There is a quote attributed to the medieval scientist Paracelcus: “Only the dose makes the poison” (Latin: dosis sola facit venenum), pointing out that every parameter can be toxic, as long as it is present in the right dose. This might sound odd, but the fact is that this dose for parameters that we don’t see as toxic for our health is just very high. Even water can be toxic, because if we drink too much of it (keyword: too), the heart will be unable to continue to pump. Within environmental research some groups of hazardous parameters are analysed so that an assessment can be made to conclude if exposure to these parameters is a danger to our health. However in these assessments we usually look at one parameter and one threshold at a time. Reality is a little more complex than that.