Laundry Dryer Lint: A Novel Matrix for Nonintrusive Environmental

Lint samples were removed from the dryer lint trap after each load of laundry was completed. ... Figure 2 Dryer lint lead levels for radiator shop emp...
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Environ. Sci. Technol. 1998, 32, 2467-2473

Laundry Dryer Lint: A Novel Matrix for Nonintrusive Environmental Lead Screening P E T E R G . M A H A F F Y , †,* NATHANIEL I. MARTIN,† KENNETH E. NEWMAN,† BILL HOHN,‡ RANDY J. MIKULA,§ AND VICENTI A. MUNOZ§ Department of Chemistry, The King’s University College, 9125 50th St. Edmonton, Alberta, Canada T6B 2H3, Environmental Health Division, Capital Health, Edmonton, Alberta, Canada T5N 4A3, and Western Research Centre, CANMET, Natural Resources Canada, Devon, Alberta, Canada TOC 1EO

North American health agencies have set ambitious goals to reduce childhood and occupational lead poisoning. A central tool in attaining lead exposure reduction objectives is screening populations to identify persons at risk. We have identified laundry dryer lint as a novel matrix with potential use as a nonintrusive, first stage screening mechanism for households with elevated lead levels. This Edmonton, AB, pilot study provides the first measures of lead levels in household laundry dryer lint. Three populations were included: a control group, a group using communal dryers at an inner city service agency (Bissell Centre), and households where a family member had occupational exposure to lead. Background levels of lead in laundry dryer lint from a Canadian urban environment were established, households with elevated lead levels resulting from the transport of occupational lead by an adult family member were identified, and scanning electron microscopy was used to identify the form of the lead particles and determine their source.

Introduction Over the past two decades, a substantial scientific effort has gone into studying the environmental chemistry and toxicology of lead, which has been described as one of the most widely dispersed toxic substances of this century (1). Anthropogenic sources are well-known, and leaded gasoline, a major source for over half of this century, has been phased out in many industrialized countries. Source reduction led to a sharp decline for several years in measured levels of lead in air particulates in urban North American areas (2). The rate of decline has slowed, and recent work focuses on remaining widespread sources, reservoirs, and pathways for human exposure. Human toxicological studies have identified several populations at risk. Young children, infants, and pregnant women have been targeted, since cognitive deficit and developmental effects are well demonstrated on infants and * Corresponding author. E-mail: [email protected]; phone: 403-465-8343; fax: 403-465-3534. † The King’s University College. ‡ Capital Health. § Natural Resources Canada. S0013-936X(97)00699-8 CCC: $15.00 Published on Web 07/17/1998

