A method for quantitative risk appraisal for pesticide risk assessments

Pesticide risk assessments are fraught with uncertainties that arise from the process of estimating exposure to and toxicity of chemicals. Regulatory agencies resolve those uncertainties in a health-protective (conservative) manner, typically acknowledging only inter- and intraspecies uncertainties quantitatively. Other uncertainties may be acknowledged qualitatively, but those safety factors (SF) are not enumerated. Quantitative risk appraisal may be used to enumerate the multiplicative SF generated by conservative assumptions regarding uncertainties. The magnitude of SF derived from decision points dealing with historically unquantified uncertainty may far exceed explicit SF used to gauge acceptable margins of exposure (MoE). Examination of the basis for some previously unenumerated SF may justify potential changes in regulatory practices and policies. Using past risk assessments of 3 pesticides (mevinphos, parathion, and methyl iodide) for which the California Department of Pesticide Regulation found unacceptable risk as examples, the previously unquantified SF ranged from 47 to 1 × 10⁶ for scenarios involving handlers, reentry workers, and bystanders.

Drinking water disinfection byproduct iodoacetic acid induces tumorigenic transformation of NIH3T3 cells

Iodoacetic acid (IAA) and iodoform (IF) are unregulated iodinated disinfection byproducts (DBPs) found in drinking water. Their presence in the drinking water of China has not been documented. Recently, the carcinogenic potential of IAA and IF has been a concern because of their mutagenicity in bacteria and genotoxicity in mammalian cells. Therefore, we measured their concentrations in Shanghai drinking water and assessed their cytotoxicity, genotoxicity, and ability to transform NIH3T3 cells to tumorigenic lines. The concentrations of IAA and IF in Shanghai drinking water varied between summer and winter with maximum winter levels of 2.18 μg/L IAA and 0.86 μg/L IF. IAA with a lethal concentration 50 (LC50) of 2.77 μM exhibited more potent cytotoxicity in NIH3T3 cells than IF (LC50 = 83.37 μM). IAA, but not IF, induced a concentration-dependent DNA damage measured by γ-H2AX staining and increased tail moment in single-cell gel electrophoresis. Neither IAA nor IF increased micronucleus frequency. Prolonged exposure of NIH3T3 cells to IAA increased the frequencies of transformed cells with anchorage-independent growth and agglutination with concanavalin A. IAA-transformed cells formed aggressive fibrosarcomas after inoculation into Balb/c nude mice. This study demonstrated that IAA has a biological activity that is consistent with a carcinogen and human exposure should be of concern.

Cytotoxic effects of primary tooth root canal filling materials on L929 cell line

PURPOSE

The purpose of this study was to determine the cytotoxic effects of five different primary tooth root canal filling materials on L929 permanent cell line with MTT assay.

METHODS

Kri 1 paste (iodoform), Diapex (iodoform+Ca(OH)(2)), Metapaste (Ca(OH)(2) with distilled water), Dentalis (iodoform+ZOE+Ca(OH)(2)) and Kalsin (Ca(OH)(2) with glycerin) were used in this study. Tested materials were in contact for 24, 48 and 72 hours with L929 cells. At the end of the test periods, MTT test solutions were added to the plates and incubated for 3 hours at 37 degrees C. Then optic densities were read using UV visible spectrophotometer. All assays were repeated three times to ensure reproducibility. The obtained data were analyzed statistically by one-way analysis of variance and Dunnett T3 post hoc test (P<0.05).

RESULTS

All tested materials were found cytotoxic on L929 cell line. It was found that Kri 1 paste group showed the highest survival rates.

CONCLUSIONS

We concluded that the use of Kri 1 paste as a root canal filling material is a better option than other medications in primary teeth. Further research is necessary to determine the effect of root canal filling materials on vital tissues.

