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.     

Self-cleaning in an estuarine area formerly affected by 226Ra anthropogenic enhancements

The estuary of the Odiel River has been affected by both direct discharges of phosphogypsum (radium enriched industrial waste) and dissolution and weathering of the exposed piles where this radium enriched waste was stored. In 1998 the waste management policy for industries changed. The direct discharges stopped and the new phosphogypsum piles were well protected against dissolution processes, avoiding any transference of radium into the environment. This work presents a study of the evolution with time (1999-2002) of the levels of 226Ra in river water and sediment samples with the new waste management policy. A liquid scintillation technique was used to measure the 226Ra activity concentration in sediment samples. A gas-proportional counter was also used to measure the 226Ra activity concentration in river water samples. The main conclusion is that a systematic and continuous decrease of the activity concentration of 226Ra with time in the Odiel River estuary is occurring. Thus, a possible self-cleaning in the estuary, once the direct waste discharges were avoided, can be inferred.     

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.     

Radioactive element contents of some granites used as building materials: insights into the radiological hazards

This study was conducted to investigate the radioactive potential hazard of granite, which is widely used as building material in Turkey. Natural radiation levels of 18 various, globally-distributed industrial granite samples imported by Turkey, were analyzed using gamma-ray spectrometer. The results are compared with the formerly published findings of granite samples from Turkey. Radioactivity levels of ²³⁸U, ²³²Th, and ⁴⁰K natural radioactive series elements of the selected 18 specimens were measured, which were from 2.4 ± 0.5 to 88.8 ± 3.6 Bq kg^?1 for ²³⁸U, from 2.4 ± 0.7 to 273 ± 0.9 Bq kg^?1 for ²³²Th, and from 169 ± 24 to 1,479 ± 94 Bq kg^?1 for ⁴⁰K. Radium equivalent activities (Ra_eq) were calculated for the granite samples to assess their radiation hazards in the construction of dwellings. The Ra_eq values of granite samples varied in the range of 39.05–570 Bq kg^?1, only one sample exceeded the safe limit value of 370 Bq kg^?1 set by the OECD-NEA (Nuclear Energy Agency. Exposure to radiation from natural radioactivity in building materials. Report by NEA Group of Experts 1979). Absorbed dose rates in air were found between 18.74 and 261 nGy h^?1 and radiogenic heat production values were calculated in the range of 0.45–6.53 μW m^?3. All rock samples used in this study were also analysed mineralogically and defined their compositions.     

An examination of groundwater discharge and the associated nutrient fluxes into the estuaries of eastern Hainan Island, China using 226Ra

The nutrient concentrations and stoichiometry in a coastal bay/estuary are strongly influenced by the direct riverine discharge and the submarine groundwater discharge (SGD). To estimate the fluxes of submarine groundwater discharge into the Bamen Bay (BB) and the Wanquan River Estuary (WQ) of eastern Hainan Island, China, the naturally occurring radium isotope (²²⁶Ra) was measured in water samples collected in the bay/estuary in August 2007 and 2008. Based on the distribution of ²²⁶Ra in the surface water, a 3-end-member mixing model was used to estimate the relative contributions of the sources to these systems. Flushing times of 3.9 ± 2.7 and 12.9 ± 9.3 days were estimated for the BB and WQ, respectively, to calculate the radium fluxes for each system. Based on the radium fluxes from groundwater discharge and the Ra isotopic compositions in the groundwater samples, the estimated SGD fluxes were 3.4 ± 5.0 m³ s⁻¹ in the BB and 0.08 ± 0.08 m³ s⁻¹ in the WQ, or 16% and 0.06%, respectively, of the local river discharge. Using this information, the nutrient fluxes from the submarine groundwater discharge seeping into the BB and WQ regions were estimated. In comparison with the nutrient fluxes from the local rivers, the SGD-derived nutrient fluxes played a vital role in controlling the nutrient budgets and stoichiometry in the study area, especially in the BB.     

