A direct exposure method to detect mutagenicity of car exhausts was applied to study the influence of the running conditions of a diesel engine functioning on an assay platform. Biological and physico-chemical approaches were carried out together to appreciate the quality of diesel emissions. Exhausts, emitted by a diesel engine (Renault, 2068 cm3) were sampled from a dilution tube connected to a constant volume sampler. Regulated pollutants (CO, NO(x), HC and particles) and some non-regulated pollutants (monoaromatic hydrocarbons (MAH) and polyaromatic hydrocarbons (PAH), aldehydes) were analysed when the engine ran al different operating conditions of load (full, 3/4, 2/4 and 1/4) and of engine speed (from 1000 to 4000 rev./min). The mutagenicity (Ames test) of diesel exhaust was assessed by a direct exposure method which does not need extraction of the particles. Bacteria are pre-seeded onto the agar plate and exposed directly to the diesel exhausts parallelly to the measurements of pollutants. The engine speed and the load influence the level, the composition and the induced mutagenicity of the diesel emissions and the results show that: when engine speed increases all the gaz phase indicators increase independantly of the load, those of the particulate phase and mutagenicity increase at low load but decrease at full load; when load increase, all the indicators of both phases decrease except NO(x) which increases.
