- Email: [email protected]
A comparison of five toxic metals among rural and urban children
Enrironmental Pollution (Series A) 29 (1982) 261 269
A COMPARISON RURAL
OF FIVE TOXIC METALS AMONG AND URBAN CHILDREN
M. RHONDA FOLIO, CYNTHIA HENN1GAN Tennessee Technological University, Cookeville, Tennessee 38501, USA &
JOHN ERRERA Bio-Medical Data, Inc., West Chicago, Illinois 60185, USA
ABSTRACT
Five toxic metals among populations of urban and rural children sampled from Middle Tennessee are compared. Children were asked to submit a small sample of hair for toxic metal analysis. Hair samples were collected by the researchers and then submitted to Bio-Medical Data, Inc., where they were analysed by three proeedures: plasma torch, graphite furnace, and atomic absorption spectroscopy. Lead and cadmium levels were significantly higher in the urban group, while the rural group demonstrated a significantly higher mean arsenic level. No significant difference existed between the two groups for nickel and mercury. Wider ranges of lead and cadmium concentrations were exhibited in the urban group, while the ranges for arsenic, mercury, and nickel were greater in the rural group. Combinations of metals were found in both groups. The most frequent combinations were a 13 % oceurrence of cadmium and lead in the urban group and a 7 % occurrence of arsenic and lead in the rural group. Sources of exposure for rural and urban groups are discussed. It was concluded that metals can be elevated in combinations, thus possibly increasing their harmful effects. When screening children for toxic substances, other metals such as cadmium and arsenic must be considered as accompanying lead.
INTRODUCTION
When lead or any other metal is present in the body in excessive amounts, toxic reactions may result. Additionally, a toxic metal may have a negative combining 261 Environ. Pollut. Set. A. 0143-1471/82/0029-0261/$02.75 © Applied Science Publishers Ltd, England, 1982 Printed in Great Britain
262
M. RHONDA FOLIO, CYNTHIA HENNIGAN, JOHN ERRERA
effect with another metal which produces an even higher total toxic level (Doctor's Data, Inc., 1980). The Surgeon General reported that in 1974 more than 400,000 American children having elevated lead would undergo treatment for some degree of lead poisoning (Graham & Graham, 1974). The majority of research regarding toxic metals among children has concentrated on lead. Although lead is not unique to any one population in particular, urban populations have been found to have consistently higher body burdens than either suburban or rural populations (Hofreuter et al., 1961; Cohen et al., 1973; de la Burde & Reames, 1973; Angle & Mclntyre, 1974; Smith et al., 1976; Perrin & Merkins, 1979; Needleman et al., 1979). Frequently, elevated lead levels are found in combination with elevated levels of other toxic metals, such as cadmium, arsenic and mercury (Lin-Fu, 1975). Few studies comparing combined elevated metal levels in rural and urban children have been reported. Studying combinations of elevated toxic metals is of relevance since combinations can sometimes be traced to a common source of exposure. The effects of combined toxic metals can be deleterious to the health of any individual. For example, arsenic is known as a metabolic inhibitor and a cellular and enzyme poison. Cadmium has been shown to damage heart and blood vessel structure, block appetite and smell centres and interfere with calcium metabolism. The effects from cadmium also include hypertension. The ill effects of lead have long been known. Its most significant effect is experienced in the central nervous system. Children, in particular, are at high risk of brain damage when massive amounts of lead accumulate in the body and reports are increasingly suggesting that large numbers are sustaining unrecognised neurological and behavioural impairment as a result of low-level exposure to lead (Needleman & Piomelli, 1978; Marlowe et al., 1980). The incidence of slightly elevated lead and accompanying elevated toxic metals remains unclear. Purpose
Most reports of lead poisoning or exposure to lead hazards have been from urban settings, with the prevalence of lead and other toxics in rural populations remaining unclear. The purpose of this study was to compare five toxic metals--lead, cadmium, mercury, nickel and arsenic--among populations of urban and rural children. Limitations
There were limiting factors in this study, including a relatively small sample size, and subjects unmatched for age, or IQ. Ninety percent of subjects were receiving special education related to mild learning problems. They were unable to be matched for sex due to a number of parents not giving permission for their children
TOXIC METALS IN RURAL AND URBAN CHILDREN
263
to participate in the study. However, Heinrich (1979) found sex not to be a variable in undue lead absorption.
METHODS
Su bjecIs Two areas of Middle Tennessee were randomly selected from which to choose subjects. The two geographical locations included an urban and a rural setting. The metropolitan county included 23 subjects from a centrally located semi-industrial area. The rural group consisted o f 67 subjects from a three-county region located adjacent to each other. A larger number of subjects was selected from the rural area due to the sparsity of the population. The total number of subjects included was 90. The ages of the urban children ranged from 1 to 4 years with a mean age of 2.4. The age range for rural subjects was 4 to 16 years with a mean age of 11.3. There were 10 females and 13 males in the urban group and 22 females and 45 males in the rural group. Subjects in both groups came primarily from the middle to lower socioeconomic levels. Residences occupied by urban subjects were classified as moderate-to-low income housing. Rural subjects were from counties where the residents were engaged in agriculturally related occupations. Rural subjects resided in moderate-to-low income housing on farms and in relatively isolated areas.
