Pb and stable lead content in fungi: Its transfer from soil

The uptake and transfer of natural radionuclides, other than ⁴⁰K, from soil to mushrooms has been somewhat overlooked in the literature. Their contribution to the dose due to the consumption of mushrooms was considered negligible. But the contribution of ²¹⁰Pb in areas unaffected by any recent radioactive fallout has been found to be significant, up to 35% of the annual dose commitment in Spain. More than 30 species of mushrooms were analyzed, and the ²¹⁰Pb detected was in the range of 0.75-202 Bq/kg d.w. A slight difference was observed between species with different nutritional mechanisms (saprophytes ≥ mycorrhizae). The ²¹⁰Pb content was correlated with the stable lead content, but not with its predecessor in the uranium radioactive series, ²²⁶Ra. This suggested that ²¹⁰Pb was taken up from the soil by the same pathway as stable lead. The bioavailability of ²¹⁰Pb in soil was determined by means of a sequential extraction procedure (NH₄OAc, 1M HCl, 6M HCl, and residue). About 30% of the ²¹⁰Pb present in the soil was available for transfer to mushrooms, more than other natural radionuclides in the same ecosystem. Lycoperdon perlatum, Hebeloma cylindrosporum, and Amanita curtipes presented the highest values of the available transfer factor, ATF. As reflected in their ATF values, the transfer from soil to mushroom of some natural and anthropogenic radionuclides was in the following order:

^228,230,232Th ≈ ⁴⁰K ≥ ¹³⁷Cs ≥ ^234,238U ≈ ²²⁶Ra ≥ ⁹⁰Sr ≥ ²¹⁰Pb ≈ ^239 + 240Pu ≈ ²⁴¹Am.     

Distribution,cycling and mean residence time of 226Ra, 210Pb and 210Po in the Tagus estuary

Results for dissolved and particulate ²²⁶Ra, ²¹⁰Pb and ²¹⁰Po in the Tagus river, estuary and coastal sea system show different distribution and chemical behaviour patterns for these radionuclides in the three aquatic environments. ²²⁶Ra from riverborne particles dissolves in the estuary and contributes to increased concentrations of dissolved ²²⁶Ra in estuarine water. In the estuary, dissolved ²¹⁰Pb and ²¹⁰Po from river discharge and atmospheric deposition are scavenged by suspended matter, which in turn becomes enriched in these nuclides in comparison with riverborne particles. As a result of these processes, the estuarine water flowing into the coastal sea contains enhanced concentrations of dissolved ²²⁶Ra, but is depleted in dissolved ²¹⁰Pb and ²¹⁰Po. Under average river flow conditions, mass balance calculations for dissolved ²¹⁰Po and ²¹⁰Pb in the estuary allowed their mean residence times to be estimated as 18 and 30 days, respectively. Due to the rapid sorption of these radionuclides on to settling particles, bottom sediments in the estuary represent a sink for ²¹⁰Pb and ²¹⁰Po from both natural sources and industrial waste releases. Results also suggest that partial re-dissolution of these radionuclides from bottom sediments and intertidal mudflats is likely to occur in the mid- and low-estuary zones. Nevertheless, box-model computations indicate that the discharge of ²¹⁰Pb and ²¹⁰Po into the coastal sea takes place mainly with the transport of sediment, whereas the discharge in the dissolved fraction can only account for one third of the activities entering the estuary in the soluble phase. Implications of these results to the cycling of radionuclides in phosphate waste releases into estuarine environments are discussed.     

