Many of the fully involuntary risks, such asunsafe water provided to a household, have risk thresh-olds set at one in one million (1 in 106). Indeed, the onein one million has become something of a gold standardof acceptable risk for involuntary exposure and has beenused in different areas such as water safety in Australiaand the US [20,21], or for increases of exposure to car-cinogens in air, sediment or soil [22]. It should be notedthat other standards have been used, and sometimes wesee ranges, such as one in a million to one in 100,000(see also [23]

AsStarr showed in his seminal paper [3], societies tend toaccept much higher risks for voluntary behaviours thanfor involuntary exposure