A fascinating sub-plot within the Deepwater Horizon disaster concerns the 4.3m litres of chemical dispersants that BP and its contractors have sprayed and pumped into and onto the spill, in an effort to break up the oil.

Most experts accept that the Corexit dispersants, made by Illinois-based Nalco, have reduced pollution along the Gulf coast. But many environmental scientists are concerned that marine life in the deep waters may pay a heavy price, if the chemicals have increased the amount of oil dispersed in “clouds” or “plumes” through the sea.

Although people have known roughly what Corexit contains – surfactants and emulsifiers, alcohols, light petroleum distillate – objective assessment of the effect and toxicity of Corexit has been hampered by the Nalco’s stubborn refusal to release publicly the full list of chemical ingredients, on grounds of commercial confidentiality.