DEVELOPMENT AND EVALUATION OF A SOURCE-SINK MODEL OF INDOOR AIR CONCENTRATIONS FROM ISOTHIAZOLONE-TREATED WOOD USED INDOORS

Airborne exposure models were developed to account for volatilizing so urces and adsorbing surface sinks of isothiazolone biocide volatilized from treated wood into glass chambers and real-world indoor environme nts. The initial effort described the time-course fate of biocide that becomes airborne and deposits onto the glass surfaces of small ventil ated test chambers containing the wood. After the biocide-treated wood was put into a clean-ventilated chamber the airborne level of biocide built slowly as the biocide initially volatilized and deposited onto the chamber walls. Subsequent re-emission from the glass walls to the air added to the airborne concentration until equilibrium was establis hed between adsorption onto and desorption from the sink, when the air borne concentration leveled off. Adsorption and apparent degradation o f the active ingredient on the chamber walls resulted in equilibrium a irborne concentrations about a third of those predicted without these mechanisms. Glass and stainless steel typically used in chamber work b ehave differently than typical residential interior surfaces. Experime nts reported herein on simulated and real rooms show a much different exposure pattern with equilibrium concentrations that are significantl y lower than those found in the glass chamber. The model developed fro m the glass chamber work is adapted and simplified for predicting airb orne concentrations in real rooms with sources of relatively constant rate. This simplified model requires only source rate and saturation c oncentration as experimentally derived inputs. It provided acceptable accuracy in that it overestimated measured room concentrations in two tests to within a factor of 2-4.