William A. Ivancic

Characterizing residue transfer efficiencies using a fluorescent imaging technique

To reduce the uncertainty associated with current estimates of childrens exposure to pesticides by dermal contact and indirect ingestion, residue transfer data are required. Prior to conducting exhaustive studies, a screening study to identify the important parameters for characterizing these transfers was designed. A fluorescence imaging system was developed (Ivancic et al., in press) to facilitate collection of surface residue transfer data for repeated contacts. Next, parameters that affect residue transfer from surface-to-skin, skin-to-other objects, and skin-to-mouth were evaluated using the imaging system and the fluorescent tracer riboflavin as a surrogate for pesticide residues. Riboflavin was applied as a residue to surfaces of interest. Controlled transfer experiments were conducted by varying contact parameters with each trial. The mass of a tracer transferred was measured and the contact surface area estimated using video imaging techniques. Parameters evaluated included: surface type, surface loading, contact motion, pressure, duration, and skin condition. Transfers both onto, and off of, the hand were measured. To efficiently identify parameter changes resulting in significant effects, the Youden ruggedness test was used to select the combination of parameters varied in each contact trial. In this way, more than one parameter could be varied at a time and the number of trials required was minimized. Results of this study showed that surface loading and skin condition (significant at alpha=0.05) are among the important parameters for characterizing residue transfers of riboflavin. Duration of contact within the time range investigated does not have a significant effect on transfer of this tracer. Results of this study demonstrate the potential for collecting dermal transfer data using the Ivancic et al. fluorescence imaging system and provide preliminary data to reduce uncertainty associated with estimating dermal exposures resulting from contact with residue-contaminated surfaces. These data will also aid in determining what additional residue transfer data should be collected and what type of microactivity data are needed to estimate dermal and indirect ingestion exposure to residues on household surfaces.

Oxygen Quenching Measurements for the S1 and S2 Fluorescence of Gas-Phase Fluoranthene

The fluorescence emission of the fluoranthene molecule has been investigated at excitation wavelengths varying from 240 to 360 nm, and conducted from near collision-free conditions to atmosphericpressure conditions. The oxygen quenching rate for the fluorescence of the F1 band (S1 → S0 transition) of fluoranthene at 340 nm excitation wavelength was found to be 1 × 109 L mol−1 s−1. The quenching rate for the F2 band (S2 → S0 transition) was found to be 100-fold greater for the wavelength region investigated. The wavelength dependency of the oxygen-quenching constants of the two transitions was also established in the excitation range from 240 to 332 nm. The influence of oxygen and nitrogen pressure on the spectral fluorescence bandwidth of fluoranthene and the oxygen-quenching constants for the S1 and S2 bands are reported. The results shed some light on fluoranthenes unusual inertness to oxygen quenching.