Semi-volatile Metals Research Articles

Gaseous CdCl2 and PbCl2 adsorption by limestone at high temperature: Mechanistic study through experiments and theoretical calculation

There is a risk of heavy metal emission during solid waste incineration, and the capture of gaseous semi-volatile metal by mineral sorbents is an effective method for its pollution control. As a cheap and common additive for combustion industry, limestone is an effective sorbent for controlling various gaseous pollutants, but its high-temperature sorption mechanism for gaseous metal chlorides has not been systematically studied yet. In this study, an experimental study in a fixed bed furnace and density functional theoretical study were conducted to investigate the adsorption mechanism of gaseous CdCl2 and PbCl2 by limestone at high temperature. The capture performance was greater at a higher temperature due to the formation of an enhanced pore structure through limestone decomposition, while the efficiency decreased at temperatures higher than 700 °C because of the negative movement of the reaction equilibrium. Additionally, the higher equilibrium constant of CdCl2 caused more effective adsorption than PbCl2. According to theoretical calculations, both limestone and lime can adsorb molecular metal chlorides while lime has higher adsorption energies due to its more active surface. For a commercial application, it is recommended to inject limestone into the furnace at a high temperature to capture heavy metal more effectively.

Theoretical study on the adsorption mechanism of PbCl2/CdCl2 by kaolinite during municipal solid waste pyrolysis

In the process of municipal solid waste (MSW) pyrolysis, kaolinite possesses an outstanding trapping effect on semi-volatile metal vapors (Pb, Cd) through physical and chemical adsorption. In this paper, the microscopic mechanism of PbCl2 and CdCl2 adsorption on the surface of Al rings and Si rings of kaolinite was investigated by combining Monte Carlo method with density functional theory (DFT). The calculations indicate that the continuously enriched pore structure in the process of dehydroxylation indirectly influences the adsorption of PbCl2/CdCl2 by kaolinite. Under the non-bond interaction and electron transfer induction, PbCl2 molecules are more conveniently adsorbed on the Al-(001) surface than CdCl2, while the adsorption sites of CdCl2 molecules are more widely distributed on the Si-(001) surface. Moreover, the transform in the Al-coordination and the exposed active oxygen atoms significantly affect the adsorption activity of kaolinite (the capability to gain and lose electrons). Considering the energy barrier and electrophilic nucleophilic sensitivity, it is more feasible for PbCl2/CdCl2 to be adsorbed near IV/V-coordinated Al and active O under Van der Waals action. Subsequently, IV/V-coordinated Al will act as an electron acceptor, and the active oxygen atoms after dehydrogenation will serve as an electron donor. Under the induction of the energy difference of frontier orbitals, the electrons transfer will encourage the formation of more stable adsorption states. The results shed new light on strengthening the adsorption activity of kaolinite to PbCl2/CdCl2 in the process of MSW pyrolysis.

Characteristics of the sub-micron ash aerosol generated during oxy-coal combustion at atmospheric and elevated pressures

This paper is concerned with the effect of pressure on the particle size distribution and the size-segregated composition of the sub-micron ash aerosol created during oxy-coal combustion under near practical self-sustaining combustion conditions. The problem is important because pressurized oxy-coal combustion has been proposed as one promising technology to minimize CO2 emissions. Sub-micron ash plays a major role in ash deposition mechanisms, which, in turn, can control boiler performance. In this work, the same bituminous coal was burned at pressures of 1, 8 and 15 bar in O2/CO2 environments. Tests employed a 100 kW (rated) oxy-fuel combustor (OFC) operated at atmospheric pressure (1 bar) and a 300 kW (rated) entrained-flow pressurized reactor (EFPR) at elevated pressures (8 and 15 bar). Although these tests were conducted under near practical combustion conditions, confounding effects of peak flame temperature variations were minimized for the 1 bar and 15 bar tests, allowing the role of elevated pressure to be isolated. For the EFPR tests, a specially designed sampling system was used to sample sub-micron ash aerosols from the pressurized combustor and is described in detail. Results showed that at the same peak temperature but higher pressure, the fractions of ash aerosol partitioned into the PM0.6 and PM1 size fractions were greatly diminished. Moreover, elevated pressures caused significant changes in the composition of the (size-segregated) sub-micron aerosol, especially in its alkali content, which increased significantly. Examination of fractions of each element that ended up in the sub-micron fume suggested that, at constant temperature, the effect of pressure on vaporization of semi-volatile metals was very different from that on the release into the gas phase of non-volatile metals and could not be explained by equilibrium.

