In June 2007 CHEM Trust wrote the briefing Chemicals Compromising Our Children, which highlighted growing concerns about the impacts of chemicals on brain development in children.
Almost 10 years later, CHEM Trust has revisited the issue with this report, which includes contributions from two of the most eminent scientists in this area, Professor Barbara Demeneix (Laboratory of Evolution of Endocrine Regulations, CNRS, Paris) and Professor Philippe Grandjean (Department of Environmental Medicine, University of Southern Denmark, Denmark & Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, USA), who also peer reviewed the report.
The report points to strong evidence of a significant global increase in certain neurological diseases and disorders among children over the past two decades – causing issues such as ADHD and lower IQ. “Some chemicals in these groups are being phased out, but similar chemicals remain in everyday use” according to the report. CHEM Trust’s particular concerns are related to hormone disruptors, the cocktail effect of chemicals and the role of chemical exposures in the early life of wildlife and humans.
The report focuses on chemicals which it claims have developmental neurotoxic (DNT) properties. It says: “Science has shown that many thousands of people have been exposed to now mostly banned chemicals such as lead and PCBs at high enough levels to have had their brain development negatively affected. This report finds that there are other chemicals which are still in routine use in our homes where there is evidence of similar developmental neurotoxic (DNT) properties, and also identifies huge gaps in our knowledge of the impacts of other chemicals on brain development. It also points out the unpleasant reality that we are constantly exposed to a cocktail of chemicals, something which is still largely ignored by chemical safety laws…In spite of the lessons of the past, regulators are continuing to only regulate after harm is caused, instead of acting to effectively protect the most precious of things; children’s developing brains.”
Our brains are astoundingly complex, made up of over 85 billion neurons, which have grown, developed and interconnected during our lives. The brain is the organ that takes the longest to develop, with initial stages of cell division, creation of neurons and their migration taking place from the first hours after fertilization and throughout the fetus’ time in the womb. However, brain development does not stop at birth – it’s not until our twenties that neurons are fully developed with their myelin coats.
Normal brain development is the result of an undisturbed harmonious interaction among cells, and between cells and hormones. Hormones play an important role in
hormones. Endocrine disrupting chemicals (EDCs) are examples of substances that can alter this delicate balance, and as thyroid hormones play a vital role in brain development, thyroid-disrupting chemicals are of particular concern. Pregnancy, childhood and adolescence are periods of brain development that are considered critically sensitive to toxic chemicals, with even small exposures at the wrong time altering the brain’s developmental programming signals in an irreversible way. Impaired brain development may result in a broad range of human health effects: from altered reproduction, metabolism and stress response, to mental retardation and subtle, subclinical intellectual deficiencies. In addition, fetal and early childhood life stages are particularly sensitive to heavy metals and EDCs and there are likely to be no safe levels which can be set with sufficient certainty. (To see which chemicals impact the fetus, go to: http://endocrinedisruption.org/prenatal-origins-of-endocrine-disruption/critical-windows-of-development/timeline-test/
Throughout this complex developmental process a range of signalling chemicals and other processes operate in order to control what happens. The thyroid hormone system is intimately involved in brain development and function, yet it is well established that this system can be disrupted – for example by a lack of iodine (essential to make thyroid hormone) or by certain chemicals. If developmental processes are disrupted, this most often creates permanent problems.
The complexity of brain development and function means that deficits can be very subtle – small reductions in IQ, disabilities that exist with a broad spectrum of seriousness such as autism, or in some cases conditions which do not have fully agreed diagnostic criteria.
In 2007, the global prevalence of just attention deficit hyperactivity disorder (ADHD) was 5.3%. In the United States, by 2012, the number of children diagnosed with ADHD was 10% of children and 4.9 million, or 8% of children, with a learning disability. (Note: while the term ADHD is often used in the United States, the term hyperkinetic disorder (HKD) is used in the EU and requires that the clinician directly observes the symptoms rather than relying on parent and teacher reports.)
For autism spectrum disorder, the increase in prevalence was equally concerning. Sweden had the highest increase in cumulative prevalence of 4.5 fold, followed by Denmark with almost 3 fold and Finland with almost double the prevalence in a decade. While at least some of the increase is thought to be due to increased awareness and increased diagnosis, there is concern that exposure to certain chemicals could have contributed to some of the incidence.