Classification of subjects' toxic metals Amounts of toxic metal in the subjects were determined via hair analysis. Numerous studies have been conducted using this method, since scalp hair is a valuable tissue for monitoring human environmental exposure to toxic metals. The determination of trace elements in the hair can be used to evaluate the total body accumulation due to exposure. Trace elements, in particular, are accumulated in hair at concentrations that are generally at least ten times higher than those present in blood or urine (Maugh, 1978).
Data collection procedures After obtaining written permission from subjects' parents, hair samples were collected at the schools or day care centres they attended. Hair was cut with stainless steel barber's scissors from the nape of the subject's neck as close to the scalp as possible, no further than 2.5 cm. About 40 mg were collected for analysis. Samples of hair were taken from at least 7 different locations on the back of the neck to account for variations in concentrations of trace metals in human hair. Hair samples were placed in specifically designed storage envelopes. Samples were submitted to Bio-Medical Data, Inc., a CDC licensed hair analysis laboratory in West Chicago, Illinois. Prior to toxic metal analysis, hair samples were washed with detergent and acetone to remove outside toxic metal contaminants. Hair was then
264
M. RHONDA FOLIO, CYNTHIA HENNIGAN, JOHN ERRERA
dried and weighed, and the samples were analysed via the vacuum induction coupled plasma torch for the five toxic metals. Precise laboratory techniques were used in analysis to ensure reliability of results and to meet reproducibility requirements. These included: 1. 2. 3.
4. 5.
6. 7. 8.
A blind sample was run from the initial steps through the entire procedure to assure reproducibility of methods. At least one of every three tests was a standard. Working standards were made to ensure proper value. The in-house pool of analytical reagents was completely remade and analysed monthly to eliminate the possibility of precipitating elements and to ensure reproducibility. Temperature and humidity were controlled to ensure reliability and consistency of the testing instruments. The hair samples were weighed to a thousandth of a gram (0.001 g is equal to approximately four hairs, 2.5 cm long) and only volumetric flasks, the most accurate available, were used in diluting the ashed sample. Lot number control sheets for all reagents were used to ensure uniformity. Records were kept and are available for inspection. All glasswater was acid-washed in-house before use and between each use, including acid pre-washed disposable test tubes. The water used at Bio-Medical Data, Inc., was virtually mineral-free, rated at 18 + MEG.
Reports summarising the significant findings of the hair analysis for each subject were received from Bio-Medical Data, Inc. subsequentlto analysis. The report from Bio-Medical Data, Inc. summarised the significant findings related to the five toxic metals, based on a statistical comparison of the levels determined in the present analysis by Doctor's Data with those observed in a random healthy population. If the analysis indicated any of these elements to be above the generally accepted upper limits, the element was printed on the report and supplemental information was enclosed with the report. Additionally, this section of the report listed both the observed hair metal level and the suggested upper limit for each metal and plotted each level in relation to the upper limit. H a i r as a diagnostic tool
A large number of elements are found in detectable amounts in human tissues. Hair, in particular, contains a higher concentration of many of these elements, as it is generally the last tissue where elements are stored after storage and passage through the body's other tissues. Scalp hair has several characteristics as an ideal tissue for study in that it is painlessly removed, normally discarded, easily collected, and its contents can be analysed relatively easily (Hammer et al., 1971). The best results have been obtained with heavy metal pollutants such as lead. Numerous
TOXIC METALS IN RURAL AND URBAN CHILDREN
265
investigations worldwide have shown that concentrations of lead and other heavy metals in the hair provide an accurate and relatively permanent record of exposure, and that there is a strong correlation between concentrations in hair and those in internal organs (Kyle & Pease, 1966; Schroeder & Nason, 1969). Many studies have used blood analysis in determining lead levels, although recent reports have indicated that blood is not a reliable index of previous exposure (Vitale et al., 1975; Chisolm, 1976). Blood lead levels may return to normal even though exposure has occurred. This is indicated when clearance of metals from the blood into storage compartments of the body, such as bone, kidney, and liver, occurs. After lead has been stored, blood lead readings may not provide an accurate measure of the total body burden of lead or other toxic metals. A strong correlation between hair and blood concentrations exists generally for individuals who are in a steady state regarding intake and excretion of lead (Chattopadhyay et al., 1977). Hair lead levels are elevated in subjects with chronic lead poisoning and those with elevated lead (Kopito et al., 1967; Pueschel et al., 1972).
RESULTS
Rural and urban groups of children were compared for five toxic metal concentrations to test the hypothesis for differences in five toxic metals for the two groups. The data were analysed by a computerised statistical package for the Social Sciences (SPSS) using a t test for two independent means. The t test was used to determine whether the two means were significantly different at the 0.05 level. Mean toxic metal levels were used since values for upper levels were established by Doctor's Data on a normally healthy random sample of the population based on age and sex for each toxic metal. Significant differences were found for three toxic metals for the two groups. No significant differences were indicated for two toxic metals. Figure 1 graphically TABLE 1 t TEST FOR INDEPENDENT MEANS BETWEEN URBAN AND RURAL CHILDREN FOR FIVE TOXIC METALS
Metal
Lead Arsenic Cadmium Mercury Nickel * P < 0.05. ** P < 0.01.
