Download Tulane ELC Crude oil is a complex mixture of organic and some

Patricia M Williams PhD, DABT
Associate Professor
Coordinator, Toxicology Research Laboratories
Pontchartrain Institute for Environmental Sciences
University of New Orleans
Cell: 504-915-1817
Crude oil is a complex mixture varying with its geologic origin. Crude oil contains
hundreds, perhaps even thousands of hydrocarbons ranging from C1 to greater than C50.
(Patty’s Toxicology, 2001). Benzene is a naturally occurring component of crude oil,
wand may be listed on MSDS sheets at concentrations up to 2% of benzene in this
complex mixture. Benzene is a confirmed Human Carcinogen (International Agency for
Research on Cancer; Occupational Safety and Health Act, National Institute for
Occupational Safety and Health). This 2% benzene is equal to 2 parts per hundred or
20,000 parts per million in concentration. The OSHA permissible exposure level for
workers is 1 ppm of benzene in an eight hour work day (OSHA 1910.1028) and the
ATSDR Minimal Risk Level of benzene for residents is 0.003 ppm for chronic exposure
(365 or longer); 0.006 ppm for intermediate exposure (15-364 days); and 0.009 ppm for
acute exposure to benzene (1-14 days) (Agency for Toxic Substances and Disease
Registry, December 2010). Benzene is a DNA-reactive carcinogen that binds to the
DNA of a cell and damages its structure resulting in adduct formation (insertion of the
benzene metabolite into the DNA) and chromosome breakage. These damaged portions
of the DNA may remain as lesions in the parental DNA strand and induce alteration or
mutations in the daughter strand of DNA during replication. The mutation may
ultimately be expressed as damaged genes that express mutant proteins that reprogram
cells for multiplication. When such cells undergo cell division, their descendants also
carry the damaged DNA and as a result have the propensity for enhanced proliferation
which is a characteristic of malignant transformation. These damaged reprogrammed
cells will continue increased proliferation with a growth advantage over normal cells.
The final outcome of the DNA damage is a tumor consisting of transformed rapidly
proliferating cells that have undergone a malignant transformation due to the original
DNA damage produced by the benzene toxicant. (Casarett and Doull, 2001)