The Dangers of Chemical Exposure to Children
The fetus, infants, and children --- more vulnerable to toxic substances
Infants and children are not little adults, and they are often more
vulnerable to the adverse effects of drugs, chemicals, radiation or
disease.
In spite of this fact, only one law, that covering pesticides, requires
regulators to base safety judgments explicitly on risks faced by the fetus,
infant and child, and even this statute has not been rigorously implemented.
For most toxic substances in commerce and consumer products, there are few if
any health studies at all. Those that are done are typically done on adult
(sexually mature) test animals.
PCBs - Levels of fetal PCB exposure that cause learning deficits that persist through adolescence, have no measurable effects on adults.
Nitrate - Prolonged exposure to tap water with 20 ppm nitrate can kill an infant, but will have no observable effect on an adult.
Honey - Infants under one year of age can contract a potentially fatal paralytic form of botulism from eating honey. In older children and adults the digestive system is more acidic and it destroys the botulism toxins present in the honey.
Lead - Doses at age 2 that cause IQ deficits throughout childhood produce no effect in adults.
Mercury - Exposure in the womb at 100 parts per billion will significantly increase the likelihood of learning deficits in childhood, while the same dose during adulthood has no measurable effect.
Radiation - Children exposed to radiation have a much higher incidence of cancer than adults exposed to the same dose.
Ritalin - This commonly prescribed drug acts as a depressant and calming agent in children, but has the opposite effect in adults.
Researchers at a 1997 EPA sponsored national conference on children's
environmental health summarize children's vulnerability in the context of
chemical exposures:
"Many organ systems in young children - the nervous system in particular, but
also the lungs, the immune system, and the reproductive organs - undergo
extensive growth and development throughout pregnancy and in the first months
and years of extra-uterine life. During this period, structures are developed
and vital connections established. These systems are not well adapted to
repair any damage that may be caused by environmental toxicants. Thus, if
cells in the developing brain, immune system, or reproductive organs are
destroyed by neurotoxicants, or if development is diverted by endocrine
disruptors, there is high risk that the resulting dysfunction will be
permanent and irreversible. Depending on the organ damaged, the consequences
can include loss of intelligence, immune dysfunction, or reproductive
impairment."
The developing human body has critical windows of vulnerability
Many studies have shown that the peak incidence of birth defects coincides
with the timing of key developmental events. This means that maternal
exposures to toxic substances on a particular day of pregnancy might cause
devastating effects to a baby, while exposures on the very next day would
cause no discernible effects whatsoever. For example:
- implantation of the egg occurs on gestational day 6 to 7
- organs begin forming on days 21 through 56
- the neural plate forms between days 18 and 20
- arm buds appear on days 29 to 30
- leg buds follow shortly after on days 31 to 32
- testes differentiation occurs on day 43
- the palate closes between days 56 and 58
Chemical substances
have been shown to be three to ten times as toxic to newborns as adults, or
in some cases to damage the newborn brain and not the adult brain, in part
due to differences in the stages of development of the blood-brain barrier
(Klassen 1996). The human brain develops in overlapping phases, each presenting unique opportunities for chemical-induced damage, beginning in the womb within days of conception, and continuing through childhood. The right chemical at the right time has the potential to disrupt any of the following processes:
- Making brain cells (neurulation and neurogensis)
- Moving the cells to their proper location (cell migration)
- Growing axons and dendrites to link nerve cells (neuronal differentiation and pathfinding)
- Developing synapses or points of communication with other cells (synaptogenesis)
- Refining the synapses (naturation and pruning)
- Forming the supportive tissue that surrounds nerve cells and makes for efficient communication among them (gliagenesis or myelination)
Ongoing sensitivity
Sensitivities continue through childhood. An increasing number of studies
are showing effects to the reproductive system and the brain following
early-life exposures to an array of chemicals. This is well-proven for
childhood exposures to lead, and is shown in laboratory animals for, among
other things, high-volume chemicals like dibutyl phthalate and
bis(2-ethylhexyl) phthalate.
References
Children's health and the environment: A new agenda for prevention research. Environmental Health Perspectives 106, Supplement 3, June 1998.
U.S. Environmental Protection Agency (EPA). 1997. Exposure Factors Handbook. Volume 1 - General Factors. EPA/600/P-95/002Fa. August 1997.
Klassen, Curtis D. Casarett & Doull's Toxicology. The Basic Science of Poisons. Fifth Edition. The McGraw-Hill Companies, Inc. 1996.
