Genotoxic effects of a sub-acute low-level inhalation exposure to a mixture of carcinogenic chemicals

Determination by chromatography and cytotoxotoxic and oxidative effects of pyriproxyfen and pyridalyl

Pyriproxyfen (PPF) is a larvicide, used to combat the proliferation of Aedes aegypti larvae. The objective of this study was to analyze the compounds of pyriproxyfen and pyridalyl (PYL) in a commercial larvicide to analyze the cytotoxic and oxidative effects of PPF and PYL. The toxic potential of PPF and PYL were assessed based on lethal concentration (LC₅₀) in Artemia salina, cytotoxicity based on the mitotic index and the chromosomal alterations in Allium cepa and the oxidative damage in Saccharomyces cerevisiae. The PPF and PYL compounds were identified by HPLC-PDA based on their retention times and spectral data. The wavelengths λ_max (258 nm) and (271 nm) of the UV spectrum of PYL and PPF and the retention times (R_T) (3.38 min) and (4.03 min), respectively. The toxicological potentials of PPF and PYL were significant at concentrations (1, 10, 100 and 1000 ppm), with an LC₅₀ of 48 h (0.5 ppm). PPF and PYL pointed out a cytotoxic effect in A. cepa at all concentrations (0.0001, 0.001, 0.01, 0.1, 1.0, 100 and 1000 ppm), genotoxic effect at concentrations only (0.0001; 0.1; 1; 100 and 1000 ppm), and mutagenic for concentrations (0.1, 100 and 1000 ppm). In relation S. cerevisiae, PPF e PYL prompted oxidative damage at concentrations (100 and 1000 ppm) in all strains (SODWT, Sod1, Sod2, Sod1Sod2, Cat1 and Sod1Cat1). Therefore, the PPF and PYL identificated in commercial larvicide by HPLC-PDA produced cytotoxic and oxidative effects that could cause health and ecosystem risks.

Effects of formaldehyde and xylene on CD4- and CD8-positive T cells in bronchus-associated lymphoid tissue in rats

The aim of this study was to determine the localization and number of CD4- and CD8-positive T lymphocytes in bronchus-associated lymphoid tissue (BALT) of the embryos and newborns or young and adult rats exposed to formaldehyde (6 ppm), technical xylene (300 ppm), or a combination of these two agents (3 ppm + 150 ppm) for 6 weeks (8 h/day). A total of 96 female Sprague-Dawley rats were used. The CD4-positive cells were localized predominately in area under the epithelium and in the periphery of BALT follicles after the exposure period. However, CD8-positive cells were localized mainly in the periphery of BALT follicles after the exposure period. The number of CD4- and CD8-positive lymphocytes significantly increased in exposed young and adult rats compared to the respective controls. These results suggest that formaldehyde and/or xylene may affect the local immunity in BALT particularly in young and adult rats.

Induction of mitotic and chromosomal abnormalities on Allium cepa cells by pesticides imidacloprid and sulfentrazone and the mixture of them

To evaluate the cytotoxic and genotoxic effects of low concentrations of pesticides in non-target organisms, seeds of Allium cepa were exposed for 24 h to the imidacloprid insecticide, sulfentrazone herbicide and to the mixture of them, followed by recovery periods of 48 and 72 h. Imidacloprid results indicated an indirect genotoxic effect by inducing different types of chromosome aberration (CA), mainly bridges and chromosomal adherences. Cells with micronucleus (MN) were not significant in the analyzed meristems. Moreover, the 72-h recovery tests indicated that the two lower concentrations of the insecticide (0.036 and 0.36 g L(-1)) had their genotoxic effects minimized after discontinuation of treatment, differently to the observed for the field concentration (3.6 g L(-1)). Sulfentrazone herbicide at field concentration (6 g L(-1)) caused cytotoxic effects by inducing nuclear fragmentation and inhibition of cell division. The other concentrations (0.06, 0.6 and 1.2 g L(-1)) indicated genotoxic effects for this herbicide. The concentration of 0.06 g L(-1) induced persistent effects that could be visualized both by the induction of CA in the recovery times as by the presence of MN in meristematic and F1 cells. The induction of MN by this lowest concentration was associated with the great amount of breakage, losses and chromosomal bridges. The mixture of pesticides induced genotoxic and cytotoxic effects, by reducing the MI of the cells. The chromosomal damage induced by the mixture of pesticides was not persistent to the cells, since such damage was minimized 72 h after the interruption of the exposure.

