Dredging in Southampton Harbour could cause marine snails to change sex, a university professor has said.

Alex Ford, professor of biology at the University of Portsmouth, has raised concerns over the use of a specific type of chemical which makes female snails grow a penis.

Works to dredge 1.1million cubic meters of sediment started on Friday and will be completed by Associated British Ports (ABP) in March.

The dredged material will be taken by barge to a licenced site at sea, south of the NAB tower in the Solent.

APB said the programme will ensure the "largest ships in the world" can continue to access the port.

However, professor Ford says this may be at the expense of marine snails.

He said: “Capital dredging typically, as a result of not being disturbed, can contain more environmental contaminants and often chemicals which have been banned.

“Before dredging takes place sediments must undergo some tests and if the chemical concentrations fall below certain thresholds, then the sediment is allowed to be dumped at sea and specific locations under license from the Marine Management Organisation (MMO).

“If they fail the tests the sediments must go to landfill. TBT (tributyltin) was used in antifouling paints on ships globally but during the 1980s it was found to be harmful to some marine species causing marine snails to change sex.”

The TBT in the sea interferes with genes in female snails which results in their masculinisation. They grow a penis and become sterile.

The professor added: “Since its ban in 2008, the incidence of imposex snails (females with a penis) has dropped considerably around our coasts but still persists in a few areas in the UK where there had been heavy shipping and ongoing dredging.

“Unfortunately, the concentrations of TBT in sediments do not need to be high to cause sexual abnormalities in marine snails.”

In a statement, a spokesperson for ABP said: “We have been working closely with our customers and licensing organisations for a number of years over plans to widen the channel within the Western Dock.

“The programme will enable continued access to the port by the largest ships in the world.”

They added: “The dredging work, which started on Friday, December 1, and will be completed by March, takes place during winter to minimise environmental disruption – especially to wildlife such as migrating salmon.

“The dredge material is relocated by barge to a licensed site at sea, south of the NAB tower.”

Dredging, which involves the removal of sediments and debris from the seabed, occurs because sedimentation – the process of sand and silt washing downstream – gradually fills channels and harbours.