M. L. Dinis

Exposure Assessment to Heavy Metals in the Environment: Measures to Eliminate or Reduce the Exposure to Critical Receptors

The anthropogenic sources for heavy metals include mining, industrial productions, untreated sewage sludge and combustion by-products produced by coal burning power plants. Atmospheric emissions are probably the most preoccupant to human health and to the environment due to either the great quantity involved, or their widespread dispersion. Mercury, lead and cadmium represent a great issue, mostly due to their ability to travel long distances in the atmosphere before deposition. Exposure assessment to emissions of heavy metals implies to identify and quantify the sources, how heavy metals may be dispersed in the environment and which adverse effects they might cause on human health and on the ecosystem. Heavy metals emissions and releases into the environment are available at the European Pollutant Release and Transfer Register (E-PRTR, 2010). In this data base main sources from 27 European countries are identified. Data concerning Cd, Hg and Pb were extracted for the year of 2007. This work focuses on the review and analysis of the principal sources of heavy metals emissions into the environment and their role in critical receptors’ environmental exposure. The review of the principal sources may give a clearer picture of the situation: the potential regions at risk and the extension of the contamination, essential to the exposure assessment by critical receptors. On the other hand, exposure assessments studies and consequent research allow a better knowledge of heavy metals sources, emissions, pathways and fate in the environment. Therefore both a complete exposure assessment and a consequent risk assessment are needed to establish the identification and implementation of measures to eliminate or to reduce the exposure.

Recycling of pultrusion production waste into innovative concrete-polymer composite solutions

In this study, the added value resultant from the incorporation of pultrusion production waste into polymer based concretes was assessed. For this purpose, different types of thermoset composite scrap material, proceeding from GFRP pultrusion manufacturing process, were mechanical shredded and milled into a fibrous-powdered material. Resultant GFRP recyclates, with two different size gradings, were added to polyester based mortars as fine aggregate and filler replacements, at various load contents between 4% up to 12% in weight of total mass. Flexural and compressive loading capacities were evaluated and found better than those of unmodified polymer mortars. Obtained results highlight the high potential of recycled GFRP pultrusion waste materials as efficient and sustainable admixtures for concrete and mortar-polymer composites, constituting an emergent waste management solution.

Integrated Methodology for the Environmental Risk Assessment of an Abandoned Uranium Mining Site

We developed an integrated approach to evaluate quantitatively the fundamental data required to perform a risk assessment induced by the existence of uranium mine tailings disposals or any other form of low activity waste storage. From the characteristics of the radioactive sources the different types of possible releases are evaluated using phenomenological models. The concentrations in the main environmental compartments are deduced. To this data we apply models of environmental transport, dispersion and fate within each environmental compartment, as well as models of inter-compartment transfer. The activity is then predicted at predefined exposition locations, in each environment compartment. Models of transfer to the food chain were also developed allowing to estimate concentration of different radioisotopes in all the media. This data, complemented with an exposure scenario, allows a quantitative environmental risk assessment.

Exposure Assessment to Radionuclides Transfer in Food Chain

Generally sites with radioactive contamination are also simultaneously polluted with many other different t oxics, especially heavy metals. Besides the radioactivity, these wastes may also hold different amounts of chemicals, toxic pollutants and precipitates. Th e radionuclides released into the environment can give rise to human exposure by the transport through the atmosphere, aquatic systems or through soil sub-compartments. The exposure may result from direct inhalation of contaminated a ir or ingestion of contaminated water, or from a less direct pathway, the ingestion of contaminated food products. Contamination of the tr ophic chain by radionuclides released into the environment will be a component of human exposure to ionizing radiations by transferring the radionuclides into animal products that are components of the human diet. Thi s can occur by first ingestion of contaminated pasture by animals and th en by ingestion of animal products contaminated. The relevant incorporation o f the radionuclides into cows milk is usually due to the ingestion of conta minated pasture. This transfer process is often called the pasture-cow-milk exposure route. A compartment dynamic model is presented to describe mathematically the radium behaviour in the pasture-cow-milk exposure route and predict the activity concentrat ion in each compartment. The dynamic model is defined by a system of linear differential equations with constant coefficients b ased in a mass balance concept. For each compartment a transient mass balance equation defines the relations between the inner transformations and the input and output fluxes. The concentration within each compartment is then trans cribed to doses values based on a simplified exposure pathway and a pre-de fined critical group.

