Apatite for Destruction

In the course of our investigations last year into reusable nappies, we found some nappies with an ‘exoskeleton’ of hydroxyl apatite (a mineral found in bones and teeth). Two out of the five had about 20% w/w of hydroxyl apatite in the fibres i.e. 20% of the weight of the dry nappy was made up of this mineral.

Read more about the background to the project here.

So far Nappy Science Gang have come up with a list of hypothesis and voted for their favourite. The top 3 hypothesis that we intend to investigate further are:

1. The calcium in the hydroxyl apatite is from hard water.

2. A nappy with HA will contain more live bacteria after washing than one with no HA under the same conditions.*

3. Insufficient detergent makes hydroxyl apatite growth more likely.

*It was later decided that there was no need  for us to investigate hypothesis 2, as there is sufficient evidence in the scientific literature that the presence of HA would increase the number of bacteria present (see live chat with Elaine and Barry who study the use of HA to concentrate bacteria). As we have limited time, we should focus on something that is unknown in current literature. 

We are currently running the following experiments and surveys: (click orange links for more details)

  • Dip and Dry booster experiment – volunteers are dipping viscose (bamboo) swatches in either toddler urine or detergent/hard-water mix for 30 consecutive days, (hanging to dry between dips), in an attempt to form HA under experimental conditions. The scientists at Cardiff Catalysis Institute (CCI) will test the swatches for HA using Raman spectroscopy.
  • pH testing – HA forms under alkaline conditions. Our volunteers are armed with pH paper and are undertaking tests, to see where alkaline conditions may be found.
    On a wet night nappy? In the nappy bucket? After the wash? Urine itself?
  • If you have a nappy you are willing to donate to the project, please fill in our survey. We will pick those most likely to contain HA to put forward for testing at Cardiff Catalysis Unit.
    Our definition of an HA candidate nappy: Viscose (bamboo) or cotton nappies with a persistent smell of barnyard or ammonia – either straight out of the wash, or after being weeed in. Possible crunchy feel and loss of absorbency.
  • All the leftover bits of nappies tested last year have been sent to CCI for more tests.
  • CCI will use co-precipitation to form HA in the lab. To mimic the conditions in the nappy wash, they will use warm water and an alkaline pH and then adjust the relative concentrations of phosphate and calcium to mimic hard / soft water, phosphate in detergent, drinking water with phosphate added and baby urine.

And a survey

If you would like to join the discussion or have some expertise you would be willing to contribute, please get in touch.