Distribution of artificial radionuclides in deep sediments of the Mediterranean Sea

Artificial radionuclides enter the Mediterranean Sea mainly through atmospheric deposition following nuclear weapons tests and the Chernobyl accident, but also through the river discharge of nuclear facility effluents. Previous studies of artificial radionuclides impact of the Mediterranean Sea have focussed on shallow, coastal sediments. However, deep sea sediments have the potential to store and accumulate pollutants, including artificial radionuclides. Deep sea marine sediment cores were collected from Mediterranean Sea abyssal plains (depth > 2000 m) and analysed for ^239,240Pu and ¹³⁷Cs to elucidate the concentrations, inventories and sources of these radionuclides in the deepest areas of the Mediterranean. The activity — depth profiles of ²¹⁰Pb, together with ¹⁴C dating, indicate that sediment mixing redistributes the artificial radionuclides within the first 2.5 cm of the sedimentary column. The excess ²¹⁰Pb inventory was used to normalize ^239,240Pu and ¹³⁷Cs inventories for variable sediment fluxes. The ^239,240Pu/²¹⁰Pb_xs ratio was uniform across the entire sea, with a mean value of 1.24 × 10^− 3, indicating homogeneous fallout of ^239,240Pu. The ¹³⁷Cs/²¹⁰Pb_xs ratio showed differences between the eastern (0.049) and western basins (0.030), clearly significant impact of deep sea sediments from the Chernobyl accident. The inventory ratios of ^239,240Pu/¹³⁷Cs were 0.041 and 0.025 in the western and eastern basins respectively, greater than the fallout ratio, 0.021, showing more efficient scavenging of ^239,240Pu in the water column and major sedimentation of ¹³⁷Cs in the eastern basin. Although areas with water depths of > 2000 m constitute around 40% of the entire Mediterranean basin, the sediments in these regions only contained 2.7% of the ^239,240Pu and 0.95% of the ¹³⁷Cs deposited across the Sea in 2000. These data show that the accumulation of artificial radionuclides in deep Mediterranean environments is much lower than predicted by other studies from the analysis of continental shelf sediments.     

(210)Po and (210)Pb in the tissues of the deep-sea hydrothermal vent mussel Bathymodiolus azoricus from the Menez Gwen field (Mid-Atlantic Ridge)

The hydrothermal deep-sea vent fauna is naturally exposed to a highly specific environment enriched in potentially toxic species such as sulfides, metals and natural radionuclides due to the convective seawater circulation inside the oceanic crust and its interaction with basaltic or ultramafic host rocks. However, data on radionuclides in biota from such environment are very limited. An investigation was carried out on tissue partitioning of ²¹⁰Po and ²¹⁰Pb, two natural radionuclides within the ²³⁸U decay chain, in Bathymodiolus azoricus specimens from the Mid-Atlantic Ridge (Menez Gwen field). These two elements showed different distributions with high ²¹⁰Pb levels in gills and high ²¹⁰Po levels in both gills and especially in the remaining parts of the body tissue (including the digestive gland). Various factors that may explain such partitioning are discussed. However, ²¹⁰Po levels encountered in B. azoricus were not exceptionally high, leading to weighted internal dose rate in the range 3 to 4 μGy h^− 1. These levels are slightly higher than levels characterizing coastal mussels (~ 1 μGy h^− 1).     

The natural radioactivity levels and radiation hazard of pumice from the East Mediterranean Region of Turkey

The concentrations of natural radionuclides in 20 pumice samples from the Toprakkale-Osmaniye area were studied using γ-ray spectrometry in order to assess the radioactivity levels and health hazard. The activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in the pumice samples ranged from 9.44 to 27.31, 12.24 to 25.43 and 289.48 to 673.18 Bq kg⁻¹, respectively. The radionuclide concentrations in pumice samples were matched with typical world values and the radium equivalent activity (Ra_eq), external (H _ex) and internal (H _in) hazard index and representative level index (I _γr) determined. All the calculated values were below the internationally accepted limits and indicate that the Toprakkale-Osmaniye pumice can safely be used in construction.      

