Biological monitoring Exposure to metals was discussed at the ACS Miami meeting
By Mat H.Ho and H. Kenneth Dillon
There are two approaches for monitoring human exposure to chemicals: ambient monitoring and biological monitoring. In a 1980 seminar sponsored by the Health and Safety Directorate of the Commission of the European Communities (CW), the U S . Occupational Safety and Health Administration, and the U.S. National Institute for Occupational Safety and Health (NIOSH), ambient monitoring was defined as “the measwment and assessment of agents at the workplace [to evaluate] ambient exposure and health risk compared to an appropriate reference.” Biological monitoring was defined as “the measurement and assessment .of workplace agents or their metabolites in tissues, secreta, excreta, expired air, or any combination of these to evaluate exposure and health risk compared to an appropriate reference.” For a long time, ambient monitoring, which considers pulmonary exposure only, has teen the major means of assessing exposure to chemicals in the work place. However, ambient monitoring does not indicate the true uptake 124 Environ. Sci. Technol.. Vol. 20. No. 2, 1986
by the exposed worker even for the chemicals that enter the body mainly through inspired air. Biological monitoring, on the other hand, evaluates exposures from all routes and thus may allow a more accurate assessment. Biological monitoring offers several advantages: It takes into account individual variability in a biological activity resulting from a chemical insult. It takes into account the effects of personal physical activity and individual life styles. It is a valuable adjunct to ambient monitoring and health surveillance. The primary purpose of biological monitoring is to detect or assess expcsure to chemical contaminants. Ideally, a biological indicator of exposure would allow the selection of an exposure index such that maintenance of biological levels below this index would prevent the development of disease. W o international symposia addressing biological monitoring have been sponsored by the Chemical Health and Safety Division of the American Chemical Society. The first one, covering the monitoring of exposure to organic chemicals, convened at the April 1984
meeting in St. Louis, Mo. Monitoring of exposure to metals was discussed in a symposium at the Miami, Fla., meeting one year later. The object of these symposia was to provide a f o m for reporting the latest advances in this rapidly growing field. Other objectives included communicating to specialists and nonspecialists alike the overall status of biological monitoring, highlighting the broad stratem of current research, and providing a forum for speculation on the likely paths of future research. Speakers at the Miami meeting came from the United States, a number of European countries, and India.
Importance of speciation Antero Aitio of the Institute of Occupational Safety and Health in Helsinki, Finland, was the keynote speaker. His presentation stressed the need for chemical and physical speciation in the biological monitoring of exposures to metals. According to Aitio, biological monitoring generally attempts to estimate the amount of a chemical absorbed into the body of an individual. To do this accurately, the investigator must know the physical and chemical
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properties of the chemical in the exposure environment, the physical and chemical mechanisms that lead to absorption, how the chemical is metabolized when absorbed by the body, and how the intact chemical or its active metabolites are transported to the target organ where health impairment occurs. Biological indicators of exposure must therefore be worked out with all of these considerations in mind. Aitio presented several examples of how chemical exposures are related to the physical and chemical properties of contaminants. He stated that inorganic arsenic compounds generally present less of an exposure hazard than organoarsenicals. For example, organically bound arsenic in crabs is absorbed by ingestion into the gastrointestinal tract more efficiently than by the inhalation of inorganic arsenic into the lungs. The uptake of chromium also has been found to vary among oxidation states, water solubility, and aerosol size distribution. In general, water-soluble chromium(VI) compounds are rapidly absorbed into the body through the lungs and excreted in the urine. This is the case in exposures to workers in two occupations-chrome plating and manual arc welding of stainless steel. However, the lungs of stainless steel welders also have been found to accumulate chromium, which is slowly cleared from the lungs and consequently affects blood and urine levels only marginally. Peter C. Bragt of the Netherlands’ Technical National Organization presented data from rat Studies confirming that insoluble chromium(V1) compounds are slowly cleared from the lungs and, therefore, accumulate. In other occupations, such as the tanning of hides, chromium(lII) (as chromium trichloride) may be absorbed and excreted rapidly and furthermore may be mistaken for the more toxic chromium(V1) in urine samples. Aitio stressed that blood analysis may offer a way to differentiate between the two oxidation states because chromium(III) is primarily associated with plasma, whereas chromium (Vr) is associated with erythrocytes. The particle size distribution of the aerosol that contains cbromium(IlI) in tannery atmospheres also may affect the primary route of uptake. One study was cited in which high urinary levels of chromium were found even though levels in ambient air were low. It was also found, however, that the air sampler excluded particles that were larger than the “respirable” size range. Unfortunately, the primary exposure was from mists of c h r o m i u m 0 in solution with mass median diameters much larger than 10pm. Consequently, the exposure was from the absorption of
these “large” particles into the gastrointestinal tract. As another example of the importance of speciation, mention was made of exposures to a chromium lignin sulfonate encountered in the pulp and paper industry. Although the chromium in this complex does not appear hexavalent, the substance has been linked with cancer. In other examples, the speciation of nickel and cobalt compounds was also demonstrated to be important. In general, soluble compounds of these two elements are absorbed readily; insoluble compounds are not.
