Malachite green identified as an environmental contaminant

Malachite green is frequently used as a veterinary medicinal product for ornamental fish. It may not be applied to fish intended for human consumption. The zero tolerance principle applies here. Detection of the substance is seen as an indication of illegal use; the fish may not be placed on the market. In a pilot project scientists at the Federal Institute for Risk Assessment (BfR) have now proven for the first time that untreated, free-living fish may be contaminated with malachite green. They examined eels captured in the wild from Berlin water bodies for residues of malachite green and found them in 20 out of 40 samples. All the samples that were tested positive came from water bodies into which cleaned wastewater from wastewater treatment plants had been discharged. For BfR this is a clear indication that malachite green must now be seen as an environmental contaminant and that the widespread use leads to the background contamination of wastewater and municipal water bodies. This situation has prompted reflections whether the zero tolerance principle can be sensibly applied to free-living food fish from inland waterways. “Irrespective of this, exposure to malachite green should be reduced”, says BfR President Professor Dr. Dr. Andreas Hensel. “In the case of fish from aquaculture we advocate the continued application of the zero tolerance principle. As the fish are kept under controlled conditions, the detection of malachite green in samples of this kind must always be interpreted as an indication of the possible illegal use of the veterinary medicinal product.”

Malachite green is a triphenylmethane dye. It was and is used both as a dye to colour synthetic fibres and silk and to dye leather and paper products. In forensic medicine malachite green is used to detect traces of blood. Furthermore, the substance is used as a veterinary medicinal product for the treatment of ornamental fish and in ornamental fish roe to combat parasites, fungal attack and bacterial infections. There are grounds for suspecting that this substance damages the genotype and triggers cancer. A tolerable daily intake cannot be established for substances of this kind on the basis of the current level of scientific knowledge.

In contrast to ornamental fish breeding and farming, malachite green is not authorised for the treatment of food-producing animals like edible fish. The zero tolerance principle applies here: fish and fish products intended for human consumption may not contain malachite green. Even fish and fish products with very low levels of malachite green may not be marketed as foods. The situation is different in the case of aquaculture products imported into the EU. They may be sold in EU Member States when the residue levels of malachite green are less than two microgram per kilogram. This intervention value was defined as a Minimum Required Performance Limit, MRPL) for analytical methods used internationally and it seeks to facilitate international trade. The MRPL value has not been established toxicologically and does not apply to products which are only traded within the EU. Although the zero tolerance applies to them in the EU, residues of malachite green and its degradation product, leucomalachite green, are detected again and again in Germany in edible fish as well as in fish roe (trout caviar), for instance in 2005 in almost 10% of edible fish samples examined by the Institute for Ichthyology in Cuxhaven during its official food control activities.

Up to now positive results were always taken as an indication of the illegal use of malachite green as a veterinary medicinal product in the production of edible fish. This situation has changed as a consequence of the results of the BfR pilot study. In a study on wild eel from Berlin inland waterways the scientists at the Institute proved that malachite green residues can also be environmental contamination. Almost half of the samples collected were tested positive for malachite green or leucomalachite green. However, the levels were very low. Depending on the fishing area they were between 0.04 und 0.8 µg/kg eel fillet. The residues could only be detected in samples of fish from water bodies into which wastewater had been discharged from wastewater treatment plants. BfR sees this as proof of background contamination of these water bodies with malachite green. Fish can then take up this substance as an environmental contaminant. The assumption is that the substance comes from various sources like e.g. ornamental fish aquaria, textiles or laboratories and reaches the water bodies from cleaned wastewater from municipal wastewater treatment plants.

The Institute estimates that the health risk for consumers who eat contaminated eels only once or occasionally is very low. Nevertheless, BfR is of the opinion that the wide distribution of malachite green in the environment is worrying given the toxicological properties of this substance. It calls on the users of malachite green to minimise the input into the environment. The competent authorities must discuss and then decide whether the zero tolerance principle should be applied to and upheld for a substance which may not be used as a veterinary medicinal product but which is widespread as an environmental contaminant in water bodies in the case of free-living edible fish until minimisation measures take effect. In the opinion of BfR the levels should not exceed the MRPL value of 2 µg/kg either.

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