I discussed in a prior post the prevalence of JP-4 in the military and the exposure servicemembers had to it. This exposure can lead to significant disabilities. Veterans need to be aware of these disabilities and how they are related to service. JP-4 causes service connected disabilities.
JP-4 is comprised of many neurotoxic and carcinogenic substances, and it is likely that chronic exposure to JP-4 can lead to severe neurological problems. The brain and peripheral nervous system is particularly vulnerable to damage from chemical exposure, as “aromatic” hydrocarbons and “volatile” organic compounds are often absorbed through the nose, which has fewer barriers between the outside world and the brain. This is compounded by the fact that many of these chemicals are lipid-soluble chemicals that are able to cross the blood-brain barrier easily. Often, relatively small losses of neurons that utilize neurotransmitters can have great repercussions. It’s sort of like how a paper cut on your finger isn’t too bad, but the thought of getting one on your eye makes your heart race. The neurological system is delicate, vulnerable, and damage is often permanent, as brain cells do not regenerate.
Parkinson’s Disease and its related syndromes are typically caused by damage or dysfunction of dopamine-secreting cells in an area of the brain called the substantia nigra. Several components of JP-4 can cause either direct damage to these cells, or cause mutations in specific genes. In fact, 20% of Parkinson patients have been found to have chronic exposure to hydrocarbons. Exposure to hydrocarbons can not only cause Parkinson’s, but often cause an earlier onset, speed up the progression of the disease, and increase the severity of symptoms. The hexane in JP-4 has been shown to create lesions in the central nervous system, which lead to both peripheral neuropathy as well as Parkinson’s. Toulene has been shown to induce changes in the expression of the SKP1 gene , which not only can cause Parkinson’s disease, but also affects tumor suppressors.
Alzheimer’s Disease and Dementia
While there seems to be at least a small genetic component of Alzheimer’s Disease and other dementias, there has been a great deal of research that shows occupational exposure to certain chemicals can cause, worsen, or accelerate dementia. Exposure to solvents such as benzene and toluene has been shown to correlate with an increased risk of Alzheimer’s Disease, and recently, there has been much research that is implicating exposure to metals such as lead (which is found in JP-4) have also been implicated in dementia.
As mentioned above, the n-hexane found in JP-4 has been shown to cause peripheral neuropathy, and distal nerve fiber degeneration throughout the nervous system. In some cases, the peripheral neurodegeneration caused by chronic exposure to n-hexane and its metabolites can lead to atrophy of the skeletal muscles.
Brain Damage/Toxic Encephalopathy
The brain is subject to damage from chemical injury, just as it is vulnerable to physical injury, and it often results in what is known as toxic encephalopathy. This isn’t a distinct disease or disorder. It just means disorder (“pathy”) relating to the brain (“encephalo”) caused by toxins. It tends to be used as a catch-all to describe damage done to the brain that can’t be labelled as “Parkinson’s” or another discrete neurological disease.
Toulene and xylene (along with trichloroethylene (TCE,) which is a solvent many in the military use on a regular basis, including many who are regularly exposed to JP-4, such as aircraft mechanics and electronics technicians) have both been shown repeatedly to cause symptoms of brain atrophy, reduction in nerve conduction, loss of both grey and white matter, and a general “clinical syndrome of premature aging of cortical function.”
Chronic exposure to toulene has been shown to affect the function of the N-methyl-D-aspartate (NMDA) receptors in the hippocampus. This leads to an average of 7% decrease in cognitive function, including visual memory, verbal memory, visual pattern perception, and even manual dexterity.
Other Neurological problems
While research on occupational exposure to chemicals and other neurological disorders such as Amyotrophic lateral sclerosis (ALS) and Huntington’s does not show a direct correlation, it is likely that the damage and oxidative stress caused by occupational exposure to the neurotoxins found in jet fuel can worsen the symptoms or progression of these disorders.