Carcinogenic risk of chromium, copper and arsenic in CCA-treated wood

Beneficial and adverse effects of dam construction in canal tannery wastewater effluent with a high content of chromium in Hazaribagh, Bangladesh

BACKGROUND

Blockage to divide downstream canals into upstream canals, into which tannery wastewater including a high concentration of trivalent chromium [Cr(III)] is directly discharged, has been constructed in Hazaribagh, a tannery built-up area in Bangladesh. However, there has been no study to verify the environmental significance of blockage construction for water pollution of Cr in nature.

METHODS

Consecutive fixed area monitoring for a total of 164 water samples collected outside and inside Hazaribagh from 2014 to 2023 was carried out to clarify the effects of stagnant and flowable canal water in the presence or absence of blockage on Cr(III) and hexavalent Cr [Cr(VI)] concentrations.

RESULTS

Since pollution of Cr(III) and Cr(VI) in Buriganga River (outside Hazaribagh) was not serious, this study then focused on their pollution in canal water (inside Hazaribagh) in the nonblockage period, blockage construction period and blockage destruction period. As expected, the mean Cr(III) concentration in downstream canal water samples in the blockage construction period was more than 98% lower than that in the upstream canal water samples in the same period, while the concentrations were comparable in downstream and upstream canal water samples in the nonblockage period and blockage destruction period. Unexpectedly, the mean concentration of Cr(VI) in the upstream canal water samples in the blockage construction period was 38.6-fold and 3.3-fold higher than that in the downstream canal water samples and the Cr(VI) guideline value by the US-EPA, respectively.

CONCLUSION

This study demonstrated for the first time not only a merit of decreased Cr(III) pollution but also a demerit of increased Cr(VI) pollution in stagnant water derived from blockage construction in natural environments. This bitter lesson obtained by the enclosure of Cr(III)-polluted water is globally applicable for water pollution of Cr(III), which is used in various industries including the leather industry.

Temporal analysis of lung injury induced by real-ambient PM2 .5 exposure in mice

Fine particulate matter (PM2.5 ) has been shown to induce lung injury. However, the pathophysiological mechanisms of PM2.5 -induced pulmonary injury after different exposure times are poorly understood. In this study, we exposed male ICR mice to a whole-body PM2.5 inhalation system at daily mean concentration range from 92.00 to 862.00 μg/m3 for 30, 60, and 90 days. We found that following prolonged exposure to PM2.5 , pulmonary injury was increasingly evident with significant histopathological alterations. Notably, the pulmonary inflammatory response and fibrosis caused by PM2.5 after different exposure times were closely associated with histopathological changes. In addition, PM2.5 exposure caused oxidative stress, DNA damage and impairment of DNA repair in a time-dependent manner in the lung. Importantly, exposure to PM2.5 eventually caused apoptosis in the lung through upregulation of cleaved-caspase-3 and downregulation of Bcl-2. Overall, our data demonstrated that PM2.5 led to pulmonary injury in a time-dependent manner via upregulation of proinflammatory and fibrosis-related genes, and activation of the DNA damage response. Our findings provided a novel perspective on the pathophysiology of respiratory diseases caused by airborne pollution.

Unexpected associations of long-term and excessive exposure to trivalent chromium with hypertension and glycosuria in male tannery workers

Serious health hazards including renal, skin and hearing disorders have been reported in Bangladeshi tannery workers (TWs) who were chronically exposed to a large amount of trivalent chromium [Cr(III)]. However, the effects of Cr(III) exposure on the prevalence of hypertension and the prevalence of glycosuria in TWs remain unknown. Since the Cr level in toenails is an established marker reflecting long-term exposure to Cr(III) in humans, the associations of Cr levels in toenails with the prevalence of hypertension and the prevalence of glycosuria in male tannery and non-tannery office workers (non-TWs) in Bangladesh were investigated in this study. The mean toenail Cr level in non-TWs (0.5 μg/g, n = 49) was comparable to that in the general population reported previously. Mean Cr levels in TWs with a low toenail Cr level (5.7 μg/g, n = 39) and those with a high toenail Cr level (298.8 μg/g, n = 61) were >10-fold and >500-fold higher, respectively, than that in non-TWs. Our univariate and multivariate analyses indicated that the prevalence of hypertension and the prevalence of glycosuria in TWs with a high toenail Cr level, but not in TWs with a low toenail Cr level, were significantly lower than those in non-TWs. This study showed for the first time that long-term and excessive exposure to Cr(III) that is more than >500-fold but not >10-fold higher than the usual exposure level could decrease the prevalence of hypertension and the prevalence of glycosuria in TWs. Thus, this study revealed unexpected effects of exposure to Cr(III) on health.

Distribution and Speciation of Heavy Metal(loid)s in Soils under Multiple Preservative-Treated Wooden Trestles

The widespread use of wood preservatives, such as chromated copper arsenate (CCA), alkaline copper quaternary (ACQ), and copper azole (CA), may cause environmental pollution problems. Comparative studies on the effect of CCA-, ACQ-, and CA-treated wood on soil contamination are rarely reported, and the behavior of soil metal(loid) speciation affected by preservatives has been poorly understood. Soils under the CCA-, ACQ-, and CA-treated boardwalks were collected to investigate metal(loid) distribution and speciation at the Jiuzhaigou World Natural Heritage site. The results showed that the maximum mean concentrations of Cr, As, and Cu were found in soils under the CCA, CCA, and CCA plus CA treatments and reached 133.60, 314.90, and 266.35 mg/kg, respectively. The Cr, As, and Cu contamination in soils within a depth of above 10 cm was high for all types of boardwalks and limited in the horizontal direction, not exceeding 0.5 m. Cr, As, and Cu in soils were mainly present as residual fractions in all profiles and increased with depth. The proportion of non-residual As in soil profiles under CCA- and CCA plus CA-treatment and exchangeable Cu in CA- and CCA plus CA-treatment were significantly higher than those in the profiles under the other preservative treatments. The distribution and migration of Cr, As, and Cu within soils were influenced by the preservative treatment of trestles, in-service time of trestles, soil properties (e.g., organic matter content), geological disasters (e.g., debris flow), and elemental geochemical behavior. With the CCA treatment for trestles successively replaced by ACQ and CA treatments, the types of contaminants were reduced from a complex of Cr, As, and Cu to a single type of Cu, achieving a reduction in total metal content, toxicity, mobility, and biological effectiveness, thus reducing environmental risks.

