The term “Highly Toxic” has been codified in the IFC as:
A material which produces a lethal dose or lethal concentration which falls within any of the following categories:
1. A chemical that has a median lethal dose (LD50) of 50 milligrams or less per kilogram of body weight when administered orally to albino rats weighing between 200 and 300 grams each.
2. A chemical that has a median lethal dose (LD50) of 200 milligrams or less per kilogram of body weight when administered by continuous contact for 24 hours (or less if death occurs within 24 hours) with the bare skin of albino rabbits weighing between 2 and 3 kilograms each.
3.A chemical that has a median lethal concentration (LC50) in air of 200 parts per million by volume or less of gas or vapor, or 2 milligrams per liter or less of mist, fume or dust, when administered by continuous inhalation for one hour (or less if death occurs within 1 hour) to albino rats weighing between 200 and 300 grams each.
Mixtures of these materials with ordinary materials, such as water, might not warrant classification as highly toxic. While this system is basically simple in application, any hazard evaluation that is required for the precise categorization of this type of material shall be performed by experienced, technically competent persons.
The Boston Regional Office (OSHA) has brought to our attention the extreme toxicity of an organometallic chemical, dimethylmercury, following the investigation of a fatal chemical exposure to a researcher. The death of a chemistry professor in June 1997 was apparently due to a single exposure to dimethylmercury.
Dimethylmercury belongs to a class of organic mercury compounds known as alkyl mercuries. It is used primarily in research. It is a colorless liquid described as having a weak, sweet odor. Dimethylmercury is readily absorbed through the skin. A severely toxic dose requires the absorption of less than 0.1mL.2 Many materials, including several plastics and rubber compounds, have also been shown to be permeable to this chemical. It is highly reactive and flammable. Because of its high vapor pressure (50-82 mm Hg at 20°C), the inhalation route of entry is also significant.
The exposure occurred when, during a transfer to another container, one to several drops of dimethylmercury were spilled on the back of the researcher’s gloved left hand. The transfer was conducted under a fume hood and the researcher was wearing disposable latex gloves. Five months later the researcher experienced progressive difficulty characterized by numbness and tingling in both lower extremities, along with difficulty in vision, walking, speaking, and hearing. When informed that her symptoms were due to mercury poisoning, the spill incident was recalled and she indicated that she had removed the gloves promptly and did not think any more about the incident. As a result, no medical monitoring or other follow-up was done until the diagnosis five months after the exposure.