Effect of methyl iodide on deiodinase activity

Methyl iodide (MeI) has been proposed as an alternative for methyl bromide in pre-plant soil fumigation applications that does not affect stratospheric ozone. Preliminary studies in rabbits noted fetal resorptions if the pregnant does were exposed to MeI during a critical period during gestation. In addition, abnormalities in thyroid hormone parameters were also observed in animals exposed to MeI. Since monodeiodination is the major metabolic pathway of the thyroid hormones, we examined the effect of MeI on deiodinase activity as a possible etiology for the alteration in thyroid hormone parameters and ultimate fetal demise. In vitro studies using tissue microsomes and cell culture showed that MeI has no effect on type I 5'-deiodinase (D1) or type II 5'-deiodinase (D2) at physiologically relevant concentrations. At high concentrations (>10 mM,>10,000 ppm), MeI caused a nonspecific inactivation of D1 and D2. Analysis of D1 and D2 activity in rats exposed by inhalation to increasing concentrations of MeI showed a significant decrease in enzyme activity at 100 ppm, while brain type III 5'-deiodinase (D3) was unaffected by MeI at the exposures studied. While the drop in D1 can be explained by the induction of a hypothyroid state in the exposed rats, there is no clear explanation for the fall in D2 levels. In the rabbit studies, there was a significant decrease in kidney D1 in the adult rabbits exposed to 20 ppm MeI. However, there was no effect on liver D1, brain D2, or placental D3 in the MeI-exposed rabbits. Similarly, there was no effect of MeI on fetal D1 or D2 activity. The lack of a significant direct effect of MeI on deiodinase activity and the absence of a change in placental or fetal deiodinase activity make it unlikely that alterations in deiodinase activity plays a role in the fetal resorptions in the MeI-exposed rabbits.

Evaluation of tissue response to MTA and Portland cement with iodoform

OBJECTIVE

The aim of this study was to evaluate the biocompatibility of Portland cement with the addition of iodoform, compared to MTA (ProRoot).

STUDY DESIGN

Eighteen Wistar albino rats were divided into 3 groups of 6 animals each. Polyethylene tubes were filled either with freshly mixed MTA or Portland cement mixed with iodoform (20% wt/wt) and implanted subcutaneously. An empty tube served as control. After 7, 30, or 60 days, the implants together with the surrounding tissues were removed in blocks. Sections were evaluated for the presence and thickness of a fibrous capsule, presence of granulation tissue, and the severity of inflammatory response. Data were submitted to nonparametric statistical analysis with individual comparisons between groups at a significance level of P < 0.05.

RESULTS

There were no differences between inflammatory responses at 7 and 30 days. After 60 days from surgical removal, there was significantly more tissue reaction to the MTA and Portland cement compared to the control group.

CONCLUSION

There were no significant differences regarding inflammatory responses between MTA and Portland cement with iodoform after 7, 30, or 60 days. After 60 days, the fibrous capsule around the Portland cement appeared more organized than tissue surrounding MTA implants. After 60 days, there was still a significantly increased tissue reaction to the 2 cements compared to the empty polyethylene tubes.

Acute methyl iodide exposure with delayed neuropsychiatric sequelae: report of a case

BACKGROUND

Methyl iodide is a monohalomethane used as an analytic and organic chemistry reagent, as a methylating agent in organic chemical synthesis, and as a fumigant. In an acute exposure, methyl iodide is a pulmonary and dermal irritant. Chronic neurotoxicity has been reported in survivors of acute exposure.

METHODS

A review of the 11 case reports of methyl iodide poisoning in the medical literature of the 20th century found that six of the patients experienced a chronic neurological syndrome characterized primarily by delayed psychiatric, behavioral, and cognitive sequelae.

RESULTS

The case patient experienced a massive exposure to methyl iodide with resulting life-threatening burns. During convalescence, various cognitive and behavioral deficits became apparent. The results of a comprehensive evaluation at our occupational toxicology clinic, which included sequential neuropsychometric testing, are described.

CONCLUSION

The findings in the case patient may advance our understanding of the mechanisms and clinical manifestations of chronic neurotoxicity after exposure to methyl iodide.