New rules for lead Alexander Berlin of the CEC Health and Safety Directorate discussed biological monitoring and its relation to ambient monitoring, with emphasis on the biological monitoring of metals. He described the health directive for lead that has been adopted by the commission. This is the first directive from the commission to include biological monitoring. Thus the degree of success in its implementation will guide future efforts to establish work place standards. The directive combines ambient air monitoring, biological monitoring, and medical surveillance into an integrated approach to reduce the risk of overexposure to lead in the work place. Action and l i t values are established for lead in ambient air and the bloodstream. These target levels and the accompanying actions to be taken, which include medical surveillance, are summarized in Table 1. The directive also established a sampling strategy for air and biological monitoring. Aluminum and cadmium A significant portion of the other presentations was directed toward the application of biological monitoring to the assessment of overexposure of workers to specific metals. Frank L. Van de
Vyver of the Department of Medicine at the University of Antwerp, Belgium, gave the results of investigations of aluminum toxicity in chronic hemodialysis (CHD) patients. Elevated aluminum levels have been found in the serum and whole blood of these patients by electrothermal atomic absorption spectrometry (AAS). Aluminum in bone samples taken from 10 CHD patients with osteomalacia was found to be markedly elevated. More sophisticated analytical techniques, such as laser microprobe mass analysis, electron probe X-ray microanalysis, aluminum staining, and secondaryion mass spectroscopy, were used to determine more specifically the sites of aluminum accumulation in bone and liver tissue and to verify the effectiveness of desferrioxamine in reading aluminum levels in bone and liver tissue. k t e r Garrett of the Department of Medicine and Nephrology at the Jarvis Street Hospital in Dublin, Ireland, also investigated aluminum toxicity in CHD patients. His project included studies of aluminum levels in water supplies at dialysis locations, clinical features in cases of dialysis encephelopathy, radiological skeletal surveys, and histomorphometry and histochemistry on bone biopsies. Aluminum staining of bone biopsies was found to be the method of choice in the diagnosis of aluminum intoxication. On the biological monitoring of cadmium, Carl G . Elinder of the National Board of Occupational Safety and Health of Sweden reported that measurements of cadmium in blood and urine can be used to assess recent and long-term exposure. Levels of cadmium in blood primarily reflect shortterm exposures; however, levels remain somewhat elevated at the cessation of exposure. The long-term halflife of cadmium in blood may be nearly a decade. Urinary cadmium is primarEnviron. Sei. Technol.. Val. 20. No. 2, 1988 125
ily related to body burden because the kidney is the target organ. If exposure is excessive, however, kidney excretion of cadmium may become excessive because there is a strong relationship between excretion and tubular proteinuria.