 1998 American Chemical Society

young children and there is no placental-fetal barrier to lead transport (3). Childhood lead poisoning is described as “the number one environmental health hazard facing American children” (4). More than three million children in the United States are estimated to have blood lead (PbB) levels greater than 15 µg/dL (5). Neurologic damage to the fetus occurs at PbB levels as low as 15-20 µg/dL (6). Goals for drastic reduction of blood lead levels in populations of concern have been set in the United States. After reviewing new data showing significant adverse health effects of lead exposure in children with PbB levels previously thought to be safe, the Center for Disease Control recommended in 1991 that the overall goal of public health programs should be to reduce children’s blood lead levels below 10 µg/dL (7, 8). Similarly, the Canadian Lead Working Group has recommended that intervention strategies be implemented for the Canadian population beginning at blood lead levels of 10 µg/dL (3). The establishment of a threshold for lead exposure is difficult, as scientific evidence for subclinical effects at increasingly lower exposure levels continues to accumulate (6, 7, 9). There may be little remaining margin of safety between typical lead exposures and those producing subtle, adverse effects on target populations, particularly if exposure is coupled with factors that increase susceptibility to the toxicity of lead, such as nutritional deficiencies (10, 11). Occupational groups have also been the target of lead reduction programs, since various lead industrial processes result in substantially elevated levels of lead in workplace air and dust. Toxicological effects demonstrated in adults include blood pressure and reproductive effects, and in certain industries, adult workers may transport lead to the home environment in substantial quantities, placing infants, children, and pregnant women at risk. The U.S. Public Health Service has declared as a health objective for the year 2000 the elimination of the estimated tens of thousands of exposures resulting in workers’ blood lead concentrations greater than 25 µg/dL (9). Successful attainment of lead exposure reduction objectives will require a multifaceted approach. Essential features of a successful approach will include the following: identifying and remediating sources and pathways for the distribution of lead in the environment, particularly the home and workplace; targeting populations at risk through the use of appropriate environmental and biological indicators, screening tools, and integrated exposure models; public education; and legislation. In focusing on the particular concerns about lead exposure in young children, the U.S. Environmental Protection Agency has developed an integrated exposure uptake biokinetic (IEUBK) model for lead in children as a risk assessment tool. This model focuses on the home and its surrounding yard as the basic unit for risk analysis, because “lead exposure for preschool children commonly occurs within this domain” (12). In the United States, initial approaches to early childhood lead poisoning programs were characterized by after-thefact medical case management and administrative regulation. Recently, there have been calls for a major paradigm shift toward approaches with a focus on prevention (4). Central to prevention strategies is the implementation of viable screening programs. The 1991 CDC statement “Preventing Lead Poisoning in Young Children” calls for universal screening of children, except in communities where large numbers of children have already been screened and found not to have lead poisoning (13). This paper reports a novel, nonintrusive environmental indicator of lead in the houseVOL. 32, NO. 16, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 1. Distribution of dryer lint lead levels for three populations: control group, Bissell Centre communal dryers, and radiator shop employees. hold domain to add to the toolbox of screening techniques available to environmental health professionals concerned with identifying persons at risk. It reports the first determination of lead levels in household laundry dryer lint, from an Edmonton, AB, pilot study. Three populations were included: a control group, a group using communal dryers at an inner city service agency (Bissell Centre), and households where a family member has occupational exposure to lead.

Experimental Section Laundry Dryer Lint Samples. Laundry dryer lint samples were collected by volunteer study participants. Each participant was provided with zip-lock bags with instructions for collecting the lint. Lint samples were removed from the dryer lint trap after each load of laundry was completed. Prior to collecting each sample, participants were asked to thoroughly clean the lint traps by hand, then vigorously tap the trap to remove residual material. Glassware was soaked in a 1 M HNO3 bath for 24 h, rinsed with 3 M HNO3, followed by repeated rinsing with distilled water. Frequent blank analyses were performed to ensure that no contamination of glassware was occurring. Samples were dried for 16 h at 80 °C. Each sample (mass range 0.2-3.4 g) was digested for 16 h in 16 M HNO3, then refluxed for 4 h. Solutions were then cooled to room temperature, filtered through glass wool, and brought to a final volume of 25 cm3 in volumetric flasks with 3 M HNO3. Four 5 cm3 aliquots were then removed, and the lead content of each was adjusted by the method of multiple standard additions (14) using a 10.5 µg/mL Pb(NO3)2 stock solution. Solutions were analyzed for lead by flame atomic absorption spectroscopy, using a Pye-Unicam SP 90A Series 2A instrument at 217 nm using an air-acetylene flame. Preliminary experiments using a method developed for the analysis of plant material using an ashing technique in a muffle furnace (15) exhibited unacceptable analyte loss and were abandoned. Similar results have previously been reported (16). Our results show that the determination of lead levels in dryer lint by atomic absorption spectroscopy can exhibit matrix effects, and appropriate use of the method of standard additions is required to ensure that these effects are adequately accounted for. Reporting of Lead Levels. The limit of detection [LOD, defined as 3σ above the average concentration found in method blanks (17)] was found to be 0.7 µg/mL solution. In 2468