Heterogeneous distribution of radionuclides, barium and strontium in phosphogypsum by-product

Phosphogypsum (PG) is a high volume by-product of the phosphate fertilizer industry which is composed mainly of CaSO₄·2H₂O. Impurities in PG include F, trace elements and naturally-occurring radionuclides. Radium-226 content is sufficiently high in some PGs that it has limited PG usage in building materials and as an amendment to agricultural soils. Radium likely exists in PG as a sulfate solid solution with Ba, and possibly Sr. This study determined the distribution of ²²⁶Ra, Ba, Sr, U, Th and ²¹⁰Pb among three size fractions (fine: <20 μm; medium: 20–53 μm; coarse: >53 μm) in PGs derived from three different phosphate rock sources. All chemical species, except for Sr in PG derived from Idaho rock, were enriched in the <20-μm fraction relative to the other size fractions and relative to unfractionated PG. On average, fine fraction ²²⁶Ra and ²¹⁰Pb contents were enriched approximately sixfold over unfractionated PG. ²²⁶Ra was enriched in the fine fraction to a greater degree than were Ba or Sr, indicating that Ra behavior in PG is distinct from these other elements. The combination of (i) particle sorting during PG deposition, and (ii) non-uniform distribution of radionuclides in PG, may contribute to radionuclide heterogeneity at PG repositories.     

Radioecological model calculations for natural radionuclides released into the environment by disposal of phosphogypsum

The Dutch phosphogypsum, 2 Tg.y^?1, is disposed of into the Rhine. This leads to an increase of the U-238 chain radionuclides along the Dutch coast off Rotterdam, decreasing in northerly direction into the German Bight. The calculated increase of activity concentrations in sea food causes an increase of the individual radiation dose of maximal 150 μSv.y^?1 and of the collective dose of the Dutch of 170 manSv.y^?1. Increase of the radiation dose from stacking phosphogypsum is one order of magnitude lower.     

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.     

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.     

Assessment of heavy metals contamination and its effects on oyster (Saccostrea cucullata) biometry parameters in the Asaluyeh port coasts,Persian Gulf,Iran

The current study examines biometric parameters and concentration of some heavy metals in soft tissues of Saccostrea cucullata in the Asaluyeh coast, Persian Gulf, Iran. The metals concentration in the soft tissue of the Saccostrea cucullata ranged as: Zn: 765–3411 mg kg^?1, Cu: 120.3–580.6 mg kg^?1, Cd: 0.13–3.5 mg kg^?1, As: 0.39–3.3 mg kg^?1, Pb: 0.05–1.64 mg kg^?1, Ni: 0.02–0.44 mg kg^?1, V: 0.06–0.32 mg kg^?1, Cr: 0.02–0.16 mg kg^?1 and Hg: 0.002–0.068 mg kg^?1. The results showed that the concentration of total heavy metals in oysters of the control station (CA) is usually lower. The results also indicated lack of correlation between oyster biometric parameters and bioaccumulated heavy metals, except between Cu and longitudinal diameter (R = 0.77). The concentration of heavy metals is higher than limits recommended by the World Health Organization, except for Cd and Pb.     

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.     

Mn and Ni contents in soils of a qualified denomination of origin region: Rioja D.O.Ca,Spain

The distribution of Mn and Ni in soils of one of the most famous winegrowing regions of Spain, Rioja D.O.Ca (Denomination of origin, Spain's top category), was studied in detail according to its geographical location. There were background concentrations of 288.81 mg kg^?1 total Mn in the surface horizon and 296.06 mg kg^?1 in the subsoil; and a total Ni content of 17.89 mg kg^?1 in the surface horizon and 24.76 mg kg^?1 in the subsoil. The amounts of Mn bio- or phytoavailable were 5.28 mg kg^?1 in the upper horizon and 4.70 mg kg^?1 in the subsurface horizon; and for Ni bio- or phytoavailable, the amounts were 0.14 mg kg^?1 in the upper horizon and 0.13 mg kg^?1 in the deeper horizon. Spatial distribution patterns were established using GIS contour maps for the two elements, showing significant variations within and between the sites. The local contamination is generally associated with the quantities that are added to the soil or water from man-made sources such as industrial discharge and volatile emissions, sewage sludge, livestock wastes and other wastes.     

