Industrial Production of Developmental Neurotoxins 

 by Jan Lamprecht

Polluting Our Future: Chemical Pollution in the U.S. that Affects Child Development and Learning

Neurotoxicity Definition

Neurotoxicity is defined as adverse effects on the structure or functioning of the central and/or peripheral nervous system that result from exposure to chemical substances. Neurotoxicants can cause morphological changes that lead to generalized damage to nerve cells (neuronopathy), injury to axons (axonopathy), or destruction of the myelin sheath (myelinopathy). It is well established that exposure to certain agricultural and industrial chemicals can damage the nervous system, resulting in neurological and behavioral dysfunction. Symptoms of neurotoxicity include muscle weakness, loss of sensation and motor control, tremors, alterations in cognition, and impaired functioning of the autonomic nervous system .

The central nervous system (CNS) is composed of the brain and spinal cord. It is responsible for the higher functions of the nervous system (conditioned reflexes, learning, memory, judgment, and other functions of the mind). Chemicals toxic to the CNS can induce confusion, fatigue, irritability, and other behavioral changes. Methyl mercury and lead are known CNS toxicants. Exposure to these metals can also cause degenerative diseases of the brain (encephalopathy). 

The peripheral nervous system (PNS) includes all the nerves not in the brain or spinal cord. These nerves carry sensory information and motor impulses. Damage to the nerve fibers of the PNS can disrupt communication between the CNS and the rest of the body. The organic solvents carbon disulfide, n- hexane,and trichloroethylene can harm the PNS, resulting in weakness in the lower limbs, prickling or tingling in the limbs (paresthesia), and loss of coordination. 

Exposure to chemical agents can trigger a wide range of adverse effects on the nervous system. Neurotoxic substances can alter the propagation of nerve impulses or the activity of neurotransmitters and can disrupt the maintenance of the myelin sheath or the synthesis of protein. As a result, neurotoxicological assessments require the administration of a battery of functional and observational tests. Neurotoxicity in humans is most commonly measured by neurological tests that assess cognitive, sensory, and motor function. 

OVERVIEW

Every year, U.S. industry releases about 24 billion pounds of toxic substances that are believed to cause developmental and neurological problems in children. That amount could fill a string of railroad cars stretching from New York City to Albuquerque, New Mexico, and yet there are no emissions standards for these harmful chemicals. This alarming finding is one of many in Polluting Our Future: Chemical Emissions in the U.S. that Affect Child Development and Learning, a joint report released Thursday by the National Environmental Trust, Physicians for Social Responsibility and the Learning Disabilities Association. 

"That is the most startling thing," said Jeff Wise, policy director for NET. "The amount and how little we know about the chemicals." 

The collaborative effort to produce Polluting Our Future came about in response to recent reports issued by the National Academy of Sciences. These studies indicate a growing consensus among leading scientists that neurological and developmental toxins are responsible for a wide range of physical and mental problems among children. Polluting Our Future looks closely, for the first time ever, at the scope and sources of neurological and developmental air pollutants. "This is the first complete snapshot we've ever had of toxic pollution in this country that can affect the way that children's bodies and brains develop," said Wise.

We're poisoning our kids, toxins report says 

Nearly one in every six, or about 12 million, children in the United States suffers from at least one developmental, learning or behavioral disability such as mental retardation, birth defects, autism or attention deficit hyperactivity disorder. 

Polluting Our Future determines that about one in every 200 American children, or more than 360,000, live with developmental or neurological disabilities caused by exposure to toxic substances including developmental and neurological toxins. 

The report also includes information about releases of developmental and neurological toxins on a national level, a ranking of all the 50 states, and data about the top releasing counties, industries and facilities across the country. All figures are gleaned from data reported by industry to the U.S. Environmental Protection Agency as is required by law. 

According to industry-reported data used in the report, Louisiana and Texas emit the most developmental and neurological toxins to air and water. Tennessee, Ohio, Illinois, Georgia, Virginia, Michigan, Pennsylvania and Florida each release a significant amount of these toxins as well. 

Electric utilities, chemical manufacturers and the makers of paper, metal and plastics are the largest emitters of neurological and developmental toxins nationwide. The researchers also found that African Americans are disproportionately affected by the release of developmental and neurological toxins. In 14 out of the 25 counties across the nation found to emit the most of these chemicals, African American populations exceed the U.S. average. 
The authors of Polluting Our Future stress that policies must be put in place to lower the health risk for children from neurological and developmental toxins. This would include pre-market screening of new chemicals, stringent testing of substances already on the market, labeling, better pollution reporting, more controls for emissions from electric power plants and exposure and disease monitoring. 


I. EXECUTIVE SUMMARY: MAJOR FINDINGS

Reported Emissions. U.S. companies reported to the Environmental Protection Agency that in 1998--the most recent year for which information is available-- they released 1.2 billion pounds of chemicals into the nation's air and water that have the potential to affect the way a child's body and brain develops. More than half (53%) of all toxic chemical emissions reported to the federal Toxics Release Inventory are known or suspected developmental or neurological toxins. 

