Environmental Engineering Reference
In-Depth Information
Table 2.9
Prevalence (%) of Elevated Blood Lead in Selected Populations
of Children in the U.S. in the Period 1988-1991
Population
Age, yrs.
≥
20
µ
g/dL
≥
15
µ
g/dL
≥
10
µ
g/dL
All
1-5
1.1
2.7
8.9
Non-Hispanic white
1-2
0.8
2.1
8.5
3-5
0.4
0.7
3.7
Non-Hispanic black
1-2
5.4
10.2
21.6
3-5
2.9
6.0
20.0
Mexican-American
1-2
1.9
2.9
10.1
3-5
0.7
1.4
6.8
Source:
Data extracted from Brody, D.J. et al.,
JAMA
, 272, 277, 1994.
have higher lead concentrations, they are reported to be in better condition,
as are floor conditions. It is also believed that black children have a lower
calcium intake than white children; calcium inhibits lead absorption.
Lead in house dust is considered to be the major risk factor for elevated
BLLs in children. As such, it is important to know what levels are excessive
and in need of remediation. The current Department of Housing and Urban
Development (HUD) floor dust clearance level for lead abatement projects
is 100
g/m
2
). This value is also a guideline action level for
residential risk assessment. A guideline value of 50
µ
g/ft
2
(1080
µ
g/m
2
) has
recently been proposed by USEPA as a lead hazard threshold. However,
there is evidence that lead dust levels <10
µ
g/ft
2
(540
µ
g/m
2
) would be
necessary to assure that 95% of the population of U.S. children would have
BLLs below the national goal of 10
µ
g/ft
2
(100
µ
µ
g/dL. Other studies indicate that a mean
lead floor dust level of 65
µ
g/ft
2
(702
µ
g/m
2
) is associated with a 10
µ
g/dL
increase in BLLs in children.
C. Health effects
Lead is a very toxic substance affecting a variety of target organs and systems
including the brain and the nervous, renal, reproductive, and cardiovascular
systems. Effects are dose dependent. They may be acute (clinically obvious)
or chronic (typically symptoms/effects are not easily diagnosed). Acute
exposures, with BLLs > 60
g/dL, may produce colic, shock, severe anemia,
nervousness, kidney damage, irreversible brain damage, and even death.
Acute responses may differ in adults and children since children under age
five are more vulnerable to the neurotoxic effects of lead. Chronic exposure
may result in a variety of symptoms, depending on the level of exposure.
Acute and chronic exposure responses associated with different BLLs in
children and adults are summarized in
Table 2.10
.
The distinction between
acute and chronic symptoms is not clear, especially for children; for adults,
acute symptoms generally occur when BLLs are >60
µ
g/dL. At the low end
of BLLs in
Table 2.10
,
health endpoints may include neurodevelopmental
effects in children, increased blood pressure and related cardiovascular
effects in adults, and possibly cancer.
µ
