RESUMO
As today the 137Cs fallout peak, in sediment cores, corresponds only to 25% of its initial concentration, alternatives to the use of 137Cs as a210Pb sediment dating validation tool are proposed. In highly industrialized bays, such as Guanabara Bay in the Rio de Janeiro metropolitan region, several chemical/compounds from the surrounding industry releases may be applied as validation tools. Chromium and copper profiles in a sediment core adequately fit the expected pattern due to the implementation of a chemical plant in 1958, reaching their maximum discharge in 1982 and subsequently decreasing due to the operation of a new wastewater treatment plant. A diffuse source such, as the PCB-based mixture Askarel, was also applied as an alternative validation tool, and the observed concentration profile reproduced the expected behavior, with increasing concentration after the Second World War and a decrease after the ban of this product in 1981. The observed Aroclor 1254 and 1260 mixture chlorination rates fit the most widely distributed PCB-based products in the country.
Assuntos
Radioisótopos de Césio , Radioisótopos de Chumbo , Monitoramento de Radiação , Radioisótopos de Césio/análise , Monitoramento de Radiação/métodos , Radioisótopos de Chumbo/análise , Poluentes Radioativos da Água/análise , América do Sul , Brasil , Sedimentos Geológicos/química , Datação Radiométrica/métodosRESUMO
The Wider Caribbean Region is an important tourist destination where agricultural, industrial and shipping activities are also carried on. Coastal zones are heavily populated and receive a high human pressure; however, few monitoring programmes allow assessing long-term anthropogenic impact trends in these areas, which are especially useful for integrated management programs. Through the support of the International Atomic Energy Agency (project RLA/7/012), sediment core activities of 210Pb and 137Cs were used to evaluate changes in sedimentation rates in 11 relevant coastal areas of the region, where environmental information is scarce, but needed to support national environmental policies. Most 210Pb activity profiles were atypical, attributed to non-steady sedimentation conditions; whereas 137Cs activity profiles, showing very low values, were of little help for 210Pb-dating corroboration. Results evidenced conspicuous changes in mass accumulation rates (MAR), specially through the Anthropocene (i.e. since ~1950s) in most cases, attributed to deforestation and land erosion (one of the clearest indicators of global change), and the input of urban and industrial untreated wastes. The recent MAR decrease in Havana Bay (Cuba) was attributed to the implementation of environmental policies, which showed that 210Pb-derived reconstruction of environmental changes is also useful to verify the effectiveness of management programs to control land-derived erosion and siltation issues. Since siltation can be detrimental to valuable coastal resources around the world, retrospective evaluations of sedimentation rates, based on 210Pb-dated cores, are highly recommended to assist integrated coastal zone management programs in the region and elsewhere.
Assuntos
Monitoramento de Radiação , Cuba , Monitoramento Ambiental , Sedimentos Geológicos , Chumbo , Radioisótopos de Chumbo/análise , Estudos Retrospectivos , Poluentes Químicos da Água/análiseRESUMO
The southern Gulf of Mexico (sGoM) is home to an extensive oil recovery and development infrastructure. In addition, the basin harbors sites of submarine hydrocarbon seepage and receives terrestrial inputs from bordering rivers. We used stable carbon, nitrogen, and radiocarbon analyses of bulk sediment organic matter to define the current baseline isoscapes of surface sediments in the sGoM and determined which factors might influence them. These baseline surface isoscapes will be useful for accessing future environmental impacts. We also examined the region for influence of hydrocarbon deposition in the sedimentary record that might be associated with hydrocarbon recovery, spillage and seepage, as was found in the northern Gulf of Mexico (nGoM) following the Deepwater Horizon (DWH) oil spill in 2010. In 1979, the sGoM experienced a major oil spill, Ixtoc 1. Surface sediment δ13C values ranged from -22.4 to -19.9, while Δ14C values ranged from -337.1 to -69.2. Sediment δ15N values ranged from 2.8 to 7.2, while the %C on a carbonate-free basis ranged in value of 0.65% to 3.89% and %N ranged in value of 0.09% to 0.49%. Spatial trends for δ13C and Δ14C were driven by water depth and distance from the coastline, while spatial trends for δ15N were driven by location (latitude and longitude). Location and distance from the coastline were significantly correlated with %C and %N. At depth in two of twenty (10%) core profiles, we found negative δ13C and Δ14C excursions from baseline values in bulk sedimentary organic material, consistent with either oil-residue deposition or terrestrial inputs, but likely the latter. We then used 210Pb dating on those two profiles to determine the time in which the excursion-containing horizons were deposited. Despite the large spill in 1979, no evidence of hydrocarbon residue remained in the sediments from this specific time period.
