Horst Monken Fernandes

Heavy metal distribution in sediments and ecological risk assessment : The role of diagenetic processes in reducing metal toxicity in bottom sediments

This paper describes the heavy metal distributions in river and lagoonal sediments of Jacarepaguá Basin, Rio de Janeiro, Brazil. The occurrence of metal phase translocation from the reducible to the oxidizable was observed for Fe, Mn and Ni, from the fluvial environment to the lagoonal. Cu was mainly associated with the oxidizable phase while Zn and Pb were mainly associated with the reducible phase in both environments. It has been demonstrated that metal sulfide formation and complexation by organic complexes are very important aspects in terms of toxicity reduction. By means of a risk assessment methodology, based on available sediment data, it was demonstrated that the lagoonal system is exposed to a low potential ecological risk and that Zn was the metal of greater concern with respect to the system pollution.

Management of uranium mill tailing: Geochemical processes and radiological risk assessment

This paper describes the geochemical processes regulating the mobilisation of heavy metals and radionuclides in the tailing dam of the uranium mining and milling facilities of Pocos de Caldas, Brazil. The operational effluent release pollution of surface and groundwater was evaluated by means of monitoring data. The potential environmental impact after the future closure of the installation was assessed by means of dose estimations assuming the absence of remedial measures. Residual tailing pyrite oxidation was found to be the critical factor in the transfer of metals and radionuclides to seepage water. No contamination of deep groundwater was observed. On the other hand, the surface water of a nearby river revealed greater uranium concentrations in the tailing dam effluent discharge area than in a background river location sampling station. Lead-210 and 210Po were the principal contributors to the total dose while vegetables were the chief pathways of exposure, both for adults and children, to the studied radionuclides after closure. The results of the dose assessment indicate that permanent remedial actions will have to be adopted in the decommissioning phase.

Acid rock drainage and radiological environmental impacts ; A study case of the uranium mining and milling facilities at Pocos de Caldas

Acid rock drainage generated as a result of sulphitic minerals oxidation is a source of pollution in many mining sites all around the world. This is the case at the Uranium Mining Site of Pocos de Caldas, Brazil. The present study was aimed at studying the geochemical mechanisms involved on the mobilization of radionuclides from the waste rocks that occurs along with the acid drainage. The environmental radiological impacts caused by these pollutants were also assessed. It has been shown that precipitation of Ra and Pb as sulfates was the most important mechanism in the reduction of both radionuclides activity concentration in the acid drainage. A result of this study was that uranium isotopes were the most important radionuclides in terms of the exposure of the critical group. It has been suggested that the recovery of uranium from the acid drainage would be a feasible practice, economical aspects taken into account. It has also been estimated that pyrite oxidation will occur for more than a thousand years. The long time scale involved on the oxidation of the pyritic material implies the need for the adoption of permanent remedial actions. To assess applicable remediation strategies it has been suggested that oxygen and temperature profile determinations should be carried out in the dump.

Assessment of acid rock drainage pollutants release in the uranium mining site of Poços de Caldas--Brazil.

We compared three different techniques to assess acid drainage occurrence connected to pyritic waste rock piles at a uranium mining and milling site in Poços de Caldas--Brazil: (1) mass balance calculations, (2) column leaching experiments and (3) geochemical modelling. The study site was chosen because all the drainage coming from the pile is collected in one holding pond and a huge database (monitoring program) was available. The three independent methods predicted similar values for the intrinsic oxidation rate (IOR) (about 10(-9) kg m-3 s-1). We estimate the total time for consumption of all oxidizable material in the dump to be greater than 500 years. Geochemical model results showed a good agreement between predicted sulphate concentrations in relation to those found in the waste pile drainage, although the Al values were overestimated and pH values were underestimated.

Heavy-metal pollution assessment in the coastal lagoons of Jacarepaguá, Rio de Janeiro, Brazil

The Jacarepaguá lagoon receives the waste from 239 industries and domestic sewage. Bottom sediment analysis revealed that metal pollution is not spread over the lagoons but restricted to the discharge areas of the main metal-carrier rivers. Metal concentrations in superficial water showed the following concentrations values in ng/ml: Zn, 9.63+/-3.59; Pb, 0.61+/-0.43; Cu, 0.94+/-0.45; Mn, 12.7+/-8.0. Metal concentration in fish (average of seven different species) presented the following results, in mg/kg wet weight: Cr, 0.08+/-0.01; Cu, 0.4+/-0.15; Zn, 4.6+/-3.4; Fe, 2.4+/-1.3; Mn, 0.4+/-0.3. These results imply, considering fish consumption rate and the RfD (USEPA Reference Dose), that the local population is not exposed to undue health risks. Metal concentrations in the water may, however, increase due to their dissolution induced by pH and redox changes in the sediments.