Number of cases
Means
Standard deviation
Urban
Rural
Urban
Rural
Urban
Rural
23 23 23 23 23
67 67 67 67 67
24.61 0-07 1-62 0.03 0.25
13.19 0.27 0.46 0.21 1.39 '
25-58 0.10 2.92 0-03 0.28
8.59 0.46 0.60 0.48 5.90
t test
Degrees of freedom
Significance level
3.20 2-09 3-09 1.73 0.92
88 88 88 88 88
0.002** 0-04* 0.003** 0.08 0.36
266
M. RHONDA FOLIO, CYNTHIA HENNIGAN, JOHN ERRERA 25 20 Rural
15 I0
Urban
5 1 .75
\
.50 #
.25 .15 .10 .05 0 Arsenic
Lead
Cadmi um
Fig. 1. Comparison of three toxic metal levels between urban and rural children.
displays the levels of the three significantly different toxic metals for the urban and rural groups. Table I gives the results for toxic metals in urban and rural groups. Relevant data, the mean, standard deviation, t value, degrees of freedom and significance level for each of the five toxic metals shown are indicated. Table 2 shows the ranges between groups for toxic metals. TABLE 2 RANGES OF FIVE TOXIC METAL LEVELS IN URBAN AND RURAL CHILDREN IN
Group Urban Rural
Lead
Arsenic
Cadmium
1.81-91.42 0.50-35.59
0-01-0.34 0.01-3.00
0.01-12.55 0.01-2.97
Mercury 0.01--0.04 0.01-2.92
ppm
Nickel 0.01-1.24 0.01-46.70
DISCUSSION
The findings of this study are consistent with those of previous studies of the toxic metals of lead and cadmium levels in urban and rural subjects. Another important fact, not clearly presented in previous studies, is the difference in arsenic, with the rural group exhibiting the highest level. The fact that combinations of toxic metals were found in both groups clearly indicates that screening for lead alone is not sufficient since combined toxic metals can be deleterious to the health of the child. This suggests implications for screening procedures to be revised. Also toxic metals among rural populations present a health concern which rural health officials need to address.
TOXIC METALS IN RURAL AND URBAN CHILDREN
267
Sources of subjects' exposure Most probably, elevated lead levels in the urban children were related to sources of lead commonly found in urban settings, such as lead-based paint, lead in gasoline, and pollution from industry. Several subjects who were living in houses built prior to 1950 were suspected of being exposed to lead from lead-based paint, and several who lived near major roadways may have been exposed to lead from automobile exhaust fumes. Elevated lead levels in rural subjects were thought to be related to emissions from farm machinery run on leaded gasoline and to the use of insecticides, fungicides, herbicides and defoliants. The higher incidence of cadmium in the urban group and the greater occurrence of elevated arsenic levels in the rural subjects were thought to bc related to the sources usually associated with the metals. Automobile exhaust and industrial pollution were probable sources of cadmium for the urban subjects; and fungicides and pesticides, activities associated with the mining industry and the burning of coal for fuel, were suspected sources of arsenic for rural subjects. Another potential source of lead exposure for the rural group was illicitly distilled whisky. 'Moonshine' is still widely consumed in Appalachian Tennessee (Heinrich, 1979). Forty per cent of all illicit whisky contains concentrations of lead salts (Carr, 1972), and cases of lead poisoning have resulted from its consumption. Public health officials have reported that illicit whisky is sometimes given to children for medicinal purposes by their parents. Some pregnant women were reported to drink it to alleviate the discomforts of pregnancy. This is a widespread Appalachian cultural practice which poses a prenatal hazard since lead has been shown to cross the placenta and concentrate in the foetus (Rom, 1976). Combinations of lead and arsenic in the rural subjects raises the issue of exposure resulting from fertiliser and pesticide applications containing these toxic metals. A staple garden food in the region where the rural group resided is potatoes. Lead arsenite has been used as a defoliant for potatoes in years when the autumn is wet and the haulms do not die back adequately. Combinations of arsenic and lead can result from coal burning. By-products of soft coal combustion are airborne lead and arsenic. It has been demonstrated that when arsenic and lead occupy the same biological site, arsenic tends to increase the toxicity and absorption of lead (Sittig, 1976). As a result of inhaling airborne arsenic, subjects may have increased their body burdens of lead. The sources mentioned warrant further investigation, since the average daily intake of lead from diet and air amounts to one-half to two-thirds of the daily permissible intake for children. This leaves a very narrow margin of safety for lead absorption (King, 1971). Lastly, the problems of elevated toxic metals among rural children must be considered as part of the problem with the entire cultural characteristics which leave many Appalachian populations apathetic, unmotivated and uneducated as to the hazards of their environment. These toxic metals should also be considered as being
268
M. RHONDA FOLIO, CYNTHIA HENNIGAN, JOHN ERRERA
possibly linked to lowered intelligence among such populations since lead, in particular, has been found to be elevated among mentally retarded children in rural areas (Routh et al., 1979; Marlowe et al., 1980). The fact that other toxic metals can combine presents a hazardous future to rural children. Public knowledge about these problems and conditions must be developed and an interest on the part of public health officials and educators to make these populations aware of protecting themselves from environmental hazards. More rural studies are needed to identify, more precisely, the sources of toxic metals and to identify populations at risk. Additionally, more comparative studies of urban and rural populations would be useful in determining the causes of different levels of toxic metal intake. Such factors as possible differences in nutrition or in genetically determined rates of absorption and excretion of lead and other toxic metals should be further explored. More research is also needed to clarify the interaction of other metals with lead. Though knowledge concerning the factors related to toxic metal absorption has grown considerably over the past several years, more research studies are needed to understand the problem fully. The value of human health is incalculable. To ignore the threat posed by toxic metals is to risk the health of all human beings.
