Henry's law constant, volatilization rate, and aquatic half-life of octamethylcyclotetrasiloxane

The undimensioned Henry's law constant (H-c) and volatilization rate constant (k(v)(c)) of the silicone fluid octamethylcyclotetrasiloxane (OMCTS) were determined experimentally. The grand mean H-c for five experiments conducted under dynamic conditions with initial concentrations ranging from 4 to 50 mu g/L (20 degrees C; 48-h equilibration period) was 3.4 +/- 1.37. An H-c of > 17 was observed under kinetic ally limited, static conditions where equilibrium was not reached in 96 h. H-c increased about 10-fold when humic acids were added to OMCTS test solutions, suggesting typical environmental cosolutes will increase the Henry's law constant for OMCTS. The measured volatilization/re-aeration ratio (k(v)(c)/K-v(o)) fdr OMCTS was 0.57, a value similar to that measured for trichloroethylene (0.57) and benzene (0.56), indicating that OMCTS will readily volatilize from water.