Contamination and restoration of an estuary affected by phosphogypsum releases

The Huelva Estuary in Huelva, Spain, has been one of the most studied environmental compartments in the past years from the point of view of naturally occurring radioactive material (NORM) releases. It has been historically affected by waste releases, enriched in radionuclides from the U-decay series, from factories located in the area devoted to the production of phosphoric acid and phosphate fertilizers.Nevertheless, changes in national regulations forced a new waste management practice in 1998, prohibiting releases of phosphogypsum into the rivers. The input of natural radionuclides from phosphate factories to rivers was drastically reduced. Because of this there was a unique opportunity for the study of the response of a contaminated environmental compartment, specifically an estuary affected by tidal influences, after the cessation of the contaminant releases to, in this case, the Huelva Estuary (henceforth referred to as the Estuary).To investigate the environmental response to this new discharge regime, the specific activities of radionuclides ²²⁶Ra and ²¹⁰Pb in water and sediment samples collected in four campaigns (from 1999 to 2005) were determined and compared with pre-1998 values.From this study it is possible to infer the most effective mechanisms of decontamination for the Estuary. Decontamination rates of ²¹⁰Pb and ²²⁶Ra in the sediments and water have been calculated using exponential fittings and corresponding half-lives have been deduced from them. The cleaning half-life in the whole area of the Estuary is about 6 and 3.5 years for ²²⁶Ra and ²¹⁰Pb respectively.The observed trend clearly shows that contamination of the Estuary by natural radionuclides is now decreasing and radioactive levels in waters and sediments are approaching the natural background references. This work attempts to evaluate whether it can be expected that the decontamination of the enhanced levels of natural radioactivity in the Estuary can be performed via natural processes.     

Concentrations of radionuclides in Lake Ontario water from measurements on water treatment plant sludges

The purpose of this investigation was to compare the results of indirect measurements of radionuclide concentrations in water with those measured directly. The levels of ¹³⁷Cs and ²²⁶Ra in western Lake Ontario nearshore waters were derived from high-resolution γ-spectrometric measurements on aluminum hydroxide sludge samples obtained from four water treatment plants. The concentrations of ¹³⁷Cs evaluated by this indirect technique averaged 0.036 compared with 0.023 pCi l⁻¹ measured directly, while those of ²²⁶Ra averaged 0.047 compared with the direct measurement of 0.03 pCi l⁻¹. The concentrations of a number of other radionuclides at these locations were also calculated from the sludge γ-ray measurements.     

Anthropogenic and natural radionuclides in caribou and muskoxen in the western Alaskan Arctic and marine fish in the Aleutian Islands in the first half of 2000s

A number of caribou and muskoxen samples from the western Alaskan Arctic and fish samples from the Aleutian Islands were collected between 1998 and 2006 and analyzed for anthropogenic (⁹⁰Sr and ¹³⁷Cs) and natural radionculides (⁴⁰ K, ²¹⁰Pb and ²²⁶Ra), as part of the radiological assessment for the regional subsistence hunting communities in the first half of 2000s. We examined the relationship between the activities of these nuclides with the size of the fish. In caribou samples, concentration of ⁹⁰Sr in muscle was below the detection limit of 0.14 Bq kg^− 1 and ¹³⁷Cs concentration in bones was below the detection limit of 0.15 Bq kg^− 1.¹³⁷Cs activity varied over an order of magnitude in caribou muscle samples with an average value of 2.5 Bq/kg wet wt. Average ¹³⁷Cs activity in muskoxen muscle was found to be 9.7 Bq/kg wet wt. However, there were a little variation (less than 60%) in ²¹⁰Pb, ⁴⁰ K, and ²²⁶Ra in both muscle and bone of both caribou and muskoxen. The activities of total ²¹⁰Pb in caribou and muskox bones were found to be 1-2 orders of magnitude higher than that of parent-supported ²¹⁰Pb indicating the potential for dating of bones of terrestrial mammals (time elapsed since the death of the animal) based on the excess ²¹⁰Pb method exists. In fish muscle samples, ¹³⁷Cs activity varied from below detection limit to 154 mBq/kg wet wt. and its content increased with the size of the fish due to its transfer through the food chain. Among the seven fish species investigated, ²¹⁰Pb activities varied almost an order of magnitude; however, ⁴⁰K and ²²⁶Ra activities varied less than a factor of two. Total annual effective dose due to ⁹⁰Sr and ¹³⁷Cs from the ingestion of those terrestrial and marine meats was estimated to be negligible (ca. 9 μSV/a) compared to the natural radionuclides present thus posing negligible radiological threat to humans.     

