Recreational exposure to surface waters during periods of increased pathogen concentration may lead to a significantly higher risk of illness. However, estimates of elementary exposure factors necessary to evaluate health risk (i.e., usage distributions and exposure durations) are not available for many non-swimming water-related activities. No prior studies have assessed nonswimming water exposure with respect to factors leading to impaired water quality from increased pathogen concentration, such as weather condition (rain events produce increased runoff and sewer overflows) and type of day (heavy recreational periods). We measured usage patterns and evaluated the effect of weather and type of day at eight water sites located within Philadelphia, by using a novel ''time lapse photography'' technology during three peak recreational seasons (May --September) 2008 --2010. Camera observations validated with simultaneous in-person surveys exhibited a strong correlation (R 2 ¼ 0.81 to 0.96) between the two survey techniques, indicating that the application of remote photography in collecting human exposure data was appropriate. Recreational activities usage varied more on a temporal basis than due to inclement weather. Only 14% (6 out of 44) of the site-specific activity combinations showed dry weather preference, whereas 41.5% (17 out of 41) of the combinations indicated greater usage on weekends as compared with weekday. In general, the log normal distribution described the playing and wading duration distribution, while the gamma distribution was the best fit for fishing durations. Remote photography provided unbiased, real-time human exposure data and was less personnel intensive compared with traditional survey methods. However, there are potential limitations associated with remote surveillance data related to its limited view. This is the first study to report that time lapse cameras can be successfully applied to assess water-based human recreational patterns and can provide precise exposure statistics for non-swimming recreational exposures. Keywords: recreational water use; exposure assessment; non-swimming water exposures; time-lapse camera applications; remote photography; exposure duration distributions
Journal of Exposure Science and Environmental Epidemiology
INTRODUCTIONThe decision to treat (disinfect) wastewater and storm water overflows is a major controversy in the US and will probably cause large cities massive investment in ''gray'' infrastructure to mitigate wet weather discharges. A rational decision would use risk-benefit or cost-benefit approaches. To assess risk, one must know how the waters are being used. Although in many cases where the dominant use is swimming, the quantification of exposure is more straightforward, for example, by using aerial photos, turnstile counts or parking fees and so on. In a context, such as the one described in this paper where non-swimming recreational activities are the principal mode of exposure to surface water bodies, the issue is both determining how ma...