Published July 17, 2015

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Soils and Health: Closing the Soil Knowledge Gap
Howard W. Mielke

T

he U.S. has a Clean Air Act and
Clean Water Act. The missing environmental component, soil, results in a
knowledge gap that has a profound influence on the lives of children. The national
issue of children’s lead exposure illustrates the effect of the soil knowledge gap.
Clinicians have evaluated low lead exposure impacts on children and throughout
one’s lifespan. The medical impacts
range from learning and behavioral
problems to some of the most difficult
and expensive chronic health conditions
known to medicine, including kidney
failure requiring dialysis, hypertension
and heart disease, diabetes, and many
nervous system dysfunctions including Alzheimer’s disease. In response to
clinical findings, the Centers for Disease Control and Prevention recognize
that there is no known safe level of lead
exposure for humans (USCDC, 2012). To
complicate the problem, the ordinary
medical method for intervention, which
focuses on lead-based paint, is deemed
ineffective. Moving forward with primary prevention of children’s exposure
to lead requires essential knowledge
about human biology, urban contamination, and soil.

Hand-to-Mouth Behavior Is
an Innate Human Trait

Children’s behavior is controlled by a
specific DNA-directed hand-to-mouth
behavior (Fig. 1). The behavior begins in
the womb during early gestation and continues after birth (Desmurget et al., 2014).
Simply stated, hand‐to‐mouth behavior
is hard-wired into the human brain, and

the exposure vulnerability to lead dust
of infants, toddlers, and young children
is tied to that fact. “The motor repertoire
of infants is narrow. Yet newborns can
accurately bring their hands toward their
mouth for self‐feeding, thumb‐sucking,
or perioral exploration, thus showing
fine coordinated movement synergies
between the hand and mouth….these
gestures of high ethological value are
selectively encoded in the human brain
and represented as integrated primitives
within the precentral gyrus, a key region
for sensorimotor processing” (Desmurget
et al., 2014). An essential requirement for
preventing children’s exposure to lead is
the need for clean air, water, and soil.

Ordinary Medical Intervention Is Ineffective

The usual medical strategy for intervention focuses on education and household
dust cleanup. Cochrane Collaboration
provides critical reviews for evaluating
the effectiveness of medical interventions. A recent Cochrane evaluation was
performed on education and household
interventions for preventing children’s
lead exposure. The Cochrane report
unequivocally states that the existing intervention method is ineffective
at reducing children’s blood lead levels
(Yeoh et al., 2012). The corollary is that
there is no known intervention for primary prevention of lead dust. The lack
of effective intervention means that even
when diagnosed, children endure continuing lead poisoning. The lifelong
medical and societal consequences are
enormous (Bellinger, 2011).

H.W. Mielke, Ph.D., Department of Pharmacology, Tulane University School of Medicine, New Orleans, LA
doi:10.2136/sh2015-56-4-gc
Published in Soil Horizons (2015).
Open access.
© Soil Science Society of America
5585 Guilford Rd., Madison, WI 53711 USA.
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means,
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without permission in writing from the publisher.

Soil Horizons

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An essential requirement for preventing
children's exposure to lead is the need for
clean air, water, and soil. Photo courtesy
of Flickr/Susy Morris.

Fig. 1. Children’s behavior is controlled
by a specific DNA-directed hand-tomouth behavior.
The situation is even more alarming
because lead intervention is triggered
by blood lead findings, and children are
being used for testing lead residues in
the environment. This violates national
and international standards for the treatment of human subjects. According to
World Medical Association (2013) criteria, if a method is shown to be ineffective,
then the medical community must revise

 the intervention to prevent harm. The
U.S. treatment protocols are thus doubly
culpable because not only do they employ
children’s blood lead as an indicator of
lead contamination, but they also use an
ineffective intervention method to prevent children from further harm.

Soil Is a Potent Reservoir of
Lead Dust

While lead-based paint is believed to be
the major source of interior dust, seasonal
changes in children’s blood lead do not
support that perception. In Detroit and
other cities, blood lead is lowest toward
the end of winter after children have
been cooped up inside (and presumably
exposed to household paint) and highest during the late summer and early fall
when the children are outside and in contact with soil (Zahran et al. 2013). Urban
soil has become severely lead contaminated, especially in inner cities (Filippelli
and Laidlaw 2009; Mielke et al. 2013).

tent exposure to soil reservoirs of lead
dust.
One major issue is that outdoor lead is
being measured in units of lead content
per weight of soil whereas interior dust
is measured in units of lead per surface
area. The interior standard is 40 micrograms per square foot. When measured
outdoors in units of lead per surface area
it is daunting to discover that the U.S. soil
standard of 400 mg/kg (ppm) is equivalent to surface loading of about 1,500
μg/ft2 (Mielke et al., 2007). The standard
measurement used to describe outdoor
soil is ineffective as a guideline for safety
because it fails to clearly communicate
how much lead children can obtain on
their hands from the soil surface (see Fig.
2).

Soil ingestion is recognized as common
among humans (Starks and Slabach, 2012).
When ingestion is involved, a factor of 10
is normally used for a margin of safety
(USEPA, 2002; USDHHS, 2005). Assuming ingestion and adding the margin
of safety, the USEPA soil lead standard
should be reduced from 400 mg/kg to 40
mg/kg. Some states and many nations
have promulgated soil lead standards at
or below 100 mg/kg (Jennings, 2013).
Accumulated lead residues in soil are a
source of lead aerosols. During seasonally drier periods such as late summer
and fall, lead dust resuspension from
contaminated soil is directly associated
with fluctuations in blood Pb (Laidlaw et
al., 2005, 2012). Empirical research shows
that if the goal is to prevent Pb exposure
≥10 μg/dL for children living in a community, then the median soil lead must
be <80 mg/kg (Mielke et al., 1999). Given
the current CDC 5 μg/dL blood lead reference value, the soil Pb standard must
be revised sufficiently downward to
ensure a margin of safety that protects
most children from the risks of inadver-

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Fig. 2. Three-dimensional map of New
Orleans showing both soil lead in µg/g
and µg/ft2. Note the large difference
between the usual soil measurement and
the lead loading in µg/ft2 of the soil
surface. The U.S. lead loading standard
of the interior floor is 40 µg/ft2, and
this compares with the lead loading of
1,500 µg/ft2 when the soil lead meets the
U.S. soil standard of 400 µg/g or ppm
(Mielke et al., 2007).

Conclusions

The soil knowledge gap among health
practitioners is related to the failure to
understand essential characteristics
about human biology in the context of
the air–water–soil nexus of children’s
environmental health. In the case of
the lead exposure issue, closing the
soil knowledge gap at least requires:
Acknowledging the innate vulnerability of less than three-year-old children
to lead residues in their environment
including, air, water, and soil; conceding
the failure of current lead-based paint
intensive interventions for preventing
exposure of children; underscoring soil
loading vs. lead content as part of risk
analysis; upgrading standards to use at
least a factor of 10 to protect children;

 exploiting federal resources such as the
USDA and the U.S. Geological Survey to
map urban soils; recognizing the value of
low lead soils that exist outside of every
city as an essential resource for revitalizing urban lands to create safe areas
for the youngest citizens; and accepting
clean soil along with air and water as
critical components of the long-term goal
of resolving national health issues.

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Laidlaw M.A.S., H.W. Mielke, G.M. Filippelli, D.L.
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