Estimated Total Emissions. Emissions reported to the federal government account for only an estimated 5% of all chemical releases in the country. Using this estimate and assuming that--like for reported chemicals--approximately half of all emissions are known or suspected developmental or neurological toxins, total estimated releases of these substances to air and water could be as high as 24 billion pounds annually. 

States with Highest Emissions. Louisiana and Texas lead the nation as the number one and two emitters of developmental and neurological toxins. 

Largest Emitter. The chemical manufacturing industry is the single largest industrial source of developmental and neurological toxin emissions (to air and water) in the U.S. Paper, metal, and plastics manufacturers as well as electric power companies are also major emitters of these substances. 

One Industry of Concern. The printing industry is the largest source of air emissions of toluene, a highly released developmental and neurological toxin. Since many printing facilities are small- to medium-sized firms, which are often closer to residential areas than other industrial facilities, this industry is potentially of major concern to child health. 

Disproportionate Impacts on African Americans. Looking at the top 25 counties in the U.S. for releases of developmental toxins--where more than 46% of all reported developmental toxins were released--African American populations in 14 of 25 of the top releasing counties exceed the U.S. average. In other words, African Americans are over-represented in many of the counties most polluted by developmental toxins. 

Increased Developmental and Neurological Effects. A growing number of scientists believe that developmental and neurological toxins could be partly responsible for the increased incidence of a range of physical and mental effects in children, including: 

A 6% increase over 8 years in very low birthweight babies born to young mothers having non-multiple births; 

A 4-1/2% increase over 8 years in premature babies born to young mothers having non-multiple births; 

A doubling of atrial septal defect (a hole in the wall between the chambers of the heart) over an 8-year period; 

A 50% increase in obstructive genito-urinary defects (blockage in the opening of the urinary tract) over 8 years; 
A probable increase in attention deficit hyperactivity disorder as measured by the explosive prescription rate of the drug Ritalin--even accounting for the possibility of overprescription (the number of children taking Ritalin has roughly doubled every 4 to 7 years since 1971); and 

An approximate doubling of the incidence of autism over 30 years. 

Estimates of Children Likely Affected. The U.S. Census Bureau estimates that 12 million U.S. children (17% of all children) suffer from one or more developmental, learning, or behavioral disabilities. The National Academy of Sciences recently estimated that about 3% of developmental and neurological defects in children are caused by exposure to known toxic substances-- including drugs, cigarette smoke, and known developmental and neurological toxins like lead, PCBs, and mercury. This means that 360,000 U.S. children (1 in every 200 U.S. children) suffer from developmental or neurological deficits caused by exposure to known toxic substances. 

Real Impacts are Likely Greater. The actual total impact of developmental and neurological toxins on U.S. children is probably greater for two reasons: The National Academy of Sciences also concluded that an additional 25% of all developmental and neurological defects were caused by environmental factors working in combination with a genetic predisposition, and that toxic substances play an important but undetermined contributory role. Additionally, the 3% estimate includes only known developmental and neurological toxins. Since the overwhelming majority of the 80,000 chemicals in commerce has never been tested for developmental and neurological effects, the number of children affected by all developmental and neurological toxins is probably much higher. 

Economic Costs. The estimated cost to our country, in medical and educational expenses and lost work and productivity, of just 18 of the most significant developmental defects is conservatively estimated to exceed $8 billion a year in aggregated lifetime costs. Using the National Academy of Sciences estimate that known toxic exposures cause about 3% of developmental and neurological disabilities, a range toxic substances including developmental and neurological toxins are responsible for at least $240 million in annual lifetime costs for just 18 developmental disabilities. Once again, when considering the effects of the much larger number of unidentified developmental and neurological toxins in the environment, the National Academy's estimate that toxic chemicals play a contributory role in an additional 25% of developmental effects, and the fact that the above estimate covers just 18 disabilities, the actual economic toll of developmental and neurological toxins is probably much higher. 

Recommended Policies. Because it has focused predominantly on cancer-causing substances, the regulatory system has not addressed the public health risk from developmental and neurological toxins. Effective policies to lower the risks from these substances include pre-market screening of new chemicals, mandatory testing of existing chemicals, product labeling, better pollution reporting, toxic chemical controls for electric power plants, and exposure and disease monitoring.


Findings: Reported Emissions of Developmental and Neurological Toxins

Overview

In 1998 (the most recent year for which records are available), U.S. companies reported to the federal Toxics Release Inventory that they released slightly more than 1.2 billion pounds of chemicals that are classified as known or suspected developmental or neurological toxins into the nation's air and water.

These are chemicals that have the potential to affect the way a fetus or a child's body and brain develops, substances that could cause premature and low birthweight births, birth defects, and learning and behavioral disabilities. More than half (53%) of all toxic chemical releases reported to the federal Toxics Release Inventory are known or suspected developmental toxins or neurotoxins. 

Because fewer than 1% of chemicals in commerce require reporting of their emissions, the emissions reported to the government account for only an estimated 5% (by weight) of all chemical releases in the country. 14 Using this estimate and assuming that--like for reported chemicals--approximately half of all emissions are developmental or neurological toxins, total estimated releases of these substances to air and water could be as high as 24 billion pounds released annually. 