Environmental radiological impact associated with non-uranium mining industries: a proposal for screening criteria

Niobium, phosphate, coal and gold mining facilities have been selected as case studies with the aim of identifying possible sources of radiological impact during and after cessation of industrial operations. The results have shown that acid drainage, as well as chemical processing of mineral ores, constitute relevant impact indicators for present-day and future scenarios. The possible use of solid wastes abandoned at the end of the operations represents a long-term radiological concern. Therefore, it is necessary that Brazilian legislation for environmental licensing be revised taking into account the potential environmental and radiological impacts caused by these industries and establishing remedial procedures for waste storage areas in the existing sites. The indicators developed and procedures carried out can be used in screening for decisions on the adoption of regulatory requirements for practices at such types of installations.

Human health risk screening of radioactive and nonradioactive contaminants due to uranium industry operation

Abstract This paper presents a human health risk screening of radioactive and non-radioactive contaminants in the off-site surface water environment downstream of an uranium mining and milling facilities. Two hypothetical critical groups were considered. Exposure pathways includes the use of river water for ingestion, swimming, irrigation of crops and cattle watering. The screening analysis pointed out that the non-radioactive contaminants —manganese, fluoride and uranium (due to its chemical toxicity)—are of more concern than the radioactive ones. Water and vegetables ingestion were assessed as the most important exposure pathways. These results indicated that despite the fact that in these kind of facilities most of the attention were focused on radiation risks, non radioactive contaminants may be of greater concern.

Identifying and overcoming the constraints that prevent the full implementation of decommissioning and remediation programs in uranium mining sites

Environmental remediation of radioactive contamination is about achieving appropriate reduction of exposures to ionizing radiation. This goal can be achieved by means of isolation or removal of the contamination source(s) or by breaking the exposure pathways. Ideally, environmental remediation is part of the planning phase of any industrial operation with the potential to cause environmental contamination. This concept is even more important in mining operations due to the significant impacts produced. This approach has not been considered in several operations developed in the past. Therefore many legacy sites face the challenge to implement appropriate remediation plans. One of the first barriers to remediation works is the lack of financial resources as environmental issues used to be taken in the past as marginal costs and were not included in the overall budget of the company. This paper analyses the situation of the former uranium production site of Poços de Caldas in Brazil. It is demonstrated that in addition to the lack of resources, other barriers such as the lack of information on site characteristics, appropriate regulatory framework, funding mechanisms, stakeholder involvement, policy and strategy, technical experience and mechanism for the appropriation of adequate technical expertise will play key roles in preventing the implementation of remediation programs. All these barriers are discussed and some solutions are suggested. It is expected that lessons learned from the Poços de Caldas legacy site may stimulate advancement of more sustainable options in the development of future uranium production centers.

Considerations about tenorm: A study case on niobium facilities

Abstract— Two niobium mining facilities located at two different geological settings were selected as case studies for assessing the radiological impacts associated with mining and milling activities. The impacts were assessed both for operational and post-operational (future unrestricted use of the area) scenarios. The work methodology encompassed sampling and analysis of different materials along the operational process, including wastes, effluents and by-products, mass balance calculations, and dose assessment. The exposure scenario considered during the operational phase included the land use by hypothetical groups of members of the general public. In the case of post-operational phase the possible occupation of contaminated areas was considered. The results pointed out that during the operational phase of the investigated industries no relevant impacts could be attributed to them. However, in the case of the potential occupation of the contaminated areas where the wastes are being deposited, the unrestricted use of these areas cannot be accepted in terms of the relevant radiation protection requirements.

Evaluation of Metal Dynamics in Sediments of a Tropical Coastal Lagoon by Means of Radiotracers and Sequential Extractions

Jacarepagua tropical coastal lagoon, located in the south of Rio de Janeiro City, Brazil, undergoes a severe process of eutrofization and heavy metal pollution. Dredging of bottom sediment is an usual practice in the system which may account for metal remobilization, and consequently, increase of their concentration in the overlying water.