Assuntos
Radioisótopos de Carbono/análise , Monitoramento Ambiental/estatística & dados numéricos , Sedimentos Geológicos/análise , Datação Radiométrica/estatística & dados numéricos , Isótopos de Carbono/análise , Golfo do México , Radioisótopos de Chumbo/análise , Nitrogênio/análiseRESUMO
Unsupported 210Pb (Pbexc) is generated in air and is subsequently deposited on soil surface. The Pbexc can be used for sediment dating, soil erosion/sedimentation and air mass studies. In many cases, 210Pb activity determination (gamma ray 46.5â¯keV) cannot be performed due to the lack of efficiency calibration curve, especially when radioactive patron source is not available. This work presents an alternative methodology to obtain the 210Pb activity values, based on the activity definition and the attenuation coefficient determinations and assuming that soil samples coming from depth higher than 25â¯cm only contain 210Pb generated in the soil (Pbexc free, i.e., for those soil layers the 210Pb activity is equal to the 226Ra activity, at secular equilibrium). The proposed methodology was evaluated using soils from La Plata region, Argentina. The same soil samples were also analyzed in a second laboratory by the conventional methodology. The obtained results indicated that the proposed procedure can be used as a good alternative in cases where a calibration sample is not available.
Assuntos
Radioisótopos de Chumbo/análise , Monitoramento de Radiação/métodos , Poluentes Radioativos do Solo/análise , Argentina , SoloRESUMO
The present study has evaluated temporal and spatial mercury trends based on surficial sediment samples and 210Pb-dated sediment profiles. The obtained results show that there are areas close to the main bay's tributary rivers where the Hg content has doubled during the last 15â¯years and regions where it has decreased by a factor of 2, mainly the area close to the navigation channel, which is submitted to periodic dredging. In the inner part of the bay, the most contaminated region, mercury shows a strong association with sulfide. In the same region, based on the 210Pb results, it was possible to calculate the yearly increment on the Hg concentration in the surface sediment, 0.62⯵gâ¯kg-1â¯y-1 to 0.29⯵gâ¯kg-1â¯y-1, according to the distance to the bay's main tributary rivers.
Assuntos
Sedimentos Geológicos/análise , Mercúrio/análise , Poluentes Químicos da Água/análise , Baías , Brasil , Isótopos de Carbono/análise , Monitoramento Ambiental/métodos , Estuários , Radioisótopos de Chumbo/análise , Isótopos de Nitrogênio/análise , RiosRESUMO
The impacts of anthropic activities have had profound effects on the nitrogen (N) and phosphorus (P) cycles in many aquatic ecosystems. We investigated the spatial and temporal distributions of carbon (C), N, and P in the sediments of a tropical Paiva Castro Reservoir (São Paulo, Brazil), as well as their release and retention in the system. In 2010, surface sediments were collected at nine sites in the reservoir, and a core was obtained in the limnetic zone, in 2010. The core was dated using the 210Pb technique. The organic C content was estimated from organic matter concentration, which was measured by the loss-on-ignition method, and the concentrations of P and N were determined by spectrophotometry. Marked spatial heterogeneity in the Paiva Castro sediments associated with both natural variations in the water body and variations induced by human impacts was observed. Heterogeneity was evidenced by a decrease in the allochthonous contribution of organic matter (C/N) in the upstream-downstream direction and increases of N and P, mainly associated with water flows in the different compartments of the reservoir. In the core, C and N concentrations display significant positive correlations with increases in population and agricultural activities in the drainage basin through time. The C/P molar ratios in surface sediments are indicative of human impacts in the region, as C:P ratios in the sediment are low (7.8:1) compared to the Redfield ratio (C:P = 108:1). Predominance of oxic conditions at the sediment surface and particles sizes < 63 µm provided favorable conditions for P retention in the sediments, which helps prevent eutrophication. Approaches used in this research should be extended to other locations, especially in mesotrophic and oligotrophic reservoirs, to provide information on historical impacts in such aquatic ecosystems.
