[This is interesting. I'm sure oil people have said this, and I've simply assumed they were lying sacks of shit. Cecil OTOH in my experience has had such a great track record for so long that I feel compelled by honor to grant his account as true until proven otherwise.]
[On his account, oil seems to biodegrade at a surprisingly fast clip so long as it is in contact with water and air. The only time it stays around forever is when it gets buried under dirt.]
http://www.straightdope.com/columns/read/2943/did-nature-clean-up-most-of-the-exxon-valdez-oil-spill
Did nature clean up most of the Exxon Valdez oil spill?
June 18, 2010
Dear Cecil:
The current drama over the gulf oil spill reminds me of an article some
years ago saying that, despite millions spent on massive coastline
cleanup following the Exxon Valdez disaster, contaminated areas
untouched by cleanup crews reverted to their pristine pre-spill
condition just as quickly as those with human help. Is this a case of
letting Mother Nature alone to do what she does best, or simply not
true?
-- Mike Hogan, Auckland, New Zealand
Cecil replies:
Apparently the good news hasn't gotten out to kiwi country. Rush
Limbaugh has already assessed the situation in the Gulf of Mexico and
announced, "The ocean will take care of this on its own if it was left
alone and was left out there. It's natural. It's as natural as the
ocean water is. Well, the turtles may take a hit for a while, but so
what?" Still, maybe you won't mind getting a second opinion from me.
The basics: First, oil is mostly biodegradable. Some of it evaporates
or breaks down with exposure to sunlight, and at least 20 types of
marine bacteria plus several types of fungi can degrade what's left.
Surprised to learn that bacteria eat oil? Don't be. Although oil spills
from tankers and wells make the news, they account for less than 15
percent of the total petroleum entering the world's oceans, while 47
percent comes from natural oil seeps. (The rest largely comes from
petroleum use.)
That doesn't mean oil biodegrades easily. Crude oil consists mainly of
various types of hydrocarbons, some of which break down readily, others
not at all. Light oils generally degrade faster than heavy ones. Very
light crude might lose 60 percent of its volume due to biodegradation
in four weeks, heavy crude just 10 percent. Temperature is important --
warmer waters encourage bacteria growth, which is one bright spot for
the gulf.
A big factor slowing oil breakdown is that oil doesn't contain much
nitrogen or phosphorus, both of which are needed for good bacterial
growth. Enter bioremediation, where fertilizer is added to encourage
natural bacteria. First tried in the 1960s, it evidently works. One
2002 study showed that adding just 0.25 percent fertilizer to oil on a
lab-simulated beach quintupled the natural biodegradation rate. Tests
in 1994 in Delaware Bay, which is already rich with bacterial
nutrients, showed fertilizer doubled the rate of oil degradation in
shallow waters. The same year, scientists fighting a spill on a beach
near Haifa, Israel, reported that bioremediation had reduced oil
contamination 88 percent in just four weeks.
Sometimes nature doesn't need much assistance. Following the 1978 wreck
of the Amoco Cadiz off the coast of Brittany, oil was broken down
quickly by local microbes, which had grown accustomed to the stuff
thanks to shipping leakage. Same for the 1980 Tanio wreck in the same
area -- biodegradation was detectable within 24 hours. The blowout of
the Ixtoc well in the Gulf of Mexico in 1979 was a different story.
Warm water and friendly bacteria raised hopes for speedy degradation,
but in this case the oil formed an emulsion, or mousse, on the surface
that proved resistant to breakdown.
To your question: It's true that human efforts didn't clean up most of
the 1989 Exxon Valdez spill. Some hydrocarbons degraded rapidly without
assistance, possibly because bacteria in Prince William Sound had
acclimated to resin emitted by pine trees on shore.
But bioremediation seemed to help. Local bacteria were found to be
starving for nutrients, and once fertilizers were added to a test area
they got busy. Within a couple weeks a "white window" of clean rocks
appeared among the gunk-covered ones. Eventually more than 70 miles of
beach were treated this way.
Later researchers questioned how much oil the process actually got rid
of, though. It's been calculated that all told, bioremediation,
skimming, spraying, and scrubbing were responsible for removing less
than a sixth of the spilled oil. Who or whatever deserves the credit,
most of the Exxon Valdez spillage did eventually disappear.
Not all of it, though -- biodegradation has its limits. Oxygen is key
in much bacterial action, and once oil gets buried under sediment
things really slow down. In 2001 researchers dug pits at 91 sites along
the shore of Prince William Sound and found oil at roughly three in
five. That may sound overly grim -- another survey of 5,000 pits by
U.S. government researchers in 2001 and 2003 found 98 percent had
little or no oil.
Conclusion? Let's break this down into more digestible bits. Do oil
spills mostly go away on their own? Yes. Does that mean we're better
off leaving them alone? Of course not. Nobody doubts we need to plug
leaks and contain spillage, and I'm persuaded bioremediation helps at
least sometimes.
But other intervention may be wasteful or harmful. Excessive use of
chemical dispersants may threaten wildlife. Animal rescue efforts may
be expensive PR exercises. The chief lesson from past spills is how
little we know about what works. We'd better find out.
-- Cecil Adams