A chemical company has been fined �23,000 after it allowed 100 tonnes of benzene to spill into the River Tees.

Sailors had to receive hospital treatment after the leak of the potentially cancer-causing substance.

Crew members from the docked cargo vessel Tarquin Trader complained of headaches and feeling sick and were sent to hospital for checks.

It later emerged that a valve had been left open on a benzene tank owned by Huntsman Petrochemicals.

The company, which took over part of the ICI complex on Teesside, has been fined �23,000 by magistrates.

Benzene is potentially carcinogenic and could do damage to organisms in the river

Howard Stoddart, Environment Agency

As well as an open valve, Environment Agency inspectors found defects in drainage systems which should have prevented any leak.

Officials said more than 100 tonnes of benzene seeped into the river over a four-day period in August.

Inspector Howard Stoddart said: "The company was doing a routine operation on a tank and unfortunately they did not shut the valve.

"Over the next few days safety systems should have kicked in, but they all failed.

'Very nasty'

"Benzene is a horrible hydrocarbon, it is potentially carcinogenic and could do damage to organisms in the river.

"It is a very nasty chemical."

Management at the plant have promised to improve operating systems.

Spokesman David Wilkins said no environmental damage was caused, but that "lessons have been learned".

Dye preparation

Benzene is a colourless and highly flammable liquid distilled from petroleum and used as a cleaning agent and a solvent for fats, oils, and resins.

It is also used in the preparation of dyes and paints.

Chronic exposure to benzene is known to lead to progressive degeneration of the bone marrow and leukaemia.

Symptoms to benzene exposure have been known to lay dormant for up to 20 years.