Seasonal erythemal UV, UVA and vitamin D effective UV exposures of office workers

Seasonal erythemal UV, UVA and vitamin D effective UV exposures of office workers

In light of the ever changing composition of the Earth's atmosphere and the consequences of ultraviolet radiation (UVR) for the biological environment, it is important to be able to determine the specific ultraviolet radiation levels that reach humans living on the Earth's surface. Optimal human health requires a balanced amount of UV exposure as both too much and too little have different but serious potential health consequences. Sun damage can be caused by both UVB (280 320 nm) and UVA (320 400 nm) with melanoma and keratinocyte cancers being linked to UVB and UVA exposures. Humans need vitamin D to maintain good health and the best natural source of vitamin D is UVB from the Sun. Vitamin D deficiency, or insufficiency, is increasingly reported as people avoid potentially damaging UV exposure.

Miniaturized dosimeters using polyphenylene oxide (PPO) as a photoactive material have been used to measure erythemal UV exposures received by humans for exposure periods of between one to seven days. In order to broaden the range of the PPO dosimeter, research was undertaken for the dual calibration of PPO dosimeters to both the erythemal and vitamin D action spectra. Through this dual calibration PPO dosimeters were able to record both types of biologically effective exposure as both are active within the UVB waveband. The calibration provided an R2 of 0.86 0.99 for erythemal UV and an R2 of 0.92 0.99 for vitamin D effective UV.

A new miniaturized dosimeter using 8-methoxypsoralen (8-MOP) as the photoactive material was characterized and a technique developed for the calibration of UVA exposures. Using Mylar as a filter to remove the UVB, the spectral response showed that 8-MOP reacts only to wavelengths between 320 400 nm. The measured cosine response had an error of less than 14% for angles between 0° and 50°. Seasonal dose response tests indicated that these UVA dosimeters are able to measure exposures greater than 21.5 kJ/m2 for a continuous period of up to seven days.

These two dosimeters were combined into one dosimeter badge; these combined badges were worn in research to record concurrently the personal erythemal UV, UVA
and vitamin D effective UV exposures received by office workers in their occupational and recreational environments over a minimum period of a week in each season of the year. The amount of time spent outdoors, general UV protection strategies employed and the ambient UV both outdoors and within the office environment were recorded. Participants were all indoor office workers located at two sites at the sub-tropical location of Toowoomba (27°33'S 151°55'E, elevation 691 m). The participants wore a combined dosimeter badge horizontally on the shoulder for a minimum of one week in each season. The median erythemal exposure was highest during the spring and lowest during winter, as was the median vitamin D effective exposure. Median UVA exposures were at a similar level in winter and summer, autumn was higher and spring at a lower level. The behaviour of participants changed in each season; in winter 45% of the time spent outdoors was between the hours of 10:00 – 14:00 h compared to 27% in summer. The daily UVA/UVB ratio is also lowest between 10:00 – 14:00 h and also changes with the season, resulting in the differences between the distributions of exposures for each of the wavebands. Each category of exposures must be assessed individually as no association was found between any of the wavebands over the whole year, indicating that each season and each waveband had different distributions.

Use of sunscreen, wearing of hats and type of clothing worn were analysed as part of the UV protection aspect of the study. Over 50% (n=128) of participants reported not using any sunscreen or wearing a hat at any time. Autumn rather than summer had the highest reported use of sunscreen and the highest proportion of people wearing hats. Clothing was separated into leg covering and arm covering. In all seasons, apart from winter, more than 25% (n=99) of participants always had short sleeves when outdoors. In winter 80% (n=29) of people had full leg cover and 30% (n=29) had full arm cover. These results indicate that the majority of people are not using UV protection on a regular basis.

The results also demonstrate that, the dual film dosimeter developed and characterized with a calibration to three different biological responses, is an effective device for the concurrent measurement of the erythemal UV, UVA and vitamin D effective UV exposures for periods of a week before needing to change the dosimeters.