Identification and quantification of Cr, Cu, and As incidental nanomaterials derived from CCA-treated wood in wildland-urban interface fire ashes

In addition to the combustion of vegetation, fires at the wildland-urban interface (WUI) burn structural materials, including chromated copper arsenate (CCA)-treated wood. This study identifies, quantifies, and characterizes Cr-, Cu-, and As-bearing incidental nanomaterials (INMs) in WUI fire ashes collected from three residential structures suspected to have originated from the combustion of CCA-treated wood. The total elemental concentrations were determined by inductively coupled plasma-time of flight-mass spectrometry (ICP-TOF-MS) following acid digestion. The crystalline phases were determined using transmission electron microscopy (TEM), specifically using electron diffraction and high-resolution imaging. The multi-element single particle composition and size distribution were determined by single particle (SP)-ICP-TOF-MS coupled with agglomerative hierarchical clustering analysis. Chromium, Cu, and As are the dominant elements in the ashes and together account for 93%, 83%, and 24% of the total mass of measured elements in the ash samples. Chromium, Cu, and As phases, analyzed by TEM, most closely match CrO₃, CrO₂, eskolaite (Cr₂O₃), CuCrO₂, CuCr₂O₄, CrAs₂O₆, As₂O₅, AsO₂, claudetite (As₂O₃, monoclinic), or arsenolite (As₂O₃, cubic), although a bona fide phase identification for each particle was not always possible. These phases occur predominantly as heteroaggregates. Multi-element single particle analyses demonstrate that Cr occurs as a pure phase (i.e., Cr oxides) as well as in association with other elements (e.g., Cu and As); Cu occurs predominantly in association with Cr and As; and As occurs as As oxides and in association with Cu and Cr. Several Cr, Cu, and As clusters were identified and the molar ratios of Cr/Cu and Cr/As within these clusters are consistent with the crystalline phases identified by TEM as well as their heteroaggregates. These results indicate that WUI fires can lead to significant release of CCA constituents and their combustion-transformed by-products into the surrounding environment. This study also provides a method to identify and track CCA constituents in environmental systems based on multi-element analysis using SP-ICP-TOF-MS.

Gene expression analysis of antioxidant and DNA methylation on the rat liver after 4-week wood preservative chromated copper arsenate exposure

Our previous 4-week repeated dose toxicity study showed that wood preservative chromated copper arsenate (CCA) induced hepatocellular hypertrophy accompanied by biochemical hepatic dysfunction and an increase in oxidative stress marker, 8-hydroxydeoxyguanosine, in female rats. To further explore the molecular mechanisms of CCA hepatotoxicity, we analyzed 10%-buffered formalin-fixed liver samples from female rats for cell proliferation, apoptosis, and protein glutathionylation and conducted microarray analysis on frozen liver samples from female rats treated with 0 or 80 mg/kg/day of CCA. Chemical analysis revealed that dimethylated arsenical was the major metabolite in liver tissues of male and female rats. CCA increase labeling indices of proliferating cell nuclear antigen and decrease terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling accompanied with increased expression of protein glutathionylation, indicating a decrease in glutathione (GSH) in hepatocytes of female rats. Microarray analysis revealed that CCA altered gene expression of antioxidants, glutathione-S-transferase (GST), heat shock proteins and ubiquitin-proteasome pathway, cell proliferation, apoptosis, DNA methylation, cytochrome P450, and glucose and lipid metabolism in female rats. Increased expression of GSTs, including Gsta2, Gsta3, Mgst1, and Cdkn1b (p27), and decreased expression of the antioxidant Mt1, and DNA methylation Dnmt1, Dnmt3a, and Ctcf were confirmed in the liver of female rats in a dose-dependent manner. Methylation status of the promoter region of the Mt1 was not evidently changed between control and treatment groups. The results suggested that CCA decreased GSH and altered the expression of several genes, including antioxidants, GST, and DNA methylation, followed by impaired cell proliferation in the liver of female rats.

Redistribution of potentially toxic elements in the hydrosphere after the relocation of a group of tanneries

Simultaneous relocation of a group of pollutant sources in a heavily polluted area is a rare event. Such a relocation has been implemented in Hazaribagh, a tannery built-up area with heavy pollution, in Bangladesh. This provides a valuable opportunity to compare the changes in environmental conditions associated with the relocation of multiple putative sources. Our environmental monitoring for a period of 6 years at the stationary areas centered on Hazaribagh geographically revealed trivalent [Cr(III)], hexavalent [Cr(VI)] chromium, lead, iron, and manganese as tannery-related elements after the legal deadline for tannery relocation. The median Cr(III) level in canal water, into which wastewater from tanneries was directly discharged, after the relocation was 97% lower of that before the relocation, indicating a beneficial effect of the relocation. In contrast, the median Cr(VI) level in water samples just after the relocation and 2 years after the relocation were approximately 5-fold and 30-fold higher, respectively, than those before the relocation. These results indicate not only a harmful effect of the relocation but also the possibility of conversion from Cr(III) to Cr(VI) in nature. Although the health hazard indexes considering all of the tannery-related elements in all of the canal water samples before the relocation exceeded the safety thresholds, the percentages of samples in which the indexes exceeded their safety thresholds after the relocation decreased by 32.5%-45.0%. Treatment with our patented hydrotalcite-like compound consisting of magnesium and iron (MF-HT) resulted in decreases in the health hazard indexes in all of the water samples in which the indexes exceeded their safety thresholds to levels lower than their thresholds. Thus, this study shows the double-edged effects associated with the relocation and a potential solution.

Antioxidant Effect of Coenzyme Q10 in the Prevention of Oxidative Stress in Arsenic-Treated CHO-K1 Cells and Possible Participation of Zinc as a Pro-Oxidant Agent

Oxidative stress is an imbalance between levels of reactive oxygen species (ROS) and antioxidant enzymes. Compounds with antioxidant properties, such as coenzyme Q10 (CoQ10), can reduce cellular imbalance caused by an increase in ROS. CoQ10 participates in modulating redox homeostasis due to its antioxidant activity and its preserving mitochondrial functions. Thus, the present study demonstrated the protective effects of CoQ10 against oxidative stress and cytotoxicity induced by arsenic (As). Antioxidant capacity, formation of hydroperoxides, generation of ROS, and the effect on cellular viability of CoQ10, were investigated to determine the protective effect of CoQ10 against As and pro-oxidant compounds, such as zinc. Cell viability assays showed that CoQ10 is cytoprotective under cellular stress conditions, with potent antioxidant activity, regardless of the concentration tested. Zn, when used at higher concentrations, can increase ROS and show a pro-oxidant effect causing cell damage. The cytotoxic effect observed for As, Zn, or the combination of both could be prevented by CoQ10, without any decrease in its activity at cellular levels when combined with Zn.