Analysis of the genotoxic potential of low concentrations of Malathion on the Allium cepa cells and rat hepatoma tissue culture

Based on the concentration of Malathion used in the field, we evaluated the genotoxic potential of low concentrations of this insecticide on meristematic and F1 cells of Allium cepa and on rat hepatoma tissue culture (HTC cells). In the A. cepa, chromosomal aberrations (CAs), micronuclei (MN), and mitotic index (MI) were evaluated by exposing the cells at 1.5, 0.75, 0.37, and 0.18mg/mL of Malathion for 24 and 48hr of exposure and 48hr of recovery time. The results showed that all concentrations were genotoxic to A. cepa cells. However, the analysis of the MI has showed non-relevant effects. Chromosomal bridges were the CA more frequently induced, indicating the clastogenic action of Malathion. After the recovery period, the higher concentrations continued to induce genotoxic effects, unlike the observed for the lowest concentrations tested. In HTC cells, the genotoxicity of Malathion was evaluated by the MN test and the comet assay by exposing the cells at 0.09, 0.009, and 0.0009mg/5mL culture medium, for 24hr of exposure. In the comet assay, all the concentrations induced genotoxicity in the HTC cells. In the MN test, no significant induction of MN was observed. The genotoxicity induced by the low concentrations of Malathion presented in this work highlights the importance of studying the effects of low concentrations of this pesticide and demonstrates the efficiency of these two test systems for the detection of genetic damage promoted by Malathion.

Benzene increases the ratio of arachidonic acids to docosahexaenoic acids and inhibits the de novo synthesis of ceramide in the rat liver

The present study investigated the effects of inhalation exposure of benzene at 0, 10, 200 and 600 ppm for 1, 2 and 4 weeks on n-6 and n-3 fatty acids and ceramide levels in the rat liver. No significant difference in the ratio of saturated fatty acid to unsaturated fatty acid was found on increasing benzene exposure levels, but the ratio of saturated fatty acid to unsaturated fatty acid decreased with increasing benzene exposure times, with the exception of the phospholipids of rats exposed to 200 and 600 ppm of benzene. A significant increase in the ratio of arachidonic acid to docosahexaenoic acid was found in the phospholipids of rats exposed to 200 and 600 ppm of benzene for 4 weeks. In our study, no change in the relative amounts of sphingomyelin in phospholipids, due to benzene exposure at 600 ppm for 4 weeks resulted in the lack of sphingomyelin turnover. However, ceramide levels in the livers of rats exposed to 600 ppm of benzene for 4 weeks were significantly reduced upon increasing the benzene concentration. This result shows that the de novo synthesis of ceramide was significantly inhibited at higher levels of benzene and that the ratio of arachidonic acid to docosahexaenoic acid in phospholipids is dose-dependently related to benzene exposure.

Single strand DNA breaks in T- and B-lymphocytes and granulocytes in workers exposed to benzene

Comet assays were carried out to evaluate DNA damage in T- and B-lymphocytes and granulocytes from 41 workers exposed to benzene in a printing company and 41 unexposed donors. In T-lymphocytes, DNA damage was slightly higher in exposed workers than in controls. The tail moments in the two groups were 1.75+/-0.29 and 1.47+/-0.41, respectively (P<0.0006). DNA damage of B-lymphocytes in the two groups showed the most significant difference among the three cell types. The tail moments were 3.86+/-0.71 and 1.51+/-0.39, respectively (P<0.0001). In granulocytes, DNA damage was also different, the tail moments being 3.61+/-0.75 and 2.60+/-0.59, respectively (P<0.0001). The comparison of DNA damage in both groups shows that B-lymphocytes could be a useful target in biomonitoring of human exposure to low levels of benzene.

