Relative Subnarcotic Potency of Solvents Predicted by Partition Co-efficients

Emil Frantík, Ludmila Vodièková, Miroslava Hornychová, Michal Nosek

Centre of Industrial Hygiene and Occupational Diseases, National Institute of Public Health, Praha, Czech Republic
 
Corresponding author: E. Frantík
National Institute of Public Health,
Šrobárova 48, 100 42 Praha 10, Czech Republic,
Tel.: (+42) 2 67082628
Fax: (+42) 2 67311236

CEJOEM 1998, Vol.4. No.1.:25-35


Key words:
Chlorinated aliphatic solvents, chemical hazard, CNS effects

Abbreviations:
Ca – air concentration
Cb – blood concentration
EC – effective concentration
ECa – iso-effective air concentration at EC30
ECb – iso-effective blood concentration
EC30 – concentration in air evoking 30% of the maximum possible value of biological response
PCba – partition co-efficient blood/air
PCfa – partition co-efficient fat/air
PCfb – partition co-efficient fat/blood
PCoa – partition co-efficient octanol-air
PCob – partition co-efficient octanol-blood
PCow – partition co-efficient octanol-water
PCwa – partition co-efficient water/air
PCwb – partition co-efficient water/blood
PCs – partition co-efficients



Abstract:
Airborne concentrations of nine chlorinated aliphatic solvents necessary to produce the same degree of inhibition of seizure discharge generation and maintenance (by 30%, ECa) were determined in rats after a single 4-hour inhalatory exposure. The corresponding blood concentrations of solvents (ECb) were measured using gas chromatography. Partition co-efficients blood/air, fat/air and water/air were determined experimentally; partition co-efficients fat/blood (PCfb) and water/blood (PCwb) were calculated.
    The equipotent air concentrations ranged from 2.2 to 6.9 mg · l–1 (403 to 1980 ppm), the corresponding blood levels from 0.08 to 0.8 mmol · 1–1. The internal relative potency (measured as reciprocal of iso-effective blood levels, 1/ECb) and less successfully the external relative potency (reciprocal of iso-effective air concentrations, 1/ECa) – were effectively represented by the fat/blood partition co-efficient or by a linear combination of fat/blood and water/blood PCs. The derived formula predicted also historical data on aromatic hydrocarbons. The regression equations based on joint data (9 chlorinated hydrocarbons, 5 aromatics and acetone) predicted iso-effective blood levels but not iso-effective air concentrations of additional 6 chlorinated hydrocarbons. PCfb could be replaced by PCoctanol/blood (PCow x PCwb) but not by PCow in most predictive equations without substantial loss of efficiency.
    The results can be interpreted in terms of constant target structure concentration and substance specific target structure/blood partition co-efficients for the acute subnarcotic effect of solvents (and anaesthetics), and support thus the feasibility of predicting such effects from partition co-efficients and blood level data. 

Received: 20 October, 1997
Accepted: 5 February, 1998 
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Posted: 15 November 1998