A second test to detect in seafood traces of the dispersants used to clean up the Deepwater Horizon-BP oil spill has been added by the National Oceanic and Atmospheric Administration and the U.S. Food and Drug Administration, according to the FDA.

This chemical analysis, along with sensory testing, should help strengthen consumer confidence in Gulf seafood, said FDA Commissioner Dr. Margaret Hamburg.  She asserted that to date the seafood testing has found no detectable residue or residue levels that would be harmful for humans.

“There is no question Gulf seafood coming to market is safe from oil or dispersant residue,” Hamburg said.

In a news release, the agency said that so far, federal analysts trained in sensory testing have examined Gulf-harvested fish, oysters, crab and shrimp, and “every seafood sample  from reopened waters has passed sensory testing” for contamination with oil and dispersant.

Nearly 9,444 square miles, or about 4 percent of the federal waters in the Gulf remain closed to commercial and recreational fishing, and NOAA and the FDA said this second, chemical test for dispersant is now being used as the agencies determine whether it’s safe to reopen more waters to fishing.

Scientists have tested 1,735 tissue samples, including more than half of those collected to reopen Gulf of Mexico federal waters, the FDA said.  Only a few samples have shown trace amounts of dispersants residue (13 of the 1,735) and the FDA claimed all were below the safety threshold of 100 parts per million for finfish and 500 parts per million for shrimp, crabs and oysters.

The new test detects dioctyl sodium sulfosuccinate, or DOSS, a major part of the dispersants used to break up the oil plumes.  DOSS is an approved chemical used in various household products and over-the-counter medication at very low levels.  According to the FDA, there is no scientific evidence that DOSS accumulates in fish tissues.

There has been previous research into how finfish metabolize DOSS, but scientists at FDA’s Dauphin Island, Alabama lab, undertook further exposure experiments on fish, oysters and crab, while NOAA’s Galveston, Texas lab pursued similar experiments on shrimp.

The FDA said these recent studies reinforced earlier findings that crustaceans and shellfish quickly clear dispersant from their tissues.