Solar ultraviolet radiation incident upon reef snorkelers determined by consideration of the partial immersion of dosimeters in the natural ocean environment

Reef snorkelling is potentially a high-risk activity for persons visiting tropical and sub-tropical waters due to possible overexposure to solar ultraviolet radiation (UVR). Measurements and modelled estimates of the UVR received by human subjects are presented for a 10 degrees latitudinal gradient of Australia's Great Barrier Reef and some Melanesian Islands (15 degrees S to 25 degrees S). A technique is described to measure the erythemally effective UVR received by the neck and the lower back. Measurements were made by application of a hybrid in-air and submerged calibration for polysulphone dosimeters. Measured exposures were used to model UVR exposure distributions at a number of popular snorkelling sites. A total of 11 snorkelling trials were held between 29 September 2009 and 26 January 2010. Exposures measured to the back and expressed relative to the horizontal plane ambient UVR have shown there to be some variation in the UVR distribution, with the neck receiving the greatest proportion of ambient UVR (0.56 +/- 0.14 (1 sigma)), followed by the lower back (0.36 +/- 0.14 (1 sigma)). Similarly high UVR exposures were determined at neck and lower back sites for different seasons, different times of day and over the latitudinal range of the study.