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this paper, analyte levels are reported as mass of lead per unit mass of dryer lint sample. Nine of the 100 samples analyzed in this study were below the LOD. These samples were generally those of low lead content and/or very small lint sample size. Exclusion of these samples did not alter conclusions drawn from the statistical analysis. Statistical Data Analysis. Distributions of dryer lint levels for the control and Bissell Centre data were determined to be log-normal at the 95% confidence limit by application of the χ2 statistic. Thus, for the purposes of statistical analysis, the mean and 95% confidence limits for each set were determined from the data in logarithmic form followed by taking antilogs. The derived means are thus geometric means. Microscopy. Micrographs in Figure 4 were obtained with a Bio-Rad MRC-600 Confocal Laser Scanning Microscope. The micrograph in Figure 5 is a backscattered electron image, obtained on a Hitachi S-2500 scanning electron microscope equipped with both energy-dispersive [EDS, 30 mm3 Si(Li) detector, TN 5402] and wavelength-dispersive (Microspec WDX) spectrometers. In backscattered electron images, the image brightness is related to the average atomic weight of the inorganic components. Metal particles thus appear very bright, while the fibers appear dark. Confocal and scanning electron microscopy are commonly used in a wide range of applications for characterization of inorganic components in an organic matrix (18, 19).

Results and Discussion The initial motivation for this study came from a 1994 intervention by the Edmonton Board of Health (EBH, now part of the Capital Health Authority) in a case where an adult male radiator mechanic was found to have elevated blood lead levels and symptoms of lead poisoning, resulting from occupational exposure. Family members were also tested, and a young child at home was found to have substantially elevated blood lead levels. To determine whether the transport of occupational lead into the home environment was an isolated case, the EBH and The King’s University College collaborated to screen the workplace and home environments of a dozen radiator workers, along with appropriate controls. Preliminary sampling and analysis protocols were developed as an undergraduate environmental chemistry class research project and used to measure lead levels in workplace floor sweepings, car floor sweepings, home vacuum dust collected from the vacuum cleaner bags in each house, and household dryer lint. While further

FIGURE 2. Dryer lint lead levels for radiator shop employees, by job classification.

FIGURE 3. Scanning electron micrograph of dryer lint (100×). refinement and validation of initial methods was required, preliminary results made it clear that lead was being transported home in substantial quantities by radiator repair workers. Arithmetic mean values obtained by the students were: workplace sweepings, 70 000 µg of Pb/g (five samples); car floor sweepings, 20 000 µg of Pb/g (12 samples); home vacuum dust, 2000 µg of Pb/g (14 samples); and household dryer lint, 100 µg of Pb/g (11 samples). Levels of lead in household dryer lint from radiator worker homes were 10-20 times greater than in lint from control homes, suggesting that this matrix might prove useful as an environmental screening tool. The present study was designed to develop protocols and analytical techniques for analysis of lead levels in this novel matrix, provide baseline data from a set of homes without known occupational exposure, and then replicate and extend the sampling from homes of workers with an identifiable occupational exposure in Edmonton. Baseline Data. Since background levels of lead (or other analytes) in dryer lint have not been previously reported, we sampled dryer lint from 20 homes of faculty and staff members at The King’s University College. Fifty-three samples were analyzed, all from homes reporting no known sources of lead of occupational or recreational origin. Lead