Fumigant combinations for Cyperus esculentum L control

The phase-out of methyl bromide as a soil fumigant has stimulated research into the use of other soil fumigants for weed control. Methyl bromide, methyl iodide, propargyl bromide, 1,3-dichloropropene (1,3-D) and metam-sodium were tested alone and in combination with chloropicrin in laboratory experiments to determine their efficacy against Cyperus esculentus L (yellow nutsedge) tubers. Propargyl bromide and metam-sodium were the most efficacious fumigants tested, with EC50 values of 3.7 and 6.5 microM, respectively. The relative potencies of methyl iodide and chloropicrin were not significantly different but were 2.6 and 2.9 times more potent than methyl bromide, respectively. The EC50 values for all fumigants other than 1,3-D were significantly lower than that of methyl bromide. Combining each fumigant with 17% chloropicrin resulted in a synergistic interaction. The greatest increase in potency between the expected result and the actual result was a relative potency of 3.8 with the methyl bromide/chloropicrin combination. The smallest increase in efficacy was with propargyl bromide and chloropicrin, with a relative potency of 1.5. There was no significant difference between the EC50 values of methyl bromide/chloropicrin and methyl iodide/chloropicrin combinations. Combining 1,3-D with 17% chloropicrin resulted in an EC50 value for C. esculentus control similar to that of methyl iodide applied alone.

Three-dimensional mapping of the lesions induced by beta-beta'-iminodiproprionitrile, methyl iodide and methyl methacrylate in the rat nasal cavity

The nasal cavity is an important target organ for toxicity, and many chemicals induce site-specific lesions in this region. The factors responsible for this site-selectivity have not been unequivocally identified, but probably include regional dosimetry and bioactivation. The purpose of this study was to map, in 3 dimensions, the lesions induced by beta-beta'-iminodipropionitrile (IDPN), methyl iodide (MeI) and methyl methacrylate (MMA) in the rat nasal cavity. Animals were administered IDPN (150 mg/kg, IP) or exposed via inhalation to MeI (100 ppm, 2 hours) or MMA (400 ppm, 4 hours) and sacrificed after 24 hours. Heads were decalcified, step-sections (1 every 400 microm) cut and stained, and the severity of the epithelial lesion graded as mild (vacuolation and pyknosis), moderate (undulation and mild stripping), or marked (complete stripping). These grades were mapped onto a 3D-model of a rat nasal cavity using the KS400 imaging system (Imaging Associates, Thame, UK). Despite the different routes of exposure the lesions induced by the 3 compounds had very similar distributions, predominantly affecting the dorsal-medial aspects of the ethmoturbinates and, in the case of MMA, the organ of Rodolfo Masera. These results suggest that, with these chemicals, local bioactivation plays a more important role than dosimetry in determining lesion distribution.

Methyl iodide toxicity in rat cerebellar granule cells in vitro: the role of glutathione

The monohalomethane methyl iodide (MeI) is toxic to a number of organ systems including the central nervous system. Clinical symptoms of neurotoxicity suggest that the cerebellum is the target within the brain, and we have now modelled the toxicity of MeI in cultured rat cerebellar granule cells. Cytotoxicity is maximal 24 h after a 5 min exposure to MeI, and the EC50 for MeI under these conditions was calculated to be 1.6 mM. The glutathione S-transferase (GST) dependent metabolism of MeI was investigated in these cultures. There was a marked decrease in intracellular glutathione (GSH) 15 min after exposure to MeI, and GSH concentrations then increased, reaching 130% of control levels 7 h after exposure. To investigate the role of conjugation with GSH in the toxicity of MeI, GSH levels were modulated prior to exposure. Depletion of GSH exacerbated the cytotoxicity of MeI while provision of a bioavailable source of GSH was protective. Inclusion of antioxidants [vitamin E, butylated hydroxytoluene (BHT) or desferrioxamine mesylate (DF)] also protected against the cytotoxicity of MeI. Our in vitro data suggest that MeI is conjugated with GSH in the cerebellum, and the resulting extensive depletion of GSH may be the first step en route to toxicity, rendering the tissue susceptible to methylation and/or oxidative stress.

