Efficient activation of peroxymonosulfate mediated by Co(II)-CeO2 as a novel heterogeneous catalyst for the degradation of refractory organic contaminants: Degradation pathway, mechanism and toxicity assessment.

A series of Co(II)-CeO2 mixed metal oxides were synthesized by a facile hydrothermal-calcination procedure for activating peroxymonosulfate (PMS) and degrading toxic and difficult biodegradable organics. Co(II)-CeO2 showed excellent degradation performance toward rhodamine B (RhB), toluidine blue, methylene blue and diclofenac. RhB is a refractory organic contaminant, and ecotoxicological evaluation unraveled its harmfulness to the biosphere. RhB was selected as the model pollutant to investigate catalytic mechanisms. Parameters affecting degradation performance were profoundly investigated, including Co:Ce feed ratio, initial pH, PMS dosage, catalyst dosage, RhB concentration, coexisting ions and reaction temperature. Reaction mechanisms were proposed based on density functional theory calculations and identifications of reactive oxygen species. Improvements have been achieved in seven aspects compared to previous studies, including 100% degradation ratio in both real water samples and each reuse of the catalyst, ultrafast degradation rate, cost-effectiveness of the catalyst, toxicity-attenuation provided by the developed degradation method, high degree of mineralization for the model pollutant, negligible leaching of active sites, and the enhancement of catalytic performance by utilizing trace leached cobalt, endowing the technique with broad applicability and prospect.

The underlying mode of action for lung tumors in a tiered approach to the assessment of inhaled cobalt compounds.

A mode of action (MOA) for cobalt substances based on the "International Programme on Chemical Safety Conceptual Framework for Evaluating a MOA for Chemical Carcinogenesis" is presented. The data recorded therein were generated in a tiered testing program described in the preceding papers of this special issue, as well as data from the public domain. The following parameters were included in the evaluation: solubility of cobalt substances in artificial lung fluids (bioelution), in vitro biomarkers for cytotoxicity, reactive oxygen species and hypoxia mimicry, inhalation toxicity following acute exposure and repeated dose inhalation effects. Two distinct groups of cobalt substances emerged: substances inducing all effects across the MOA form one group, associated with the adverse outcome of lung cancer in rodents upon chronic exposure. Another group of cobalt substances induces no or very limited effects in the in vitro and acute testing. Higher tier testing with a representative of this group, tricobalt tetraoxide, showed a response resembling rat lung overload following exposure to high concentrations of poorly soluble particles. Based on the fundamental differences in the lower tier toxicological profile, cobalt substances with an unknown hazard profile can be assigned to either group based on lower tier testing alone.

In vitro and in vivo genotoxicity assessment of ferric ferrocyanide and potassium-cobalt ferrocyanide.

Ferric hexacyanoferrate(II) (Fe4[Fe(CN)6]3), i.e. Prussian blue (PB) has been used for many years to remove from the body the two toxic isotopes of cesium and thallium following irradiation. Recently, potassium cobalt hexacyanoferrate(II) (K2COFe(CN)6), which has shown a better efficacy for decontamination, is also being considered for use to enhance the elimination of cesium isotopes. In view to its preclinical and clinical development, in vitro and in vivo GLP-compliant genotoxicity studies were carried out on this product as well as on PB for comparison. Several tests dissecting the main events leading to genotoxicity, i.e. mutagenicity and chromosomal aberrations, both structural and quantitative were implemented. In vitro, no mutagenic effect was observed in the Ames test but both compounds were positive in the mouse lymphoma assay on TK locus and induced clastogenic effects in the in vitro chromosomal aberrations test on human lymphocytes, either in absence or in presence of metabolic activation. K-Co-ferrocyanide was also assayed in vivo in the mouse bone marrow micronucleus assay and PB was assessed for DNA fragmentation in the rodent Comet assay in both glandular stomach and colon. In the in vivo micronucleus mouse bone marrow, K-Co-ferrocyanide did not display any genotoxic activity up to 2000 mg/kg/d (x2) by oral route. In opposite, PB induced a significant increase in DNA fragmentation both in the glandular stomach and in the colon of rat treated 3 times with intake ranging from 2000 to 500 mg/kg. PB should be considered as an in vivo mutagen as well as Potassium cobalt hexacyanoferrate(II) since the in vitro genotoxicity profiles of both ferrocyanides are quite similar. Their use as cesium/ thallium decontamination agents in human should be assessed following a benefit/risk approach to enable a robust decision-making.

