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On their own, many chemicals are harmless to human health. But in combination with other chemicals, they may become deadly. That was the finding of a two-year study by a group of scientists. They were asked to investigate the cancer-causing possibility of chemical mixtures. Linda Gulliver was one of 174 scientists on the task force. They were told to study the cancer-causing potential of 85 chemicals. All 85 are considered to be common in the environment. Linda Gulliver is also on the medical faculty of Otago University in Dunedin, New Zealand. She says chemicals have the ability to form dangerous mixtures. Even simple minerals can become dangerous when mixed with chemicals from plastic or beauty products. While the chemicals are safe on their own, she says, the researchers found that many chemical mixtures cause cancer in human cells. Working in groups, the scientists explored how different chemical mixtures could lead to cancer. Ms. Gulliver’s team looked at the ability of different combinations to support the increase of malignant human cells. She says the current way to identify whether chemicals cause cancer is to test them one at a time. This method leads, she adds, to a long list of supposedly “safe” chemicals. She and her team say that approach to testing needs to change. An estimated one in five cancers has been linked to chemical exposure. It may be that a cancer-causing substance is not a single chemical at all; it could be a deadly combination. The task force published its findings in the journal Carcinogenesis.