Ecotoxic, genotoxic, and cytotoxic potential of leachate obtained from chromated copper arsenate-treated wood ashes

Preservative treatments increase the durability of wood, and one of the alternative treatments involves the use of chromated copper arsenate (CCA). Due to the toxicity of CCA, the disposal of CCA-treated wood residues is problematic, and burning is considered to provide a solution. The ecotoxicological potential of ash can be high when these components are toxic and mutagenic. The aim of this study was to evaluate the toxicity and genotoxicity of bottom ash leachates originating from CCA-treated wood burning. Physical-chemical analysis of the leachates revealed that in treated wood ashes leachate (CCA-TWBAL), the contents of arsenic and chromium were 59.45 mg.L^-1 and 54.28 mg.L^-1, respectively. In untreated wood ashes leachate (UWBAL), these contents were 0.70 mg.L^-1 and 0.30 mg.L^-1, respectively. CCA-TWBAL caused significant toxicity in Lactuca sativa, Allium cepa, and microcrustacean Artemia spp. (LC50 = 12.12 mg.mL^-1). Comet assay analyses using NIH3T3 cells revealed that concentrations ranging from 1.0 and 2.5 mg.mL^-1 increase the damage frequency (DF) and damage index (DI). According to MTT assay results, CCA-TWBAL at concentrations as low as 1 mg.mL^-1 caused a significant decrease in cellular viability. Hemolysis assay analyses suggest that the arsenic and chromium leachate contents are important for the ecotoxic, cytotoxic, and genotoxic effects of CCA-TWBAL.

Sustainable Strategies for the Agricultural Development of Shaanxi Province Based on the Risk Assessment of Heavy Metal Pollution

Heavy metal elements in farmland soil can be absorbed by crops and endanger food security. To assess the risk of heavy metal elements in farmland soil to crops in Shaanxi Province, we collected 693 soil samples and analyzed the concentrations of nine heavy metals (As, Hg, Pb, Cd, Cr, Mn, Cu, Zn, and Ni). According to the National Standard (GB 15619-2018) of the People’s Republic of China, the proportions of soil sample points in which the concentration of heavy metals was higher than the risk screening value were 2.02% (Cd), 0.29% (Cr), 0.29% (Zn), 2.31% (Cu), 1.15% (Ni), and 0.14% (Pb). The proportions of areas in which the concentration of heavy metal was higher than the background value were as follows, from largest to smallest: Zn (53.20%) > Mn (49.86%) > Cd (29.51%) > Hg (26.77%) > As (26.58%) > Ni (14.95%) > Cu (13.90%) > Pb (6.49%) > Cr (1.40%). The assessment of the risk of heavy metal exposure (geo-accumulation index (Igeo), pollution load index (PLI), and potential ecological risk index (RI)) determined that Hg was the most concerning heavy metal in the farmland soil of Shaanxi Province. Moreover, 11.56% of these areas had Hg contamination, and they were mainly distributed in the western Guanzhong region. The farmland soil in the Guanzhong region was the most contaminated, followed by the southern Shaanxi region and then the northern Shaanxi region. The main sources of heavy metal contamination causing large-scale farmland soil pollution are agricultural production activities, transportation, and air pollution caused by coal combustion in Shaanxi Province. Therefore, sustainable strategies for the prevention and control of heavy metal pollution and agricultural development must be applied in different regions. Heavy metal pollution should be managed, and relevant policies should be created and enforced, such as the standardization of the use of qualified pesticides and fertilizers, improved treatment of livestock and poultry manure, development of the clean energy industry structure, and promotion of renewable energy vehicles. In terms of the high-quality development of agriculture, developing modern and local agriculture in different regions should be based on local geographical, climatic, and economic conditions.

Development of an efficient remediation system with a low cost after identification of water pollutants including phenolic compounds in a tannery built-up area in Bangladesh

Water pollution caused by tannery wastewater is an important issue in developing countries. Most studies have focused on inorganic chemicals represented by chromium as a tannery-related main pollutant. This is the first study in which pollution of water by tannery-related organic chemicals was assessed by a combination of qualitative and quantitative analyses. Our quantitative analysis showed that the maximum concentration of total phenolic compounds (phenols), consisting of phenol, bisphenol F, p-cresol and chlorocresol, in canal water in a tannery built-up area in Bangladesh was >67-fold higher than the Environmental, Health and Safety (EHS) guideline value. Mapping of our results indicated tanneries as the sources of phenols pollution. Our original depurative, a hydrotalcite-like compound consisting of magnesium and iron (MF-HT), could adsorb all kinds of phenols and exhibited the highest phenol adsorption ability (115.8 mg/g) among reported hydrotalcite-like compounds. The levels of phenols in canal water samples were reduced to levels below the guideline value by using MF-HT with assistance of a photocatalytic reaction. Moreover, the mean level of chromium (112.2 mg/L) in canal water samples was decreased by 99.7% by using the depurative. Thus, the depurative has the potential for solving the problem of tannery-related water pollution by phenols and chromium.

Circular RNA circ_Cabin1 promotes DNA damage in multiple mouse organs via inhibition of non-homologous end-joining repair upon PM2.5 exposure

Fine particulate matter (PM_2.5) has been shown to induce DNA damage. Circular RNAs (circRNAs) have been implicated in various disease processes related to environmental chemical exposure. However, the role of circRNAs in the regulation of DNA damage response (DDR) after PM_2.5 exposure remains unclear. In this study, male ICR mice were exposed to PM_2.5 at a daily mean concentration of 382.18 μg/m³ for 3 months in an enriched-ambient PM_2.5 exposure system in Shijiazhuang, China, and PM_2.5 collected form Shijiazhuang was applied to RAW264.7 cells at 100 µg/mL for 48 h. The results indicated that exposure to PM_2.5 induced histopathological changes and DNA damage in the lung, kidney and spleen of male ICR mice, and led to decreased cell viability, increased LDH activity and DNA damage in RAW264.7 cells. Furthermore, circ_Cabin1 expression was significantly upregulated in multiple mouse organs as well as in RAW264.7 cells upon exposure to PM_2.5. PM_2.5 exposure also resulted in impairment of non-homologous end joining (NHEJ) repair via the downregulation of Lig4 or Dclre1c expression in vivo and in vitro. Importantly, circ_Cabin1 promoted PM_2.5-induced DNA damage via inhibiting of NHEJ repair. Moreover, the expression of circ_Cabin1 and Lig4 or Dclre1c was strongly correlated in multiple mouse organs, as well as in the blood. In summary, our study provides a new perspective on circRNAs in the regulation of DDR after environmental chemical exposure.