Mercury and selenium Jens C. Hansen of the Institute of Hygiene at the University of Aarhus in Denmark reported on mercury and selenium levels in blood samples taken from mothers and infants in Greenland. Significant positive correlations were found between the levels of these two metals and the amount of seafood consumed by the individuals studied. It was concluded that their diet provides relatively high exposures to mercury and selenium. The selenium present, however, may protect against the risk of mercury poisoning. Karl H. Schaller of the Institut fiir Arbeits und Sozialmedizin und Poliklinik fir Berufskrankheiten der Universitat Erlangen, in Nuremberg, West Germany, reported a study of mercury exposures recorded in a mercury recycling plant. Levels of mercury in air were determined with passive samplers. Internal mercury exposure was determined by blood and urine analyses. Nervous system effects were monitored by determining nerve conduction velocities and by psychometric tests; kidney function was assessed by determining proteins and specific enzyme activities in urine samples. Exposure levels higher than accepted standards were found, but adverse health effects were not manifest. As a result of the study, work practices were modified and the workers were enrolled in a medical surveillance program. Nickel E William Sunderman, Jr., of the University of Connecticut’s School of Medicine reported serum levels of nickel in patients with iatrogenic exposures to the metal by determining nickel in serum with electrothermal AAS. Hypernickelemia was documented among patients in hemodialysis and disulfiram treatment. Contrary to work published by others, Sunderman’s research indicated that hypernickelemia did not occur in most patients fitted with stainless steel hip prostheses. Hans Raithel of the Institut fiir Arbeits und Sozialmedizin und PoliMinik fiir Bemfskrankheiten der Universitat Erlangen presented a study’ of nickel exposure among workers in the hollowglass industry, the nickel-cadmium battery industry, and the nickel-refining industry. High external and internal nickel exposures were found among employees in the hollow-glass works 126 Environ. Sci. Technol., Vol. 20,No. 2, 1986
and refineries, andrdust control was proposed to reduce exposures. The determination of nickel in urine proved a reliable indicator of exposure and was recommended for future studies.
Lead-monitoring techniques Several presentations were given concerning the biological monitoring of lead exposure. Magnus Svantengren of the Karolinska Institute in Stockholm, Sweden, compared human feces and blood lead levels in Belgium, Malta, Mexico, and Sweden. Lead levels in both types of specimen were found to be highest in Malta (245 pg/L). The study revealed that the most important route of exposure seemed to be absorption into the gastrointestinal tract. Also, the correlation between lead in feces and in blood seemed to be curvilinear with a-greater slope at low exposure concentrations. D. J. Parikh of the Indian National Institute of Health reported on lead levels found in the general population of Ahmedabad as determined by AAS with the Delves cup technique. Samples were obtained from a quality control laboratory set up in connection with the Biological Monitoring Program of the World Health Organization/United Nations Environment Program (UNEP), A surprising finding was that smoking did not seem to have a significant effect on blood lead levels. Male smokers showed median blood lead levels of 116 pg/L; male nonsmokers had slightly higher levels-1 29 pg/L. Brian Alleyne of the Worker’s Health, Safety, and Compensation Department of Alberta, Canada, reported on an assessment of radiator shop workers for lead exposure. He found that although many radiator repair shops are small, the degree of worker exposure to lead can be very large. A questionnaire was administered to 142 workers to determine how many had experienced symptoms known to be associated with lead poisoning. Blood and urine samples were collected and tested for blood lead, zinc protoporphyrin, and aminolevulinic acid. Reported symptoms of lead toxicity appeared to be better correlated with zinc protoporphyrin levels than with blood lead levels. The aminolevulinic acid levels seemed to indicate long-term exposure. Edoardo DeRosa of the University of Padova in Padova, Italy, presented a study of lead exposure to workers in the Italian ceramics industry. An initial survey involved the determination of blood lead levels in several hundred workers. Follow-up surveys were conducted for a portion of these workers over a period of several years. The original survey found that there was a higher risk of overexposure in the pro-
