Did I just kill someone with my denim? *gasp*
Most probably not. But with those 8 pairs of denim jeans👖 you've abandoned in the back of your cupboard or the 4 denim shorts that you just threw away? Or that 5 pairs of jeans that almost every girl on the planet (in the developed part of the world) owns? Possibly.
If you’re too tired to read, scroll till the end to watch a 2-min video. 😊
LET'S GET THIS STRAIGHT. WHAT ARE DENIMS?
When I say denim, I mean everything denim. Not just jeans, but also shirts, shorts, dresses, skirts, etc.
Denim and jeans seems like interchangeable terms, but if you look at the diagram below, you’ll get the feel that denim is more like a type of fabric that can be used across multiple garment categories.
In short, denim describes a way that a fabric is weaved, or it can mean a type of fabric (whatever, it doesn’t really matter at this point). Classical denim is a heavy fabric made from 100% cotton and woven using dyed and undyed yarns.
The usual colour is blue, that we call ‘indigo’. The usual material used is cotton.
Just to clarify, denim itself isn’t something evil. It is just a way a fabric is weaved. But what’s problematic is the way it is dyed and how we want the denim to look.
SO... WHY ARE THEY ‘KILLER’ JEANS?
Well, the sense of smell, lungs, skin, reproductory systems etc. of the workers (and people who live around the factories) are ruined. Important 'lifelines' (aka rivers because they contain fresh water) is polluted. All aquatic life dead...
Are we supposed to know this? Well, we’re not supposed to. Every bit of this ‘secret’ unlocks when we breaks down the manufacturing process [processes info from 1].
A - THE DYE ITSELF
Simply put: (1) these dyes are toxic, (2) they are released into the rivers untreated.
Indigo is a very beautiful but challenging colour.
Beautiful because some claim that it is the world’s oldest textile dye . Although blue exists in flowers and berries, unlike indigo, most of them are not suitable for dyeing & not long lasting [2a]. Natural indigo is achieved by very skilfully fermenting the leaves of certain plants [2a].
Challenging because indigo is not soluble in water. It also does not bind chemically to fabric. How on earth do we dye fabrics in blue? We add reducing agent, an alkaline substance that is used to deprive oxygen.  A natural fermenting indigo dye vat operates at pH 9.5, but in order to improve efficiency, people use very strong alkaline reducing agent like sodium hydroxide . As you can probably bet, modern denim manufacturing will most likely take the latter, making all the dye liquid extremely alkaline. Such liquid is enough to pollute rivers and kill marine life.
“Unlike most natural dyes that, when heated, penetrate cloth fibres directly... indigo binds externally to the cloths’ threads, coaxed by a chemical agent called a mordant.”  Mordants most commonly used by clothing companies are metals like chromium or aluminium. When discharged in large amount untreated, both can kill off plants, destroy ecosystems, poison drinking water, etc.
[Postscript September 26, 2018] I have since then read several more sources and have reasonable doubt that the above statement is inaccurate. Here’s what I have found:
Mordants are commonly used to affix colour on to the fibre, it creates a link between the dyestuff and the fibre. The more effective mordants are heavy metals. 
Indigo is the few natural dyes that does not require a mordant. 
However, in cases where super dark indigo tones are required, mordants are required. 
Indigo achieves the best results when it is applied on natural fibres.  Unfortunately, there is no guarantee that denim these days are made with 100% cotton yarns, as such, there can be synthetic fibres (for instance elastane that improves the stretch). For dyeing synthetics, it’s better to use mordants.
In any case, it is undeniable that indigo requires an alkaline reducing agent and a mordant that is most likely heavy metals.
Making matters worse, most of the world’s indigo dye is synthetic. Synthetic indigo begins by extracting petroleum (which is non-renewable btw) + high heat = benzene, then + toxic chemicals (cyanide & formaldehyde).
Not only that, when they are released into rivers untreated, indigo darkens the water. The living stuff are starved of sunlight... so there you have a very polluted river + no sunlight.
A - THE DYEING PROCESS
For denim, the yarn is dyed before it is made into a fabric. The cotton yarns needs to be dipped in a dozen or more times in the dyebath to get the right shade. This alone is extremely water-intensive.
In developed countries, the technology is advanced so that the used dye liquid can be reused. The factory can measure and get the right shade for the next dyebath by adding the right amount of new dye.  But in developing countries, who gives a shit? Just use that unlimited load of freshwater and dump them in the river.
B - SLASHING
Cotton yarns are then treated with starch to increase its strength (who wants a pair of jeans that is not durable? I mean, what’s the point of jeans anyway??). It is then bathed in paraffin (from oil) to smoothen and lubricate it. Starch is biodegradable, but it doesn’t mean it’s problem-free. When dumped in waterways, the microbes that eat it consumes oxygen. A little bit is ok, but like a whole load of factory waste? That means that fishes and other living stuff in the river don’t get oxygen.
The river doesn’t have sunlight, super polluted, AND NO OXYGEN. Congrats! We just killed a river.
C - FINISHING
Who invented distressed denim????? Why did we ever created something new just so that they can look old on day 1?
The last stage of the garment production involves a series of chemical and mechanical processes. (Unless otherwise specified, the source below is )
The ironic thing is - for the most part of the lighter denims, they are dyed super dark blue and repeatedly bleached so that we can get the lighter shade. Why don’t we just dye them in a lighter shade? I don’t know!! If you want just a lighter shade at some specific locations? Great! Workers had to manually sponge or spray toxic bleaches onto the garment. The potassium permanganate bleach can cause health problems such as decreased fertility for men & women, liver & kidney problems .
To replace ‘stone-washing’. Not too evil compared to other processes. If you want to know more, see .
The chemicals used can burn skin & irritate eyes, nose and throat. Sodium bisulphite to bleach to surface to make it softer and creating a distressed look.
This is quite old fashioned, but pumice stones are put in a gigantic washing machine together with the garment to make it look ‘worn’. 
Sandblasting uses a high pressure machine to spray the jeans with sand. It is so dangerous to workers’ lungs that it has been banned in many countries,  but who cares in developing countries? Machine sanding and hand sanding are similar. In these workstations, if there are no strong ventilation to remove the sand suspended in the air, workers are exposed to sand dust. When breathed in, they can cause an illness called silicosis that makes breathing difficult and can cause auto-immune diseases, lung cancer, and death.
SO... WHAT TO DO?
There are multiple ways we can do ‘the lesser evil’ other than buying these ‘killer jeans’:
Try not to purchase jeans made with conventional cotton. It is notorious for being super water & chemical-intensive. Try organic / BCI cotton?
Look for ones that are certified to produce waste water that are safe (e.g. GOTS for organic materials and Oeko-tex for both organic / non-organic) Don’t bother between natural / synthetic indigo. Both don’t dissolve water and always involve chemical solvents.
Don’t buy distressed denim.... If you must, look for ones that are certified with good labour conditions.
Most importantly, just don’t buy too many denims...
THE HONG KONG OPTIONS
In the next blog post, I will look into 2 companies that makes denim garments (shirts & jeans) that are founded by our beloved Hong Kongers! It is not an ad - I will feature both pros and cons about them. We’re not scientists or technology developers that can change how the world create denims in one day, but we can always begin as a consumer.
General info: https://en.m.wikipedia.org/wiki/Denim
Inspiration: The River Blue Documentary
Why indigo are used to make jeans for the various degree of blue shade - the dye is only applied on the surface of the yarn, hence making it easier to wash out and achieve the shade that is desired (https://www.youtube.com/watch?v=2HQL-bgWySw)