142 Ecology and Applied Environmental Science
in dangerous concentrations in foods, in milk and in the fatty parts of the
human body. The persistent parasiticides along with the products of their
breakdown, which in many cases are even more toxic, move along the food
chains and biomagnification occurs. There are also other risks, such as the
appearance of adverse effects. For example, in the aqueous environment,
parasiticides such as parathion hydrolyse into substances that are capable,
in the presence of chlorine, of being transformed into other extremely toxic
organic compounds. When such water is used for drinking, serious risks for
human health are created. In such cases, the chlorine comes from the artificial
chlorination of drinking water for the purpose of protecting public health.
Of particular importance among the biocides are the chlorinated hydrocarbons (DDT, Aldrin, Dieldrin, etc.), which began to be used massively
after World War II. Knowledge about them is mainly based on the study
of the one most widely used, DDT. The chlorinated hydrocarbons are only
slightly soluble in water but highly soluble in fats, and therefore they tend to
concentrate rapidly in the bodies of organisms. They are highly mobile and
adhere to dust particles and travel along with them over great distances in
the atmosphere. If DDT is present in a body of water it escapes along with
water vapour into the atmosphere. Chlorinated hydrocarbons have been
found in polar ice and in the bodies of animals in the arctic zone.
Chlorinated hydrocarbons are highly stable. DDT has a half-life (the time
needed for 50% of its mass to disintegrate) in the environment of around
4 years. Due to the phenomenon of biomagnification, the chlorinated hydrocarbons tend to become concentrated in the higher trophic levels. They act
on various organisms in many different ways. In insects, they exert their
lethal effect on the central nervous system. Fish appear to be especially
susceptible, perhaps because they inhibit the uptake of oxygen through the
gills, resulting in death by asphyxiation. The chlorinated hydrocarbons
also appear to inhibit photosynthesis in some categories of phytoplankton,
something which may have more general ecological impacts. Slower rates
of reproduction in birds belonging to higher trophic levels have also been
noted. DDT, at high concentrations in the bodies of birds due to biomagnification, reduces the production of estrogen hormones, with adverse
impacts on sexual behaviour and also on eggshell strength due to lack of
calcium. Research in this regard has shown that the concentration of DDT
in a marine food chain is:
• In marine plants: 0.04 ppm
• In herbivorous fish: 0.23 ppm
• In carnivorous fish: 2.07 ppm
• In higher carnivorous birds: 13.8 ppm
The chlorinated hydrocarbons have a very low direct toxicity to humans
and other mammals, but they appear to have adverse long-term impacts.
in dangerous concentrations in foods, in milk and in the fatty parts of the
human body. The persistent parasiticides along with the products of their
breakdown, which in many cases are even more toxic, move along the food
chains and biomagnification occurs. There are also other risks, such as the
appearance of adverse effects. For example, in the aqueous environment,
parasiticides such as parathion hydrolyse into substances that are capable,
in the presence of chlorine, of being transformed into other extremely toxic
organic compounds. When such water is used for drinking, serious risks for
human health are created. In such cases, the chlorine comes from the artificial
chlorination of drinking water for the purpose of protecting public health.
Of particular importance among the biocides are the chlorinated hydrocarbons (DDT, Aldrin, Dieldrin, etc.), which began to be used massively
after World War II. Knowledge about them is mainly based on the study
of the one most widely used, DDT. The chlorinated hydrocarbons are only
slightly soluble in water but highly soluble in fats, and therefore they tend to
concentrate rapidly in the bodies of organisms. They are highly mobile and
adhere to dust particles and travel along with them over great distances in
the atmosphere. If DDT is present in a body of water it escapes along with
water vapour into the atmosphere. Chlorinated hydrocarbons have been
found in polar ice and in the bodies of animals in the arctic zone.
Chlorinated hydrocarbons are highly stable. DDT has a half-life (the time
needed for 50% of its mass to disintegrate) in the environment of around
4 years. Due to the phenomenon of biomagnification, the chlorinated hydrocarbons tend to become concentrated in the higher trophic levels. They act
on various organisms in many different ways. In insects, they exert their
lethal effect on the central nervous system. Fish appear to be especially
susceptible, perhaps because they inhibit the uptake of oxygen through the
gills, resulting in death by asphyxiation. The chlorinated hydrocarbons
also appear to inhibit photosynthesis in some categories of phytoplankton,
something which may have more general ecological impacts. Slower rates
of reproduction in birds belonging to higher trophic levels have also been
noted. DDT, at high concentrations in the bodies of birds due to biomagnification, reduces the production of estrogen hormones, with adverse
impacts on sexual behaviour and also on eggshell strength due to lack of
calcium. Research in this regard has shown that the concentration of DDT
in a marine food chain is:
• In marine plants: 0.04 ppm
• In herbivorous fish: 0.23 ppm
• In carnivorous fish: 2.07 ppm
• In higher carnivorous birds: 13.8 ppm
The chlorinated hydrocarbons have a very low direct toxicity to humans
and other mammals, but they appear to have adverse long-term impacts.