The effect of surgical medicaments on peripheral nerve function

Surgical medicaments are often placed in close proximity to peripheral nerves and may be responsible for some postoperative sensory disturbances. In this study we investigated the effect of four medicaments -- BIPP, (bismuth iodoform paraffin paste), Whitehead's varnish (compound iodoform paint), Surgicel (oxidized regenerated cellulose) and Carnoy's solution (ethanol, chloroform and acetic acid) -- on peripheral nerve function. The experiments were carried out on the saphenous nerve in anaesthetized adult rats. Electrical stimuli (30 V, 0.1 ms duration) were applied to the saphenous nerve through electrodes placed distally (at the ankle) to evoke a compound action potential (CAP) which was recorded proximally (in the thigh). The CAP was recorded before, and for 2 h after, the application of the medicament to a 1 cm length of nerve between the electrodes. In other animals (n = 4 in each group) recordings were made after the medicament had been placed in a connective tissue pocket immediately overlying the nerve for a 2-week period. BIPP (n = 4) had no immediate or delayed effect on neural function, whereas Whitehead's varnish (n = 4) and Carnoy's (n = 4) solution both blocked neural conduction within 2 min of being placed adjacent to the nerve. The effect of Surgicel (n = 8) was more variable; axonal conduction was blocked within 2 h in five of the eight experiments undertaken. After the application of Whitehead's varnish or Surgicel for 2 weeks, the CAPs had regained characteristics which were similar to those of the controls, but after the application of Carnoy's solution they remained significantly diminished (P < 0.004). These results suggest that, with the exception of BIPP, the medicaments tested could be responsible for some postoperative sensory disturbances, and the effects of Carnoy's solution on neural function may be persistent.

Investigations of the pathways of toxicity of methyl iodide in the rat nasal cavity

The monohalomethane methyl iodide (MeI) is a site specific toxin within the nasal cavity of the rat, selectively damaging the olfactory epithelium (OE) whilst respiratory epithelium (RE) is spared. The aim of this study was to investigate the rates and routes of metabolism of MeI within the nasal cavity, in order to understand the reasons for the observed site-selectivity. Cytosolic glutathione S-transferases (GSTs) of both OE and RE catalysed the conjugation of MeI with glutathione (GSH), but rates were 4-fold higher in OE than RE. The product of this reaction was confirmed as S-methyl GSH. In both OE and liver the GST catalysing the conjugation of MeI was shown to belong to the theta class. No cytochrome P450-dependent oxidation of MeI to formaldehyde could be detected in incubations containing hepatic or olfactory microsomes. Intact nasal turbinates were incubated with [14C]-MeI, and a dose- and time-dependent covalent binding of MeI to olfactory protein was demonstrated. The rates of protein methylation were found to be similar in OE and RE. Thus the only parameter that correlates with the site-selectivity of the observed lesion is the rate of conjugation of MeI with GSH. Whether toxicity is due to production of a reactive metabolite or GSH depletion per se, remains to be elucidated.

Olfactory toxicity of methyl iodide in the rat

The monohalomethanes (methyl iodide, methyl bromide and methyl chloride) are widely used industrial methylating agents with pronounced acute and chronic toxicity in both experimental animals and man. Recently inhalation exposure of rats to methyl bromide has been shown to result in severe olfactory toxicity. This study examined the effects on the rat nasal cavity of inhalation of methyl iodide (100 ppm for 0.5-6 h), and demonstrated that methyl iodide is a more potent olfactory toxin than methyl bromide. Within the nasal cavity the olfactory epithelium was the principle target tissue, and it was only at high doses (600 ppm.h) that limited damage to transitional epithelium occurred. The squamous and respiratory epithelia were consistently unaffected. Within olfactory epithelium the sustentacular cells were the primary cellular target and damage to sensory cells appeared to be a secondary event. Methyl iodide induced olfactory damage was reversible, and 2 weeks after exposure almost complete repair had taken place.

In vitro antimicrobial and cytotoxic effects of Kri 1 paste and zinc oxide-eugenol used in primary tooth pulpectomies

The antimicrobial and cytotoxic effects of Kri 1 paste, an iodoform-based primary tooth filling material, were compared with zinc oxide-eugenol (ZOE), using in vitro techniques. Antimicrobial evaluation involved measuring inhibition zones of Streptococcus faecalis on brain heart agar. Cytotoxicity evaluation involved direct cell-medicament contact experiments of 4-hr and 24-hr duration using fresh and set medicaments, and indirect cell-medicament contact experiments of 24-hr duration using fresh and set medicaments. ZOE produced a greater zone of bacterial inhibition than Kri 1 paste. Kri 1 paste cytotoxicity remained high regardless of the amount of setting time in the 4-hr direct contact experiment, while ZOE cytotoxicity decreased with setting time. Both Kri 1 paste and ZOE had high cytotoxicity regardless of setting time in the 24-hr direct cell-medicament contact test. ZOE cytotoxicity decreased to control levels after only 1 day of setting in the indirect contact experiments, compared with greater than 7 days for Kri 1 paste. The results suggest ZOE has better antimicrobial activity than Kri 1 paste. ZOE also has lower cytotoxicity, although prolonged cell-medicament contact may result in both medicaments having similarly high cytotoxicity.