ATSDR evaluation of health effects of chemicals. V. Xylenes: health effects, toxicokinetics, human exposure, and environmental fate

Xylenes, or dimethylbenzenes, are among the highest-volume chemicals in production. Common uses are for gasoline blending, as a solvent or component in a wide variety of products from paints to printing ink, and in the production of phthalates and polyester. They are often encountered as a mixture of the three dimethyl isomers, together with ethylbenzene. As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that are of greatest concern for public health purposes. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of the bulk of this profile (ATSDR, 1995) into the mainstream scientific literature. An extensive listing of known human and animal health effects, organized by route, duration, and end point, is presented. Toxicological information on toxicokinetics, biomarkers, interactions, sensitive subpopulations, reducing toxicity after exposure, and relevance to public health is also included. Environmental information encompasses physical properties, production and use, environmental fate, levels seen in the environment, analytical methods, and a listing of regulations. ATSDR, as mandated by CERCLA (or Superfund), prepares these profiles to inform and assist the public.

Genetic toxicology of epichlorohydrin: a review

Epichlorohydrin (ECH) is one of the more commercially important aliphatic epoxides used extensively as an industrial intermediate, a laboratory reagent, and as an insecticide. It is a volatile, colourless liquid with an ethereal odour. It behaves as an alkylating agent. Reports have shown it to cause the respiratory and dermal toxicity in animals and humans. It has also been reported to be carcinogenic in experimental models. Thus, the wide-spread use of this aliphatic epoxide is of great concern in human health problem. The purpose of this paper is to critically review and update the mutagenic and clastogenic effects of ECH based on available literature.

Xylene: its toxicity, measurement of exposure levels, absorption, metabolism and clearance

Xylene is an aromatic hydrocarbon widely used in industry and medical technology as a solvent. Health and safety authorities in most countries, including Australia, recommend a threshold limit value (TLV) of 100 ppm in the working environment. Recently, the amount of the major metabolite of xylene, methylhippuric acid (MHA), in urine has been recommended as a better indicator of exposure. The American Conference of Governmental Industrial Hygienists has recommended an upper limit for this indicator, called a biological exposure index (BEI), of 2.0 g MHA/L urine (SG 1.016). Xylene vapour is absorbed rapidly from the lungs, and xylene liquid and vapour are absorbed slowly through the skin. Of the xylene absorbed, about 95% is metabolised in the liver to MHA and 70 to 80% of metabolites are excreted in the urine within 24 hours. However, the many variables which affect the absorption, metabolism and clearance of xylene include exercise, alcohol intake, cigarette smoking, co-exposure to other solvents, gender, and gastrointestinal, hepatic and renal pathology. Xylene in high concentrations acts as a narcotic, inducing neuropsychological and neurophysiological dysfunction. Respiratory tract symptoms are also frequent. More chronic, occupational exposure has been associated with anemia, thrombocytopenia, leukopenia, chest pain with ECG abnormalities, dyspnea and cyanosis, in addition to CNS symptoms. Concomitant exposure to xylene and other solvents, including toluene, affected hematological parameters, liver size, liver enzymes, auditory memory, visual abstraction, and vibration threshold in the toes. Normal metabolic pathways were altered and significant increases in some serum bile acids may reflect early liver damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone marrow micronucleus assay: a review of the mouse stocks used and their published mean spontaneous micronucleus frequencies

