Modified Toxicity Characteristic Leaching Procedure Research Articles

Buyer beware: Inexpensive, high cadmium jewelry can pose severe health risks

The use of cadmium to produce inexpensive jewelry has recently been documented. Governments have adopted varying standards, with US states focused on either total cadmium content or extractable cadmium from children's jewelry, while the European Union has adopted a limit of 100 mg/kg cadmium for all jewelry. This study evaluated 80 items purchased at a discount jewelry store. The objective was to determine prevalence of cadmium in this jewelry, the amount of cadmium released by simulated mouthing or ingestion, and to confirm previous reports that damage to jewelry can increase cadmium release. Finally, a modified toxicity characteristic leaching procedure (TCLP) assessed the potential for jewelry to release cadmium after disposal. Thirty-two (40%) items showed detectable cadmium by X-ray fluorescence. Nine high‑cadmium pendants and rings with cadmium content ranging from 31.3 to 89.2% were subjected to extractions simulating mouthing or ingestion. Seven of nine items extracted in dilute saline to simulate mouthing released more than the US recommended maximum of 18 micrograms. Damaged jewelry released more cadmium for most items tested, with one ring yielding an average of 10,600 micrograms. Two pendants small enough to be swallowed were tested using dilute HCl to simulate ingestion. While one pendant did not release cadmium in excess of the US recommended maximum of 200 micrograms even when damaged, the other released an average of 63,100 micrograms after being damaged. Fourteen of fifteen samples of two high cadmium charms extracted using a modified TCLP extraction exceeded the 1.0 mg/L TCLP limit for cadmium, averaging 13.1 and 9.6 mg/L respectively for the two charms. These results demonstrate that high‑cadmium jewelry may pose a serious hazard if mouthed or ingested, and that regulatory standards that do not take into account the potential for increased release of cadmium resulting from damage to jewelry electroplating are inadequate.

Stability of mercury on a novel mineral sulfide sorbent used for efficient mercury removal from coal combustion flue gas.

Nano-structured zinc sulfide (Nano-ZnS) has been demonstrated to be a promising alternative to activated carbon (AC) for controlling mercury emission from coal combustion flue gas. The ultimate fate of the mercury-laden Nano-ZnS after mercury capture is mostly disposed in landfill with fly ashes. Thus, the stability of mercury adsorbed on the Nano-ZnS is of considerable significance in the secured disposal of fly ash after mercury removal and in the commercial application of the Nano-ZnS sorbent for removal of mercury from coal combustion flue gas. In this work, a modified toxicity characteristic leaching procedure (TCLP) was conducted to evaluate the leachability of mercury on the Nano-ZnS. The effects of leachate pH value, leaching time, liquid-to-solid ratio, and acid rain types on mercury leaching from the mercury-laden Nano-ZnS were systematically investigated. The TCLP results show that the concentration of mercury in leachate was far below the safe limit (200μg/L) as imposed by the US Environmental Protection Agency (EPA) for classifying a material as a hazardous waste. All the key parameters that generally affected metal leaching rate exhibited slight effect on mercury leaching from the mercury-laden Nano-ZnS. Leaching tests at various highly severe conditions resulted in less than 0.01% mercury leaching from the mercury-laden Nano-ZnS. Sequential selective extraction tests demonstrated that mercury sulfide (HgS) was the dominant adsorption product on the Nano-ZnS, which guaranteed the excellent stability of mercury adsorbed on the Nano-ZnS. Graphic abstract ᅟ.

Emulsified cold recycled mixtures using cement kiln dust and coal waste ash-mechanical-environmental impacts