Assuntos
Carbono/análise , Água Doce/análise , Sedimentos Geológicos/análise , Nitrogênio/análise , Fósforo/análise , Agricultura , Brasil , Ecossistema , Monitoramento Ambiental , Eutrofização , Água Doce/química , Radioisótopos de Chumbo/análise , Análise Espaço-Temporal , Clima TropicalRESUMO
The Brazilian Nuclear Energy Agency (CNEN) is responsible for any radioactive waste storage and disposal in the country. The storage of radioactive waste is carried out in the facilities under CNEN regulation and its disposal is operated, managed and controlled by the CNEN. Oil NORM (Naturally Occurring Radioactive Materials) in this article refers to waste coming from oil exploitation. Oil NORM has called much attention during the last decades, mostly because it is not possible to determine its primary source due to the actual absence of a regulatory control mechanism. There is no efficient regulatory tool which allows determining the origin of such NORM wastes even among those facilities under regulatory control. This fact may encourage non-authorized radioactive material transportation, smuggling and terrorism. The aim of this project is to provide a geochemical signature for oil NORM waste using its naturally occurring isotopic composition to identify its origin. The here proposed method is the modeling of radioisotopes normally present in oil pipe contamination such as 228Ac, 214Bi and 214Pb analyzed by gamma spectrometry. The specific activities of elements from different decay series are plotted in a scatter diagram. This method was successfully tested with gamma spectrometry analyses of oil sludge NORM samples from four different sources obtained from Petrobras reports for the Campos Basin/Brazil.
Assuntos
Resíduos Industriais/análise , Indústria de Petróleo e Gás , Resíduos Radioativos/análise , Gerenciamento de Resíduos/métodos , Bismuto/análise , Brasil , Radioisótopos de Chumbo/análise , Radioisótopos/análiseRESUMO
This study focused on dating of a sediment core from the Alvarado Lagoon System, Veracruz, Mexico, calculating the sedimentation rate by using 210Pb to determine the tendency towards pollution by polycyclic aromatic hydrocarbons, organochlorides, the metals Cd, Cr, Cu, Hg, Ni, Pb, and V, and organic matter content. The activity of total Pb and supported Pb in the samples was 83.1 and 29.5 Bq kg-1, respectively, whereas the average estimated sedimentation rate was 0.48 ± 0.09 cm per year-1. The organic matter values exhibited linear behavior throughout the historical profile, with values under 2.5%. Metal concentrations followed the order V > Cr > Ni > Cu > Pb > Hg > Cd. Variations found in Cr, Ni, Pb, and V concentrations are basically due to three meteorological phenomena that hit the region: hurricanes Gladys, Hilda, and Janet in September of 1955. V, Ni, and Hg input comes from anthropogenic and lithogenic sources. The presence of individual polycyclic aromatic hydrocarbons showed no ascending accumulation pattern over time, nor did it show any significant statistical correlation to OM. As for the organochlorine pesticides, 63.61% of the total sum of these compounds were from the ciclodienics family. Concentration of p,p'-DDT was observed only in the earliest profile, from 1929.