Developmental and Neurological Effects In Children
Incidence and Potential Trends

Health Effects Incidence and the Role of Toxic Exposure While the National Academy of Sciences attributes approximately 3% of developmental and neurological deficits to exposure to a range of toxic substances--including developmental and neurological toxins--the Academy also concludes that environmental factors--which include toxic substances--can cause approximately 25% of all developmental and neurological deficits working in combination with a genetic predisposition. 17 

Both of the National Academy panel's estimates should be considered conservative: 

The 3% estimate was only for known and identified toxic substances such as cigarette smoke, drugs, and toxic chemicals like PCBs, lead, and mercury. When considering the thousands of substances in commerce that are still as yet unidentified developmental and neurological toxins, a more realistic estimate of the actual the role of developmental and neurological toxins in causing developmental and neurological deficits would have to be higher. 

In its estimate that environmental triggers working together with a genetic predisposition can cause approximately 25% of developmental and neurological deficits, the Academy is only referring to well recognized and clinically diagnosed mental and physical disabilities. There is a strong possibility--widely recognized among epidemiologists--that there may be many subtle mental and physical deficits that have not been diagnosed yet and are, therefore, not captured in this estimate.

Even though the National Academy's 3% estimate probably vastly underestimates the role of all developmental and neurological toxins in contributing to all developmental and neurological deficits, it is the only firm and authoritative estimate available to calculate a rough approximation of the role that known toxic substances may play in contributing to clinically diagnosed disabilities: 

The Census Bureau estimates that nearly 12 million U.S. children under 18 (17% of children) suffer from one or more developmental, learning, or behavioral disabilities.18 If, according to the National Academy of Sciences, known toxic exposures are directly implicated in approximately 3% of these disabilities, then 360,000 U.S. children--or 1 in every 200 children--suffer from developmental or neurological defects caused by exposure to known toxic substances including developmental and neurological toxins.

Once again, considering the fact that 25% of all deficits have an undetermined environmental component and that we have not considered the number of unidentified toxins or undiagnosed deficits, the above estimate is likely to be highly conservative. 

Possible Upward Trends in Developmental and Neurological Effects
With the increased production and use of developmental and neurological toxins over the last several decades, one would expect to see an increased incidence of developmental and neurological effects in U.S. children. In fact, this is exactly what we may be seeing. 19 

The developmental and neurological conditions discussed below are the only ones for which some statistical data has been gathered. In each case, there is statistical evidence for increases in incidence. Whether other conditions are on the increase is unclear because statistics are not collected for the vast majority of developmental, learning, and behavioral conditions. While toxic exposures have been clearly associated with a wide range of developmental and neurological effects, there are very little data that allow for an accurate assessment of the specific role that toxins play in the incidence of specific developmental and neurological deficits in U.S. children. 

Low Birthweight and Premature Births

Exposure to a number of environmental agents, such as solvents, pesticides, lead, PCBs, benzene, carbon tetrachloride, and toluene, have been found to have negative impacts on birthweight. While fewer toxic substances have been directly implicated in causing premature births,20 a number of studies have demonstrated increased levels of premature births in communities located near hazardous waste sites or facilities. 21 

Low birthweight and premature births have been rising steadily since the mid-1980s among a range of ethnic and maternal age groups. This has occurred despite increased prevention efforts. Low birthweight and age of gestation still provide the best predictive indicators of the risk of several major permanent developmental or neurological impairments, such as cerebral palsy and mental retardation. They are also strongly associated with Sudden Infant Death Syndrome, infant mortality in general, a range of infections, and other major disabilities. 
From 1990-1997, very low birth weight babies increased by 6% for white mothers aged 20-34 having single births. 22 

Premature babies increased 4.6% among the same group during a similar time range. 23

Structural Birth Defects

Birth defects are the leading cause of infant mortality in the U.S., causing about 70% of all neonatal deaths (before 1 month of age) and about 22% of the 6,000 deaths of infants (less than 12 months of age). 24 While about 20% of birth defects have known causes, the causes of 80% of all birth defects are unknown. 

Evidence is mounting that environmental factors play an important role in contributing to the incidence of birth defects and developmental disorders. In addition to the conclusions of the National Academy of Sciences, the Pew Environmental Health Commission lists more than a dozen studies linking a range of toxic substances in the environment with structural birth defects. 25 

Few states keep adequate records that would allow for meaningful conclusions about birth defect trends. Nevertheless, some trends have been substantiated across a large number of states:

The number of infants born with atrial septal defect (a hole in the wall between the two chambers of the heart) rose 2-1/2 times over an eight-year period (1989-1996). Part of this dramatic increase may be due to increased diagnosis and part to increased incidence. Without additional data over a longer period of time, it will be difficult to make specific determinations. 26 

The number of infants born with obstructive genito-urinary defects (complete or partial blockage in the opening of the urinary tract) increased 1.6 times over eight years (1990-1997). Once again, more information will be needed to determine specific causes of the increase. 27

[For more information about additional increases of specific birth defects recorded in individual states or regions of the country, see Healthy from the Start, Pew Environmental Health Commission, November 1999.

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