Indicator

The time for 50% of larval fish to die is the LT50, in hours, and is a function of both PAH exposure (phototoxic PAH concentration in larval fish) and UV-A exposure.

The concentration of phototoxic PAHs1 in fish is estimated from sediment PAHs. The UV dose is calculated from incident solar radiation and attenuation in the water column as estimated from a measurement of suspended particulate matter and spectral attenuation in surface water.

Measurements

PAHs A composite sediment sample is taken at a coastal site and analyzed for organic carbon and 9 phototoxic PAHs1. The concentrations are summed, normalized by organic carbon, and multiplied by the biota-sediment accumulation factor to estimate the total phototoxic PAH concentration in larval fish. This is converted to dry weight concentration using the % lipid in larval fish (assume 10 % if not known).

UV A grab sample of surface water is taken, filtered to determine suspended particulate matter and the filtrate run on a spectrophotometer for % transmittance from 334-370 nm. The resulting attenuation coefficient is put into the following relationship we developed for the Great Lakes:

and

where T is the fraction transmittance at 10 cm in the water column for a given UV absorbance measurement. The percent transmittance is calculated as .