Assuntos
Sedimentos Geológicos/análise , Metais Pesados/análise , Praguicidas/análise , Poluentes Químicos da Água/análise , DDT/análise , Monitoramento Ambiental , Hidrocarbonetos Clorados/análise , Radioisótopos de Chumbo/análise , Mercúrio/análise , México , Hidrocarbonetos Policíclicos Aromáticos/análiseRESUMO
We collected seven cores from five coastal ponds in St Thomas, USVI, dated them via 210Pb, and measured their Hg profiles. Levels ranged from 20 to 100ngg-1 and always increased upward to the surface or a shallow mixed zone. Taking into account differences in sediment accumulation rates and the presence or absence of a mixed zone, all sites revealed similar deposition histories. Mercury levels were at low, possibly pristine, values until the early to mid-20th century. Then they then doubled or quadrupled steadily until about 1990, after which Hg became relatively constant. We conclude that Hg in the sediments of these ponds came from long range deposition directly to the ponds and to their watersheds. Constant levels in recent years may be caused by transfer from watersheds, a pathway that is delayed compared to direct deposition from the atmosphere.
Assuntos
Sedimentos Geológicos/análise , Mercúrio/análise , Poluentes Químicos da Água/análise , Monitoramento Ambiental , Radioisótopos de Chumbo , Lagoas , Ilhas Virgens AmericanasRESUMO
Hanabanilla and Paso Bonito Reservoirs are the main fresh water sources for about half a million inhabitants in central Cuba. Prior to this investigation precise information about the losses of storage capacity was not available. Sedimentation is the dominant process leading to reduction in water storage capacity. We investigated the sedimentation process in both reservoirs by analyzing environmental radionuclides (e.g. 210Pb, 226Ra and 137Cs) in sediment cores. In the shallow Paso Bonito Reservoir (mean depth of 6.5 m; water volume of 8 × 106 m3), we estimated a mean mass accumulation rate (MAR) of 0.4 ± 0.1 g cm-2y-1 based on 210Pb chronologies. 137Cs was detected in the sediments, but due to the recent construction of this reservoir (1975), it was not possible to use it to validate the 210Pb chronologies. The estimated MAR in this reservoir is higher than the typical values reported in similar shallow fresh water reservoirs worldwide. Our results highlight a significant loss of water storage capacity during the past 30 years. In the deeper and larger Hanabanilla Reservoir (mean depth of 15.5 m; water volume of 292 × 106 m3), the MAR was investigated in three different sites of the reservoir. The mean MARs based on the 210Pb chronologies varied between 0.15 and 0.24 g cm-2y-1. The MARs calculated based on the 137Cs profiles further validated these values. We show that the sediment accumulation did not change significantly over the last 50 years. A simple empirical mixing and sedimentation model that assumes 137Cs in the water originated from both, direct atmospheric fallout and the catchment area, was applied to interpret the 137Cs depth profiles. The model consistently reproduced the measured 137Cs profiles in the three cores (R2 > 0.9). Mean residence times for 137Cs in the water and in the catchment area of 1 y and 35-50 y, respectively were estimated. The model identified areas where the catchment component was higher, zones with higher erosion in the catchment, and sites where the fallout component was quantitatively recorded in the sediments.
Assuntos
Radioisótopos de Césio/análise , Radioisótopos de Chumbo/análise , Monitoramento de Radiação , Poluentes Radioativos da Água/análise , Cuba , Sedimentos Geológicos/químicaRESUMO
210Po and 210Pb activity concentrations in spas groundwaters occurring at São Paulo (SP) and Minas Gerais (MG) states, Brazil, have been reported in this paper with a dual purpose: to compare different indices for evaluating the radionuclides mobility into waters and to evaluate the drinking water quality from dose calculations. The waters (75 sampling points) are extensively used for drinking in public places, bottling and bathing purposes, among other. The samples were taken from springs and wells drilled at different aquifer systems inserted in Paraná and Southeastern Shield hydrogeological provinces. The WHO guideline reference value for 210Pb and 210Po of 0.1 Bq/L in drinking water was not reached for 210Pb but the 210Po levels were equal or above it in four spas groundwaters from MG State. The maximum WHO guidance dose level of 0.1 mSv/yr was also reached or surpassed in them. The 210Pb "mobility index" taking into account the ratio of the weight of the dissolved 210Pb per unit volume of solution to its weight per unit weight of the rock matrix yielded values in the range of 0.01-5.2 kg/m3. Another "mobility index" (Preference Ratio) expressing the ratio of 210Pb and 238U in the waters divided by the ratio of 210Pb and 238U in the rock matrices provided values between 0.004 and 7994. The 210Pb/238U activity ratios of some spas groundwaters suggested preferential 238U transport relative to 210Pb into the liquid phase, whereas the ratio of the 210Pb to 238U mobility indices indicated the opposite. Such finding showed a better usefulness of the mobility indices for evaluating processes affecting the radionuclides release into the liquid phase during the water/rock interactions.
