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To assess photosynthesis as a bioindicator of toxicity from polycyclic aromatic hydrocarbons (PAHs), the response of chlorophyll-a fluorescence to creosote exposure was compared with effects on population-level plant growth. Large, outdoor, freshwater microcosms containing Eurasian watermilfoil (Myriophyllum spicatum) received either a single application or multiple applications of liquid creosote at nominal concentrations from 0.109 to 32.7 mg L(-1). For several weeks following treatment, photosynthetic electron transport was measured using pulse amplitude-modulated chlorophyll-a fluorescence. The maximum efficiency of photosystem II electron transport (Fv/Fm) and the quantum yield of photochemistry (deltaF/F'm) were diminished in plants shortly after the addition of creosote. In microcosms that received a single treatment of creosote only, the 50% effective concentrations (EC50s), expressed as the aqueous concentration of 15 of the most abundant PAHs, were 0.28 mg L(-1) for Fv/Fm and 0.30 mg L(-1) for deltaF/F'm. Chlorophyll-a fluorescence was diminished to a greater extent in microcosms that received multiple treatments of creosote, with EC50s of 0.13 mg L(-1) for Fv/Fm and 0.10 mg L(-1) for deltaF/F'm. Plant biomass accumulation was inhibited in a concentration-dependent manner in all microcosms treated with creosote, but this inhibition occurred to a greater degree in microcosms treated with multiple creosote applications. The response of chlorophyll-a fluorescence, measured only 8 d after creosote treatment, was similar to plant growth over the entire growing season, indicating that this technique can be used to estimate potential effects of contaminants before detrimental impacts on populations.

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 (Fv/Fm) and the effective yield of photochemistry (or steady state photosystem II activity) (μF/Fm′) were measured from phytoplankton exposed for 30 min in sunlight to polycyclic aromatic hydrocarbons at concentrations from 40 to 2,000 μgL−1. Anthracene, fluoranthene, and phenanthrenequinone were most toxic to phytoplankton, with EC50s for ΔF/Fm′ inhibition of 314, 118 and 90 μgL−1, respectively. Anthraquinone, 1,2-dihydroxyanthraquinone, and phenanthrene were less toxic, with EC50s ranging from 684 to > 2,000 μgL−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.

Chlorophyll-a fluorescence induction is a rapid technique for measuring photosynthetic electron transport in plants. To assess chlorophyll-a fluorescence as a bioindicator of effects of polycyclic aromatic hydrocarbon mixtures, chlorophyll-afluorescence parameters and plant growth responses to exposure to the wood preservative creosote were examined in the aquatic plants Lemna gibba and Myriophyllum spicatum. Exposure to creosote inhibited growth of L. gibba (EC50 = 7.2 mg/L total polycyclic aromatic hydrocarbons) and M. spicatum (EC50 = 2.6 mg/L) despite differences in physiology. Creosote also diminished maximum PSII efficiency (Fv/Fm) (EC50 = 36 and 13 mg/L for L. gibba and M. spicatum) and the effective yield of photosystem II photochemistry (ΔF/F′m) (EC50 = 13 and 15 mg/L for L. gibba and M. spicatum). The similarity between growth and chlorophyll-a fluorescence EC50s and slopes of the response curves suggests a close mechanistic link between these end points. The predictive power of chlorophyll-a fluorescence as a bioindicator of whole-organism effects applied to complex contaminant mixtures is discussed.

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 phototoxicity from sediment-bound polycyclic aromatic hydrocarbons. To test photosynthesis as a bioindicator of contaminant impacts on algae, water samples containing natural assemblages of phytoplankton were 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-dihydroxyanthraquinone for 60 min in darkness or in 50% sunlight, to mimic exposure of phytoplankton in the photic zone of a mixed water column. Photosynthetic efficiency was determined from filtered phytoplankton immediately after exposure using a pulse-amplitude modulated chlorophyll fluorometer. Phytoplankton incubated with chemicals in the dark demonstrated chlorophyll fluorescence values similar to those of controls. However, exposure to anthracene or 1,2-dihydroxyanthraquinone in sunlight diminished photosystem II photosynthetic efficiency and photosynthetic quantum yield in a concentration-dependent manner. Anthracene inhibited photosynthesis at lower concentrations than 1,2-dihydroxyanthraquinone, which is consistent with the different modes of action and toxic strengths of these two contaminants. These results demonstrate that phytoplankton in Lake Erie can be subject to phototoxicity from intact and photomodified polycyclic aromatic hydrocarbons after very short exposures. Further, chlorophyll fluorescence was found to be an effective bioindicator in the field for this form of chemical stress.

