We are fortunate in that we are endowed with excess capacity in all our organ systems. We have two kidneys but can survive on the functional capacity of one normal kidney. We have two lungs but can survive on just one. The capacity of most of our enzymes and biochemical processes is greater than we usually require. Because of the excess capacity in all our organ systems, we are able to sustain considerable injury and diminution in functional capacity before there is any organ malfunction and therefore any symptoms.
Xenobiotic chemicals do their damage to our body's chemical mechanisms one molecule at a time.
Individuals exposed to xenobiotic chemicals on a regular basis will experience regular injuries that will accumulate over time to eventually result in organ malfunction. Whether or not one develops illness from chemicals depends upon the extent of the injury caused by any given exposure, the rate at which the injury can be repaired, and the frequency with which the exposure and the injury are repeated. If one goes to work and sustains an eight-hour exposure to a solvent, some of the solvent will enter the body and combine with some of the tissue components causing a finite amount of injury. This sequence of events will be repeated each work day and the individual will accumulate injuries, injuries which will eventually lead to erosion of the excess functional capacity and organ malfunction. This process will remain unnoticed until the loss of functional capacity results in symptoms.