Activation of peroxymonosulfate by cobalt-impregnated biochar for atrazine degradation: The pivotal roles of persistent free radicals and ecotoxicity assessment.

Cobalt-mediated activation of peroxymonosulfate (PMS) has been extensively investigated for the degradation of emerging organic pollutants. In this study, PMS activation via cobalt-impregnated biochar towards atrazine (ATZ) degradation was systematically examined, and the underlying reaction mechanism was explicated. It was found that persistent free radicals (PFRs) contained in biochar play a pivotal role in PMS activation process. The PFRs enabled an efficient transfer electron to both cobalt atom and O2, facilitating the recycle of Co(III)/Co(II), and thereby leaded to an excellent catalytic performance. In contrast to oxic condition, the elimination of dissolved oxygen significantly retarded the ATZ degradation efficiency from 0.76 to 0.36 min-1. Radical scavenging experiments and electron paramagnetic resonance (EPR) analysis confirmed that the ATZ degradation was primarily due to SO4·- and, to a lesser extent, ·OH. In addition, dual descriptor (DD) method was carried out to reveal reactive sites on ATZ for radicals attacking and predicted derivatives. Meanwhile, the possible ATZ degradation pathways were accordingly proposed, and the ecotoxicity evaluation of the oxidation intermediates was also conducted by ECOSAR. Consequently, the cobalt-impregnated biochar could be an efficient and environmentally friendly catalyst to activate PMS for abatement and detoxication of ATZ.

Assessment of exposure to cobalt and its compounds in Italian industrial settings.

BACKGROUND: Adverse health effects of occupational exposure to cobalt and its compounds are well-documented. OBJECTIVES: The aim of the study is to evaluate exposures to cobalt in Italian industrial settings. METHODS: Data on cobalt and its compounds were collected from an occupational exposure registry. Statistical analysis was carried out for some exposure-related variables (i.e., cobalt compound, activity sector, occupational group, firm size). The number of workers potentially exposed was estimated for selected industrial sectors. RESULTS: Overall 1,701 measurements were analyzed in the period 1996-2016. The geometric mean of cobalt airborne concentration was 0.33 µg/m3. Most exposures occurred in the manufacture of fabricated metal products (50%) and among metal finishing-, plating- and coating-machine operators (42%). A total of 30,401 workers potentially exposed to cobalt was estimated, over 72% were male. CONCLUSIONS: Identifying professional groups at high-risk of exposure can help to control the most dangerous situations for workers' health. Surveillance systems based on occupational exposure registries contribute to support systematic improvement of working conditions.

Development and Assessment of Nano-Technologies for Cancer Treatment: Cytotoxicity and Hyperthermia Laboratory Studies.

Cancer treatment by magnetic hyperthermia offers numerous advantages, but for practical applications many variables still need to be adjusted before developing a controlled and reproducible cancer treatment that is bio-compatible (non-damaging) to healthy cells. In this work, Fe3O4 and CoFe2O4 were synthesized and systematically studied for the development of efficient therapeutic agents for applications in hyperthermia. The biocompatibility of the materials was further evaluated using HepG2 cells as biological model. Colorimetric and microscopic techniques were used to evaluate the interaction of magnetic nano-materials (MNMs) and HepG2 cells. Finally, the behavior of MNMs was evaluated under the influence of an alternating magnetic field (AMF), observing a more efficient temperature increment for CoFe2O4, a desirable behavior for biomedical applications since lower doses and shorter expositions to alternating magnetic field might be required.

Toxicological potential of cobalt in forage for ruminants grown in polluted soil: a health risk assessment from trace metal pollution for livestock.

