This paper is focused on alkylphenols, compounds which are formed by the biodegradation of polyethoxilatedalkylphenols detergents. Our experiments show that alkylphenols act not only as detergents, but also as uncouplers of the oxidative phosphorylation. This eff~ot, can be observed at very low doses, thus suggesting that the preferential target ofnonylphenols in living organisms are mitochondfia.

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The interactions of the antifouling compound TCMS (2,3,5,6-tetrachloro-4-methylsulphonyl pyridine) with rat liver mitochondria have been investigated. The results indicate that the compound inhibits ATP synthesis. Further investigations regarding the ATP synthesis mechanism suggest that TCMS inhibits succinic dehydrogenase of the mitochondrial respiratory chain. As the respiratory chain is similar in all living organisms, it can be concluded that the toxic effect of TCMS most likely depend on the different bioavailability of the compound and on the different importance of mitochondria in the ATP production in the animal species.

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A rapid and relatively low cost bioassay, usable in routine screening water test has been developed modifying the beef heart mitochondria test. In our experiments, mitochondria (FM22) were frozen at )22°C, instead of )80°C (FM80), and their applicability and sensitivity was verified. The oxygen consumption was measured by a Clark electrode that was interfaced to a PC to collect test analysis data. Blank tests were carried out to verify the oxygen consumption linear fitting. Toxicity tests were performed using pure organic and inorganic compounds, such to verify the FM22 sensitivity. A piecewise regression, through an Excel â Macro, identified the break-point in the oxygen consumption and calculated the toxicity. The IC 50 s of the tested compounds were calculated and ranged from 0.123 to 0.173 mg/l for heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) and from 0.572 to 10.545 mg/l for organics (benzene, DMSO, DDE, endrin, dichloromethane, chlorobenzene, 1,2-dichlorobenzene and 1,3-dichlorobenzene). Water effluent samples were then tested. The FM22 gave different toxic reactions to them. Water samples were characterised for heavy metals. The FM22 bioassay had a higher sensitivity than the FM80 and a high reproducibility in the toxicity test with pure compounds. The FM22 test was a good predictor of toxicity for water samples; the bioassay is easy, low cost and rapid, then usable for routine tests.