ACKNOWLEDGEMENTS
The Department of Civil Engineering at Tennessee Technological University and Dr Paul Bonner cooperated with this project by surveying the home environments of rural subjects. Also, assistance and consultation concerning trace mineral analysis of hair was provided by Bob Smith of Bio-Medical Data, Inc. This work was funded by a Tennessee Technological University Faculty Research Grant.
REFEREN CES
ANGLE, C. R. & MCINTYRE, M. S. (1974). Lead in air, dustfall, soil, house dust, milk and water. Proceedings of the University of Missouri's 8th Annual Conference on Trace Substances in Environmental Health, 8, 23-9.
DELABURDE,B. & REAI~S,B. (1973). Preventionof pica, the major causes of lead poisoning in children. Am. J. Publ. Hlth, 63, 737-43. CARR,J. (1972). The second oldest profession: An informal history of moonshine in America. Englewood Cliffs, New Jersey, Prentice Hall. CHATTOPADHYAY,A., ROBERTS,T. M. 8£ JERVIS,R. E. (1977). Scalp hair as a monitor of community exposure to lead. Arch. environ. Hlth, 31, 226-36. CHISOLM,J. (1976). Current status of lead exposure and poisoning in children. Southern Medical J., 69, 528-31. COHEN,C. J., BOWERS,G. N. & LEPOW,M. L. (1973). Epidemiologyof lead poisoning. J. Am. reed. Ass., 226, 1430--3. DOCTOR'SDATA,INC. 0980). Nutrient mineral level and toxic metal level laboratory reference. West Chicago, Illinois.
TOXIC METALS IN RURAL AND URBAN CHILDREN
269
GRAHAM,A. & GRAHAM,F. (1974). Lead poisoning and the suburban child. Today's Health, 52, 38-41. HAMMER, D. I., FINKLEA, J. F., HENDRICKS, R. H., SHY, C. M. & HORTON, R. (1971). Hair trace metal levels and environmental exposure. Am. J. Epidemiol., 93, 84-92. HEINRICH, W. S. (1979). The detection and management of children exposed to low body burdens of lead. Master's thesis, Tennessee Technological University. HOFREUTER, D. H., COTCOTT, E. J., KEENAN,R. G. & XINTARAS,C. (1961). The public health significance of atmospheric lead. Arch. environ. Hlth, 3, 568-74. KING, B. G. (1971 ). Maximum daily intake of lead without excessive body lead burden in children. Am. J. Dis. ChiM., 122, 337 40. KOPtTO, L., BYERS,R. & SHWACHMAN,H. (1967). Lead in hair of children with chronic lead poisoning. New England J. Medicine, 276, 949 53. KYLE, R. A. & PEASE, G. L. (1966). Hematologic aspects of arsenic intoxication. New England J. Medicine, 273, 18-23. LIN-Fu, J. S. (1975). Undue lead absorption and lead poisoning. Paper presented at the International Conference on Heavy Metals in the Environment, Toronto, 27-3l October 1975. MARLOWE, M., FOLIO, M. R. & HEINRICH, S. (1980). Low elevated lead levels in mentally retarded Appalachian children. Educational Catalyst, 10, 13 19. MAUGH, T. H. (1978). Hair: A diagnostic tool to complement blood serum and urine. Science, N.Y., 202, 1271-3. NEEDLEMAN, H. L., GUNNOL, C., LEVITON,A., REED, R., PERESIE,n., MAHER,C. & BARRETT, P. (1979). Deficits in psychologic and classroom performance of children with elevated dentine lead levels. New England J. Medicine, 300, 689-95. NEEDLEMAN, H. L. & PIOMELLI,S. (1978). The effects of low level lead exposure. New York, NY, Natural Resources Defence Council PERRIN, J. M. & MERKINS, M. J. (1979). Blood lead levels in a rural population; Relative elevations among migrant farmworkers' children. Pediatrics, 64, 540-2. PUESCHEL, S. M., KOPITO, M. S. & SHWACHMAN, H. (1972). Children with increased lead burden: A screening and follow-up study. J. Am. Med. Ass., 222, 150-4. ROM, W. N. (1976). Effects of lead on the female and reproduction: A review. Mount Sinai J. Med., 43, 542-52. ROUTH, C. K., MUSHAK, P. & BOONE, L. (1979). A new syndrome of elevated blood lead and microcephaly. J. Ped. Psych., 4, 67-76. SCHROEDER, H. A. & NASON,A. P. (1969). Trace metals in human hair. J. Investigative Dermatology, 53, 71-8. SITTIG, M. (1976). Toxic metals: pollution control and worker protection. Park Ridge, N J, Nayes Data Corporation. SMITH, P. J., NELSON, D. M. & STEWART,R. E. (1976). Lead poisoning among migrant children in New York State. Am. J. Pub. Hlth, 66, 383-4. VITALE, L. F., JOSELOW, M. N., WEDEEN, R. P. & METHODI, P. (1975). Blood lead: an inadequate measure of occupational exposure. J. occup. Med., 17, 155-6.