levels in dryer lint samples from this control group, given in Figure 1, ranged from 6 to 110 µg of Pb/g of dryer lint, with a geometric mean of 20 µg/g. Only one value was over 100 µg/g, all other values were under 60 µg/g. The distribution of lead levels from this control group was determined to be log-normal using a χ2 test [χ2 (computed) ) 3.01; 3 degrees of freedom; P ) 0.05]. As an extension of this baseline study, we collected 20 dryer lint samples from communal dryers available for public use at the Bissell Centre, an agency providing a range of social services to lower income residents of several inner city communities in Edmonton, where some of the older homes in the city are located. Users of the dryers were asked to place samples in zip-lock bags when cleaning out the lint traps on the dryers. Since the traps were not always cleaned out between dryer loads, these samples represent a composite measure of lead levels on the clothing of users of this facility. Lead levels in dryer lint samples from the Bissel Centre dryers, given in Figure 1, ranged from 6 to 55 µg of Pb/g of dryer lint, with a geometric mean of 18 µg/g. The distribution of lead levels from the Bissel group was also determined to be lognormal using a χ2 test [χ2 (computed) ) 0.40; 1 degree of freedom; P ) 0.05]. A two-sample t-test on the control group and Bissell Centre lead levels showed that the two populations were not significantly different from each other (p ) 0.52). Data from Homes of Radiator Repair Workers. A dozen shops advertising radiator repair services in Edmonton were contacted regarding participation in this study. Seven shops agreed to cooperate, and we obtained 30 dryer lint samples from 12 volunteer participants in six of these shops. The facilities were all small, generally with six or fewer employees. Managers at all of the shops were aware of concerns about exposure by workers to elevated levels of lead: one of the shops had made substantial changes to the shop environment in response to occupational health and safety concerns several years previously. The distribution of lead levels in samples from the homes of radiator shop employees (Figure 1) ranged from 11 to 1593 µg of Pb/g of dryer lint. Table 1 summarizes the ranges and mean values for lead levels in the radiator shop group relative to the other two populations. Figure 2 shows that there was a substantial difference in the distribution of levels found in primary workers (i.e., mechanics working directly with solder) and secondary workers (i.e., clerical, office or managerial workers). The geometric mean value for secondary radiator workers was 41.5 µg/g, although there were too few data points to do a χ2 analysis. A two-sample t-test showed that the secondary radiator worker population was significantly different (p ) 0.027) from the control group. Figure 2 shows clearly that levels are much VOL. 32, NO. 16, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 4. Confocal laser scanning micrograph of particle adhering to lint fiber (top). After focusing laser beam on it, the particle melted, suggesting it was a piece of solder (bottom). higher and more variable for radiator workers with primary exposure. This primary worker population did not have a log-normal distribution [χ2 (computed) ) 14.14; 1 degree of freedom; P ) 0.05]. Variability likely reflects differences in occupational exposure and industrial and personal hygiene. The substantial increase in lead dryer lint values in the homes of radiator shop employees suggests that workers are bringing lead home, with potential health risks for themselves and family members. While many of the primary lead 2470

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workers wore coveralls at work, some did not take them off before going homesand none of the workers we interviewed changed socks or footwear before going home. This is consistent with our preliminary 1994 data, which showed extreme elevation of lead levels in car floormat sweepings and household dust for radiator shop employees. With the assistance of environmental health professionals from the Capital Health Authority, six individuals who had at least one household dryer lint sample with a level greater

TABLE 1. Lead Levels in Laundry Dryer Lint for Three Populations: Control Group, Bissell Centre Communal Dryers, and Radiator Shop Employees

sample population

n

arithmetic mean (µg/g)

geometric mean (µg/g)

control group Bissel Centre radiator shop secondary exposure primary exposure

53 22

23.8 21.4

20.2 18.5

12 18

63.1 349.0

41.5 379.8

95% confidence interval (µg/g) for geometric mean

range (µg/g)

17-24 15-24

6-110 6-55

23-76 272-531

9-218 11-1593

TABLE 2. Blood Lead Levels for Radiator Shop Employees with Elevated Levels of Lead in Laundry Dryer Lint subject

description

exposure

no. of dryer lint samples

lint lead range (µg/g)

blood lead level (µg/dL)

1 2 3 4 5 6 7

adult male adult male adult female 4 year old 7 year old adult male adult female

radiator mechanic radiator mechanic wife of subject 2 child of subject 2 child of subject 2 radiator mechanic wife of subject 6

2 4 4 4 4 2 2

710-1569 120-371 120-371 120-371 120-371 216-329 216-329

52 35 4 18 12 18 7

FIGURE 5. Backscattered electron image micrograph, showing the metal particle as a bright area on the fiber.

