Few would deny human behaviour is influenced by diet and the environment.

We know alcohol, for example, can cause anti-social behaviour and it is ultimately our own choice whether we experiment with it.

In the case of other hazards affecting our brain chemistry and behaviour, we may not have that privilege.

I spoke to Dr Neil Ward, senior lecturer in analytical and environmental chemistry at the University of Surrey, who takes samples from water, plant, soil, dust, hair and analyses their chemical components.

He has published more than 200 scientific papers on such topics as the effects of food additives on children's behaviour or the toxic metal status of young offenders.

He has also investigated the contamination caused by toxic run-off from motorways and the aluminium pollution found in the Camelford water supply.

Dr Ward studies and compares the effects of toxic substances on our minds and bodies.

I spoke to him after his recent trip to Argentina, returning with hair samples from 40 hyperactive children in a remote community in the Rio Negro valley of Patagonia.

Surrounded by desert, the Negro river flows from the Andean mountains into the Atlantic creating a hugely fertile agricultural environment which is famous for its orchards and vineyards.

Much of the water in the river, however, is contaminated by agro-chemicals and high in toxic heavy metals.

The local diet is mostly home-grown, consisting of beans, rice, cereals and vegetables - all irrigated by the same polluted water.

Although common ailments are treated by local practitioners using native plants, these remedies are also contaminated by the single major source of heavy metal pollution - the river.

Dr Ward has found many hyperactive children have a unique chemical profile which is reflected in their hair samples.

Deficiencies in selenium, zinc and chromium are commonplace and play an important role in behavioural problems.

A dietary deficiency of zinc alone is known to lead to aggression and depression in some individuals.

Toxic elements, such as aluminium, cadmium and lead have long been associated with hyperactivity in children, as well as juvenile delinquency and violence.

In addition, toxic metals block the utilisation of essential trace elements such as calcium, iron, magnesium and zinc, required for the normal development of a child's brain and immune system.

The current medical approach to ADHD and other mental health problems involves taking drugs to suppress symptoms but does not explore biochemical causes.

Some of our agro-chemicals may be yielding a dark harvest.

Dr Ward believes there is an urgent need to conduct further studies into the role of diet and chemical substances on human behaviour.

He is analysing the hair samples from the children in Patagonia and will present his findings for the first time at the Children's Mental Health Conference on October 9 at Ort House, Albert Street, Camden, London.

For further details, call 0870 1613505 or visit www.pavpub.com
Martina Watts is a qualified Nutritional Therapist at the Crescent Clinic of Complementary Medicine, Brighton (call 01273 202221), and the Dolphin House Clinic, Brighton (call 01273 324790), or visit www.thehealthbank.co.uk