But are they still “safe” if mixed with other chemicals? That's the big question.

　　On its own, each chemical seems harmless.

　　But in combination with other chemicals, they may become deadly. That is the finding of a two－year study by a high－profile task force of scientists. The task force was told to investigate the cancer－causing possibility of chemical mixtures.

　　Linda Gulliver was one of 174 scientists on the task force. Their job was to study the cancer－causing potential of 85 chemicals. All 85 are said to be common in the environment.

　　Ms Gulliver explains that chemicals have the potential to form dangerous mixtures. Even simple minerals can become dangerous when mixed with chemicals found in plastics or beauty products. While the chemicals are safe on their own. She says, the researchers found that many chemical compound 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 (恶性的) human cells.

　　She says the big issue－what she calls “the $ 64 million dollar question”－is, “Which common, everyday chemicals do people need to avoid？”

　　“The $ 64 million dollar question that everybody wants to ask is,

　　‘Which chemicals should we be looking out for？’ And the answer to that is, ‘We don't know yet.’”

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