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One possibility he says is that tears discharge certain chemicals from your body, chemicals that build up during stress.

他说，一种可能性是，眼泪会从身体中释放出某些化学物质，这些化学物质是在压力下积聚起来的。

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The developing brain, the report says, is particularly vulnerable to the toxic effects of certain chemicals these products may contain, and the damage they cause can be permanent.

报告说，正在发育的大脑特别容易受到这些产品里可能含有的某些化学物质的毒性影响，而这些化学物质造成的损害可能是永久性的。

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As tissue decays, he said, certain chemicals are produced that inhibit the formation of disease.

CNN: CDC, EPA: Little risk to public from sites

Congress has taken a step toward banning the use of certain chemicals in the manufacture of children's toys.

NPR: Ban Weighed On Children's Toy Ingredient

An unwanted by-product, they are formed when heating processes create certain chemicals - chlorine is the best known.

BBC: Foot-and-mouth pyres: Dioxin danger?