Environmental and Health Hazards of Chromated Copper Arsenate-Treated Wood: A Review

Copper chrome arsenate (CCA) water-borne solution used to be widely used to make timber highly resistant to pests and fungi, in particular, wood products designed for outdoor use. Nowadays, CCA is a restricted chemical product in most countries, since potential environmental and health risks were reported due to dermal contact with CCA residues from treated structures and the surrounding soil, as well as the contamination of soils. However, large quantities of CCA-treated timber are still in use in framings, outdoor playground equipment, landscaping, building poles, jetty piles, and fencing structures around the world, thus CCA remains a source of pollutants to the environment and of increasing toxic metal/metalloid exposure (mainly in children). International efforts have been dedicated to the treatment of materials impregnated with CCA, however not only does some reuse of CCA-treated timber still occur, but also existing structures are leaking the toxic compounds into the environment, with impacts on the environment and animal and human health. This study highlights CCA mechanisms and the documented consequences in vivo of its exposure, as well as the adverse environmental and health impacts.

Bio-Based Hydrogels With Ion Exchange Properties Applied to Remove Cu(II), Cr(VI), and As(V) Ions From Water

Hydrogels with ion exchange properties were synthesized from compounds derived from wood biopolymer hemicellulose and from commercial vinyl monomers to be tested as active materials for the removal of Cu(II), Cr(VI), and As(V) ions. The hemicellulose O-acetyl galactoglucomannan (GGM) was used as the precursor material, and through a transesterification reaction, GGM was converted into a macromonomer GGM–glycidyl methacrylate (GGM-GMA). Subsequently, the GGM-GMA macromonomer, containing more than one methacrylate group, was used as a crosslinking agent in the synthesis of hydrogels through free-radical polymerization reactions in combination with a 2-acrylamido-2-methyl-1-propanesulfonic acid monomer to produce a cation exchange hydrogel. Also, (3-acrylamidopropyl)trimethylammonium chloride monomer was applied together with the GGM-GMA to form hydrogels that can be used as anion exchange hydrogel. The hydrogels were characterized by Fourier transform-infrared (FT-IR), ¹H-NMR spectroscopy, and thermogravimetric analysis (TGA), as well as derivative thermogravimetry (DTG). The microstructure of the hydrogels was characterized by scanning electron microscopy (SEM) analysis with X-ray microanalysis energy-dispersive spectroscopy (EDS). The results obtained regarding the absorption capacity of the Cu(II), Cr(VI), and As(V) ions were studied as a function of the pH value and the initial concentration of the metal ions in the solutions. Absorption was carried out in consecutive batches, and it was found that the poly(GGM-GMA/AMPSH) hydrogel reached an absorption capacity of 90 mg g^–1 for Cu(II). The poly(GGM-GMA/APTACl) hydrogel reached values of 69 and 60 mg g^–1 for Cr(VI) and As(V) oxyanions, respectively. Tests with polymer blends (mixtures of anionic and cationic hydrogels) were also carried out to remove Cu(II), Cr(VI), and As(V) ions from multi-ionic solutions, obtaining satisfactory results.

Intranasal levels of lead as an exacerbation factor for allergic rhinitis in humans and mice

BACKGROUND

Air pollutants are suspected to affect pathological conditions of allergic rhinitis (AR).

OBJECTIVES

After detecting Pb (375 μg/kg) in Japanese cedar pollen, the effects of intranasal exposure to Pb on symptoms of AR were investigated.

METHODS

Pollen counts, subjective symptoms, and Pb levels in nasal epithelial lining fluid (ELF) were investigated in 44 patients with Japanese cedar pollinosis and 57 controls from preseason to season. Effects of intranasal exposure to Pb on symptoms were confirmed by using a mouse model of AR.

RESULTS

Pb levels in ELF from patients were >40% higher than those in ELF from control subjects during the pollen season but not before the pollen season. Pb level in ELF was positively associated with pollen counts for the latest 4 days before visiting a hospital as well as scores of subjective symptoms. Intranasal exposure to Pb exacerbated symptoms in allergic mice, suggesting Pb as an exacerbation factor. Pb levels in ELF and nasal mucosa in Pb-exposed allergic mice were higher than those in Pb-exposed nonallergic mice, despite intranasally challenging the same amount of Pb. Because the increased Pb level in the nasal mucosa of Pb-exposed allergic mice was decreased after washing the nasal cavity, Pb on the surface of but not inside the nasal mucosa may have been a source of increased Pb level in ELF of allergic mice.

CONCLUSIONS

Increased nasal Pb level partially derived from pollen could exacerbate subjective symptoms of AR, indicating Pb as a novel hazardous air pollutant for AR.

Toxicity and Anti-Proliferative Properties of Anisomeles indica Ethanol Extract on Cervical Cancer HeLa Cells and Zebrafish Embryos

In this study, we showed that crude extract of Anisomeles indica (AI-EtE) expressed its toxicity to HeLa cells with an IC50 dose of 38.8 µg/mL and to zebrafish embryos with malformations, lethality and hatching inhibition at 72-hpf at doses higher than 75 µg/mL. More interestingly, flow cytometry revealed that AI-EtE significantly promoted the number of cells entering apoptotic. Accordingly, the transcript levels of BAX, CASPASE-8, and CASPASE-3 in the cells treated with AI-EtE at IC50 dose were 1.55-, 1.62-, and 2.45-fold higher than those in the control cells, respectively. Moreover, treatment with AI-EtE caused cell cycle arrest at the G1 phase in a p53-independent manner. Particularly, percentages of AI-EtE-treated cells in G1, S, G2/M were, respectively 85%, 6.7% and 6.4%; while percentages of control cells in G1, S, G2/M were 64%, 15% and 19%, respectively. Consistent with cell cycle arrest, the expressions of CDKN1A and CDNK2A in AI-EtE-treated cells were up-regulated 1.9- and 1.64-fold, respectively. Significantly, treatment with AI-EtE also decreased anchorage-independent growth of HeLa cells. In conclusion, we suggest that Anisomeles indica can be considered as a medicinal plant with a possible use against cervical cancer cells; however, the used dose should be carefully monitored, especially when applying to pregnant women.

