NEUROBEHAVIORAL DISORDERS: Childhood Exposure to Environmental Toxins

Alice Brock-Utne, MD

In a familiar scene, a pediatrician spends a well-child visit tirelessly reassuring a mother that the benefits of vaccines outweigh the risks. The doctor’s frustration grows as she tackles the mother’s fears that her child will get autism or attention deficit hyperactivity disorder (ADHD). Soon the doctor is led down a path of trying to create a competing fear of vaccine-preventable diseases.

Frustration from these types of visits has led some doctors to recoil at the mention of vaccine refusal. It has even led some to ban patients who refuse vaccines. In other cases, doctors have stopped advocating for vaccines in order to serve a patient base convinced vaccines are too toxic. For parents, the vaccine debate has proven confusing and dangerous. Marin County now leads the way in low vaccination rates and outbreaks of pertussis and measles. Nonetheless, parents are onto something: exposure to toxic substances does play a role in our children’s health.

In 2000, the National Research Council estimated that 3% of all neurobehavioral disorders were caused directly by toxic environmental exposures.[1] They also estimated that 25% of these disorders were caused by the interaction between environmental factors and inherited susceptibilities. Based on this research, a group of environmental medicine researchers recently published a list of the 10 chemicals most suspicious for developmental neurotoxicity.[2] The list was narrowed down from the 80,000 synthetic chemicals developed in the last 50 years; to the 3,000 chemicals with the greatest potential for human exposure; to the 200 chemicals detectable in virtually all Americans; and finally to the 10 most suspicious culprits in the rise of neurobehavioral disorders: lead, methyl mercury, polychlorinated biphenyls, organophosphate and organochlorine pesticides, endocrine disruptors, automotive exhaust, polycyclic aromatic hydrocarbons, brominated flame retardants, and perfluorinated compounds.

According to the CDC, 1.1% of American children had autism in 2008.[3] In 2000, that same statistic was 0.7%. Since autism is five times more prevalent in boys than girls, 1.9% of American boys are affected by the disorder. ADHD has similarly frightening statistics: a full 8% of American children now have ADHD, and 80% of those children are boys.[4] While overdiagnosis and changing diagnostic criteria partly explain the increased prevalence of these neurobehavioral disorders, they only account for a small bump, not the exponential rise we are seeing.[5] Beyond the statistics, the toll on families, schools, and our communities is tragic. At the front lines, our teachers, parents, caregivers and physicians are seeing children afflicted with neurobehavioral disorders in ever-increasing numbers. This is not good news for our children, especially our little boys.

The cocktail of environmental exposures that can affect our children’s neurodevelopment begins preconception. Exposures to sperm, body burden in a preconception mother, and exposures during fetal life all contribute to a child’s future risk of disease.[6] For a decade, the research community has been distracted by the question of whether vaccines could be the cause of the rising rates of neurobehavioral disorders. Could the thimerosal preservative in vaccines be to blame? No, we phased that out in the early 2000s and rates continued upward without a blip. Could it be we are overwhelming the young immune system with more vaccines than before? No, we used to give the pertussis vaccine as a whole-cell vaccine, thus subjecting the young immune systems of my generation to vastly more antigens.

Vaccines may be the best-monitored, most well-studied exposure in our children’s lives. Vaccines have clear, measurable, important benefits. Sadly, by avoiding vaccines, parents are unlikely to have any positive impact on their child’s neurodevelopment. Instead, they place their children and the immune-suppressed of our community at risk of serious infection. It is time to leave the scapegoat of vaccines behind. Instead, we need to consider how we can reduce our children’s environmental exposures to the more likely causes of neurobehavioral disorders. In my view, the five best ways to reduce those exposures are to (1) watch what your family eats, (2) avoid insecticides and herbicides, (3) advocate against flame retardants, (4) spend time outdoors with your family, and (5) stay vigilant against older toxic threats.

Watch what your family eats

Several of the 10 most suspicious chemicals in the rise of neurobehavioral disorders can be found in a child’s diet, in the chemicals passed from mother to fetus via the placenta, and in the chemicals stored in the mother’s body from food she ate even before pregnancy. Endocrine disruptors and neurotoxins (organophosphates and organochlorines) are common classes of pesticides found in food. Differing levels of methyl mercury are found in fish, depending on the type of fish and where it was caught. Automotive exhaust and polycyclic aromatic hydrocarbons are released when food is transported.

