A proposed occupational exposure limit for 2,3,7,8-tetrachlorodibenzo-p-dioxin.

One contaminant produced unintentionally during the manufacture of chlorophenols and phenoxy herbicides is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The resulting TCDD-containing wastes have been detected at many hazardous waste sites which in recent years have been in the process of remediation. Concerns about worker exposure to TCDD-contaminated soil (dust) during remediation of hazardous waste sites have produced a need for an occupational exposure limit (OEL) for TCDD.

A physiologically based pharmacokinetic model for 2,3,7,8-tetrachlorodibenzo-p-dioxin in C57BL/6J and DBA/2J mice.

A five-compartment physiologically based pharmacokinetic (PB-PK) model was developed to describe the time course of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the tissues of both C57BL/6J and DBA/2J mice. The PB-PK model included binding in blood and two hepatic binding sites, one in the cytosol and the other in the microsomes. First-order metabolism occurred in the liver.

Bioavailability of soil-bound TCDD: oral bioavailability in the rat.

The implications to the public health of trace amounts of 2,3,7,8-TCDD in the environment are under evaluation by regulatory agencies in the United States and Western Europe. One major consideration in such evaluations is the contribution to human exposure via ingestion of TCDD-contaminated soil. An 80% figure is under consideration by some regulators for estimated human exposure.

Bioavailability of soil-bound TCDD: dermal bioavailability in the rat.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), an unwanted by-product formed during the manufacture of hexachlorophene and phenoxyherbicides, has been found as an environmental contaminant in many U.S. and Western European sites.

Assessment of the developmental risks resulting from occupational exposure to select glycol ethers within the semiconductor industry.

This risk assessment evaluates the potential human hazards of adverse developmental effects posed by exposure to 2-ethoxyethanol (2-EE), 2-ethoxyethanol acetate (2-EEA), 2-methoxyethanol (2-ME), and 2-methoxyethanol acetate (2-MEA) as they are currently used in semiconductor manufacturing. These glycol ethers are contained in positive photoresists used in the wafer fabrication process. The available data on the developmental toxicology of these glycol ethers indicates that each can selectively affect the offspring of pregnant animals that have been exposed to relatively low vapor concentrations.

Toxicological evaluation of substituted dicyclopentadienyliron (ferrocene) compounds.

The acute toxicity of 3 substituted ferrocenes: acetylferrocene, ethylferrocene, and 2,2-bis(ethylferrocenyl)propane (Catocene) were studied in rats, rabbits and monkeys. Acetylferrocene was found to be the most toxic. The oral lethal dose was less than 5 mg/kg for female rats, between 5 and 50 mg/kg for male rats, and between 10 and 100 mg/kg for monkeys.

Radionuclide content of and 222Rn emanation from building materials made from phosphate industry waste products.

The radionuclide content and 222Rn emanation coefficients of selected construction materials were determined. The materials were analyzed for 226Ra, 228Ra and 40K by gamma-ray spectrometry. Mineral wool insulation, which is made from Tennessee phosphate slag, and commonly used insulation, which is made from blast furnace slag, had similar concentrations of these radionuclides.

A linear systems approach to analyzing the pharmacokinetics of carbon tetrachloride in the rat following repeated exposures of 8 and 11.5 h/day.

Ten- and 12-h workdays are relatively common in the chemical and other non-labor intensive industries both in the United States and Europe. Based on pharmacokinetic principles, persons who work 10-12 h shifts and are exposed to chemicals with a terminal half-life between 5 and 200 h will absorb a larger quantity of the toxicant or have higher peak blood levels than persons who work 8-h shifts. To evaluate the effects of exposure duration and repeated exposure on the elimination of carbon tetrachloride (CCl4), rats were repeatedly exposed to 100 ppm 14CCl4 for either 8 or 11.

Adjusting exposure limits for long and short exposure periods using a physiological pharmacokinetic model.

The rationale for adjusting occupational exposure limits for unusual work schedules is to assure, as much as possible, that persons on these schedules are placed at no greater risk of injury or discomfort than persons who work a standard 8 hr/day, 40 hr/week. For most systemic toxicants, the risk index upon which the adjustments are made will be either peak blood concentration or integrated tissue dose, depending on what chemical's presumed mechanism of toxicity. Over the past ten years, at least four different models have been proposed for adjusting exposure limits for unusually short and long work schedules.

A critical evaluation of the use of mutagenesis, carcinogenesis, and tumor promotion data in a cancer risk assessment of 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Regulatory agencies in the Western Hemisphere are currently assessing the potential human health risks of environmental contamination by 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD). Some U.S.

A critical examination of assumptions used in risk assessments of dioxin contaminated soil.

Environmental standards for 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin, TCDD) are currently being considered by regulatory agencies worldwide. Among these are limits for tap water, soil at industrial sites, residential soil, fish, ambient air, and fly ash. Thus far, in the United States, no standards have been promulgated but a few have been suggested.

The effect of an 11.5-hr/day exposure schedule on the distribution and toxicity of inhaled carbon tetrachloride in the rat.

This study evaluated the differences in toxicity and tissue distribution for 16 groups of male rats repeatedly exposed to 100 ppm of 14CCl4 vapors for 8 or 11.5 hr/day for periods of 1 to 10 days. Serum sorbitol dehydrogenase (SDH) was also evaluated for its sensitivity at detecting CCl4-induced hepatotoxicity.

A comparative study of the pharmacokinetics of carbon tetrachloride in the rat following repeated inhalation exposures of 8 and 11.5 hr/day.

To evaluate whether exposure to inhaled vapors for periods longer than 8 hr/day could affect the rates and routes of elimination, male Sprague-Dawley rats were repeatedly exposed to 100 ppm of radiolabeled carbon tetrachloride (14CCl4) in a closed-loop chamber. One group was exposed for 8 hr/day for 5 days and another group for 11.5 hr/day for 4 days.

A dynamic closed-loop recirculating inhalation chamber for conducting pharmacokinetic and short-term toxicity studies.

Tests for evaluating the hazard of inhalation exposure generally require large quantities of the chemical of interest. This paper describes an inhalation technique that involves a dynamic closed-loop recirculating system which uses only small amounts of toxicant since the test atmosphere to which the animals are exposed is recycled. Carbon dioxide and water are continually removed while the oxygen and test substance absorbed by the animals are replenished.