Inhalation teratology study on monochlorobenzene in rats and rabbits

Micronuclei induction and chromosomal aberrations in Rattus norvegicus by chloroacetic acid and chlorobenzene

Chloroacetic acid (CAA) and chlorobenzene (CB) have been evaluated for in vivo mutagenic potential in Rattus norvegicus, employing the following criteria : (i) chromosomal aberrations (CAs) such as breaks, gaps, exchanges, rings, and multiple aberrations and (ii) micronuclei (MN) induction. Three sublethal doses, 0.008, 0.01, and 0.012 mg/g b. wt. of CAA and 0.75, 1.0, and 1.25 mg/g b. wt. of rat of CB were administered and the bone marrow cells evaluated in each of the three treated groups at 12, 24, and 48 h, respectively. Mean MN frequencies of 4.40+/-0.2 and 5.42+/-0.3, obtained respectively for CAA and CB. The higher induction of MN by CAA and CB was dose- and time-dependent. Most significant impact (P<0.05) for either of the compounds was observed at 24h post administration, when the recorded mean frequency of CAs was maximum for CAA (4.33+/-0.6) as well as for CB (4.66+/-0.5).

Effect of proximity to hazardous waste sites on the development of congenital heart disease

The authors sought to determine whether the risk of congenital heart disease (CHD) was greater for the children of mothers who lived close to a hazardous waste site (HWS) than for those who lived farther away. All cases (n = 1283) of confirmed CHD, and a random sample of 2,292 controls, born in Dallas County, Texas, from 1979-1984 were linked with 276 HWSs present during the study. The authors ascertained locations of households and determined the distance to the nearest HWS. They obtained odds ratios (ORs) for CHD. A 20% increased risk for CHD was found in association with maternal residence within 1 mile of an HWS (OR = 1.2, 95% confidence interval = 1.1-1.4). The results of this study suggests that a statistically significant additional risk for CHD is associated with maternal proximity to an HWS.

Quantitation of urinary chlorobenzene metabolites by HPLC: concentrations of 4-chlorocatechol and chlorophenols in urine and of chlorobenzene in biological specimens of subjects exposed to chlorobenzene

A simple method for the determination of 4-chlorocatechol (ClCh, 4-chloro-1,2-benzenediol) and chlorophenols (ClPh), metabolites of monochlorobenzene (ClBz), in urine by high performance liquid chromatography (HPLC) is described. Enzymatic hydrolysates of urine were applied to a stainless-steel column packed with octadecyl-silanized silica gel, and a mixed solution of 20 mM potassium phosphate monobasic: acetonitryl (75:25, v/v) was used as a mobile phase. The procedures for ether extraction and evaporation of extract could be omitted. The accuracy and precision of the present HPLC method were satisfactory. The excretion kinetics of ClCh and p-ClPh were investigated over 35 h after cessation of ClBz inhalation. Proportional relationships between concentrations of ClBz in air and of its metabolites in urine were observed. The slopes of regression lines predicting the levels of ClCh, p-ClPh and total ClPh in urine taken during the last 2 h of exposure to ClBz in air were 6.56, 1.13 and 2.83 mg/g creatinine for 1 ppm ClBz, respectively. ClBz in the blood and the end exhaled air of subjects at the end of exposure were identified by gas chromatography (GC) and mass spectrometry. A proportional relationship was observed between the concentration of ClBz in air and that in blood. The validity of the threshold limit value (TLV) for ClBz as evaluated from the subjective and objective symptoms is discussed.

A tier system for developmental toxicity evaluations based on considerations of exposure and effect relationships

The backlog of untested chemicals and the rate at which new substances enter the marketplace exceed our capacity for developmental effects testing by standard in vivo methods. However, conservative use of two observations in a manner consistent with present day understanding of abnormal developmental biology can more accurately focus attention and resources on those agents in greatest need of complex testing for effects on in utero development. These two observations are 1) most chemicals are no more toxic to embryonic development than they are to adult homeostasis and 2) most human exposure to chemicals is de minimus, i.e., so small that it is inconsequential. Recently devised in vitro assays to quantitatively rank chemicals according to their developmental hazard index, when used in conjunction with more conventional in vivo methods and appropriate considerations of exposure, permit evaluation of a significantly larger number of chemicals than is currently achieved. The methods described apply a tier approach to establish testing priorities that markedly reduce the time, cost, and number of laboratory animals needed for evaluation of developmental toxicity.