Sorption behavior of cesium on silt and clay soil fractions.

The effect of clay mineral composition on Cs adsorption behavior of silt and clay fractions (SC-fractions) of soil was investigated. Surface soil samples were collected within 2 km of Kori and Wolsong nuclear power plants in South Korea, and SC-fractions (<20 µm) were separated. The physicochemical properties of SC-fractions and types of clay minerals contained in the SC-fractions were analyzed. The cesium adsorption capacity of the SC-fractions, and affinity between the SC-fractions and Cs, were investigated by isothermal adsorption analysis using the dual-site Langmuir adsorption model. To understand selective adsorption of Cs, the radiocesium interception potential and distribution coefficient of the SC-fractions were analyzed in the presence or absence of competing ions. The radiocesium distribution coefficient of the SC-fractions showed a trend similar to that of the Langmuir sorption coefficient of high-affinity binding sites for Cs in the SC-fractions. The SC-fractions of Kori soils that contain only non-expandable clay minerals including highly weathered mica had low Cs adsorption capacity. However, the SC-fractions of Kori soils showed higher Cs adsorption selectivity compared to the SC-fractions of Wolsong soils containing expandable clay minerals and micaceous mineral with a low degree of weathering. It is predicted that the highly weathered micas have high affinity to Cs, and such clay minerals contribute the most to the adsorption process in dilute solutions.

Characterization of mesoporous aluminosilicate materials by means of inverse liquid chromatography.

Estimation of the properties of mesoporous aluminosilicates in various environments is important when assessing their sorption capacity. Using inverse liquid chromatography (ILC), Hansen solubility parameters (HSP) and linear free energy relationship (LFER) parameters were calculated to determine the properties of aluminosilicates in a protic and an aprotic system, using water and acetonitrile as the mobile phase, respectively. The calculated Hansen parameters, reflecting the ability of the material under investigation to different types of intermolecular interactions, slightly differ depending on the mobile phase used. It was found that in the presence of water the surface of aluminosilicates shows a weaker ability to interact, as evidenced by negative or near-zero e, s, a, b, v coefficients. Additionally, it was found that the Si/Al ratio in aluminosilicates structure has little effect on the determined parameters.

Sorption and desorption of radiocesium by muscovite separated from the Georgia kaolin.

Radiocesium (137Cs) sorption by moderately weathered, sand-sized muscovite, obtained as a byproduct of kaolin ore processing, was observed at various concentrations of added stable Cs (0-100 µmol/L) over a 130 d period. After 18 h of batch sorption with 1 mmol/L NaCl as background electrolyte, conditional 137Cs Kd values were near 2000 L/kg across the entire range of added stable Cs. Over four succeeding months, the Kd values increased by large factors for suspensions with little added Cs but increased only slightly for the suspensions with the most added Cs. The large grains of muscovite used in this study behaved distinctly differently than previously studied, much finer illite in that highly Cs-selective but low-abundance cation exchange sites appeared to be unavailable to the aqueous Cs during the first few days of the experiment. Diffusion pathways to highly Cs-selective sites were thought to be much longer in the muscovite than in frayed edges of illite, causing the highly Cs-selective sites to be isolated from the bulk solution. The longer diffusion pathways may be due to much greater stiffness of the material bounding interlayer wedges in the muscovite than in illite. This isolation from solution led to slow uptake at trace levels of Cs though the final Kd values (after 130 d) at those levels were comparable to those found for some illite. After 130 days, the original solutions were replaced by new electrolyte solutions containing no Cs, to observe 137Cs desorption over another 130 d period. There was no indication of desorption of 137Cs from the slowly accessible, highly Cs-selective sites apparently reached by most of the 137Cs during sorption at the low Cs levels. The byproduct mica from kaolin processing might serve effectively as a chemically stable sorbent to isolate accidently released radiocesium and to hold it until the 137Cs is virtually gone.

Fabrication and environmental applications of multifunctional mixed metal-biochar composites (MMBC) from red mud and lignin wastes.

