Introduction
Lead poisoning is a recognized threat to children
living in urban areas of the United States (1). There is, however, little
information available on the prevalence of lead poisoning in the rural
areas of the United States, particularly as it relates to point sources
such as lead mining and smelting. Ilene Danse, et al., reviewed published
literature of blood lead surveys on persons residing in proximity to lead
mining wastes and found evidence to suggest that lead found in mill tailings
(lead sulfate) is not readily bio-available and therefore poses a low risk
for children (2). In contrast to tailings, Danse, et al., found that active
smelter sites were more often associated with elevations in blood lead
levels (2).
A study of Swedish preschool children living in
a community with high lead levels from mine waste found that there was
no correlation between the mine waste and increased blood lead levels (3).
The study presented here evaluates blood lead and urine cadmium levels
in persons Diving in an abandoned lead mining, milling, and smelting area
of southwestern Missouri that is on the National Priority List of hazardous
waste sites (Superfund). A study by the EPA in 1986 reported lead soil
levels from 73 to 7,300 ppm with a mean of 2,501 ppm and cadmium from 5.9
to 250 ppm with an average of 80 ppm (4).
The Jasper County Missouri Superfund Site is a portion
of the old Tri-State Mining District of Missouri, Kansas, and Arkansas.
From the 1840s through the Civil War years, over 200 widely dispersed primitive
log smelting furnaces were operated in the Tri-State Mining District. Ore
production consisted of mining, crushing, and grinding the rock to a standard
size, ore separation, and tailings disposal. Environmental contamination
with lead and cadmium was a common by-product of these operations. Mine
production in the Missouri portion went on to reach its peak in 1916 when
over 123 million rock-tons were processed to yield approximately 304 thousand
tons of zinc concentrates and 41 tons of lead concentrates. The site is
generally characterized by extensive surface land disturbances and piles
of mine waste that resulted from the mining operations.
Disturbed areas of the Jasper County Superfund Site
in Missouri are spread over approximately 240 square miles. This mining
waste contains differing levels of residual lead and cadmium depending
upon when the mining took place. Smelting operations in the 1800s resulted
in higher levels of residual lead and cadmium in the waste than modern
smelting techniques. Approximately eight million cubic yards of waste milling
and mining products are scattered throughout the area. Some areas have
been reclaimed for residential and industrial use by leveling the remaining
piles of mine waste and incorporating the waste into the soil.
Open mine shafts, subsided areas having steep, unstable
slopes, and open pits containing deep pools of water exist throughout the
region. The general site is primarily uncontrolled and routinely used for
recreational purposes. In addition, water-quality problems result from
artesian flow of mine waters from open shafts, rainwater runoff, and seepage
from waste piles and settling ponds. Mine waste has been used as railroad
ballast, road materials, and aggregates in asphalt paving and concrete.
Sands and smaller sizes have been used for abrasives, roofing granules,
pipe coatings, filter sands, and even children's sandboxes and play areas.
Mine waste is also blown into the homes of residents in the area and is
mixed with other materials originating inside and outside the home, including
paint flakes, to form a mixture referred to in this paper as "dust".
This study hypothesized that the average soil, dust,
and blood lead and urine cadmium levels would be higher in the lead mining
area (study) than in a comparison community with no exposure to lead mining
(control). This study also hypothesized that the proportion of children
with blood lead levels above the level of concern established by the Centers
for Disease Control and Prevention (CDC) - greater than or equal to 10
[microgram]/dl - would be significantly greater in the study area than
in the control area.
Methods
The sampling frame was determined through a census
of all of the homes in both the study and control areas to ascertain individuals
eligible for the study. Individuals stratified into three age groups, 6
through 71 months (children), 6 through 14 years (youth), and 15 through
44 years (adults), were randomly selected for the study if they had lived
at their current residence at least 60 days before study commencement.
Because our primary interest was childhood lead poisoning, children were
over-sampled. TABLE Demographic Characteristic Gender Male Female Age 6-71
6-14 15-44 Race White Black Asian/Pacific Am. Income/year [less $15,000-24,999
[less Educ. [greater High Technical Some Year [greater 1960-1979 1980-present
* The study area was the Jasper County Missouri Superfund Site. It included
portions of Webb City and Joplin and all of Duenweg, and Carterville, Missouri.
The control area was chosen to be socio-economically
similar, geographically close, but physically outside the Superfund and
lead mining area. It included parts of Neosho and all of Goodman, Missouri.