Cold recycling is a widely recommended asphalt pavement rehabilitation technology with potentially significant economic and environmental benefits. One of the advantages of cold recycling is that its operations are performed at ambient temperature. However, there are still some concerns regarding the use of emulsified cold recycled mixtures (ECRMs). These pavements are susceptible to problems such as raveling, stripping, low initial strength, and long curing time, which are often countered by the use of additives. This study examined the mechanical outcomes and environmental implications of using cement kiln dust (CKD), which is a byproduct of cement production plant, and coal waste ash (CWA), which is obtained by igniting coal waste, in ECRMs as additives. The effects were compared with the additive-free or reference mixture and the mixtures with 1% and 2% cement content. To evaluate the mechanical properties, Marshall stability, indirect tensile strength and moisture susceptibility tests were performed on the specimens of different ages at different temperatures. Environmental impact was assessed using the modified toxicity characteristic leaching procedure (MTCLP) test. Finally an economical-environmental analysis was performed on designed pavements with each type of ECRM. The results showed that the combined use of CKD and CWA improved the mechanical properties, especially after prolonged curing periods. In some cases, this improvement was even greater than the improvement resulting from the addition of cement. The results of the MTCLP test showed that even after five extractions, the concentration of heavy metals in the leachate of CKD- and CWA-containing mixtures remained below the regulatory levels. Overall, it was found that using CKD and CWA as additives in ECRMs had remarkable economical and environmental benefits, especially if they are employed together.

Fe(III)–As(V) precipitates obtained from a sulphate system and their leach stability

ABSTRACTFe(III)–As(V) precipitates were synthesised from the Fe(II)-As(V)-SO42--H2O system at a temperature of 90°C and a constant pH maintained at 1.5 ± 0.05. The precipitates obtained were characterised by X-ray diffraction (XRD), chemical composition analysis, scanning electron microscope (SEM) and Raman spectrum, thermogravimetric analyzer (TGA) and electron probe micro-analyzer (EPMA). The precipitates were in irregular aggregation of about 1–4 μm in size. The precipitates consisted of scorodite, ferric arsenate and an amorphous ferric hydroxide sulphate formulated as Fe(OH)x(SO4)y. The precipitates were stable in modified Toxicity Characteristic Leaching Procedure (TCLP) tests at pH 4.93 for 60 h. Arsenic concentrations in the leaching solutions of 0.27 mg L−1 and 0.59 mg L−1 were obtained for the precipitates prepared initial Fe(II)/As(V) molar ratios of 4.0 and 5.0, respectively. Significantly more iron than arsenic was dissolved with up to 280 mg L−1 of iron reporting to solution. Long-term stability tests of the precipitates were carried out by leaching them for 40 days at 25°C under various media of pH between 9.50 and 10.57. The results showed that the precipitates tested in this study were more stable than those by previous researchers owing to a preferential dissolution of the amorphous ferric hydroxide sulphate.

Chromium immobilization in soil using quaternary ammonium cations modified montmorillonite: Characterization and mechanism

The potential risk of heavy metal in soil can be reduced by stabilization techniques. Stabilizing amendments, montmorillonites modified with tetramethylammonium (TMA) and hexadecyltrimethylammonium (HDTMA) at different loadings were prepared, characterized and assayed for remediation of hexavalent chromium contaminated soil. Characterization results demonstrated that TMA modification resulted in increased surface area and pore volume, whereas HDTMA modification resulted in decreased surface area and pore volume. For HDTMA modified montmorillonites (H-Monts), the arrangement model of surfactant molecules and the structural characteristics strongly depended on the surfactant loading density. Less pronounced packing density dependence was observed for TMA modified montmorillonites (T-Monts). Modified toxicity characteristic leaching procedure (TCLP) was utilized to evaluate the chromium immobilizing capacity of the prepared organo-montmorillonites, and the results revealed that both T-Monts and H-Monts can be reasonably effective in chromium stabilization under different leaching condition. The comparison of chromium leaching behavior manifested by T-Monts and H-Monts suggested that mechanisms for chromium immobilization by organo-montmorillonites amendment proceeded via two adsorption approaches. Each approach involves different functional groups, depending on the leaching pH and surfactant loading concentration. In addition, the effect of HDTMA loading concentration, amendment dosage, initial chromium concentration and incubation time on the immobilizing efficiency of H-Monts was investigated.

Leaching Behavior of Heavy Metals from Cement Pastes Using a Modified Toxicity Characteristic Leaching Procedure (TCLP).

