Environmental Medicine

Abstract

An environmental pathogen may be defined as a physical, chemical, or biological agent that, when present in the environment, causes an increased risk of disease. Environmental pathogens are usually present at only very low levels and the diseases that they cause may go unnoticed as only a small increase in disease incidence above “natural” background levels. Environmental pathogens have very different effects depending on their concentration. At a high level, toxic chemicals cause disease by direct damage to tissues. Such toxins are of course a major environmental concern. Their presence in the environment is a serious but avoidable event. Our major concern will be with environmental pathogens present at much lower doses than a direct toxic level. Low-level environmental pathogens cause disease mostly by damaging DNA. The effect of low-level environmental pathogens on other molecules is usually insignificant. For example, the ultraviolet component of sunlight causes slow deterioration of subcutaneous connective tissue, but this does not cause significant disability. When sunlight damages DNA, however, the result may be a squamous-cell carcinoma. The real danger of an environmental pathogen is a mutagenic event resulting from damage to DNA. The accumulation of mutagenic events has the potential to transform a cell into a cancer. It is this biological amplification of a single base-pair mutation resulting in a large malignant tumor that makes environmental pathogens a health risk at very low doses.