BBC News Online's environment correspondent Alex Kirby outlines the facts behind the fears of disposing of hazardous waste.

What is hazardous waste?

It is waste defined by the European Union as anything liable to cause harm or damage when it is thrown away. A similar category is special waste, a UK not an EU definition, which requires a licence before you can dispose of it. The sorts of waste covered by the definitions are highly flammable, irritant, harmful, toxic, carcinogenic or corrosive.

Where do hazardous and special wastes go?

They go to special landfill sites which are allowed to deal with different categories of waste. Each site has a working plan detailing what sorts of waste it can treat, and how it must deal with them. Some sorts of hazardous waste are meant to be kept out of landfills altogether. Highly volatile organic solvents, for example, would be more likely to go to a high-temperature incinerator. Whatever goes into a landfill should not cause a hazard if it is properly dealt with in line with the site's working plan.

How close to a landfill taking hazardous waste is it safe to live?

A 2001 UK study found that babies born to mothers living near all landfill sites were more likely to suffer minor birth defects. Mothers living near landfill sites containing hazardous waste were at a 7% higher risk of having a baby with congenital defects. The Environment Agency recommends a 250-metre safety zone around landfills. One waste industry source told BBC News Online: "I wouldn't choose to live at the edge of the zone myself. And perhaps there were mistakes made in the past, though I think there should be no problem nowadays."

What happens to the waste when it goes into a landfill site?

The site will have a mineral barrier around it, usually 1m of compacted clay. Inside this there will be a primary liner to make an impermeable layer. It may be high-density polyethylene, or perhaps bentonite, a highly expansive clay which can be mixed with sand. The main problems with decaying waste come from gas and liquid ("leachate") which leak from the site. These will be monitored, and the leachate removed - the gas can be captured and used. After it is filled, the site has to be monitored until the Environment Agency is satisfied it poses no threat to the environment, a period which may last 30 years.

Is landfill disposal the best option for hazardous waste?

Some experts say landfill is probably the least preferable option, even if it is the only one. One told BBC News Online: "Site operators are better now, because they are regulated better. But there is a historical record of them not doing a good job. Sticking everything in a big hole in the ground doesn't seem the best way. You're leaving the problem for future generations to sort out. And if the lining is breached, it can take time to find the problem and deal with it." Other options include recycling the waste, incinerating it, and subjecting it to heat treatment that does not involve actually burning it.

What should you do if you are worried about a landfill site?

Contact your local environmental health department, which should be able to help you.