The trace metal pollution in the environment is a highly concerned issue in these days. One of the important causes of trace metal pollution is the exhaust gases released from the vehicles on the roads. These dangerous gases pose life-threatening effects on the forage plants grown along the roadside as these plants are at direct risk to these trace metals. The aims of the present study were to determine the cobalt (Co) concentrations in soil, forages, and blood plasma of the buffaloes and to evaluate the Co deficiencies and toxicities in these samples. All samples were collected from six sites (Faisalabad roadside, Bhalwal roadside, Shaheenabad roadside, Mateela roadside, 50 Chak roadside, and Dera Saudi-control) of Sargodha city. The Co concentrations in these samples were determined by atomic absorption spectrophotometer (AA-6300 Shimadzu Japan). In soil samples, Co level ranged from 1.958 to 3.457 mg/kg in the six sampling sites. The highest Co level was observed at site 6 and the lowest at site 2. In forage samples, Co level ranged from 0.770 to 2.309 mg/kg in the six sampling sites. The highest Co level was observed at site 3 and the lowest at site 2. In blood plasma samples, Co level ranged from 2.644 to 4.927 mg/kg in the six sampling sites. The highest Co level was observed at site 1 and the lowest at site 3. The results showed higher Co values in the samples collected from the site IV while the bioconcentration factor for forage-soil was found highest in the samples collected from Site III. On the other hand, a correlation was found positively significant when soil and forage were correlated, and it was found negatively significant when blood and forage were correlated.

Toxicity assessment of cobalt ferrite nanoparticles on wheat plants.

Cobalt ferrite nanoparticles (NPs) have received increasing attention due to their widespread therapeutic and agricultural applicability. In the environmental field, dry powder- and ferrofluid-suspended cobalt ferrite NPs were found to be useful for removing heavy metals and metalloids from water, while diluted suspensions of cobalt ferrite NP have been promisingly applied in medicine. However, the potential toxicological implications of widespread exposure are still unknown. Since cobalt ferrite NPs are considered residual wastes of environmental or medical applications, plants may serve as a point-of-entry for engineered nanomaterials as a result of consumption of these plants. Thus, the aim of this study was to assess the effects of dry powder and fresh cobalt ferrite NP on wheat plants. Seven-day assays were conducted, using quartz sand as the plant growth substrate. The toxicity end points measured were seed germination, root and shoot lengths, total cobalt (Co) and iron (Fe) accumulation, photosynthetic pigment production, protein (PRT) production, and activities of catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GPX). Increasing total Co and Fe in plant tissues indicated that wheat plants were exposed to cobalt ferrite NP. Seed germination and shoot length were not sufficiently sensitive toxicity end points. The effective concentration (EC50) that diminished root length of plants by 50% was 1963 mg/kg for fresh ferrite NPs and 5023 mg/kg for powder ferrite NP. Hence, fresh ferrite NPs were more toxic than powder NP. Plant stress was indicated by a significant decrease in photosynthetic pigments. CAT, APX, and GPX antioxidant enzymatic activity suggested the generation of reactive oxygen species and oxidative damage induced by cobalt ferrite NP. More studies are thus necessary to determine whether the benefits of using these NPs outweigh the risks.

Environmental risk assessment of cobalt and manganese from industrial sources in an estuarine system.

A total of 74 samples of soil, sediment, industrial sludge, and surface water were collected in a Mediterranean estuarine system in order to assess the potential ecological impact of elevated concentrations of Co and Mn associated with a Terephthalic (PTA) and Isophthalic (PIPA) acids production plant. Samples were analyzed for elemental composition (37 elements), pH, redox potential, organic carbon, and CaCO3 content, and a group of 16 selected samples were additionally subjected to a Tessier sequential extraction. Co and Mn soil concentrations were significantly higher inside the industrial facility and around its perimeter than in background samples, and maximum dissolved Co and Mn concentrations were found in a creek near the plant's discharge point, reaching values 17,700 and 156 times higher than their respective background concentrations. The ecological risk was evaluated as a function of Co and Mn fractionation and bioavailability which were controlled by the environmental conditions generated by the advance of seawater into the estuarine system during high tide. Co appeared to precipitate near the river mouth due to the pH increase produced by the influence of seawater intrusion, reaching hazardous concentrations in sediments. In terms of their bioavailability and the corresponding risk assessment code, both Co and Mn present sediment concentrations that result in medium to high ecological risk whereas water concentrations of both elements reach values that more than double their corresponding Secondary Acute Values.

