In situ monitoring with the Tradescantia bioassays on the genotoxicity of gaseous emissions from a closed landfill site and an incinerator

A dual monitoring system composed of the Tradescantia-Micronucleus (Trad-MCN) and Tradescantia-Stamen-Hair-Mutation (Trad-SHM) bioassays was utilized to monitor directly the genotoxicity of the gaseous emission at a closed landfill site and around an incinerator. Four of the commonly emitted gaseous agents from the landfill flare pipes, i.e. toluene, ethylbenzene, trichloroethylene and ethyltoluene were also evaluated for their genotoxicity in the laboratory. The in situ monitoring trips (360 km one way) were carried out by transporting the plant cuttings in a clean air box or in an air-tight plastic bag to the site and exposing these test cuttings for 5–7 h. The exposed plant samples were examined for micronuclei frequencies or the pink mutation rate after the appropriate recovery periods (24 h for MCN, 7–11 days for SHM). A total of 20 monitoring trips were made to the landfill, and 8 to the nearby surroundings (100–500 m from the chimney) of the incinerator site in a two year period. The major findings of the Trad-MCN test on the clastogenicity of the gaseous emission from the flare pipe of the landfill site showed positive responses or toxic effects in 6 out of 20 trips, and that from the incinerator showed positive responses in 5 out of the 8 trips. These positive responses were closely associated with the weather, i.e. low wind velocity, high temperature and relative humidity, and especially the distance from the chimney of the incinerator. The MCN frequencies and mutation rates of the Elementary School site (E. Sch) which is about 200 m from the fence of the landfill site were mostly negative, except the test results of three trips. Trad-SHM tests on the mutagenicity of gaseous emissions from the flare pipe of the landfill showed 12 positive responses out of 20 trials and 2 positives out of 4 trials from the incinerator gaseous emissions. The average mutation rate from 20 Trad-SHM monitoring trips is positive when the ANOVA and Dunnett's t-statistic were applied to the consolidated data. There is a significant (0.01) difference between the lab control and the gas exposed groups, and between the field control and gas exposed groups. Results of the Trad-SHM test at the E. Sch. site were mostly negative except for one trip. In general, micronuclei frequencies and mutation rates of the field control groups were relatively higher than those of the lab controls. The Trad-MCN test on pure gases showed positive responses in all 3 repeated tests on toluene (50–892 ppm). The test results of ethylbenzene yielded positive responses at 172 ppm/min and 1549 ppm/min dosages and exhibited toxicity at higher concentrations. Trad-MCN tests on trichloroethylene and ethyltoluene yielded positive responses at around 100–200 ppm/min level. Three repeated Trad-SHM tests on toluene yielded no positive response at low concentrations (4.3–12.9 ppm).