Polycyclic aromatic hydrocarbons (PAHs) and metals are toxic to animals, plants and microorganisms. Both these groups of contaminants coexist in the industrialized environments. Therefore, it is important to study the mixture toxicity of such pollutants on biological systems. In the present study, we have used the aquatic higher plant Lemna gibba as a test organism to study the mixture toxicity of an oxy-PAH 1,2-dihydroxyanthraquinone (1,2-dhATQ), and the metal copper. 3 μ,Ml,2-dhATQ inhibited photosynthetic electron transport downstream of photosystem II at the cytochrome b6/f complex. Such an inhibition results in the alteration of the redox status of the chloroplast to a reduced state because the plastoquinone pool goes to a net reduced state. Under such circumstances, when 4 μM CuSO4 was administered to L. gibba, there was a synergistic inhibition of growth and protein expression. We infer from these results that the synergistic toxicity caused by the mixture of 1,2-dhATQ plus CuSO4 is due to the catalytic transfer of electrons by Cu2+ from the reduced plastoquinone pool to O2. Such a mediation of electrons leads to the generation of reactive oxygen species, which could cause greater toxicity of 1,2-dhATQ.
Polycyclic aromatic hydrocarbons (PAHs) and metals are common contaminants in industrialized environments. Both these groups of chemicals are highly toxic to a variety of biological organisms (Martineau et al. 1994, McConkey et al. 1997, Wetzel and Werner 1995). In addition to their direct effects on biological systems, most PAHs have been shown to undergo photomodification under sunlight and they have an increased toxicity following photomodification (Arfsten et al. 1996, Huang et al. 1997b).