We have examined published negative control data from 581 papers on micronucleated bone marrow polychromatic erythrocytes (mnPCE) for differences in mean frequency and the frequency distribution profile among the mouse stocks used with the bone marrow micronucleus assay. For the 55 mouse stocks with published micronucleus assay data, the overall mean frequency is 1.95 mnPCE/1,000 PCE (1.95 mnPCE/1,000); for the 13 stocks most commonly used in the assay, it is 1.88 mnPCE/1,000. During the last 5 years, the mnPCE rate for these 13 major stocks has been 1.74 mnPCE/1,000. This current mean frequency is a substantial decrease from the mean of 3.07 mnPCE/1,000 observed for these 13 stocks for data published prior to 1981. Of the major stocks, the highest mean mnPCE negative control frequencies were observed for MS/Ae > BALB/c > C57Bl/6, and the lowest for CD-1 < Swiss Webster. We note that hybrid mouse stocks appear to have lower and less variable negative control frequencies than either of their parent strains and that the negative control frequency for some progeny stocks have diverged significantly from that of the parent stocks. Overall mean negative control frequencies appear to be correlated with breadth of the frequency distribution profile of published mean negative control values. Furthermore, a possible correlation between negative control frequency in the micronucleus assay and sensitivity to clastogens of different mouse strains may be indicated. The databases generated here allow us to define a range of norms for both the historical mean frequency and individual experimental mean frequencies for most stocks, but in particular, for the more commonly used mouse stocks. Our analysis, for the most part, bears out the recommendation of the first Gene-Tox Report on the micronucleus assay that the historical negative control frequency for a mouse stock should fall between 1 and 3 mnPCE/1,000. Eighty-six percent of the most commonly used mouse stocks have historical mean frequencies within this range. Though individual experimental mean values would not necessarily be expected to fall within the 1-3.00 mnPCE/1,000 range, 65.3% of the 2,327 published negative control values do, and 83.5% are < 3 mnPCE/1,000. The frequency with which an individual experimental mean value lies outside the 1.00 to 3.00 mnPCE/1,000 range differs among stocks and appears related to the mouse mean frequency. We suggest that the recommended range for historical mean frequency be extended slightly, to approximately 3.4 mnPCE/1,000, to accommodate some commonly used strains with overall mean negative control frequencies just above 3.00 mnPCE/1,000.(ABSTRACT TRUNCATED AT 400 WORDS)

Mouse and human micronucleus models for assessing genotoxicity of whole foods in intervention studies

There is an emerging need to apply classical genotoxicity assays to assess, in vivo, the carcinogenic or anti-carcinogenic potential of traditional and novel foods. The micronucleus techniques in peripheral blood erythrocytes and lymphocytes are two of the methods that have been used for assessing chromosome-damaging effects following and during dietary interventions with whole foods. The advantage of this approach stems from the practicality of the methods and the possibility of using these techniques in both human and rodent models. The potential application of these methods is illustrated by comparison of recent examples in the literature and from ongoing research.

Effect of cooked meat on micronucleus frequency

The possibility that inclusion of cooked meat in the diet could elevate chromosome damage risk was investigated in mice fed either a cereal diet only or a cereal diet supplemented with mutton cooked by microwaving, pan-frying or charcoal-barbecueing. The meat was provided as a supplement to the standard cereal-based diet on an approximately one-to-one basis. Chromosome damage indices included the cytokinesis-block micronucleus assay in spleen lymphocytes, the bone marrow micronucleus assay in erythrocytes and two versions of the colonic micronucleus assay. These indices were assessed after 3 or 6 months of feeding, and under each circumstance no increment in the micronucleus frequency in any of the tissues could be detected in the groups fed cooked meat when compared with each other or with the group fed the cereal diet only. There was also no correlation between the micronucleus index in lymphocytes and body weight. These data suggest that, over the time-frame studied, inclusion of meat in the diet and the extent to which meat is cooked are unlikely to be important variables affecting the micronucleus index.

The mutagenic effects of low level sub-acute inhalation exposure to benzene in CD-1 mice

Benzene is a widely used chemical and common environmental contaminant. It is carcinogenic in man and animals and is genotoxic in mice, rats, and occupationally exposed humans at doses above one part per million. In order to evaluate the genotoxic effects of prolonged exposures to very low concentrations of benzene, we exposed CD-1 mice to benzene by inhalation for 22 h per day, seven days per week for six weeks at 40, 100 and 1000 parts per billion (ppb). Additional groups were exposed to purified air or were housed in standard plastic cages. The effects of in vivo exposure to benzene were evaluated by using an autoradiographic assay to determine the frequency of mutants which represent mutations at the hypoxanthine-guanine phosphoribosyl transferase (hprt) locus in spleen lymphocytes. At the end of the six weeks exposure period lymphocytes were recovered from the spleens of the mice and cryopreserved prior to assay. Mutant cells were selected on the basis of their ability to incorporate tritiated thymidine in the presence of 6-thioguanine. The weighted mean variant (mutant) frequencies (Vf) of female mice (three per group) were 7.2 x 10(-6) at 0 ppb; 29.2 x 10(-6) at 40 ppb; 62.5 x 10(-6) at 100 ppb and 25.0 x 10(-6) at 1000 ppb. The Vf of unexposed mice housed in standard cages was 13.2 x 10(-6). In male mice the same pattern of response was observed, but the increases in Vf in response to benzene were not as great. In both sexes of mice, the increases at 40 and 100 ppb were significantly greater than at 0 ppb (P less than 0.05). The increase in Vf with exposure to 100 ppb and the decline at 1000 ppb parallel the results observed for chromosome damage in spleen lymphocytes from the same animals (Au et al., Mutation Res., 260 (1991) 219-224). These results indicate that sub-chronic exposure to benzene at levels below the current Occupational Safety and Health Administration Permitted Exposure Limit may induce gene mutations in lymphocytes in mice.