Participants were interviewed and blood and urine were collected at sites
centrally located to the study and control areas. Specimen collection and
analysis were performed according to a standard protocol of the Environmental
Health Laboratory Sciences Division of the CDC, which performed the urine
cadmium and blood lead analyses using the Zeeman graphic furnace atomic
absorption method. Quality control was established by duplicate analysis
of whole blood pools, where target values were established by thermal ionization
isotopic dilution mass spectroscopy.
This study also included environmental measurements
in a sample of study and control homes for lead and cadmium in drinking
water, soil, and house dust, and for lead in interior house paint. All
environmental sampling and analysis was done by the Environmental Protection
Agency (EPA) under a standard protocol. Soil and dust were analyzed for
lead using digestion EPA SW-846 method 3050 and analysis EPA SW 846 method
7420. Lead paint was classified as present in the home if it was detected
by XRF in any areas inside the home in which the child played. The soil
lead value of 150 ppm was chosen as the background level because this value
was approximately equal to the mean plus two standard errors of the mean
from the control area. It was also the value indicated by risk assessment
to be associated with elevated blood lead levels (5). Statistical analysis
was performed using the Statistical Package for the Social Sciences (SPSS).
Statistical significance was set at .05 with two-tailed tests of significance.
Results
Demographic and socio-economic characteristics of
the study and control groups are presented in Table 1. The only characteristic
that differed between groups was age of house. A higher percentage of homes
in the study area were built prior to 1960 (p[less than].001), however
a similar percentage of homes were built after 1980. There were 412 persons
in the study group and 283 in the control group. Blood samples for lead
were obtained from 391 study and 271 controls and urine samples for cadmium
from 356 study and 249 controls. Blood samples could not be obtained from
some young children because of small veins, nor could urine samples because
some children were too young to provide adequate samples. Table 2 presents
blood lead, urine cadmium, and environmental lead and cadmium data by study
group and age class.
Environmental measurements were taken in 125 study
and 26 control homes for lead and cadmium in drinking water, soil, and
house dust, and for lead in interior house paint. Of the 125 study area
samples, 105 were randomly selected using a table of random numbers from
homes in which a child resided and 20 were tested because a child in the
household had an elevated blood lead level. All 26 tested homes in the
control area were randomly selected using a table of random numbers from
homes in which a child resided. All homes where children with elevated
blood lead levels resided received environmental testing.
All environmental measurements of lead and cadmium,
except water, were higher in the study group compared to the controls.
Lead in soil was over six times higher in the study area compared to the
control area and lead in dust and interior paint was three times higher.
Cadmium in soil and dust was also considerably higher in the study area.
Average blood lead levels in children were almost twice as high in study
area children compared to controls. Analysis of covariance indicated that
blood lead levels remained significantly higher in the study compared to
the control group after controlling for indoor paint lead levels (p = .030,
n = 179). Blood lead levels were also significantly higher after controlling
for the age of the house (p [less than] .001, n = 353). In addition, average
blood leads were significantly higher for youths and adults. Although soil
and dust cadmium levels were significantly higher in the study group, urine
cadmium levels were not statistically different between the study and control
areas for any age group. Over 84% of all children tested did not have a
detectable level of cadmium in their urine. Figure 1 shows cumulative frequency
for blood lead levels in children. In the study group, 14 percent of the
children had blood lead levels greater than 10 [microgram]/dl (the level
of concern indicated by the CDC) and 5% had levels greater than 15 microgram]/dl.
None of the control children had blood leads that were greater than 10
[microgram]/dl.
Children with elevated blood lead levels did not
have other known sources of lead exposure such as parental occupation or
hobbies, household renovation, use of lead cooking and storage containers,
use of medicinal products containing lead, consumption of fish from contaminated
streams, or any other identifiable sources of lead exposure. Figure 2 indicates
that 76% of children with blood lead levels greater than 10 [microgram]/dl
lived in homes in which the soil lead was greater than 150 ppm and there
was lead-based paint in the home. Twenty- four percent of the children
with elevated blood lead levels came from homes with lead levels greater
than [TABULAR DATA FOR TABLE 2 OMITTED] 150 ppm in the soil, but no lead-based
paint in the home. This is probably due to the fact that approximately
31% of indoor dust has an origin of outdoor soil (6). None of the 17 children
living in homes with lead-based paint but without elevated levels of lead
in the soil (greater than 150 ppm) had elevated blood leads.
