Nitro musks are a family of synthetic compounds which have been widely used as fragrances in detergents, soaps and cosmetics for more than 20 years.
The chemicals appear to have gone unnoticed in the UK environment, but research elsewhere in Europe and Japan has shown that they bioaccumulate and are poorly biodegradable. A Japanese study found that discharges of nitro musks in Tokyo's sewage effluents had led to elevated concentrations in fish and shellfish. Levels of up to 140ppb on a wet weight basis were measured in freshwater fish.
The toxicity of nitro musks has also given cause for concern. Musk xylene, the most commonly used member of the group, caused tumours in laboratory mice. Another compound, musk ambrette, was found to be neurotoxic in mammals and mutagenic in bacteria. The substances are structurally similar to nitrotoluenes, a group of compounds with widely recognised toxic and mutagenic properties.
Nitro musks are permitted as flavouring agents within the EC, although the evidence of toxicity has led to the withdrawal of musk xylene in Japan and musk ambrette in the USA under voluntary agreements.
However, recent studies in Germany have found significant levels of nitro musks in human milk - and concluded that the major exposure route was not food intake but absorption through the skin from detergent and cosmetic products. Levels of up to 1.22mg/kg fat of musk xylene and 0.24mg/kg fat of musk ketone were found in breast milk.
Last November, Germany asked parties to the Oslo and Paris Conventions, which regulate pollution of the North Sea, to consider discontinuing the use of musk xylene. They agreed to consult industry on the use and properties of the compound and report later this year.
Concern over the bioaccumulation and persistence of nitro musks may also be reflected in the forthcoming EC eco-label for detergents. According to Germany's Environment Agency, which is developing the eco-label criteria, nitro musks feature on a list of excluded ingredients which is currently under debate with the detergent industry (ENDS Report 226, 26-27 ).
Germany's trade association for the detergent and cosmetic industries, IKW, agreed a voluntary embargo on nitro musks last year. Industry in other parts of Europe is also feeling the pressure and the market for the chemicals appears to be in rapid decline.
The fragrance industry is preparing a defence of nitro musks through the International Fragrance Research Association (IFRA). The issue is the first challenge to an ingredient on environmental grounds the industry has faced.
An IFRA spokesman told ENDS that nitro musks meet the industry's safety criteria. There is no firm evidence that they bioaccumulate, it maintains, because levels in older people have not been shown to be higher than in younger ones. IFRA's own research has also shown that nitro musks are not genotoxic and the tumours produced in a strain of mice are not relevant to humans.
However, the defence from parts of the fragrance industry may be half-hearted because other synthetic musks are now widely available. Although more expensive, these appear to produce fewer skin sensitivity reactions.
Musk xylene production in the UK ceased several years ago. The material is now mainly imported from the Third World. According to the Soap and Detergent Industry Association, about 20 tonnes are used annually in the UK, mainly in detergents and household cleaning products.
Detergent manufacturer Procter & Gamble told ENDS that musk xylene was phased out of its laundry and cleaning products in 1992, and other nitro musks were removed by early 1994. Its rival, Lever, expects to end its use of nitro musks within a year. Both firms do not believe there is a scientific case against the compounds, but say the phase-out is a risk avoidance measure. P&G is keen "to avoid concern to consumers and a possible negative effect on business".
Nitro musks look set to join the lengthening list of industrial chemicals which have been through the cycle of development, use and abandonment. However, consumers might reasonably ask whether manufacturers know any more about their replacements.
Detergent producers say they will not be using new compounds to replace nitro musks, but admit that their products are under continual "evolution". Without comprehensive data on the toxicity and biodegradation of new fragrances, risk avoidance measures may simply prove to be the start of another turn of the cycle of development and abandonment.
According to IFRA, the industry's screening programme has concentrated mainly on skin sensitivity and toxicity issues, with environmental performance being a new concern. IFRA's existing guidelines contain no specific rules on biodegradation and biaccumulation.