Intact and photomodified polycyclic aromatic hydrocarbons inhibit photosynthesis in natural assemblages of Lake Erie phytoplankton exposed to solar radiation

Recently, there has been a trend toward less turbid water and greater light penetration in parts of western Lake Erie. This could lead to greater phot otoxicity from sediment-bound poly cyclic aromatic hydrocarbons. To test ph otosynthesis as a bioindicator of contaminant impacts on algae, water sampl es containing natural assemblages of phytoplankton mere collected from the western and central basins of Lake Erie. These samples were incubated with 0.2 to 2 mg L-1 anthracene or its photomodified product 1,2-dihydroxyanthra quinone for 60min in darkness or in 50% sunlight, to mimic exposure of phyt oplankton in the photic zone of a mixed water column. Photosynthetic effici ency was determined from filtered phytoplankton immediately after exposure using a pulse-amplitude modulated chlorophyll fluorometer. Phytoplankton in cubated with chemicals in the dark demonstrated chlorophyll fluorescence va lues similar to those of controls. However, exposure to anthracene or 1,2-d ihydroxyanthraquinone in sunlight diminished photosystem II photosynthetic efficiency and photosynthetic quantum yield in a concentration-dependent ma nner. Anthracene inhibited photosynthesis at lower concentrations than 1,2- dihydroxyanthraquinone, which is consistent with the different modes of act ion and toxic strengths of these two contaminants. These results demonstrat e that phytoplankton in Lake Erie can be subject to phototoxicity from inta ct and photomodified polgcyclic aromatic hydrocarbons after very short expo sures. Further, chlorophyll fluorescence was found to be an effective bioin dicator in the field for this form of chemical stress. (C) 1999 Academic Pr ess.