Human exposure to pesticides can occur directly, especially for agricultural
workers and their families. Individuals residing in areas near farms where
pesticides are heavily applied may also be directly exposed. Indirect exposure
can also occur, e.g., when pesticide residues on food or contaminated fish are
ingested. Some synthetic organic pesticides are slow to degrade and persist in
the environment for years. Accumulation of various types of pesticides in
human tissues can therefore occur and result in health problems.
It is clear that an enormous effort has been made in the U.S. by
government, industries, and the public in an attempt to reduce environmental
pollution. Such effort has led to a number of encouraging results. According to
the U.S. Environmental Protection Agency’s 1994 annual assessment of urban
air pollution, air quality in the U.S. was improving; however 43 metropolitan
regions, home to nearly 100 million Americans, had O 3 levels at more than
0.12 ppm, exceeding federal health standards. In the Los Angeles Basin, in
particular, the pollution is so bad that it was given a deadline of 2010 to meet
the federal standards.
3.7 ACUTE AND CHRONIC EFFECTS
3.7.1 INTRODUCTION
In studying the health effects of toxicants on living organisms, researchers often
identify effects as acute or chronic. An acute effect refers to that manifested by
severe injuries or even death of an organism, and is characterized by exposure
to high concentrations of a toxicant or toxicants for a short period of time. A
chronic effect is characterized by a long-term or recurrent exposure to relatively
low concentrations of toxicants. Signs and symptoms vary depending on the
types of toxicants, their concentrations, and species of exposed organisms.
3.7.2 ACUTE EFFECTS
A number of acute pollution episodes have occurred in different parts of the
world since 1930. A brief review of several major ones follows, and readers are
referred to detailed reviews published elsewhere.
5
3.7.2.1 Meuse Valley, Belgium, 1930
This episode occurred on December 1, 1930 in Meuse Valley, Belgium, where a
large number of industrial plants were located. A thermal inversion caused
pollutants, such as SO 2 , sulfuric acid mist, and particulates, emitted from these
plants, to be trapped in the valley. Many people became ill with respiratory
discomforts. Reported casualties include 60 human deaths and some deaths in
cattle.
36
Environmental Toxicology
[16:54 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-003.3d]
Ref: 4365 MING-HO YU Chap-003 Page: 36 31-44
workers and their families. Individuals residing in areas near farms where
pesticides are heavily applied may also be directly exposed. Indirect exposure
can also occur, e.g., when pesticide residues on food or contaminated fish are
ingested. Some synthetic organic pesticides are slow to degrade and persist in
the environment for years. Accumulation of various types of pesticides in
human tissues can therefore occur and result in health problems.
It is clear that an enormous effort has been made in the U.S. by
government, industries, and the public in an attempt to reduce environmental
pollution. Such effort has led to a number of encouraging results. According to
the U.S. Environmental Protection Agency’s 1994 annual assessment of urban
air pollution, air quality in the U.S. was improving; however 43 metropolitan
regions, home to nearly 100 million Americans, had O 3 levels at more than
0.12 ppm, exceeding federal health standards. In the Los Angeles Basin, in
particular, the pollution is so bad that it was given a deadline of 2010 to meet
the federal standards.
3.7 ACUTE AND CHRONIC EFFECTS
3.7.1 INTRODUCTION
In studying the health effects of toxicants on living organisms, researchers often
identify effects as acute or chronic. An acute effect refers to that manifested by
severe injuries or even death of an organism, and is characterized by exposure
to high concentrations of a toxicant or toxicants for a short period of time. A
chronic effect is characterized by a long-term or recurrent exposure to relatively
low concentrations of toxicants. Signs and symptoms vary depending on the
types of toxicants, their concentrations, and species of exposed organisms.
3.7.2 ACUTE EFFECTS
A number of acute pollution episodes have occurred in different parts of the
world since 1930. A brief review of several major ones follows, and readers are
referred to detailed reviews published elsewhere.
5
3.7.2.1 Meuse Valley, Belgium, 1930
This episode occurred on December 1, 1930 in Meuse Valley, Belgium, where a
large number of industrial plants were located. A thermal inversion caused
pollutants, such as SO 2 , sulfuric acid mist, and particulates, emitted from these
plants, to be trapped in the valley. Many people became ill with respiratory
discomforts. Reported casualties include 60 human deaths and some deaths in
cattle.
36
Environmental Toxicology
[16:54 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-003.3d]
Ref: 4365 MING-HO YU Chap-003 Page: 36 31-44