This study fabricated a new and multifunctional mixed metal-biochar composites (MMBC) using the mixture of two abundant industrial wastes, red mud (RM) and lignin, via pyrolysis under N2 atmosphere, and its ability to treat wastewater containing various contaminants was comprehensively evaluated. A porous structure (BET surface area = 100.8 m2 g-1) was created and metallic Fe was formed in the MMBC owing to reduction of Fe oxides present in RM by lignin decomposition products during pyrolysis at 700 °C, which was closely associated with the transformation of liquid to gaseous pyrogenic products. The potential application of the MMBC was investigated for the removal of heavy metals (Pb(II) and Ni(II)), oxyanions (As(V) and Cr(VI)), dye (methylene blue), and pharmaceutical/personal care products (para-nitrophenol and pCBA). The aluminosilicate mineral, metallic Fe, and porous carbon matrix derived from the incorporation of RM and lignin contributed to the multifunctionality (i.e., adsorption, chemical reduction, and catalytic reaction) of the MMBC. Thus, engineered biochar composites synthesized from selected industrial wastes can be a potential candidate for environmental applications.

Deposition of mullite in peatlands of southern Poland: Implications for recording large-scale industrial processes.

Mullite, a pure aluminosilicate (Al6Si2O13), is a rare natural rock component, known for centuries as a very resistant ceramic material. It is also a common waste product of high-temperature coal combustion that is emitted in quantity from coal-based power stations. The occurrence of mullite in two Sphagnum-dominated peatlands located near the Upper Silesia industrial region in southern Poland is described. For the first time, a complete record of mullite deposition in the peat profiles has been obtained by XRD analyses of ashed peat samples. The mullite distribution is compared with records of Hg, Pb and Cu. While mullite is supplied during high temperature processes only, Cu, Pb and Hg show more complex pattern of distribution. Both peat profiles contain elevated amounts of mullite in the time span between ca 1950-1990 with a maximum content in ca 1980. The first appearance (∼1900) of mullite is indicative of the beginning of energy production in coal-based power plants in the region. Mullite is proposed here as an indicator of industrialization in geological records. It is resistant to post-depositional processes, emitted globally, and restricted to large-scale industry.

An indigenous strain of potassium-solubilizing bacteria Bacillus pseudomycoides enhanced potassium uptake in tea plants by increasing potassium availability in the mica waste-treated soil of North-east India.

AIM: Potassium (K) is one of the three major nutrients required of plant growth and muriate of potash (MoP) is the only recognized chemical fertilizer used in agriculture. In many countries, 100% of the applied MoP is imported costing huge revenue. Application of suitable potassium-solubilizing bacteria (KSB) as biofertilizer could be an integral part of K management in arable soil. The object of this study was to evaluate K-solubilizing ability of a ubiquitous micro-organism as KSB to supplement K in soil. METHODS AND RESULTS: Strain (O-5) was isolated from tea-growing soil and identified as Bacillus pseudomycoides. Phylogenetic analysis revealed that the nearest neighbours of B. pseudomycoides strain O-5 were Bacillus cereus, Bacillus thuringiensis and Bacillus toyonensis. Though the species was first identified in 1998 and is ubiquitous in soil, the role of this group of micro-organisms in nutrient cycling in soil has not been studied before. Strain solubilized 33·32 ± 2·40 µg K ml-1 in mica waste (MW; muscovite type mineral)-amended broth after 7 days incubation at 30 ± 1°C. In a soil microcosm study under laboratory condition, B. pseudomycoides strain O-5 increased K availability by 47·0 ± 7·1 mg kg-1 after 105 days incubation, while the strain released 104·9 ± 15·3 mg K kg-1 in MW-treated soil. In this study, application of isolated B. pseudomycoides with MW significantly increased K availability in soil, and that in turn facilitated K uptake by tea plants. CONCLUSION: Based on the data, it could be inferred that B. pseudomycoides could mobilize K from bound form in soil and can be utilized as K-solubilizing biofertilizer especially in combination with MW for supplementing K in soil. SIGNIFICANCE AND IMPACT OF THE STUDY: Bacillus pseudomycoides strain O-5 has potential to be used as K-solubilizing biofertilizer in agriculture.

