Exposure to airborne particulate matter has adverse effects on human health and ecosystem. Mutagenic activity of airborne particulate organic matter extracts in three time periods from total suspended particles (TSP) and particles less than 10 microm (PM10) was evaluated in an area under the influence of a petrochemical industry located in the town of Triunfo, Brazil. The extracts were investigated using the Salmonella/microsome assay, with the microsuspension method. The extracts were obtained by sonication extracted using dichloromethane (DCM) solvent. The fractions were tested for mutagenicity with the Salmonella typhimurium strains TA98 (with and without metabolic activation), TA98NR and TA98/1,8DNP(6); or YG1021 and YG1024. A positive frameshift mutagenic response was observed for the environmental samples during the different periods. The responses according to percentage of extractable organic matter (EOM%), EOM/m(3), revertants/microg (rev/microg) and revertants/m(3) (rev/m(3)) were lower for TSP than for PM10 extracts. The highest rev/m(3) values were observed in PM10 extract samples collected in winter, July 2005, in the presence (13.79 rev/m(3)) or absence (6.87 rev/m(3)) of S9 fraction. Similarly in the first (1995) or second period (2000) the highest values for TSP were observed in winter, but with lower activity (3.00 and 0.89 rev/m(3) respectively). The responses observed for the nitrosensitive strains suggest the contribution of nitro, amino and/or hydroxylamino derivatives of PAHs to the total mutagenicity of matter extracted from airborne particles. The Salmonella/microsome assay was a sensitive method to define areas contaminated by genotoxic compounds, even in samples with TSP or PM10 values that are acceptable according to legal environmental quality standards, favoring environmental control measures with an effective response seen in the population's improved quality of life.