Assuntos
Água Subterrânea/química , Fontes Termais/química , Radioisótopos de Chumbo/análise , Polônio/análise , Monitoramento de Radiação , Poluentes Radioativos da Água/análise , Brasil , Abastecimento de ÁguaRESUMO
A survey of 210Pb activity concentration, one of the major internal natural radiation sources to man, has been carried in the most common species of beans (Phaseolus vulgaris L.) grown and consumed in Brazil. The representative bean types chosen, Carioca beans and black type sown in the Brazilian Midwestern and Southern regions, have been collected in this study and 210Pb determined by liquid scintillation spectrometry after separation with chromatographic extraction using Sr-resin. Available values in data set of radioactivity in Brazil (GEORAD) on the 210Pb activity concentration in black beans grown in Southeastern region have been added to the results of this study with the purpose of to amplify the population considered. Concerning the multiple detection limits and due to the high level of censored observations, a robust semi-parametric statistical method called regression on order statistics (ROS) has been employed to provide a reference value of the 210Pb in Brazilian beans, which amounted to 41 mBq kg-1 fresh wt. The results suggest that the 210Pb activity concentration in carioca beans is lower than in black beans. Also evaluated was the 210Pb activity concentration in vegetable component of a typical diet, which displays lower values than those shown in the literature for food consumed in Europe.
Assuntos
Radioisótopos de Chumbo/análise , Modelos Estatísticos , Phaseolus/química , Poluentes Radioativos do Solo/análise , Brasil , Europa (Continente) , HumanosRESUMO
Sediment cores were collected from three sites (1000-1200 m water depth) in the northeastern Gulf of Mexico from December 2010 to June 2011 to assess changes in benthic foraminiferal density related to the Deepwater Horizon (DWH) event (April-July 2010, 1500 m water depth). Short-lived radioisotope geochronologies (²¹°Pb, ²³4Th), organic geochemical assessments, and redox metal concentrations were determined to relate changes in sediment accumulation rate, contamination, and redox conditions with benthic foraminiferal density. Cores collected in December 2010 indicated a decline in density (80-93%). This decline was characterized by a decrease in benthic foraminiferal density and benthic foraminiferal accumulation rate (BFAR) in the surface 10 mm relative to the down-core mean in all benthic foraminifera, including the dominant genera (Bulimina spp., Uvigerina spp., and Cibicidoides spp.). Cores collected in February 2011 documented a site-specific response. There was evidence of a recovery in the benthic foraminiferal density and BFAR at the site closest to the wellhead (45 NM, NE). However, the site farther afield (60 NM, NE) recorded a continued decline in benthic foraminiferal density and BFAR down to near-zero values. This decline in benthic foraminiferal density occurred simultaneously with abrupt increases in sedimentary accumulation rates, polycyclic aromatic hydrocarbon (PAH) concentrations, and changes in redox conditions. Persistent reducing conditions (as many as 10 months after the event) in the surface of these core records were a possible cause of the decline. Another possible cause was the increase (2-3 times background) in PAH's, which are known to cause benthic foraminifera mortality and inhibit reproduction. Records of benthic foraminiferal density coupled with short-lived radionuclide geochronology and organic geochemistry were effective in quantifying the benthic response and will continue to be a valuable tool in determining the long-term effects of the DWH event on a larger spatial scale.
