Phthalates and organophosphorus compounds as cholinesterase inhibitors in fractions of industrial hexane impurities

Cholinesterase (ChE) inhibitors have been described in the distillation residue of hexane and other industrial solvents. The residue of a commercial hexane has been fractionated by preparative chromatography. The anticholinesterase (antiChE) activity was isolated in two fractions (F-5, F-7) which contained only 0.61 and 0.16% respectively of the original dry weight hexane residue. In the former fraction, reversible and irreversible progressive inhibition was observed, and organophosphorus compounds (OPs) were detected colorimetrically and by gas chromatography. This fraction was subfractionated in a second chromatographic step. One subfraction containing the highest antiChE activity and 88% phosphorus of F-5 was isolated. In this subfraction triphenylphosphate and other not definitely identified OP compounds were detected by gas chromatography/mass spectrometry, together with several adipates and phthalates, including di-n-butylphthalate. This phthalate could explain the reversible inhibition of ChE by the hexane residue, and triphenylphosphate and the unidentified OP the irreversible inhibition. A possible toxicological role of these impurities is discussed in relation to occupational neuropathies by exposure to solvents.