Companies that mine and process trona, a mineral used to make baking soda, animal feed and soda ash, a key ingredient in glass, had sued the American Conference of Governmental Industrial Hygienists (ACGIH), which in 1999 proposed a Threshold Limit Value for trona dust of .5 mg/m3 of respirable dust. The companies argued that trona has no long-term health effects, that the nuisance dust TLV is protective, and that the trona TLV is scientifically unfounded.

More broadly, the companies claimed ACGIH's process for establishing TLVs is not based on openness, independent peer review, consensus and prohibitions of conflict, resulting in poor quality control.

The settlement was reached after information obtained during the pre-trial discovery period showed that plaintiffs were given incorrect information and were led to believe that ACGIH had not acted in good faith, according to a statement on ACGIH's Web site.

The statement said a senior member of the TLV Committee, who plaintiffs reasonably believed spoke as though he had authority to commit ACGIH, provided factually incorrect information to plaintiffs on when the trona TLV was to be acted upon by the Full Committee and Board of Directors; and led plaintiffs to initiate a study and made promises to plaintiffs that led them to believe that ACGIH would delay development of the trona TLV until plaintiffs' pending study was completed and submitted to the committee.

Because ACGIH did not know of the actions of this person, it did not correct plaintiffs' belief that ACGIH was acting in bad faith by ratifying a trona TLV without giving consideration to plaintiffs' study, as promised by the senior member of the TLV Committee, according to the statement.

The statement continues: "ACGIH agrees that while there is evidence of irritation caused by exposure to any dust at some threshold level, there is no evidence at this time of health effects, other than a potential transient irritant effect, from exposure to trona.

"ACGIH further agrees that the publication of its TLV for trona on the Notice of Intended Change list was preliminary and was never meant to communicate that there was a scientific basis at this time that exposure to trona causes health effects, other than a potential transient irritant effect.

"ACGIH hereby withdraws its Notice of Intended Change for trona (sodium sesquicarbonate)."

"ACGIH will agree to continue to study and improve its conflict of interest policy, its TLV process, and its overall operation."