Assuntos
Foraminíferos/efeitos dos fármacos , Hidrocarbonetos Policíclicos Aromáticos/toxicidade , Poluentes Químicos da Água/toxicidade , Biodiversidade , Foraminíferos/fisiologia , Sedimentos Geológicos/química , Golfo do México , Radioisótopos de Chumbo , Oxirredução , Dinâmica Populacional/estatística & dados numéricos , Água do Mar/química , TórioRESUMO
The radiometric composition of bulk deposition samples, collected monthly for one year, February 2010 until January 2011, at a site located in Cienfuegos (22° 03' N, 80° 29' W) (Cuba), are analysed in this paper. Measurement of (7)Be and (210)Pb activity concentrations were carried out in 12 bulk deposition samples. The atmospheric deposition fluxes of (7)Be and (210)Pb are in the range of 13.2-132 and 1.24-8.29 Bq m(-2), and their mean values are: 56.6 and 3.97 Bq m(-2), respectively. The time variations of the different radionuclide have been discussed in relation with meteorological factors and the mean values have been compared to those published in recent literature from other sites located at different latitudes. The annual average flux of (210)Pb and (7)Be were 47 and 700 Bq m(-2) y(-1), respectively. Observed seasonal variations of deposition data are explained in terms of different environmental features. The atmospheric deposition fluxes of (7)Be and (210)Pb were moderately well correlated with precipitation and well correlated with one another. The (210)Pb/(7)Be ratios in the monthly depositions samples varied in the range of 0.05-0.10 and showed a strong correlation with the number of rainy days.
Assuntos
Poluentes Radioativos do Ar/análise , Berílio/análise , Radioisótopos de Chumbo/análise , Monitoramento de Radiação , Radioisótopos/análise , Cuba , Tempo (Meteorologia)RESUMO
In this study, we report the (210)Po and (210)Pb concentrations of bone, muscle and liver samples that were obtained from twelve different marine bird species stranded on beaches in the central-north region of Rio de Janeiro State. Both radionuclides were highly concentrated in the liver samples; however, the lowest mean (210)Po/(210)Pb activity ratio (1.3) was observed in bones compared with liver and muscle (16.8 and 13.8, respectively). Among the species that were studied, Fregata magnificens, with a diet based exclusively on fish, had the lowest (210)Pb and (210)Po concentrations and the lowest (210)Po/(210)Pb activity ratio. The (210)Po concentrations in Puffinus spp. liver samples followed a log-normal distribution, with a geometric mean of 300 Bq kg(-1)wet weight. Only two references pertaining to (210)Po in marine birds were found in a Web of Science search of the literature, and each study reported a different concentration value. The values determined in this experiment are consistent with those in one of the previous studies, which also included one of the species studied in this work. No values for (210)Pb in marine birds have been published previously.
Assuntos
Aves , Radioisótopos de Chumbo/metabolismo , Polônio/metabolismo , Monitoramento de Radiação , Animais , Osso e Ossos/metabolismo , Brasil , Fígado/metabolismo , Músculos/metabolismoRESUMO
The radioactivity of NORM was measured in ashes collected from a fuel-oil power plant in Cienfuegos, Cuba, using an HPGe gamma-ray spectrometer. The (226)Ra, (210)Pb, (40)K, (232)Th and (238)U activity concentrations reached 240, 77, 59, 70 and 15 Bq kg(-1), respectively. The potential radiological hazard of these residuals was assessed. The radium equivalent activities of the samples varied from 54 to 345 Bq kg(-1). The gamma index was calculated to be lower than that of the reference values, and the gamma absorbed dose rate was higher than the average reported for the earth's crust; however, the assessed annual effective dose was slightly lower than the annual effective dose limit for public, i.e. 1 mSv. Therefore, these bottom ashes were not dramatically enriched with radionuclides and may be used as an additive for building materials without restrictions from a radiological protection point of view.