Chemical and mineral composition of fly ashes from home furnaces, and health and environmental risk related to their presence in the environment.

The study presents the results of an analysis of fly ashes produced from burning of solid fuels mixed with municipal waste and assesses the environmental and health risk associated with infiltration of the selected metals to the environment. The phase composition suggests that the material is extremely mixed and diverse. Low-temperature components were mixed with substances formed in high temperatures. The variable composition of waste from different home furnaces with high content of the amorphous phase (which dissolves in water more easily than its crystalline equivalents) may be harmful to the environment and for the people. The dominant elements were silicates and aluminosilicates, such as: quartz, feldspar and plagioclase (albite). Clay minerals (kaolinite and mullite), carbonates (calcite), oxides/oxidehydroxides of iron and sulfate minerals (gypsum and anhydrite) were also abundant. The particles' major constituents were Si, Al, Ca and Fe oxides (85.5%), while S, Mg, Na, K and Ti oxides accounted for 12.6% of the total content. The risk assessment code suggested: Low Risk for As, Co, Cr, Ni, Medium Risk for Cd, Cu and Pb, and High Risk for Zn. Hazard Index (HI) calculated for non-cancerogenic substances for children was 2.35E+00. The total Risk index for children was 4.88E-05. As for adults, HI was 2.42E-01 for women, and 2.89E-01 for men, while the Risk index value was 6.85E-05 for women, and 8.48E-05 for men. The value HI > 1 points to the risk of adverse health impact on children exposed to fly ashes.

Enhanced irreversible fixation of cesium by wetting and drying cycles in soil.

The retention of radioactive cesium (Cs) in soil is significantly related to the types of clay minerals, while the weathering process affects the irreversible adsorption sites in clay minerals. In this study, the effect of weathering (exposure duration of Cs and repeated wetting and drying cycles) on fractionation of Cs in soils was investigated using fractionation analysis by the sequential extraction. The residual fraction of Cs increased slowly with exposure time but increased rapidly by repeated wetting and drying cycles. XRD analysis shows that a 1.43 nm of interlayer size for vermiculite is shortened to 1.00 nm, i.e., similar to that of illite. The change implies the potential that the structure of expandable clay minerals is transformed to the non-expandable structure by weathering process after Cs retention. Based on the result, the residual fraction of Cs, most stable form of Cs in the soil, reached relatively rapidly to a maximum. However, the process is much slower kinetically in the field because the bench-scale weathering process used in this study is more aggressive. This study implies that Cs fractionations in the soil are converted into a more stable fraction by weathering processes in the soil. Therefore, Cs removal should be conducted as soon as possible after accidental release of Cs in an environmental side.

Assessment of chemical fractionations and mobilization potentials for heavy metals in wastes and other solid matrices in a mining site in the inland Aegean Region in Turkey.

The natural soil, processing products, and wastes generated in a colemanite mining site were studied according to their mineral structures, contents of As, Cr, Cu, Ni, Mn, Zn, Al, and Fe. The possible sources, chemical distributions, and the mobilization behaviors of the metals and the correlations between the metal mobilization ratios and their chemical partitioning were also examined and evaluated. The mineralogical composition of the materials was determined, and the correlations between the mineralogical sources of the determined metals with each other were investigated by using principal component analysis. The results showed that mica and smectite were considered to be the source of Cr, Cu, Ni, and Zn, and As was found in the mineral structure of the colemanite. On the other hand, the distributions of the metals in the binding forms indicated that Cr, Ni, Zn, Al, and Fe were mostly bound on the residual fraction, while Cu, Mn, and As were distributed in labile forms. Arsenic was recognized as the most mobile element with 10.37% mobility. Fe mobilization was originated from exchangeable fraction, where As mobilization was significantly correlated with its reducible and organic fractions.