Spatial distribution of radionuclides in soil around a coal-fired power plant: 210Pb, 210Po, 226Ra, 232Th, 40K emitted with the fly ash and 137Cs from the worldwide weapon testing fallout

To determine the effect of airborne emissions of radionuclides from coal-fired power plants on the environment, the concentrations of the most important radionuclides were measured in soil samples from the local environments (0.4–5.2 km) as well as in fly ash. The spatial distribution of the radionuclides in the soil did not indicate any significantly increased concentrations in the area downwind of the plant compared to other areas; the ratios ²¹⁰Pb/²²⁶Ra and ²¹⁰Po/²²⁶Ra were within the range observed for unaffected soils. The emissions from the plant, though present, are obviously too small to significantly change the natural local distribution pattern of the radionuclides in the soil. A highly significant correlation between ⁴⁰K and ²³²Th was observed which was independent of the different types of soils found in this area. The concentration of ¹³⁷Cs in topsoil, which is the result of worldwide fallout from nuclear weapons testing, varied at some places even within a small distance (～ 2 km) by up to one order of magnitude. Furthermore, it was observed that the concentration of ¹³⁷Cs in soils from cropland was on average a factor of 2 less than in those from grassland. This variability has to be considered in planning monitoring programs around nuclear power plants, which may also release this radionuclide.     

Distribution and biokinetic analysis of Pb and Po in poultry due to ingestion of dicalcium phosphate

Dicalcium phosphate (DCP) is used as a calcium supplement for food producing animals (i.e., cattle, poultry and pig). When DCP is produced via wet acid digestion of the phosphate rock and depending on the acid used in the industrial process, the final product can result in enhanced ²¹⁰Pb and ²¹⁰Po specific activities (∼ 2000 Bq·kg⁻¹). Both ²¹⁰Pb and ²¹⁰Po are of great interest because their contribution to the dose received by ingestion is potentially large. The aims of this work are to examine the accumulation of ²¹⁰Pb and ²¹⁰Po in chicken tissues during the first 42 days of life and to build a suitable single-compartment biokinetic model to understand the behavior of both radionuclides within the entire animal using the experimental results. Three commercial corn-soybean-based diets containing different amounts and sources of DCP were fed to broilers during a period of 42 days. The results show that diets containing enhanced concentrations of ²¹⁰Pb and ²¹⁰Po lead to larger specific accumulation in broiler tissues compared to the blank diet. Radionuclides do not accumulate homogeneously within the animal body: ²¹⁰Pb follows the calcium pathways to some extent and accumulates largely in bones, while ²¹⁰Po accumulates to a large extent in liver and kidneys. However, the total amount of radionuclide accumulation in tissues is small compared to the amounts excreted in feces. The single-compartment non-linear biokinetic model proposed here for ²¹⁰Pb and ²¹⁰Po in the whole animal takes into account the size evolution and is self-consistent in that no fitting parameterization of intake and excretions rates is required.     

Radioactivity of anthropogenic origin in the Tejo Estuary and need for improved waste management and environmental monitoring