Assuntos
Óleos Combustíveis , Monitoramento de Radiação/métodos , Radioisótopos/análise , Poluentes Radioativos do Solo/análise , Espectrometria gama/métodos , Absorção , Cuba , Geografia , Radioisótopos de Chumbo/análise , Radioisótopos de Potássio/análise , Centrais Elétricas , Rádio (Elemento)/análise , Tório/análise , Urânio/análiseRESUMO
The accumulation, enrichment and provenance of selected trace metals (Ag, As, Cd, Cr, Cu, Hg, Ni, Pb, V and Zn) were studied in sediment cores collected from three lakes located in the Central Mexican Plateau, selected on the basis of their contrasting degree of urbanization: Santa Elena Lake, in a rural and remote area; El Tule Lake, in a rural and slightly urbanized area; and Chapala Lake, in a highly urbanized area. Grain size, magnetic susceptibility and sedimentary constituents such as organic carbon, calcium carbonate, as well as major (Al, Fe, Mn) and minor (Ca, Li, Rb, Sr, Th) elements were analyzed to explain the concentration trends of trace metals. Factor analysis (FA) was used to assess the provenance of the trace elements. The highest metal enrichment factor (EF) above natural concentration levels was found at Chapala Lake for Ag (EF = 3.9), although other trace element EF in all lakes was <2.0, indicating slight contamination. However, the concentration levels of Cr and Ni in all lakes, Hg and Zn in Chapala Lake, Cu in El Tule Lake and As in Santa Elena Lake were above international benchmarks for which adverse effects are expected to occur frequently, even for those metals only slightly enriched (e.g. As, Cr). Through FA, the terrigenous contribution was identified as the most important source of trace metals to the three lakes, most likely related to deforestation and erosion of the surrounding areas, followed by atmospheric transport of volcanic ashes, rather than to direct sources.
Assuntos
Monitoramento Ambiental/estatística & dados numéricos , Poluição Ambiental/análise , Sedimentos Geológicos/química , Lagos/química , Radioisótopos de Chumbo/análise , Metais Pesados/análise , Monitoramento Ambiental/métodos , Análise Fatorial , México , Tamanho da PartículaRESUMO
A study of the impact of forest harvesting operations on sediment mobilization from forested catchments has been undertaken in south-central Chile. The study focused on two sets of small paired catchments (treatment and control), with similar soil type, but contrasting mean annual rainfall, located about 400 km apart at Nacimiento (1200 mm yr(-1)) and Los Ulmos (2500 mm yr(-1)). The objective was to study the changes in the relative contribution of the primary sources of fine sediment caused by forestry operations. Attention focused on the pre-harvest and post-harvest periods and the post-replanting period was included for the Nacimiento treatment catchment. The sediment source fingerprinting technique was used to document the contributions of the potential sources. Emphasis was placed on discriminating between the forest slopes, forest roads and channel erosion as potential sources of fine sediment and on assessing the relative contributions of these three sources to the sediment yield from the catchments. The fallout radionuclides (FRNs) (137)Cs and excess lead-210, the environmental radionuclides (226)Ra and (40)K and soil organic matter (SOM) were tested as possible fingerprints for discriminating between potential sediment sources. The Kruskal-Wallis test and discriminant function analysis were used to guide the selection of the optimum fingerprint set for each catchment and observation period. Either one or both of the FRNs were selected for inclusion in the optimum fingerprint for all datasets. The relative contribution of each sediment source to the target sediment load was estimated using the selected fingerprint properties, and a mixing model coupled with a Monte Carlo simulation technique that takes account of uncertainty in characterizing sediment source properties. The goodness of fit of the mixing model was tested by comparing the measured and simulated fingerprint properties for the target sediment samples. In the Nacimiento treatment catchment the relative contribution from the forest slopes and forest roads increased from 16 to 25% and from 37 to 45%, respectively, after clearcutting. Similar changes in source contributions associated with clearcutting were documented for the Los Ulmos treatment catchment, where the relative contribution of the forest slopes increased from 10.5 to 30% and that of the roads from 10 to 20%. The results indicate that the changes in sediment source are closely related to the disturbance of the catchment by clearcutting, but are also influenced by the amount of rainfall that occurred after clearcutting. They also emphasise the need to implement better management practices during forest harvesting, to reduce the increase in sediment mobilization from catchment slopes and roads, which can result in loss of valuable soil and associated nutrients from the forest floor and cause degradation of the water quality of adjacent streams.
