Behavioral evaluation of the irritant properties of formaldehyde

The effects of formaldehyde were determined using a behavioral technique that permits the estimation of the aversiveness of airborne chemical irritants. Eight mice were initially trained to terminate presentations of ammonia by poking their nose into a conical sensor; five pokes terminated the presentation and produced a facial shower of clean air. Ammonia (1000 ppm) or formaldehyde (1.0-10 ppm) was delivered to the mice for a maximum of 60 sec followed by a 60-sec washout period; this cycle repeated 25 times per session. All animals consistently terminated 100% of ammonia deliveries. Mice also terminated delivery of formaldehyde. At the lowest concentration examined (1.0 ppm), significantly (p < 0.0005) more deliveries of formaldehyde were terminated than were deliveries of air. Mice differed in their sensitivity to formaldehyde: one mouse failed to terminate any more than 10% of deliveries of formaldehyde up to concentrations of 10 ppm; graded concentration-related increases in the number of deliveries terminated were observed in five mice; the two remaining mice consistently terminated 80% or more of the deliveries at each concentration of formaldehyde. As the concentration of formaldehyde increased, the amount of time taken to terminate the exposure decreased. A significant shift to the left of the concentration-effect curves occurred on the second exposure to the series of formaldehyde concentrations. These studies indicate that formaldehyde is aversive to mice at concentrations which approximate those at which humans also report sensory irritation, and that enhanced sensitivity is associated with repeated exposure.