A COMPARISON RURAL
OF FIVE TOXIC METALS AMONG AND URBAN CHILDREN
M. RHONDA FOLIO, CYNTHIA HENN1GAN Tennessee Technological University, Cookeville, Tennessee 38501, USA &
JOHN ERRERA Bio-Medical Data, Inc., West Chicago, Illinois 60185, USA
ABSTRACT
Five toxic metals among populations of urban and rural children sampled from Middle Tennessee are compared. Children were asked to submit a small sample of hair for toxic metal analysis. Hair samples were collected by the researchers and then submitted to Bio-Medical Data, Inc., where they were analysed by three proeedures: plasma torch, graphite furnace, and atomic absorption spectroscopy. Lead and cadmium levels were significantly higher in the urban group, while the rural group demonstrated a significantly higher mean arsenic level. No significant difference existed between the two groups for nickel and mercury. Wider ranges of lead and cadmium concentrations were exhibited in the urban group, while the ranges for arsenic, mercury, and nickel were greater in the rural group. Combinations of metals were found in both groups. The most frequent combinations were a 13 % oceurrence of cadmium and lead in the urban group and a 7 % occurrence of arsenic and lead in the rural group. Sources of exposure for rural and urban groups are discussed. It was concluded that metals can be elevated in combinations, thus possibly increasing their harmful effects. When screening children for toxic substances, other metals such as cadmium and arsenic must be considered as accompanying lead.
INTRODUCTION
When lead or any other metal is present in the body in excessive amounts, toxic reactions may result. Additionally, a toxic metal may have a negative combining 261 Environ. Pollut. Set. A. 0143-1471/82/0029-0261/$02.75 © Applied Science Publishers Ltd, England, 1982 Printed in Great Britain
262
M. RHONDA FOLIO, CYNTHIA HENNIGAN, JOHN ERRERA
effect with another metal which produces an even higher total toxic level (Doctor's Data, Inc., 1980). The Surgeon General reported that in 1974 more than 400,000 American children having elevated lead would undergo treatment for some degree of lead poisoning (Graham & Graham, 1974). The majority of research regarding toxic metals among children has concentrated on lead. Although lead is not unique to any one population in particular, urban populations have been found to have consistently higher body burdens than either suburban or rural populations (Hofreuter et al., 1961; Cohen et al., 1973; de la Burde & Reames, 1973; Angle & Mclntyre, 1974; Smith et al., 1976; Perrin & Merkins, 1979; Needleman et al., 1979). Frequently, elevated lead levels are found in combination with elevated levels of other toxic metals, such as cadmium, arsenic and mercury (Lin-Fu, 1975). Few studies comparing combined elevated metal levels in rural and urban children have been reported. Studying combinations of elevated toxic metals is of relevance since combinations can sometimes be traced to a common source of exposure. The effects of combined toxic metals can be deleterious to the health of any individual. For example, arsenic is known as a metabolic inhibitor and a cellular and enzyme poison. Cadmium has been shown to damage heart and blood vessel structure, block appetite and smell centres and interfere with calcium metabolism. The effects from cadmium also include hypertension. The ill effects of lead have long been known. Its most significant effect is experienced in the central nervous system. Children, in particular, are at high risk of brain damage when massive amounts of lead accumulate in the body and reports are increasingly suggesting that large numbers are sustaining unrecognised neurological and behavioural impairment as a result of low-level exposure to lead (Needleman & Piomelli, 1978; Marlowe et al., 1980). The incidence of slightly elevated lead and accompanying elevated toxic metals remains unclear. Purpose
Most reports of lead poisoning or exposure to lead hazards have been from urban settings, with the prevalence of lead and other toxics in rural populations remaining unclear. The purpose of this study was to compare five toxic metals--lead, cadmium, mercury, nickel and arsenic--among populations of urban and rural children. Limitations
There were limiting factors in this study, including a relatively small sample size, and subjects unmatched for age, or IQ. Ninety percent of subjects were receiving special education related to mild learning problems. They were unable to be matched for sex due to a number of parents not giving permission for their children
TOXIC METALS IN RURAL AND URBAN CHILDREN
263
to participate in the study. However, Heinrich (1979) found sex not to be a variable in undue lead absorption.
METHODS
Su bjecIs Two areas of Middle Tennessee were randomly selected from which to choose subjects. The two geographical locations included an urban and a rural setting. The metropolitan county included 23 subjects from a centrally located semi-industrial area. The rural group consisted o f 67 subjects from a three-county region located adjacent to each other. A larger number of subjects was selected from the rural area due to the sparsity of the population. The total number of subjects included was 90. The ages of the urban children ranged from 1 to 4 years with a mean age of 2.4. The age range for rural subjects was 4 to 16 years with a mean age of 11.3. There were 10 females and 13 males in the urban group and 22 females and 45 males in the rural group. Subjects in both groups came primarily from the middle to lower socioeconomic levels. Residences occupied by urban subjects were classified as moderate-to-low income housing. Rural subjects were from counties where the residents were engaged in agriculturally related occupations. Rural subjects resided in moderate-to-low income housing on farms and in relatively isolated areas.