Histopathologic approaches to chemical toxicity using primary cultures of dissociated neural cells grown in chamber slides

Morphologic lesions have received only limited attention as in vitro endpoints of toxicity. In the present work, "tissue" and cell morphology of control and toxicant-treated primary dissociated cerebrocortical cell cultures from fetal mice were examined using phase-contrast and bright-field microscopy. In untreated control cultures, a reproducible sequence of developmental events included cellular reaggregation, intercolony bridging with cell migration, and neuronal apoptosis, with maturation yielding confluent monolayers containing both neurons and glia. Because even mature cultures had regions of varying differentiation, an understanding of the normal developmental sequence was essential when assessing toxicant-treated cultures for damage. Chemicals induced neuronotoxic, gliotoxic, and cytotoxic (i.e., nonspecific) patterns of morphologic damage in growing (< 6 day old) or mature (6-15 day old) cultures in both a concentration-dependent and cell type-specific manner. In addition, exposure to some toxicants consistently reduced the staining intensity for glial fibrillary acidic protein in the astrocyte carpet prior to the appearance of structural damage. These data indicate that histopathologic endpoints, including methods for neural-specific markers, represent potentially valuable criteria for in vitro assessments of neurotoxicity.

[DNA methylation of monohalogenated methanes of F344 rats]

Monohalogenated methanes (methyl chloride, methyl bromide and methyl iodide) are mutagenic and carcinogenic. The possible mechanism of these effects, DNA methylation, was studied. DNA adducts from organs of F344 rats exposed to these chemicals were separated and identified with high performance liquid chromatography (HPLC) and gas-chromatography/mass-spectrometry (GC/MS). DNA adducts, 7-methylguanine (7-MeG) and O6-Methylguanine(0(6)-MeG), incorporation of 14C into de novo synthesis of nucleobases could be observed in enzymatic DNA hydrolysates by HPLC and determination of the radioactivity in the fractions. The formation of DNA adducts in the studied organs was only quantitatively different. The formation of O6-MeG was further proved by analysing the acidic hydrolysates using HPLC with non-radioactive O6-MeG as internal standard. 7-MeG and 3-MeA were identified with GC/MS analysis.

Mechanisms of carcinogenicity of methyl halides

Methyl chloride, bromide, and iodide are used as methylating agents. These compounds are mutagenic in short-term tests and do not require activation by exogenous S9 mix. In DNA-binding studies performed in rats and mice, 14C-labeled methyl chloride was given by inhalation, and methylation of DNA bases was examined. The compound did not lead to specific DNA adducts. In particular, methylation of DNA bases was not observed. In contrast, methyl bromide and methyl iodide, upon oral and inhalation administration to rats and mice, caused systemic DNA methylation. Specifically, 3-methyl-adenine, 7-methyl-guanine, and O6-methyl-guanine were formed. Long-term inhalation bioassays have been performed in rats and mice with methyl chloride and methyl bromide. Methyl chloride induced renal tumors, but only in male mice at the highest concentration tested (1000 ppm). Under these special conditions, a number of secondary effects occur subsequent to glutathione depletion in the target tissue, resulting in DNA damage (DNA-protein cross-links and probably DNA single-strand breaks). The particular coincidence of secondary high-dose effects precludes a risk extrapolation to man. Methyl bromide did not induce tumors in rats and mice when administered by inhalation. However, experimental data point to a possible local carcinogenic effect on the rat forestomach when the compound is given by gavage. A factor that accounts for the discrepancy between systemic DNA methylation and apparent noncarcinogenicity upon inhalation might be the preference of 7-N over O6 methylation of guanine. An extrapolation of the negative rodent inhalation bioassay of methyl bromide to man might be problematic because rodents metabolize methyl bromide very quickly whereas in humans there is a particular subpopulation that only poorly metabolizes the compound ("nonconjugators"). Such individuals can be characterized by incubation of erythrocytes with methyl chloride or methyl bromide and measurement of the substrate decline. Methyl iodide has been tested, with positive outcome, in early carcinogenicity bioassays not based on modern methodology. However, these results, along with the proven systemic methylating potency of methyl iodide, argue in favor of a carcinogenic effect of the compound.

