Once in air, it breaks down to other chemicals. Plants and animals living in environments contaminated with TMB can store small amounts of the chemical. Effects of 1,2,4-trimethylbenzene on human health and the environment depend on how much TMB is present and the length and frequency of exposure. Effects also depend on the health of a person or the condition of the environment when exposure occurs. Breathing large amounts of 1,2,4-trimethylbenzene for short periods of time adversely affects the human nervous system.
Effects range from headaches to fatigue and drowsiness.
TMB vapor irritates the nose and the throat. Prolonged contact with liquid TMB irritates the skin. These effects are not likely to occur at levels of 1,2,4-trimethylbenzene that are normally found in the environment. Human health effects associated with breathing or otherwise consuming smaller amounts of 1,2,4-trimethylbenzene are not known. The petroleum industry has conducted several studies on the C9 fraction in response to an EPA request for testing.