Research results
Examination of effectiveness of mercury vapor personal exposure monitor using rat
National Institute for Minamata Disease (○Masumi Marumoto, Koji Marumoto), The National Institute of Advanced Industrial Science and Technology (Kazutoshi Noda)
1. Introduction.
To date, a simple measuring device for mercury in air (QCM-Hg) using the Quartz Crystal Microbalance (QCM) method has been developed to monitor mercury concentrations in air relatively cheaply and easily. The effectiveness of this device as an area monitor in small-scale human-powered gold mining sites in Brazil and other countries and the surrounding area has already been studied, but its effectiveness as an individual exposure monitor has not been studied so far.
Mercury vapour exposure experiments have been conducted in rats and various other laboratory animals. It is known that even short-time exposure at concentrations of a few mg/m3 has effects on the organism, but exposure concentrations of a few µg/m3 have no effect on the organism and long-term exposure experiments can be carried out. In this experiment, mercury vapour exposure experiments were conducted at mercury concentrations with no effect on living organisms, and the effectiveness of a simple measuring device for mercury vapour as an individual exposure monitor was investigated by animal experiments using rats.
2. Research methods.
Rats wearing a jacket with QCM-Hg were placed in a chamber and exposed to an average mercury concentration of 20 µg/m3 using metallic mercury for 1 hour. The mercury concentration in the chamber was measured using a portable mercury measuring device (Nippon Instruments Corporation, EMP-2Hi). After 1, 3 and 24 hours of exposure, the rats were necropsied under diethyl ether deep anaesthesia. Blood was collected, refluxed with saline, and the liver, spleen, kidney, heart, lung, skeletal muscle, nasal mucosa, olfactory bulb, urine, cerebellum, cerebrum and brain stem were sampled and cryopreserved. Mercury in the organs was analysed by reducing vaporisation-atomic absorption spectrophotometry (Sanso Seisakusho, HG201) after wet decomposition, and mercury adsorbed on elements was analysed by heating vaporisation-gold amalgam-atomic absorption spectrophotometry (Nippon Instruments, MA-2), according to the Mercury Analysis Manual of the Ministry of the Environment. The results were.
3. Results and Discussion
The results of the measurement of total mercury concentrations in the organs showed that the concentrations in the retrieved organs were significantly different from the controls after 1 hour of exposure, but after 3 and 24 hours the concentrations had already decreased to the same level as the controls. Many mercury vapour exposure experiments have been carried out in laboratory animals for various purposes. Many of these experiments, such as the experiment conducted in the present study, involved long-term exposure to low concentrations, ranging from a few days to several weeks. In the present experiment, it was found that in the low-concentration one-hour exposure experiment, the mercury taken into the body was quickly metabolised and eliminated from the body.
The amount of mercury adsorbed on the element correlated with the mercury concentration in the retrieved organs after 1 h of exposure, indicating that the amount of mercury adsorbed on the element reflected the amount of mercury taken up by the rat body. However, no relationship was found between the concentration of mercury in the organs and the vibration frequency.
The oscillation frequency fluctuations of the QCM-Hg in the chamber were increased compared to those of the QCM-Hg attached to the rats. No difference was observed in the amount of mercury deposited on the elements, suggesting that the increase in frequency was influenced by humidity.
4. Summary.
No relationship was found between the concentration of mercury in the organs and the vibration frequency. It is considered that the vibration frequency fluctuates due to changes in water vapour content caused by the movement of the rats, their surroundings and respiration, so measures such as dehumidification may be necessary. However, a good correlation was obtained between the mercury concentration in rat organs and the amount of mercury adhering to the QCM-Hg element, and measuring the amount of mercury adhering to the element would allow the effects of mercury vapour exposure to be evaluated. This indicates the effectiveness of the QCM-Hg as an individual exposure monitor.
Acknowledgements.
This research was funded by the Comprehensive Environmental Research Promotion Fund of Environmental Restoration and Conservation Agency (No. 5-1704). The authors would like to thank Satoko Furukawa, The National Institute of Advanced Industrial Science and Technology; Mao Uchikado and Miwa Chijiiwa, Department of Basic Medical Science, National Institute for Minamata Disease (NIMD); Shigemi Onizuka, Fumika Hashimoto and Akane Morimoto, Department of Environment and Public Health (NIMD); and Shinichi Murakami, Animal Care Ltd.