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From the Archives
Introduction
We are all exposed to chemicals every day at very low levels. These chemicals are in our food, water, air, and products. These chemicals accumulate in our bodies and we can measure them in the blood and urine to determine our body burden. For example, between 2005 and 2006 the Centers for Disease Control and Prevention (CDC) sampled 212 chemicals from 2400 people in the US and found that 100% of the participants had polybrominated diphenyl ethers (PBDEs) and perfluorooctanoic acid (PFOA) in their blood.1 90% of people sampled had bisphenol A. We are exposed to these chemicals daily. There have been numerous reports linking them to hormonal conditions and cancer. These chemicals also affect cognition due to their effects on the nervous system.
Neurotoxicity
The nervous system is a unique target for toxic chemicals in several ways. They can damage neurons that can't be replaced. Neurons have high surface areas and therefore increased exposure to toxins. Chemicals cause changes in neurotransmitters – especially serotonin and dopamine. Chemicals alter intracellular signaling processes. These signals not only are essential for the function of the nervous system, but also play a key role in nervous system development. Because of high lipid content in the brain there is an accumulation of lipophilic chemicals. The blood–brain barrier does not block lipophilic chemicals from entering the brain.2 The placental barrier also does not block toxic chemicals.
In Utero Exposure
Often a woman's body burden of chemicals can be passed in utero through the placental barrier, affecting fetal neurological development. In 2004, the Environmental Working Group (www.ewg.org) commissioned five laboratories to examine the umbilical cord blood of 10 US babies of African-American, Hispanic, and Asian heritage and found more than 287 chemicals in each newborn. In 2013, testing done by Environmental Defence, a Canadian environmental action organization, found 137 chemicals in the umbilical cord blood of 3 newborns.3 These chemicals affect cognition whether one is exposed in utero, childhood, or adulthood. Some examples of the cognitive effects of chemicals include:
- ADD
- ADHD
- depression
- anxiety
- autism
- learning difficulties
- poor intellect
Below is evidence linking chemicals to these conditions.
Bisphenol A (BPA): Anxiety, Depression, and Hyperactivity
Childhood exposure to BPA has been associated with hyperactivity, anxiety, and behavioral problems. Prenatal exposure could also affect cognition. A recent study measured BPA in urine from mothers during pregnancy and children at 5 years of age (n= 292). Child behavior was assessed by mother and teacher report at age 7 years, and direct assessment at age 9 years. Prenatal urinary BPA concentrations were associated with increased internalizing problems in boys, including anxiety and depression, at age 7. No associations were seen with prenatal BPA concentrations and behaviors in girls. Childhood urinary BPA concentrations were associated with increased externalizing behaviors, including conduct problems, in girls at age 7 and increased internalizing behaviors and inattention and hyperactivity behaviors in boys and girls at age 7. This study is significant due to how common BPA exposure is in the US and how difficult it is to avoid. BPA is present in food and beverage containers, cash register receipts, canned foods, and dental sealants.4
Polychlorinated Biphenyls (PCBs): Cognition, Development, and Intellect
Several studies have shown the adverse affects of in utero and childhood exposure to dietary PCBs. Children exposed in uteroto PCBs via fish consumption exhibited problems with intellectual functioning. A study in Germany revealed that in uteroexposures to PCBs affected the mental and motor neurological development of children. Childhoodexposure to PCBs results in increased cognitive defects, poor gross motor function, and decreased visual recognition memory.5 PCBs are in our food, meat, dairy products, and farmed fish.
Polybrominated Diphenyl Ethers (PBDEs): Attention, Coordination, and Cognition
PBDEs are used as flame retardants in textiles, electrical equipment, plastics, and building materials. PBDEs are structurally similar to PCBs. They bioaccumulate in our food through contaminated food and water. Exposure through lactation leads to poor infant mental development. Impaired neurobehavioral development has been shown in connection to both prenatal and childhoodexposures, resulting in decreased attention, fine motor coordination, and cognition.6,7
Lead and Cadmium: Cognition and Attention
Most people are aware of how childhood exposure to lead may lower cognitive potential. Sources of exposure can be from lead paint in homes and on toys, ceramics and china. Lead can be in food, water, and household dust. Lead exposure also occurs in utero. When children were exposed to high levels of lead in uterofrom their mothers' bone stores, they showed reduced mental abilities at age 24 months.8 Cadmium is another heavy metal that is neurotoxic. It is found in the soil, water, and food. A study assessed cadmium exposure in 1305 women in early pregnancy and their children at 5 years of age by measuring concentrations in urine. Early-life low-level cadmium exposure was associated with lower child intelligence scores.9 Prenatal methylmercury exposure from eating fish is associated with attention deficit/hyperactivity disorder (ADHD) in childhood.10
Air Pollution, Pesticides, Phthalates, and Mercury: Autism