The Tejo Estuary is a large water body surrounded by seven municipalities and industries with liquid effluent discharges containing contaminants that reach the estuary. This is the case for man-made radionuclides used in nuclear medicine, present in liquid effluents discharged by medical facilities. Radionuclide measurements in seaweeds, mussels, fish, water and sediments sampled along the North bank of the estuary revealed the presence of ¹³¹I and ^99mTc, originating from nuclear medicine facilities in Lisboa. Concentrations reached 90 Bq kg^?1 (wet weight) of ^99mTc in fish, and 18 Bq kg^?1 (wet weight) of ¹³¹I in mussels, and were even higher in the water. Another anthropogenic source of radionuclides is industrial waste, such as phosphogypsum the by-product of phosphoric acid production stockpiled at the South bank of the estuary. Main radionuclides present in phosphogypsum are ²²⁶Ra, ²¹⁰Pb, ²¹⁰Po and uranium. Concentrations of ²²⁶Ra in phosphogypsum are about 1000 Bq kg^?1, which is a high value in comparison with ²²⁶Ra in soils of the Tejo valley, <100 Bq kg^?1. ²²⁶Ra, in particular, is dissolved by rainwater from phosphogypsum stacks and seeps into the estuary. Other potential sources of radioactivity are discharges from naval nuclear powered vessels and merchant ships transporting radioactive materials that berth in the Lisboa harbour. A whole survey of the estuary indicated low concentrations of ¹³⁷Cs in sediments, mostly attributed to radioactive fallout. Since waste discharges are undergoing deep modifications due to enhanced urban waste treatment, but economic activities have changed and the use of radiopharmaceuticals increases, the periodic radioactivity monitoring of the Tejo Estuary is advised and should provide feedback to enhanced waste management.     

Natural radionuclides in mineral waters

Concentration levels of natural radionuclides in mineral waters have been studied in several European countries. In the Federal Republic of Germany in recent years a nationwide investigation was carried out by several institutions.The concentrations of ²²⁶Ra, uranium isotopes, ²¹⁰Pb and ²¹⁰Po found are similar to those in other European countries. While for adults the health risk from drinking mineral water is comparable to the risk from terrestrial radiation, special consideration has to be given to the risk of infants when mineral water is used for preparing their food.     

Unusually high (210)Po activities in the surface water of the Zhubi Coral Reef Lagoon in the South China Sea

Recent researches revealed the exciting application of ²¹⁰Po in tracing carbon and nitrogen cycling in the coral reef system. In order to quantify the recycling of particulate organic nitrogen (PON), both ²¹⁰Po and ²¹⁰Pb were examined at both high and low tides in the Zhubi Coral Reef lagoon, the South China Sea. Unusually, much higher ²¹⁰Po activities and ²¹⁰Po/²¹⁰Pb ratios, in comparison with those found in the open seawater and the lagoon subsurface water, showed additional input of ²¹⁰Po besides production from in situ²¹⁰Pb in the lagoon surface water. Statistical analysis identified that the reef flat seawater was the additional ²¹⁰Po source. Based on a mass balance model, the input rates of ²¹⁰Po varied from 0.04 Bq m⁻³ year⁻¹ to 8.41 Bq m⁻³ year⁻¹. On average, the additional ²¹⁰Po contributed more than 60% of the total ²¹⁰Po. The particulate ²¹⁰Po significantly correlated with the concentrations of PON, indicating that diffusion of ²¹⁰Po from sediment could be used to quantify the recycling of nitrogen. The average input rate of nitrogen was 16 mmol m⁻³ year⁻¹, which can support up to 11% of the primary production rate. These results suggested that the unusual behavior of ²¹⁰Po could provide new insight into the nitrogen recycling in the coral reef system.     

Sediment reworking rates in deep sediments of the Mediterranean Sea

Different pelagic areas of the Mediterranean Sea have been investigated in order to quantify physical and biological mixing processes in deep sea sediments. Herein, results of eleven sediment cores sampled at different deep areas (> 2000 m) of the Western and Eastern Mediterranean Sea are presented.²¹⁰Pb_xs and ¹³⁷Cs vertical profiles, together with ¹⁴C dating, are used to identify the main processes characterising the different areas and, finally, controlling mixing depths (SML) and bioturbation coefficients (D_b). Radionuclide vertical profiles and inventories indicate that bioturbation processes are the dominant processes responsible for sediment reworking in deep sea environments.Results show significant differences in sediment mixing depths and bioturbation coefficients among areas of the Mediterranean Sea characterised by different trophic regimes. In particular, in the Oran Rise area, where the Almeria-Oran Front induces frequent phytoplankton blooms, we calculate the highest values of sediment mixing layers (13 cm) and bioturbation coefficients (0.187 cm² yr⁻¹), and the highest values of ²¹⁰Pb_xs and ¹³⁷Cs inventories. Intermediate values of SML and D_b (~ 6 cm and ~ 0.040 cm² yr⁻¹, respectively) characterise the mesothrophic Algero-Balearic basin, while in the Southern Tyrrhenian Sea mixing parameters (SML of 3 cm and D_b of 0.011 cm² yr⁻¹) are similar to those calculated for the oligotrophic Eastern Mediterranean (SML of 2 cm and D_b of ~ 0.005 cm² yr⁻¹).     

