Sun exposure at school

Photochemistry and Photobiology, Aug 1999 by Moise, A F, Buttner, P G, Harrison, S L

ABSTRACT

There is strong evidence that sun exposure during childhood and adolescence plays an important role in the etiology of skin cancer, in particular cutaneous melanoma. Between the age of 6 and 18, most children and adolescents will spend around 200 days per year at school and may receive a substantial fraction of their daily total solar ultraviolet radiation (UVR) exposure while at school. This study estimated the average daily erythemally effective dose of 70 grade 8 students from a high school in Townsville during 5 school days in July 1998. Through UV measurements of shade locations at the school and a combination of frequency counts and a questionnaire of grade 8 students, it was possible to determine the fraction of solar UVR reaching under the shade structures during lunch breaks and routine outdoor activities. Also, a routinely operating UV-Biometer provided the annual variation of the daily dose that was used to calculate exposure levels for the 70 students. Our results suggest that up to 47% of the daily total dose fell within the time periods where students were outdoors during school hours. For students not seeking shade structures during the breaks (which usually was the case when involved in sport activities such as basketball or soccer), the average daily dose could have been as high as 14 SED (standard erythemal dose). Using results from the questionnaire of 70 grade 8 students, their average annual dose while at school was 414 SED or 2 SED per schoolday. However, the distribution of average daily erythemal effective dose per grade 8 student over the whole year showed that on 31% of all school days in 1998, this dose was exceeded. Because most previous attempts to change arguably poor sun-protective behavior of young Australian children and adolescents at school showed little success, one way of decreasing the amount of harmful UVR reaching unprotected skin is the more careful design of shade structures at schools.

^Abbreviations: CIE, Commission Internationale d'Eclairage; EED, erythemal effective dose; MED, minimal erythemal dose; SED, standard erythemal dose; UVR, ultraviolet radiation.

INTRODUCTION

Sun exposure has long been discussed as a strong risk factor for all types of skin cancer (1). Located in the dry tropics of North Queensland, Australia, Townsville (19oS, population: 130000) experiences high levels of ambient solar ultraviolet radiation (UVR)t because of its geographical location (2,3). During summer in Australia, the earth's elliptical orbit brings it closer to the sun than during the northern summer, resulting in 7% additional intensity of solar UVR. This, coupled with clearer atmospheric conditions and the more significant ozone depletion observed over the Antarctic, may result in a measured ambient UVR that is 12-15% higher for geographical locations in the southern hemisphere than at comparable locations in the northern hemisphere (4,5).

It is well established that Queensland has the highest rates of skin cancer in the world (6,7). Incidence rates for 1997 for nonmelanoma skin cancer (basal cell carcinoma, squamous cell carcinoma) and cutaneous melanoma in Townsville (histologically confirmed and age-adjusted to world standard population), were 2058.2, 1332.3 and 49.1 per 100 000, respectively, for males, and 1194.5, 754.8 and 41.7 per 100 000 for females (7).

Studies investigating personal exposure to solar UVR are important in assessing personal risk and preventive actions. While there have been various personal exposure studies focusing on occupational and recreational exposure levels of adults to solar UVR (8-13) and some studies about children (14-17), of which one has included exposure at school (18), no information is available about solar UVR exposure levels while at school only. In order to provide insight into the UVR exposure received during a school year, we present results from a study conducted with school children in Townsville.

MATERIALS AND METHODS

As part of a joint school project, ambient solar UVB radiation was assessed at the school yard of Townsville High School in July 1998.

UVB instrumentation. The solar UVB broadband meters used in this study were manufactured by International Light and consisted of a SED240 vacuum photodiode detector, a UVB-1 filter and a teflon diffuser. The N.I.S.T. traceable calibration of the meters was less than I year old when taking the measurements. The meters were attached to a International Light IL1400A Radiometer that allowed measuring solar UVB radiation instantaneously as well as integrated over a fixed time period. The sensors were mounted on standard tripods and leveled out to either horizontal or vertical direction.

Sites. The measurement sites were selected according to variation in shade and frequency of students visiting that site during their lunch and sport breaks. In general, four different settings were chosen, including the types of locations occupied by most of the students during these breaks: ( l) under NO shade (i.e. on sports courts and other open areas); (2) on verandahs along the sides of the school buildings (these verandahs were covered by the extended roof of the buildings: height of roof, 4.5 m; width of verandah, 2 m); (3) rest area close to the kiosk (selling lunch meals and beverages), which was covered by a combination of black shade cloth and/or tree foliage; the height of the cover was around 5 m; and (4) under dense tree foliage. Being inside a school building was considered to be in a zero UVB exposure environment.