duction of tiles than there was in the production of artistic articles. This difference was attributed to the lower lead content of the glaze used in the production of art objects. In the follow-up surveys, it was found that improvements in working conditions and personal hygiene, and probably the reduction of the lead content of the glazes, lowered blood lead levels in tile producers to the same levels found in the makers of art objects. R. Subramanian of Jawaharlal Nehm University in New Delhi, India, reported that the use of hair shows some promise as a biological indicator of long-term exposure to lead and chromium. His work continues as part of the Global Environmental Monitoring System of UNEP Eugene Brams of Texas A&M University in College Station, Tex., presented evidence of lead accumulation in brain and bone tissue of goats that feed in contaminated fields. Jean-Pierre Farant of McGill University in Montreal, Que., Canada, presented evidence supporting the use of 6-aminolevulinic acid dehydratase as a biological index of metal intoxication. Several metals were discussed, including lead, zinc, copper, cadmium, and mercury. The activity of the enzyme was found to depend on the pH of the analysis medium. In the monitoring of lead exposure, the most reliable responses were obtained when monitoring the ratio of activities at pH of 6.4 and 7.2. The enzyme activity was not specific for individual metals. Aluminum may activate the enzyme. Raymond Singer of Occupational Health Consulting in New York, N.Y., discussed a somewhat nontraditional form of biological monitoring that may offer considerable promise. He outlined a method that uses nervous system monitoring for early signs of chemical toxicity, particularly heavy metal toxicity. Because of the susceptibility of the nervous system to contaminant exposure and the relative ease with which nerve performance tests can be done, Singer said that irreversible damage to the nervous system could be prevented through early detection. He suggested that the functions to be monitored should include memory, concentration, psychomotor reaction time, visual perception, and manual dexterity.
Biological sample analyses Several presentations addressed the application of state-of-the-art analytical techniques to the determination of metals in human blood, urine, and tissue. R. Delon Hull of NIOSH reported on multielement determinations in blood, urine, and tissue by inductively coupled plasma-atomic emission spec-
troscopy (ICP/AES). Urine samples required extraction of the metals with a polydithiocarbamate resin prior to digestion and analysis. Blood and tissue samples were satisfactorily digested with a 3: 1:1 mixture of nitric, perchloric, and sulfuric acids. J. R. Boyle and Shane S. Que Hee of the University of Cincinnati in Ohio determined numerous metals in blood and urine by ICP/AES. Boyle found conventional hot-plate wet digestion with a nine-bone ratio of nitric acid to perchloric acid suitable for red blood cells. Serum was diluted 10-fold with water and then analyzed. Que Hee found 10fold dilution of urine with a mixture of hydrochloric and nitric acids suitable for detection of many elements. Other elements were determined with reasonable success after concentration on Chelex-100 resin. Henry K. Matusiewicz of the U S . Food and Drug Administration reported on work performed at the Elemental Analysis Research Center on the enhancement of sensitivity with the ICP/AES technique. He described a preconcentration step for metals in hiological samples that involves controlled-potential electrolysis at a hanging mercury drop electrode or graphite mercury thin film. The concentrated samples are then introduced into the IC plasma by electrothermal vaporization. Mary M. Kimberly of the Centers for Disease Control (CDC) in Atlanta, Ga., described a urinary screening procedure for metals that uses IC argon plasma optical emission spectroscopy. After preliminary identification of suspected toxic metals on the basis of signs and symptoms in an affected population urine samples are acidified and analyzed. Results from screening after outbreaks of metal poisoning in Pakistan and other places have illustrated the usefulness of the method. R. Nath of the Postgraduate Institute of Medical Education and Research in Chandigarh, India, presented the results of a comparison of determinations of copper and zinc in standard reference biological materials hy direct current plasma (DCP) emission spectroscopy with determination by AAS. DCP results were similar to AAS results, although the DCP results were less accurate. He reported that the choice of optimum wavelength was critical to reproducibility in DCP analySeS.
