Catálogo de publicaciones - libros

Experimental methods and models for assessing the risks of recycling waste products are described in this chapter. The basic processes determining the fate of the chemicals in the recycled waste products are also introduced. Two hydrological models are presented: MIKE SHE, which is an integrated groundwater and surface water model, and the MACRO model, which is a relatively simple one-dimensional leaching model. The four case studies included in this chapter give examples on how work on the risk of recycled waste products containing potential hazardous substances (e.g., pesticides, boring chemicals, pesticide residues and antibiotics) has been carried out.

Portland cement concrete (PCC) is widely used in transportation networks. In addition to its use in pavements, PCC is the primary construction material in bridges, tunnels, over passes, under passes, and similar vital structures in our highway systems. Other related applications include grouting, pipe bedding, and soil stabilization. Use of PCC is also associated with the use of a large number of admixtures. The leaching of chemical constituents from PCC and the effect of removal, reduction, and retardation (RRR) processes on these constituents were assessed by a series of laboratory tests and analyses. PCC leachate was subjected to chemical and toxicity testing to identify specific constituents that are responsible for the observed aquatic impacts. PCC leachate without the plasticizer admixture exhibited a low aquatic toxicity for the test organisms and . PCC-with-plasticizer leachate indicated high growth inhibition (toxicity) for . It is likely that the small amount of plasticizing admixture and significant levels of aluminum in the leachate contributed to the toxicity observed in the PCC leachate. Complete detoxification of PCC leachates by three representative test soils, Woodburn soil (), Olyic soil (), and Sagehill soil (), was observed during soil sorption tests. No significant changes in the algal EC values by photolysis, but a three fold decrease in toxicity due to biodegradation, were observed for when compared with the control leachate. Results suggest that the observed toxicity in PCC with-plasticizing-admixture leachates is readily reduced or removed only by the environmental processes of soil sorption and biodegradation.

Combustion residues, such as alkaline lignite fly ashes, are produced worldwide in ever-increasing quantities. Combustion residues, however, may pollute the environment because they are enriched in potentially toxic elements relative to soils and sediments. For a proper assessment of the environmental impact of the utilisation and disposal of the ash it is necessary to understand the effect of the mobilisation of potentially hazardous elements from ash residues. Trace metals, though present as a relatively small fraction in fly ash, are of special interest, due to their cumulative build up, long life, and high toxicity to man, plants, and animals. Since trace elements existing in fly ash can leach out and contaminate soil as well as surface and groundwater resources, their study has recently been regarded as important in connection with the protection of the environment.

The management of fly ash produced by coal fired power plants remains a major problem in many parts of the world. Although significant quantities are being used in a range of applications and particularly as a substitute for cement in concrete, large amounts are not used which requires disposal. Those quantities are disposed sometimes on unlined landfills. The original ash contains certain amounts of toxic elements and heavy metals. Such material, if inadequately deposited, can produce surface and ground water leachate pollution.

Uses of fly ash have included the manufacture of lightweight aggregate, road base construction, landfill liners, sewage sludge treatment, as a filler in plastic composite materials, as well as the manufacture of Portland cement, etc. The use of fly ash in the ceramics industry and particularly as a component in the manufacture of bricks and tiles has also been investigated. This industry uses large volumes of silicate-based raw materials and therefore has the potential to utilize significant amounts of fly ash. Research is therefore needed to develop new alternative applications that can further exploit fly ash, which needs to be increasingly regarded as a raw material with a potential for processing into new products rather than a waste.

Samples of lignite fly ash from the thermal power plant "Nikola Tesla" (Serbia) were investigated in the Case Study. Sintering, as a method of fly ash recycling, reduces leaching concentrations of elements. Special attention was paid to the determination of leaching properties by the Generalized Acid Neutralizing Capacity Procedure (GANC). Results of the analysis emphasise that the fly ash samples sintered at different temperatures have much lower leaching concentrations than the raw fly ash samples.

