Chapter 17
Hair Mercury Analysis and Its Application to Exposure Studies in NHEXAS and NHANES IV 1
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G. M . Cramer , K. Bangerter , R. Fernando , G. M . Meaburn , and E . Pellizzari 3
Office of Seafood, U.S. Food Administration, Washington, D C 20204 Medical University of South Carolina, Charleston, SC 29425 Research Triangle Institute, Research Triangle Park, NC 27709 National Ocean Service, Charleston, SC 29412
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The results of a scoping probability-based population study utilizing biological measurements of methylmercury exposure suggests that exposure from fish in six Great Lakes states may be considerably lower among the general population than historic public health limits. Due to concerns that historic limits may not be adequately protective of the developing fetus, the federal government has begun a national survey using methods from the Great Lake study to characterize the distribution of methylmercury exposure for U.S. population sub-groups that are considered most sensitive to the effects of methylmercury.
Introduction The massive methylmercury (MeHg) poisoning which occurred in Minimata Japan in the 1950s and 1960s alerted the world to the presence of MeHg in fish and to the hazards of consuming large quantities of fish that are heavily contaminated with MeHg (/). Subsequent studies have demonstrated that MeHg occurs in essentially all fishery products and for most people, the relatively low levels in fish represent the predominant source of exposure to all forms of mercury (2).
© 2001 American Chemical Society Lipnick et al.; Persistent, Bioaccumulative, and Toxic Chemicals I ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
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Over the past several years, the extent of MeHg exposure among U.S. fish consumers as well as the public health consequences of such exposure has been the subject of considerable debate within the Federal government and at state level. This debate has been fueled by concern about the sensitivity of the developing fetus to the effects of prenatal M e H g exposure, the emergence of new public health studies on the effects of MeHg exposure, and concern that mercury emissions may have a potential impact on MeHg exposure among fish consumers. This paper does not deal with these latter points. Instead, it reports on the results of a pilot MeHg exposure study and describes the application of analytical methods from that study to die development of a national data base that is intended to resolve some of the MeHg exposure debate and provide a framework for more accurate characterization of the risks to U.S. fish consumers. In the U.S., fish consumption is highly variable, reflecting the influence of geographic location, season of the year, ethnicity, and personal food preferences. The extent of MeHg exposure from fish meals is also variable since the concentration of MeHg in fish varies by species, size of fish, age of fish, and location of harvest. Although dietary modeling approaches are routinely used to estimate MeHg exposure, the outcomes of such efforts are model dependent and their accuracy in predicting MeHg exposure within the context of a complex diet which includes fish with different MeHg content has been the subject of considerable debate. Another approach for characterizing dietary exposure to MeHg is to use biomarker data, such as blood or hair mercury levels, which provide a direct measure of dietary MeHg intake. Hair and blood mercury levels are routinely used as a biomarker of MeHg exposure in health effect studies of populations who are dependent on fish consumption (3, 4, 5, 6, 7). Studies with radiolabeled MeHg have shown that once it is ingested, it is quantitatively absorbed from the diet, distributed throughout the body within a few hours, and after a 20-30 hour clearance phase, blood levels decrease exponentially with a half life of about 50 days (8). B y allowing for the rapid clearance phase, changes in blood mercury levels have been shown to be directly proportional to the levels of MeHg ingested, with nearly all of the mercury found in blood in the form of M e H g (9). In the case of scalp hair, the concentration is approximately 250 times the blood concentration at the time the hair is formed. Once formed, hair strands grow at the rate of approximately 1 cm per month, providing a record of previous mercury exposures that remains unchanged for periods of up to 11 years (70). Although blood and hair can both be used to document MeHg exposure, hair-strand analysis is preferred because it provides a simple, non-invasive sampling procedure that allows monitoring of MeHg intake. Since MeHg accounts for about 80% of the total mercury levels found in hair (//, 12), total mercury determination is typically used to characterize MeHg exposure from fish.
Lipnick et al.; Persistent, Bioaccumulative, and Toxic Chemicals I ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
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In 1995, at the E P A sponsored National Forum on Mercury in Fish, it was suggested that a national data base be developed on total hair mercury levels. Such a data base would provide direct measure of the extent of MeHg exposure that occurs among U.S. fish consumers. Importantly, such information would help resolve the MeHg exposure debate and allow direct comparison of MeHg exposure measurements in the U.S. with populations who were the subject of MeHg human health studies.
Experimental In 1996, F D A and the National Marine Fisheries Service (NMFS) had the opportunity to collaborate with Research Triangle Institute (RTI) to develop a hair mercury data set in conjunction with the National Human Exposure Assessment Survey (NHEXAS), an E P A sponsored project headed by RTI (13). One component of this survey involved a 300 home probability-based sampling in E P A Region V (Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin). The primary focus of the study was to document multi-media exposure to various metals, pesticides, and other organics, and characterize the exposure distribution for the general population of a relatively large area. The target population of the study had racial, ethnic, socioeconomic, and other demographic characteristics similar to the national profile. Since dietary records for a four day period along with duplicate diet portions were collected from each participant providing a hair sample, the N H E X A S study provided the opportunity to not only characterize the distribution of hair mercury levels among N H E X A S participants, but the opportunity to examine the relationship of hair mercury levels to short term fish consumption information. Hair samples for the N H E X A S study were obtained by cutting a bundle of hair approximately the size of an eraser in diameter from the occipital region of the head. The bundle was cut with clean stainless steel scissors as close to the scalp as possible and the bundle was kept intact during cutting and storage using a plastic clip. The 3cm segment of hair closest to the scalp, representing approximately 3 months of integrated exposure to MeHg, was used for analysis. Hair strands less than 3-cm were analyzed in their entirety. In order to describe the entire range of total mercury levels in N H E X A S hair samples, a sensitive analytical procedure which would permit the analysis of 5 mg samples of hair was developed by RTI based on atomic fluorescence spectrometry. Hair samples, washed with acetone to remove surface contamination, were digested in sulfuric acid in airtight vials at 90 °C for 6-8 hours. Following the conversion of all forms of Hg to H g (11) using a bromide/bromate solution, hydroxy lamine addition to remove excess bromide/bromate, and tin chloride addition to reduce Hg (11) to Hg (0), the samples were analyzed by cold vapor atomic fluorescence spectrometry (CVAFS) using a H g specific fluorescence detector.
Lipnick et al.; Persistent, Bioaccumulative, and Toxic Chemicals I ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
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Hair samples were analyzed in batches of 25-30 samples. Each batch included 4-5 matrix standards (hair composite spiked with Hg reference standards), triplicate reagent blanks, and triplicate performance evaluation samples (a certified hair mercury sample). In addition, duplicate analyses were performed on a subset of 12% of the hair samples as well as a subset of 12% of the sample extracts. A Q C check standard was analyzed every 10th sample. The method performance was evaluated for total H g measurement in human hair. The correlation coefficient for standard curves in the hair matrix was 0.9983, while the precision and the bias were