An exposure-risk assessment for potentially toxic elements in rice and bulgur.

Rice and wheat are rich sources of essential elements. However, they may also accumulate potentially toxic elements (PTE). Bulgur, the popular alternative to rice in the eastern Mediterranean, is produced by processing wheat, during which PTE content may change. This study determined PTE concentrations in rice and bulgur collected from 50 participant households in the city of Izmir, Turkey, estimated ingestion exposure, and associated chronic-toxic and carcinogenic human health risks. Comparison of the determined concentrations to the available standard levels and the levels reported in the literature revealed that Cd, Co, and Pb in rice might be of concern. The estimated health risks of individual participants supported this result with exceedance of respective threshold or acceptable risk levels at the 95th percentile. Population risk estimates indicated that the proportion with higher than the threshold or acceptable risk is about 10, 24, and 12% for Cd, Co, and Pb in rice, respectively. Results of this study showed that health risks associated with PTE exposure through bulgur consumption are lower than those of rice, and below the threshold or acceptable risk levels.

Characteristics and properties of nano-LiCoO2 synthesized by pre-organized single source precursors: Li-ion diffusivity, electrochemistry and biological assessment.

BACKGROUND: LiCoO2 is one of the most used cathode materials in Li-ion batteries. Its conventional synthesis requires high temperature (>800 °C) and long heating time (>24 h) to obtain the micronscale rhombohedral layered high-temperature phase of LiCoO2 (HT-LCO). Nanoscale HT-LCO is of interest to improve the battery performance as the lithium (Li+) ion pathway is expected to be shorter in nanoparticles as compared to micron sized ones. Since batteries typically get recycled, the exposure to nanoparticles during this process needs to be evaluated. RESULTS: Several new single source precursors containing lithium (Li+) and cobalt (Co2+) ions, based on alkoxides and aryloxides have been structurally characterized and were thermally transformed into nanoscale HT-LCO at 450 °C within few hours. The size of the nanoparticles depends on the precursor, determining the electrochemical performance. The Li-ion diffusion coefficients of our LiCoO2 nanoparticles improved at least by a factor of 10 compared to commercial one, while showing good reversibility upon charging and discharging. The hazard of occupational exposure to nanoparticles during battery recycling was investigated with an in vitro multicellular lung model. CONCLUSIONS: Our heterobimetallic single source precursors allow to dramatically reduce the production temperature and time for HT-LCO. The obtained nanoparticles of LiCoO2 have faster kinetics for Li+ insertion/extraction compared to microparticles. Overall, nano-sized LiCoO2 particles indicate a lower cytotoxic and (pro-)inflammogenic potential in vitro compared to their micron-sized counterparts. However, nanoparticles aggregate in air and behave partially like microparticles.

Assessment of mutagenicity of water from Lake Sevan, Armenia with application of Tradescantia (clone 02).

For many decades water resources in Armenia have been affected by anthropogenic activity, therefore, a regular bioindication of genotoxic effects of the water bodies is desirable. The genotoxicity of water samples collected from different parts of Lake Sevan were assessed by means of Trad-SHM (stamen hair mutation) assay using Tradescantia (clone 02). Here we report a significant increase in the frequency of somatic mutations and morphological changes in the Tradescantia inflorescences exposed to the water samples compared to the control. The somatic mutations (recessive mutation and white mutation events) were mostly linked to the concentration of Al, Ni, As, Co and Pb in Artanish, Tsapatakh and Karchaghbyur, Noradus, Martuni and Litchk, while morphological changes (non-surviving hairs) were related to Co level in Tsapatakh and Karchaghbyur. The results obtained show that Lake Sevan contains substances which may cause genotoxicity and teratogenicity in Tradescantia and probably also in aquatic animals. The results also show that Trad-SHM assay can be used for monitoring natural resources.

