Charlotte McInnes, of Kaikoura Suburban School, asks :-

Some people like to chew paper. What chemicals are in paper?

Graeme Robertson, a chemical engineer and CEO of the Cawthron Institute in Nelson, responded.

Paper is made up of lots of different chemicals. The main one is called cellulose and forms long chains, or fibres. It is very common in nature, you can find it in many plants, even seaweeds. It is a bit like starch. Under a microscope, the cellulose fibres look a bit like drinking straws, long and skinny with a hole down the middle. They are soft enough to squash flat when the paper is made, and they stick together without any glue!

When the paper gets wet, they fall apart. Papermakers can stop that by adding small amounts of gums or resins. Paper also has some traces of alum, an aluminium compound often used to treat drinking water to get rid of dirt. In papermaking, it's used to make sure the paper is nice and even, not blotchy or lumpy.

Newspaper has lots of the chemicals from the wood it was made from such as resins and gums, the sort of thing you would find around the bark of a pine tree. Sunlight makes wood resins turn dark (have you seen a piece of newspaper left in the sun for a while? It soon goes yellow. )

White papers have had nearly all wood resins removed by bleaching. Fine white clay, or 'fillers', are added to make them less transparent and hide print on the other side of the page. These fillers can make up almost a third of the weight of glossy magazine papers (which is why those papers are not as strong). Coloured papers have had dyes added. The dyes have to be safe, because paper is often used to package food.

If you look hard enough, it is even possible to find tiny traces of chemicals called organochlorines, created when chlorine is used for bleaching. Some of these, such as `dioxins', are harmful to people, but most scientists would agree that you would have to eat a mountain of paper before you ate enough to cause any effects!