Impact of microgravity on radiobiological processes and efficiency of DNA repair

Three major plant bioassays, i.e., the Allium root anaphase aberration (Allium-AA), the Tradescantia-micronucleus (Trad-MCN) and the Tradescantia stamen hair mutation (Trad-SHM) tests, were utilized in soil solutions or shallow well water samples to determine the degree of their genotoxicity. Shallow well water samples were collected from five different farms, and soil solutions were extracted with distilled water or dimethyl sulfoxide (DMSO) from pesticide-contaminated (metolachlor, atrazine, extrazine, and 2, 4-D) and pesticide-free soil samples. Genotoxicity was expressed in terms of anaphase aberration (AA) frequencies in the Allium-AA test, in terms of micronuclei frequencies in the Trad-MCN test, and in terms of pink mutation events in the Trad-SHM test. On average, results of Allium-AA tests showed a 2.78-3.01 fold increase in anaphase aberration frequencies in contaminated soil solution samples and well water samples as compared with the negative control. Results of Trad-MCN tests showed a 1.66-4.75 fold increase of MCN frequencies in contaminated soil solution samples and shallow well water samples as compared with the frequencies of the controls. Results of Trad-SHM tests showed a 2.7-2.86 fold increase of pink mutation events in the contaminated soil solution samples over that of the controls. Control groups of the Allium-AA tests had an average of 0.75/1000 anaphase figures, and control groups of the Trad-MCN tests had an average of 3.2 MCN/100 tetrads, while control groups of the Trad-SHM tests had an average of 1.4 mutation events/1000 hairs. In general, soil solutions of DMSO extracts showed higher genotoxicity than that of distilled water extracts. Among these three plant bioassays, the Trad-MCN test has the highest efficiency. The highest toxicity, based upon the Trad-MCN test results, was found in the pesticide contaminated soil samples from Monroe's farm. Water samples from the Fountain Green/Bushnell area ranked second in genotoxicity.