Desulfurization using limestone during sludge incineration in a fluidized bed furnace: Increased risk of particulate matter and heavy metal emissions

Incineration of sludge can be an effective method to minimise waste whilst producing useful heat. However, incineration can cause secondary pollution issues due to the emission of SO2, therefore a set of experiments of sludge incineration in a bubble bed furnace were conducted with limestone addition to study desulfurization of sludge incineration flue gas. As expected, over 93% emission of SO2 was reduced with limestone addition, and that of CO and NOx were increased and decreased respectively when the fuel feeding rate raised. The distribution of fly ash was also increased by raising the fuel feeding rate due to increasing fragmentation of the ash. However, distributions of PM2.5 and heavy metals in submicron particles have dramatically increased with limestone desulfurization. The mechanism was revealed by SEM and EDS statistical analysis, indicating that the reaction between aluminosilicate and calcium made particles agglomerate and eutectic mixtures form, these larger ash particles were found to divide between collection as cyclone ash and fragmentation into finer particles that bypassed the cyclone. Those fine particles provided more surface area for heavy metal condensation. Furthermore, it was found that the reaction mechanism for semi-volatile metals involved them being released from the sludge and forming PM1 particles due to the vaporization-condensation mechanism, leading to higher emission of PM1 and distribution of heavy metals in PM1. Thus, it should be considered that there may actually be higher emission risks of PM and heavy metal emissions when aiming to desulfurize a flue gas using Ca-based minerals in certain circumstances.

Use of semi-volatile metals as a new vectoring tool for VMS exploration: Example from the Zn-rich McLeod deposit, Abitibi, Canada

Volcanogenic massive sulfide (VMS) deposits are small targets (100's of meters) hosted in a hectometric to kilometric-scale zoned alteration halo, comprising narrow proximal chlorite and wider distal sericite zones. For exploration, identification of the distal fine-grained sericite halo related to fertile VMS systems is critical but remains challenging. Sericitization is a low-temperature hydrothermal alteration and its geochemical signature could be very similar to clay assemblages produced as the results of simple low-temperature prolonged seawater interaction with volcanic rocks on the seafloor. Currently, classical lithogeochemical methods (e.g., mass balance, element ratios) are not very efficient to decipher sericite alteration related to distal fertile VMS systems. However, semi-volatile metals have good potential as pathfinders, as they have a wider dispersion than major, or trace elements commonly used due to their enhanced mobility in hydrothermal fluids. New analytical improvements, involving four-acid digestion and advanced ICP-MS technology, now allows the accurate determination of semi-volatile metals at the ppb level.Using the Zn-rich McLeod deposit in the Matagami district (Abitibi, Canada) as a case study, we tested first the representativeness and advantage of the new analytical method, and secondly, the capacity of the semi-volatile metals for vectoring exploration. The new method is both accurate and precise and provided good resolution with low detection limits. The performance of classical lithogeochemical methods was compared with semi-volatile metal distribution (As, Se, Cd, In, Sn, Sb, Te, Hg, Tl, Bi) in the footwall rhyolite. Although the classical tools efficiently identified both the proximal chlorite and distal sericite zones, most of them (except Rb/Sr) cannot efficiently vector, as there is no systematic increase or decrease towards the mineralization. Conversely, overlapping alteration halos were identified using semi-volatile metals. The proximal signature (chlorite zone) is characterized by enrichment of Sb, Li ± Mo, W and U. The distal signature (sericite zone) is defined by successive appearance of higher values of Sn, W, and Tl up to 750 m, 1000 m and 1400 m away from the mineralization, respectively. This zoned spatial distribution of semi-volatile metals clearly allows better localization of a given altered sample within a wide and distal alteration halo, thus providing a solid vectoring tool for VMS exploration. This is especially true since the signal of semi-volatile metals extends far beyond both the visual sericite alteration (up to 200 m from mineralization) and classical lithogeochemical tools (up to 1000 m away). Specifically, the Tl/Co ratio records the widest footprint of the mineralization, up to 1400 m away from the deposit. It is well known that Tl is enriched in Zn-rich VMS. Thallium in the sericite alteration halo is here considered as an indicator for discriminating fertile volcanogenic hydrothermal systems from barren low-temperature convective cells.

