Physiological effects of gamma irradiation in the honeybee, Apis mellifera.

Terrestrial ecosystems are exposed to various kinds of pollutants, including radionuclides. The honeybee, Apis mellifera, is commonly used in ecotoxicology as a model species for evaluating the effects of pollutants. In the present study, honeybees were irradiated right after birth for 14 days with gamma rays at dose rates ranging between 4.38 × 10-3 and 588 mGy/d. Biological tissues (head, intestine and abdomen) were sampled at D3, D10 and D14. Ten different physiological markers involved in nervous (acetylcholinesterase (AChE)), antioxidative (catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione-S-transferase (GST)), immune system (phenoloxidase (PO)) and metabolism (carboxylesterases (CaEs) and alkaline phosphatase (ALP)) were measured. Univariate analyses were conducted to determine whether each individual biomarker response was positively or negatively correlated with the dose rate. Then, multivariate analyses were applied to investigate the relationships between all the biomarker responses. Although no mortality occurred during the experiment, several biomarkers varied significantly in relation to the dose rate. Globally, the biomarkers of antioxidant and immune systems decreased as the dose rate increased. Reversible effects on the indicator of the neural system were found. Concerning indicators of metabolism (carboxylesterases), variations occurred but no clear pattern was found. Taken altogether, these results help better understand the effects of ionizing radiation on bees by identifying relevant physiological markers of effects. These results could improve the assessment of the environmental risk due to ionizing radiation in terrestrial ecosystems.

Common and inter-specific toxic effects in three wild fish species after chronic gamma irradiation of early stages.

The objective of this study was to investigate the effects of gamma irradiation on the aquatic environment. We used three wild fish species to compare phenotypic responses with a fish model such as Danio rerio. We focused on embryonic development, a sensitive life stage to stressors like ionizing radiation, to evaluate the effects of exposure to 0.5 and 5 mGy h-1 on Arctic char, trout and stickleback embryos from fertilization to free-swimming larvae. Irradiation did not cause mortality but induced an acceleration of hatching in the three species. These new data on wild species, obtained under comparable irradiation conditions, did not go against the threshold values for the protection of freshwater aquatic ecosystems. Moreover, irradiation caused inter-specific sublethal effects, such as an increase in non-eyed egg proportion in Arctic char, an increase in the incubation period in trout and an acceleration of larval mortality in stickleback. The consequences of these early effects on the adult stage remain to be studied.

External gamma irradiation-induced effects in early-life stages of zebrafish, Danio rerio.

In the general context of validation of tools useful for the characterization of ecological risk linked to ionizing radiation, the effects of an external gamma irradiation were studied in zebrafish larvae irradiated for 96 h with two dose rates: 0.8 mGy/d, which is close to the level recommended to protect ecosystems from adverse effects of ionizing radiation (0.24 mGy/d) and a higher dose rate of 570 mGy/d. Several endpoints were investigated, such as mortality, hatching, and some parameters of embryo-larval development, immunotoxicity, apoptosis, genotoxicity, neurotoxicity and histological alterations. Results showed that an exposure to gamma rays induced an acceleration of hatching for both doses and a decrease of yolk bag diameter for the highest dose, which could indicate an increase of global metabolism. AChE activity decreased with the low dose rate of gamma irradiation and alterations were also shown in muscles of irradiated larvae. These results suggest that gamma irradiation can induce damages on larval neurotransmission, which could have repercussions on locomotion. DNA damages, basal ROS production and apoptosis were also induced by irradiation, while ROS stimulation index and EROD biotransformation activity were decreased and gene expression of acetylcholinesterase, choline acetyltransferase, cytochrome p450 and myeloperoxidase increased. These results showed that ionizing radiation induced an oxidative stress conducting to DNA damages. This study characterized further the modes of action of ionizing radiation in fish.

Soil nematode assemblages as bioindicators of radiation impact in the Chernobyl Exclusion Zone.

In radioecology, the need to understand the long-term ecological effects of radioactive contamination has been emphasised. This requires that the health of field populations is evaluated and linked to an accurate estimate of received radiological dose. The aim of the present study was to assess the effects of current radioactive contamination on nematode assemblages at sites affected by the fallout from the Chernobyl accident. First, we estimated the total dose rates (TDRs) absorbed by nematodes, from measured current soil activity concentrations, Dose Conversion Coefficients (DCCs, calculated using EDEN software) and soil-to-biota concentration ratios (from the ERICA tool database). The impact of current TDRs on nematode assemblages was then evaluated. Nematodes were collected in spring 2011 from 18 forest sites in the Chernobyl Exclusion Zone (CEZ) with external gamma dose rates, measured using radiophotoluminescent dosimeters, varying from 0.2 to 22 µGy h(-1). These values were one order of magnitude below the TDRs. A majority of bacterial-, plant-, and fungal-feeding nematodes and very few of the disturbance sensitive families were identified. No statistically significant association was observed between TDR values and nematode total abundance or the Shannon diversity index (H'). The Nematode Channel Ratio (which defines the relative abundance of bacterial- versus fungal-feeding nematodes) decreased significantly with increasing TDR, suggesting that radioactive contamination may influence nematode assemblages either directly or indirectly by modifying their food resources. A greater Maturity Index (MI), usually characterising better soil quality, was associated with higher pH and TDR values. These results suggest that in the CEZ, nematode assemblages from the forest sites were slightly impacted by chronic exposure at a predicted TDR of 200 µGy h(-1). This may be imputable to a dominant proportion of pollutant resistant nematodes in all sites. This might result from a selection at the expense of sensitive species after the accident.