Solar radiation spectra were measured in mesotrophic Lake Erie in 1997 to determine the principal factors influencing ultraviolet radiation (UVR) attenuation. Water clarity ranged widely, with the diffuse vertical attenuation coefficient for photosynthetically active radiation (KdIPAR) varying from 0.26 to 17.2 m-1, and UVR attenuation varied positively and significantly with KdIPAR. Particle concentration (total suspended solids, TSS) was the single most useful water quality characteristic for predicting broadband UVB (305-320 nm) and UVA (320-400 nm) attenuation. Dissolved organic carbon concentration (DOC) and fluorescence were much less important than TSS in predicting UVR attenuation over the typical range of water clarity (KdIPAR < 2 m-1). The predominant role of TSS in UVR attenuation could not be explained by phytoplankton or other absorbing organic matter in the particulate phase, suggesting instead an important role for scattering. Attenuation spectra through the UV region were not monotonic at the higher particle concentrations and could not be modelled solely as a function of DOC as previously reported for other lakes. Attenuation at 310 and 320 nm confirmed the conclusion from spectrally integrated measurements that particles are the dominant agents of variable UVR attenuation in Lake Erie.

— Although the effects of ultraviolet B (UVB, 290–320 nm) radiation have been studied in plants extensively, little is known about the potential impacts on maturation of chloroplasts. To address this problem, the effects of supplementary UVB on chloroplast development were examined in the aquatic higher plant Spirodela oligorrhiza. Dark-grown Spirodela-containing proplastids were exposed to photosynthetically active radiation (PAR) and ultraviolet A (UVA, 320–400 nm), plus supplementary UVB equivalent to 1% of PAR on a photon basis. The biosynthesis and assembly of chlorophyll (Chi) into reaction centers was followed for 4 days in situ by low temperature (77 K) Chi fluorescence. Impacts on chloroplast development were detected after only 1 h incubation in light with supplementary UVB. Fluorescence emission signals from Chi associated with the photosystem (PS) II antenna, PSII reaction centers and PSI reaction centers were detected at the same time with or without UVB, but the magnitude of PS fluorescence was diminished up to 60% in plants incubated in UVB. The Chi content was also lower in UVB-treated plants, but to a lesser degree than anticipated by low temperature fluorescence, suggesting lack of organization and/or association of Chi with PS. Electron transport, measured with room temperature fluorescence induction, was not consistently different in plants exposed to UVB. These results suggest that with UVB, fewer and/or smaller PS form during chloroplast development, but there is not a large inhibition of Chi synthesis or PSII activity.

Previous studies have indicated that tire tread particles are toxic to aquatic species, but few studies have evaluated the toxicity of such particles using sediment, the likely reservoir of tire wear particles in the environment. In this study, the acute toxicity of tire and road wear particles (TRWP) was assessed in Pseudokirchneriella subcapita, Daphnia magna, and Pimephales promelas using a sediment elutriate (100, 500, 1000 or 10000 mg/l TRWP). Under standard test temperature conditions, no concentration response was observed and EC/LC(50) values were greater than 10,000 mg/l. Additional tests using D. magna were performed both with and without sediment in elutriates collected under heated conditions designed to promote the release of chemicals from the rubber matrix to understand what environmental factors may influence the toxicity of TRWP. Toxicity was only observed for elutriates generated from TRWP leached under high-temperature conditions and the lowest EC/LC(50) value was 5,000 mg/l. In an effort to identify potential toxic chemical constituent(s) in the heated leachates, toxicity identification evaluation (TIE) studies and chemical analysis of the leachate were conducted. The TIE coupled with chemical analysis (liquid chromatography/mass spectrometry/mass spectrometry [LC/MS/MS] and inductively coupled plasma/mass spectrometry [ICP/MS]) of the leachate identified zinc and aniline as candidate toxicants. However, based on the high EC/LC(50) values and the limited conditions under which toxicity was observed, TRWP should be considered a low risk to aquatic ecosystems under acute exposure scenarios.

Light, especially UV radiation, greatly elevates the toxicity of PAHs to plants. We have previously shown that chlorosis is an excellent indicator of PAH toxicity. Usually when chlorophyll (Chl) content is diminished, photosynthesis is also inhibited. Therefore, we tested if photosynthesis was indeed inhibited by PAHs in the presence of Simulated Solar Radiation. A Commonly used measure of in vivo photosynthetic activity in plants is chlorophyll a (Chl a) fluorescence, an assay of electron transport in photosystem II (PS II). This assay can be performed in situ on intact plants within 24 h of application of the chemical. In this study, two methods of collecting Chl a fluorescence data are described. Fluorescence induction was used to measure maximal PS II efficiency and photosynthesis downstream from PS II, with the finding that both were predictive of growth inhibition. Pulse amplitude modulated (PAM) fluorometry which measures steady state PS II efficiency was also used. This technique also detected negative impacts of photomodified anthracene on the plants.