Johannesburg was built because of mining. The city is surrounded by huge, sandy dumps – a side-effect of the search for gold.

I’ve lived in South Africa for ten years (on and off) and I had never thought about the dumps and what might be inside them. It was only when my colleague, the brilliant Sophie Ribstein, showed me reports from a number of NGOs that I realised they might not be as benign as they seem.

Armed with a variety of research papers we discovered that these dumps are packed with deadly heavy metals including a huge amount of uranium. In fact according to the researchers we interviewed Johannesburg is one of the most radioactive cities in the world – and thousands of people live in poverty on top of or next to the dumps.

The film we made is what I think of as a mini-doc. It’s not the most beautiful film I’ve ever made but I’m proud of it. It was mainly shot on my Sony Z90 and edited in FCPX.

Additional drone footage was supplied by my friend and colleague Barnaby Mitchell.