Fine particulate matter PM2.5 generated by building demolition increases the malignancy of breast cancer MDA-MB-231 cells

OBJECTIVES

This study investigates the effects of water-extracted PM_2.5 on a triple-negative breast cancer (TNBC) cell line, MDA-MB-231, by sampling suspended particulates around a building demolition site.

METHODS

PM_2.5 particles were obtained using a high-flow TISCH sampler. Water-soluble PM_2.5 were extracted by an ultrasonic oscillator and then freeze-dried. The heavy metal components of soluble PM_2.5 was analyzed by ICP-MS. Cell viability was evaluated by MTT assay for cells that were exposed to PM_2.5 (200, 400 and 600 μg/mL). Wound healing and transwell cell migration and invasion assays were used to measure cell motility and the invasiveness of cancer cells that had been exposed to PM_2.5 into a chemo-attractant substance. Interrelated mechanisms of cancer malignancy were analyzed by Western blot analysis.

RESULTS

Nearby PM_2.5 concentrations increased significantly during the deconstruction of buildings, and the Cd, Cu, Pb, Zn and Cr contents of soluble PM_2.5 also significantly increased. Following exposure to PM_2.5, the survival rate of breast cancer cells was significantly higher than that of the control group. Soluble PM_2.5-treated cells had a higher migration capacity. The signaling pathway of FAK/PI3K/AKT proteins was more activated in PM_2.5-treated cells than the control group. Increased levels of Aurora B and Bcl-2 were associated with cell proliferation. Elevated levels of cathepsins D, β-catenin, N-cadherin, vimentin and MMP-9 were associated with breast cancer cell metastasis.

CONCLUSION

Soluble PM_2.5 from building demolition may promote/progress in surviving TNBC cells, increasing the malignancy of breast cancer. This study offered evidence of a link between demolition PM_2.5 and cancer progression.

Lithium promotes malignant transformation of nontumorigenic cells in vitro

Because of the deficiency of water caused by the regional disparities of rainfall due to global warming, attention has been given to the use of well water as drinking water in developing countries. Our fieldwork study in Afghanistan showed that there was a maximum value of 3371 μg/L and an average value of 233 μg/L of lithium in well drinking water. Since the level of lithium in well water is higher than the levels in other countries, we investigated the health risk of lithium. After confirming no influence of ≤1000 μM lithium on cell viability, we found that lithium at concentrations of 100 and 500 μM promoted anchorage-independent growth of human immortalized keratinocytes (HaCaT) and lung epithelial cells (BEAS-2B) but not that of human keratinocytic carcinoma cells (HSC-5) or lung epithelial carcinoma cells (A549). The same concentrations of lithium also promoted phosphorylation of c-SRC and MEK/ERK but not that of AKT in the keratinocytes. Inhibitors of c-SRC (PP2) and MEK (PD98059) suppressed the lithium-induced increase in anchorage-independent growth of the keratinocytes. Our results suggested that lithium promoted transformation of nontumorigenic cells rather than progression of tumorigenic cells with preferential activation of the c-SRC/MEK/ERK pathway. Since previous pharmacokinetics studies indicated that it is possible for the serum level of lithium to reach 100 μM by drinking 2.5 L of water containing 3371 μg/L of lithium per day, the high level of lithium contamination in well drinking water in Kabul might be a potential oncogenic risk in humans.

Application of Nanotechnology in Wood-Based Products Industry: A Review

Wood-based industry is one of the main drivers of economic growth in Malaysia. Forest being the source of various lignocellulosic materials has many untapped potentials that could be exploited to produce sustainable and biodegradable nanosized material that possesses very interesting features for use in wood-based industry itself or across many different application fields. Wood-based products sector could also utilise various readily available nanomaterials to enhance the performance of existing products or to create new value added products from the forest. This review highlights recent developments in nanotechnology application in the wood-based products industry.

High levels of boron promote anchorage-independent growth of nontumorigenic cells

WHO has presented a health-based guideline value for boron in drinking water. That fact indicates that a high level of boron is toxic for humans. However, there is no direct evidence of boron-mediated malignant transformation. In this study, human lung epithelial nontumorigenic BEAS-2B cells and tumorigenic A549 cells were used to investigate the tumorigenic toxicity of boron in vitro. Anchorage-independent growth, a hallmark of malignant transformation, was increased by boron at concentrations of 50, 250 and 500 μM in BEAS-2B cells, though the same concentrations of boron had no influence on anchorage-independent growth of A549 cells. Moreover, boron at concentrations of 250 and 500 μM activated the c-SRC/PI3K/AKT pathway of BEAS-2B cells. The results of our in vitro study suggest that exposure to high levels of boron promotes transforming activity of nontumorigenic cells.

Human Health Risk Assessment through Roasted Meats Consumption

Data on the content of metals and metalloids in roasted meats with different types of wood and charcoal are still scarce in the literature. The concentrations of metals (Al, Cr, Cd, Cu, Fe, Mg, Mn, Mo, Ni, V, and Zn) and metalloid (As) were determined by inductively coupled plasma mass spectrometry (ICP-OES) after microwave digestion, and the estimated daily intake (EDI) for adults was assessed to determine the hazard quotient (HQ). The concentrations of Al, Cr, Cu, and Fe in raw meats were below the data obtained in other countries. The concentration of As (0.17 ± 0.42-0.23 ± 0.10 mg/kg), Mg (206.77 ± 3.99-291.95 ± 8.87 mg/kg), V (0.42 ± 0.14-6.66 ± 0.80 mg/kg), and Zn (6.66 ± 0.80-48.13 ± 0.56 mg/kg) in raw meats exceeded the values in the literature. The concentrations of Mg, As, Cr, Fe, V, and Zn are high when the meat is roasted using wood. All levels of Al, As, Cr, Cu, Fe, Mg, Mn, Mo, V, and Zn in raw meats are lower than those of meat roasted with coal and wood. The content of As in meat roasted with Chromed Copper Arsenate (CCA) wood (15.10 ± 0.27-26.25 ± 1.47 mg/kg) is higher than meat roasted with charcoal (0.46 ± 0.09-1.16 ± 0.50 mg/kg). EDI and HQ values revealed a minimal exposure of the adult population to those metals through roasted-meats consumption. However, EDI values of As in some roasted meats are above standard limits. Roast meats with wood showed higher levels of major and trace elements than meats roasted with coal. High exposures, in the long-term, may cause damage to health.

