Photoinduced toxicity to Lake Erie phytoplankton assemblages from intact and photomodified polycyclic aromatic hydrocarbons

Pulse amplitude modulated (PAM) chlorophyll-a fluorescence is a simple, rapid technique for measuring photosynthetic efficiency in plants and algae that could be a useful biomarker of toxicity in the aquatic environment. PAM Chlorophyll fluorescence was used to detect inhibition of photosynthesis in natural assemblages of Lake Erie phytoplankton incubated with both intact and photomodified polycyclic aromatic hydrocarbons. The maximum efficiency of electron transport in photosystem II (F-v/F-m) and the effective yield of photochemistry (or steady state photosystem II activity) (muF/F-m') were measured from phytoplankton exposed for 30 min in sunlight to polycyclic aromatic hydrocarbons at concentrations from 40 to 2,000 mugL(-1). Anthracene, fluoranthene, and phenanthrenequinone were most toxic to phytoplankton, with EC50s for DeltaF/F-m' inhibition of 314, 118 and 90 mugL(-1), respectively. Anthraquinone, 1, 2-dihydroxyanthraquinone, and phenanthrene were less toxic, with EC50s ranging from 684 to > 2, 000 mugL(-1). Recovery of photosynthetic function in darkness occurred to varying degrees, and was related to the regions of the photosynthetic apparatus on which the chemicals are thought to act. Inhibition of chlorophyll fluorescence parameters demonstrated a reciprocity-like response between concentration and duration of exposure, implying chronic exposures to lower concentrations of PAHs, such as those found in the Great Lakes, could cause inhibition of photosynthesis in phytoplankton assemblages.