Apatite for Destruction experiment summary

This is a summary of the experiments we’ve been doing. We’ll get the results of most of them on Saturday (18th Feb) at the results event in Cardiff. 
Making hydroxyl apatite (HA) in the lab 

 The people in Cardiff (Cardiff Catalysis Institute, our partners in this project) have been trying to make HA on pieces of nappy, using solutions with known concentrations of calcium and phosphate. These concentrations have been chosen to mimic hard and soft water and with /without wee or detergent. 

 Why?: We think that HA forms ‘microcrystals’ in solution, and that this is the first step in the formation of exoskeletons on the nappies. These artificial tests let us closely control the conditions and find out what is important for forming these microcrystals. 

 We’ll find out: If they’ve been successful in forming HA microcrystals in the lab, and what concentrations were needed. How do these compare to ‘real life’ conditions that nappies are likely to be in? 

Looking at last year’s test nappies  

3 out of 5 nappies we got tested last year appeared to have a coating of HA on them. The Cardiff lab have been looking at what remained of the test nappies from last year in a Raman spectrophotometer. 

Why: One of the HA experts we talked to said that the test used to identify HA wasn’t accurate enough, and it could instead have been struvite (i.e. magnesium phosphate instead of calcium phosphate). The Raman is more accurate and can definitely tell which metal ion is involved. 

 We’ll find out: For definite what mineral is in the nappies. Is it HA, or is it struvite? 

Ash tests on more nappies and other items 

 The lab (Shirley Technologies Ltd) who did the tests for us last year, are doing some more testson some more nappies, supplied by members of the group. We have two pairs of nappies where one was washed in full dose of detergent and one washed in half-dose. But in the same machine, on the same water, etc. So that is a natural experiment to see if detergent dose makes a difference.  

Some of the nappies they are taking TWO samples from – one from the wee zone, and one from away from the wee zone. 

 They are also testing viscose wipes from two of these households. 


  • Can we find more examples of HA on nappies? 
  • To find out if how much detergent you use makes a difference? 
  • To find out if sitting in lots of wee makes a difference? 

We’ll find out: Is there a difference between nappies washed in full dose detergent and nappies washed in half-dose of detergent?

 Is there a difference between things that have been soaked in wee for ages and things that haven’t? 

‘Dip and dry’ tests 

Some brave volunteers have been doing tests at home, to see if they can make HA on some new viscose boosters we sent them. 

 Some have been dipping them in fresh toddler wee, and letting them dry for a day, before dipping them again. 

 Some have been dipping them in a water and detergent mixture and doing the same. 

Why: The nappies we had tested last year were coated in mineral HA. We think the HA formed as the nappies dried; as water evaporates, leaving behind minerals. So dipping and drying is the best way to mimic that. And the Cardiff lab weren’t able to do this test for us as they are ananalytical chemistry lab and don’t have procedures for using human samples. 

 The laundry testing lab we used for the nappy tests last year had not come across such high levels of HA in anything they’d ever tested before. (The nappies had 20% HA; the highest they had ever seen was 10% HA). 

Maybe that is just because nappies get washed a lot, and in the right conditions, some HA is added in each wash? Or maybe it is something to do with nappies? We wondered if the HA has actually formed from wee? The dip and dry tests were one way of trying to form HA from wee alone. 

We’ll find out: Has HA formed a coating on the fibres from water and detergent, or from wee?

Smelly nappy survey 

The nappies we got tested last year all had smell problems (usually, smelling of ammonia, or ‘barnyardy’ as soon as weeed in). Maybe this was just a coincidence? Or maybe the HA build-up is what causes the smell issues? 

We have done a nappy survey, asking if people have similar smell problems, and about their wash routines and water hardness. 

Why: To see if we can spot any patterns in where people are getting smell problems. 

We’ll find out: Where are smelly nappies happening? Are there any things that seem to go along with smelly nappies? (Water hardness? Wash routine?) 

pH Testing 

Our experts have told us that HA forms best in Alkaline conditions (pH greater than 7). Volunteers used pH paper to test their nappies at various points in their nappy using and washing routine and then completed a survey with their results and some basics about their routine. 

Why: If we can spot times when our nappies are alkaline, perhaps this is when HA is forming? 

We’ll find out: When are pH conditions ideal for formation of HA?     

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