Assuntos
Radioisótopos de Césio/análise , Agricultura Florestal , Sedimentos Geológicos/análise , Radioisótopos de Chumbo/análise , Chile , Modelos Teóricos , Radioisótopos de Potássio/análise , Monitoramento de Radiação , Rádio (Elemento)/análise , Chuva , ÁrvoresRESUMO
Monthly sampling in northwestern Mediterranean coastal waters was undertaken to better understand the relationship between zooplankton biomass and the cycling of the natural radionuclide (210)Po/(210)Pb pair during a one-year period (October 1995-November 1996). In conjunction with mesozooplankton collections and (210)Po/(210)Pb measurements in seawater, zooplankton and their fecal pellets, the biochemical composition of particulate organic matter (POM) was also examined at three depths (0, 20 and 50 m) as an indicator of trophic conditions. During May 1996, a strong zooplankton "bloom" was observed which was preceded by a prolonged increase in POM (protein + carbohydrates + lipids) starting at the end of March, and further demonstrated by a concomitant increase in the concentration of smaller particles, two features that are typical of mesotrophic waters. Simultaneous measurements of (210)Po in sea water and zooplankton showed an inverse trend between these two parameters during the sampling period, with the two lowest (210)Po concentrations in the dissolved phase of seawater coincident with the highest radionuclide concentrations in the zooplankton; however, this apparent relationship was not statistically significant over the entire year. Freshly excreted mesozooplankton and salp fecal pellets, which have been strongly implicated in the removal and downward transport of these radionuclides from the upper water column, contained (210)Po and (210)Pb levels ranging from 175 to 878 and 7.5-486 Bq kg(-1) dry weight, respectively. Salp pellets contained 5 and 10 times more (210)Po and (210)Pb than in fecal pellets produced by mixed zooplankton, a finding most likely related to their different feeding strategies. During the zooplankton biomass peak observed in May, the (210)Po concentration in zooplankton was at a minimum; however, in contrast to what has been reported to occur in some open sea oligotrophic waters, over the year no statistically significant inverse relationship was found between zooplankton biomass and (210)Po concentration in zooplankton. This observation may have resulted from the general lack of very low biomass concentrations (<1 mg m(-3)) measured in these coastal waters, biomass levels which commonly occur in open ocean oligotrophic regions.
Assuntos
Radioisótopos de Chumbo/análise , Polônio/análise , Poluentes Radioativos da Água/análise , Zooplâncton/química , Animais , Biomassa , Mar Mediterrâneo , Monitoramento de RadiaçãoRESUMO
This paper focuses on a survey of uranium and thorium decay chain radionuclides in food and drinking water from the thorium-rich (monazite-bearing) region of Buena, which is located in the state of Rio de Janeiro, Brazil. The radionuclide concentration values in the food and drinking water from Buena reached values higher than 100-fold the international reference values. The daily intake of radionuclides by the local population is similar to that of another high background radiation area in Brazil, but the intake is higher than that of residents from a normal background radiation area. Approximately 58 % of the food consumed by Buena inhabitants is produced locally. Based on that figure, locally produced food and the dilution of total radionuclides in the diet of residents caused by food importation are both highly relevant to a population's intake of radionuclides. The concentration values for (210)Pb and the radium isotopes in drinking water from Buena are among the highest values to be reported in the literature. (228)Ra is the most important radionuclide ingested with both food and water among the inhabitants of Buena.