Musk Xylene - Safety - Environmental Concerns

Environmental Concerns

The first concerns about musk xylene arose in the early 1980s, with the detection of musk xylene residues in fish from the Tama River near Tokyo, and subsequently in the river water itself, especially at the outlets of sewage treatment plants. This led to a voluntary moratorium on the use of musk xylene in Japan from 1982. Similar residues were subsequently found in European waters such as the Elbe, Stör and Ruhr rivers in Germany, the German Bight area of the North Sea and sewage treatment plant outlets in Sweden. Typical concentrations were >0.001 µg/l in sea water, 0.001–0.01 µg/l in river water and 0.01–0.1 µg/l (sometimes higher) in the effluent from sewage treatment plants.

These findings indicate that musk xylene is not completely removed from wastewater by the sewage treatment process. Two studies in Germany found compared musk xylene concentrations in incoming wastewater and sewage treatment plant effluent, and found removal rates of 82% and 58%. However, they are not concentrations which are expected to be toxic to aquatic life. The European Union Risk Assessment Report reviewed more than a dozen studies of the toxicity of musk xylene to algae and to aquatic vertebrates and invertebrates, and all found no observed effect concentrations greater than 10 µg/l, the chronic aquatic toxicity threshold in the EU REACH Regulation.

The biodegradation of musk xylene in sea water and in mixed sea water/sediment systems was studied in laboratory simulations using carbon-14 labelled musk xylene, and the results discussed in an addendum to the European Union Risk Assessment Report. The half-life in marine sediment was esimated to be 60 days or less, with biodegradation occurring by anaerobic reduction of the nitro groups. The half-life in sediment-free sea water was estimated to be more than 150 days, far above the "very persistent" threshold of 60 days. The 2008 addendum also discussed the photolysis of musk xylene in water and in air, which are rapid: however, photolysis was not considered to be relevant in the persistence of musk xylene in the environment, and was not taken into account in classifying it as a "very persistent" substance.

Several different primary bioaccumulation studies were reviewed in the European Union Risk Assessment Report, with bioaccumulation factors varying between 640 l/kg and 6740 l/kg. Given that musk xylene has a very high octanol–water partition coefficient (log K_ow = 4.9), the higher bioaccumulation factors were considered to be the more significant. The 2008 addendum considered a further laboratory study from the Japanese Ministry of International Trade and Industry which was not available to the authors of the original Risk Assessment Report and which also showed bioaccumulation factors in fish (Cyprinus carpio) that were higher than the REACH threshold of 5000 l/kg for "very bioaccumulative" substances. Bioaccumulation factors of more than 5000 l/kg (wet weight basis) have also been found in carp (Carassius carassius) and eels (Anguilla anguilla) from a sewage treatment pond.