When families choose to buy organic, they can avoid the endocrine disruptors and neurotoxins in pesticides. When they are picky about their fish, they can provide beneficial brain nutrients but avoid methyl mercury. When they buy locally produced food, they can minimize the automotive exhaust and polycyclic aromatic hydrocarbons released during transport. To make these informed choices, families can shop at a market that provides reliable information on which foods are organic, which fish is lower in mercury, and where the foods are produced.

Other resources abound. The Environmental Working Group website, for example, offers a list of the “clean 15” fruits and vegetables lowest in pesticides, along with the “dirty dozen” fruits and vegetables highest in pesticides.[7] According to the EWG, onions, sweet corn and pineapples are among the cleanest, whereas apples, celery and strawberries are among the dirtiest.

For fish, the Monterey Bay Aquarium website offers a Seafood Watch guide that recommends the safest varieties.[8] Their recommendations include wild salmon and farmed tilapia, as opposed to farmed salmon and canned tuna.

Another resource is the local farmer’s market, where families can ask questions directly of the person who produced the food. The Natural Resources Defense Council website features a complete guide to farmer’s markets in Marin County.[9]

Avoid insecticides and herbicides

The insect and weed killers we use on our pets, in our kitchens and in our yards end up in the bodies of our children. Some of these pesticides and herbicides are of the organophosphate class. By using alternative strategies, families can minimize their children’s exposure to organophosphates. The Natural Resources Defense Council website lists several steps you can take to control pests.[10] Among the suggestions: clean frequently, seal entryways, use traps or try low-risk pesticides, such as boric acid.

Advocate against flame retardants

Brominated flame retardants and perfluorinated compounds, which are found in flammable household products, are possible carcinogens, with endocrine, immune and neurotoxic effects.[11] Flame retardants have been found in the bodies of children and mothers, in mother’s milk, and in the placentas of newborns.[12]

To reduce deaths from fire, California law requires the addition of flame retardants to flammable household products. Unfortunately, experience over the past 30 years has shown that flame retardants actually increase death from fire by boosting carbon monoxide and hydrogen cyanide gas levels during fires.[13] Coalitions of chemists, fire fighters and environmental activists have been working for over a decade to overturn California laws requiring flame retardants.

Physicians can advocate for children’s neurobehavioral health by informing patients that flame retardants don’t serve any useful purpose and have clear dangers. A good resource for scientifically accurate, detailed information on flame retardants is the Green Science Policy Institute website.[14]

Spend time outdoors with your family

The idea behind environmental enrichment is that the brain can be stimulated by its surroundings. Studies on rats fed lead-laced food have shown that an enriched environment can mitigate some of the toxic effects lead has on learning; this effect may be more pronounced in boys.[15] In the case of ADHD, early research is pointing to an enriched environment and physical play as modalities that can modify the long-term developmental trajectory of the disorder.[16]

Outdoor play is another environmental enrichment with potential to modify neurodevelopment. In the outdoors, children can play freely, imagine, create and explore. Outdoor experiences offer a chance for the family to connect in a healthy way, far from television, computer screens and adult distractions. Letting your children experience free play and family togetherness may be one of the most important choices a parent takes toward a healthy neurodevelopmental environment.[17] For further details, visit the Children & Nature Network website.[18]

Stay vigilant against older toxic threats

Reductions in exposure to lead and polychlorinated biphenyls (PCBs) are two great success stories in environmental health. Both of these chemicals were eliminated from use at their major sources about 30 years ago. Leaded gasoline and leaded home paint are no longer used, and PCBs are no longer employed to insulate electric equipment or in caulking. Yet, these chemicals persist as health problems for our children since they are still found in old buildings. Lead is found in the paint of homes built before 1978, and PCBs are found in the caulking and electrical transformers of buildings built or renovated between 1950 and 1970.