Classification of subjects' toxic metals Amounts of toxic metal in the subjects were determined via hair analysis. Numerous studies have been conducted using this method, since scalp hair is a valuable tissue for monitoring human environmental exposure to toxic metals. The determination of trace elements in the hair can be used to evaluate the total body accumulation due to exposure. Trace elements, in particular, are accumulated in hair at concentrations that are generally at least ten times higher than those present in blood or urine (Maugh, 1978).
Data collection procedures After obtaining written permission from subjects' parents, hair samples were collected at the schools or day care centres they attended. Hair was cut with stainless steel barber's scissors from the nape of the subject's neck as close to the scalp as possible, no further than 2.5 cm. About 40 mg were collected for analysis. Samples of hair were taken from at least 7 different locations on the back of the neck to account for variations in concentrations of trace metals in human hair. Hair samples were placed in specifically designed storage envelopes. Samples were submitted to Bio-Medical Data, Inc., a CDC licensed hair analysis laboratory in West Chicago, Illinois. Prior to toxic metal analysis, hair samples were washed with detergent and acetone to remove outside toxic metal contaminants. Hair was then
264
M. RHONDA FOLIO, CYNTHIA HENNIGAN, JOHN ERRERA
dried and weighed, and the samples were analysed via the vacuum induction coupled plasma torch for the five toxic metals. Precise laboratory techniques were used in analysis to ensure reliability of results and to meet reproducibility requirements. These included: 1. 2. 3.
4. 5.
6. 7. 8.
A blind sample was run from the initial steps through the entire procedure to assure reproducibility of methods. At least one of every three tests was a standard. Working standards were made to ensure proper value. The in-house pool of analytical reagents was completely remade and analysed monthly to eliminate the possibility of precipitating elements and to ensure reproducibility. Temperature and humidity were controlled to ensure reliability and consistency of the testing instruments. The hair samples were weighed to a thousandth of a gram (0.001 g is equal to approximately four hairs, 2.5 cm long) and only volumetric flasks, the most accurate available, were used in diluting the ashed sample. Lot number control sheets for all reagents were used to ensure uniformity. Records were kept and are available for inspection. All glasswater was acid-washed in-house before use and between each use, including acid pre-washed disposable test tubes. The water used at Bio-Medical Data, Inc., was virtually mineral-free, rated at 18 + MEG.
Reports summarising the significant findings of the hair analysis for each subject were received from Bio-Medical Data, Inc. subsequentlto analysis. The report from Bio-Medical Data, Inc. summarised the significant findings related to the five toxic metals, based on a statistical comparison of the levels determined in the present analysis by Doctor's Data with those observed in a random healthy population. If the analysis indicated any of these elements to be above the generally accepted upper limits, the element was printed on the report and supplemental information was enclosed with the report. Additionally, this section of the report listed both the observed hair metal level and the suggested upper limit for each metal and plotted each level in relation to the upper limit. H a i r as a diagnostic tool
A large number of elements are found in detectable amounts in human tissues. Hair, in particular, contains a higher concentration of many of these elements, as it is generally the last tissue where elements are stored after storage and passage through the body's other tissues. Scalp hair has several characteristics as an ideal tissue for study in that it is painlessly removed, normally discarded, easily collected, and its contents can be analysed relatively easily (Hammer et al., 1971). The best results have been obtained with heavy metal pollutants such as lead. Numerous
TOXIC METALS IN RURAL AND URBAN CHILDREN
265
investigations worldwide have shown that concentrations of lead and other heavy metals in the hair provide an accurate and relatively permanent record of exposure, and that there is a strong correlation between concentrations in hair and those in internal organs (Kyle & Pease, 1966; Schroeder & Nason, 1969). Many studies have used blood analysis in determining lead levels, although recent reports have indicated that blood is not a reliable index of previous exposure (Vitale et al., 1975; Chisolm, 1976). Blood lead levels may return to normal even though exposure has occurred. This is indicated when clearance of metals from the blood into storage compartments of the body, such as bone, kidney, and liver, occurs. After lead has been stored, blood lead readings may not provide an accurate measure of the total body burden of lead or other toxic metals. A strong correlation between hair and blood concentrations exists generally for individuals who are in a steady state regarding intake and excretion of lead (Chattopadhyay et al., 1977). Hair lead levels are elevated in subjects with chronic lead poisoning and those with elevated lead (Kopito et al., 1967; Pueschel et al., 1972).
RESULTS
Rural and urban groups of children were compared for five toxic metal concentrations to test the hypothesis for differences in five toxic metals for the two groups. The data were analysed by a computerised statistical package for the Social Sciences (SPSS) using a t test for two independent means. The t test was used to determine whether the two means were significantly different at the 0.05 level. Mean toxic metal levels were used since values for upper levels were established by Doctor's Data on a normally healthy random sample of the population based on age and sex for each toxic metal. Significant differences were found for three toxic metals for the two groups. No significant differences were indicated for two toxic metals. Figure 1 graphically TABLE 1 t TEST FOR INDEPENDENT MEANS BETWEEN URBAN AND RURAL CHILDREN FOR FIVE TOXIC METALS
Metal
Lead Arsenic Cadmium Mercury Nickel * P < 0.05. ** P < 0.01.