Typical Gaseous Semi-Volatile Metals Adsorption by Meta-Kaolinite: A DFT Study.

Kaolinite can be used as in-furnace adsorbent to capture gaseous semi-volatile metals during combustion, incineration, or gasification processes for the purposes of toxic metals emission control, ash deposition/slagging/corrosion inhibition, ultrafine particulate matter emission control, and so on. In this work, the adsorptions of typical heavy metals (Pb and Cd) and typical alkali metals (Na and K) by meta-kaolinite were investigated by the DFT calculation. The adsorption energies followed the sequence of NaOH-Si surface > KOH-Si surface > PbO-Al surface ≈ CdO-Al surface ≈ NaOH-Al surface > KOH-Al surface > NaCl-Al surface ≈ Na-Si surface > Na-Al surface > KCl-Al surface > Pb-Al surface > PbCl2-Al surface > CdCl2-Al surface ≈ K-Si surface ≈ PbCl-Al surface > K-Al surface > CdCl-Al surface > NaCl-Si surface > KCl-Si surface > Cd-Al surface. Si surface was found available to the adsorptions of Na, K, and their compounds, although it was invalid to the adsorptions of Pb, Cd, and their compounds. The interactions between adsorbates and surfaces were revealed. Furthermore, the discussion of combining with the experimental data was applied to the subject validity of calculation results and the effect of chlorine on adsorption and the effect of reducing atmosphere on adsorption.

Applications and limitations of constrained high-resolution peak fitting on low resolving power mass spectra from the ToF-ACSM

Abstract. The applicability, methods and limitations of constrained peak fitting on mass spectra of low mass resolving power (m∕Δm50 ∼ 500) recorded with a time-of-flight aerosol chemical speciation monitor (ToF-ACSM) are explored. Calibration measurements as well as ambient data are used to exemplify the methods that should be applied to maximise data quality and assess confidence in peak-fitting results. Sensitivity analyses and basic peak fit metrics such as normalised ion separation are employed to demonstrate which peak-fitting analyses commonly performed in high-resolution aerosol mass spectrometry are appropriate to perform on spectra of this resolving power. Information on aerosol sulfate, nitrate, sodium chloride, methanesulfonic acid as well as semi-volatile metal species retrieved from these methods is evaluated. The constants in a commonly used formula for the estimation of the mass concentration of hydrocarbon-like organic aerosol may be refined based on peak-fitting results. Finally, application of a recently published parameterisation for the estimation of carbon oxidation state to ToF-ACSM spectra is validated for a range of organic standards and its use demonstrated for ambient urban data.

Causes, Mechanisms and Prevention of Environmental Diseases

The onset of non-communicable disease has been attributed in large part to environmental exposure to toxic chemicals, including persistent organic pollutants, volatile and semi-volatile organic compounds and transition metals. This review summarizes recent research into the causes and mechanisms of environmental disease onset and examines the role of oxidative stress as well as steps that can be taken to predict and lower the incidences of environmental diseases.