Low-level lead exposure can cause attention problems, cognitive delay and speech delay. Despite the success we’ve had in lowering childhood exposure by universal lead screening and interventions for elevated blood lead levels, many American children continue to live, learn and play in substandard buildings with chipped and peeling leaded paint. Children are also exposed through toys or ceramic painted dishes sold with illegally elevated lead levels.

PCBs continue to persist as well. They are found in every creature on earth at levels proportional to their level on the food chain. They persist on surfaces, soil and in the air. They are also still found in elevated levels in schools and other buildings, as older caulking and electrical insulation deteriorate. Since PCBs have known neurotoxic effects, they present not only a health burden on the children in those buildings, but also a financial burden on the institutions responsible for maintaining the buildings. New methods of covering old caulking with new varieties offer more affordable options at remediation.

Much of what we know about the dangers of PCBs and lead was discovered well after their use was ended. Both were removed from production due to their persistence in the environment, prolific presence in humans, and potential risks suggested by early studies and likely mechanisms of action. The experience with these two toxins teaches us that we don’t have to wait until all the research is finished and agreed upon to prudently control our children’s exposure to neurotoxic chemicals. It also teaches us that when a chemical persists in the environment, its effects can be felt long after its use is ended.

To lessen possible exposure to lead and PCBs, families are advised to keep homes, particularly windows, well maintained. Families should also follow careful construction and remediation practices when working in older homes. The EPA offers two websites with helpful advice on dealing with lead and PCBs.[19,20]

Conclusion

By using the five strategies discussed above, families can maximize their ability to protect the developing brains of their children. We need to acknowledge that the environmental cocktail of toxins in our children is contributing to the alarming rise in neurobehavioral disease. With the promise of new collaborative research on ADHD and autism, we may be able to slow or even halt the rising tide of neurobehavioral disorders in our children.

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Dr. Brock-Utne, a pediatric hospitalist for the Physician’s Choice Medical Group, was formerly a pediatrician for Marin Community Clinics.

 

Email: abrockutne@gmail.com

References

1. Landrigan PJ, et al, “Environmental pollutants and disease in American children.” Enviro Health Perspec, 110:721-728 (2002).

2. Landrigan PJ, et al, “A research strategy to discover the environmental causes of autism and neurodevelopmental disabilities,” Enviro Health Perspec (Apr 25, 2012: epub ahead of print).

3. CDC, “Prevalence of autism spectrum disorders,” MMWR Surveill Summ, 61:1-19 (2012).

4. Bloom B, et al, “Summary health statistics for U.S. children,” Vital Health Stat, 10:1-80 (2011).

5. Cuffe SP, et al, “Prevalence and correlates of ADHD symptoms in the national health interview survey,” J Atten Disord, 9:392-401 (2005).

6. Sutton P, et al, “Toxic environmental chemicals,” Am J Ob-Gyn, (Mar 8, 2012: epub ahead of print).

7. www.ewg.org/foodnews/

8. www.montereybayaquarium.org/cr/seafoodwatch.aspx

9. www.nrdc.org/greengate/guides/mar_mari.asp

10. http://www.nrdc.org/health/pesticides/gpests.asp

11. Herbstman JB, et al, “Prenatal exposure to PBDEs and neurodevelopment.” Enviro Health Perspec, 118:712-719 (2010).

12. Main KM, et al, “Flame retardants in placenta and breast milk and cryptorchidism in newborn boys,” Enviro Health Perspec, 115:1519-26 (2007).

13. Shaw SD, et al, Halogenated flame retardants: do the fire safety benefits justify the risks?” Rev Enviro Health, 25:261-305 (2010).

14. www.greensciencepolicy.org

15. Anderson DW, et al, “Sex and rearing condition modify the effects of perinatal lead exposure on learning and memory,” Neurotoxicology (Apr 21, 2012: epub ahead of print).

16. Halperin JM, Healey DM, “Influences of environmental enrichment, cognitive enhancement and physical exercise on brain development,” Neurosci Biobehav Rev, 35:621-634 (2011).

17. Milteer RM, et al, “Importance of play in promoting healthy child development and maintaining strong parent-child bond,” Pediatrics, 129:204-213 (2012).

18. www.childrenandnature.org

19. http://www.epa.gov/lead/

20. http://www.epa.gov/epawaste/hazard/tsd/pcbs/index.htm