As the standard toxicity characteristic leaching procedure (TCLP) can not exhaust the acid neutralizing capacity of the cement rotary kiln co-processing solid wastes products which is particularly important for the assessment of the leaching concentrations of heavy metals. A modified TCLP was proposed. The extent of leaching of heavy metals is low using the TCLP and the leaching performance of the different metals can not be differentiated. Using the modified TCLP, however, Zn leaching was negligible during the first 180h and then sharply increased (2.86±0.18 to 3.54±0.26mg/L) as the acidity increased (pH<6.0). Thus, Zn leaching is enhanced using the modified TCLP. While Pb leached readily during the first 126h and then leachate concentrations decreased to below the analytical detection limit. To conclude, this modified TCLP is a more suitable method for these cement rotary kiln co-processing products.

Stabilization of simulated lead sludge with iron sludge via formation of PbFe12O19 by thermal treatment

This study investigated the feasibility of stabilizing lead sludge by reaction with iron sludge via the formation of PbFe12O19 through a thermal treatment process. Lead hydroxide was used to simulate lead-laden sludge and the sintering procedure was performed by firing a mixture of this simulated sludge together with iron sludge at a Fe/Pb molar ratio of 12 over the temperature range from 650 to 1400°C. The accompanying phase transformations as well as the surface characteristic of sintered samples were observed by XRD and SEM, while the leaching behavior of the stabilized sludge in an acidic environment was evaluated by a modified Toxicity Characteristic Leaching Procedure (TCLP) test. The results confirmed that PbFe12O19 acts as a stabilization phase for lead, and showed that the formation of a PbFe12O19 phase began at 750°C with the lead completely incorporated into the PbFe12O19 phase at 1050°C. Above 1100°C, the PbFe12O19 phase began to decompose, accompanied by the reappearance of Fe2O3. The volumes of compressed sludge samples were reduced significantly after thermal treatment, with accompanying volume reductions of 40% at 1050°C. This study compared the leaching of lead from PbO and sintered sludge samples using a prolonged TCLP test, and the data showed that the PbFe12O19 phase was superior to the PbO and that the sintered sludge sample exhibited very high stability under acidic environments. These results suggest a promising and reliable method of reducing lead sludge mobility and toxicity has been identified.

Composition of inorganic elements and the leaching behavior of biomass combustion ashes discharged from wood pellet boilers in Japan

To evaluate the characteristics of wood ash as fertilizer, composition of inorganic elements and the leaching behavior were studied. The leaching behavior was evaluated by three leaching methods using different solvents (water, hydrochloric acid, and acetic acid: Japanese leaching test Nos. 18 and 19 and modified toxicity characteristic leaching procedure prescribed by the US Environmental Protection Agency). The ash composition varied according to raw materials for fuel and ash collection systems. Concentration of Na, Al, Si, and V became higher in bark ashes while that of K became higher in wood ashes. Pb, Cd, Se, and Zn were more volatile and enriched in fly ashes. Of the nutrient elements, K showed high water solubility and its phytoavailability also appeared high, although the amount of water-soluble K was low in bark ash. Ca and Mg had intermediate solubility while P was less soluble in both water and acetic acid. The amount of hazardous substances having leached was low for most, but not all the ashes, in terms of Pb, Cr and As. Nevertheless, the phytoavailability of these hazardous substances after their application to the forest appeared low, due to their amphoteric leaching behavior and the acidity of Japanese forest soils.

Stabilization and phase transformation of CuFe 2O 4 sintered from simulated copper-laden sludge

The feasibility of stabilizing copper-laden sludge by high-temperature CuFe 2O 4 ferritization process is investigated with different sintering temperature, and the prolonged leaching test. The thermal behavior, structural morphology, phase composition, and phase transformation of the stabilized sludge were investigated by using thermal gravimetry-differential scanning calorimetry, scanning electron microscopy and X-ray diffraction. The leaching behavior of the stabilized sludge under acidic environment was evaluated by modified Toxicity Characteristic Leaching Procedure (TCLP). The results indicated that CuFe 2O 4 could be effectively formed at around 800 °C by the iron oxide precursor with a 3 h of short sintering. The transformation was discovered on crystallographic spinel structures: the low-temperature (800–900 °C) tetragonal phase (t-CuFe 2O 4) and the high-temperature (∼1000 °C) cubic phase (c-CuFe 2O 4). At higher temperatures (∼1100 °C), the formation of cuprous ferrite delafossite phase (CuFeO 2) from the dissociation of CuFe 2O 4 was also noticed. Both CuFe 2O 4 spinel and CuFeO 2 delafossite phase have a better intrinsic resistance to acidic environment when compared to that of CuO phase by the modified TCLP test. The sintering strategy designed for copper-laden sludge is proven to be beneficial in stabilizing copper.

The fate of Cu, Zn, Pb and Cd during the pyrolysis of sewage sludge at different temperatures

In the present study, a sequential extraction procedure, recommended by the Community Bureau of Reference (BCR), was used for the fractionation of the heavy metals Cu, Zn, Pb and Cd in sewage sludge and its residues produced after pyrolysis at different temperatures from 250 to 700 °C. The results show that, in the sludge sample, the sum of the percentages of the reducible and oxidizable fractions for all metals except Cu was very high (65.4% for Cd, 85.7% for Pb, 78.7% for Zn), whereas the sum of the percentages of the oxidizable and residual fractions for Cu was very high (88.8%). The same result could be attained in the residues. Statistical analysis shows that at low temperatures the variation in pyrolysis temperature did not effectively contribute to the distribution of metal speciation in the residues. Meanwhile a modified Toxicity Characteristic Leaching Procedure (TCLP) was employed to determine the leachability of these four metals. The result indicates that the TCLP concentration of Cu, Zn, Pb and Cd dropped sharply after the temperature reached 350 °C, 550 °C, 500 °C and 400 °C respectively, which means pyrolysis can enhance the stability of these four metals when the temperature is high enough.

Assessment of leaching potential of highly leaded jewelry

Lead is a potent neurotoxin particularly toxic to young children, and in response to recent poisonings of children and high levels of lead contamination in children's jewelry, US regulatory standards for lead content in these items have become much more stringent. Parents are often advised to throw out suspect items in the trash. While household wastes are generally exempt from consideration as hazardous waste, the potential for leaching of hazardous quantities of lead from such items is unknown. A modified Toxicity Characteristic Leaching Procedure (TCLP), in which intact jewelry components were subjected to leaching, was used to evaluate the potential for leaching of lead from highly leaded jewelry. Of 62 jewelry components tested, 61 exceeded the US regulatory standard for lead of 5 mg/L, and leachate lead concentrations averaged 1460 mg/L. Twenty-six of the component items tested yielded TCLP lead concentrations exceeding 1000 mg/L. These results demonstrate that highly leaded jewelry items may leach significant amounts of lead, and provide another reason to remove lead from these products. Furthermore, these results suggest that while the volume of such items in the municipal solid waste (MSW) stream is small, they have the potential to contribute significant quantities of lead to MSW leachates.

Thermal and chemical stability of Cu–Zn–Cr-LDHs prepared by accelerated carbonation

Layered double hydroxides Cu x Zn 6 − x Cr 2(OH) 16(CO 3)·4H 2O with different molar ratios of Cu/Zn/Cr were synthesized by accelerated carbonation. The products were characterized by XRD, SEM, FT-IR and TG-DTG-DSC-MS. The chemical stability was tested by the modified Toxicity Characteristic Leaching Procedure (TCLP). The results showed that the products were the mixture of Cu x Zn 6 − x Cr 2(OH) 16(CO 3)·4H 2O and (CuZn) 2(CO 3)(OH) 2, with similar thermal behavior. All products were chemically stable with reduced leaching at pH > 6 (Cu 2+, Zn 2+) or > 5 (Cr 3+).

Effects of field application of phosphate fertilizers on the availability and uptake of lead, zinc and cadmium by cabbage (Brassica chinensis L.) in a mining tailing contaminated soil

