In the grand scheme of things…
June 5, 2010 politics, science 2 Comments
…it will take 24.9 million times more oil than the worst projected levels of the current spill to make the gulf toxic.
Ok, ok. I’m not usually for snap analysis of such serious issues as the current Gulf of Mexico oil crisis. Every effort to stop the leak should be made and any party determined responsible should be held accountable, of course!
But FWIW, I used to be a chemical analyst for an environmental laboratory and tested for petroleum related compounds on a daily basis usually against EPA regulatory limits. All I want to know how toxic this oil spill will make the Gulf of Mexico given the worst case scenario. So the following haphazard conglomeration of tidbits from internet articles and references will, at the very best, give a spotty, blurry and narrow view of the big picture of the Gulf’s future.
That said, here’s what I came up with:
Volume of oil spilled (worst case scenario) as x in gallons: 112.7 million
Volume of the Gulf of Mexico (gallons) as y: 660 quadrillion (2.5 × 1015 m3)
This makes a total concentration (x/y = C) of 0.000000000171 per one , or 0.171 parts per trillion (PPT). Caveat: This number represents a “uniform mixture” scenario, whereas oil is currently dispersed in specific areas of much denser concentrations drifting about, each causing their own unique havoc in specific areas, but hypothetically thinking down the road if / when the oil actually and inevitably mixes…
Lethal dose for gulf killfish (LD50): .00425 per one, or 4250 parts per million (PPM)

Factor needed to raise worst-case-scenario-levels of oil in the gulf to make entire gulf toxic: LD50 / C = 24900000 or 24.9 million times more oil than that.
Ok. Last disclaimer: In reality given that BP has used chemical dispersants and the like to help dissipate the surface oil (Which BTW would raise the toxicity level of the resultant crude oil product by a factor of 11), and if they used that same dispersant–called Corexit 9500—on all of the resulting leaked oil, then this would reduce the number of equally sized oil leaks needed for the above mentioned lethal dose to only 2.26 million. This is still not to make light of the drastic shock to the livelyhood of people living near the damage, or the drastic short and long-term effects of the oil on marine life and habitats there! But for those of us who believe we are the custodians of this planet’s entire ecosystem, yes we must work diligently to clean this up, but at the same time, this single incident will not, on a grand and ultimate scale, come anywhere near destroying the Gulf of Mexico.
Note: Couldn’t find a study of oil toxicity on humans. No volunteers i guess, but EPA does regulate Benzene in drinking water at 0.005mg/L or parts per million (PPM). Here is the Material Safety Data Sheet (PDF) on crude oil which features more info like lethal doses (LD 50) of Benzene for rats, for instance (0.93 to 5.96g/kg or PPT). It says that the level of benzene in crude oil varies but usually contains “small amounts of benzene, polynuclear aromatic hydrocarbons (PAH’s) and compounds of sulphur.”