Volatilization of Heavy Metals (As, Pb, Cd) During Co-Processing in Cement Kilns

Abstract Heavy metals emitted by flue gas during co-processing hazardous waste (HW) in cement kilns presents a serious threat to the environment. Volatilization characteristics of three semivolatile metals (As, Pb, and Cd) in different chemical forms (As2S3, NaAsO2, Na2HAsO4, PbS, PbO, PbCl2, CdO, CdS, CdCl2) during co-processing with cement raw materials were studied. Thermogravimetric experiments were performed to tentatively predict the lower limits of volatilization temperatures. Experiments involving co-processing of these compounds with cement raw meals was carried out at different temperatures over different time periods in an electric heated tube furnace to gain more insight into the macroscopic kinetic characteristics of volatilization. Volatilization of As, Pb, and Cd during co-processing with cement raw materials increases with time initially, and after 25 min, they do not volatilize. Temperature and compound speciation significantly affect metal volatilization. For Pb and Cd, volatilization wa...

Sources of elemental fractionation and uncertainty during the analysis of semi-volatile metals in silicate glasses using LA-ICP-MS

We investigate elemental fractionation and sources of analytical uncertainty during in situ determination of a range of semi-volatile trace metals (e.g., Cd, Sn, Pb, Zn, Cu, Mo) in silicate glasses using laser ablation-ICP-MS (LA-ICP-MS), and compare the performance of single-volume and two-volume ablation chambers. In a single-volume ablation chamber we document the differential response of volatile and refractory elements relative to 43Ca at different ablation sites within the ablation chamber as a primary source of analytical uncertainty. This fractionation is unrelated to interaction between the laser pulse and solid material during progressive ablation, but does correlate with the local He velocity at the position of analysis. Evidence suggests that fractionation relates to differences in behaviour of refractory and volatile elements during condensation from the laser-induced plasma, and interaction between condensate and the carrier gas. The dependence of fractionation on local He flow regime results in relatively poor reproducibility in 43Ca normalized ratios (up to ∼20%, 2 s) for a number of volatile metals as well as some with siderophile and chalcophile tendencies (e.g., B, Co, Cu, Zn, Mo, Ag, In, Sn, Sb, W, Pb). Fractionation of this type may be a major feature of many single-volume ablation chambers and also may occur in other instances where the He flow regime varies substantially with location in the ablation chamber. Analyses within a two-volume sample chamber, where the He flow rate at the site of ablation remains more uniform across the chamber, show no evidence for this style of elemental fractionation, and normalized ratios measured for volatile trace metals show reproducibilities for normalized ratios that are typically <10% (2 s).

High-temperature sorbents for Hg, Cd, Pb, and other trace metals: Mechanisms and applications

This paper is concerned with the sequestration of mercury, cadmium, lead, sodium and potentially other volatile and semi-volatile metals by high-temperature mineral, non-carbon based dispersed sorbents. The focus here is on kaolinite and lime powders (for Pb, Cd, and Na), and on intimate kaolinite/calcite/lime mixtures (for Hg), both of which undergo morphological and chemical changes when exposed to high temperatures. These changes play critical roles in the metal capture mechanisms, initially enhancing metal capture, either through a eutectic melt on the surface, or through some other transformation, but ultimately causing sorbent de-activation through a catastrophic melt that causes pore closure. Results and interpretation from two types of experiments are presented. The first employed a 20 kW downflow combustor, a low-pressure impactor and application of the aerosol fractionation method to quantitatively determine the fraction of metal sequestered by the sorbent at the sampling point. The second employed an externally heated quartz reactor and simulated flue gases containing mercury and injected sorbent. Quantitative, rate models have been extracted from the data to describe the global reactions of dispersed kaolinite with lead, sodium, and cadmium metal vapors. They have also been derived for the global reaction of cadmium with dispersed hydrated lime, which was ineffective for Na and Pb but very effective for Cd. Qualitative results showing the effective scavenging of Pb and Cd by the intimate kaolinite/calcite/lime mixture are also presented. The intimate kaolinite/calcite/lime mixture was also shown to capture metallic mercury through two mechanisms, namely, an in-flight mechanism and one involving interactions between Hg, the sorbent and the quartz reactor walls. The in-flight mechanism had similarities to those observed previously between kaolinite, lead, cadmium and sodium, in that mineral transformations played a key role in both sorbent activation and sorbent de-activation. At a constant residence time, the in-flight mechanism exhibited a maximum effectiveness at 900 °C, followed by apparent de-activation. Spent in-flight sorbent showed the presence of calcium silicates and calcium aluminosilicates. The wall deposit mechanism increased in efficacy with temperature and did not show a maximum, and showed the presence of substantial amounts of captured mercury. Adding to the complexity of this process is that Hg capture by this mixture required the presence of O 2 in the flue gas, albeit at low levels of 4000 ppm.