Ecotoxicological assessment of cobalt using Hydra model: ROS, oxidative stress, DNA damage, cell cycle arrest, and apoptosis as mechanisms of toxicity.

The mechanisms underlying cobalt toxicity in aquatic species in general and cnidarians in particular remain poorly understood. Herein we investigated cobalt toxicity in a Hydra model from morphological, histological, developmental, and molecular biological perspectives. Hydra, exposed to cobalt (0-60 mg/L), were altered in morphology, histology, and regeneration. Exposure to standardized sublethal doses of cobalt impaired feeding by affecting nematocytes, which in turn affected reproduction. At the cellular level, excessive ROS generation, as the principal mechanism of action, primarily occurred in the lysosomes, which was accompanied by the upregulation of expression of the antioxidant genes SOD, GST, GPx, and G6PD. The number of Hsp70 and FoxO transcripts also increased. Interestingly, the upregulations were higher in the 24-h than in the 48-h time-point group, indicating that ROS overwhelmed the cellular defense mechanisms at the latter time-point. Comet assay revealed DNA damage. Cell cycle analysis indicated the induction of apoptosis accompanied or not by cell cycle arrest. Immunoblot analyses revealed that cobalt treatment triggered mitochondria-mediated apoptosis as inferred from the modulation of the key proteins Bax, Bcl-2, and caspase-3. From this data, we suggest the use of Hydra as a model organism for the risk assessment of heavy metal pollution in aquatic ecosystems.

Toxicity assessment of arsenic and cobalt in the presence of aquatic humic substances of different molecular sizes.

The release of contaminants in aquatic ecosystems can be influenced by humic acids. In this study, toxicity tests using environmentally relevant concentrations of arsenic and cobalt were conducted both in the presence and absence of aquatic humic substances (AHS) and the fractions of different molecular sizes in the range of (<5, 5-10;10-30; 30-100 and >100kDa) using the microcrustacean Ceriodaphnia dubia. AHS together with arsenic reduced the toxicity, and the toxicity decreased in fractions of larger molecular size AHS. Despite the presence of cobalt, the reduction in toxicity was not observed and that depended on the molecular size of AHS. There was a trend of enhanced toxicity for Co in fractions of larger molecular sizes, opposed to that found for arsenic. Thus, the humic substances alter toxicity of trace elements, and this effect varies depending on the size of the humic substances.

In Vitro Toxicological Assessment of Cobalt Ferrite Nanoparticles in Several Mammalian Cell Types.

Nanoparticles have been widely used in various fields due to the superior physicochemical properties and functions. As a result, human exposure to nanoparticles increases dramatically. Previous researches have shown that nanoparticles could travel through the respiratory, digestive system, or skin into the blood and then to the secondary organs such as the brain, heart, and liver. Besides, the nanoparticle toxicity is controversial and dependent on the sensitivity of the cell type, route of exposure, and condition, as well as their characteristics. Similarly, cobalt ferrite nanoparticles (CoFe2O4-NPs) have been used in different industrial fields, and have also various application possibilities in medical and biomedical fields. CoFe2O4-NPs induce toxic responses in various organisms such as human, mice, and algae. However, there is a serious deficit of information concerning their effects on human health and the environment. We aimed to investigate the toxic effects of CoFe2O4-NPs on liver (HepG2), colon (Caco-2), lung (A549), and neuron (SH-SY5Y) cells, which reflect different exposure routes in vitro, by using various toxicological endpoints. The cytotoxicity, genotoxicity, oxidative damage, and apoptosis induction of CoFe2O4-NPs (39 ± 17 nm) were evaluated. After 24 h, the nanoparticles decreased cell viability at ≤100 µg/mL, while increasing viability at >100 µg/mL. CoFe2O4-NPs induced DNA and oxidative damage with increased malondialdehyde (MDA) and 8-hydroxy deoxyguanosine (8-OHdG) levels and decreased glutathione (GSH) levels with no change in protein carbonyl (PC) levels. CoFe2O4-NPs had apoptotic effect in HepG2 and Caco-2 cells in a concentration-dependent manner and necrotic effects on SH-SY5Y and A549 cells. Consequently, the adverse effects of CoFe2O4-NPs should raise concern about their safety in consumer products.

