Saddam Hussein's gassing of Halabja in 1988 was the worst chemical weapons attack ever. Geneticist Christine Gosden went there and was appalled by people's continuing agony and by how little we know about the effects of these deadly agents.

People asked why on earth I should consider going to one of the most dangerous countries in the world at a time when it was racked by internal conflict and in dispute with the United Nations. The reasons for travelling to Northern Iraq earlier this year were clear to me, even if they were not so obvious to my colleagues and friends. In 1988 the people of Halabja in Northeast Iraq had been the victims of a massive aerial bombardment which showered them with chemical weapons. I had seen the award-winning film of the immediate aftermath of this attack, The Winds of Death, made by the British filmmaker Gwynne Roberts, an expert on Northern Iraq. Roberts wanted to go back and make a documentary on the tenth anniversary of the bombing; to take a team of doctors and scientists to study the long-term effects.

Unfortunately, by the time visas became available and the narrow window of opportunity for getting into Northern Iraq appeared, the situation in the Gulf was pretty aggressive. The other clinicians and scientists who were due to go withdrew one by one. As the only doctor left I now felt almost compelled to make the trip, despite personal difficulties because two of my closest friends and family were very ill. The film-makers assured me that I could contact my sick friends by satellite phone to check on their progress and be in constant touch with the teams looking after them. So I went.

On March 16 1988, an Iraqi military strike bombarded Halabja, a Kurdish city of about 80,000 people in Northern Iraq, with more chemical weapons than had ever been used against a civilian population. The attack began in the evening when waves of aircraft began dropping chemical bombs. There were a number of aircraft sorties during the night, and the attacks continued until March 19. This was not the first chemical attack by Saddam Hussein's forces. Previous attacks had been launched against 20 small villages in 1987. However, the scale and intensity of the campaign against Halabja was entirely different. The victims included women, children and the elderly. Halabja's citizens are mainly Kurdish and had sympathised with Iran during the Iran-Iraq war. The gassing was in retaliation.

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The chemicals drenched the people's skin and clothes, they breathed in the toxic gas mixture and ingested the chemicals in contaminated food and water. Many (an estimated 5,000 people) simply died where they stood. A few of the survivors were given brief and immediate treatment abroad - in Europe, the United States or Iran. Most returned to Halabja.

I was concerned that in the decade since the attack, no one had succeeded in reaching Halabja to monitor the effects of these weapons. In conjunction with the local doctors, I wanted to learn about the effects and try to help the people.

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My field of medical genetic research is particularly relevant to chemical weapons use, because it is directed towards trying to understand the genetic causes of birth defects and cancers. I am studying a group of 14 genes called tumour suppressor genes which involve the breast/ovarian cancer, prostate and colon cancer and some early childhood cancer genes. These genes are very important in preventing cancers from occurring in later life. Loss or mutation of these genes causes congenital malformations, miscarriage, cancers and infertility.

What I found in Halabja was worse than I had feared. Mustard gas, one of the ingredients in the cocktail of chemicals unleashed by Saddam, had seriously affected people's skin, eyes and respiratory tracts. Many were blind or partially sighted. Others still suffered blistering or severe scarring and in some the skin problems had progressed to lethal skin cancers. Cancers including laryngeal, nasopharyngeal, respiratory, oesophagal, gastrointestinal, breast and childhood were at least three to four times more frequent than in the control population in the city of Suleymania, about two hours drive from Halabja.

There is something which sets Halabja apart from other known chemical weapons attacks. The Halabja attack involved multiple chemical agents. It probably also involved a biological weapon - aflatoxin, which was distributed in tear gas. Certainly, the figures for liver malignancies in the children suggest that aflatoxin was used. Most strategies developed against chemical or biological weapons attacks have been directed towards a single threat. There has been no tactical planning directed towards countering a cocktail of agents.

Handbooks for Iraqi doctors demonstrated sophisticated medical knowledge of the effects of chemical weapons. The doctors knew that those used in the Halabja attack were carcinogenic, mutagenic, toxic to embryos and capable of making people sterile. For mustard gas there is no defence or antidote. Iraqi agents' choice of nerve agents was particularly cruel since one of the chief treatments against nerve agents pyridostigmine bromide (which was issued to all the allied troops during the Gulf War) is virtually ineffective against most of the agents the Iraqi military used.

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The weapons have also poisoned the environment, destroying plants and animals. The town has not been rebuilt and there is no sanitation or clean water supply. There is no effective treatment for most of the medical problems the people have. There is no chemotherapy or radiotherapy and no palliative care, so people are dying young in great pain. There is no access to paediatric surgery - children with severe disfigurements such as cleft palates are not operated on. Children die of congenital heart malformations, survivable conditions elsewhere.

The chemicals used cause mutations in DNA. If the mutations occur in ordinary body cells, they cause cancers. If the mutations occur in germ cells, however, (women's eggs or men's sperm), then the mutations may be passed on to any children. The attack on the parents can thus continue into succeeding generations. There may be long-term effects exploding in people's lives long after the original bombardment.

The people of Halabja desperately need help to try to rebuild their damaged lives, families and town. There is also a need to recognise that chemical and biological weapons are "inhumane" and must never again be deployed. The terrible visions from Halabja persist in my nightmares and disturb my waking thoughts. We must learn from this terrible act and discover how to treat the medical tragedies that result.

There are a number of steps which should now be taken urgently. Although the UN-imposed sanctions against Iraq are a crude instrument, at least we can hope that the sanctions are effective in preventing Saddam's further acquisition of horrific weaponry. The sanctions, after all, are only in place for as long as the Iraqi authorities fail to disclose and destroy their weapons of mass destruction and their production capability.

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Nonetheless many questions remain unanswered, evaded by governments and agencies. Why were countries and governments allowed to export banned chemicals to Iraq, enabling it to manufacture nerve gases and mustard gas in contravention of the Geneva Convention? Why, when this was the worst chemical weapons attack the world has even seen, has nothing been done for ten years to help these people? Why are they, even today recieving no aid, not even small amounts from the Oil for Food Programme under resolution 986 of the UN?

Special research, treatment and monitoring programmes were put in place to investigate the long-term effects of the atomic bombs on Hiroshima and Nagasaki. The chemicals used in this attack have effects on the body similar to that of ionising radiation. Governments and aid agencies must provide help on an adequate scale and the UN must take steps to protect the people of Halabja. Research programmes are needed to investigate the effects of these weapons and determine the best ways of treating the devastating results of their use.

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Christine Gosden is professor of medical genetics at the University of Liverpool.