In-furnace capture of cadmium and other semi-volatile metals by sorbents

An 18 kW, cylindrical (inside diameter = 15-cm), 6-m high, laminar, downflow furnace was used to investigate the mechanisms governing reactive scavenging of cadmium vapors from combustion environments, by hydrated lime and kaolinite powder sorbents. Two major physical mechanisms dominate the reaction rate and sorbent utilization during the capture of semi-volatile metal by kaolinite, temperature-activated eutectic-melting-enhanced capture and excessive-melt deactivation, initiated at a higher temperature than the enhancement. However, cadmium forms higher temperature eutectics than other semi-volatile metals such as lead and sodium, which have a transition to a deactivating melt below 1100 °C. The network modifier responsible for the reaction enhancement is the metal/sorbent reaction product itself, which forms a eutectic with the remaining, unreacted sorbent. Global rate models were developed to describe the reaction of kaolinite with lead, sodium, and cadmium metal vapors. The following reaction scheme was valid for all three metal vapors, Na/Pb/Cd: Na 2 O / PbO / CdO + 1 2 ( Al 2 O 3 · 2 SiO 2 ) ⇒ P Na / Pb / Cd . Followed by the substrate (melting) deactivation step for Na and Pb, but not for Cd: P Na / Pb + 1 2 ( Al 2 O 3 · 2 SiO 2 ) ⇒ D + P Na / Pb . Eutectic-melting enhancement of cadmium capture by both kaolinite and hydrated lime was initiated between 1160 and 1280 °C. Cadmium is more effectively captured at higher temperatures (i.e., ∼1300 °C) than other semi-volatile metals, such as lead and sodium, and requires even higher temperatures to cause sorbent deactivation by excessive melting. Unlike cadmium, lead and sodium were poorly scavenged by hydrated lime.

Bioavailability of Soil-Borne Chemicals: Method Development and Validation

ABSTRACT Chemicals present in contaminated soils generally exhibit altered bioavailability compared to other vehicles used in studies of chemical toxicity. Methods used to assess the bioavailability of soil-borne chemicals have generally been modified versions of methods that are widely used in biomedical research. Oral and dermal bioavailability of semivolatile organic chemicals and metals in soil has been assessed by a variety of in vivo and in vitro methods. Due to variations in metabolism and excretion of different chemicals, approaches to measuring bioavailability must be selected with an understanding of disposition of the chemical being studied. Standard methods need to be modified due to constraints associated with doses relevant to environmental concentrations, the need to reflect weathering behavior in soils over time, and the need to generate data applicable to human health risk assessments. Estimates of relative bioavailability for chemicals in soil can be used directly to modify exposure estimates. Application of bioavailability data in a site-specific risk assessment requires regulatory acceptance of the data. Acceptance of the data will generally be dependent on either the use of a validated test method or a careful scientific review of the test method employed. A process for validating newly developed alternative toxicity methods for routine use developed by the Interagency Coordinating Committee on the Validation of Alternative Methods provides relevant guidance for assessing in vitro methods, but method validation should not be the only litmus test for inclusion of bioavailability data in risk assessments.