Determination of the Settling Rate of Clay/Cyanobacterial Floccules.

The mechanisms underpinning the deposition of fine-grained, organic-rich sediments are still largely debated. Specifically, the impact of the interaction of clay particles with reactive, planktonic cyanobacterial cells to the sedimentary record is under studied. This interaction is a potentially major contributor to shale depositional models. Within a lab setting, the flocculation and sedimentation rates of these materials can be examined and measured in a controlled environment. Here, we detail a protocol for measuring the sedimentation rate of cyanobacterial/clay mixtures. This methodology is demonstrated through the description of two sample experiments: the first uses kaolin (a dehydrated form of kaolinite) and Synechococcus sp. PCC 7002 (a marine coccoid cyanobacteria), and the second uses kaolin and Synechocystis sp. PCC 6803 (a freshwater coccoid cyanobacteria). Cyanobacterial cultures are mixed with varying amounts of clay within a specially designed tank apparatus optimized to allow continuous, real-time video and photographic recording. The sampling procedures are detailed as well as a post-collection protocol for precise measurement of chlorophyll a from which the concentration of cyanobacterial cells remaining in suspension can be determined. Through experimental replication, a profile is constructed that displays sedimentation rate.

Kinetics of human serum albumin adsorption at silica sensor: Unveiling dynamic hydration function.

Adsorption kinetics of human serum albumin (HSA) at a silica substrate was studied using the QCM-D and AFM methods. Measurements were performed at pH 3.5 for various bulk suspension concentrations and ionic strengths. The QCM experimental data were compared with the dry coverage of HSA derived from AFM and from the solution of the mass transfer equation. In this way, the dynamic hydration functions and water factors of HSA monolayers were quantitatively evaluated as a function of dry coverage for various ionic strengths. Using the hydration functions, the HSA adsorption runs derived from QCM-D measurements were converted to the dry coverage vs. the time relationships. In this way, the maximum coverage of irreversibly bound HSA molecules was determined. It was equal to 0.35 and 1.4 mg m-2 for NaCl concentration of 0.001 and 0.15 M, respectively. These results agree with previous experimental data derived by streaming potential measurements for mica and with theoretical modeling. Therefore, the side-on mechanism of HSA adsorption at silica sensor at pH 3.5 was confirmed. Also, a quantitative analysis of the desorption runs allowed one to calculate the binding energy of the reversibly bound HSA fraction. Beside significance to basic science, these results enable to develop a robust technique of preparing HSA monolayers at silica sensor of well-controlled coverage and molecule orientation.

Effects of clay combined with moisture management on Cd immobilization and fertility index of polluted rice field.

A field-scale trial was conducted to investigate the remediation effects of sepiolite on Cd-polluted paddy soils under different moisture managements, using a series of variables (pH and extractable Cd of soil, plant Cd concentration, plant nutrition and enzyme activity in soil). Results revealed that soil pH increased significantly after sepiolite addition, which promoted the reduction in extractable Cd in soil. After applying 0.5-2.5% sepiolite into soil, due to higher pH and lower TCLP Cd concentration, brown rice Cd reduced by 17-67% under continuous flooding, 14-62% under conventional irrigation, and 13-61% under wetting irrigation (p < 0.05). The activities of phosphatase and invertase increased compared with unamended soil (p < 0.05). The available phosphorus in clay treated soil showed a remarkable raise, with a maximum increase by 14.5%, 16.9% and 18.1% under three moisture managements (p < 0.05). The increasing values of enzyme activity and then plant nutrition in soil revealed that clay application improved the ecological condition of Cd-contaminated paddy soil. The sepiolite application in combination with continuous flooding provided an efficient and safe remediation technology for Cd-polluted rice field.

Radiocesium distribution in aggregate-size fractions of cropland and forest soils affected by the Fukushima nuclear accident.

