There is a long blog post written by Tomas on the Wellcome Trust blog:
Making a game about dirt was never going to be the easiest topic. As a concept it is both broad and narrow. A game about throwing mud around, for example, would be fun but would miss the many facets to the subject that the Dirt exhibition had to it. Many ideas looked around the contrast between being clean and dirty and the conflict we often perceive there. We liked these but were looking for something that we also felt had a very broad appeal – we all have a relationship with dirt, after all.
We wanted to create game that everyone could explore at their own level, and looked long and hard to find the right people with the right approach. What emerged from this process is a puzzle/trivia word game developed by Guildford-based developers Toytek. They had already received a degree of acclaim for their work on The Ultimate Alphabet app, so we took the core idea for this game and made it, well, dirtier.