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Korean Journal of Preventive Medicine 1980;13(1): 27-34.
Some Statistical Considerations for the Estimation of Urinary Mercury Excretion in Normal Individuals.
Hee Sook Park, Kyou Chull Chung
Purpose of this study is to find out proper means of estimating the urinary mercury excretion the normal individuals. Whole void volume was collected every 2 hours beginning from 6 o'clock in the morning until 6 o'clock next morning. Mercury excretion in each urine specimen was measured by NIOSH recommended dithizone colorimetric method (Method No. : P & CAM 145). Urinary concentration of mercury was adjusted by two means : specific gravity of 1.024 and a gram of creatinine excretion per liter of urine comparing the data with the unadjusted ones. Mercury excretion in 24-hour urine specimen was calculated by adding the amounts measured with the hourly collected specimens of each individual. Statistical analysis of the urinary mercury excretion revealed the following results : 1. Frequency distribution curve of mercury excreted in urine of hourly specimens was best fitted to power function expressed in the form of y=ax(b), Adjustment of the urinary mercury concentration by creatinine excretion was shown to be superior (y=1674x(-1.52)), r(2)=0.95) over nonadjustment(y=2702x(-1.57)), r(2)=0.92) and adjustment by specific gravity of 1.024(y=4535x(-1.66), r(2)=0.93). 2. Both log-transformed mercury excretion in hourly voided specimens and mercury excretion itself in 24 hour specimens showed the normal distributions. 3. The frequency distribution of mercury adjusting the urinary concentration of mercury by creatinine excretion was best fitted to a theoretical normal distribution with the sample means and excretion was best fitted to a theoretical normal distribution with the sample means and standard deviation than those unadjusted or adjusted with specific gravity of 1,024. 4. Average urinary mercury excretions in 24-hour urine specimen in an individual were as follows : a) Unadjusted urinary mercury excretions. mean and standard deviation :18.6+/-13.68 microgramHg/liter. median : 16.0 microgramHg/liter. range : 0.0-55.10 microgramHg/liter. b) Adjusted with specific gravity. mean : 20.7+/-11.76 microgramHg/liter x 0.024/(S.G.-1.000). median : 20.7 microgramHg/liter x 0.024/(S.G.-1.000). range : 0.0-52.9 microgramHg/liter x 0.024/(S.G.-1.000). c) Adjuested with creatinine excretion. mean and standard deviation : 10.5+/-6.98 microgramHg/g creatinine/liter. median : 9.4 microgramHg/g creatinine/liter. range : 0.0-26.7 microgramHg/g creatinine/liter. 5. No statistically significant differences were found between means calculated from 24-hour urine specimens and those from hourly specimens transformed into logarithmic values. (P<0.05).
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