The Fukushima Daiichi nuclear power plant accident caused serious radiocesium (137Cs) contamination in soils in a range of terrestrial ecosystems. It is well documented that the interaction of 137Cs with soil constituents, particularly clay minerals, in surface soil layers exerts strong control on the behavior of this radionuclide in the environment; however, there is little understanding of how soil aggregation-the binding of soil particles together into aggregates-can affect the mobility and bioavailability of 137Cs in soils. To explore this, soil samples were collected at seven sites under different land-use conditions in Fukushima and were separated into four aggregate-size fractions: clay-sized (<2 µm); silt-sized (2-20 µm); sand-sized (20-212 µm); and macroaggregates (212-2000 µm). The fractions were then analyzed for 137Cs content and extractability and mineral composition. In forest soils, aggregate formation was significant, and 69%-83% of 137Cs was associated with macroaggregates and sand-sized aggregates. In contrast, there was less aggregation in agricultural field soils, and approximately 80% of 137Cs was in the clay- and silt-sized fractions. Across all sites, the 137Cs extractability was higher in the sand-sized aggregate fractions than in the clay-sized fractions. Mineralogical analysis showed that, in most soils, clay minerals (vermiculite and kaolinite) were present even in the larger-sized aggregate fractions. These results demonstrate that larger-sized aggregates are a significant reservoir of potentially mobile and bioavailable 137Cs in organic-rich (forest and orchard) soils. Our study suggests that soil aggregation reduces the mobility of particle-associated 137Cs through erosion and resuspension and also enhances the bioavailability of 137Cs in soils.

Erodibility of calcareous soils as influenced by land use and intrinsic soil properties in a semiarid region of central Iran.

The most important properties affecting the soil loss and runoff were investigated, and the effects of land use on the soil properties, together with the erodibility indices in a semiarid zone, central Iran, were evaluated. The locations of 100 positions were acquired by cLHS and 0-5-cm surface soil layer samples were used for laboratory analyses from the Borujen Region, Chaharmahal-Va-Bakhtiari Province, central Iran. To measure in situ runoff and soil erodibility of three different land uses comprising dryland, irrigated farming, and rangeland, a portable rainfall simulator was used. The results showed that the high variations (coefficient of variation, CV) were obtained for electrical conductivity (EC), mean weight diameter (MWD), soil organic carbon (SOC), and soil erodibility indices including runoff volume, soil loss, and sediment concentration (CV ~ 43.6-77.4%). Soil erodibility indices showed positive and significant correlations with bulk density and negative correlations with SOC, MWD, clay content, and soil shear strength in the area under investigation. The values of runoff in the dryland, irrigated farming, and rangeland were found 1.5, 28.9, and 58.7 cm3; soil loss in the dryland, irrigated farming, and rangeland were observed 0.25, 2.96, and 76.8 g; and the amount of sediment concentration in the dryland, irrigated farming, and rangeland were found 0.01, 0.11, and 0.15 g cm-3. It is suggested that further investigations should be carried out on soil erodibility and the potential of sediment yield in various land uses with varying topography and soil properties in semiarid regions of Iran facing the high risk of soil loss.

Settling fluxes and ecotoxicological risk assessment of fine sedimentary metals in Tema Harbour (Ghana).

Sediment traps were deployed in the Tema Harbour to estimate the settling fluxes of silt-clay particles and associated metals (Fe, Mn, Pb, Cr, Cu, Zn, Ni, Hg, Sn and As) and characterise their potential ecotoxicological risks. The mean daily settling fluxes of the silt-clay particles and associated metals ranged from 42.7 to 85.0gm-2d-1 and 1.3×10-2 to 49.4mgm-2d-1, respectively, and were characterised by large fluctuations at each station. The silt-clay and metal fluxes strongly correlated, indicating the important role of the silt-clay particles in metal transport and distribution in the harbour. Geochemical indices indicated anthropogenic influences on the harbour as the Pb, Cr, Zn, Hg, Sn and As content in the settling silt-clay particles exceeded their average crustal concentrations. Sediment quality guidelines indicated these metals pose appreciable ecotoxicological risks, particularly As. Increasing temporal trends in As necessitates increased pollution control efforts at the harbour.

