Effects of ionising radiation exposure on plants, fish and mammals: relevant data for environmental radiation protection

In order to develop a framework for the assessment of the environmental impact of radiation, it is necessary to establish the relationship between exposure (dose rate, accumulated dose) and the effects that may be induced in plants and animals. With this purpose in mind, the data available on effects induced by ionising radiation in various wildlife groups have been reviewed as part of the FASSET project. This paper has highlighted that the available information on the effects of low dose rate, continuous irradiation (< 10(3) microGy h(-1)) is reasonable for plants, fish and mammals, but is scarce or non-existent for other wildlife groups. Thus, the effects induced in plants, fish and mammals after chronic exposure to radiation are presented in this paper. The fragmentary nature of the available, relevant information has made it very difficult to characterise the desired dose rate-response relationships in any detail. However, it can be broadly concluded that, although minor effects may be seen at lower dose rates in the most sensitive species and systems, the threshold for statistically significant effects in most studies is about 10(2) microGy h(-1). The responses then increase progressively with increasing dose rate and usually become very clear at dose rates > 10(3) microGy h(-1) sustained for a large fraction of the lifespan.

A possible approach for the assessment of radiation effects on populations of wild organisms in radionuclide-contaminated environments?

It is frequently asserted that measures to protect the biotic environment from increased radiation exposures arising from human activities should be focussed on the population rather than the individual. It is, however, difficult (if not impossible) to identify any population-specific attributes that can be affected by radiation exposure directly rather than through the mediation of direct, known and identifiable effects in individual organisms. Indeed, it is often conceded that this difficulty forces attention to be refocussed onto the effects in individuals. Regulatory controls on radioactive waste management and disposal could then be implemented to ensure that any radiation effects in individual native plants and animals remain at, or below, some acceptable level (yet to be defined). Nevertheless, the question remains as to whether such controls would also provide for the protection of the population. An answer to this question depends on the availability of a model that allows the integration of the known effects of radiation exposure on the mortality, morbidity, fertility and fecundity of individuals into an assessment of the possible impact at the population level. The utility of one such approach, the Leslie Matrix Model, is explored in respect of a fish population (the plaice, Pleuronectes platessa). This initial implementation of the population model is simplistic (and, certainly, environmentally unrealistic), but it is concluded that the output from the model does provide some insights into how the population might respond to radiation-induced changes in individual attributes, and that further development in the direction of increased realism is fully warranted.

A system for protecting the environment from ionising radiation: selecting reference fauna and flora, and the possible dose models and environmental geometries that could be applied to them

In order to demonstrate, explicitly, that the environment can be protected with respect to controlled sources of ionising radiation, it is essential to have a systematic framework within which dosimetry models for fauna and flora can be used. And because of the practical limitations on what could reasonably be modelled and the amount of information that could reasonably be obtained, it is also necessary to limit the application of such models to a 'set' of fauna and flora within a reference' context. This paper, therefore, outlines the factors that will need to be considered to select such 'reference' fauna and flora, and describes some of the factors and constraints necessary to develop the associated dosimetry models. It also describes some of the most basic environmental geometrics within which the dose models could be set in order to make comparisons amongst different radiation sources.

Effects of chronic gamma-irradiation on the gonads of adult Ameca splendens (Osteichthyes: Teleostei)

The effects of chronic gamma-irradiation on the gonads of adult Ameca splendens (Osteichthyes: Teleostei) have been investigated at a mean dose rate of 7.3 mGy hour-1 for 5-244 days. Spermatogenesis was disrupted after an accumulated dose of 0.95 Gy (5 days exposure) and after 52 days (9.7 Gy) there was no further production of sperm. The secondary spermatogonia were the most radiosensitive cell type and the primary spermatogonia the most radioresistant, not completely disappearing until day 95 (16 Gy). Males removed from the irradiated aquaria after accumulating doses of 3.9 Gy (21 days) and 7.0 Gy (40 days) showed a high degree of recovery from the radiation damage to spermatogenesis when examined after 125, 174 and 236 days. The developing oocytes were less sensitive to the effects of radiation than the stages of spermatogenesis, not showing any depletion in numbers until day 38 (6.9 Gy).

The effects of chronic irradiation on the breeding performance of the guppy, Poecilia reticulata (Osteichthyes:Teleostei)

The effects of chronic irradiation on the life-time breeding performance of the small tropical fish, Poecilia reticulata, have been investigated at mean dose-rates of 0.17, 0.40 and 1.27 rad hour-1. The total fecundity was markedly (P less than 0.001) reduced at all dose-rates owing to a decrease in mean actual brood-size and an increase in temporary and permanent infertility. Minor progressive changes in the interbrood time with age and dose-rate were noted. The neonatal death-rate, incidence of abnormalities, and survival and sex ratio of the offspring were unaffected by irradiation. The brood-size data have been used to derive estimates of the dominant lethal mutation rate which are of the same order as those determined for mammals. Histological studies indicate that functional sterility is not necessarily dependent on the destruction of the gonads, and it is possible that radiation effects on pituitary function are responsible for much of the observed infertility.

The biological effects of radioactive waste

The discharge of radioactive waste into the marine environment is, in general, limited by the requirement that the resulting increments of dose to members of the general public are within internationally agreed limits. The implicit assumption is made that when this require­ment is met the fauna and flora of the marine ecosystem, which are generally less radiosensitive than man, are not at risk. The data relating to the effects of both acute and chronic irradiation on marine species are reviewed and the dose rates which can occur in contaminated environments due to the recon­centration of activity, either by the animals themselves or by some component of their habitat, e. g. silt, are indicated. From this it is possible to predict that present waste disposal practices are unlikely to have any observable effect in the natural environment. Nevertheless, further research is necessary to find more sensitive indicators of damage at both the individual and population levels.