The National Rivers Authority, the water pollution watchdog, is pinning the blame for the highly toxic and persistent contamination in the river Doe Lea on the nearby Coalite plant at Bolsover. Yesterday it said it was planning legal action against the company.
Laboratory tests on animals have shown that dioxins can cause skin and liver damage, tumours, and affect the immune system and fertility - all at extremely low concentrations. Once in the environment they break down very slowly.
The dioxin pollution, alleged to be from the Coalite plant which makes a range of chemicals from coal tar, is thought to extend at least 13 miles downstream into the river Rother and then on into the Don.
The rivers authority said there were no drinking water intakes downstream of the contamination, so there should be no threat to human health. But the high dioxin levels jeopardise the chances of rivers that have been been polluted for decades by industry and sewage ever making a reasonable recovery.
The dioxins are also likely to flow eventually down the Ouse and the Humber into the sea, albeit at much lower concentrations. They may already be reaching the North Sea.
The authority commissioned the Water Research Centre, of Swindon, Wiltshire, to test the effects of the contamination on carp. Scientists found that the livers of the fish kept in tanks with polluted sediment from the Doe Lea became enlarged after several months.
Upstream of Coalite Chemicals' outfall into the Doe Lea, where the river is about 12 feet wide, dioxin levels in the sediments are at two parts per million (ppm). Just below it the authority says they are 10,000 times higher, at 20,269 ppm.
A survey commissioned by the authority found the world's next worst contaminated watercourse was a Norwegian fjord, where a magnesium processing plant was to blame for levels of 749 ppm. In Britain the second highest level was 16 ppm in the River Alt in Lancashire.
Thirteen miles downstream of Coalite's outfall, in the Don in Rotherham, dioxin levels are still at 300 ppm. Ironically, the rivers authority and the pollution inspectorate believe the cause of the Doe Lea contamination is an anti-air pollution system in the chemical wastes incinerator at the Coalite Chemicals plant. A wet scrubber, which forced water through the incinerator exhaust gases, was meant to reduce the formation of dioxins and remove pollutants. Although this water was then treated, some of the chemicals appear to have flowed down a discharge pipe into the river. The incinerator has been closed for more than two years.
Gerard Morris, the authority's regional quality manager, said: 'Even in such tiny quantities, dioxins are powerfully polluting and the NRA is in the process of taking legal action against Coalite Chemicals to try to get the problem dealt with properly.'
But the best environmental option may be to leave the dioxin in the river. If the contaminated sediments were dredged out there would be serious problems in disposing of them safely, and dioxins might be spread in the process.
The authority wants to establish that Coalite is liable and make it pay for the costs of its investigation and survey work, which run to around pounds 100,000. Ken Shelton, the firm's environmental manager, said the contamination was 'a fairly insignificant environmental problem'.
Of 210 different types of dioxin, only 17 were harmful to life and the vast majority of the dioxins in the sediments were non-harmful.