Alison Bates, age 11, of Veradale, Washington, for her question:

Are they finding thermometer mercury in fish?

Thermometer mercury is a more or less pure metallic element. One does not handle it because just about all the known forms of mercury are poisonous or in some way harmful to living tissues. True, the mercury we discard from broken thermometers does not amount to much. But much larger quantities are used in dry cell batteries and other everyday items that wear themselves out. These waste items are often consumed in city trash incinerators.

The mercury vapor that emerges is a poisonous compound. It is carried by the air and much of it washed into the sea by the rains. There bacteria converts it into methyl mercury. This is the dangerous mercury compound found in fishes and in the bodies of people who eat them. Still more mercury reaches the sea in certain industrial wastes    and it too is changed into the dangerous compound.