Organismal Responses

The consequences of UVB exposure on an individual organism are dependent on intensity, spectral quality, duration of exposure, and effectiveness of protection and repair capabilities. The biological effects of UVB are wavelength dependent and best described by spectral weighting functions (Figure 5). Doses comprised of short intense exposures can have different effects from the same amounts of UVB delivered over longer time periods (i.e., reciprocity usually does not hold).

Differential species responses are an important consideration relative to biodiversity and ecological implications of UVB stress. In addition, there are

<1 nm X-rays Visible Microwaves >1000s m

Gamma rays UV Infrared Radio waves

I Solar radiation at Earth's surface

<1 nm X-rays Visible Microwaves >1000s m

Gamma rays UV Infrared Radio waves

I Solar radiation at Earth's surface

Figure 5 Comparison of intensity of incident UV wavelengths (solid red line) and generalized biological inactivation curve (blue line, data from Tyrrell RM and Pidoux M (1987) Action spectra for human skin cells: Estimates of the relative cytotoxicity of the middle ultraviolet, near ultraviolet, and violet regions of sunlight on epidermal keratinocytes. Cancer Research 47: 1825-1829). The estimated shift in UVB wavelength and intensity with 50% ozone depletion is represented by the interrupted red line. The electromagnetic spectrum shows the full scale of solar radiation at the top of the atmosphere. Incident radiation falls within the wavelengths bracketed by the yellow bar.

Wavelength (nm)

Figure 5 Comparison of intensity of incident UV wavelengths (solid red line) and generalized biological inactivation curve (blue line, data from Tyrrell RM and Pidoux M (1987) Action spectra for human skin cells: Estimates of the relative cytotoxicity of the middle ultraviolet, near ultraviolet, and violet regions of sunlight on epidermal keratinocytes. Cancer Research 47: 1825-1829). The estimated shift in UVB wavelength and intensity with 50% ozone depletion is represented by the interrupted red line. The electromagnetic spectrum shows the full scale of solar radiation at the top of the atmosphere. Incident radiation falls within the wavelengths bracketed by the yellow bar.

intraspecies variations at the population and individual level. Life history and stage of development also need to be considered. Eggs, embryos, larvae, and juveniles are more sensitive to UVB exposure than larger adult stages; thus, UVB exposure can play a significant role in the age structure and maintenance of populations.

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