[en] This Annex considers the combined action of radiation with potentially important environmental conditions. Since there is a scarcity of systematic data on which an analysis of combined effects can be based, this Annex will be more hypothetical and will attempt to suggest definitions, to identify suitable methods of analysis, to select from a large amount of diffuse information the conditions and the data of importance for further consideration and to provide suggestions for future research. For humans in environmental circumstances the UNSCEAR Committee has been unable to document any clear case of synergistic interaction between radiation and other agents, which could lead to substantial modifications of the risk estimates for significant sections of the population.