The Environment Agency’s risk assessment for dodecamethylcyclohexasiloxane (D6) is based on the methods outlined in the European Union (EU) Technical Guidance Document. Persistent, bioaccumulative, and toxic assessment D6 does not meet the screening criteria for a persistent, bioaccumulative, and toxic(PBT) substance on the basis of all the available measured and calculated data. D6 is not readily biodegradable in a standard biodegradation test, and no biodegradation or biodegradation-simulation test results are available for it. Based on information for related substances, D6 is not expected to biodegrade rapidly in aquatic systems or to hydrolyse rapidly at near neutral pHs. D6 therefore has the potential to meet the screening persistent or very persistent (vP) criteria. The bioconcentration factor (BCF) of D6 in fish is 1160 l/kg (determined experimentally). Thus it does not meet the bioaccumulative or very bioaccumulative (vB) criteria. D6 causes no lethality in fish exposed over periods of up to 49 days and no adverse effects to the invertebrate Daphnia magna in a 21-day reproduction test. Based on predictions and comparison with the known toxicity of similar substances, D6 is also expected to show little or no toxic effect with algae at concentrations up to its water solubility. In addition, it is not classified as carcinogenic, mutagenic, or reprotoxic compound. Thus, D6 does not meet the screening criteria for toxicity. The overall conclusions of the PBT assessment are that D6 does not meet the criteria for a PBT or a vPvB substance. Quantitative risk assessment The risks from the normal use of D6 to water, sediments, soil, and predators are assessed using standard models and the information available. The property data set is not complete and in some areas further information will be valuable. This assessment therefore makes recommendations about the significance of the data gaps and uncertainties, and suggests the focus for further research. The main uses of D6 are as an intermediate in the production of other chemicals (silicone polymers) and in personal care products (e.g. cosmetic products, and skin- and hair-care products). Use as an intermediate to make silicone polymers effectively consumes the D6, although trace amounts are still present in the final products can be subsequently released to the environment. Use of D6 in personal care products results in widespread exposure in the environment. Estimates of the potential emissions to the environment from D6’s key life-cycle stages are based on industry research and Emission Scenario Documents or, in the absence of any other information, worst-case default assumptions. Using the available information, risk characterisation ratios could only be generated for predators and top predators. No risk characterisation ratios above one are identified for any of the scenarios considered (above one indicates an unacceptable risk to the environment). However, a lack of suitable toxicity data means it is not currently possible to assess fully the risks to freshwater sediment, soil, and marine sediment. An assessment of human exposure via the environment concludes that D6 is unlikely to pose a risk to human health. Some information provided by industry is treated as confidential and not given in this report, although the data are used to develop appropriate emission scenarios. These data are included in a confidential annex that supports the assessment, which is available via the Project Manager, where appropriate.