[Middle molecular weight peptides from rat blood serum during acute liver injury and administration of iodinated oil]

A spectrum of mean-molecular blood serum peptides in rats with experimental toxic hepatitis and parenteral injection of iodinated oil has been studied using the method of gel-filtration on a sephadex G-25. It is established that the toxic hepatitis is characterized by the expressed rearrangement of the stock of mean-molecular peptides with a preferential growth in the blood serum and normalization of their concentrations 24h after the injection of iodinated oil accompanied by attenuation of the organism intoxication phenomena. An increase in the content of mean-molecular peptides was registered 48 hours after the iodinated oil injection.

Mutagenesis at the ouabain-resistance locus of 3.7.2C L5178Y cells by chromosomal mutagens

Chemical mutagens including methyl methanesulfonate, N-methyl-N'-nitro-N-nitrosoguanidine, iodomethane, and epichlorohydrin have been classified as "chromosomal mutagens" in the L5178Y/thymidine kinase (TK) gene mutation assay by Clive and coworkers [Mutat Res 59:61-108, 1979; and "The Predictive Value of Short-Term Screening Tests in Carcinogenicity Evaluation." Amsterdam: Elsevier/North Holland, pp 103-123, 1980] who observed mutagen-dependent increases in small TK-deficient mutant colonies with detectable damage to the chromosome (11) that carries the TK locus. In this study, we tested these four chemicals for the induction of gene mutations at the ouabain-resistance (ouares) locus of 3.7.2C L5178Y cells to determine if presumptive chromosomal mutagens would go undetected at a gene locus that is unresponsive to chromosomal damage. A final concentration of 375 micrograms/ml ouabain in soft-agar medium selected against the ouabain-sensitive phenotype without loss of the mutagen-induced ouabain-resistant phenotype. Verification of the mutant phenotype was completed for six individual soft-agar ouares colonies derived from mutagen-treated cultures via growth for 10-11 days in nonselective medium followed by retesting for colony formation in selective soft-agar medium. Dose-related reproducible increases in the frequency of ouabain-resistant mutants were observed for 3.7.2C L5178Y cells that had been exposed for 3 hr to 24-46 micrograms/ml epichlorohydrin, 1.9-3.6 micrograms/ml iodomethane, 0.006-0.011 micrograms/ml N-methyl-N'-nitro-N-nitrosoguanidine and and 2.0-5.4 micrograms/ml methyl methanesulfonate. Also, treatments with EMS, which induced sufficient numbers of ouares colonies to permit analysis of colony size distribution, showed the existence of a bimodal size distribution similar to those reported for TK-deficient mutants. This discovery suggests that mutant colony size in this cell line may be independent of specific gene locus effects. We conclude that (1) chemicals that induce a high proportion of chromosomal mutants, as detected at the TK locus in earlier studies, also induce single gene mutations at the ouabain-resistance locus and (2) a bimodal distribution of mutant colony sizes in soft-agar medium after short expression periods may be a distinctive characteristic of the 3.7.2C L5178Y cell line and is not confined to the TK locus.

Blood glutathione as a measure of exposure to toxic compounds

Blood and liver glutathione levels were measured under the effect of an acute exposure to high doses of glutathione-depleting substances. Among direct-acting glutathione-depleting substances, diethyl maleate (0.3, 0.7 and 1.4 ml kg-1) caused a marked reduction of both blood and liver glutathione, whereas methyl iodide (320 mg kg-1) led to a decrease in liver glutathione stores immediately and in blood stores with a longer latency. Indirectly glutathione-depleting substances, like paracetamol (0.5-1.0 g kg-1) and styrene (250 mg kg-1), caused a reduction of liver glutathione, but not a similar reduction of blood glutathione. Blood glutathione is not a good measure of organ glutathione stores when dealing with indirect-acting glutathione-depleting substances.