Use of in vivo genetic toxicity data for risk assessment

Mutagenicity studies have been used to identify specific agents as potential carcinogens or other human health hazards; however, they have been used minimally for risk assessment or in determining permissible levels of human exposure. The poor predictive value of in vitro mutagenesis tests for carcinogenic activity and a lack of mechanistic understanding of the roles of mutagens in the induction of specific cancers have made these tests unattractive for the purpose of risk assessment. However, the limited resources available for carcinogen testing and large number of chemicals which need to be evaluated necessitate the incorporation of more efficient methods into the evaluation process. In vivo genetic toxicity testing can be recommended for this purpose because in vivo assays incorporate the metabolic activation pathways that are relevant to humans. We propose the use of a multiple end-point in vivo comprehensive testing protocol (CTP) using rodents. Studies using sub-acute exposure to low levels of test agents by routes consistent with human exposure can be a useful adjunct to methods currently used to provide data for risk assessment. Evaluations can include metabolic and pharmacokinetic endpoints, in addition to genetic toxicity studies, in order to provide a comprehensive examination of the mechanism of toxicity of the agent. A parallelogram approach can be used to estimate effects in non-accessible human tissues by using data from accessible human tissues and analogous tissues in animals. A categorical risk assessment procedure can be used which would consider, in order of priority, genetic damage in man, genetic damage in animals that is highly relevant to disease outcome (mutation, chromosome damage), and data from animals that is of less certain relevance to disease. Action levels of environmental exposure would be determined based on the lowest observed effect levels or the highest observed no effect levels, using sub-acute low level exposure studies in rodents. As an example, the known genotoxic effects of benzene exposure at low levels in man and animals are discussed. The lowest observed genotoxic effects were observed at about 1-10 parts per million for man and 0.04-0.1 parts per million in subacute animal studies. If genetic toxicity is to achieve a prominent role in evaluating carcinogens and in characterizing germ-cell mutagens, minimal testing requirements must be established to ascertain the risks associated with environmental mutagen exposure. The use of the in vivo approach described here should provide the information needed to meet this goal.(ABSTRACT TRUNCATED AT 400 WORDS)

Chromosome aberrations in lymphocytes of mice after sub-acute low-level inhalation exposure to benzene

Male and female CD-1 mice were exposed to near ambient air concentrations of benzene by inhalation for 22 h per day, 7 days per week for 6 weeks. The concentrations were 0, 40, 100 and 1000 ppb. Significant increases in chromosome aberrations in spleen lymphocytes were observed in exposed compared with control mice except in the high-dose group (p less than 0.05 for female mice in 2 experiments and for male mice in 1 experiment; p less than 0.15 for male mice in the second experiment). A lack of increase in aberrations among mice of the high-dose group may be due to an induction of detoxifying enzymes as observed by us in a previous study (Au et al., 1988b). We also found that the female mice were more sensitive to the clastogenic activity of benzene than male mice under our experimental conditions. Our study serves to emphasize the need to conduct subchronic, low-dose in vivo genotoxicity studies using exposure conditions similar to those of humans, for evaluation of potential hazards. Our data suggest that the current occupational exposure concentrations for benzene (less than 1000 ppb) may still be hazardous to humans.