Number of cases
Means
Standard deviation
Urban
Rural
Urban
Rural
Urban
Rural
23 23 23 23 23
67 67 67 67 67
24.61 0-07 1-62 0.03 0.25
13.19 0.27 0.46 0.21 1.39 '
25-58 0.10 2.92 0-03 0.28
8.59 0.46 0.60 0.48 5.90
t test
Degrees of freedom
Significance level
3.20 2-09 3-09 1.73 0.92
88 88 88 88 88
0.002** 0-04* 0.003** 0.08 0.36
266
M. RHONDA FOLIO, CYNTHIA HENNIGAN, JOHN ERRERA 25 20 Rural
15 I0
Urban
5 1 .75
\
.50 #
.25 .15 .10 .05 0 Arsenic
Lead
Cadmi um
Fig. 1. Comparison of three toxic metal levels between urban and rural children.
displays the levels of the three significantly different toxic metals for the urban and rural groups. Table I gives the results for toxic metals in urban and rural groups. Relevant data, the mean, standard deviation, t value, degrees of freedom and significance level for each of the five toxic metals shown are indicated. Table 2 shows the ranges between groups for toxic metals. TABLE 2 RANGES OF FIVE TOXIC METAL LEVELS IN URBAN AND RURAL CHILDREN IN
Group Urban Rural
Lead
Arsenic
Cadmium
1.81-91.42 0.50-35.59
0-01-0.34 0.01-3.00
0.01-12.55 0.01-2.97
Mercury 0.01--0.04 0.01-2.92
ppm
Nickel 0.01-1.24 0.01-46.70
DISCUSSION
The findings of this study are consistent with those of previous studies of the toxic metals of lead and cadmium levels in urban and rural subjects. Another important fact, not clearly presented in previous studies, is the difference in arsenic, with the rural group exhibiting the highest level. The fact that combinations of toxic metals were found in both groups clearly indicates that screening for lead alone is not sufficient since combined toxic metals can be deleterious to the health of the child. This suggests implications for screening procedures to be revised. Also toxic metals among rural populations present a health concern which rural health officials need to address.
TOXIC METALS IN RURAL AND URBAN CHILDREN
267
Sources of subjects' exposure Most probably, elevated lead levels in the urban children were related to sources of lead commonly found in urban settings, such as lead-based paint, lead in gasoline, and pollution from industry. Several subjects who were living in houses built prior to 1950 were suspected of being exposed to lead from lead-based paint, and several who lived near major roadways may have been exposed to lead from automobile exhaust fumes. Elevated lead levels in rural subjects were thought to be related to emissions from farm machinery run on leaded gasoline and to the use of insecticides, fungicides, herbicides and defoliants. The higher incidence of cadmium in the urban group and the greater occurrence of elevated arsenic levels in the rural subjects were thought to bc related to the sources usually associated with the metals. Automobile exhaust and industrial pollution were probable sources of cadmium for the urban subjects; and fungicides and pesticides, activities associated with the mining industry and the burning of coal for fuel, were suspected sources of arsenic for rural subjects. Another potential source of lead exposure for the rural group was illicitly distilled whisky. 'Moonshine' is still widely consumed in Appalachian Tennessee (Heinrich, 1979). Forty per cent of all illicit whisky contains concentrations of lead salts (Carr, 1972), and cases of lead poisoning have resulted from its consumption. Public health officials have reported that illicit whisky is sometimes given to children for medicinal purposes by their parents. Some pregnant women were reported to drink it to alleviate the discomforts of pregnancy. This is a widespread Appalachian cultural practice which poses a prenatal hazard since lead has been shown to cross the placenta and concentrate in the foetus (Rom, 1976). Combinations of lead and arsenic in the rural subjects raises the issue of exposure resulting from fertiliser and pesticide applications containing these toxic metals. A staple garden food in the region where the rural group resided is potatoes. Lead arsenite has been used as a defoliant for potatoes in years when the autumn is wet and the haulms do not die back adequately. Combinations of arsenic and lead can result from coal burning. By-products of soft coal combustion are airborne lead and arsenic. It has been demonstrated that when arsenic and lead occupy the same biological site, arsenic tends to increase the toxicity and absorption of lead (Sittig, 1976). As a result of inhaling airborne arsenic, subjects may have increased their body burdens of lead. The sources mentioned warrant further investigation, since the average daily intake of lead from diet and air amounts to one-half to two-thirds of the daily permissible intake for children. This leaves a very narrow margin of safety for lead absorption (King, 1971). Lastly, the problems of elevated toxic metals among rural children must be considered as part of the problem with the entire cultural characteristics which leave many Appalachian populations apathetic, unmotivated and uneducated as to the hazards of their environment. These toxic metals should also be considered as being
268
M. RHONDA FOLIO, CYNTHIA HENNIGAN, JOHN ERRERA
possibly linked to lowered intelligence among such populations since lead, in particular, has been found to be elevated among mentally retarded children in rural areas (Routh et al., 1979; Marlowe et al., 1980). The fact that other toxic metals can combine presents a hazardous future to rural children. Public knowledge about these problems and conditions must be developed and an interest on the part of public health officials and educators to make these populations aware of protecting themselves from environmental hazards. More rural studies are needed to identify, more precisely, the sources of toxic metals and to identify populations at risk. Additionally, more comparative studies of urban and rural populations would be useful in determining the causes of different levels of toxic metal intake. Such factors as possible differences in nutrition or in genetically determined rates of absorption and excretion of lead and other toxic metals should be further explored. More research is also needed to clarify the interaction of other metals with lead. Though knowledge concerning the factors related to toxic metal absorption has grown considerably over the past several years, more research studies are needed to understand the problem fully. The value of human health is incalculable. To ignore the threat posed by toxic metals is to risk the health of all human beings.
