In California, anti-knock fuel additives have transitioned form tetraethyl lead
ID: 798740 • Letter: I
Question
In California, anti-knock fuel additives have transitioned form tetraethyl lead to benzene, to MTBE, to ethanol. Unfortunately, it is likely that we will not be able to produce enough ethanol as a gasoline additive. Conduct an analysis between two fuel additives we have available data on. Compare and contrast the potential environmental fate and transport between the gasoline additives Iso-octane (CAS# 540-84-1) and ethanol (CAS 64-17-5). Which one is a safer gasoline additive? Use the Hazardous Substance Data Bank (HSDB) at http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB and other provided databases to find the relevant chemical and physical properties needed to determine the potential fate and transport in the environment (air, water, and soil). Discuss the following in your essay:
a. Partitioning in air, soil and groundwater
b. Transport in soil and groundwater
c. Environmental half-life
d. Bioconcentration factor (BCF)
e. General human toxicity
f. General ecotoxicity
Explanation / Answer
Vapour pressure should be high for a ideal safe chemical. Amone these MTBE has more vapor pressure and hence it is safe to use.So, it cannot miscible with atmospheric air.
For environmentally benign condition, the chemical should be water soluble. We can easily remove while wash with water. Hence a good reagent should have water solubility more. Here again, MTBE has high solubility in water and is found to be good reagent to use without affecting environment.
log Kow= 2.13 for benzene.log Kow = 0.94 for MTBE, it should be low for good additive
Log K value should be less for a good chemical, amone three MTBE found to be less and is best.
Henry's law constant indicates, its volatilability into atmosphere from the soil. It should be as less as possible to avoid the atmosphoric pollution. MTBE has less henrys law constant and is good choice of chemicals.
Rate oral LD50 should to less. This value indicates its harmfull concentration to aquatic and human and animals, it should be less. So, MTBE is best. General human toxicity is also less than benzene.
Rat inhalation LC50 should be more, since this indicates the minimum concentration required for biological effect on living aquatics, animals and humans. Among three, MTBE has very high LC50 so it is suitable for all purposes . Its eco toxicity is less compared to benzene.
Its carcinogenicity is not reported. since benzene can intercalate with DNA and is a carcinogen. MTBE is safe to use.
A BCF of 1.5 was measured in Japanese carp(1). According to a classification scheme(2), this BCF suggests that bioconcentration in aquatic organisms is low. Methyl t-butyl ether is not expected to bioaccumulate in surface water aquatic organisms. Benzene has a BCF ranging from 1.1-20.
Transport in soil and groundwater is high for MTBE compared to benzene.
OVerall, MTBE is foun to be better anti-knock additive than benzene.