9 Pollution and Human Health Risks from Chemical
Pesticides
Increasing concerns regarding the effects of environmental contaminants on human
disease or morbidity, as well as, on ecological systems, such as on organisms
important to agricultural productivity, like fish, and pollinators, have driven a great
deal of community-based “citizen science”, research, pollution prevention technologies, and policy outcomes.
9.1 Zone of Influence
The effect of the pesticides on target organisms, as well as on possible fringe or
nontarget organisms, is a critical component to be fully examined prior to selection
of pesticides as a control measure. There are numerous examples of unintended harm
to nontarget organisms from pesticides that were developed for a useful purpose:
from the impact of the organochlorine DDT on avian eggs to more recent examples
of neonicotinoid pesticides on the navigation ability of insect pollinators.
Tolerance figures are arrived at, for the most part, by studying the influence of the
poisoning agent on small samples of organisms under laboratory conditions for
relatively short durations. The objective of these studies is the evaluation of the
survival or death of the organism as expressed in LC 50 values. These are a statistical
estimate of the concentration of the pesticide required to kill 50% of the population
under study. Such values are usually reported for a given length of exposure.
Sometimes this information is reported as survival time for a given percentage of
organisms at a given concentration of lethal agent. The point is, however, that these
data do not tell us much about survival rates in nature since the level of the chemical
agent causing death depends on the organism’s physiology and total environment.
Variation in these factors modifies the laboratory-based LC 50 value. In addition, to
kill or not to kill is only part of the role played by the poisonous agent. The effect on
growth and development for nontarget and target organisms that survive is a role of
longer duration and far greater complexity that remains to be unraveled for most
chemical pesticides.
For aquatic life, toxicity of an agent is commonly reported as a TLm96 value.
These aquatic toxicity ratings are defined as the 96-hour static or continuous flow
concentration producing a toxic effect. For aquatic life, toxicity of an agent generally
decreases with increasing salinity, turbidity, or organic content of the water. These
effects appear to be the result of decreasing the concentration of the toxic agent either
by decreasing its aqueous solubility or by adsorption to particulate matter. In
general, the toxic effect of the pesticide is proportional to temperature, reflecting
the increased metabolic activity of organisms to a certain maximum level as temperature is elevated.
A compendium of toxicity values for selected aquatic organisms to various
pesticides is the National Institute of Occupational Safety and Health Registry [14].
406
L. S. Clesceri and E. J. Clesceri
Pesticides
Increasing concerns regarding the effects of environmental contaminants on human
disease or morbidity, as well as, on ecological systems, such as on organisms
important to agricultural productivity, like fish, and pollinators, have driven a great
deal of community-based “citizen science”, research, pollution prevention technologies, and policy outcomes.
9.1 Zone of Influence
The effect of the pesticides on target organisms, as well as on possible fringe or
nontarget organisms, is a critical component to be fully examined prior to selection
of pesticides as a control measure. There are numerous examples of unintended harm
to nontarget organisms from pesticides that were developed for a useful purpose:
from the impact of the organochlorine DDT on avian eggs to more recent examples
of neonicotinoid pesticides on the navigation ability of insect pollinators.
Tolerance figures are arrived at, for the most part, by studying the influence of the
poisoning agent on small samples of organisms under laboratory conditions for
relatively short durations. The objective of these studies is the evaluation of the
survival or death of the organism as expressed in LC 50 values. These are a statistical
estimate of the concentration of the pesticide required to kill 50% of the population
under study. Such values are usually reported for a given length of exposure.
Sometimes this information is reported as survival time for a given percentage of
organisms at a given concentration of lethal agent. The point is, however, that these
data do not tell us much about survival rates in nature since the level of the chemical
agent causing death depends on the organism’s physiology and total environment.
Variation in these factors modifies the laboratory-based LC 50 value. In addition, to
kill or not to kill is only part of the role played by the poisonous agent. The effect on
growth and development for nontarget and target organisms that survive is a role of
longer duration and far greater complexity that remains to be unraveled for most
chemical pesticides.
For aquatic life, toxicity of an agent is commonly reported as a TLm96 value.
These aquatic toxicity ratings are defined as the 96-hour static or continuous flow
concentration producing a toxic effect. For aquatic life, toxicity of an agent generally
decreases with increasing salinity, turbidity, or organic content of the water. These
effects appear to be the result of decreasing the concentration of the toxic agent either
by decreasing its aqueous solubility or by adsorption to particulate matter. In
general, the toxic effect of the pesticide is proportional to temperature, reflecting
the increased metabolic activity of organisms to a certain maximum level as temperature is elevated.
A compendium of toxicity values for selected aquatic organisms to various
pesticides is the National Institute of Occupational Safety and Health Registry [14].
406
L. S. Clesceri and E. J. Clesceri