Agriculture Reference
In-Depth Information
A great many commercial copper-containing fungicides are available.
Some are mixtures of copper compounds. Others include lime, other metals,
and other fungicides.
There are several copper-arsenic compounds, such as Paris Green, still
used in some agricultures. Toxicity of these is chiefly due to arsenic content.
c.
Mercury Compounds
All organic and inorganic mercurial fungicides have lost their registrations
and are no longer available for any purposes.
Mode of Action
The fungicidal activity organic mercury compounds cannot be attributed to
the Hg ion or metallic Hg in the vapor phase. Since the organic residue of the
molecule affects the disinfectant activity very strongly, it may be a con-
tributing factor. As with copper the mercurial ion reacts with enzymes con-
taining iron and /or having a reactive sulfhydryl group.
Toxicity
The mercurial fungicides are among the most toxic pesticides ever devel-
oped in terms of chronic as well as acute hazard. Epidemics of severe, often
fatal, neurologic disease have occurred when indigent residents of less devel-
oped countries consumed methyl mercury-treated grain intended for planting of
crops. Poisoning has also occurred when meat from animals fed mer-
cury-treated seed was eaten. Most of what is known of poisoning by organic
mercurial fungicides has come from these occurrences.
d.
Organic Tin (Organotin) Compounds
Mode of Action
Most of the organotin fungicides tested were too phytotoxic to be used as
foliar fungicides. These included the trialkyktin compounds. However, the
triphenyltin compounds are much less phytotoxic and still possess strong
fungicidal activity. These compounds interfere with fungal growth by their
inhibition of oxidative phosphorylation (energy production).
Toxicity
Most of the organotin salts are moderately toxic, and some are labeled
“Poison” (triphenyltin chloride). They have a low oral LD
50
and require the
signal word “Warning” on the label.
These agents are irritating to the eyes, respiratory tract, and skin. They
are probably absorbed to a limited extent by the skin and gastrointestinal tract.
Manifestations of toxicity are due principally to effects on the brain: headache,
