Gasoline toxicity through ingestions seems to be a topic where there's not a great deal of in-depth information available. I don't know how this works for chronic use, as most literature refers to acute scenarios. Either way, orally ingested, 30-50g is said to be toxic to humans while 350g can be fatal.[3].
So...
Gasoline's Constituents
A lot of components that make up gasoline are toxic to humans. This includes for example, benzene, toluene, xylene and butadiene. It's a mixture of more than 500 hydrocarbons and additives made up of:
* 60–70% alkanes (paraffins)
* 25–30% aromatics
* 6–9% alkenes (olefins).[2].
If you really want to know specifics about metabolism of gasoline, you can probably check out how some of the constituents are metabolised (processed) and their effects. This is because different components have varying metabolic pathways.
If you want to check this out, see <PERSON>, et al at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1520023/pdf/envhper00383-0118.pdf.[3].
Ingestion and Toxicity
Apparently, most reported cases of toxicity from gasoline occur from inhalation or absorption through the skin (intravenous use has also been reported). Even though ingestion is a frequent occurrence, there's not much data on outcomes after oral ingestion.[1],[2]. Gasoline can however be well absorbed through the gastrointestinal tract[2].
The main target organ of gasoline toxicity is the nervous system and at high doses, this effect can cause death within minutes.[3]. However, generally, the primary cause of mortality seems to be related to gasoline's toxicity to the lungs. There are severe effects on the pulmonary system. Other effects of ingestion hasn't been as well documented.[1],[2].
It's suggested that these compounds have a direct effect on lung tissue and disrupts gas exchange and causes fluid buildup in the lungs (pulmonary edema). This in turn causes the oxygen levels in the body to drop (hypoxemia).[2]. There are many other toxic effects on the lungs as well.
Additionally, liver damage, kidney damage, damage to blood cells, gastric ulcers and toxicity in the heart can occur.[2],[3]. Again, this is discussed in <PERSON>, et al.
Hope that helps!
1. 978
Rahman I. Gasoline ingestion: a rare cause of pancytopenia. Am J Med Sci. 2009. 338(5):433-4.
2. Domej W. Successful outcome after intravenous gasoline injection. J Med Toxicol. 2007. 3(4):173-7.
3. <PERSON>, et al. Acute Toxicity of Gasoline and Some Additives. Environmental Health Perspectives. 1993. 115-131. 978