ACKNOWLEDGEMENTS
The Department of Civil Engineering at Tennessee Technological University and Dr Paul Bonner cooperated with this project by surveying the home environments of rural subjects. Also, assistance and consultation concerning trace mineral analysis of hair was provided by Bob Smith of Bio-Medical Data, Inc. This work was funded by a Tennessee Technological University Faculty Research Grant.
REFEREN CES
ANGLE, C. R. & MCINTYRE, M. S. (1974). Lead in air, dustfall, soil, house dust, milk and water. Proceedings of the University of Missouri's 8th Annual Conference on Trace Substances in Environmental Health, 8, 23-9.
DELABURDE,B. & REAI~S,B. (1973). Preventionof pica, the major causes of lead poisoning in children. Am. J. Publ. Hlth, 63, 737-43. CARR,J. (1972). The second oldest profession: An informal history of moonshine in America. Englewood Cliffs, New Jersey, Prentice Hall. CHATTOPADHYAY,A., ROBERTS,T. M. 8£ JERVIS,R. E. (1977). Scalp hair as a monitor of community exposure to lead. Arch. environ. Hlth, 31, 226-36. CHISOLM,J. (1976). Current status of lead exposure and poisoning in children. Southern Medical J., 69, 528-31. COHEN,C. J., BOWERS,G. N. & LEPOW,M. L. (1973). Epidemiologyof lead poisoning. J. Am. reed. Ass., 226, 1430--3. DOCTOR'SDATA,INC. 0980). Nutrient mineral level and toxic metal level laboratory reference. West Chicago, Illinois.
TOXIC METALS IN RURAL AND URBAN CHILDREN
269
GRAHAM,A. & GRAHAM,F. (1974). Lead poisoning and the suburban child. Today's Health, 52, 38-41. HAMMER, D. I., FINKLEA, J. F., HENDRICKS, R. H., SHY, C. M. & HORTON, R. (1971). Hair trace metal levels and environmental exposure. Am. J. Epidemiol., 93, 84-92. HEINRICH, W. S. (1979). The detection and management of children exposed to low body burdens of lead. Master's thesis, Tennessee Technological University. HOFREUTER, D. H., COTCOTT, E. J., KEENAN,R. G. & XINTARAS,C. (1961). The public health significance of atmospheric lead. Arch. environ. Hlth, 3, 568-74. KING, B. G. (1971 ). Maximum daily intake of lead without excessive body lead burden in children. Am. J. Dis. ChiM., 122, 337 40. KOPtTO, L., BYERS,R. & SHWACHMAN,H. (1967). Lead in hair of children with chronic lead poisoning. New England J. Medicine, 276, 949 53. KYLE, R. A. & PEASE, G. L. (1966). Hematologic aspects of arsenic intoxication. New England J. Medicine, 273, 18-23. LIN-Fu, J. S. (1975). Undue lead absorption and lead poisoning. Paper presented at the International Conference on Heavy Metals in the Environment, Toronto, 27-3l October 1975. MARLOWE, M., FOLIO, M. R. & HEINRICH, S. (1980). Low elevated lead levels in mentally retarded Appalachian children. Educational Catalyst, 10, 13 19. MAUGH, T. H. (1978). Hair: A diagnostic tool to complement blood serum and urine. Science, N.Y., 202, 1271-3. NEEDLEMAN, H. L., GUNNOL, C., LEVITON,A., REED, R., PERESIE,n., MAHER,C. & BARRETT, P. (1979). Deficits in psychologic and classroom performance of children with elevated dentine lead levels. New England J. Medicine, 300, 689-95. NEEDLEMAN, H. L. & PIOMELLI,S. (1978). The effects of low level lead exposure. New York, NY, Natural Resources Defence Council PERRIN, J. M. & MERKINS, M. J. (1979). Blood lead levels in a rural population; Relative elevations among migrant farmworkers' children. Pediatrics, 64, 540-2. PUESCHEL, S. M., KOPITO, M. S. & SHWACHMAN, H. (1972). Children with increased lead burden: A screening and follow-up study. J. Am. Med. Ass., 222, 150-4. ROM, W. N. (1976). Effects of lead on the female and reproduction: A review. Mount Sinai J. Med., 43, 542-52. ROUTH, C. K., MUSHAK, P. & BOONE, L. (1979). A new syndrome of elevated blood lead and microcephaly. J. Ped. Psych., 4, 67-76. SCHROEDER, H. A. & NASON,A. P. (1969). Trace metals in human hair. J. Investigative Dermatology, 53, 71-8. SITTIG, M. (1976). Toxic metals: pollution control and worker protection. Park Ridge, N J, Nayes Data Corporation. SMITH, P. J., NELSON, D. M. & STEWART,R. E. (1976). Lead poisoning among migrant children in New York State. Am. J. Pub. Hlth, 66, 383-4. VITALE, L. F., JOSELOW, M. N., WEDEEN, R. P. & METHODI, P. (1975). Blood lead: an inadequate measure of occupational exposure. J. occup. Med., 17, 155-6.