CHRONIC RADIATION INDUCED CHROMOSOMAL ABERRATIONS IN NATIVE SHRUBS AT NEVADA TEST SITE Diane M. Varney and W.A. Rhoads EG&G, Santa Barbara Operations ABSTRACT Radiation effects at the morphological and phenological level within vegetation at NTS have been looked for almost from the start of nuclear testing in Nevada, and have, within the last decade been described both for areas contaminated with nuclear debris and for the vicinities of experimental radiation sources. Radiation effects at the chromosomal level of plant organization in radiation contaminated natural environments apparently have neither been sought nor observed. Artemisia spinescens shrubs from Site D, Area 11, Plutonium Valley NTS which have been irradiated since 1956 with uncertain doses estimated to range from 35 R to 140 R for a ten year period proved to have chromosomes quite suitable for microscopic examination. Meiotic pollen mother celis from A. sptnescens showed, among seven classes of chromosome aberrants, 14.2% aberrants chromosomes compared to 3.8% from plants about one mile south outside the Plutonium Valley enclosure where background radiation levels occurred, These values were not statistically significant at conventionally accepted levels of significance; however when the highest percentage occurrence ‘in each population was omitted, the difference was significant at the 95% level. For comparison two other shrub species from UCLA's Rock Valley experimentally irradiated plot, also chronically irradiated at 2.5 to 4.8 R/day since 1964 to doses very much higher than those at Site D were also investigated. Both species showed chromosome aberrations and in one species, Krameria parvifolia, the difference in occurrence of chromosome aberrants was different statistically for the higher radiation doses. The same kinds of chromosome aberrants were noted for all species studies and these were the kinds of aberrants noted as resulting from experimental radiation doses in the laboratory. 351