| Abstract |
The research carried out here was in response to the request by NIOSH to develop easy-to-use, direct-reading instruments and test kits for measuring exposures rapidly and inexpensively in a variety of workplaces for routine monitoring. This directive, in part, follows from the workshop hazards conference in Chicago in March 1998 sponsored by NIOSH in which non-ionizing radiation was identified as one the 6 priority areas for further study and research. Development of methodology to aid in the exposure assessment of ultraviolet radiation in the workplace is the goal of the work carried out in this phase I SBIR proposal. UV exposure or dose can be measured with either an electronic metering device such as a radiometer, or by means of chemical actinometry in which an aqueous solution upon irradiation undergoes a measurable change detected by absorbance or fluorescence. Rahn (see references) has described the use of chemical actinometers which utilize the formation of triiodide as an endpoint which is easily measured by absorption spectroscopy. Triiodide is formed when either iodouracil (IU) is irradiated in the presence of iodide (I-) or when iodide is irradiated in the presence of an electron scavenger such as iodate. Triiodide can be measured using its absorbance maximum at 352 nm. From this measurement, carried out using 1-cm path quartz optical cells for both irradiation and absorbance measurements, the UV fluence can be determined. In order to develop an inexpensive and portable light-detection device, we have decided to use as the light source a light emitting diode (LED). Because LEDs are not available at 352 nm where triiodide absorbs, thyodene, a starch derivative, was used to react with triiodide to form the starch iodine complex, which absorbs strongly at 470 nm, a wavelength at which an LED is commercially available. The research carried out here demonstrates that chemical actino-metry using 3 mm ID quartz tubes along with a photometer constructed from a light emitting diode and a light sensitive diode, constitutes an inexpensive, accurate system capable of determining the exposure of workers to ultraviolet hazards. The prototype photometer developed here utilizes recently available light emitting diodes and a light sensitive chip to measure the UV -induced formation of the starch-iodine complex. Individuals in the workplace where UV radiation is present may wear quartz tubes, used to hold the actinometric solutions. The change in the absorbance of the solution due to the formation of triiodide and its reaction with starch can then be monitored using the photometer developed here. The following objectives were accomplished: (1) A photometer was constructed with inexpensive components for use with chemical actino-meters to permit quantitation of accumulated dose of UV-B and/or UV-C. (2) The photometer design was optimized for reproducibility and its dynamic range and linear response characteristics determined. Also, the effect of ambient temperature on the instrument response was measured. (3) The feasibility of using small quartz tubes for long-term storage, radiation exposure and photometric measurements of the actinometric solutions was demonstrated. (4) Tubes filled with the actinometric solution containing thyodene were irradiated and the absorbance measured in the prototype photometer as a function of the fluence determined using a radiometer. The results were compared with the same solution irradiated in 1-cm quartz cuvettes and measured in a commercial spectrophotometer. The results demonstrate an equivalency between the two methods of measurement. Hence, the prototype system proposed here can be used to determine accurately UV fluence using chemical actinometry. (5) The effect of temperature on the long-term stability of the actinometric solutions was determined by holding samples of either iodide/iodate or iodouracil/iodide at either 8 C or room temperature for up to 7 weeks. Only the iodide/iodate solution showed appreciable formation of triiodide upon storage. The rate of this spontaneous thermal oxidation process was reduced 2-fold at 8 C. The slope of the dose response curves showed at most a small effect of storage provided background corrections were made. |