Sorption kinetics, isotherms, and mechanism of aniline aerofloat to agricultural soils with various physicochemical properties.

Aniline aerofloat (AAF), a high-toxic organic flotation reagent, is widely used in mineral processing industry. However, little information on its environmental fate is available. AAF sorption to four types of agricultural soils at low concentrations (1-10 mg/L) was investigated using batch experiments. AAF sorption kinetics involved both boundary layer diffusion and intraparticle diffusion, following pseudo-second-order kinetics with equilibrium time within 120 min. Both Langmuir and Freundlich models fitted well the AAF sorption with the former better. Sorption of AAF to soils was a spontaneous and favorable physical sorption that was controlled by ion bridge effect and hydrophobic interaction that was related to van der Waals force and π-π coordination based on FTIR analyses. AAF sorption was remarkably affected by soil constituents, positively correlating with the contents of organic matter and clay. The relatively higher logKoc values (3.53-4.66) of AAF at environmental concentrations (1-5 mg/L) imply that soils are serving as a sink of AAF from beneficiation wastewater, posing great potential risks to environment and human health.

Uptake kinetics of pesticides chlorpyrifos and tebuconazole in the earthworm Eisenia andrei in two different soils.

Agriculture is today indispensably connected with enormous use of pesticides. Despite tough regulation, their entrance into soil cannot be excluded and they might enter soil organisms and plants and continue further to terrestrial food chains. This study was conducted to investigate the bioaccumulation of two pesticides currently used in large amounts, the insecticide chlorpyrifos (CLP) and the fungicide tebuconazole (TBZ). Their detailed uptake kinetics in the model earthworm species Eisenia andrei were measured in two arable soils differing in organic carbon content (1.02 and 1.93% respectively). According to our results, a steady state was reached after 3-5 days for both pesticides and soils. The values of bioaccumulation factors calculated at the steady state ranged from 4.5 to 6.3 for CLP and 2.2-13.1 for TBZ. Bioaccumulation factors were also calculated as the ratio of uptake and elimination rate constants with results comparable with steady-state bioaccumulation factors. The results suggested that the degradation and bioaccumulation of tested compounds might be influenced by other factors than only total organic carbon (e.g. clay content). The lower Koc and hydrophobicity of TBZ relative to CLP probably led to higher availability of TBZ through pore water exposure. On the other hand, CLP's higher hydrophobicity probably caused an increase in availability by its additional uptake via ingestion. To enable a proper ecological risk assessment of current pesticides in soils, it is necessary to accurately determine their bioaccumulation in soil invertebrates. We believe that our study not only brings such information for two specific pesticides but also addresses key methodological issues in this area.

Physico-chemical characterization of playground sand dust, inhalable and bioaccessible fractions.

Dust is a mixture of natural and anthropogenic particles originated from multiple sources, which can represent an hazard for human health. Playgrounds are a site of particularly concern, due to sand dust ingestion by toddlers and inhalation. In this study, 37 sands used in public playgrounds in the city of Barcelona were physico-chemically characterized also in relation to routine maintenance activities such as disinfection and sand renewal. The analyzed sands show a felsic mineralogy dominated by Na-feldspar, quartz, and, to a lesser extent, K-feldspar, with minor amounts of clay minerals, carbonates and hematite. Particle fractions below 10, 2.5 and 1 µm represent, on average, 0.65%, 0.17% and 0.07% of bulk volume, respectively, although, due to the human grinding, these initial fractions increased every year by a 18%, 5% and 2% respectively. Disinfection of sands effectively reduced only the NH4+ concentration, among inorganic species. The average metal content was anthropogenically enriched, with respect to the upper continental crust, only for Sb and As. Both elements show high spatial variation indicating local sources such as road traffic for Sb (contributing mostly to the total concentration), and industry for As (also contributing with highly bioaccessible Sb, Cu and Zn). A clear inverse relationship between total concentrations of some elements and their leachable (Sb) and bioaccessible (Sb and Cr) fractions is observed. The most bioaccessible elements were Ca > Ni > Cu > Sr > Cd > Pb, all above the 25% of the total concentration. Bioaccessibility was higher for the carbonate-bearing particles and for the anthropic emitted metals (>50% of Ba, Cu, K, Pb and Zn).

