Do or dye: synthetic colours in wastewater pose a threat to food chains worldwide.

A recent study has shed light on the environmental and health risks associated with the discharge of synthetic dyes into wastewater systems, prompting calls for global legislation on water management and immediate investment in sustainable treatment methods, and underscores the need for regulations compelling industrial producers to eliminate dyes before they enter public sewage systems or water bodies.

Billions of tons of wastewater containing dyes enter water systems annually. Synthetic dyes, commonly utilised in the textile, food, and pharmaceutical sectors, pose a substantial menace to human, animal, and plant well-being, along with ecosystems on a global scale, according to the findings of a new study, published in Nature Reviews Earth & Environment.

The study, entitled “Environmental Impacts and Remediation of Dye-Containing Wastewater”, was authored by academics from the University of Bath, the Chinese Academy of Sciences, the Fujian Agriculture and Forestry University, the Korea Institute of Energy Technology (KENTECH), and KU Leuven, Belgium.

The research emphasises that currently, up to 80% of dye-containing industrial wastewater generated in low- and middle-income countries is released into waterways without treatment or used for direct irrigation. This poses diverse threats to human, animal, and plant health, both directly and indirectly.

Despite the severe risks posed to health and ecosystems, the authors point out the lack of infrastructure, investment, and regulatory efforts to make dye usage more sustainable and to treat dye-containing wastewater.

Dr. Ming Xie, a lecturer in the Department of Chemical Engineering at the University of Bath (UK), believes that a multifaceted approach is necessary to address this issue. He says, “Dyes create several problems when they reach water systems, from stopping light reaching the microorganisms that are the bedrock of our food chains, preventing their reproduction and growth, to more direct consequences like the toxic effects on plants, soils, animals, and humans.”

“A worldwide regulatory effort is needed to stop dyes from reaching wastewater or other water systems, such as irrigation. Given the complexity of treating dye-containing wastewater, one solution would be to shift from the concept of centralized or regional treatment methods to decentralized and site-specific treatment at the source, compelling industries to remove dyes from the wastewater they create before it reaches public water systems.”

Textile industry: the leading consumer of dyes.

The global dye industry traces its roots back to the discovery of mauveine, the first synthetic organic dye, in 1865. Since then, more than 10,000 different types of dyes have been synthesised, with annual global production now estimated at 1 million tons.

Dyes find applications in various industries, including rubber, leather tanning, paper, food, pharmaceuticals, and cosmetics. However, the textile industry stands out as the largest consumer, accounting for 80% of synthetic dye production and generating approximately 70 billion tons of dye-containing wastewater each year.

China, India, and Bangladesh together discharge around 3.5 billion tons of textile wastewater annually. Synthetic dyes further exacerbate water contamination, which is a critical concern given the prevailing issues of water scarcity, making dyes a pivotal environmental and sustainable development challenge.

Untreated dyes alter the color of water bodies, reducing the amount of visible light that penetrates the surface layer. This hinders photosynthesis in aquatic plants, setting off a cascade of effects throughout the food chain.

Microalgae, which constitute the foundation of the aquatic food chain, are particularly sensitive to reduced photosynthesis. They experience inhibited growth and cell deformities when exposed to synthetic dyes. This disruption, along with the subsequent compromised transfer of energy and nutrients up the food chain, can lead to the collapse of entire aquatic ecosystems.

These impacts extend to fish as well. Dyes can accumulate in fishes’ gills, lateral lines, or brains, resulting in toxicological effects such as uncoordinated movement, respiratory distress, liver damage, and kidney dysfunction. These effects not only diminish the nutritional value of fish for predators but also reduce their reproductive rates.

Toxic dyes can also bioaccumulate in the fatty tissue of fish, posing health risks to humans and animals up the food chain.

The adverse effects of dyes are not limited to water bodies. They disrupt the balance of microbial communities in soil and can have harmful consequences on human health, leading to allergies, asthma, dermatitis, central nervous system disorders, and organ dysfunction, while also increasing the risk of cancer.

No single solution for dye removal.

The study explores a range of technologies for remediating dye-containing wastewater, including chemical, biological, physical, and emerging advanced membrane-based methods. However, the authors found that no single technique is a panacea for dye removal, and several promising methods are not yet technologically mature for large-scale implementation.

In light of these findings, the authors recommend a collaborative effort led by policymakers to promote the adoption of advanced remediation technologies and encourage changes in textile processing methods to reduce the use of the most toxic dyes.

The authors also emphasise the potential for industries to create new revenue streams by processing, separating, and reusing wastewater materials.

Co-author Dr. Dong Han Seo, from the KENTECH Energy Materials and Devices/Environmental and Climate Technology Track, states, “Dye-containing wastewater is one of the most challenging wastewater streams, impacting lives and the environment in several countries.

Our review provides the latest insight on how we can effectively manage the challenge from the perspective of a circular economy, effectively recycling dyes from wastewaters using treatment strategies such as advanced membrane-based separation to recover both useful dyes as well as clean water.”

Dr. Jiuyang Lin, from the Chinese Academy of Sciences, adds, “This review provides examples of how we can reduce the dye footprints from production stages using new dyeing techniques. Guidance on effective solutions to dye-containing wastewaters could be used to treat other challenging wastewater streams, safeguarding lives and the environment for future generations.”