Inhalation cancer risk assessment of cobalt metal.

Cobalt compounds (metal, salts, hard metals, oxides, and alloys) are used widely in various industrial, medical and military applications. Chronic inhalation exposure to cobalt metal and cobalt sulfate has caused lung cancer in rats and mice, as well as systemic tumors in rats. Cobalt compounds are listed as probable or possible human carcinogens by some agencies, and there is a need for quantitative cancer toxicity criteria. The U.S. Environmental Protection Agency has derived a provisional inhalation unit risk (IUR) of 0.009 per µg/m(3) based on a chronic inhalation study of soluble cobalt sulfate heptahydrate; however, a recent 2-year cancer bioassay affords the opportunity to derive IURs specifically for cobalt metal. The mechanistic data support that the carcinogenic mode of action (MOA) is likely to involve oxidative stress, and thus, non-linear/threshold mechanisms. However, the lack of a detailed MOA and use of high, toxic exposure concentrations in the bioassay (≥1.25 mg/m(3)) preclude derivation of a reference concentration (RfC) protective of cancer. Several analyses resulted in an IUR of 0.003 per µg/m(3) for cobalt metal, which is ∼3-fold less potent than the provisional IUR. Future research should focus on establishing the exposure-response for key precursor events to improve cobalt metal risk assessment.

Toxicological Assessment of CoO and La2O3 Metal Oxide Nanoparticles in Human Small Airway Epithelial Cells.

Cobalt monoxide (CoO) and lanthanum oxide (La2O3) nanoparticles are 2 metal oxide nanoparticles with different redox potentials according to their semiconductor properties. By utilizing these two nanoparticles, this study sought to determine how metal oxide nanoparticle's mode of toxicological action is related to their physio-chemical properties in human small airway epithelial cells (SAEC). We investigated cellular toxicity, production of superoxide radicals and alterations in gene expression related to oxidative stress, and cellular death at 6 and 24 h following exposure to CoO and La2O3(administered doses: 0, 5, 25, and 50 µg/ml) nanoparticles. CoO nanoparticles induced gene expression related to oxidative stress at 6 h. After characterizing the nanoparticles, transmission electron microscope analysis showed SAEC engulfed CoO and La2O3nanoparticles. CoO nanoparticles were toxic after 6 and 24 h of exposure to 25.0 and 50.0 µg/ml administered doses, whereas, La2O3nanoparticles were toxic only after 24 h using the same administered doses. Based upon the Volumetric Centrifugation Methodin vivoSedimentation, Diffusion, and Dosimetry, the dose of CoO and La2O3nanoparticles delivered at 6 and 24 h were determined to be: CoO: 1.25, 6.25, and 12.5 µg/ml; La2O3: 5, 25, and 50 µg/ml and CoO: 4, 20, and 40 µg/ml; and La2O3: 5, 25, 50 µg/ml, respectively. CoO nanoparticles produced more superoxide radicals and caused greater stimulation of total tyrosine and threonine phosphorylation at both 6 and 24 h when compared with La2O3nanoparticles. Taken together, these data provide evidence that different toxicological modes of action were involved in CoO and La2O3metal oxide nanoparticle-induced cellular toxicity.

Assessment of thyroid endocrine system impairment and oxidative stress mediated by cobalt ferrite (CoFe2 O4 ) nanoparticles in zebrafish larvae.

