Speech-language pathologists and audiologists continue to be challenged by increasing numbers of children on their caseloads who present with a variety of developmental and learning disabilities of unknown or undetermined origin. Apart from the budget and service delivery concerns associated with larger caseloads in schools, parents and professionals alike seek explanations for why so many of our children are receiving diagnoses such as attention deficit hyperactivity disorder or those under the autism spectrum.
Recent research reveals that exposures to neurotoxicants such as lead, mercury, and pesticides can have a particularly detrimental impact on brain function and in turn lead to the expression of learning and developmental disabilities, including speech, language, and hearing disorders (Miller & Snow, 2004; Schettler, Stein, Reich, Valenti, & Wallinga, 2000). The complex interaction of genetics and the environment during windows of vulnerability may lead to the expression of various disabilities. These environmental contributors to disability are often the least appreciated yet the most preventable.
Children are uniquely susceptible to hazardous environmental exposures-they are not little adults (National Academy of Sciences, 1993). Exposures that occur before conception and continue through late adolescence can cause or contribute to disease and can disrupt development, learning, and behavior. For example, a child's biological system is still developing: pound per pound they eat, drink, and breathe far more than adults and their behavior, such as crawling on the ground and putting their hands in their mouths after touching the floor, results in higher toxic exposure. Metabolism of many compounds, even common ones such as caffeine, is limited during the first six months of life, making them more vulnerable.
In comparison to adults, children have periods of rapid brain growth in utero and during the first few months of life through puberty and up to 20 years of age when the brain reaches its maximum weight. The greatest neurological difference between adults and children includes the immaturity of the blood brain barrier, which is not fully developed until after 6 months of age. Rigid and predictable periods of nervous system cell proliferation, migration, and differentiation create windows of vulnerability for the young brain. These two features combined make the young brain a less stable organ and a more culpable target of toxicity when compared to the adult counterpart.
To date, most learning and developmental disability groups have focused on identifying affected children and getting them the services they need-something that is, of course, very important. However, there is a parallel need for prevention of exposures that lead to or exacerbate these disabilities. Prevention of communication disorders has always been a part of the scope of practice for SLPs and audiologists.
Science typically can't identify a single chemical "cause" of a developmental or learning disability. There are hundreds of neurotoxicants and suspected neurotoxicants in production that have not been thoroughly tested for adverse health effects. Given the knowledge and experience we have gained about developmental effects of neurotoxicants, we have an ethical responsibility to protect our children (Gilbert, 2005). Therefore environmentalists and public health officials are beginning to adopt the "precautionary principle" with regard to chemical exposures. The precautionary principle states:
When an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically. In this context the proponent of an activity, rather than the public, should bear the burden of proof. The process of applying the precautionary principle must be open, informed, and democratic and must include potentially affected parties. It must also involve an examination of the full range of alternatives, including no action. (Science and Environmental Health Network, 1998).
Lead provides an important example of hazardous environmental exposures that may lead to disabilities because it is the most researched neurodevelopmental toxicant. Lead exposure in schools can occur through older drinking water systems with leaded pipes or from cracking and peeling paint that produces lead dust. This lead dust may be inhaled or inadvertently ingested by children, teachers, and administrators alike. More recently lead has been found in children's jewelry, school lunch boxes, and even candy. Lead has an affinity for the central nervous system (CNS) and it deposits in bone as a substitute for calcium. Very high lead levels in blood can result in encephalopathy; very low levels can result in cognitive impairment and behavioral difficulties. In 1979 Herbert Needleman published a research paper that found an association between lead levels in teeth and difficulty following classroom instruction, unruly behavior, greater distractibility, and reduced auditory and verbal processing (Needleman et al., 1979). Lesser known CNS effects from lead include hearing and balance (Bhattacharya, Shukla, Bornschein, Dietrich, & Keith, 1990).
Although blood lead levels in children and adults have been declining over the past 30 years, deterioration or renovation of homes and complexes constructed prior to 1980 can result in exposure to contaminated paint chips or dust. Lead-tainted soil can persist as long as 2,000 years and contaminated house dust remains a significant source of lead exposure for children in urban communities (Koger, Schettler, & Weiss, 2005). Children also may be exposed through inhalation of lead dust from home renovation or take-home occupational exposures of adults in the household. Poor academic performance and low intelligence test scores have been associated with even low lead levels (Needleman et al., 1979).
