Female rotifer, Brachionus manjavacas, with eggs: R. Rico-Martinez et al. Environmental Pollution. http://dx.doi.org/10.1016/j.envpol.2012.09.024

A new study finds that adding Corexit 9500A to Macondo oil—as BP did in the course of trying to disperse its 2010 oilspill disaster—made the mixture 52 times more toxic than oil alone. The results are from toxicology tests in the lab and appear in the scientific journal Environmental Pollution.

Using oil from the Deepwater Horizon blowout and Corexit the researchers tested the toxicity of oil, dispersant, and a mixture of oil and dispersant on five strains of rotifers—the lab rats of marine toxicology testing. Among the results:

The oil-dispersant mixture killed adult rotifers

As little as 2.6 percent of the mixture inhibited egg hatching by 50 percent

The inhibition of egg hatching in bottom sediments is particularly ominous because rotifer eggs hatch each spring to live as adults in the water column where they are important food sources for larval and juvenile fish, for shrimp, crabs and other marine life in estuarine and shoreline ecosystems—including fisheries humans depend on.

“Dispersants are preapproved to help clean up oil spills and are widely used during disasters,” said lead author Roberto-Rico Martinez currently at the Universidad Autonoma de Aguascalientes, Mexico. “But we have a poor understanding of their toxicity. Our study indicates the increase in toxicity may have been greatly underestimated following the Macondo well explosion.”

I wrote here about the dramatic decline in microscopic life on BP’s dispersed oil beaches and here about how using dispersant allowed oil to penetrate much more deeply into beaches possibly extending the toxic lifespan of the mix. I wrote here about how BP’s oilspill has hammered Gulf fish.

The paper: