Initial study in rats evaluating the effects of 1,4-dichlorobutene-2 (DCB) on the respiratory tract.

Rats were exposed by inhalation to either 0.5 ppm 1,4-dichlorobutene-2 (DCB) for two years or to 5.0 ppm for seven months, 2.5 ppm for five months, and no further exposure for 12 months prior to sacrifice. Malignant and non-malignant tumors of the nasal tissues were seen in both test groups with the incidence and proportion of malignant tumors being much higher in the 5.0/2.5 ppm rats. Under the conditions of this study, DCB is carcinogenic in rats of both sexes.

Genome sequence of the plant pathogen and biotechnology agent Agrobacterium tumefaciens C58.

Agrobacterium tumefaciens is a plant pathogen capable of transferring a defined segment of DNA to a host plant, generating a gall tumor. Replacing the transferred tumor-inducing genes with exogenous DNA allows the introduction of any desired gene into the plant. Thus, A. tumefaciens has been critical for the development of modern plant genetics and agricultural biotechnology. Here we describe the genome of A. tumefaciens strain C58, which has an unusual structure consisting of one circular and one linear chromosome. We discuss genome architecture and evolution and additional genes potentially involved in virulence and metabolic parasitism of host plants.

Nasal tumors in rats following long-term inhalation exposure to 1,4-dichlorobutene-2 (DCB).

This study was conducted to elucidate the time- and dose-response relationships of long-term, low-level 1,4-dichlorobutene-2 (DCB) inhalation exposure to nasal tumor induction in rats. Male Crl:CD BR rats were exposed 6 hours per day, 5 days week to 0, 0.1, 0.3, or 1.0 ppm DCB for up to 19 months; some rats were sacrificed at various time intervals during the study. After 19 months of exposure, surviving rats were held without treatment for an additional 5 months. Tissues from the respiratory tract, lymph nodes, and brain were evaluated microscopically. Compound-related non-neoplastic lesions were observed in the nasal cavities of rats in the 1.0 ppm group after three months of exposure and in the other two groups after twelve months of exposure. The lesions were progressive in severity and frequency. A statistically significant increase in benign nasal tumors (adenomas) occurred in rats from all three DCB-exposed groups. The adenomas occurred in the respiratory region of the nasal cavity and were first observed in the 1.0 ppm group at study month 10. Malignant nasal tumors occurred in the olfactory region of the nasal cavity and were statistically increased at 1.0 ppm.

Regulating and assessing risks of cholinesterase-inhibiting pesticides: divergent approaches and interpretations.

This document presents a revised framework for conducting worker and dietary risk assessments for less-than-lifetime exposures to organophosphate or carbamate pesticides based on red blood cell (RBC) or brain acetylcholinesterase (AChE) inhibition or the presence of clinical signs and symptoms. The proposals for appropriate uncertainty factors are based on the biological significance of the cholinesterase (ChE) inhibition noted at the lowest-observed-effect level (LOEL) and the degree of uncertainty in the extrapolation between human and animal data. An extensive evaluation of industry data, not previously summarized, and the available literature indicate that the following risk assessment principles are supportable and protective of human health: Plasma ChE inhibition is not an adverse effect, and therefore should not be utilized in risk assessments. Red blood cell AChE is not associated with the nervous system and inhibition is not per se an adverse (neurotoxic) effect. When available, cholinergic effects or brain AChE inhibition data should take precedence over RBC AChE for determining no-observed-effect levels (NOELs). When available, human RBC AChE inhibition or cholinergic effects data should take precedence over animal data for determining NOELs. Due to the lack of adversity associated with inhibition of RBC AChE, the use of a 10-fold (10x) uncertainty factor from the NOEL is adequate when RBC AChE inhibition data from either animal or human studies are used to assess human risk. Due to greater potential for adversity, NOELs for brain AChE inhibition and cholinergic effects identified in animal studies should receive a default uncertainty factor of 100x; lower uncertainty factors may be used on a case-by-case basis. NOELs based on cholinergic effects noted in human studies should only require a 10x uncertainty factor, since an interspecies extrapolation factor from animals to humans is unnecessary. For RBC and brain AChE activity the threshold for defining a NOEL should be less than or equal to 20% difference from control activity in all species. For risk assessment purposes, duration and route of the study should reflect the expected duration and route of exposure for humans (i.e., a 21-d or 28-d dermal study for subchronic occupational dermal exposure assessment). When dermal data are not available, a subchronic oral toxicity study and an appropriate dermal penetration factor should be used. A general default of 10% absorption should be used, analogous to the United Kingdom and German exposure models that are widely used in Europe. The recommendations in this document are generally consistent with current risk assessment procedures used by Canada, the European Community (EC), and the United Kingdom (UK).

Investigation of a mechanism for Leydig cell tumorigenesis by linuron in rats.

In a previously conducted 2-year study, a concentration-dependent increase in Leydig cell adenomas was observed in Crl:CD BR(CD) rats fed diets containing the herbicide linuron. Linuron has been shown to be negative in a battery of six tests for genotoxicity; therefore, a nongenotoxic mechanism of tumorgenesis was investigated. Linuron is structurally related to the nonsteroidal antiandrogen, flutamide. Flutamide has also been shown to produce Leydig cell tumors within 1 year, presumably due to sustained hypersecretion of luteinizing hormone (LH) which occurs following disruption of the hypothalamic-pituitary-testicular (HPT) axis. To investigate whether linuron possesses antiandrogenic activity, sexually immature and mature CD rats were administered either 200 mg/kg linuron or 10 mg/kg flutamide (positive control) for 2 weeks. Accessory sex organs were weighed and serum hormone levels were measured to assess androgen status and alterations in the HPT axis. Serum from a multigeneration reproduction study with linuron was also analyzed for serum hormone levels. In addition, competitive receptor binding studies were conducted to evaluate the ability of linuron to bind to the androgen receptor. Linuron decreased accessory sex organ weights in sexually immature and mature linuron-treated rats. Increased serum estradiol and LH levels were observed in sexually mature linuron-treated rats. Serum estradiol and LH levels were also elevated in P1 and F1 male rats from the multigeneration reproduction study. These accessory sex organ and hormonal changes are consistent with those seen with the antiandrogen flutamide, the only exception being serum testosterone, which was elevated following exposure to flutamide but not to linuron. The inability of linuron to increase testosterone levels may reflect the lower potency of linuron as an antiandrogen compared with that of flutamide, which is a potent antiandrogen. Additionally, linuron competed with [3H]testosterone for binding to the androgen receptor. The IC50 data for competition to the androgen receptor suggest that linuron is approximately 3.5 times less potent than flutamide. These data are consistent with the effects seen with flutamide and demonstrate that linuron is a less potent antiandrogen than flutamide. Collectively, these data support the hypothesis that linuron produces Leydig cell tumors via an antiandrogenic mechanism where sustained hypersecretion of LH appears to be responsible for the development of Leydig cell hyperplasia and adenomas.

Eye irritation response of humans to formaldehyde.

Human panelists sensitive to formaldehyde eye irritation were exposed to low concentrations of formaldehyde vapor (0.35 to 1.0 ppm) for 6 minutes. Eye irritation was evaluated by time to detection of the first trace of irritation and by subjective ranking of severity. Both time to response and severity appeared to be functions of formaldehyde concentration. Severity of response was above "slight" only with highest test concentration, 1.0 ppm.