Scientists say that a spill of the fuel Orimulsion, which contains obnoxious chemicals already thought to be reducing human sperm counts, in the Haven would be far more dangerous and much more difficult to clean up than the slick from the Sea Empress. But, thanks to an astonishing legal loophole, neither of the Government's two official pollution control agencies can take the consequences of such an accident into account when giving advice on the plans.
National Power wants to bring 35 tankers the size of the Sea Empress and laden with Orimulsion from Venezuela into Britain's busiest port every year - the equivalent of one shipment every 10 days, carrying an annual total of 5 million tons.
It wants to burn the fuel in its Pembroke power station because it is much cheaper, as well as much dirtier, than crude oil.
It says it would then be able to turn the oil-burning station, which is now running at only 5 per cent of capacity because of the cost of its fuel, into a "very competitive and economic plant" and create another 160 permanent jobs. An application to build a special jetty for the tankers goes before Dyfed County Council on Tuesday.
The company says that the hazards of bringing the fuel into the port, which has experienced two groundings in the past four months, are "manageable". But official Government watchdogs have been alarmed by the fiasco of the Sea Empress.
Dr Malcolm Smith, director of Science and Policy at the Countryside Council for Wales, the Government's wildlife adviser, told the Independent on Sunday last week: "We had been led to believe that the tug capacity of Milford Haven was sufficient to control a supertanker if it got into difficulties. Now we know that is not the case.
"Knowing what we now know, we are not at all confident that Orimulsion could be brought in safely. And we would be even more concerned about a major Orimulsion spill in the Estuary than about the spill from the Sea Empress." He said it would kill "a large amount of wildlife", particularly on the sea bed.
The National Rivers Authority (NRA) warned in a report four years ago that it would be far more difficult to control an Orimulsion spill than an oil one. This is because, as the fuel is already mixed with water, it would disperse rapidly into the sea rather than lying on the top like oil. The NRA said last week that its concerns remained and that a spill would particularly affect fish.
Environmentalists are most concerned about chemicals in the fuel that mimic Oestrogen. Such chemicals have already been found to make male trout produce female proteins, and last week scientists at the Medical Research Council reported that similar substances could be partially responsible for a 25 per cent drop in human sperm counts over the past quarter of a century.
Friends of the Earth calculates that Orimulsion imports will bring in 10,000 tons of Alkyl Phenol Ethoxylates a year. The use of these chemicals is being reduced in Britain, Friends of the Earth says, because they can be dangerous.
Jeffrey Sinclair, of the Council for the Protection of Rural Wales, fears that an accident would cause the chemicals ultimately to affect people. He says that a spill "could effectively destroy the reproductive processes of the fish and get into the food chain - and one can extrapolate from there".
Astonishingly, both the NRA and the HM Inspectorate of Pollution (HMIP) say they are legally unable to take the consequences of an accident at sea into account in their official advice on the plan.
The HMIP has to confine its attention to the effects of burning the fuel in the power station, while the NRA can only address the risks of an accident at the proposed jetty itself.
Government bodies have repeatedly pressured National Power for more than 18 months for an assessment of the consequences of a spill, but the company has only just produced it. As a result, councillors are likely to defer a decision on Tuesday, though environmentalists are pressing for a public inquiry.Reuse content