Handbook of Solvents - George Wypych - ChemTech - Ventech!

866 Tilman Hahn, Konrad Botzenhart
Table 14.4.2.1. Toxicity of organic solvents - examples
Solvent Microorganisms References
Toluene, benzene, ethylbenzene, propylbenzene,
xylene, hexane, cyclohexane
Terpenes, e.g., alpha-pinene, limonene,
β-pinene, terpinolene
Pseudomonas putida
Bacillus sp., Saccharomyces
cerevisiae, isolated mitochondria
Isken et al. (1999) 3
Gibson et al. (1970) 4
Andrews et al. (1980) 5
Uribe et al. (1985) 6
Styrene soil microorganisms Hartmans et al. (1990) 7
Cyclohexane yeast cells, isolated mitochondria Uribe et al. (1990) 8
Aromatic hydrocarbons
Ethanol yeasts
isolated bacterial and liposomal
membranes
Sikkema et al. (1992) 9
Sikkema et al. (1994) 1
Cartwright et al. (1986) 10
Leao and van Uden (1984) 11
14.4.2.2.2 Mechanisms of solvent toxicity for microorganisms
The toxicity of organic solvents or hydrophobic substances for microorganisms depends
mainly on their effects on biological membranes 1,9,12-14 - similar to membrane effects of several
anesthetics. This concerns especially effects on cytoplasmatic membranes. The following
main changes of membrane structures and functions have been observed:
• Accumulation of hydrophobic substances such as organic solvents in cytoplasmatic
membranes. This accumulation causes structural and functional changes in the
cytoplasmatic membranes and microbial cells.
• Structural changes in cytoplasmatic membranes, e.g., swelling of membrane
bilayers, increase of surface and thickness of the membranes, changes in the
composition of the membrane (e.g., changes in the fatty acid composition),
modification of the microviscosity, damage of membrane structures (see below).
• Loss of membrane integrity, especially disruption of cytoplasmatic membranes, less
damage of outer membranes. Because of these damages often complex cellular
structures (e.g., vesicula) or cell functions (decrease of respiratory activities of
mitochondria) are destroyed or inhibited.
• Interactions of the accumulated lipophilic substances with the cytoplasmatic
membranes and especially hydrophobic parts of the cell or cell membranes.
Lipid-lipid interactions and interactions between proteins and lipids of the
membrane structure (lipid bilayers, membrane-embedded proteins) are discussed.
• Effects on passive and active membrane transport systems, e.g., increase of passive
efflux and flux of ions such as protons, cations Mg ++ and Ca ++ or small molecules,
stimulation of the leakage of protons and potassium, changes in the uptake of
compounds (e.g., solvents) and excretion (e.g., metabolic products), inhibition of
active transport systems (e.g., ATP depletion).
• Damage of cellular homeostasis and cell physiology, e.g., reduction of
transmembrane electrical potentials and proton chemical potentials or proton
motive forces as a result of membrane changes (efflux of ions), changes of pH
gradients.