Exposures to chemicals with DNT properties, which can be found in the environment and the food supply, are preventable causes of impaired brain development. While several of these chemicals have been restricted, exposure can still take place as many of them are persistent (long-living) and some, like PCBs, can bio accumulate, i.e. build up in our bodies over time. Additionally, we are exposed to numerous substances with similar properties which may act in an additive way and yet safety assessment is usually only focused on one substance at a time.
While genetics could explain some of the observed changes, the fast pace at which these trends have occurred are inconsistent with the much slower rate at which genetic changes take place, suggesting that environmental factors, chemical and non-chemical like the ones mentioned above, are probably responsible. It has been concluded that overall, genetic factors seem to account for no more than perhaps 30-40% of all cases of neurodevelopmental disorders, and therefore that non-genetic, environmental exposures, including chemicals, are involved.
Clinical manifestations associated with impaired brain development can be put into two major categories:
- learning disabilities
- impaired memory
- verbal comprehension
- reasoning and executive skills
- impaired social interactions in general
But the brain is a collection of interconnected networks, so these categories are closely related.
In the United States, exposures to mercury, lead and organophosphate pesticides have been associated with the loss of around 40 million IQ points in a population of 25 million children up to 5 years of age. Most if not all chemical exposures can be reduced by putting policy measures into place (such as bans and restrictions). One such strategy was removing lead from gasoline. Making that change had a great difference to children born after 2000, who were estimated to have IQ scores 2.2 – 2.7 points higher than children born in the 1970s before lead was removed.
So what chemicals are we talking about?
- Lead: has been known to cause intellectual disabilities for many years, with no known safe blood level. (used in textile dyestuffs)
- Mercury: exposure to mercury during development prevents neurons from finding their appropriate place in the brain, causing lower language, attention and memory scores, reduced cognitive performance and psychomotor deficiencies in children. (also used in textile dyestuffs, and as a catalyst in the dyeing process)
- Polychlorinated biphenyls (PCBs): used in textile dyestuffs; banned from most uses in the 1970s in many countries. Known to interfere with the normal function of the thyroid hormone, and growing evidence indicated PCBs adversely affects neurodevelopment.
- Bisphenol A (BPA) Bisphenol S (BPS): used as an intermediary in the production of flame retardants, textile dyes, polymers. Used in the production of polyester fabrics. Emerging human data suggests that BPA affects humans just as it does animals (which have been reported for many years): it has been described that Spanish children with higher concentrations of BPA in urine had worse behavioural scores and social problems. In the USA, pre-teen and teenage children with higher BPA in urine had a higher prevalence of ADHD. Bisphenol S is a substitution that may have similar or worse health effects.
- Phthalates: a family of chemicals with multiple uses, widely used in the textile industry. Three member of this calls, dibutyl phthalate (DBP), benzylbutyl phthalate (BBP) and diethylhexyl phthalate (DEHP) are known for their anti-androgenic properties and association with altered reproductive organ development in boys.
- Polybrominated diphenyl ethers (PBDEs): used in flame retardants; widespread contaminants of the environment and the human body. Persist in the environment and some bioaccumuate. A recent Dutch study reported that PBDEs were associated with lower mental and psychomotor development and IQ in pre-school children, and poorer attention for those in school.
- Organophosphate pesticides: a recent study concluded that prenatal and to a lesser extent postnatal exposure may contribute to neurodevelopmental and behavioural deficits in preschool and school children.
What to do to reduce your exposure:
- Eat organic food and avoid pesticides in your own house and garden.
- Minimize eating tuna and/or swordfish, which contains methylmercury.
- Avoid microwave popcorn (which contains PFC chemicals).
- Reduce your use of packaged food. Store cereals and rice etc. in glass jars.
- Minimize use of cleaning products or use baking soda + vinegar or other non-toxic cleaning products.
- Check all shampoos, soaps and cosmetics for listed ingredients which are safe.
- Because dust has been found to have high levels of problematic chemicals, it’s a good idea to clean your home frequently to reduce the build-up of dust.
- Minimize your handling of receipts, as they contain BPA.