General principles of microbial pathogenesis : Robbins & Cotran : Pathology : Frank , McAdam

Many diseases are caused or influenced by environmental
factors. Broadly defined, the term ambient environment
encompasses the various outdoor, indoor, and occupa-
tional settings in which humans live and work. In each of
these settings, the air people breathe, the food and water
they consume, and the toxic agents they are exposed to are
major determinants of health. Other environmental factors
pertain to the individual (“personal environment”) and
include tobacco use, alcohol ingestion, therapeutic and
“recreational” drug consumption, diet, and the like. It is
generally believed that factors in the personal environment
have a larger effect on human health than that of the
ambient environment, but new threats related to global
warming (described later) may change this equation.
The term environmental disease refers to disorders
caused by exposure to chemical or physical agents in the
ambient, workplace, and personal environments, includ-
ing diseases of nutritional origin. Environmental diseases
are surprisingly common. The International Labor Organi-
zation has estimated that work-related injuries and ill-
nesses kill more people per year globally than do road
accidents and wars combined. Most of these work-related
problems are caused by illnesses rather than accidents. The
burden of disease in the general population created by
nonoccupational exposures to toxic agents is much more
difficult to estimate, mostly because of the diversity of
agents and the difficulties in measuring the dose and dura-
tion of exposures. Whatever the precise numbers, environ-
mental diseases are major causes of disability and suffering
and constitute a heavy financial burden, particularly in
developing countries.
Environmental diseases are sometimes the consequence
of major disasters, such as the methyl mercury contamina-
tion of Minamata Bay in Japan in the 1960s, the leakage of
methyl isocyanate gas in Bhopal, India, in 1984, the Cher-
nobyl nuclear accident in 1986, the Fukushima nuclear
meltdown following the tsunami in 2011, and lead poison-
ing resulting from contaminated drinking water in the city
of Flint in the United States in 2016. Fortunately, these are
unusual and infrequent occurrences. Less dramatic, but
much more common, are diseases and injury produced by
chronic exposure to relatively low levels of contaminants.
It should be noted that a host of factors, including complex
interactions between pollutants producing multiplicative
effects, as well as the age, genetic predisposition, and dif-
ferent tissue sensitivities of exposed persons, create wide
variations in individual sensitivity. Disease related to mal-
nutrition is even more pervasive. In 2010, it was estimated
that 925 million people were malnourished—one in every
seven persons worldwide. Children are disproportionately
affected by undernutrition, which accounts for more than
50% of childhood mortality worldwide.
In this chapter, we first consider the emerging problem
of the health effects of climate change. We then discuss the
mechanisms of toxicity of chemical and physical agents,
and address specific environmental disorders, including
those of nutritional origin.