Natural radioactivity in various surface waters in stanbul, Turkey

Gross-α and gross-β, activities of eight well and five tap water samples taken in stanbul were determined. Ra²²⁶, Rn²²², Pb²¹⁴, Bi²¹⁴, K⁴⁰, Cs¹³⁷ activity concentrations in four lake, four sea water, one snow and one rain water samples were also analyzed in order to determine their radioactivity. The results obtained showed that, in general, natural activities in drinking water samples did not exceed WHO and ITS guidelines. In sea and lake water, four samples were over WHO and TSI guidelines. Concentrations ranging from 0.007 to 0.04 Bq l⁻¹ and from 0.02 to 0.1 Bq l⁻¹ were observed for drinking water and the gross-α and gross-β activities, respectively. For all samples the gross-β activities were higher than the corresponding gross-α activities. In order to evaluate the annual effective dose equilavent of ingestion of these waters, a conservative dosimetric calculation was carried out using dose conversion factor suggested by the ICRP. An average annual effective dose equivalent of 0.84 μSv y⁻¹ for Ra²²⁶ was calculated.     

Dry deposition of gaseous radioiodine and particulate radiocaesium onto leafy vegetables

Radionuclides released to the atmosphere during dry weather (e.g. after a nuclear accident) may contaminate vegetable foods and cause exposure to humans via the food chain. To obtain experimental data for an appropriate assessment of this exposure path, dry deposition of radionuclides to leafy vegetables was studied under homogeneous and controlled greenhouse conditions. Gaseous ¹³¹I-tracer in predominant elemental form and particulate ¹³⁴Cs-tracer at about 1 μm diameter were used to identify susceptible vegetable species with regard to contamination by these radionuclides. The persistence was examined by washing the harvested product with water. The vegetables tested were spinach (Spinacia oleracea), butterhead lettuce (Lactuca sativa var. capitata), endive (Cichorium endivia), leaf lettuce (Lactuca sativa var. crispa), curly kale (Brassica oleracea convar. acephala) and white cabbage (Brassica oleracea convar. capitata). The variation of radionuclides deposited onto each vegetable was evaluated statistically using the non-parametric Kruskal-Wallis Test and the U-test of Mann-Whitney. Significant differences in deposited ¹³¹I and ¹³⁴Cs activity concentration were found among the vegetable species.For ¹³¹I, the deposition velocity to spinach normalized to the biomass of the vegetation was 0.5-0.9 cm³ g^− 1 s^− 1 which was the highest among all species. The particulate ¹³⁴Cs deposition velocity of 0.09 cm³ g^− 1 s^− 1 was the highest for curly kale, which has rough and structured leaves. The lowest deposition velocity was onto white cabbage: 0.02 cm³ g^− 1 s^− 1 (iodine) and 0.003 cm³ g^− 1 s^− 1 (caesium). For all species, the gaseous iodine deposition was significantly higher compared to the particulate caesium deposition. The deposition depends on the sensitive parameters leaf area, stomatal aperture, and plant morphology. Decontamination by washing with water was very limited for iodine but up to a factor of two for caesium.     

