With increasing environmental concerns raised by synthetic dyes, sustainably produced natural dyes are the need of the hour. These dyes should be safe, stable, non-toxic, non-carcinogenic, and non-allergic
Colour is the key visible ingredient in how we perceive a product in our everyday lives and is one of the ultimate deciding factors in purchasing clothes. India is renowned for its diverse traditional and regional dyeing styles, such as Bandha from Odisha, Telia Rumal from Andhra Pradesh, Patola, Chandrokhani, Gharchola, and Bandhani from Gujarat, and Piliya, Lehariya, and Bandhej from Rajasthan. One of India’s oldest natural dyes, indigo, serves as a metaphor for the nation's struggle for independence. However, the discovery of the first synthetic dye, Perkin’s Mauve, in the 1850s initiated a long trail of petrochemical-based synthetic colours. They are stable, have low production costs, and offer an extensive range of hues. Currently, several commercial products from the cosmetics, textiles, and food industries utilise petrochemical-based dyes.
Toxic Effects of Synthetic Pigments
Synthetic dyes have adverse effects on animals and humans. These include hyperactivity in children, allergenicity, disruption of endocrine hormones, and acute toxicity. Common synthetic colours include Allura red, carmoisine, ponceau 4R, quinoline yellow WS, sunset yellow, and tartrazine. They come with the warning that they'may have an adverse effect on activity and attention in children’. The dyes used in the textile industry are non-biodegradable and are one of the major pollutants of many Indian rivers. One tonne of cloth (8,000 T-shirts) requires 200 tonnes (200,000 litres) of water to dye, which is then released into the environment as contaminated effluent. The fashion sector also contributes 10 percent (3.3 million tonnes) of the world's greenhouse gas (GHG) emissions. While azo dyes have carcinogenic amines, other colours contain heavy metals with irreversible bio-accumulative effects.
Natural vs Sustainable
With increasing environmental concerns raised by synthetic dyes, sustainably produced natural dyes are the need of the hour. These dyes should be safe, stable, non-toxic, non-carcinogenic, and non-allergic. Their production should be cost-effective and pose no risks to the environment. Plant-based colours require a large area for crop production and are subject to seasonal variations and low yield. Cutting acres of farmed land to obtain just a few kilogrammes of the dyes seems unsustainable. Their natural counterparts, microbial dyes (from bacteria, fungi, algae, and lichens), have an edge in scalability with lower production costs and no seasonal variations. They can either be by-products of biofuel production or be produced in large fermenters. These dyes further have health benefits with anticancer, antimicrobial, antioxidant, and anti-fouling properties, giving them an upper hand in dyeing technical textiles. Commercially available microbial flavins, anthraquinones, monascins, and violacein are used in textiles to a lesser extent.
Microbial Pigments – A Reality?
The art of dyeing with mushrooms is widely recognised, while the use of lichens for dyeing, historically referred to as "peasant dyeing," has deep roots in the northern regions of the world. For a microorganism to be selected for dye production, it should have high growth rate, high productivity, all-season production, and be non-pathogenic, non-carcinogenic, non-toxic, and tolerant of a broad range of industrial conditions. Amongst various microbes, fungi are known to harbour colours with remarkable biological properties and unique chemical diversity. These colours, isolated from endophytic fungi (fungi that live inside plant tissues), have been found to be potent antimicrobials, comparable to the commercially available antibiotics, reducing the requirement for antimicrobial finishing in textiles. Once an ideal fungal candidate is selected, optimisation, smarter screening, and engineering techniques improve the microbe for uniform and effective production of dyes. Utilising cheap agro-industrial waste as raw material for fungi also significantly lowers investment costs and enhances the environmental friendliness of the process. Microbes have successfully entered the textile market with global initiatives such as the Vienna Textile Lab, Huue, Pili, Fabulous Fungi, and others. Colorifix, a textile company in England, produces a large range of microbial dyes on a commercial scale and is endorsed by well-known brands such as Forster Rohner and Tintex. They also conducted a life cycle analysis showing microbial dyeing reduced water consumption by 77 percent, energy consumption by 53 percent, and carbon dioxide emissions by 31 percent.
In India, researchers at TERI are bioprospecting dye-producing microbes from various biological sources. One such study explored endophytic fungi isolated from the biodiversity hotspot of India, the Western Ghats. These fungi have been found to produce intense red dyes with anticancer, antimicrobial, anti-inflammatory, and antioxidant activities. The process led to the development of an eco-friendly technology for producing natural red dyes, which are highly efficient in dyeing proteinaceous fibres. The optimised process and thoroughly characterised dyes are being modified for large-scale textile dye production and dyeing units. A circular outlook for utilising waste materials such as rice husks to grow pigmented microbes is also underway. The exploration of sustainable microbial dyes presents a promising avenue towards a more eco-conscious future and stands as a beacon of sustainable innovation. Embracing these alternatives is not merely an option but a necessity for a planet seeking equilibrium between innovation and ecological preservation.
(Dr. Mayurika Goel, Fellow, Sustainable Agriculture Division, The Energy and Resources Institute and Dr. Arvind Kapur, Distinguished Fellow, Sustainable Agriculture Division, TERI.)