Ultraviolet radiation exposure of children and adolescents in Durban, South Africa

Photochemistry and Photobiology, Mar 2003 by Guy, Caradee, Diab, Roseanne, Martincigh, Bice

Influence of age and gender on PSFB dose

There is little difference in the mean and median PSFB dose as a function of age group (last three columns of Table 2), and statistical application of a nonparametric analysis of variance test revealed no significant differences at the 95% confidence level. There is some indication that the 95% ranges were smaller in the case of adolescents (0.4-10.0) than in the two younger age groups, most likely a reflection of the longer school day of high school students. A similar pattern was noted by Diffey et al. (11) for children aged 9-10 years and 14-15 years in a study conducted in England.

A comparison of the mean and median PSFB doses of male and female subjects (Table 2) showed that male subjects generally received higher PSFB doses than females, again confirming the findings of Diffey et al. (11). The mean (95% range in parentheses) and median daily PSFB doses for males were 2.4 SED (0.6-14.4) and 1.4 SED, whereas for females were 1.8 SED (0.4-12.6) and 1.0 SED, respectively. This was confirmed through the statistical application of the Wilcoxon two-sample test revealing a significant difference between the two groups at the 95% confidence level.

Influence of nature of activity on PSFB dose

The variability in individual PSFB dose was found to be dependent on the nature of activities in which an individual engaged. This was reflected first in the differences in PSFB dose on weekdays when compared with weekends (Table 3). The differences were most marked in the case of the two older age groups who were clearly able to spend more time on activities that involved greater UVR exposure on weekends than they were on weekdays. Differences were statistically significant in these cases but not in the youngest age group, which exhibited a more consistent daily UVR exposure.

Time spent outdoors is also a reflection of the nature of activity patterns. Based on the journal entries, the mean time spent outdoors for all age groups during the study period, including weekdays and weekends, was 2.3 h per day. This compares well with a similar study by Gies et al. (12), who found that Australian children spent on average 2.2 h per day outdoors during the school term. The time spent outdoors is seldom experienced as a singleexposure event but comprises intermittent brief exposure periods, which accumulate to a total of approximately 2 h. Although this represents a relatively small fraction of the day, the timing of exposure periods is critical in determining the intensity of PSFB dose received by an individual. Peak exposure frequently occurs between 10:00 and 11:00 A.M., a period that brackets the first tea break for all age groups in the daily school routine. The lunch break varies across age groups, accounting for the absence of a second dominant exposure period. After school closes (12:00, 1:15 and 2:30 P.M. for the three age groups) there is a wide range of activities undertaken, most of them of an outdoor nature. The contrast in exposure between afternoon and morning hours reflects this. Generally, before 10:00 A.M. the number of exposure periods based on the exposure of all subjects on all days of the study period is less than 40 per hour, whereas throughout the afternoon (after 12:00 P.M.) the corresponding value is above 60 per hour and often exceeds 80 per hour.