Anti-fouling paint on ships and nets can
Shellfish living in marine environments are threatened by toxic organotin compounds which invade their eco-systems. The chemicals are introduced through anti-fouling paints on boats and nets. Legislation to limit the use of these coatings has been implemented, but in order to make sure that it is followed, accurate measurements are needed for monitoring schemes to be of any use. Through a project funded by the Standards, Measurements and Testing programme, laboratories from across Europe joined forces to improve the reliability of the measurements they perform in their fight against organotin pollution.
The paints covering ships and boats may present a real risk to sea life. Anti-fouling coatings are used to prevent the build up of barnacles, sea weed and other organisms, so that the sea-faring vessels can travel more quickly through the water. Nets are also treated to give them a longer life. Even with all these benefits however, there is a flip side to the coin: many of these coatings contain organotin compounds which are a life threatening hazard to larvae, mussels, oysters and fish.
Some organotin compounds are highly toxic to the marine organisms even at extremely low concentrations. The chemicals are leached out of the paints and coatings, into the water and then into the sea life. Consequently, organotin-based paints containing tributyl tin (TBT) and triphenyl tin (TPT) have been banned in many European countries and several EC Directives require organotin levels to be monitored regularly.
TPT is also used in agriculture as a fungicide and other tin compounds are used widely in PVC production processes and as industrial catalysts. The world-wide organotin industry pumped out 35,000 tonnes of the chemicals in 1980, with at least 16,000 tonnes being produced for uses that may result in sea water contamination.
There is much concern about the risk of organotin amongst environmentalists,
government regulators and the fishing and shellfish industries. TBT, TPT and other related chemicals can wipe out large numbers of oysters and mussels and leave the fishing community with lower profits.
To satisfy the requirements of all these parties, accurate and precise measurements are vital. The laboratories performing the tests must have good quality control procedures to ensure that their measurements are providing meaningful results. Without these checks, no-one can be sure that they can rely on their measurements. If tests show a region to be safe when it is not, the sea life is at risk. Conversely, if an area is deemed to be teeming with organotin compounds when it is in fact safe, the fishing industry may suffer unnecessarily. Either way, the price of an inaccurate measurement is costly.
In 1988, experts in organotin measurements formed a consortium to evaluate the methods used to analyse sediments and marine organisms. They had been hampered by inconsistent results across Europe and it was impossible to tell where exactly the errors were. They were not helped by the actual measurement methods then available. Many of these involved analysis for total tin content, rather than for specific organotin compounds. This was useless because many other tin compounds, such as oxide and sulphate, are not known to be toxic.
This group of ca. 20 laboratories went through many studies together. They tested the analytical techniques by making their measurements on the same samples and then comparing the results. At first, the answers they found varied a lot from laboratory to laboratory. They improved their methods through a step-by-step process in which each small part of the measurement procedure was checked for accuracy. Technical discussion then followed. The measurements are very complex and consist of many steps. It is easy for small mistakes to be multiplied into much more drastic ones.
The only way to check the accuracy of the methods was to work with other experts in the field. No one organisation can ever spot where they could improve, especially if they have been following the same procedure for a long time and have no reason to think that their results are not perfect.
The complexity of the work
gets more challenging
As time went on, the group tested more challenging samples. When they first started, they performed tests with straight-forward solutions. They then moved on to test sediment, spiked in the laboratory with contaminants, followed by harbour and coastal sediments which contained organotins. Finally, they tested their methods on mussel tissue, beginning in 1994. The complexity of each test sample increased and this is why the measurements became increasingly difficult to test and verify for accuracy.
The team not only improved their own techniques and procedures, but they also developed and produced two certified reference materials suitable for use by government testing laboratories, environmental regulators and universities performing research into the effects of organotins. The materials help analysts to verify the performance and accuracy of their methods. This is possible because the group made hundreds of samples, all containing the same, known levels of various organotin compounds.
mussel samples help testing laboratories
The production of the mussel material, for example, involved finding a contaminated region to harvest hundreds of kilograms of mussels. The group found a gulf in Italy which has intense maritime traffic and dockyard activity as well as one of the biggest mussel farms. This leads to high organotin content in the mussels. The batch, once obtained, had to be carefully prepared to ensure that each and every sample had the same levels of the toxic chemicals. All the samples had to be checked for stability as well, since some organotin compounds are transformed into other chemicals when the sample is exposed to light. The certification of the material required much detailed analysis.
The reference materials are now available to any laboratory who needs them to check that they are producing reliable and comparable measurements. With the vast improvements made to optimise the measurement of organotin in marine environments, we can better use the results to take reliable decisions to protect sea life from the threat of toxic chemicals.
For reference, the two CRMs described are CRM 462 (coastal sediment) and CRM 477 (mussel tissue).