Daniel C. Paschal, also of CDC, reported that he found AAS with Zeeman background correction to provide accurate determination of arsenic in urine. Mat H. Ho of the University of Alabama at Birmingham described the application of flow injection analysis (FIA) to instrumental methods, such as
control samples in the United States. Singer summarized quality control practices for nervc function testing. He emphasized the need for baseline testing of all employees to establish results that can be used for comparison when overexposure to metals is suspected. Finally, Aitio presented Alexander Berlin’s 10 criteria for the development of methods for biological monitoring. The proceedings of the St. Louis meeting and other contributions from iiivitrd authors are soon to be published by John Wiley and Sons. The detailed proceedings of the Miami symposium are being assembled by the organizers of the meeting and are expected to be published, together with other invited contributions, as a second volume. The papers presented at the St. Louis meeting have been summarized in ES&T (June 1984, pp. 188-WA).
Additional reading The Use of Biological Specimens for the Assesmmr of Human Exposure to Environmrmul Pollurants; Berlin, A,; Wolff, A. H.; Hasegawa, Y., Eds.; Martinus Nijhoff: Borton, Mass., 1979. Baselt, R. C . Biological Monitoring Methods for lndustrial Chemicals; Biomedical Fublications: Davis, Calif., 1980.
ICP-AES and AAS, that are useful for the determination of metals. FIA offers the advantages of fast sample throughput, highly reproducible determinations, and the need for very small sample volumes. Several FIA techniques, such as on-line dilution, diffusion, and preconcentration on Chelex-100, were also described.
Quality control The last session of the 1985 symposium was devoted to a discussion of quality control in biological monitoring. Aitio led the discussion and introduced several speakers, who made brief presentations on various specific quality control concerns. He described a number of quality control measures specific to biological monitoring and stated that the precise selection and documentation of sampling times relative to exposure times are important considerations in obtaining meaningful, representative samples. Sunderman reviewed internal quality control measures, including specific techniques used to avoid sample contamination in the laboratory. Kimberly reviewed external quality control measures, including proficiency analytical testing programs available for biological samples. The National Bureau of Standards in Gaithersburg, Md., and CDC are sources of external quality
Arsessmenr of Human Exposure to Lead and Cadmium through Biological Monitoring; Vahtrr, M.,Ed.; National Swedish Institute of Environmental Medicine and Karolinska Institute: Stockholm, Sweden, 1982 Lauwerys, R. R. Industrial Chemical Exposure: Guidelines for Biological Monitoring: Biomedical Publications: Davis. Calif.. 1983. “Human Biological Monitoring of lndustrial Chemical Series,” EUR 8476 EN; Alessia, L. et al., Eds.; Commission ofthe European Communities: Brussels, Belgium, 1983. Roi, R. et al. “Occupational Health Guidelines for Chemical Risk,” EUR 8513; Cornmission of the European Communities: Brussels, Belgium. 1983. Evaluarim of Analyrical Merhods in Biological Sysrems-Hazardous Merals in H u m n Toxieulogy; Vercruysse, A,, Ed.; Elsevier: Amsterdam, the Netherlands, 1984. Biologic01 Monitoring and Surveillance of Worker Exposure to Chemicals; Aitio, A.; Riihimaki, V.; Vainio, H., Eds.; Hemisphdre Publishing: Washington, D.C., 1984. “Biological Indicators for the Assessment of Human Exposure to Industrial Chemicals,” EUR 8903 EN; Aleasio, L. et al., Eds.; ComrniSaion of the European Communities: Brussels, Belgium. 1984. Assessment of ‘hxic Agenls at the Workplace: Roles of Ambient and Biological Monitoring; Berlin, A , ; Yodaiken, R. E.; Henman, B. A , . Edr.: Martinus Niihoff: Boston, Mass.’, 1984.’ Biological Monitoring of Exposure to Chrmicols: Organic Cmpounds: Ho, M. H.; DilIon, H. K . , Eds.; Wilcy Interscience: New York, N.Y., 1985.
Mar H. Ho is un assisrant professor in the Chemistry Depurtment of the University of Alabama ur Birmingham.
H . Kenrieth Dilloii is an associate professor in rhe School of Public Health of the University of Alabama at Birminghum. Environ. Sci. Technol.. Vol. 20, No. 2. 1986 127