High-temperature interactions between multiple-metals and kaolinite

High-temperature combustion flue gases provided the environments for this investigation of multiple-metals interactions with dispersed kaolinite. Whereas previous research was restricted to interactions of single-metals with kaolinite powders, this work focuses on understanding how kaolinite transformations induced by reaction with one metal species can affect the mechanisms of interaction with other metal species. Experiments were performed in an 18 kW downflow furnace, by doping combinations of semi-volatile metals through a natural gas flame, and injecting supermicron sized powder kaolinite sorbent into the post flame. An aerosol size fractionation method was used to quantify the fraction of metal captured. It was found that the melt-associated restructuring of the meta-kaolinite crystal, caused by eutectics formed with lead and sodium reaction products (self-enhancing for lead and sodium capture), enhances the capture of cadmium by kaolinite at 1160°C. Cadmium reaction products by themselves fail to initiate a self-enhancing eutectic-melt at this temperature, because cadmium forms a higher temperature eutectic with the meta-kaolinite crystal than does lead or sodium. In fact, at temperatures in the range 1000°C to 1300°C, cadmium enhances the capture of lead and sodium by slowing down the deactivating excessive-melt driven by the lead or sodium/sorbent eutectic at these temperatures. Hence, total metal capture is enhanced in this temperature range for the Cd/Pb and Cd/Na systems by the formation of an optimum eutectic-melt, whereby significant melt-enhancement is induced without sorbent deactivation. Lead and sodium reaction products form similar high-temperature eutectics with kaolinite. However, sodium capture dominates over lead capture with a slightly higher reaction rate than lead, thus achieving capture before the most significant sorbent deactivation occurs. Sodium also dominates by effectively displacing lead previously captured on sorbent sites. These observations are quantified using models that extend those developed for single-metal capture to multiple-metal situations.

Quantitative Analysis of High Temperature Toxic Metal Sorption Rates Using Aerosol Fractionation

The airborne emission of toxic metals, such as lead, arsenic, and cadmium, from coal-fired boilers and incinerators is a major problem. These metals, which are considered to be semivolatile, are vaporized in the flame and subsequently form submicron particles. Since submicron particles are difficult to remove, one strategy to prevent emission is to inhibit ultra-fine particle formation within the combustor. Recent work has demonstrated that the sorbents such as kaolinite and lime are able to capture semivolatile metal vapors at high temperatures, thus preventing nucleation and condensation at lower temperatures. However, to develop practical scale technology, the rate of metal sorption by sorbents must be quantified. In this paper, an aerosol size fractionation approach is proposed to determine the extent of metal vapor-sorbent interactions above the metal dew point. The applicability of this methodology is illustrated by determining the rate of capture of cadmium by powdered, kaolinite sorbent at high co...

A model for the particulate matter enrichment with toxic metals in solid fuel flames

A mathematical model for predicting the fate of toxic heavy metals during combustion is presented. The model accounts for the formation of new particles through nucleation and the growth of existing particles through the combined effects of condensation and coagulation. A key simplification enabling the development of a usable methodology is the subdivision of the particle size distribution into just two modes, one comprising fine particles and the other coarse particles. The toxic heavy metal calculations are embodied in a post-processor appended to a parent code for the prediction of the aerodynamics and combustion. Three flames are studied for a coal fuel, sewage sludge fuel and a blend of these two fuels. The partitioning and emissions of the semi-volatile metals, lead and cadmium, are predicted and compared with data collected in a large-scale laboratory combustor. The predicted metal enrichments on the small particles are remarkably well-predicted. However, it is concluded that heterogeneous condensation of the metal vapours alone is insufficient to explain fully the fate of metal vapours. Surface reaction and gas phase chemical reaction should also be considered, but the necessary chemical kinetic data are currently lacking. The results indicated that ash mineral matter, such as kaolinite, is an effective sorbent for lead, but not for cadmium. As expected, the coagulation of fine particles is influenced more by the particles number density than by combustion variables. It is also found that the scavenging of fine particles by coarse particles has little effect on the metal partitioning.

