We continue our two part blog on synthetic dyes with understanding the wastewater process to better how runoff ends up in our waterways...


Understanding the Wastewater Process

We wanted to have a better understanding of what happens to postproduction dye runoff water. We spoke with a specialist in the San Diego wastewater department. This is what we found out, and please note that this is just the water system for Southern California. The United States does have regulations for runoff water, or in other words a waste water treatment system that tests for toxicity before release into water systems. The goal of this system is to release nontoxic water into our waterways, and the following are steps that runoff water goes through before entering into our waterways:

Step 1: Runoff leaves Dye house and goes to a treatment plant.

Step 2: Runoff reaches a settling tank where a coagulant binds waste solids together at the bottom of a tank.

Step 3: A biological breakdown occurs from rotating reactors (micro-organisms, bugs, and bacteria) and oxygen pumps, which break down the waste.

Step 4: Another coagulant is used for a second settling round to finalize a nontoxic level to the environment.

Step 5: Pipes are scattered along water ways releasing treated wastewater through small, perforated holes to avoid dumping large quantities at one time.

In the USA, we have a wastewater infrastructure with treatment centers, regulations, required permits, audits, and policies, but other countries do not. Many Asian countries that do not have regulations are a haven for fast fashion apparel companies because there is cheap labor and low overall cost. These countries are where garment workers are exploited, the environment sees a hazardous effect, and surrounding communities live in toxic conditions. Fast fashion companies are exploiting the people and the planet without any regulations on dyes and wastewater.

Photo from the documentary River Blue of toxins in a river of a community, found round the world. https://riverbluethemovie.eco/


The wastewater system in the USA is a step in the right direction, and a factor to consider when companies are deciding on location of their production. We believe further regulations need to be made and government grants needs to be available for dye houses to make the change to “low impact” dyes and processes. A big factor, when using synthetic dyes, to have a lower impact on the environment  is staying domestic and choosing a dye house with good reports and certifications.


Properties of Dyes

When trying to understand the impact of dyes, it’s important to look for dye toxicity, absorption rate, water use, and energy use (https://www.cattermoleconsulting.com/explaining-low-impact-dyes/).

Dye toxicity refers to the make-up of the actual dye and is considered non-toxic if it excludes heavy metals, carcinogens, and allergic reactions (https://www.cattermoleconsulting.com/explaining-low-impact-dyes/).

Absorption rate refers to the amount of dye that stays fixed to the garment or fabric. Higher absorption rate means that the dye sticks to the fabric with a stronger bond and has less dye concentration in the runoff water. Low absorption rate means there is higher runoff since less dye is fixed to the fabric. This often is seen with vintage effects or faded looking dye jobs.

In addition to absorption rate we’d also like to mention wash fastness. Not only is it important that there is a high absorption rate in the dye process to minimize runoff, but it is also important that the dye stays fixed to the garment throughout the rest of its life cycle. In other words as consumers wash their garment, it is important that the dye is not continuously running off each wash cycle.

Water and energy use should also be noted, as some dyes require more washes, chemicals, and energy to affix the color to the fabric. Low impact dyes “require less rinsing” so they use less water and energy in the process (https://www.cattermoleconsulting.com/explaining-low-impact-dyes/). 


“Low Impact” Synthetic Dyes

We researched what “low impact” dyes are and found a broad definition through the Oeko-Tex Standard 100 international certification process. To get certified as “low impact” from this international standard, dyes can’t have any toxic ingredients that are harmful to human health (Oeko-tex). This certification is helpful in understanding the effects on humans, but it’s a bit of an assumption to guess that it wouldn’t be harmful to the environment as well. Other sources mention that Oeko-tex 100 certified dyes are eco-friendly, but we could not find any statements on their website specifically about the environment.

To be considered a “low impact” dye, according to Oeko-Tex, the dyes must have an absorption rate of higher than 70%(https://www.cattermoleconsulting.com/explaining-low-impact-dyes/). This means the dyes must affix 70% of their dye to the fabric, with only 30% running off. 

Looking for certifications is one way to recognize “low impact” dyes. In addition to Oeko-Tex, there is also Bluesign, GOTS, and Cradle to Cradle that recognize non-toxic dyes (https://www.cattermoleconsulting.com/explaining-low-impact-dyes/). In addition to certifications, there are specific types of synthetic dyes that have a lower impact on the environment than others.

