Health is a state of physical, mental, and social well-being, not merely the absence of disease or infirmity. Environmental health focuses on health risks in the natural, social, cultural, and technological worlds in which we live.
The world is now undergoing a dramatic epidemiological transition. The traditional killers—infectious diseases, maternal and perinatal complications, and nutritional deficiencies—still take a terrible toll in the developing world, but health problems such as heart attack, depression, and traffic accidents, once thought to occur only in rich countries, are now becoming the leading killers everywhere as people live longer and adopt Western lifestyles and diets.
Disability-adjusted life years (DALYs) measure the disease burden arising both from premature deaths and the loss of healthy life resulting from illness and disability.
Emergent diseases are those not previously known or that have been absent for at least 20 years. Some examples are SARS (severe acute respiratory syndrome), West Nile virus, and AIDS (acquired immune deficiency syndrome). AIDS is currently the most deadly of these diseases, infecting about 65 million people and killing some 3 million every year.
Only 10 percent of all medical expenditures go to the major diseases that effect 90 percent of the world population. Currently, the United States donates only 0.01 percent of its GDP for health care in the developing world. Investing more would not only save millions of lives, but could boost the world economy significantly.
CWD (chronic wasting disease), a rapidly spreading brain disease in deer, is an emergent ecological disease. Some other examples are sudden oak death in California, black band coral disease in the Caribbean, and domoic acid poisoning, which is killing marine mammals in the Pacific.
Toxins are poisons. They can be very specific because they interact with and disrupt the metabolic machinery that keeps cells alive. Some materials are so supertoxic that a single molecule can cause cell death.
Allergens, carcinogens, mutagens, neurotoxins, teratogens, and endocrine disrupters all are examples of toxins that cause specific health problems. Diet, also, is an important health factor.
Solubility, persistence, chemical reactivity, and bioaccumulation all are important factors in toxicity as are timing, dose, and route of exposure. Characteristics and condition of the target organism also are very influential in determining effects of toxins.
Children are much more sensitive to most toxins than are adults. Pound for pound, children drink more water, eat more food, and breathe more air than adults. How best to protect children from environmental hazards is a difficult, but important, question.
Some persistent organic pollutants (POPs) such as PBDE, PFOS, PFOA, and BPA are now found throughout the world. Every human has them in his or her blood. The health effects of these compounds are not yet known, but there are concerns about chronic exposures.
We depend on animal testing for much of our assessment of toxins, but great differences in sensitivity between species makes risk evaluation difficult. Just because something can be detected, doesn't mean that it's present in a dangerous form or concentration.
Our perception of risk is strongly influenced by emotion and factors such as whether the hazard is voluntary, familiar, has a lag before its effects are known, and whether those at risk benefit from the source of exposure.
Health experts generally regard a 1 in 1 million risk of death to be acceptable, but some people ask, "Acceptable to whom?" We often disregard familiar but serious risks, while demanding protection from other, highly improbable risks.
