Abstract
Application of PAL protocols was performed for hydrogen sulfide (H2S) as experimental data permitted. The data base includes human experimental studies, worker exposure evaluations, as well as case studies on acute and repeated exposure. The data base of animal studies is substantial covering multiple species and addressing acute, repeated, and subchronic exposure scenarios. PAL estimates were approved by the Expert Consultation Panel for Provisional Advisory Levels in November 2006.
No reliable data were found on oral exposure, making it impractical to estimate PALs for drinking water. Since H2S exists as a gas, partitioning to air is likely to occur with an environmental release. H2S inhalation PAL values for 24 hr exposure are: PAL 1 = 1.2 ppm; PAL 2 = 7.0 ppm; and PAL 3 = 27 ppm; the 30-d and 90-d inhalation exposure values are: PAL 1 = 0.85 ppm and PAL 2 = 3.0 ppm. PAL 3 values for 30-d and 90-d are not recommended due to insufficient data. Long-term data were insufficient to estimate 2-year inhalation PALs.