Maureen Rouhi C&E News 2/22/99

The alleged presence of a chemical warfare agent precursor in a soil sample obtained near a Sudanese pharmaceutical plant served as justification for a U.S. cruise missile attack on the plant last August.

No details were released to support the U.S. claim that the El Shifa Pharmaceutical Industries plant in Khartoum was producing O-ethylmethylphosphonothioic acid (EMPTA), a precursor to the nerve gas VX. U.S. officials said, and continue to say, only that they have physical evidence in the form of a soil sample that analysis revealed to contain EMPTA. Supposedly the sample was collected two months before the attack but analyzed one month after collection. Little other information was offered. See figure.

In September, the pharmaceutical plant's owner, Salah Idris, commissioned a study of samples from the facility's remains to bolster his and the Sudanese government's vehement denials that EMPTA was being produced or used in the plant. The European labs analyzed the samples for EMPTA, its immediate breakdown product EMPA (O-ethylmethylphosphonic acid), and 25 organophosphorus pesticides.

This lab carried out R&D work to establish the optimum parameters for detecting EMPTA, including spiking experiments to determine its persistence. "We found in actual Sudan soil samples that even after one day a considerable amount of EMPTA is broken down and that after five days less than 2% of the spiked EMPTA can be recovered". Furthermore, everything in the literature suggests that the hydrolysis product, EMPA, should be much more difficult to break down than EMPTA, and it likely can last for years.

Indirect evidence for EMPA's persistence comes from analysis of the chemical warfare agent sarin and its degradation product in samples collected from a Kurdish village in northern Iraq four years after the village was attacked with chemical agents. Sarin rapidly hydrolyzes to O-isopropyl methylphosphonic acid (iPMPA). The study of the Kurdish samples, by scientists at the Chemical & Biological Defense Establishment, Porton Down, England, found iPMPA in soil samples at levels ranging from 6 to 200 ppb. After four years, a compound very similar to EMPA still was detectable. It's reasonable to assume that EMPA will behave similarly.

Of all the samples obtained at the pharmaceutical plant site for the study commissioned by the plant's owner, none turned up with any EMPTA or EMPA.