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Ecotoxicological information

Sediment toxicity

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Description of key information

The key study Harlan 2010 demonstrated that there was no significant reduction in emergence of adult midges up to the highest test concentration of 1000 mg precipitated tin (IV) (hydr)oxides/kg. The study was performed in compliance with GLP and to the current standardised guideline OECD 218. The study was considered reliable for assessment and therefore assigned a reliability score of 1.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater sediment:
1 000 mg/kg sediment dw

Additional information

As an element, tin will not degrade in the environment. The available Kd values indicate that it is likely to bind to sediment. In addition, any dissolved tin in water is expected to rapidly precipitate as tin hydroxides. The difficulties in conducting aquatic ecotoxicity tests with tin have been discussed previously in this dossier. At a workshop entitled “Environmental Toxicity Issues For Metals Which Change Speciation And/Or Form Precipitates Under Natural Environmental Conditions – How To Treat This Under REACH” on 26 January 2010 at ECHA upon initiative of the metals industry the aquatic toxicity testing of insoluble and unstable metals was discussed. The issue was raised that if any tin released to the aquatic environment was not likely to be present in dissolved forms in water then the potential toxicity of the precipitated form in sediment should also be investigated.

A new study was therefore been commissioned to investigate the toxicity of the precipitated tin matter arising from unstable tin solutions to sediment dwelling larvae of Chironomus riparius. Tin precipitate was formed just prior to the experiment and then added to the sediment used in the test. This experiment is seen as analogous to testing a degradation product of an organic substance that is rapidly removed from the environment. No significant effects were observed on Chironomus riparius up to a loading of 1000 mg/kg of the precipitated material. This fresh degradation product resulting from the hydrolysis of tin ions was found to contain 17% tin which equates to 22% SnO2 when characterised . However, the mineral composition of the precipitated material will change with time as further dehydration occurs.