Multicomponent coagulation and condensation of toxic metals in combustors

The temporal evolution of the size-segregated composition of multiple, heavy metal, combustion-generated aerosols was investigated. The purpose was to gain insight into the competition between metal condensation and aerosol coagulation processes that affect the partitioning of toxic, heavy metals during combustion and their impact on the environment. Experiments were conducted on a2-to 16-kW downflow combustor, which supported a natural gas flame through which aqueous solutions of metal salts were sprayed. The behavior of both single metals and binary mixtures of lead and cadmium (which are both considered semivolatile) and of cadmium and nickel (the latter of which is refractory) was investigated. Particulate samples were withdrawn isokinetically through a rapid-dilution sampling probe from which they were quickly size segregated in a Berner low pressure impactor, allowing physical and chemical resolution in the submicron particle size range. Experimental data agreed with theoretical predictions using an existing literature model. This model solved the general dynamic equation numerically but was modified here to include the effects of film condensation in a simple manner. For samples withdrawn above the semivolatile metal dew points, theory showed that nucleation of the semivolatile metal in the probe, followed by coagulation, could explain completely, the measured size-segregated composition. With similar dew points and number concentrations, cadmium and lead particles interacted primarily through coagulation. However, cadmium and nickel particles did not interact by coagulation in the probe because of disparties in particle size and number concentrations. Further down the furnace, both model and data showed that compositions of particles were determined by condensation on existing nickel particles, rather than by nucleation of the semivolatile component (cadmium), followed by coagulation. These results are consistent with a literature hypothesis, on the effect of temperature quench rate on pertinent aerosol mechanisms.

Evaluation of the public health risks associated with semivolatile metal and dioxin emissions from hazardous waste incinerators.

The public health impacts associated with stack emissions from hazardous waste incinerators have become a major concern in recent years. Most evaluations of incinerator stack emissions have focused on three classes of compounds: metals, semivolatile, and volatile compounds. These investigations have been complicated by the difficulty and expense of analyzing the emissions and the limited amount of toxicity information for many of the compounds that have been detected. The results of over 20 trial burns at hazardous waste incinerators were assembled in an attempt to determine which compounds may pose a significant threat to the public health. The risks associated with semivolatile emissions were found to be inconsequential, although further study of dioxins and dibenzofurans emissions appears to be warranted. The risk associated with the emission of cadmium and perhaps chromium (VI) may pose a significant risk to public health at certain facilities. Controls on waste feed or air pollution control devices should be employed to reduce the emission of these metals. Any monitoring of metal emissions from hazardous waste incinerators should focus on cadmium and chromium (VI).

Evaluation of the Public Health Risks Associated with Semivolatile Metal and Dioxin Emissions from Hazardous Waste Incinerators

The public health impacts associated with stack emissions from hazardous waste incinerators have become a major concern in recent years. Most evaluations of incinerator stack emissions have focused on three classes of compounds: metals, semivolatile, and volatile compounds. These investigations have been complicated by the difficulty and expense of analyzing the emissions and the limited amount of toxicity information for many of the compounds that have been detected. The results of over 20 trial burns at hazardous waste incinerators were assembled in an attempt to determine which compounds may pose a significant threat to the public health. The risks associated with semivolatile emissions were found to be inconsequential, although further study of dioxins and dibenzofurans emissions appears to be warranted. The risk associated with the emission of cadmium and perhaps chromium (VI) may pose a significant risk to public health at certain facilities. Controls on waste feed or air pollution control devices should be employed to reduce the emission of these metals. Any monitoring of metal emissions from hazardous waste incinerators should focus on cadmium and chromium (VI).