Effects of chronic low-level irradiation on Gambusia affinis

The work on Gambusia in White Oak Lake, which was exposed to a chronic low level irradiation, was reviewed. The dose rate to Gambusia has decreased from a high of 2,196 Ci in 1960 to 13 Ci in 1975. The frequency of nonviable embryos was significantly greater in the population of Gambusia from 1966 to 1978 and in these progeny of laboratory-reared females. The dose rate of decommissioned waste pond at the sediment surface averaged 1,149.6 rad/year. The Gambusia had a significantly lower mean temperature and showed more variability in their response to a Critical Thermal Maxima Test than control populations. It suggested an increased frequency of deleterious and recessive lethal genes in its gene pool. However the chemical pollutants must also be taken into account. (Nakanishi, T.)