Naked Science Forum

Life Sciences => Physiology & Medicine => Topic started by: Ian Baker on 25/05/2008 22:28:42

Title: Why does blood on a tissue turn from red to brown in the toilet?
Post by: Ian Baker on 25/05/2008 22:28:42

Ian Baker  asked the Naked Scientists:

Dear Naked Scientists,

Having just had a nose bleed, 2 questions occurred to me.  What is the best way to quickly stop the bleeding? and why, when I threw the bloody tissue into the toilet did the previously clean water appear to go brown? Possibly a slightly weird question but puzzling none the less.

Ian Baker

What do you think?

Title: Why does blood on a tissue turn from red to brown in the toilet?
Post by: chris on 27/05/2008 09:40:09

I think that you have made a very astute observation!

I also think that you probably use some kind of bleach, or oxidising cleanser, in your toilet!

How do I know?

Well, blood is red because it contains haemoglobin, which is the molecule that ferries oxygen from the lungs to our tissues. As the name suggests, each molecule of haemoglobin contains an atom of iron  at its centre in a structure called a porphyrin ring.

Like a number of metals, iron has more than one oxidation state. Commonly it donates 3 electrons to make Fe3+ ions (like rust - Fe2O3), but it can also donate just 2, forming Fe2+ ions (like iron II sulphate FeSO4).

The iron in haemoglobin is in the 2+ oxidation state (Fe2+), and this is critical because if the haemoglobin is oxidised (to "methaemoglobin" containing Fe3+) then it can no longer work as an oxygen carrier. Some drugs and toxins can do this.

In the case of your blood-soaked tissue, I suspect that when you threw it into the toilet the toilet water contained something like bleach, which is a strong oxidising agent (it contains hypochlorite). Perhaps you've got one of those little tablets that sits in the cistern or dangles beneath the rim of the toilet and dissolves slowly with every flush?

Either way, these chemicals would have oxidised the Fe2+ in your haemoglobin to Fe3+, altering the colour (methaemoglobin is brown, like rust), hence your observation!

Chris

Title: Why does blood on a tissue turn from red to brown in the toilet?
Post by: Yan174 on 28/05/2008 15:13:38

Thanks, that's really interesting Chris, the bleach was probably there because the toilet had recently been cleaned.

Title: Why does blood on a tissue turn from red to brown in the toilet?
Post by: chris on 30/05/2008 00:13:27

That's a relief, I was on the right track!

Welcome to the forum.

Chris

Title: Why does blood on a tissue turn from red to brown in the toilet?
Post by: Madidus_Scientia on 30/05/2008 13:24:38

I once had a pair of white shorts that my girlfriend at the time washed with a pocket full of red paper napkins from her work, and it stained them pretty bad, no amount of bleach would work. So I figured the stains must be already oxidised and bleaching it would do nothing, so I filled the basin with 2 litres of coke (because its acidic) and soaked the shorts in it overnight, and it worked, never been cleaner. Go science!

Title: Why does blood on a tissue turn from red to brown in the toilet?
Post by: qazibasit on 09/06/2008 21:11:52

its because of the lysis of hemoglobin into hematin which is a timely reaction and its colour is brown.