At some point in our lives, perhaps when we have children, we worry about pollutions and the risk its poses to our health and the health of those we love. We read about traces of DDT in milk, radioactive particles on a beach or the growing ozone hole. Modern science has enabled us to detect chemicals and radioactivity at very low levels. We could take comfort from this technical breakthrough, but often it only increases our anxiety. When we are told that a brand of apple sauce contains 14 parts per billion of a pesticide, we wonder how much that really is and how great a risk it is to our child. We have become afraid of the unseen, it is hard for us to assess the significance of the risk to ourselves. In this topic, we will look at three areas of concern – radioactivity, pesticides and chlorofluorocarbons – and examine how improved methods of detecting these pollutants at low levels also changed the public’s perception of them. Why do we find it hard to assess the risk posed by these traces?