Dyes to Notice and Avoid

There are numerous classes of dyes that could be discussed; however, we would like to highlight some of the more common dyes that consumers may hear of, the most “low impact” dyes, and more known toxic dyes.

Analyzing our research, it appears that most eco-friendly type of synthetic dyes are reactive dyes, which we consider to have the lowest impact. Reactive dyes have a chemical bond that directly reacts with the fabric and makes a strong bond (https://textilelearner.net/synthetic-dyes-in-textiles/). This strong bond made with the fabric and dye creates a very permanent dye, leaving little dye in post-production runoff and a minimal—if any—amount throughout the rest of the garment’s wash life cycle. Reactive dyes are known as the most “permanent” dye (https://textilelearner.net/synthetic-dyes-in-textiles/). Reactive dyes do not use any heavy metals or toxins and doesn’t need any mordants to aid in affixing the dye to the fabrics (https://organiclifestyle.com/articles/fibre-reactive-low-impact-dyes). It also uses less water, salt, and chemicals since it has a shorter dye cycle, compared to other fabric dyes (https://organiclifestyle.com/articles/fibre-reactive-low-impact-dyes). In addition to our online research, the chemist we spoke to confirmed that reactive dyes have the least impact on the environment and are nontoxic.This type of dye is our first choice when it comes to synthetic dye types, as it uses nontoxic ingredients, has a high absorption rate, and lower water and energy use.

We hear about “sustainable” brands using pigment dye, and it certainly creates a nice faded vintage look. Our team wanted to investigate. We also would like to note that some new garments that have that vintage fade to them are not just dyes, but also treated with an additional chemical to make it look faded. So, it’s an extra step of adding more chemicals to the garment and environment. However, pigment dyes are known for their process of applying pigment to the surface of garments. The pigment does not hold well and washes away with wastewater, leaving a faded color. This weak bond creates a low absorption rate and higher density of pigment in runoff water. Garments that are pigment dyed can continue to fade and loose pigment throughout its life cycle. This type of dye also has to use a binding ingredient along with the pigment which aids in absorption rate. We have come across some binder and pigment dyes that claim they are non-toxic but could not find any certifications. We are intrigued by the idea of garment dying with certified pigment dyes (if they exist), but do feel concerned about the amount of pigment that is lost in the dye process and lifecycle.

One of the most toxic dyes we continued coming across in our research are Azo dyes; however the ingredients of these dyes can vary in levels of toxicity. Some Azo Dyes can include carcinogens and are not only harmful to the environment, but also to your skin (https://www.fashionrevolution.org/the-true-cost-of-colour-the-impact-of-textile-dyes-on-water-systems/). These dyes can degrade and form carcinogenic amines and are banned in EU member states, as well as China but still persist in clothing (https://www.fashionrevolution.org/the-true-cost-of-colour-the-impact-of-textile-dyes-on-water-systems/).

More on Dyes

Dyes can also be applied in various stages of the production process, including to fibers, yarns, fabric, or garments. There are arguments proposing that dying garments is a better choice because it uses less dye and water, by eliminating the fabric that is not included in the garment. However it seems that many of these garment dyes are often pigment dyes. So water usage may be less, but the density of dye in the runoff may be higher.


We are stoked on finally compiling years of research together into these comprehensive blogs on synthetic dyes. We are feeling confident only in the use of reactive synthetic dyes with nontoxic certifications in the USA. We are motivated to know that our domestic production is the lowest impact way to go. Type of dyes, nontoxic certifications, and location should be considered when trying to select or look for low impact dyes.

Overall, there needs to be more transparency in the supply chain from clothing brands about the dyes they are using and where they are dying their product. There also needs to be more regulations on types of dyes to decrease toxicity for garment workers and the environment. We believe governments needs to provide funding to dye houses to convert them to low-impact dyes and more energy efficient innovative technologies. Fashion brands also need to create demand for nontoxic dyes and more energy efficient processes to push for these changes in dye production. Change is imperative to lessening the impact that synthetic dyes have on the people and the planet.










June 22, 2022 — Emily Karrer