This report describes a study, carried out in 2006–2007, of the potential toxicity to the environment (ecotoxicity) of cationic bitumen emulsions used for chipsealing (surface dressing) in New Zealand. The ecotoxicities of the separate components of bitumen emulsions are reviewed to assess their contribution to emulsion ecotoxicity. Overseas reports on the environmental dangers of a non-ionic bitumen emulsion (a power station fuel) and runoff from cold mix asphalt are examined for relevant applications to sealing emulsions. Ecotoxicities are measured for four representative New Zealand emulsions. The implications of the findings for possible environmental classification of emulsions by environmental authorities are discussed.