Source of Lead in Dryer Lint. Our dryer lint samples were heterogeneous mixtures of cotton and synthetic fibers, hair, and other material. Figure 3 shows a scanning electron micrograph of the predominant cotton fibers in one of our typical lint samples. The low levels of lead in lint samples from the control group, who had no known occupational or recreational exposure, could come from a variety of sources. Due to the ubiquitous nature of lead in Canadian urban environments (2), the lead may be picked up on clothing due to normal activity. Homes in the control group varied in age from 3 to more than 80 years old, and no meaningful correlation between age of home and lint lead levels was found. Such a correlation might be expected if lead-based paint were a significant source of the background dryer lint lead. Background levels of lead in soils and dust in Canadian urban environments are variable, with typical values ranging from 100 to 300 µg/g in rural environments to over 1000 µg/g in urban environments (3). A marked decline in background lead levels in air has been seen since lead additives in gasoline were essentially eliminated in Canadian cities at the end of 1990. Finally, it is possible that the clothing contains some lead prior to being worn, due either to the phtyoextraction capacity of cotton plants, or subsequent processing of fabric. To determine whether the lead in the lint might be present prior to environmental exposure, 10 new cotton fabric samples of different colors were purchased from a fabric store, digested in concentrated nitric acid and analyzed for lead by AAS. While lead values ranged from 2 to 5 µg of Pb/g of fabric, they were not reliably above the limit of detection, set as 3σ above the average concentration found in method blanks.

than 200 µg/g (10 times the geometric mean value for the control group) were contacted and offered the opportunity to obtain blood lead levels for themselves and family members. Sixteen referrals to medical laboratories were made (five employees and 11 family members). Seven of the sixteen followed through with providing blood samples. Results are given in Table 2, with the corresponding range of lead levels in household dryer lint from these homes. Subjects 1 and 4 were over the recommended action thresholds for their ages, and were referred to physicians for further assessment and/or treatment. Subject 1 was subsequently found to have been previously treated for lead poisoning.

