Toxicity of Fourteen Volatile Chemicals as Measured By the Chick Embryo Method

An overview of butanol-induced developmental neurotoxicity and the potential mechanisms related to these observed effects

The purpose of this article is to briefly review the published literature on the developmental neurotoxic effects, including potential mechanisms, of four butanols: n-butanol, sec-butanol, tert-butanol, isobutanol, and identify data gaps and research needs for evaluation of human health risks in this area. Exposure potential to these four butanols is considerable given the high production volume (>1 billion lb) of n- and tert-butanol and moderate production volumes (100-500 million lb) of sec- and isobutanol. With the impetus to derive cleaner gasoline blends, butanols are being considered for use as fuel oxygenates. Notable signs of neurotoxicity and developmental neurotoxicity have been observed in some studies where laboratory animals (rodents) were gestationally exposed to n- or tert-butanol. Mechanistic data relevant to the observed developmental neurotoxicity endpoints were also reviewed to hypothesize potential mechanisms associated with the developmental neurotoxicity outcome. Data from the related and highly characterized alcohol, ethanol, were included to examine consistencies between this compound and the four butanols. It is widely known that alcohols, including butanols, interact with several ion channels and modulate the function of these targets following both acute and chronic exposures. In addition, n- and sec-butanol have been demonstrated to inhibit fetal rat brain astroglial cell proliferation. Further, rat pups exposed to n-butanol in utero were also reported to have significant increases in brain levels of dopamine and serotonin, but decreases in serotonin levels were noted with gestational exposure to tert-butanol. tert-Butanol was reported to inhibit muscarinic receptor-stimulated phosphoinositide metabolism which has been hypothesized to be a possible target for the neurotoxic effects of ethanol during brain development. The mechanistic data for the butanols support developmental neurotoxicity that has been observed in some of the rodent studies. However, careful studies evaluating the neurobehavior of developing pups in sensitive strains, as well as characterizing the plausible mechanisms involved, need to be conducted in order to further elucidate the neurodevelopmental effects of butanols for risk evaluation.

Sub-lethal effects of acetone on Daphnia magna

There is increasing concern about the sub-lethal effect of hydrophobic chemicals in the water medium. Even though acetone is a commonly used solvent in toxicity testing, few studies have focussed on its chronic toxicity to Daphnia magna and the available results are often contradictory. In this study, acetone was tested on D. magna in a 21-day exposure experiment and the effects on mortality, fertility and morphology of exposed organisms (F(0)) and offspring (F(1)-F(2), reared without acetone) were evaluated. No significant reduction of survival was observed with increasing concentrations, and no significant reduction in fecundity in any treatment group in terms of average number of daphnids per mother was observed. Abnormal development of second antennae was observed on F(1) from F(0) exposed to 79 mg l(-1) solvent. The ET50 of acetone on the number of mothers that produced deformed offspring over time was 12.5 days. Our results suggest that the acetone concentration should not exceed 7.9 mg l(-1), which is 10 times less than the allowed concentration as determined by OECD chronic assays on D. magna. More attention should be paid to small, water-soluble molecules usually considered of low concern for chronic toxicity because they might affect other metabolic pathways.

Biological effects of acetamide, formamide, and their monomethyl and dimethyl derivatives

The industrial use of certain acetamides and formamides (particularly DMAC and DMF) for their solvent properties has resulted in rather extensive examination of their biological properties. Both DMAC and DMF are rapidly absorbed through biological membranes and are metabolized by demethylation first to monomethyl derivatives and then to the parent acetamide or formamide. Relatively high single doses to various species following oral, dermal, i.p., i.v., or inhalation exposures generally are required to produce mortality. The liver is the primary target following acute high level exposure, but massive doses can also produce damage to other organs and tissues. Repeated sublethal treatment by various routes also shows the liver to be the target organ with the degree of damage being proportional to the amount absorbed. With MMF, the potential usefulness as a cancer chemotherapeutic agent needs to be measured against the hepatotoxic effects produced in man. Acetamides and formamides are generally inactive in mutagenicity tests. Mammalian test systems do not appear to be genetically sensitive and DMF has been recommended for use as the vehicle in microbial assays designed to test for genetic activity of hard-to-dissolve chemicals. Embryotoxicity can be demonstrated at high doses; doses which generally show toxicity to the maternal animals. Structural abnormalities in sensitive species such as the rabbit are produced following exposure at near-lethal levels. The spectrum of abnormalities seen is broad and fails to show any time or site specificity in terms of developing organs/organ systems. Inhalation exposures to DMAC and DMF at levels producing some maternal toxicity in rats have produced no teratogenic response and only slight evidence of embryotoxicity. Long-term feeding of relatively high levels of acetamide produces liver cancer in rats. DMAC and DMF appear to be noncarcinogenic. The environmental toxicity of these chemicals is low. Liver damage can be produced by overexposure to these chemicals in man. Airborne concentrations need to be controlled and care should be taken to avoid excessive liquid contact as the chemicals are absorbed through the skin. A relationship exists between the amount of DMAC or DMF absorbed and the amount of MMAC or MMF excreted in the urine so that biomonitoring of the urinary metabolites can indicate situations in which total exposures, both dermal and inhalation, are excessive. An interaction between DMF and ethanol occurs such that signs, including severe facial flushing, appear when DMF-exposed individuals consume alcoholic beverages.

The effects of short- and long-term exposure of chick embryos to neutral red on the frequency of sister-chromatid exchange

The chick embryo was used to study the effects of neutral red (NR) on the frequency of sister-chromatid exchange (SCE) in specific tissues exposed to this mutagen for short and long periods as development proceeded. In short-term trials, aqueous NR at doses of 10, 25 and 100 micrograms was injected in 3-day and 6-day embryos. In each case, embryos were also treated with 5-bromodeoxyuridine (BrdU) for a 24-h period (two cell cycles) and harvested at 4 days and 7 days, resp. A long-term exposure (about 8 cell cycles) was achieved by exposing embryos to NR from day 3 to day 7 of incubation. At a NR dose of 25 micrograms, the chronic exposure resulted in a doubling of the rate of SCE (11.4/cell) over that observed in embryos exposed for only 24 h at either days 3-4 (6.0/cell) or days 6-7 (6.0/cell). At 100 micrograms of NR, the same relationship held with SCE rates of 14.2/cell for the chronic exposure versus rates of 8.0/cell (3-4 days) and 6.9/cell (6-7 days). At 10 micrograms of NR, no such accumulation of SCE occurred upon long-term treatment. These results show an enhanced SCE response upon growth of embryonic cells in the presence of NR for several days. This may be the result of the persistence of past lesions with the addition of more lesions upon continued exposure to NR.

Effects of methylene chloride, trichloroethane, trichloroethylene, tetrachloroethylene and toluene on the development of chick embryos

Toluene and 5 aliphatic chlorinated hydrocarbons of wide industrial use were injected into the air space of fertilized chicken eggs at 2, 3 and 6 days of incubation. The embryotoxicity was evaluated as survival and death incidences after 14 days of incubation, and also the weights and lengths of the embryos were recorded. The approximate LD50 value for trichloroethylene and trichloroethanes varied between 50 and 100 mumol/egg while for toluene, tetrachloroethylene and methylene chloride it was over 100 mumol/egg. Macroscopic malformations of various kinds were produced with doses of 5-100 mumol/egg. The teratogenic potential of the tested compounds decreased in the following order: 1,1,1-trichloroethane greater than trichloroethylene greater than methylene chloride, tetrachloroethylene, 1,1,2-trichloroethane greater than toluene greater than olive oil control.