Cladding prevents radioactive fission fragments from escaping the fuel into the coolant and contaminating it. Waste material leeches underground, contaminating aquifers. Radioactive water leaked from the storage units, minimally contaminating the soil and water nearby. They are then cooled forming a vacuum seal which prevents microorganisms from contaminating the foods. They were also destroying native vegetation, contaminating water supplies and destroying cultural sites. This removes the upper layers of dead skin cells along with their contaminating bacteria. A purification step is necessary to remove contaminating substances. Preventing human faeces from contaminating pig feeds also plays a role. The issues have ranged widely from cancer-causing toxins contaminating new residential properties to financial fraud. The cleanup cost $16.2 million and wound up contaminating local groundwater anyway. He demonstrated that his normal human cell strains were free from contaminating viruses. Studies on mycotoxins show that there are three ways to preventing them from contaminating feed. Hairnets are used to prevent loose hair from contaminating food or work areas. These are now contaminating lakes, rivers and the ground water in the region. Scientists are particularly worried about accidentally contaminating the subglacial lakes with life forms from outside.