The 7 last plagues start with boils.  Boils are the body's method to rid itself of toxins.  What toxins?  Maybe these ones that are floating around the air at ridiculous levels in the Gulf of Mexico (taken from EPA report):
Hydrogen sulfide - safe levels 5-10 parts per billion (ppb) - Gulf Air Levels: 1200ppb
Benzine - safe level 0-4 ppb - Gulf Air Levels: 3000ppb
Metholine chloride - safe level 61ppb, Gulf Air Levels: 3000-3400 ppb 

Alex Jones had on his show (11th of June, 2010) Lindsey Williams, who spoke about the unfolding Gulf Oil disaster.  Williams was made famous (or perhaps infamous) by his prediction of the drop and subsequent spike in oil prices that was instrumental in precipitating the 2008 Financial Crisis. In the show Williams, evidently in a state of anxiety, revealed the EPA report of the chemical levels that are currently being pumped into the atmosphere by this spill at a very rapid rate.  

He also showed that the pressure of the well is between 20,000 and 70,000psi, compared to the standard 1,500psi of a well of this type.  To verify this you only need to look closely at this streaming video here.  The site is 5000ft below sea level, meaning the water pressure is roughly 2500psi.  To put it in basic terms, the oil in these conditions if a normal 1500psi well burst, would be more of a glug than a flow.  It is clear from this also that the metal from the pipe has been eroded away, as the oil is coming from all directions, not just the pipe.  This will make it almost impossible (if not impossible) to contain.

So what does this mean?  You can't shift this amount of liquid out of the ground, and not have a significant effect on the tectonics of the earth.  The last plague is the greatest earthquake ever.  Does this fit? Maybe.

There are also the 2 plagues of death of every creature in the ocean (not universal), and then every creature in the rivers (also not universal).  This could certainly be a side effect of this oil spill if it continues as long as is being said.