Stockton » Work to destroy thousands of small cartridges containing mustard agent has stopped because higher-than-expected levels of mercury were detected.

Deseret Chemical Depot workers began incinerating the 4-inch cartridges last week as part of a larger project to get rid of the agent stored for decades at the depot, which is about 30 miles southwest of Salt Lake City.

Alaine Grieser, a depot spokeswoman, says work was halted over the weekend after the mercury levels were detected in furnace exhaust. She says the mercury did not exceed permitted levels.

A new mercury filtration system is scheduled to be installed later this year. Grieser says destruction of the cartridges will resume this fall. In the meantime, work will continue on larger containers.