Several of the radiator employee lint samples were examined by optical and scanning electron microscopy to identify and characterize the lead-rich particles. Some of the larger lead-rich particles were identified by confocal laser scanning microscopy. A 10 µm particle attached to a cloth fiber is shown in Figure 4. Subsequent focusing of a laser beam on the particle caused it to melt, suggesting it was a piece of solder. Further characterization of the lead-rich particles was obtained by SEM (scanning electron microscopy) combined with XRF (X-ray fluorescence spectroscopy). The backscattered electron image in Figure 5 shows a bright area on the fiber, which XRF showed to contain both lead and tin, confirming that the origin of this particle is leadbased solder. Radiator employee lint samples showed large VOL. 32, NO. 16, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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variability between laundry loads from the same household, suggesting that direct deposition of lead onto clothing at the workplace may be the primary mechanism for introduction of lead into these lint samples. It is remarkable that relatively high levels of lead from an occupational source such as solder remain in the dryer lint, which is formed as a result of extremely vigorous agitation of fabrics in the washing and drying processes. Indeed, an alternative pathway for lead from the clothing of radiator workers to reach the dryer lint is through accumulation in the dust of their basements or laundry rooms, with subsequent uptake through the air intake of the dryer, followed by filtering and entrapment on the dryer lint (20). However, the high load-to-load variation in dryer lint lead noted above suggests that this alternative pathway is less likely. Dryer Lint as an Environmental Lead Indicator: Advantages and Disadvantages. Existing environmental lead screening matrixes include soil, household dust, paint, air, water, and food. Soil and household dust data are particularly important in risk assessment for young children, since a substantial percentage of their lead burden comes from dust ingested as a result of hand-to-mouth activity (21). Thus soil and dust levels are central indicators in risk assessment tools such as the IEUBK Model for Lead in Children (12). While sampling and analysis protocols for the determination of lead in soils have become standardized, household dust determinations pose unique difficulties. Samples are inherently heterogeneous, and many standard samplers, including household vacuum cleaners, trap only the larger particles and redistribute the smaller ones. Thus, consistent protocols for collection and analysis of household dust have been difficult to establish. Both dust lead concentrations and dust lead loading have been measured by different research groups, and it has been suggested that dust lead loading levels do not provide a meaningful sampling method for risk assessment (22). The collection of dust samples is best carried out by a trained technician, using a dedicated sampler and consistent protocols to ensure uniformity. As with other environmental matrices, dryer lint has both advantages and disadvantages as an indicator for levels of lead in the immediate environment of young children. Protocols for the use of dust and soil levels as environmental indicators require certain assumptions about relative exposure of children to home, outdoor, playground, daycare, and other environments. One potentially significant advantage of utilizing samples derived from children’s clothing is that clothing may more accurately reflect the variability resulting from the composite patterns of exposure of the occupants of a particular household. From a toxicological perspective, the most definitive indicators of both exposure and health risk are obtained from direct measures of lead in human subjects. A variety of methods have been employed, including lead in blood (PbB), Erythrocyte Protoporphrin (EP) levels, lead in shed teeth, chelatable lead, lead in hair, and the determination of accumulated body lead by the X-ray fluorescence analysis of bones. PbB determinations are usually considered to be the best single measure of recent (1-3 months) lead exposure as well as the toxicologically active fraction of lead burden in various soft tissues (3). Unfortunately, these definitive indicators are also the most intrusive, and require health care professionals to obtain samples. It is not surprising that participation in screening programs involving relatively intrusive techniques is often discouragingly low. A recent study of California workplaces estimated that only 2.6% of 52 700 facilities reporting lead-using process had ever done any environmental monitoring for lead (23). Due to the cost and insufficient evidence for effectiveness of comprehensive blood level screening programs, the Canadian Working Group on Lead has recommended that blood level screening of 2472

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children in the general Canadian population not be undertaken (3). This is in contrast to the U.S. CDC recommendation to undertake universal screening of children. The principal advantage of selectively adding laundry dryer lint to the toolbox for preliminary screening is that collection and analysis of samples is simple, inexpensive, and nonintrusive relative to presently used approaches. This would not replace, but rather complement, existing first stage indicators, by providing a new screening tool where samples can be easily collected by individuals in their own homes and sent or given to a laboratory for a relatively inexpensive analysis. The more definitive (and intrusive) indicators could be used in second stage screening for individuals in houses or geographic areas targeted by elevated lint levels. The apparent advantages of the dryer lint matrix warrant its consideration as one component of the EPA-integrated national implementation plan, which includes substantial emphasis on lead indicator monitoring. The EPA approach is based on elevated blood lead (EBL) level surveillance to identify geographic “hot spots”, areas with concentrations of EBL cases and lead-based paint contaminated housing. Selective use of screening through the dryer lint matrix would help locate geographic “hot spots” in an inexpensive and nonintrusive manner. A second major goal of the EPA plan is public awareness enhancement (24). Anecdotal experience from this pilot study indicates that the adult participants who were directly involved in collecting and submitting their own samples became keenly interested in the findings and their implications for their health and that of their families. Dryer lint also has obvious limitations as a matrix for heavy-metal screening. Lint samples are highly variable and inherently inhomogeneous, consisting of cloth fibers, hairs, and miscellaneous material. Clothes dryer lint will only reflect individual exposure if laundry is sorted by individual, which is not normally done. Variability within samples taken from a particular home will reflect the nature of the clothing being laundered, as well as the differences in seasonal activity, particularly for children. One would expect lead level differences resulting from different types of clothing, the age of individuals, and the nature of their activities. Socks and pants, for example, might show elevated levels due to occupational exposure for employees who do not change their clothes at work and also for children who play in dirt or dust contaminated with lead. While mean values for different homes may reveal important differences in exposure, the presence of spikes in samples from a particular home may be even more important. Dryer lint will not reveal lead exposure from water or dietary sources, and it will simply indicate existing lead in the environment of a child rather than accumulated lead burdens. This pilot study established background levels of lead in laundry dryer lint from a Canadian urban environment, successfully identified households with elevated lead levels resulting from the transport of occupational lead by an adult family member, and utilized scanning electron microscopy to identify the form of the lead particles. To integrate this novel matrix into comprehensive risk assessment strategies, correlations first must be established between lead levels in dryer lint and lead sources (e.g., household dust, soils, leadbased paints) or biological indicators (e.g., PbB levels). Further work is in progress in our laboratories to establish quantitative correlations, to explore whether this matrix will prove useful in the risk assessment of other metals of toxicological concern, such as cadmium, and to further characterize the lead species involved. Speciation studies will help assess the bioavailability and toxicity of the environmental lead, and assist in apportioning sources (25, 26).