Effects of feeding bentonite clay upon ochratoxin A-induced immunosuppression in broiler chicks.

A presence of mycotoxins in feed is one of the most alarming issues in the poultry feed industry. Ochratoxins, produced by several Aspergillus and Penicillium species, are important mycotoxin regarding the health status of poultry birds. Ochratoxins are further classified into to several subtypes (A, B, C, etc) depending on their chemical structures, but ochratoxin A (OTA) is considered the most important and toxic. Bentonite clay, belonging to phyllosilicates and formed from weathering of volcanic ashes, has adsorbent ability for several mycotoxins. The present study was designed to study the effects of bentonite clay upon OTA-induced immunosuppression in broiler chicks. For this, 480 day-old broiler chicks were procured from a local hatchery and then different combinations of OTA (0.15, 0.3, or 1.0 mg/kg) and bentonite clay (5, 10, and 20 g/kg) were incorporated into their feed. At 13, 30, and 42 days of age, parameters such as antibody responses to sheep red blood cells, in situ lymphoproliferative responses to mitogen (PHA-P), and in situ phagocytic activity (i.e., via carbon clearance) were determined respectively. The results indicated there was a significant reduction of total antibody and immunoglobulin titres, lymphoproliferative responses, and phagocytic potential in OTA-treated birds, suggesting clear immunosuppression by OTA in birds in a dose-dependent manner. These results were also significantly lower in all combination groups (OTA with bentonite clay), suggesting few to no effects of feeding bentonite clay upon OTA- induced alterations in different immune parameters.

Composition, Respirable Fraction and Dissolution Rate of 24 Stone Wool MMVF with their Binder.

BACKGROUND: Man-made vitreous fibres (MMVF) are produced on a large scale for thermal insulation purposes. After extensive studies of fibre effects in the 1980ies and 1990ies, the composition of MMVF was modified to reduce the fibrotic and cancerogenic potential via reduced biopersistence. However, occupational risks by handling, applying, disposing modern MMVF may be underestimated as the conventional regulatory classification -combining composition, in-vivo clearance and effects- seems to be based entirely on MMVF after removal of the binder. RESULTS: Here we report the oxide composition of 23 modern MMVF from Germany, Finland, UK, Denmark, Russia, China (five different producers) and one pre-1995 MMVF. We find that most of the investigated modern MMVF can be classified as "High-alumina, low-silica wool", but several were on or beyond the borderline to "pre-1995 Rock (Stone) wool". We then used well-established flow-through dissolution testing at pH 4.5 and pH 7.4, with and without binder, at various flow rates, to screen the biosolubility of 14 MMVF over 32 days. At the flow rate and acidic pH of reports that found 47 ng/cm2/h dissolution rate for reference biopersistent MMVF21 (without binder), we find rates from 17 to 90 ng/cm2/h for modern MMVF as customary in trade (with binder). Removing the binder accelerates the dissolution significantly, but not to the level of reference biosoluble MMVF34. We finally simulated handling or disposing of MMVF and measured size fractions in the aerosol. The respirable fraction of modern MMVF is low, but not less than pre-1995 MMVF. CONCLUSIONS: The average composition of modern stone wool MMVF is different from historic biopersistent MMVF, but to a lesser extent than expected. The dissolution rates measured by abiotic methods indicate that the binder has a significant influence on dissolution via gel formation. Considering the content of respirable fibres, these findings imply that the risk assessment of modern stone wool may need to be revisited based on in-vivo studies of MMFV as marketed (with binder).