Long-term variation study of blood plasma levels of chloroform and related purgeable compounds.

Values for circulating plasma chloroform of 25 white adult females were monitored for 6 months during the first phase of a four-phase long-term variation study. The data suggested four major exposure categories. Category I (20%) had average chloroform levels less than 10 ppb and variation ranges less than or equal to 10 ppb. Category II (24%) had average levels of 10-25 ppb and ranges of less than or equal to 10 ppb. Category III (20%) had average levels of 10-25 ppb and ranges greater than 20 ppb. Category IV (28%) had average chloroform levels of greater than 25 ppb and variation ranges greater than 20 ppb. Although the participants had been carefully screened to exclude incidents of occupational and recreational exposure, three subjects in category IV experienced obvious incidences of acute exposure to either chloroform or a chloroform precursor. In these situations circulating plasma chloroform levels were between 1655 ppb and 4000 ppb.