Cr(VI) adsorption from aqueous streams on eggshell membranes of different birds used as biosorbents

The discharges enriched with heavy metals, particularly Cr(VI), are a serious environmental problem. In this work, it is presented the use of biosorbents from eggshells membranes of ostrich, quail, duck and chicken; the membranes were easily prepared and studied for the removal of Cr(VI) from aqueous solutions. Maximum uptake of 1.41 mmol g−1 membrane permitted the identification of ostrich membrane as the material with the highest Cr(VI) uptake. N2 adsorption experiments permitted to classify ostrich membranes as mesoporous materials, since they had pore size of 14.8 nm. This represented an advantage on the nature of these membranes to be used as biosorbents with respect to other membranes. The adsorption isotherm models such as Langmuir and Freundlich were verified using experimental data. Langmuir model described the adsorption process satisfactorily at pH 1 and 2 whereas Freundlich model fitted data better at pH 3 and 5. The adsorption kinetic data were adjusted to a pseudo-second order kinetic model. TGA results permitted demonstrating a low thermal stability of ostrich membrane, since it starts decomposing at around 50°C due to the fact that membranes have about 60% protein. Through SEM microscopy was possible to observe the morphology of the membrane surfaces before and after Cr(VI) uptake which reflects the textural characteristics of the biosorbent. FTIR and XPS analyses suggested that Cr was adsorbed on ostrich membranes through the amine groups of proteins conforming the fibers of membranes. Despite the oxygen shows higher electronegativity than N, Cr shows more preference toward N due to fact that pH conditions favor the positive charges on the surface of the membrane. Our results make evident that this waste material is a novel and efficient option for the removal of Cr(VI) from aqueous solutions.

Increased levels of renal damage biomarkers caused by excess exposure to trivalent chromium in workers in tanneries

BACKGROUND

The process for leather material production is carried out in developing countries using a large amount of trivalent chromium [Cr(III)]. Assesment of health risks for millions of workers in tanneries worldwide that are highly polluted with Cr(III) is needed.

METHODS

Levels of total Cr and its chemical species in wastewater samples from tannery built-up areas of Bangladesh were investigated. Cr-mediated renal damage was assessed in 100 male tannery workers by epidemiological analysis consisting of questionnaires and measurements of levels of urinary Cr and urinary renal damage markers [urinary levels of total protein and kidney injury molecule-1 (KIM-1)].

RESULTS

High levels of total Cr (mean ± standard deviation = 1,908,762 ± 703,450 μg/L) were detected in wastewater samples from 13 sites of tanneries. More than 99.99% of total Cr in the wastewater was Cr(III), indicating that workers in the tanneries were exposed to large concentrations of Cr(III). Cr levels (mean ± standard, 2.89 ± 4.23 μg/g creatinine) in urine samples from the workers in tanneries were >24-fold higher than the levels in a general population previously reported. Multivariate analysis showed significant correlations between urinary levels of Cr and urinary levels of renal damage biomarkers. Nagelkerke Pseudo R² values also showed that Cr level is the strongest contributor to the levels of renal damage biomarkers in the workers.

CONCLUSION

Our results newly suggest that excess exposure to Cr(III) could be a risk for renal damage in humans.

Synthetic melanin nanoparticles as peroxynitrite scavengers, photothermal anticancer and heavy metals removal platforms

Melanin is a ubiquitous natural polyphenolic pigment with versatile applications including physiological functions. This polymeric material is found in a diversity of living organisms from bacteria to mammals. The biocompatibility and thermal stability of melanin nanoparticles make them good candidates to work as free radical scavengers and photothermal anticancer substrates. Research studies have identified melanin as an antioxidative therapeutic agent and/or reactive oxygen species (ROS) scavenger that includes neutralization of peroxynitrite. In addition, melanin nanoparticles have emerged as an anticancer photothermal platform that has the capability to kill cancer cells. Recently, melanin nanoparticles have been successfully used as chelating agents to purify water from heavy metals, such as hexavalent chromium. This review article highlights some selected aspects of cutting-edge melanin applications. Herein, we will refer to the recent literature that addresses melanin nanoparticles and its useful physicochemical properties as a hot topic in biomaterial science. It is expected that the techniques of Dynamic Light Scattering (DLS), Scanning Electron Microscopy (SEM), and time-resolved Electron Paramagnetic Resonance (EPR) will have a strong impact on the full characterization of melanin nanoparticles and the subsequent exploration of their physiological and chemical mechanisms.

Multidisciplinary approach to assess the toxicities of arsenic and barium in drinking water

Well water could be a stable source of drinking water. Recently, the use of well water as drinking water has been encouraged in developing countries. However, many kinds of disorders caused by toxic elements in well drinking water have been reported. It is our urgent task to resolve the global issue of element-originating diseases. In this review article, our multidisciplinary approaches focusing on oncogenic toxicities and disturbances of sensory organs (skin and ear) induced by arsenic and barium are introduced. First, our environmental monitoring in developing countries in Asia showed elevated concentrations of arsenic and barium in well drinking water. Then our experimental studies in mice and our epidemiological studies in humans showed arsenic-mediated increased risks of hyperpigmented skin and hearing loss with partial elucidation of their mechanisms. Our experimental studies using cultured cells with focus on the expression and activity levels of intracellular signal transduction molecules such as c-SRC, c-RET, and oncogenic RET showed risks for malignant transformation and/or progression arose from arsenic and barium. Finally, our original hydrotalcite-like compound was proposed as a novel remediation system to effectively remove arsenic and barium from well drinking water. Hopefully, comprehensive studies consisting of (1) environmental monitoring, (2) health risk assessments, and (3) remediation will be expanded in the field of environmental health to prevent various disorders caused by environmental factors including toxic elements in drinking water.

