Role of Pesticides in Produce Production, Preservation, Quality, and Safety 371
regions but does not affect cell elongation. It is an isomer of the pyrimidine base
uracil, and thus it may interfere with DNA or RNA synthesis [1]. Chlorpropham
and propham are carbamate herbicides that also inhibit cell division (microtubule
organization). Tecnazene is a fungicide used for control of Fusarium rot of potatoes,
so the suppression of sprouting is an additional benefit of this pesticide [5,68].
11.2.10 DESICCANTS AND DEFOLIANTS
Desiccants are compounds that accelerate drying of plant tissues. The most widely
used desiccants are the contact herbicides diquat and paraquat, and also sulfuric acid
or sodium chlorate. Preharvest destruction of potato haulms (vines) is probably the
most important example of the application of desiccants in produce production. The
main reason for vine desiccation is to promote tuber maturity, which, apart from
other things, involves skin thickening and hardening, called skin set [87]. A good
skin set reduces bruising of tubers during harvest and handling, water loss during
storage, and susceptibility to infection by spoilage microorganisms.
Defoliants are substances intended for causing the leaves (foliage) of a plant to
abscise, or fall off. In agriculture, defoliants are mainly applied to cotton and hops
to facilitate mechanical harvest. Sodium chlorate was among the first chemicals used
as a defoliant (and also desiccant), and this nonselective herbicide is still extensively
utilized for this purpose. Modern defoliants from the group of PGRs, such as tribufos
or thidiazuron, are absorbed by leaves and stimulate formation of an abscission layer
between the plant stem and the leaf petioles, causing the dropping of entire green
leaves [5].
A defoliant known as “Agent Orange,” consisting of herbicides 2,4-D and 2,4,5-T
(2,4,5-trichlorophenoxyacetic acid), was infamously used in the Vietnam War to
remove the plant cover and was later shown to cause postexposure carcinogenic and
teratogenic effects in humans due to contamination by the dioxin TCDD (2,3,7,8-
tetrachlorodibenzo-p-dioxin) [88].
11.3 RISKS ASSOCIATED WITH PESTICIDES AND
STRATEGIES TO REDUCE THEMPotential risks associated with pesticide use relate mainly to their impact on human
health and the environment. The concerns about pesticides may be legitimate, based
on the results of scientific studies [89], or perceived. Unfortunately, a thorough
scientific evaluation of the risks is practically impossible due to the high number of
variables involved [90,91]. Toxicological studies can determine acute toxicity and
other effects induced in tested animals, but chronic toxicity from pesticide exposure
at actual concentrations found in food is unknown. Analytical chemists provide
valuable data about pesticide levels in the human diet and about their fate in the
environment. Epidemiological and environmental studies try to correlate pesticide
use with the observed incidence of diseases or other adverse effects in humans and
wildlife. Those are the main sources of information currently available for assess-
ments that may indicate potential risks, but they hardly provide all the answers,
especially in terms of the long-term effects involving cancer and other chronic