Britain’s green and pleasant land has just got that bit pleasanter, researchers have concluded after measuring pollution levels.

Levels of a group of toxic chemicals polluting gardens and fields have fallen to their lowest point for more than 100 years, a nationwide survey has revealed.

Emissions of dioxins from factories and power plants have been stemmed so effectively by bans and caps that contamination levels in soil have fallen for the first time since the Industrial Revolution.

The most comprehensive survey of toxic chemicals polluting Britain’s towns and countryside has revealed that carcinogenic dioxin levels have fallen by 70 per cent since the late 1980s.

“Britain is definitely a pleasanter land than it was 30 years ago,” said Declan Barraclough, of the Environment Agency, who led the research that measured toxins at 200 locations across Britain.

It showed that while dioxin levels rose steadily from 1850 to 1985, they have fallen sharply in the past 20 years.

However, researchers found that while levels have fallen, they are still twice as high in urban and industrial areas as they are in rural locations.

Previously, levels of dioxins in the atmosphere have been shown to have fallen but the survey was the first to address soil contamination levels, where the toxins last much longer.

Dioxins are an unwanted byproduct of combustion processes involving organic material, including fossil fuels, with traces of chlorine. They have been linked to several cancers.

Dr Barraclough said: “These are the big, bad boys of the environment. These are the mafia of contaminants – you don’t want them round for dinner, they’re not nice.

“A lot of them are either toxic to us or to wildlife. A lot of them are carcinogenic. They hang around for years and accumulate in the body.

“But they’ve fallen very significantly and this is hugely important. It means by regulating dioxin emissions we’ve reversed an upward trend that went on for more than 100 years.”

Other toxins were assessed by the researchers, including poly-chlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs).

Concerns about the toxicity of PCBs first emerged in the 1960s. By the early 1990s, the levels found in soils had been cut to one eight-hundredth of their peak.

TheUK Soil and Herbage Pollutant Survey published yesterday showed that levels have fallen slightly further in the past 15 years, but towns and industrial areas contained up to twice as much as rural parts of the country. Researchers were concerned to find more PCBs than were expected still in the soil, and said it is likely that the toxins, which are similar to dioxins and are carcinogenic, are still escaping from sources such as window sealants.

Dr Barraclough said of PAHs, which are another cancer-causing contaminant and can be found in cigarette smoke, that levels appear to be falling, but more research needed to be done to be sure.

The risk to human beings from such pollutants is thought to come from inhaling them after they break free from substances containing them, and from eating plants that absorb them from the soil.

Though contaminant levels were within acceptable levels, it remained important to monitor them, he maintained, especially as they can damage wildlife.

“We know PCBs can cause deformities in bird chicks, particularly herons, and we can still pick them out in birds of prey,” he said. “We don’t want another peregrine falcon crash.”

The researchers measured levels of 12 metals, arsenic, 22 PAHs, 26 PCBs and 17 dioxins.

— Genetically modified crops that make their own insecticide are less harmful to butterflies, honey bees and other nonpest species than conventionally farmed equivalents, according to research (Mark Henderson writes).

A review of 42 field experiments, led by Michelle Marvier, of Santa Clara University in California, has concluded that crops engineered to produce Bacillus thuringiensis, a natural pesticide, cause significantly less ecological damage than the chemicals sprayed on ordinary fields of cotton and maize.

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