Overview of biochar production from preservative-treated wood with detailed analysis of biochar characteristics, heavy metals behaviors, and their ecotoxicity

Concerns over the disposal of preservative-treated wood waste and its related environmental problems are the main driving forces of research into the recycling of preservative-treated wood. Preservative-treated wood waste composed of cellulose, hemicellulose, and lignin with several types of heavy metals can be recycled in various ways, such as wood-based composites, heavy metal extraction, energy recovery, etc. In particular, thermochemical conversion has attracted considerable attention recently because energy can be recovered from biomass as liquid fuel and bio-oil, as well as produce bio-char with a high carbon content, which can be applied to valuable products, such as soil amendment, adsorbents, solid fuels, and catalyst supports. On the other hand, environmental issues, such as heavy metal volatilization and heavy metal leaching, are still a challenge. This review reports the state-of-the-art knowledge of biochar production from preservative-treated wood with the main focus on the feedstock, process technology, biochar characteristics, application, and environmental issues. This review provides important information for future studies into the recycling of preservative-treated woods into biochar.

Metal(loid)s inhalation bioaccessibility and oxidative potential of particulate matter from chromated copper arsenate (CCA)-contaminated soils

Field-collected chromated copper arsenate (CCA)-contaminated soils and associated particulate matter (PM) were characterized for their total metal(loid)s content (As, Cr, Cu, Fe, Mn, Ni, Pb and Zn) and physicochemical properties. Copper, Ni, Pb and Zn fractionation (using sequential extraction) and inhalation bioaccessibility (using two lung fluids) of trace elements were assessed in PM samples. In Gamble's solution (GS), low average bioaccessibility (up to 12%) was observed for As, Cu, Mn, and Ni. A strong correlation (r = 0.92, p < 0.005, n = 9) between the soluble and exchangeable fraction (F1) and bioaccessibility in GS was observed for Cu. Inhalation bioaccessibility in artificial lysosomal fluid (ALF) was higher for Cu (avg. 78.5 ± 4.2%), Mn (avg. 56.8 ± 12.1%), Zn (avg. 54.8 ± 24.5%) and As (avg. 45.4 ± 18.8%). Strong correlations between inhalation bioaccessibility in ALF and the mobile (i.e. F1+F2) metal fraction were observed for all tested metals (i.e. (Cu (r = 0.95, p < 0.005), Ni (r = 0.79, p < 0.05), Pb (r = 0.92, p < 0.005) and Zn (r = 0.98, p < 0.005)), n = 9). The oxidative potential (OP) of PM was also assessed using an ascorbate (AA) depletion assay (OP_AA). Mobile Cu fractions were deemed to be the main factor influencing OP_AA ((F1 (r = 0.99, p < 0.005), F2 (r = 0.97, p < 0.005)), n = 9) in PM samples. A strong correlation (r = 0.94, p < 0.005, n = 10) was also observed between Cu bioaccessibility in GS and OP_AA.

Comparative Cr, As and CCA induced Cytostaticity in mice kidney: A contribution to assess CCA toxicity

CCA (Chromium Copper Arsenate) treated wood, widely used in outdoor residential structures and playgrounds, poses considerable dangers of leaching of its components to the environment. In this study, mouse kidney samples were used to evaluate the effects of CCA, chromium trioxide (CrO₃) and arsenic pentoxide (As₂O₅) on cell pathophysiology by flow cytometry. Samples were collected after 14, 24, 48 and 96 h of animal exposure. While Cr had no statistically significant cytostatic effects, As₂O₅ induced a S-phase delay in animals exposed for 24 h, and over time a G0/G1 phase blockage. The effects of CCA in S-phase were similar, but more severe than those of As₂O₅. Since environmental and public health hazards due to the long durability of CCA-treated wood products, these data confirm that CCA has profoundly toxic effects on cell cycle, distinct from the compounds themselves. These cytostatic effects support cell cycle dynamics as a valuable endpoint to assess the toxicity of remaining CCA-treated infrastructures, and the expected increased waste stream over the coming decades.

Experimental modeling of the acute toxicity and cytogenotoxic fate of composite mixtures of chromate, copper and arsenate oxides associated with CCA preservative using Clarias gariepinus (Burchell 1822)

Concurrent occurrence of chromium (Cr), copper (Cu) and arsenic (As) from chromated copper arsenate (CCA) wood preservative in aquatic ecosystems demands that their joint-actions in eliciting toxic effects be assessed for adequate understanding of the health risk they may pose to biota. Clarias gariepinus was exposed to As₂O₃ , CrO₃ and CuO and their composite mixtures (1:1 and 1:1:1) at various concentrations (0 – 600 mg/L) for 96-h to determine the acute toxicity using OECD (1992) protocol. C. gariepinus was then exposed to sub-lethal concentrations corresponding to 6.25, 12.5, 25.0, 50.0 and 100% of the 96-h LC₅₀ for 7 days to assess the cytogenotoxic effects using piscine micronucleus (MN) test. The 96-h LC₅₀ showed that the metals/metalloid demonstrated differential interactions in a concentration dependent pattern. The 96-h LC₅₀ showed that Cr was the most toxic while Cu and As:Cu were indeterminate (Cr > Cr:Cu > As:Cr > As > As:Cr:Cu > Cu = As:Cu indeterminate). Isobologram and synergistic ratio (SR) models predicted antagonistic interaction between Cu:Cr and As:Cr and synergism between As:Cu in the causation of morbidity and mortality of C. gariepinus. Interaction factor model predicted antagonism as common interactive mechanism among the metal/metalloid mixtures in the induction of MN and abnormal nuclear erythrocytes in C. gariepinus. Predicted interactions among the three metals/ metalloid were largely antagonism and synergism towards the induction of acute toxicity and cytogenotoxicity. The models employed herein may be useful in establishing environmental safe limits for mixtures of metals/metalloids against the induction of acute toxicity and DNA damage in lower aquatic vertebrates.

Manganese in toenails is associated with hearing loss at high frequencies in humans

PURPOSE

Elevated hearing thresholds from high frequencies are known to be one of the hallmarks of age-related hearing loss. Our recent study showed accumulation of manganese (Mn) in inner ears resulting in acceleration of age-related hearing loss in mice orally exposed to Mn. However, there is no evidence showing an association between Mn in non-invasive biological samples and hearing loss in humans evaluated by pure tone audiometry (PTA). In this study, we evaluated Mn in non-invasive biological samples as a possible biomarker for hearing loss in humans.

MATERIALS AND METHODS

We determined hearing levels by PTA and Mn levels in toenails, hair and urine with an inductively coupled plasma mass spectrometer (ICP-MS) in 145 healthy subjects in Bangladesh.

