Page 604 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

VetBooks.ir Chapter 45

Toxicity of Fungicides

Pawan K. Gupta

INTRODUCTION other organic materials now account for 90% of fungicide
use. Newer groups, such as benzimidazoles, conazoles,
Fungicides are agents that are used to prevent or eradicate
dicarboximides, and metal organic compounds, account
fungal infections from plants or seeds. Numerous sub-
for approximately 10% of fungicide use (Osteen and
stances having widely varying chemical constituents are
Padgitt, 2002). In this chapter, fungicides are discussed
used as fungicides (Gupta, 1988, 2016). Fungicides have
using a chemical classification system.
been classified according to chemical structures or have
been categorized agriculturally and horticulturally accord-
ing to their mode of action (Ballantyne, 2003). According
to the mode of application, fungicides are grouped as BACKGROUND
foliar, soil, and dressing fungicides. Foliar fungicides are
The earliest fungicides were inorganic materials such as
applied as liquids or powders to the aerial green parts of
sulfur, lime, copper and mercury compounds. The use of
plants, producing a protective barrier on the cuticular sur-
elemental sulfur as a fungicide was recommended as early
face and systemic toxicity in the developing fungus. Soil
as 1803. It has become an important component of inte-
fungicides are applied as liquids, dry powders, or granules,
grated pest management systems because it can be used in
acting either through the vapor phase or by systemic prop-
“organic farming.” There are an increasing number of
erties. Dressing fungicides are applied to the post-harvest
instances of dermatitis in human farmworkers and diseases
crop as liquids or dry powders to prevent fungal infestation
in ruminants caused by exposure to high levels of sulfur
of the crop, particularly if stored under less than optimum
(Gammon et al., 2010). The mercury-containing fungicides
conditions of temperature and humidity. Thus, effective
have been responsible for many deaths or permanent neu-
fungicides must be protective, curative, or eradicative and
rological disability. Some of the earlier inorganic metallic
should possess the following properties: (1) low toxicity to
fungicides have been withdrawn in many countries
the plant/animal but high toxicity to the particular fungus;
because of their toxicity and adverse environmental effects
(2) activity per se or the ability to convert themselves (by
(Ballantyne, 2003). Another compound, hexachloroben-
plant or fungal enzymes) into toxic intermediates; (3) the
zene (HCB), was extensively used from the 1940s through
ability to penetrate fungal spores or the developing myce-
the 1950s as a fungicidal dressing applied to seed grains as
lium to reach the site of action; (4) low ecotoxicity; and
a dry powder. Between 1955 and 1959, an epidemic of
(5) the ability to form a protective, tenacious deposit on
poisoning occurred in Turkey and resulted in a syndrome
the plant surface that will be resistant to weathering from
called black sore and caused more than 4000 deaths.
sunlight, rain, and wind (Phillips, 2001). With a few
Although use of this agent has greatly diminished, it is still
exceptions, most of the newly developed chemicals have a
being used in developing countries. It is a highly toxic
low order of toxicity to mammals. Public concern has
compound and can lead to severe skin manifestations
focused on the positive mutagenicity tests obtained with
including hypersensitivity (Hayes, 1982; Gupta, 2010a).
many fungicides and the predictive possibility of both tera-
Carbamic acid derivatives, including ethylenebisdithiocar-
togenic and carcinogenic potential. The quantity of fungi-
bamates (EBDCs), are a group of fungicides that have
cides used on major crops is estimated to have increased
been used widely throughout the world since the 1940s.
2.3-fold between 1964 and 1997. Use of inorganics (pri-
The important members of this class include mancozeb,
marily copper compounds) and dithiocarbamates has
maneb, metiram, zineb and nabam. All the members have
declined since the 1960s, but captan, chlorothalonils, and
an EBDC backbone, with different metals associated with
Veterinary Toxicology. DOI: http://dx.doi.org/10.1016/B978-0-12-811410-0.00045-3
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