Whole effluent toxicity (WET) tests are useful, predictive tools for assessing toxicity impacts on the environment. The general purpose of the WET tests is to identify and characterize the toxic effects of effluents or leachates on aquatic resources. WET tests are applied for ecotoxicological assessment of solid wastes and industrial byproducts for use as highway materials, including coal fly ash and bottom ash, steel-slags, municipal incinerator bottom ash, Portland cement concrete, and phosphogypsum. WET tests integrate interactions among complex mixtures of contaminants and measure total toxic effect, regardless of physical and chemical compositions. They are holistic, simple, cost effective and conducted under controlled conditions. However, there are also limitations in the assessment, such as inherent variability of these tests, differences in species sensitivity, and differences in environmental conditions between the laboratory and the receiving environment. In addition, waste and industrial by-products bring in their own set of complexities with respect to the composition of their leachates, which may include pH, alkalinity and hardness values that fall outside the acceptable toxicity test range. Altering these factors to suit the test conditions may effectively alter the speciation and subsequently the bioavailability of chemicals in the waste leachate. For instance, altering the pH of a waste material leachate can cause precipitation of some chemicals effectively altering their bioavailability. Because of these complexities, it is imperative that caution be exercised when interpreting the WET test results and using these values as primary decision guidelines for use of waste and industrial by-products in highway construction.

Prior to the 1970s, principles involving the fate and transport of hazardous chemicals from either hazardous waste spills or landfills into ground water and/or surface water were not fully understood. In addition, national guidance on proper waste disposal techniques was not well developed. As a result, there were many instances where hazardous waste was not disposed of properly, such as the Love Canal environmental pollution incident. This incident led to the passage of the Resource Conservation and Recovery Act (RCRA) of 1976. This act gave the United States Environmental Protection Agency regulatory control of all stages of the hazardous waste management cycle. Presently, numerous federal agencies provide guidance on methods and approaches used to evaluate potential health effects and assess risks from contaminated source media, i.e., soil, air, and water. These agencies also establish standards of exposure or health benchmark values in the different media, which are not expected to produce environmental or human health impacts. The risk assessment methodology is used by various regulatory agencies using the following steps: i) hazard identification; ii) dose-response (quantitative) assessment; iii) exposure assessment; iv) risk characterization. The overall objectives of risk assessment are to balance risks and benefits; to set target levels; to set priorities for program activities at regulatory agencies, industrial or commercial facilities, or environmental and consumer organizations; and to estimate residual risks and extent of risk reduction.

The chapter will provide information on the concepts used in estimating risk and hazard due to exposure to ground and surface waters contaminated from the recycling of hazardous waste and/or hazardous waste materials for each of the steps in the risk assessment process. Moreover, this chapter will provide examples of contaminated water exposure pathway calculations as well as provide information on current guidelines, databases, and resources such as current drinking water standards, health advisories, and ambient water quality criteria. Finally, specific examples of contaminants released from recycled hazardous waste materials and case studies evaluating the human health effects due to contamination of ground and surface waters from recycled hazardous waste materials will be provided and discussed.

Chemodynamics (the fate and transport) of leachates from recycled solid waste materials (SWMs) of complex organic mixtures (COMs) is a basic need in environmental planning, restoration and engineering management. Sorption/desorption, an important chemodynamic behavior of leachates, can greatly influence the mobility and bioavailability of compounds from recycled wastes in the multimedia environment. Similar to all interphase mass-transfers, the sorption/desorption process can be defined by the final-phase equilibrium of the contaminant at the aqueous-solid phase interface and the time required to approach final equilibrium. Accordingly, aqueous-solid phase interfaces are significant in determining: (1) the route and rates by which organic contaminants can transfer to and/or from these interfaces, (2) the chemodynamics of contaminants, and (3) their toxicity, genotoxicity and bioavailability to the ambient microorganisms. When the rates of such processes are known, environmental fate modeling can provide an educated estimate and prediction of the accessibility and bioavailability of a target contaminant leached from SWMs to a specific transport mechanism in the environment. Therefore, the present chapter is an attempt to assess fate (in terms of contaminant mobility using predictive sorption or desorption coefficients), as well as effects (in terms of bioavailability) of various contaminants, and to correlate these observations for development of predictive relationships.

To fulfill this general objective, the following interdisciplinary approaches are covered in the present chapter: (1) a review of the most widely used models analyzing sorption/desorption data generated for leachates from recycled SWMs, discussion of their chemical kinetics, and estimates of their transport parameters from laboratory studies; (2) a discussion of the fundamentals of both quantitative structure-activity and structure-property relationships (QSARs and QSPRs, respectively), with special emphasis on using molecular connectivity indices as useful properties to predict contaminant mobility and bioavailability, and (3) a review of the multicomponent (multicontaminant) joint toxic/genotoxic effect models (additivity, synergism, antagonism) used to predict the bioavailable fraction and action of organic contaminants at aqueous-solid phase interfaces. The applicability of these interdisciplinary approaches is discussed and evaluated using a group of toxic and carcinogenic contaminants, such as polycyclic aromatic hydrocarbons (PAHs), which are frequently characterized in most recycled solid wastes of complex organic mixtures.