RESULTS

Multivariable analyses showed that Mn levels in toenails, but not in hair and urine samples, were significantly associated with hearing loss at 8 kHz and 12 kHz. Moreover, our experimental study showed a significant correlation between Mn levels in inner ears and nails, but not hair, in mice orally exposed to Mn.

CONCLUSIONS

The results provide novel evidence that Mn in toenails is a possible biomarker for hearing loss at high frequencies in humans.

Pathological and Clinical Pathological Changes Induced by Four-week, Repeated-dose, Oral Administration of the Wood Preservative Chromated Copper Arsenate in Wistar Rats

Chromated copper arsenate (CCA) is used as a wood preservative worldwide. Exposure to it may adversely affect human health. Some events have increased human exposure to CCA, including the Great East Japan Earthquake, which generated a large amount of lumber debris from CCA-treated woods. We elucidated the toxicity due to daily exposure to CCA over a 4-week period at doses of 0, 8, 40, and 80 mg/kg/day in Wistar Hannover rats. Chromium (Cr) and arsenic (As), but not copper, were detected in the plasma samples of rats treated with various doses of CCA. Males and females showed sedation, and males had poor body weight gain. The clinical pathologies observed in both sexes included hypochromic and microcytic anemia, hepatic and renal dysfunction, and changes in lipid and glucose levels. Histopathologically, males and females showed forestomach hyperkeratosis, mucosal epithelial hyperplasia in the small intestine, rectal goblet cell hypertrophy, and lipofuscin deposition in the proximal renal tubule. Females showed diffuse hepatocellular hypertrophy with increased 8-hydroxydeoxyguanosine levels. These results indicated that oral administration of CCA mainly affected hematopoietic, gastrointestinal, hepatic, and renal systems owing to the toxic effects of As and/or Cr. Major toxic effects were observed in both sexes receiving 40 and 80 mg/kg/day.

Melanin-embedded materials effectively remove hexavalent chromium (CrVI) from aqueous solution

Background

Currently, it is recognized that water polluted with toxic heavy metal ions may cause serious effects on human health. Therefore, the development of new materials for effective removal of heavy metal ions from water is still a widely important area. Melanin is being considered as a potential material for removal of heavy metal from water.

Methods

In this study, we synthesized two melanin-embedded beads from two different melanin powder sources and named IMB (Isolated Melanin Bead originated from squid ink sac) and CMB (Commercial Melanin Bead originated from sesame seeds). These beads were of globular shape and 2–3 mm in diameter. We investigated and compared the sorption abilities of these two bead materials toward hexavalent-chromium (Cr^VI) in water. The isotherm sorption curves were established using Langmuir and Freundlich models in the optimized conditions of pH, sorption time, solid/liquid ratio, and initial concentration of Cr^VI. The FITR analysis was also carried out to show the differences in surface properties of these two beads.

Results

The optimized conditions for isotherm sorption of Cr^VI on IMB/CMB were set at pH values of 2/2, sorption times of 90/300 min, and solid-liquid ratios of 10/20 mg/mL. The maximum sorption capacities calculated based on the Langmuir model were 19.60 and 6.24 for IMB and CMB, respectively. However, the adsorption kinetic of Cr^VI on the beads fitted the Freundlich model with R² values of 0.992 for IMB and 0.989 for CMB. The deduced Freundlich constant, 1/n, in the range of 0.2–0.8 indicated that these beads are good adsorption materials. In addition, structure analysis data revealed great differences in physical and chemical properties between IMB and CMB. Interestingly, FTIR analysis results showed strong signals of –OH (3295.35 cm^− 1) and –C=O (1608.63 cm^− 1) groups harboring on the IMB but not CMB. Moreover, loading of Cr^VI on the IMB caused a shift of broad peaks from 3295.35 cm^− 1 and 1608.63 cm^− 1 to 3354.21 cm^− 1 and 1597.06 cm^− 1, respectively, due to –OH and –C=O stretching.

Conclusions

Taken together, our study suggests that IMB has great potential as a bead material for the elimination of Cr^VI from aqueous solutions and may be highly useful for water treatment applications.

Assessing the impact of geogenic chromium uptake by carrots (Daucus carota) grown in Asopos river basin

A methodology was developed to assess the impact of geogenic origin hexavalent chromium uptake by carrots, and the risk of human consumption of carrots grown in Asopos River basin in Greece. A field scale experiment was conducted with carrots cultivated in treatment plots, with and without compost amendment, in order to assess the impact of carbon in the mobility and uptake of chromium by plants. The results suggested that there is a trend for chromium mobilization and uptake in the surface and the leaves of the carrots cultivated in the treatment plot with the higher carbon addition, but not in the core of the carrots. Limited mobility of hexavalent chromium in the soil-plant-water system is presented due to the affinity of chromium to be retained in the solid phase and be uptaken by plants. Hexavalent chromium tolerant bacterial strains were isolated from the carrots. These endophytic bacteria, present in all parts of the plant, were able to reduce hexavalent chromium to trivalent form to levels below the detection limit. Finally, a site-specific risk assessment analysis suggested no adverse effects to human health due to the consumption of carrots. These findings are of particular importance since they confirm that carrots grown in soils with geogenic origin chromium does not pose any adverse risk for human consumption, but could also have the beneficial effect of the micronutrient trivalent chromium.

Manganese-mediated acceleration of age-related hearing loss in mice

Despite the fact that manganese (Mn) is known to be a neurotoxic element relevant to age-related disorders, the risk of oral exposure to Mn for age-related hearing loss remains unclear. In this study, we orally exposed wild-type young adult mice to Mn (Mn-exposed WT-mice) at 1.65 and 16.50 mg/L for 4 weeks. Mn-exposed WT-mice showed acceleration of age-related hearing loss. Mn-exposed WT-mice had neurodegeneration of spiral ganglion neurons (SGNs) with increased number of lipofuscin granules. Mn-exposed WT-mice also had increased hypoxia-inducible factor-1 alpha (Hif-1α) protein with less hydroxylation at proline 564 and decreased c-Ret protein in SGNs. Mn-mediated acceleration of age-related hearing loss involving neurodegeneration of SGNs was rescued in RET-transgenic mice carrying constitutively activated RET. Thus, oral exposure to Mn accelerates age-related hearing loss in mice with Ret-mediated neurodegeneration of SGNs.