Quantifying solar spectral irradiance in aquatic habitats for the assessment of photoenhanced toxicity

The spectra and intensity of solar radiation (solar spectral irradiance [SS I]) was quantified din selected aquatic habitats in the vicinity of an oil field on the California coast. Solar spectral irradiance measurements consi sted of spectral scans (280-700 nm) and radiometric measurements of ultravi olet (UV): UVB (280-320 nm) and UVA (320-400 nm). Solar spectral irradiance measurements were taken at the surface and at various depths in two marsh ponds, a shallow wetland, an estuary lagoon, and the intertidal area of a h igh-energy sandy beach. Daily fluctuation in SSI showed a general parabolic relationship with time: maximum structure-activity relationship (SAR) was observed at approximate solar noon. Solar spectral irradiance measurements taken at 10-cm depth at approximate solar noon in multiple aquatic habitats exhibited only a twofold variation in visible light and UVA and a 4.5-fold variation in UVB. Visible light ranged from 11,000 to 19,000 mu W/cm(2). U VA ranged from 460 to 1,100 mu W/cm(2), and UVB ranged from 8.4 to 38 mu W/ cm(2). In each habitat, the attenuation of light intensity with increasing water depth was differentially affected over specific wavelengths of SSI. T he study results allowed the development of environmentally realistic light regimes necessary for photoenhanced toxicity studies.