They were heartbreaking scenes. Dead and dying birds littered the south coast beaches of Devon, Cornwall and Dorset, their feathers glued together by a mystery substance.
It was identified by scientists soon after the first incident in February as polyisobutylene – or PIB – which is used in chewing gum, adhesive tape, cosmetics and as an oil additive.
Scores of dead seabirds, mostly guillemots, were washed ashore that month and while concerns were raised by conservationists, it was thought the worst was over.
But two months later, a second wave of pollution hit the region's shores, this time focused on South East Cornwall and South Devon, rapidly increasing the death toll.
In all, some 3,500 seabirds died as a result of the contamination, while a further 500 were rescued. Many, though, had to be euthanased. The bodies of thousands of other birds are thought to have been taken by the sea.
Unsurprisingly, environmentalists called for an immediate ban on the dumping of PIB, which can legally be disposed of at sea under certain conditions.
The Government pledged action and an investigation was launched by the Maritime and Coastguard Agency (MCA) which has so far narrowed the source to seven ships.
"Since tests confirmed the product was PIB, the MCA has been collecting data of the ships that passed through the area during a specific time frame, and has been looking through detailed cargo manifests," a spokesman for the agency said.
"Information is also being sought from authorities in Portugal, the Netherlands and the USA, along with ports, the chemical and shipping industry.
"If the MCA can locate any ship that was responsible for an illegal discharge then we will take steps to prosecute."
Transport Minister Stephen Hammond said "informal discussions" had taken place between the MCA and the International Maritime Organisation (IMO), the global shipping regulator, "on the classification of PIB".
"Investigations are ongoing," he said in a written answer, "and once the reasons for the incidents are established, we will if appropriate formally approach the IMO to review the carriage requirements for polyisobutylene."
Regulations for what the IMO calls the "operational discharge of noxious liquid substances carried in bulk by ships" are set out in the International Convention for the Prevention of Pollution by Ships – known as the MARPOL Convention.
PIB is listed in "Category Y" which covers "substances which, if discharged into the sea from tank cleaning or deballasting operations, are deemed to present a hazard to either marine resources or human health or cause harm to amenities or other legitimate uses of the sea and therefore justify a limitation on the quality and quantity of the discharge into the marine environment".
Nevertheless, the regulations allow for PIB to discharged at sea when the ship is "proceeding en route at a speed of at least seven knots in the case of self propelled ships or at least four knots in the case of ships which are not self propelled".
The discharge should also be made through underwater outlets "at a distance of not less than 12 nautical miles from the nearest land in a depth of water of not less than 25 metres".
PIB's status was last reviewed in 2004. These revised regulations came into force in 2007.
The IMO said evaluation of such chemicals was carried out by the snappily-titled "Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP)-Evaluation of Safety and Pollution Hazards (ESPH) Working Group".
In turn, it reports to the IMO sub committee on "Bulk Liquids and Gases".
A spokesman for the IMO said: "As a scientific peer review body, the group are able to reassess ratings but this would normally only be undertaken following the provision of new studies/test data to demonstrate that the basis utilised for the initial assignment was inaccurate and at odds with the new information being made available."
He added: "Any specific consideration of more rigid controls would be addressed but this would need to be based on a fully documented case which was presented in accordance with the submission procedures employed by the organisation.
"This would require a formal submission to be made either through one of the member states or via one of the non-governmental organisations having consultative status at IMO."
The seafarers' union Nautilus has previously criticised the IMO for its "glacial" pace of change.
"One of our concerns is that initially the Government seemed to be talking quite dynamically about pushing this up the agenda, however recent statements from ministers appear to have gone a bit lukewarm," spokesman Andrew Linington said.
"Whether we are reading too much into it or whether they have had some feedback from the IMO about how long this is likely to take, we don't know.
"Even with the best will in the world it can take years to get stuff through because it has to go through sub committees and be assessed by technical and legal experts.
"Even if everyone was behind it, you are looking at a minimum of two years for it to get through the process. It isn't going to be quick."
Mr Linington stressed that seafarers took their environmental responsibilities seriously.
He said they supported action to prohibit PIB discharges but said it also had to be supported by action ashore.
"Where it falls apart is in the countries and ports which don't provide the facilities to dispose of such wastes," he added. "Sometimes when they do have the facilities, they charge extortion amounts to use them.
"Any new regulations must be practical and workable otherwise it is like asking people who go to the beach to dispose of their litter responsibly and then not providing bins or charging a fortune for them to use it."
Conservationists, backed by public petitions with tens of thousands of signatures, remained determined that the Government, and the IMO, act sooner rather than later.
The RSPB said previous pollution incidents involving PIB – in the Irish Sea in 1994, and in the North Sea in 1998 and 2010 – proved tank washing should be banned.
Tony Whitehead, from the RSPB in the South West, said: "The seabird disaster along the South West coast earlier this year highlighted the risks attached to the rapid increase in the use, transportation and discharge of non-oil products such as PIB – the so-called "Hazardous and Noxious Substances" (HNS).
"RSPB is calling for a review into the response to such incidents involving HNS and the way these products are tested and classified under international shipping regulations.
"If it's found, when tested in real conditions, these substances are harmful for wildlife there should then follow a ban on their discharge in any quantity.
"And we would urge all organisations involved to act quickly in response to the growing global trade. Global consumption of PIB alone is forecast to increase by around 40% by 2017 to 1.2 million tonnes per year."
Image may be NSFW.
Clik here to view.