Uses and Environmental Pollution of Biocides - Pesticides: Evaluation of Environmental Pollution - page 7

with several comprising multiple subgroups as follows: disinfectants and general biocidal
products, preservatives, pest control (pesticides) and other biocidal products.
Pesticides fall into three main categories—fungicides, herbicides, and insecticides. These
three types are used to combat different pests. Most pesticides are toxic to human beings;
WHO has classified their toxic effects from class Ia (extremely hazardous) to class III
(slightly hazardous) and then to “active ingredients unlikely to present acute hazard”
(WHO 2001).
Chemical insecticides are usually divided into four major classes: Chlorinated hydro-
carbons or organochlorines—these pesticides break down chemically very slowly and can
remain in the environment for long periods of time (dieldrin, chlordane, aldrin, DDT, and
heptachlor). Organophosphates—these pesticides are highly toxic to humans but do not
remain in the environment for long periods of time (parathion, malathion, thimet, and
trichlorphone). Carbamate compounds—these pesticides are considered highly toxic to
humans (carbaryl, methomyl, carbofuran, and aldicarb). Pyrethroids—the first synthetic
pyrethroids that combined high toxicity to insects with low mammalian toxicity and
greatly increased stability were announced in 1973, and since then many new pyrethroids
have been synthesized and marketed, such as cypermethrin. In addition to these four
classes, there are now a number of new compounds representing other smaller classes, for
example, insect growth regulators, imidates, and phenylpyrazoles.
The first synthetic broad-spectrum pesticide, the organochlorine, caused a revolution in
the efficacy of pest control, especially of the malaria mosquito and other disease vectors
of mankind. Additionally, they offered cheap, sure, and long-lasting control of crop pests.
Organochlorine pesticides are substances containing chemically combined chlorine and
carbon. They may be grouped into three general classes: dichlorodiphenylethanes (DDT,
DDD, dicofol, etc.), chlorinated cyclodienes (aldrin, dieldrin, heptachlor, etc.), and hexa-
chlorocyclohexanes (lindane). These compounds differ substantially between and within
groups with respect to toxic doses, skin absorption, fat storage, metabolism, and elimina-
tion. The signs and symptoms of toxicity in humans, however, are remarkably similar
except for DDT (Hayes 1991).
Organochlorine pesticides persist and tend to bioaccumulate in the environment. These
qualities make them the most dangerous group of chemicals to which natural systems
can be exposed. It is well known that the widespread use of organochlorine compounds
have caused serious problems to man due to their bioaccumulation in several organs. The
majority of these compounds are toxic in high levels and few are carcinogenic, as shown
by few animal tests (Fytianos et al. 1985).
1.2.3 Pesticide Market in the Worldwide
As many pesticides were determined to be harmful to human health and/or the envi-
ronment, pesticides have come under more scrutiny and some have been banned by the
government. In addition, the number of species resistant to major classes of pesticides has
increased dramatically in recent years; some pesticides are becoming obsolete as pests
develop genetic resistance to them. These factors have increased the need for alternative
approaches to control pests. The 1993-1994 annual report of the German Association of
Chemical Industries (GACI) indicates that the value of world chemical pesticides sold was
about US $23 billion. The distribution of this value by region is summarized in Table 1.2
and compared by the distribution percentages for the year 2008.
About three quarters of pesticide use occurs in developed countries. In these regions,
the pesticide market is dominated by herbicides, which tend to have a lower acute, or