Photobiological transformation of azaarenes in the water column: towards a new approach for the assessment of toxic and genotoxic hazards of azaarenes
Wiegman, S.; Van Beusekom, S.A.M.; van Vlaardingen, P.L.A.; Bleeker, E.A.J.; Kraak, M.H.S.; Admiraal, W.; Krop, H.; de Voogt, P.; Vriezekolk, G.; Vonck, W.; Klamer, H.J.C.; Pastor, D.; Evers, E.H.G.; Peijnenburg, W.J.G.M. (1998). Photobiological transformation of azaarenes in the water column: towards a new approach for the assessment of toxic and genotoxic hazards of azaarenes. BEON Rapport = BEON-report, 98(10). RIKZ: Den Haag. 59 pp.
Part of: BEON Rapport = BEON-report. Programma Bureau BEON: Den Haag. ISSN 0924-6576
In ecological test schemes the influence of light on ecotoxicological effects, especially UV, is hardly included. The relationship between acute toxic and phototoxic effects of azaarenes to aquatic organisms is sparsely investigated, while the toxicity of degradation products is virtually unknown. In the present study these problems were investigated, using different marine algae as test-organisms. In the first stage of the project, acute toxicity of eight azaarenes, ranging from two-ringed to five-ringed structures, was determined in growth experiments with the green algae Dunaliella tertiolecta. The toxicity of azaarenes to Dunaliella tertiolecta with increasing number of aromatic rings and consequently lipophilicity. This pattern is also observed for toxicity to freshwater algae, midges and daphnids. Furthermore, toxicity of isomer structures of three-ringed and four-ringed azaarenes differed, probably due to photo-enhanced toxicity. So, for some of the azaarenes a higher toxicity can be found in situ, than expected based on their solubilities (chapter2). The second stage of the project focused on the photokinetics of azaarenes and the effects of photolytic products, formed under influence of short wavelength radiation, on algae (toxicity) and bacteria (genotoxicity). For acute toxicity of azaarenes and mixtures with phototransformed azaarenes the marine diatom Phaeodactylum tricornutum was chosen, with inhibition of photosynthetic activity as endpoint. For genotoxicity, the sensitive Mutatox test was used. In chapter 3 photolysis rates of the eight azaarenes were quantified. Azaarenes were shown to degradate rapidly in the presence of short-wavelength light, with half-life periods of 11 hours in the UV-B region (300 nm) and 3,6 days in the UV-A region (350 nm). Acute toxicity of azaarenes increased also with increasing number of rings, and was in the same order as for Dunaliella, although different algae and endpoints were used. Here, no differences between toxicity of isomers were found. Photolysis of azaarenes by UV-B irradiance led to detoxification. By UV-A irradiance, toxicity was generated upon lysis. For the two-ringed structures toxicity increased one to two orders of magnitude compared to parent compounds (chapter 4). All azaarenes tested caused genotoxic effects. Photolysis of azaarenes results in higher genotoxic activities, despite occasional detoxification. In addition, light in the 350 nm range (UV-A) was equally or more active in formation of genotoxic than 300 nm (UV-B) radiance. It is concluded that photolysis by UV-A or UV-B enhances toxic and/or genotoxic effects of azaarenes. Furthermore, UV-A has a higher impact on the adverse effects of azaarenes mixtures than UV-B, by the formation of both genotoxic and toxic products (chapter 5). In the last section degradation of acridine by marine algae and in situ, acute toxicity on phytoplankton were investigated. Bacteria and fungi are known to metabolize PAHs, especially the low ringed PAHs. This study showed that the marine algae Dunaliella and Phaeodactylum can metabolize low concentrations of acridine. In addition, co-action of metabolism and light enhanced lysis rates. In outdoor experiments the phototoxicity of acridine for natural marine phytoplankton. This study demonstrates that incorporation of phototoxicity and biological effects of degradation products are essential in risk assessment of azaarenes. In addition, monitoring of genotoxic and specific toxic effects, including the effects of these products, have to complete PAH/azaarenes-monitoring.
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