinone belongs to the aniline group of colorants and has been tested with polylactide fabrics.It is used in cosmetics but not allowed for products in contact with mucous membranes.(D) Methyl violet is a family of dyes that has been the subject of extensive studies focusing on adsorption and bioremediation[29].(E) Malachite green is a chemically formed triarylmethane dye that is recognized by laccase.