The World Wide Fund for Nature (WWF) study found two-month-old British babies are consuming levels of dioxins 43 times the safe level. The government has known dioxins are present in breast milk since 1996 but has just finalised a contract with the University of Leeds to study the problem.
First-born children ingest the strongest concentrations of pollutants because traces of chemicals from perfume to pesticides are breathed in by their mothers and enter the blood stream from where they are stored in body fat. Second babies benefit because their sibling will have effectively "detoxified" the mother.
The WWF report, published today, says: "Some of the contaminants have the ability to cause cancer and some can impair the immune system." But the government was keen to stress they felt the pollutants are "an issue not a problem".
A spokesman for the Ministry of Agriculture Fisheries and Food (MAFF) yesterday agreed with the Department of Health in stressing the benefits of breast-feeding. "The potential, and I stress, potential risk as a result of residual contaminants is far, far outweighed by the clear and proven nutritional, health and other benefits of breast feeding."
MAFF confirmed yesterday that evidence of high levels of dioxins in breast milk was first presented to the Advisory Committee on Toxicity three years ago. It had been assessed by various groups before the Leeds study was agreed. Scientists are finalising details of the methodology.
More than 1,000 Yorkshire mothers will give milk to be analysed over 15 months. The Committee on Toxicology said the exposure to infants was of a short duration, outweighed by the benefits of breast-feeding but it warranted further study.
Another MAFF spokesman said: "The levels of dioxin were significant but in view of the suggestions from the World Health Organisation in terms of the safe limits over a lifetime it was not a cause for concern.
"The total amount we are talking about fits comfortably into the total amount somebody is supposed to get, especially given that environmental exposure to this sort of thing has been falling over recent years."
The WWF report and the study marks a departure for the government and environmentalists who have been reluctant to publicise the transfer of chemicals to babies from their mothers for fear of putting women off breast- feeding.
Human milk is known to immunise infants from disease and the process of suckling builds strong bonds between parent and child.
The author of the WWF report, Gwynne Lyons, believes the best way tackle the problem is for harmful substances to be prohibited to end the "toxic inheritance".