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.      

Self-cleaning in an estuarine area formerly affected by 226Ra anthropogenic enhancements: numerical simulations

A numerical model of the Odiel-Tinto estuary (Spain) has been developed to study the self-cleaning process that was evidenced from 226Ra measurements in water and sediments collected in the period 1999-2002, after direct releases from a fertilizer complex ceased (in 1998). The hydrodynamic model is first calibrated, and standard tidal analysis is carried out to calculate tidal constants required by the dispersion code to determine instantaneous water currents and elevations over the estuary. In this way, long-term simulations may be carried out. The dispersion code includes advective/diffusive transport of radionuclides plus exchanges with bottom sediments described through a kinetic approach. The dispersion model is first tested by comparing computed and measured 226Ra concentrations over the estuary resulting after releases in the Odiel and Tinto rivers. Next, it is applied to simulate the self-cleaning process of the estuary. The time evolution of radium concentrations in bed sediments is in generally good agreement with observations. The computed sediment halving time of the estuary is 510 days, which also is in good agreement with that estimated from 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.     

Naturally Pb-contaminated soils in uranium and thorium anomaly

The paper reports an examination of the primary sources of stable lead (Pb) occurring in rocks and soils on dairy farms in the municipalities of Pedra and Venturosa in Pernambuco, Brazil. Lead in rock and soil was quantified by flame atomic absorption spectrophotometry. The Pb concentration in calcium silicate rock varied from 21 to 1124.00 mg.kg^?1 and soil varied from 18 to 96 mg.kg^?1. The lead concentration in granite rock varied from 6 to 440 mg.kg^?1 and soil varied from 8 to 15 mg.kg^?1. The results point to the rocks as the primary sources of lead.     

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.     

Pre-operational environmental survey at the uranium mine and mill site,Poços de Caldas,Minas Gerais,Brazil

The first Brazilian uranium mine and mill are located on the Poços de Caldas plateau, in the Central State of Minas Gerais. The pre-operational environmental survey was carried out over a period of two years by the Brazilian Nuclear Energy Commission (CNEN), through the Instituto de Radioproteção e Dosimetria (IRD). The selection of the materials to be monitored, the sampling points and the radionuclides to be analysed were based on critical parameters taking into account the meteorological and hydrological characteristics of the site as well as land use. The results obtained are sufficient to characterize the environmental background of the area, and will allow an assessment of the environmental impact due to the operation of the facility and an evaluation of the adequacy of the effluent emmission control measures. In relation to their contribution to the population dose, the results indicated that ²²⁶Ra and ²¹⁰Pb will be the important radionuclides.     

Radioactivity of fertilizers in Finland

Concentrating of ²³⁸U, ²²⁶Ra, ²²⁸Th, ²³⁵U and ⁴⁰K in 81 samples of Finnish fertilizer were measured with Ge (Li) spectrometers. The samples represented 28 different types of fertilizer including those for agriculture, forests and gardens. The ratios of activity concentrations of ²³⁸U to ²²⁶Ra in the samples varied from 1.0 to 67 with a geometric mean of 3.6 and the ratios of ²²⁸Th ²²⁸Ra varied from 0.95 to 9.5 with a geometric mean of 2.4. The weighted means of radionuclide concentrations per unit weight of phosphorus in fertilizers were estimated to be 3800 Bq/kgP of ²³⁸U, 1100 Bq/kgP of ²²⁶Ra, 78 Bq/kgP of ²²⁸Ra, 190 Bq/kgP of ²²⁸Th and 210 Bq/kgP of ²³⁵U. The weighted mean of the ⁴⁰K concentrations in fertilizers was 3500 Bq/kg. The estimated total activities spread on tilled soils during the 1982–1983 season were 260 GBq of ²³⁸U, 72 GBq of ²²⁶Ra, 5.3 GBq of ²²⁸Ra, 13 GBq of ²²⁸Th, 14 GBq of ²³⁵U and 3800 GBq of ⁴⁰K. The amounts of the uranium isotopes correspond to about 21 000 kg of natural uranium.