Deposition of Ra on surfaces during precipitation and leaching of (Ba, Ra)SO4

Formation of a barium-radium sulphate precipitate occurs during the treatment of uranium tailings decants with barium chloride to remove ²²⁶Ra. This note presents results from experiments designed to identify the importance of radium adsorption onto the (Ba, Ra)SO₄ precipitate as a mechanism for removal. Adsorption was investigated indirectly by forming a precipitate and then measuring radium release during leaching.In the conduct of the precipitation/leaching experiments serious difficulties were encountered initially in obtaining satisfactory mass balances—radium recoveries were quite low. EDTA extractions of apparatus revealed that significant quantities of ²²⁶Ra were adhering to apparatus surfaces during both precipitation and leaching. This has important implications for treatment process design, the behaviour of radium in the environment and for the conduct of experimental work. Although the amounts of radium adhering to surfaces were significant relative to levels in solution, the total release of radium from sludge during distilled water leaching was not large. The results of the leaching tests indicated that during precipitation the radium is incorporated into the precipitate rather than adsorbed on its surface.     

Natural radionuclide distribution in quartzite sands of East Mediterranean Region (Turkey)

The study examined 15 sites in the Ovacik-Kargicak (Mersin, Turkey) open pit mines and obtained two quartzite samples from each. Gamma-ray spectrometric measurements were undertaken on the quartzite rocks and sands to quantify the concentrations of the natural radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K. In addition, the mean radioactivity concentrations of these natural nuclides were calculated to be 6.94, 7.34 and 140.05 Bqkg⁻¹. Also the mean radioactivity concentrations of the natural nuclides in old Ovacik quartzite sands ²²⁶Ra, ²³²Th and ⁴⁰K were calculated to be 9.85, 10.54, and 226.40 Bqkg⁻¹, respectively.     

Estimation of ionizing radiation impact on natural Vicia cracca populations inhabiting areas contaminated with uranium mill tailings and radium production wastes

Industrial areas in proximity to the Vodny settlement in the Komi Republic, Russia, have been contaminated by uranium mill tailings and radium production wastes. These areas, exhibiting high activity concentrations of naturally occurring radionuclides in soils, constitute a field laboratory where the effects of combined chronic exposures to α-, β- and γ-emitting radionuclides on natural plant populations can be studied. The aim of the present work was to determine dose–effect relationships and the range of doses that cause biological effects in natural Vicia cracca L. populations inhabiting the study area. The studied plant species is native to the area and is found ubiquitously. Soil and vegetation samples were taken at a reference location and six contaminated sites characterized by distinct floodplain depositional units with different enhanced levels of naturally occurring radionuclides. A large fraction of the dose at the study sites (including the reference location) was attributable to internal irradiation and ²²⁶Ra was found to be an important contributor to this component of dose. The relationship between the frequency of chromosome aberrations in seedlings' root tip cells and the absorbed dose was found to be quadratic. An exponential model provided the best result in describing the empirical dependence between the absorbed dose and both the germination capacity of seeds and the survival rate of sprouts of V. cracca. For V. cracca plants inhabiting areas contaminated with uranium mill tailings and radium production wastes, a weighted absorbed dose of 0.2 Gy (weighting factor for alpha particles = 5) during the vegetation period could be considered to be a level below which no increase in genetic variability and decrease in reproductive capacity might be observed above background.     

Effects of naturally occurring aquatic organic fractions on cadmium toxicity to Simocephalus serrulatus (daphnidae) and Gambusia affinis (poeciliidae)

Cadmium toxicity to Simocephalus serrulatus and Gambusia affinis in soft well water, highly organic pond water and well water containing various sized organic fractions isolated from pond water was determined and compared to Cd binding capacity of each water type. Pond organics were separated into three nomial molecular diameter fractions (> 0.0183 μm; 0.0183 < > 0.0032 μm; 0.0032 < > 0.0009 μm) using ultrafiltration. Cadmium binding capacity was determined using selective ion electrodes. Pond water and organic fractions bound Cd. reducing the amount of free Cd²⁺ as determined by Cd selective ion electrode. Whole pond water reduced Cd toxicity to S. serrulatus but had little effect on Cd toxicity to G. affinis. The three larger molecular diameter organic fractions reduced Cd toxicity to S. serrulatus, while the smallest fraction slightly increased Cd toxicity. Cadmium 96 h LC₃₀ values cannot be predicted from Cd binding capacities determined by selective ion electrode.