A field trial was conducted to evaluate the reduction of bioavailability of heavy metals including lead (Pb), zinc (Zn) and cadmium (Cd) in a soil contaminated by mining tailings in Shaoxing, Zhejiang, China. Three commercial phosphate (P) fertilizers including phosphate rock (PR), calcium magnesium phosphate (CMP), and single superphosphate (SSP) were applied to the plot at three P application rates, 50, 300, and 500 g/m2 with 9 treatments and control (CK). Plants, water soluble and exchangeable (WE) extraction procedure and modified toxicity characteristic leaching procedure (TCLP) were employed. It was found that the addition of all three P fertilizers significantly decreased WE Pb (22.0%-81.4%), Cd (1.5%-30.7%) and Zn (11.7%-75.3%, exception of SSP treatments with no significant difference) and TCLP Pb concentration (27.1%-71.2%), compared with the control, leading to reduced uptake of Pb (16.0%-58.0%), Cd (16.5%-66.9%) and Zn (1.2%-73.2%) by cabbage (Brassica chinensis L.). It was suggested that P fertilizers induced immobilization of heavy metals such as Pb, Cd, and Zn. CMP provided the most effective method of reducing metal toxicity, mobility, and phytoavailability. At the P application rate of 300 g/m2, CMP would be cost-effective to decrease WE Pb, Zn, and Cd concentration from 666 to 137 mg/kg, from 31.2 to 8.71 mg/kg, and from 1.69 to 1.36 mg/kg, respectively. SSP was more effective in reducing Pb bioavailability than PR but had variable effects on Zn bioavailability. Cd uptake by cabbage was negatively correlated with soil pH rather than with WE or TCLP, indicating that Cd uptake by cabbage was a complex process. It should be careful to evaluate the impact of phosphate application on Cd availability in soil.

Optimum Dose Of Lime And Fly Ash For Treatment Of Hexavalent Chromium–Contaminated Soil

The presence of hexavalent chromium, Cr(VI), in soil is an environmental concern due to its effect on human health. The concern arises from the leaching and the seepage of Cr(VI) from soil to groundwater. In this paper, a stabilization technology to prevent this problem was simulated on an artificial soil contaminated with hexavalent chromium. The process is a physico-chemical treatment in which the toxic pollutant is physically entrapped within a solid matrix formed by the pozzolanic reactions of lime and fly ash to reduce its leachability and, therefore, its toxicity. This paper presents the optimum ratio of fly ash and lime in order to stabilize artificial soils contaminated with 0.4 wt.% of Cr (VI) in a brief term process. The degree of chromium released from the soil was evaluated using a modified Toxicity Characteristic Leaching Procedure (TCLP) by US Environmental Protection Agency (EPA). Overall, experimental results showed reduced leachability of total and hexavalent chromium from soils treated with both fly ash and quicklime, and that leachability reduction was more effective with increasing amount of fly ash and quicklime. Stabilization percentages between 97.3% and 99.7% of the initial chromium content were achieved, with Cr(VI) concentration in the TCLP leachates below the US EPA limit for chromium of 5 mg/l. Adequate treatment was obtained after 1 day of curing with just 25% fly ash and 10% quicklime.

English

In a joint project, the mine waste-piles at the Rattler Mine near Idaho Springs, Colorado, were sampled and analyzed by scientists from the U.S. Geological Survey (USGS) and the Colorado School of Mines (CSM). Separate sample collection, sample leaching, and leachate analyses were performed by both groups and the results were compared. For the study, both groups used the USGS sampling procedure and the USGS Field Leach Test (FLT). The leachates generated from these tests were analyzed for a suite of elements using ICP-AES (CSM) and ICP-MS (USGS). Leachate geochemical fingerprints produced by the two groups for composites collected from the same mine waste showed good agreement. In another set of tests, CSM collected another set of Rattler mine waste composite samples using the USGS sampling procedure. This set of composite samples was leached using the Colorado Division of Minerals and Geology (CDMG) leach test, and a modified Toxicity Characteristic Leaching Procedure (TCLP) leach test. Leachate geochemical fingerprints produced using these tests showed a variation of more than a factor of two from the geochemical fingerprints produced using the USGS FLT leach test. We have concluded that the variation in the results is due to the different parameters of the leaching tests and not due to the sampling or analytical methods.