Discussion
The primary objective of this study was to determine
the prevalence of blood lead levels greater than the CDC level of concern
(10 [microgram]/dl) among children living in an old lead mining area and
to compare this to the prevalence in an area not affected by mining. The
results indicate that children living in the study area had greater exposure
to lead as indicated by the significantly higher prevalence of elevated
blood lead levels - 14% compared to 0%. Mean blood lead levels were almost
twice as high in children living in the study area (6.25 [microgram]/dl)
compared to children living in the control area (3.59 [microgram]/dl).
Environmental sampling indicated that soil lead levels in the study area
were over six times higher than in the control area. Lead levels in dust
and paint samples were also significantly higher in the study area. Indoor
dust derives from both indoor and outdoor sources. As previously stated,
it has been estimated that approximately 31% of indoor dust comes from
exterior soil (6).
Both the number of persons with elevated blood lead
levels and the mean blood lead levels for the mining area were significantly
greater than those for the control area. These mean differences continued
to be statistically significant after controlling for indoor paint levels
and age of the home. Age of home was controlled for because more homes
in the study area were built prior to 1960, the year that lead was beginning
to be phased out of residential paint. As indicated in Figure 2, all of
the children with elevated blood lead levels lived in homes that had soil
lead levels greater than background levels of 150 ppm and most of these
also had lead paint in the home. None of the 60 children from the study
and control areas who lived in homes without lead paint or soil lead had
elevated blood lead levels.
It is not possible to determine from this study
what proportion of the biological lead burden results from mining and smelting
waste and what proportion comes from other sources such as paint and gasoline
residue deposited in soil. The evidence suggests that some portion of the
difference in blood lead levels between the mining and non- mining areas
is the result of exposure to the mining waste, since the difference can
not be accounted for by differences in paint lead levels between the two
areas.
Although paint lead levels were somewhat higher
in the study area, blood lead levels continue to be significantly higher
in the study area after controlling for paint lead levels and after controlling
for an indicator of lead paint - age of house. Also, some of the children
with elevated lead levels came from homes in which leaded paint was not
found but elevated soil lead levels were. Although both dust and soil cadmium
levels were significantly higher in the study area, the urine cadmium levels
were not different between the study and control children. This is possible
due to the lack of biological availability of cadmium from soil since cadmium
could not be detected in the urine of 84% of the children.
Conclusion
Children living in the Jasper County Superfund Site
where soil is contaminated with lead from mining and smelting operations
have a higher prevalence of elevated blood lead levels compared to children
living in areas without soil contamination. The data suggest that this
increased prevalence of elevated blood lead levels may be due to a combination
of soil lead from mining and smelting operations and other sources of lead,
such as household lead paint.
Corresponding Author: Ana Maria Murgueytio, M.D., M.P.H., School of Public Health, Saint Louis University, 3663 Lindell Blvd., St. Louis, MO 63108. Acknowledgements This study was supported by a grant from the Agency for Toxic Substances and Disease Registry, U.S. Public Health Service, Department of Health and Human Services.
REFERENCES
1. Centers for Disease Control (1991), Preventing Lead Poisoning in
Young Children, U.S. Department of Health and Human Services.
2. Danse, I.H.R., L.G. Garb, and R.H. Moore (1995), "Blood Lead Surveys of Communities in Proximity to Lead-Containing Mill Tailings," Am. Ind. Hyg. Assoc. J., 56(4):384-393.
3. Bjerre, B., M. Berglund, K. Harsbo, and B. Hellman (1993), "Blood Lead Concentrations of Swedish Preschool Children in a Community With High Lead Levels from Mine Waste in Soil and Dust," Scand. J. Work Environ. Health, 19 (3):154-161.
4. U.S. Environmental Protection Agency (1986), Final Report for the Tri-State Mining Area Joplin, Missouri, Region VII, Kansas City, Ks.
5. Bassinger-Daniels, Sherry (Jan. 5, 1995), Personal Communication, Missouri Dept. of Health.
6. Calabrese, E.J., and E.J. Stanek (1992), "What Proportion of Household Dust is Derived from Outdoor Soil," J. Soil Cont, 1(3):253-263.
COPYRIGHT 1996 National Environmental Health Association Murgueytio, Ana Maria; Evans, R. Gregory; Roberts, Daryl; Moehr, Tony, Prevalence of childhood lead poisoning in a lead mining area.., Vol. 58, Journal of Environmental Health, 06-01-1996, pp 12(6). Copyright © 1998 Infonautics Corporation. All rights reserved. - Terms and Conditions