Acknowledgments We thank the King’s University College Chemistry 440 students for their participation in the early stages of data collection and analysis and Cindy Slupsky for her assistance throughout. We also thank Elson Zazulak from Capital Health for his assistance with blood lead sampling and follow-up work with radiator employees. Larry Derkach from the Bissell Centre provided lint samples from the communal dryers. Financial support was provided by a summer research grant from the PEW Foundation and The King’s University College.

(13) (14) (15) (16) (17)

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Children; EPA 540-R-93-081; National Technical Information Service: Springfield, VA, 1994; pp 1-2. Center for Disease Control. Preventing Lead Poisoning in Young Children: A Statement by the Centers for Disease Control, Department of Health and Human Services; Atlanta, GA, 1991. Cherimisinoff, P. N.; Cherimisinoff, N. P. Lead: A Guidebook to Hazard Detection, Remediation and Control; Prentice Hall: Englewood Cliffs, NJ, 1993; pp 119-121. Nanda Kumar, P. B. A.; Dushenkov, V.; Motto, H.; Raskin, I. Environ. Sci. Technol. 1995, 29, 1232-1238. Jorhem, L. J. AOAC Int. 1993, 76 (4), 798-813. Keith, L. H. Environmental Sampling and Analysis; Lewis: Chelsea, MI, 1991; Chapter 10. Munoz, V. A.; Lam, W. W.; Payette, C.; Mikula, R. J. Proceedings of the 49th EMSA and 25th MAS, San Jose, CA, 1991. Mikula, R. J.; Munoz, V. A.; Lam, W. W. J. Can. Pet. Technol. 1989, 28 (6), 29-32. We are grateful to a referee for suggesting this alternative pathway. Thornton, I.; Watt, J. M.; Davies, D. J. A.; Hunt, A.; Cotter-Howells, J.; Johnson, D. L. Environ. Geochem. Health 1994, 16 (3/4), 113122. Sutton, P. M.; Anthanasoulis, M.; Flessel, P.; Guirguis, G.; Haan, M.; Schlag, R.; Goldman, L. R. Environ. Res. 1995. 68, 45-57. Rudolph, L.; Sharp, D. S.; Samuels, S.; Perkins, C.; Rosenberg, J. Am. J. Public Health 1990, 80 (8) 921-925. Cook, B. T. In Lead Poisoning: Exposure, Abatement, Regulation; Breen, J. J.; Stroup, C. R., Eds.; CRC Press: Boca Raton, FL, 1995; pp 86-87. Hunt, A.; Johnson, D. L.; Watt, J. M.; Thornton, I. Environ. Sci. Technol. 1992, 26, 1513-1523. Manceau, A.; Boisset, M.; Sarret, G.; Hazemann, J.; Mench, M.; Cambier, P.; Prost, R. Environ. Sci. Technol. 1996, 30, 15401552.

Received for review August 6, 1997. Revised manuscript received May 14, 1998. Accepted May 26, 1998. ES970699H

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