Organotin compounds, and especially tributyltin (TBT), are widely diffused contaminants in the aquatic environment, mainly due to their widespread past use as biocides in antifouling paints. Human exposure to organotins mainly occurs through ingestion of contaminated seafood, especially molluscs which efficiently incorporate these xenobiotics in their tissues but less efficiently degrade and expel them with respect to crustacean and fish. The exposure to many lipophilic contaminants can cause possible changes at the physical state of membranes and, consequently, affect important cellular functions. We investigate the influence of tributyltin (TBT) on the physical state of biological membranes of a bioindicator organism: the bivalve mollusc Mytilus galloprovincialis. These molluscs have been cultured in suitable tanks and exposed to the organotins via water phase or through the food. Physico-chemical studies of mitochondrial membranes isolated from the mantle have been performed by steady-state fluorescence spectroscopy, using Laurdan as fluorescent probe. Its fluorescent naphthalene ring is located at the hydrophilic-hydrophobic interface of the phospholipids bilayer and its emission spectra maxima depend both on the polarity of the environment surrounding the probe and on the rate of relaxation of water molecules, or molecular residues, that can reorient during its excited state lifetime . The exposition to 0.5 mg/L of TBT for 24 hours does not induce membrane phase change but decreases the bilayer polarity (water content) and decreases the packing of the phospholipids.

The observed physico-chemical perturbations in mitochondria membranes prepared from exposed molluscs could affect membrane functions, such as enzyme activities, and may mediate some of their toxic effects.