revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY 312
2. HEALTH EFFECTS
The mean total mercury levels in whole blood and urine of the general population are approximately
1–8 µg/L and 4–5 µg/L, respectively (Gerhardsson and Brune 1989; WHO 1990). Recently, the
International Commission on Occupational Health (ICOH) and the International Union of Pure and Applied
Chemistry (IUPAC) Commission on Toxicology determined that a mean value of 2 µg/L was the
background blood level of mercury in persons who do not eat fish (Nordberg et al. 1992). These blood and
urine levels are "background" in the sense that they represent the average levels in blood in the general
population and are not associated with a particular source for mercury. However, the intra- and interindividual
differences in these biomarkers are substantial, possibly due to dental amalgams (urine) and
ingestion of contaminated fish (blood) (Verschoor et al. 1988; WHO 1991). Long-term consumption of fish
is the source of nearly all of the methylmercury measured in the general population, and individuals in
communities with high fish consumption rates have been shown to have blood levels of 200 µg/L, with daily
intake of 200 µg mercury (WHO 1990). However, acute inhalation exposure to low levels of metallic
mercury resulted in much lower levels in the blood (0.028 and 0.18 µg/100 mL) and urine (from 94 to
>438 µg/L) (Kanluen and Gottlieb 1991; Rowens et al. 1991).
Urine mercury measurement is reliable and simple, and it provides rapid identification of individuals with
elevated mercury levels (Naleway et al. 1991). It is a more appropriate marker of inorganic mercury,
because organic mercury represents only a small fraction of urinary mercury. Yoshida (1985) found that
urinary mercury levels were better correlated with exposure than were blood inorganic mercury
concentrations in workers exposed to metallic mercury vapor.
Several studies have reported a correlation between mercury in blood and urine; however, results vary, and
it is not known whether the ratio between concentrations in urine and blood remains constant at different
exposure levels (Lindstedt et al. 1979; Roels et al. 1987; Smith et al. 1970). Significant correlations
between occupational exposure to mercury vapor and mercury levels in the blood and urine of 642 workers
in 21 chloralkali facilities were reported by Smith et al. (1970). According to the investigators, an air
concentration (8-hour TWA) of 0.1 mg/m 3 was associated with blood levels of 6 µg/100 mL and urine
levels of 220 (not corrected for specific gravity), 200, or 260 µg/L (corrected to specific gravities of
1.018 or 1.024, respectively). It is likely that current worker exposure is significantly less than this study
indicates, because practices such as requiring showers after workshifts and cleaning work clothes after use
have been implemented since 1970, when the Smith study was conducted. Another group of investigators,
Henderson et al. (1974), found the concentrations reported in Smith et al. (1970) to be 2–10 times higher
than those found 2 years later. As suggested by Roels et al. (1982), the actual mercury absorption by