Air pollution exposure during pregnancy has been reported to have physical and developmental effects on the fetus. High levels of air pollution, including carbon monoxide, nitrogen dioxide, and ambient particulate matter (PM), have been associated with very low and low birth weight, preterm birth, and infant mortality. Data from the Childhood Autism Risks from Genetics and the Environment (CHARGE) study showed that autism was also associated with residential proximity to a freeway during the third trimester. This study observed an increased risk of autism among the 10% of children living within 309 miles of a freeway around the time of birth.11 Pesticide exposure is linked to autism as well. Children born to mothers who had been exposed to organochlorine (OC) insecticides that were applied within 500 miles of the home between gestational days (GD) 26 and 81 were 7.6 times more likely to be diagnosed with autism than the children of mothers who lived in the lowest exposure quartile.12 Prenatal phthalate and mercury exposure are also linked to autism. There is a 3.7% increase in autism rates associated with living near mercury power plants.13,14
Solutions
Given the increase in childhood conditions such as ADHD, hyperactivity, autism, anxiety, depression, and mild learning disabilities, the connection to low-dose chemical exposure cannot be ignored. People need to be educated on how to avoid exposure to these chemicals, especially if considering pregnancy. Based on recent body-burden studies mentioned above, most children and adults have chemicals circulating in the body. Physician-prescribed detoxification has been proved as a method of treatment to decrease body burden of chemicals and improve health.15 The importance of this approach for women considering pregnancy cannot be overemphasized. However, very few physicians are properly trained in the area of environmental medicine. A shift in the medical community needs to occur. Until we get these chemicals out of our food, air, water, and products, we will always be battling unwanted exposure and adverse health effects. The burden should not be on the average person living in the US, but on legislators and regulators to keep these harmful chemicals out of our lives.
Summary
Neurotoxicity of low-dose chemical exposure is often overshadowed by hormonal effects of toxicants, including the chemical link to breast cancer. However, as more research is published showing that prenatal and childhood exposure to chemicals is contributing to the rise in cognitive and behavioral problems, the emphasis may switch. Children with autism, ADHD, anxiety, depression, and learning difficulties grow up to become adults struggling with the same conditions. Through education, avoidance, and detoxification, these health risks can be minimized.
Dr. Marchese is the author of 8 Weeks to Women's Wellness: The Detoxification Plan for Breast Cancer, Endometriosis, Infertility, and other Women's Health Conditions. She maintains a private practice in Phoenix, Arizona. www.drmarchese.com
Notes
1. US Centers for Disease Control and Prevention. Fourth National Report on Human Exposure to Environmental Chemicals. 2009. Available at www.cdc.gov/ExposureReport.
2. Kodavanti PR. Neurotoxicity of persistent organic pollutants: possible mode(s) of action and further considerations. Dose Response. 2005;3(3):273–305.
3. Pre-Polluted: A Report on the Toxic Substances in the Umbilical Cord Blood of Canadian Newborns [online document]. Environmental Defence. June 2013. Available at http://environmentaldefence.ca/prepolluted. Accessed July 26, 2013.
4. Harley KG, et al. Prenatal and early childhood bisphenol-A concentrations and behavior in school-aged children. Environ Res. Epub Jul 16, 2013.
5. Crinnion WJ. Polychlorinated biphenyls: persistent pollutants with immunological, neurological, and endocrinological consequences. Altern Med Rev. 2011;16(1):5–13.
6. Eriksson P, Jakobsson E, Fredriksson A. Brominated flame retardants: a novel class of developmental neurotoxicants in our environment? Environ Health Perspect. 2001;109(9):903–908.
7. Eskenazi B et al. In-utero and childhood polybrominated diphenyl ether (PBDE) exposures and neurodevelopment in the CHAMACOS study. Environ Health Perspect. 2013;121(2):257–262.
8. Crinnion WJ. Maternal levels of xenobiotics that affect fetal development and childhood health. Altern Med Rev. 2009;14(3):212–222.
9. Kippler M et al. Early life cadmium exposure and child development in 5-year old girls and boys: A cohort study in rural Bangladesh. Environ Health Perspect. 2012;120:1462–1468.
10. Boucher O et al. Prenatal methylmercury, postnatal lead exposure, and evidence of attention deficit/hyperactivity disorder among Inuit children in Arctic Québec. Environ Health Perspect 2012;120:1456–1461.
11. Volk HE et al. Residential proximity to freeways and autism in the CHARGE study. Environ Health Perspect. 2011;119(6):873–877.
12. Roberts EM et al. Maternal residence near agricultural pesticide applications and autism spectrum disorders among children in the California Central Valley. Environ Health Perspect. 2007;115:1482–1489.
13. Miodovnik A et al. Endocrine disruptors and childhood social impairment. Neurotoxicology. 2011 Mar;32(2):261–267.
14. Palmer RF, Blanchard S, Wood R. Proximity to point sources of environmental mercury release as a predictor of autism prevalence. Health and Place. 2008; doi:10.1016/j.healthplace.2008.02.001.
15. Marchese M. 8 Weeks to Women's Wellness: The Detoxification Plan for Breast Cancer, Endometriosis, Infertility and Other Women's Health Conditions. Petaluma, CA: Smart Publications; 2010.
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