ONE out of every five large fish sampled at a popular angling spot on the Eastern Seaboard contained mercury levels in excess of the health standard, Chulalongkorn University researchers reported.
Although the study was only a small one, it is the first solid evidence that seafood caught off of Rayong and Chon Buri may be seriously contaminated by mercury, a dangerous neurotoxin, and therefore unsafe to eat.
Other recent studies have documented high mercury levels in fish around natural gas production platforms in the central gulf, and climbing mercury levels in the water and sediment around the Mab Ta Phud industrial port on the Eastern Seaboard. But no information has been released to the public about the mercury levels of marine animals in the eastern region.
''The thing which is worrying is that the mercury levels in fish are higher now than when we measured 10 years ago," said Prof Piamsak Menasveta, a marine scientist at Chulalongkorn University who supervised the study.
''We still don't know what the source is for the mercury contamination, whether it's coming from the central gulf or from onshore industries."
The study was carried out at Bang Sarae Bay, a popular recreational fishing site in Chon Buri province. It lies about 30 kilometres west of the Mab Ta Phud industrial estate, which contains many petrochemical plants and has been at the centre of efforts to find the source of the mercury contamination.
Piamsak speculated that prevailing westerly currents could have taken mercury discharged at Mab Ta Phud in Rayong province to Bang Sarae, but an official at the Pollution Control Department (PCD) noted that there were many other possible point sources for mercury on the Eastern Seaboard.
''Some local industrial activities may be causing the mercury contamination there," said the PCD official, ''and mercury levels are also a little bit high at Laem Chabang [industrial estate in Chon Buri], as well."
But a petrochemical industry expert who has worked in Mab Ta Phud is convinced that the problem largely stems from there.
''The amount of mercury being discharged from natural gas production platforms is quite small compared to that coming out of Mab Ta Phud," asserted the industry source, who sought anonymity.
''But the problem on the Eastern Seaboard hasn't been exposed for political reasons."
The natural gas produced in the central gulf by Unocal and Total is known to contain mercury.
Mercury-contaminated water discharged from the platforms into the sea has been blamed for the relatively high levels of mercury found by Piamsak in fish around some of the older platforms. Both oil companies are now taking further steps to control the toxic pollution.
The source of the mercury problems on the Eastern Seaboard, however, remains a mystery. The toxic heavy metal is present in the gas and condensate sent from the production platforms to factories in Mab Ta Phud, and is also used as a catalyst in some petrochemical processes.
Mercury may also crop up naturally in the runoff from rivers along the eastern coast.
''It's a very complicated problem," said the industry source.
''I don't think it's a crisis yet, but we should take care of the situation now, before it turns into one. What concerns me is that there has been no published data about mercury levels in marine life along the eastern coast."
Along with the PCD, the Industrial Estates Authority of Thailand (IEAT), the Harbour Department and the Fisheries Department have all conducted mercury studies in the area, but few results have been revealed to the public. Piamsak is also planning to do another study for the Department of Mineral Resources (DMR).
The PCD and the IEAT tested waste water from some factories in Mab Ta Phud, but officials say they could not find any releasing mercury over the legal standard.
''We also looked at a small sample of marine animals along the eastern coast and most of them had mercury under the standard," added the PCD source, who said a more comprehensive study will be undertaken early next year.
The Chulalongkorn study was carried out over a one-year period by master's student Piyanat Toonworn and looked at how, unlike other heavy metals, mercury concentrations in marine life grows as the toxin moves up the food chain a process known as biomagnification.
The paper is due to be presented at a meeting of the Toxicological Society of Thailand on Nov 28 and will be published in the Thai Journal of Aquatic Science.
Piyanat took samples from four different levels of the marine food chain at Bang Sarae and found that the 30 carnivorous fish collected including grouper, sea bass, jack, barracuda, spanish mackerel and loach had average mercury levels roughly equal to the health standard of 0.5 parts per million (ppm). Twenty per cent of these large fish were found to have mercury concentrations over the standard, with the highest recorded level being in a loach at 1.5 ppm.
Comparing the study to his examination of fish at Unocal's Erawan platform, Piamsak said, ''At Erawan, there were fewer fish [11.6 per cent] that had mercury levels over the standard, but those that were contained relatively high concentrations around 2.0 or even 3.0 ppm. At Bang Sarae, there were more fish over the standard, but they were not very much higher."
Questioned about the accuracy of the Eastern Seaboard study, he said that the results were double-checked using a process known as the ''recovery system" and found to be accurate within a 10 per cent range.
''That is satisfactory for a master's thesis, but for the public [DMR] study, we will send our samples to be double-checked at an outside lab, and we hope the two sets of results will be within 5 per cent of each other," Piamsak explained.
''We also plan to focus our studies on mercury levels within a single species of fish, the cobia, at sites on the eastern coast, the central gulf, off Chumphon province and in the Andaman Sea."
Commenting on the findings at Bang Sarae, the PCD official suggested that, ''We need to find out just how many fish can be allowed with mercury levels over the standard before it becomes a health risk."
The industrial source, meanwhile, stated bluntly: ''I don't eat fish when I'm in Rayong."