Government should charge cruise ships for the cost of sewage treatment and disposal, the National Trust has argued.

Trust marine environmental committee chairman Wayne Carey said the ships -- which produce up to 60 percent of the total volume of sewage on the Island during the summer -- should also be governed by regulations on sewage.

Mr. Carey also called for a Clean Water Act to be passed to prevent further water contamination of inshore water by chemicals, detergents and sewage.

Speaking at Hamilton Rotary Club, Mr. Carey said Government's cruise ship policy was due to expire next month and he said a 1999 Trust study showed that larger cruise ships could have a serious effect on the Island's marine environment.

Mr. Carey said the study showed that during the cruise ship season, cruise ships contribute up to 60 percent of the total volume of sewage on the island.

"We are concerned about the effect that this largely untreated sewage may have on Bermuda waters,'' he said.

The Trust also recommended that several studies be done on the sedimentation threshold of the reefs to discover what happens when the sediment is stirred up by the larger cruise ships.

Mr. Carey said that greater wake that would be created by the larger cruise ships would result in a higher disturbance in the bottom sediments which eventually settle on and kill the coral colonies.

The Trust study also showed that certain harbours and channels would have to be dredged or cleared to accommodate the larger ships.

The dredging would again result in a large amount of silt and sediments being turned up in the water.

"The Trust Study noted that cruise ships are exempted from the 1989 legislation controlling the use of tri-butyl tin (TBT),'' Mr. Carey said. He explained that TBT is an anti-fouling paint and that internationally there is a great deal of concern about its toxicity and effects on marine life.

"High levels of TBT persist in Hamilton Harbour despite the 1989 legislative controls,'' he said. "There is also concern for the unknown toxicity of the copper-based replacement to TBT.'' Another issue raised by the Trust study is the release of metals, detergents and other cleaning agents into the water from cruise ships being allowed to do dockside cleaning.

A review of the port marketing concept was suggested, to reduce the amount of cruise ship movement in the channels.

Mr. Carey said: "The introduction of larger cruise ships to Bermuda raises serious questions about the Island's carrying capacity with respect to physical infrastructure, including transport and solid and liquid waste management.'' He explained that even though the percentage of recyclable material cruise ships leave behind is high, the volume of recyclable material generated by cruise ship activity has never been measured.

Also the ships have never been charged to cover any of the costs of the recycling.

Government has already begun to react on the Trust recommendations by creating an inter ministerial planning team aimed at reviewing the cruise ship industry and options for future cruise ship policy.

Mr. Carey believes Bermuda should develop a niche market for smaller cruise vessels by quoting the Conde Nast Traveller Magazine survey that said `smaller ships score big' with their readers.