Health World News and Features

Bracken is polluting water supplies worldwide – and causing cancer. You may not be surprised to get cancer if you smoke, or drink too much alcohol, but no one expects to get it from drinking water.

Glugging plenty of glasses each day is supposed to be good for us, but now you might want to think twice before turning on the tap.

New research, being presented at the British Ecological Society Annual Meeting in Lancaster in north-west England, has revealed that a common fern may be poisoning water supplies all over the world.

Bracken is a fern that grows on every continent except Antarctica.

Its curling green fronds decorate many British hillsides, dying down and turning a distinctive rusty-red color through the winter. Due to changes in farming practices over the past hundred years, bracken has proliferated and now it sprawls across much of Scotland and northern Britain.

For a long time scientists have known that bracken contains a carcinogenic compound called ptaquiloside (PTQ), but thought it dangerous only if eaten.

Now Lars Holm Rasmussen, a scientist at The Royal Veterinary and Agricultural University in Denmark, has shown that PTQs from bracken can enter the water supply and that some of us may be gulping poison every day.

Scientists have already shown that the PTQs ingested from eating bracken can increase your chances of getting gastric and oesophageal cancer.

In Brazil and Japan, young bracken shoots are often used in salads and cooking.

“The young ferns are quite tasty, a bit like asparagus with almonds,” says Holm Rasmussen.

But their toxic qualities are also quite clear, with higher incidence of cancer in both these countries. Now he has shown that eating bracken isn’t the only way of ingesting PTQs.

Last year, Holm Rasmussen measured the concentration of PTQs in water from wells on Danish and Swedish farms, which had lots of bracken growing in the area.

To his horror, some of the water had PTQ levels that were over 20,000 times higher than the suggested tolerable levels for environmental carcinogens.

The story is likely to be similar for many other farms and villages worldwide, where water is sourced from a brackenstrangled borehole or well.

“PTQ is somewhat like sugar, it dissolves easily and is just as mobile as pollutants like nitrates,” says Holm Rasmussen.

By measuring PTQ levels in soil and soil-water at different times of year, he has shown that the highest levels are found after heavy summer rainfall.

“PTQ is washed out of the bracken fronds by rain and since the bracken has the most biomass in summer, this is when we find the highest concentrations of PTQ in water,” he explains.

Particularly high levels were found on farms where the water table was high, five to 10 meters below ground.

Soil type is also important in helping or hindering PTQ to travel.

Sandy soils act like motorways to the water supply, while peat soils and chalks are more like very windy country roads.

“The situation is worst in sandy soils with a pH between five and six. Once the soil gets too acid (peat for example), or alkaline (limestone or chalk for example), then it becomes less mobile and degrades before reaching the groundwater,” explains Holm Rasmussen.

To make matters worse, families living on dairy farms may have also been drinking contaminated milk.

PTQs can be transferred into milk when cows nibble on bracken, particularly during the spring when the shoots are young and tasty.

Farmers often keep the buttermilk for their family, giving it to their children as a healthy drink. This buttermilk will have had the highest proportion of PTQs because it has not been diluted with milk form other, less bracken-infested farms.

What is more, PTQs are attracted towards water, so tend to concentrate in the buttermilk, rather than enter the cream, butter and cheese that will have been made from the fat that was skimmed off.

“Bracken certainly could be an environmental factor that explains the raised levels of cancer in certain areas,” says Holm Rasmussen.

What is perhaps more concerning is that it may not just be bracken that we need to worry about.

A number of important agricultural crops such as canola and clover already produce toxic natural products with similar structures to PTQ. These toxins are not carcinogenic, but may behave in a similar way in the soil.

Furthermore, many of the new GM crops, such as GM maize, are developed with an increased natural defence against pests and weeds, by inserting genes that code for the high production of toxic compounds.

“Some of these toxic natural products have a similar structure to PTQ and I think they will behave in a similar way,” says Holm Rasmussen.

Given that crops are often planted on sandy soils with a high water table, some crops could have an even worse effect on the water supply than bracken.

There are no easy solutions to this problem.

Farmers and landowners are trying to reduce the amount of bracken, but it is difficult to get rid of and the most effective mechanism is to spray hillsides with a noxious pesticide: not ideal for improving the water supply.

Meanwhile, Holm Rasmussen is hoping to carry out more research to discover which GM crops and which type of environment present the greatest threat to our water.

In the meantime, don’t give up drinking water but to keep trampling down the bracken when you’re out for a walk.

KATE RAVILIOUS IN LONDON, September 19, 2004, Manila Bulletin

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