Long-term follow up of children with early childhood exposures reveals the irreversibility of lead's effects on cognitive and behavioral impairment (Needleman, 1998). These studies have been substantiated elsewhere (Schwartz, 1994). Recent evidence suggests that lead exposure below the current Centers for Disease Control and Prevention standard of 10 µg/dL blood lead level results in cognitive deficits (Lanphear et al., 2005). The effects of a developmental disorder last a lifetime with societal costs measured in the billions of dollars (Landrigan, Schechter, Lipton, Fahs, & Schwartz, 2002). Prevention of childhood lead exposure at home and school is the best course of action to protect the potential of our children.
Over the years, many schools have relied on pesticide applications to control pests. However, recent research reminds us that pesticides are poisonous and many are neurotoxicants. Exposure to pesticides is linked with cancer, birth defects, and most notably, neurological and behavioral disorders.
There is a movement across the nation to eliminate pesticide use at schools to manage pests and this safer alternative is called Integrated Pest Management (IPM). IPM is a method of pest control that emphasizes prevention of pests and allows the use of "least toxic" pesticides when necessary to protect human health. IPM is a shift in thinking to prevention in the first place. It eliminates the cause of pests by minimizing their access to food, water, and hiding places. Many schools are finding that implementing IPM as an "ounce of prevention" can save time and money with the added benefit of being safer for children's neurological development and the environment. Recent examples include the Seattle, WA IPM policy (www.seattleschools.org/area/facilities/IPM/IPM.htm) and the Pennsylvania IPM policy (http://paipm.cas.psu.edu/schools/PSBApolicy.html).
A good place to find more information and resources on an IPM program for schools is the Safer Pest Control Project (http://spcpweb.org) based in Chicago, IL. This project conducts site assessments, workshops, and ongoing technical assistance and maintains a speaker's bureau that travels the surrounding states educating school administrators, homeowners, and even garden clubs on IPM implementation. The project also has a 12-minute video available for purchase entitled, "Integrated Pest Management in Schools: A Better Method." See The ASHA Leader Online for more resources.
Elemental Mercury Exposure
Elemental mercury exposure in schools occurs from broken thermometers and thermostats, spills from improperly stored or handled mercury in the chemistry lab, and accidents when using mercury in the science lab for experiments. In 2004, six Environmental Protection Agency (EPA) regional offices responded to mercury spills that included 12 emergency removals from schools. EPA cleanup costs for elemental mercury in 2004 ranged from $1,000 to $200,000 per school.
Elemental mercury is most toxic in its vapor form. It slowly vaporizes at room temperature and more quickly when heated. Children exposed to elemental mercury can be seriously poisoned by breathing in the invisible vapor. Elemental mercury vapor, like lead, is a well-known neurotoxicant that can disrupt normal brain development in the child and fetus. Children exposed to elemental mercury for long periods of time may have trouble learning in school, and exposure to mercury can result in communication and learning disabilities that may be irreversible (Skavroneck & Stenstrup, 1998).
The EPA has developed a program, with funding, to help schools get rid of elemental mercury and many other harmful chemicals that could adversely affect children's health. The Schools Chemical Cleanout Campaign (SC3) was started in 2004 to help schools remove potentially harmful chemicals, conduct chemical management training for lab instructors, and raise national awareness of the issue of chemicals in schools (see the Resources online for more information.)
Understanding the role that exposures to neurotoxicants play in the etiology of communication disorders in our most vulnerable of populations-young children-is an important landmark because many of these exposures are either preventable or amenable to change. Through self-directed learning, SLPs and audiologists become better prepared to serve as important members of the health profession/research team. Education regarding children's environmental health will enable the practicing SLPs and audiologists to provide parents with information using brochures and Web site information about exposures commonly found in their child's environment.
Partnerships with the Learning and Developmental Disabilities Initiative (LDDI) and its member organizations will afford researchers in the field of communication disorders opportunities to forge into new territory, taking into consideration the possible role of neurotoxicant dose and timing on the nature of hearing loss, language delays, and a host of other communication disorders in children.
Educators and public health professionals can make powerful partners in taking action at local, state, and national levels to prevent exposure to neurotoxicants that lead to learning disabilities.