Leachability of Lead and Cadmium from Cementitious Wastes

AbstractIn this paper, the leachability of lead and cadmium from cementitious waste was investigated to determine the leaching mechanism of these heavy metals from a cement matrix so that a more appropriate leaching test can be designed. The leaching studies were carried out using a modified Toxicity Characteristic Leaching Procedure (TCLP), and variations in leaching parameters such as leachate pH, the duration of agitation, the particle size, and the liquid to solid ratio were investigated. The main finding of these studies was that the leachability of Pb and Cd in cementitious waste was highly dependent on the pH of the leachate. Other findings included: (i) the leachability of metals initially decreased with increasing leaching duration but increased after the leachate pH reached equilibrium; (ii) the particle size of the cementitious waste affected the rate of leaching of alkalinity from cement and hence the leachability of the heavy metal ions; and (iii) the total metals in the leachate, increased with increasing liquid to solid ratio. Overall, the TCLP was found to be inappropriate for assessing the leachability of heavy metals from cementitious waste due to the high buffering capacity of the calcium ions in the cement. This maintained the pH of the leachate at a value where heavy metals are insoluble. The test was found to underestimate the concentration of heavy metal ions leached from cementitious waste relative to the concentration in the actual landfill environment.

Evaluating the applicability of a modified toxicity characteristic leaching procedure (TCLP) for the classification of cementitious wastes containing lead and cadmium

Having the toxicity characteristic leaching procedure (TCLP) as a starting point, this study examined the effect of the various leaching parameters on the leaching of Pb and Cd from cementitious wastes. Using modified TCLP procedures, the parameters investigated were the acid concentration, leaching duration, particle size of the crushed waste, liquid to solid ratio, and the acid type. The main finding was that the final leachate pH controls the leachability of metals due to its influence on their solubility. The high alkalinity of cementitious waste buffers the leachate at a pH where most metals become insoluble. The TCLP was found to result in an unrealistic condition for cementitious wastes due to the high resultant leachate pH.

Toxicity of Scrap Tire Leachates in Estuarine Salinities: Are Tires Acceptable for Artificial Reefs?

Shredded scrap tires were leached in a modified toxicity characteristic leaching procedure (TCLP) extraction method in synthetic saltwater solutions for three sequential 7-d periods. Test salinities were 5, 15, and 25‰. Acute toxicity tests were conducted with larval sheepshead minnows Cyprinodon variegatus and daggerblade grass shrimp Palaemonetes pugio. Mortality decreased following multiple sequential leaching periods. Toxicity decreased with increasing salinity. The fish were more sensitive than the grass shrimp. Dilution series toxicity bioassays were performed with fish and grass shrimp at 5‰ salinity and at 15‰ with fish only. The 96-h LC50s (lethal concentration for half of the test animals) for fish were 10% leachate at 5‰ and 26% at 15‰. The 96-h LC50 for grass shrimp at 5‰ was 63%. The 96-h lowest observed effect concentrations (LOEC) for fish survival were 12.5% at 5‰ and 25% at 15‰. The 96-h LOEC for grass shrimp survival was 50% at 5‰. Growth LOEC values were 12.5% at both salinities for fish and 50% for grass shrimp at 5‰. Chemical analyses revealed no specific components as the cause of observed toxicity. Antagonism between sea salt and toxic chemicals is hypothesized to cause differential toxicity at varying salinities, as opposed to differential solubility of the toxicants. Extrapolation of laboratory results indicates that proposed tire reefs should not pose a serious threat to water quality in Chesapeake Bay. No observed effects concentrations (NOEC) were an order of magnitude or greater above field concentrations calculated from simplified methods. Toxic substances appear to leach from the surface of the tires not from the tire matrix. The use of tires in higher salinity environments appears to pose little direct toxicological risk to resident organisms. However, because unknown toxic chemicals were present in leachates at all test salinities, no assessment can be made regarding persistence, fate, transport, or possible bioaccumulative effects.

Stabilization of a Mixed Waste Sludge for Land Disposal

ABSTRACT A solidification and stabilization technique was developed for a chemically complex mixed waste sludge containing nitrate processing wastes, sewage sludge and electroplating wastewaters, among other wastes. The sludge is originally from a solar evaporation pond and has high concentrations of nitrate salts; cadmium, chromium, and nickel concentrations of concern; and low levels of organic constituents and alpha and beta emitters. Sulfide reduction of nitrate and precipitation of metallic species, followed by evaporation to dryness and solidification of the dry sludge in recycled high density polyethylene with added lime was determined to be a satisfactory preparation for land disposal in a mixed waste repository. The application of post-consumer polyethylene has the added benefit of utilizing another problem-causing waste product. A modified Toxicity Characteristic Leaching Procedure was used to determine required treatment chemical dosages and treatment effectiveness. The waste complexity prohibi...