Cytogenetic assays in genotoxic studies: somatic cell effects of benzene and germinal cell effects of dibromochloropropane

We have reviewed the results of our cytogenetic studies to evaluate the usefulness of these assays in genotoxic studies. In one study, we observed unusual dose-response in lymphocyte chromosome aberration frequencies after exposure of mice to low doses of a chemical mixture (benzene, chloroprene, epichlorohydrin, and xylene). The frequency in the high dose group is lower than those of the medium and low dose groups. This reduction of genotoxicity is correlated with a significant induction of a detoxifying enzyme, glutathione-S-transferase. The data also suggest that extrapolation of effects from high to low doses for risk assessment may be erroneous. Using benzene as a model clastogen, we found that the clastogenic effect persists for a long time after termination of exposure in mice. This phenomenon is probably due to a gradual release of benzene from absorption of the chemical in body fat. In an inhalation study, we observed that chromosome aberrations are induced in mice after exposure to benzene at below the occupational exposure limit of 1 ppm. Since benzene is a ubiquitous environmental contaminant, it may interact with other environmental agents to modify its genotoxic effects. We found that a nongenotoxic drug, praziquantel, and a free radical scavenger, DMSO, can enhance or reduce respectively the clastogenic activities of benzene in mice. Both modifying agents acted by altering the metabolic pathways of benzene. In a study with rats, we showed that carcinogenic doses of benzene can induce chromosome aberrations in lymphocytes of rats long before the expression of cancer. With dibromochloropropane, we observed that this chemical can induce dominant lethality in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

A combined testing protocol for assessing genotoxicity in individual animals: application to environmental toxicology

A multiple end-point approach to assessing genetic toxicity (the combined testing protocol, CTP) was evaluated in male and female CD-1 mice exposed subacutely (3 and 6 weeks) to low levels of a custom-blended gas mixture (epichlorohydrin, benzene, chloroprene and xylene, at 50, 100, 100, and 100 ppb, respectively, as the low dose, with concentration levels 10-fold and 100-fold higher as the intermediate and high doses, or 0.1, 1 and 10 ppm of benzene). Urine mutagenicity was tested in the Salmonella/microsome assay, chromosome aberrations were examined in bone marrow and spleen lymphocytes, micronuclei were measured in bone marrow and peripheral erythrocytes, and cytochrome P450 and glutathione S-transferases were measured in the liver. Structural aberrations in alveolar macrophages and spermatocytes, and thioguanine resistance in spleen lymphocytes were examined for their suitability for incorporation into the overall protocol. Spleen lymphocytes were the most sensitive indicator cells, and showed a dose-related increase (P less than 0.01) in structural chromosome aberrations and in cytotoxicity after 6 weeks of exposure. Analysis of micronucleus formation and metaphase aberrations in the bone marrow, and micronuclei in peripheral erythrocytes showed an overall statistically non-significant but positive trend at the high dose. No mutagenicity was detected in pooled urine samples. Liver microsomal cytochrome P450 was not increased, but cytosolic glutathione S-transferases were significantly increased in a dose-related manner. Since the probability of detecting a genotoxic effect increases with the number of endpoints and tissues examined, this approach should be applicable to many situations without having to perform separate experiments for each tissue examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Advantages of a combined testing protocol (CTP) with multiple endpoints: the reverse tier approach

A multi-endpoint CTP approach provides an efficient procedure to investigate the hazards of chemicals in our environment. Genotoxicity to multiple tissues is assessed after an exposure of limited duration by using a variety of sensitive short-term tests. Resources are thus conserved and results obtained without long delays. Additional information helpful in understanding the observed genotoxic effects is readily obtained in the same experiment by inclusion of additional nongenotoxic endpoints. Numbers of animals required to test chemicals are substantially decreased by increasing the amount of information obtained from each animal. Flexibility is a basic asset of a CTP approach. Therefore, pharmacokinetics of the test chemical or mixture and concerns about subpopulations of exposed humans can guide all aspects of the design of CTP protocol including the animal species, the exposure protocol and the endpoints. The procedures selected for evaluating potential mutagens should be based primarily on the usefulness of the information generated and secondarily on the cost and resources required to perform the procedure. The most expensive procedure is that procedure which does not generate useful information, regardless of the initial cost. The CTP as presently discussed is an attempt to maximize useful information in the most efficient manner possible. Although considerably more expensive than in vitro procedures, the protocol is far less expensive than conducting individual short-term animal procedures, and a fraction of the cost and time required to perform a typical cancer bioassay. Chemicals that are of major concern, for example as in the case of extensive human exposure, would be a prime candidate for initial testing by this methodology.