Mutagenic activity of some clastogenic chemicals at the hypoxanthine guanine phosphoribosyl transferase locus of Chinese hamster ovary cells

4 presumptive clastogens (caffeine, dimethyl sulfoxide, diethylstilbestrol and p,p'-DDE) and 4 chemicals thought to induce chromosomal mutations in L5178Y mouse lymphoma cells (procarbazine X HCl, epichlorohydrin, hycanthone and iodomethane) were tested in the CHO/HGPRT gene mutation assay for the induction of 6-thioguanine-resistant ( 6TGR ) mutants. Of the clastogens, p,p'-DDE was mutagenic at several concentrations and diethylstilbestrol (DES) increased the 6TGR mutant frequency over control levels at the 6.7 and 8.0 micrograms/ml doses, but the results for DES were neither convincing nor significant. Caffeine was not mutagenic although at very high concentrations (6667-8000 micrograms/ml) there was a slight elevation in mutant frequency over background. This was probably due to a selective effect of caffeine against the HGPRT+ phenotype, for 2 different HGPRT- cell lines were refractory to the toxic effects of caffeine at the highest test level (8000 micrograms/ml). All 4 'chromosomal mutagens' produced dose-related increases in mutant frequencies at the HGPRT locus of these CHO cells. 6TGR colonies were generally uniform in size when normal precautions were taken to prevent the formation of satellite (secondary) colonies. Excepting DES, dimethyl sulfoxide, and caffeine, these data demonstrate that 5 of 8 clastogenic chemicals reproducibly induce mutations at the HGPRT locus of CHO cells which lack the small colony-forming potential of 3.7.2C L5178Y cells.

Chemical reactivity and mutagenicity of some dihalomethanes

Four dihalomethanes; dichloromethane, bromochloromethane, dibromomethane and diiodomethane, have been studied with respect to their reactivities towards nucleophilic compounds of different strengths in water solution and with respect to their toxicities and mutagenic effectiveness in bacterial test systems. The correlation between biological activity (toxicity and mutagenic effectiveness in Salmonella TA100) and reactivity towards strong nucleophiles indicates that reactions with nucleophilic groups of high reactivity in the biological material, possibly SH or amino groups in proteins, are involved in their mechanism of action.

Morphological transformation of C3H/10T1/2 CL8 cells by alkylating agents

The standard method of the C3H/10T1/2 cell transformation assay cannot adequately detect alkylating agents. A modification of the standard procedure as described by Bertram and Heidelberger using a large number of synchronized cells and high levels of toxicity was evaluated for transformation using several alkylating agents. By using this method, N-methyl-N' -nitro-N-nitrosoguanidine (MNNG), beta-propiolactone (BPL), methyl methanesulfonate (MMS), methylnitrosourea (MNU) and 1,3-propane sultone (PS) transformed these cells. However, methyl iodide (MI) failed to induce any transformed foci.

Subacute inhalation toxicity testing with iodoform vapor

Subacute inhalation experiments were conducted to determine the LC50 value for adult Sprague-Dawley rats exposed to iodoform vapor. Each dose consisted of 5 males and 5 females that were together for a 7-h exposure or sham exposure and then separated for observation over the subsequent 24-h period. The rats were deprived of food and water during actual exposure or sham exposure. Exposures were conducted in a custom-designed 75-l glass chamber. Vapor concentrations were verified in samples taken from the exposure chamber. Under the conditions of the experiments the 7-h LC50 was found to be 183 ppm. The second objective of these experiments was to determine the toxic effect of iodoform vapor on rats exposed for 7 h/d for 7 consecutive days. Three groups of 5 young adult male and 5 female rats were used. One group served as a sham control and the other groups were exposed to 1 and 14 ppm iodoform vapor. No significant differences were noted in food and water intake, urine and feces output, and intestinal transit performance in either exposed group. No remarkable changes were noted in SMA 12/60 blood values for either exposed group. The only histopathological manifestation noted was the presence of mineralized deposits in the medullary renal tubules of some of the rats from the 14-ppm group.