Fascinating super paramagnetic uniqueness of iron oxide particles at nano-scale level make them extremely useful in the state of the art therapies, equipments, and techniques. Cobalt ferrite (CoFe2 O4 ) magnetic nanoparticles (MNPs) are extensively used in nano-based medicine and electronics, results in extensive discharge and accumulation into the environment. However, very limited information is available for their endocrine disrupting potential in aquatic organisms. In this study, the thyroid endocrine disrupting ability of CoFe2 O4 NPs in Zebrafish larvae for 168-h post fertilization (hpf) was evaluated. The results showed the elevated amounts of T4 and T3 hormones by malformation of hypothalamus pituitary axis in zebrafish larvae. These elevated levels of whole body THs leads to delayed hatching, head and eye malformation, arrested development, and alterations in metabolism. The influence of THs disruption on ROS production and change in activities of catalase (CAT), mu-glutathione s-transferase (mu-GST), and acid phosphatase (AP) were also studied. The production of significantly higher amounts of in vivo generation of ROS leads to membrane damage and oxidative stress. Presences of NPs and NPs agglomerates/aggregates were also the contributing factors in mechanical damaging the membranes and physiological structure of thyroid axis. The increased activities of CAT, mu-GST, and AP confirmed the increased oxidative stress, possible DNA, and metabolic alterations, respectively. The excessive production of in vivo ROS leads to severe apoptosis in head, eye, and heart region confirming that malformation leads to malfunctioning of hypothalamus pituitary axis. ROS-induced oxidative DNA damage by formation of 8-OHdG DNA adducts elaborates the genotoxicity potential of CoFe2 O4 NPs. This study will help us to better understand the risk and assessment of endocrine disrupting potential of nanoparticles. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 2068-2080, 2016.

Genotoxicity assessment of cobalt chloride in Eisenia hortensis earthworms coelomocytes by comet assay and micronucleus test.

Cobalt and its different compounds are extensively used worldwide and considered as possible environmental pollutant. Earthworms are useful model organism and its different species are used to monitor soil pollution. No study has been found to detect cobalt chloride (CoCl2) genotoxicity in earthworms. So, current study aimed to evaluate CoCl2 induced genotoxicity in Eisenia hortensis earthworms coelomocytes by alkaline comet assay (CA) and micronucleus (MN) test. The earthworms (n = 10 for each group) were exposed to different series of CoCl2 concentrations (100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm) to find LD50. The LD50 for CoCl2 was found at 226 ppm. Then, doses of LD50/2, LD50 and 2XLD50 for 48 h were used. CA and MN demonstrated the significant increase (P < 0.05) in DNA damage and chromosomal aberrations. Dose dependent relationship was found. Highest DNA damage and chromosomal aberrations were noticed at 2XLD50. The results concluded that CoCl2 induced DNA damage, cytokinesis failure and chromosomal aberrations in E. hortensis earthworms.

New investigations into the genotoxicity of cobalt compounds and their impact on overall assessment of genotoxic risk.

The genotoxicity of cobalt metal and cobalt compounds has been widely studied. Several publications show induction of chromosomal aberrations, micronuclei or DNA damage in mammalian cells in vitro in the absence of S9. Mixed results were seen in gene mutation studies in bacteria and mammalian cells in vitro, and in chromosomal aberration or micronucleus assays in vivo. To resolve these inconsistencies, new studies were performed with soluble and poorly soluble cobalt compounds according to OECD-recommended protocols. Induction of chromosomal damage was confirmed in vitro, but data suggest this may be due to oxidative stress. No biologically significant mutagenic responses were obtained in bacteria, Tk(+/-) or Hprt mutation tests. Negative results were also obtained for chromosomal aberrations (in bone marrow and spermatogonia) and micronuclei at maximum tolerated doses in vivo. Poorly soluble cobalt compounds do not appear to be genotoxic. Soluble compounds do induce some DNA and chromosomal damage in vitro, probably due to reactive oxygen. The absence of chromosome damage in robust GLP studies in vivo suggests that effective protective processes are sufficient to prevent oxidative DNA damage in whole mammals. Overall, there is no evidence of genetic toxicity with relevance for humans of cobalt substances and cobalt metal.