Although, besides a few reported hotspots, predicted and actually measured concentrations of nanomaterials in the environment are very low, little is known about long term effects resulting from chronic exposure. Indeed, (bio)accumulation and the associated hazard may become a concern after years (decades) of exposure. The possibly adverse effects will be controlled by the (bio)persistence/stability. For short-lived nano-enabled products this phenomenon might occur within a relatively short timeframe, since, in the case of cosmetics for example, the release into the environment happens within hours of the initial use. This is particularly true for sunscreens which, for the most part, are directly released in aquatic environments. The mineral UV filters in sunscreens, and especially TiO2, are supposed to be the answer to the concerns raised by the use of organic UV absorbers. However, their environmental safety rests entirely on their long term chemical stability. Here, commercial TiO2 nanocomposites used in sunscreens are examined in terms of surface speciation. Indeed, these materials are core-shell composites whose surface chemistry governs their mobility (i.e. exposure) as well as their toxicity (i.e. hazard). In other words, it is a long term risk assessment issue. Here, it is reported that the integrity of the shells around depends on the composite, with a general trend showing their removal in relatively short periods of time. Implications in terms of environmental risks and product design are discussed.