WASHING up your coffee mug could be damaging sea-life, Hampshire scientists claimed today.

Researchers from the University of Portsmouth claim that anti-depressants - as well as caffeine in coffee - is changing the behaviour of shrimps and could damage the food chain.

Large amounts of the chemicals are washed away in waste water and end up in the sea.

Now, the rising levels of antidepressants in coastal waters could change sea-life behaviour and potentially damage the food-chain, scientists said today.

Research into the behaviour of shrimps exposed to the antidepressant fluoxetine showed that their behaviour was dramatically affected.

The shrimps are five times more likely to swim toward the light instead of away from it, making them more likely to be eaten by fish or birds, researchers said.

They fear this could have devastating effects on the shrimp population.

Dr Alex Ford, from the University of Portsmouth's Institute of Marine Sciences, said: ''Crustaceans are crucial to the food chain and if shrimps' natural behaviour is being changed because of antidepressant levels in the sea this could seriously upset the natural balance of the ecosystem.

''Much of what humans consume you can detect in the water in some concentration.

''We're a nation of coffee drinkers and there is a huge amount of caffeine found in waste water, for example.

It's no surprise that what we get from the pharmacy will also be contaminating the country's waterways.''

The study, published in the journal Aquatic Toxicology, found that the shrimps' behaviour changes when they are exposed to the same levels of fluoxetine found in the waste water that flows to rivers and estuaries as a result of the drugs humans excrete in sewage.

Dr Ford said: ''Effluent is concentrated in river estuaries and coastal areas, which is where shrimps and other marine life live - this means that the shrimps are taking on the excreted drugs of whole towns.''

Prescriptions for antidepressants have risen rapidly in recent years, according to the Office for National Statistics.

In 2002, there were 26.3 million antidepressant prescriptions handed out by doctors in England and Wales but Dr Ford said the environmental effect of pharmaceuticals in sewage had been left largely unexplored.