Monitoring mercury exposure

Wildlife indicators of mercury exposure and trends are important elements of a comprehensive approach to assess mercury in the environment and the monitoring of trends that may assist regulators and the regulated community in long-term evalnation of the need and usefulness of mercury somce controls. It is important to understand, however, that bioindicator data alone are insufficient to answer snch critical qnestions as identification of mercniy sonrces, or the relative importance of local, regional, and global inputs of mercury somces to atmospheric deposition and errvirorrmerrtal loading in specific areas. 

Studies from New Zealand and the Faroe Island indicate that adverse effects in children can be correlated with maternal hair levels as low as 10-20 pg/g [44]. Mercury analyses conducted on a single human hair can be used to monitor daily variations in methyl mercury exposure among fish eaters [45,46], and have been utilized to track maternal fish consumption and risk of preterm delivery [47]. Other investigators [48] have utilized measurements of total mercury in hair, toenails and urine to assess exposures in a group of non-occupationally exposed women in relation to renal tubular effects. 

Mason HJ, Hindell P, Williams NR. Biological monitoring and exposure to mercury. Occup Med 2001 51(1) 2-11. 

Reliable evaluation of the potential for human exposure to mercury and various mercury compounds depends in part on the reliability of supporting analytical data from environmental samples and biological specimens. Concentrations of mercury in unpolluted atmospheres and in pristine surface waters are often so low as to be near the limits of detection of current analytical methods even for determining total mercury. In reviewing data on mercury levels monitored or estimated in the environment, it should also be noted that the amount of chemical identified analytically is not necessarily equivalent to the amount that is bioavailable. The analytical methods available for monitoring mercury and various inorganic and organic mercury compounds in a variety of environmental media are discussed in Chapter 6. 

Exposure Registries. New York State has instituted a Heavy Metals Registry that monitors occupational exposure to heavy metals, including mercury. Cases are reported when mercury exposure is equal to or exceeds 50 g/L (ppb) in blood or 20 g/L (ppb) in urine. Between 1982 and 1986, 1,000 cases of mercury exposure were reported and linked to 47 companies. Most exposures (494 cases) occurred in workers in the alkali and chlorine industry, where mercury is used as a cathode because exposure occurs when the cells are opened the median blood mercury concentration was 76 g/L (ppb) (maximum concentration 916 g/L [ppb]). The second most frequent exposure category (213 cases) was the manufacture of industrial instruments, such as the manual assembly and fabrication of thermometers median blood mercury concentration was 145 g/L (ppb) and the maximum concentration was 889 g/L (ppb) (Baser and Marion 1990). 

The purpose of this chapter is to describe the analytical methods that are available for detecting, and/or measuring, and/or monitoring mercury, its metabolites, and other biomarkers of exposure to and effects of mercury. The intent is not to provide an exhaustive list of analytical methods. Rather, the intention is to identify well-established methods that are used as the standard methods of analysis. Many of the analytical methods used for environmental samples are the methods approved by federal agencies and organizations such as EPA and the National Institute for Occupational Safety and Health (NIOSH). Other methods presented in this chapter are those that are approved by groups such as the Association of Official Analytical Chemists (AOAC) and the American Public Health Association (APHA). Additionally, analytical methods are included that modify previously used methods to obtain lower detection limits, and/or to improve accuracy and precision. 

Franchi E, Loprieno G, Ballardin M, et al. 1994. Cytogenetic monitoring of fishermen with environmental mercury exposure. Mutat Res 320 23-29. 

Hansen JC. 1991. Mercury and selenium concentrations in Greenlandic mother-infant blood samples. In Dillon HK, Ho MJ, eds. Biological monitoring of exposure to chemicals Metals. New York, NY John Wiley and Sons, 11-25. 

Roels et al. [38] points out that the analytical techniques identified in Table 1 are not easily available and are not well-suited for routine biomonitoring of occupational or environmental exposures. Instead, indirect biomarkers such as urinary enzymes are often used with success to evaluate mercury exposure and injury. Zalups [35] identifies numerous methods used to detect renal tubular injury induced by mercury. These methods monitor the urinary excretion of enzymes that leak from injured and necrotic proximal tubules, including lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and N-acetyl-P-D-glucosaminidase (NAG). Although advocated by Zalups (35) to detect renal tubular injury, Mason et al. (48) questions the practical utility of such biomarkers in occupational surveillance. According to Mason et al., small increases in NAG, leucine... 

The primary method used to analyse for mercury is CVAAS (cold vapour atomic absorption spectroscopy). This has a sensitivity of parts per trillion for urine while determination of mercury in fish, shellfish, pharmaceuticals and foodstuffs has a sensitivity in the low parts per billion range, as has the analysis of mercury in samples of tissues and hair. Mercury levels in newly formed hair reflect those in blood the concentration however is about 250 times greater in hair. Once the mercury has interacted with the sulphur-containing proteins in hair it is essentially "fixed" and so provides an accurate monitor of exposure and accumulation. Analysis of the hair length can therefore be used to estimate the dates of contamination by mercury and also the peak blood levels achieved. 

Diagnosis is by estimation of blood and urine mercury concentrations (Table 1). Long-term monitoring of exposure, such as may be necessary with those working with dental amalgam, may be carried out using hair or nail clippings. 

Blood is often used for biological monitoring of exposure to Hg(0) vapour and MeHg. The type of compound is determinative for the distribution of mercury between blood cells and plasma. 

Bimetallic strip thermometers are preferred for monitoring oven temperatures. Mercury thermometers should not be mounted through holes in the tops of ovens so that the bulb hangs into the oven. Should a mercury thermometer be broken in an oven of any type, the oven should be closed and turned off immediately, and it should remain closed until cool. All mercury should be removed from the cold oven with the use of appropriate cleaning equipment and procedures (see Chapter 5, section 5.C. 11.8) in order to avoid mercury exposure. After removal of all visible mercury, the heated oven should be monitored in a fume hood until the mercury vapor concentration drops below the threshold limit value (TLV). 

In Plant 2 the project team focused the exposure monitoring effort on personnel involved in the change out of mole sieve desiccant. Plant operators as well as contractors involved in the desiccant change out operation were monitored on a 24-hour basis for several days. In addition, area air sampling stations were set up to monitor mercury concentrations arormd the work area. All personal and area sampling results were below the action limit. Results from the analysis of process samples are presented in the following table ... 

In designing a mercury monitoring network that includes a wildlife component, a principal objective would be to docrrment changes in merctrry exposure (and potentially effects) relative to changes in merctrry loadings to an ecosystem. More specific objectives might include the ability to ... 

Stone SF, Backhads FW, Byrne AR. Gangadahran S, Horvat M, Kratzer K, Parr RM, ScHiADOT JD, Zeisler R (1995) Production of hair intercomparison materials for use in population monitoring programmes for mercury and methylmercury exposure. Fresenius J Anal Chem 352 184-187... 

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