Simulation of Liberation and Transport of Radium from Uranium Tailings

The uranium tailings contain a large amount of radium, besides other radionuclides like uranium, thorium, polonium and lead. The transport and fate of radionuclides in groundwater are assumed to follow the theoretical approach represented by the basic diffusion/dispersion — advection equation. Our algorithm uses the analytical solution for the one dimensional steady-state transport problem of a reactive substance with simultaneous retardation and radioactive decay. The final output is the radionuclides concentration in a hypothetical well location as function of the elapsed time.

Using Monte-Carlo simulation for risk assessment: application to occupational exposure during remediation works

The aim of this study was to apply the Monte-Carlo techniques to develop a probabilistic risk assessment. The risk resulting from the occupational exposure during the remediation activities of a uranium tailings disposal, in an abandoned uranium mining site, was assessed. A hypothetical exposure scenario was developed and two different pathways were compared: internal exposure through radon inhalation and external through gamma irradiation from the contaminated tailings material. The input variables, such as the inhalation rate and the external exposure parameters, were considered as specific probabilistic distributions, each one characterized by its central tendency and dispersion parameters. Using the cumulative distribution function, a probabilistic value for each variable can be generated using a single random number. Thus, this methodology allows performing a probabilistic risk assessment generating a risk distribution.

Simulation of the Radon Flux Attenuation in Uranium Tailings Piles

Tailings wastes are generated during the milling of certain ores to extract uranium and thorium. In the recent past uranium mill tailings consisted of fine-grained sand and silt materials, usually disposed in large piles in an open air area. Radium is probably the most hazardous constituent of uranium tailings. It produces radon, a radioactive gas which can easily spread into the environ- ment. Airborne radon decays into a series of short half-life products that are hazardous if inhaled. Tailings also emit gamma radiation which can increase the incidence of cancer and genetic risks. Post closure and site rehabilitation involves, among other situations, controlling and estimating radon release from the surface of the tailings pile. Generally the primary cleanup method consists of enclosing the tailings with compacted clay or native soil to prevent the release of radon and then covering this layer with rocks and vegetation. This implies a cover design and placement which will give long term stability and control to acceptable levels of radon emission and gamma radiation, preventing also erosion and water infiltration into the tailings. An algorithm based on the theoretical approach of diffusion was developed to estimate radon attenuation originated by a cover system placed over the tailings pile and subsequently the resulting concentration in the breathing atmosphere. The one dimensional steady-state radon diffusion equation was applied to a porous and multiphase system to estimate the radon flux from the tailings to the surface. The thickness of a cover that limits the radon flux to a stipulated value was performed for a particular contaminated site. The efficiency of the cover attenuation was evaluated from the comparison with the resulting radon concentration in the absence of any cover system.

Dispersion Modelling of Natural Radionuclides 238U, 232Th and 40K Released from Coal-Fired Power Plants Operations

The aim of this work was to simulate the radionuclides dispersion in the surrounding area of a coal-fired power plant, operational during the last 25 years. The dispersion of natural radionuclides (236Ra, 232Th and 40K) was simulated by a Gaussian plume dispersion model with three different stability classes estimating the radionuclides concentration at ground level. Measurements of the environmental activity concentrations were carried out by γ-spectrometry and compared with results from the air dispersion and deposition model which showed that the stability class D causes the dispersion to longer distances up to 20 km from the stacks.

MODELING THE TRANSPORT AND FATE OF CONTAMINANTS IN THE ENVIRONMENT: SOIL, WATER AND AIR

The environmental effects originated by u ranium mining activities result mainly from the wastes generated by the ore processing. Large quantities of radioactive wastes are generated in this extract ive process requiring a safe management. Besides the radioactivity these wastes may also hold different amounts of chemicals used in the extraction process , toxic pollutants associated with the mineralization and precipitates provoked b y pH or Eh alterations. The main concern of waste management and long term stabilization is to confine the residues in order to reduce the dispers ion of contaminants to concentrations that not exceed the trigger values c onsidered to be safe: there is thus a need to ensure that the environmental and he alth risk from these materials are reduced to an acceptable level. Howev er, the confinement will always represent a potential source of environmenta l contamination to the air, soil, superficial water and groundwater, due to the contaminants release and transport in the environment, which may occur by na tural erosion agents like rainfall or wind.

Simulation of Liberation and Dispersion of Radon from a Waste Disposal

Radon emissions from a radioactive waste disposal may constitute a major source of environment contamination and consequently a potential health hazard to the nearby population. Gaseous Radon-222 is generated from the radioactive decay of Radium-226 present in the tails. When it is formed, radon is free to diffuse along the pores of the residues to the surface and escape to the atmosphere.