30 pesticides a restricted use pesticide defined as

30

PESTICIDES

A restricted use pesticide , defined as generally
causing undesirable effects on the environment,
applicator, or workers can only be purchased and
applied by an individual who is licensed to do that

Based on toxicity potency pesticides are classified

Adjust categories LD50

Category I: highly hazardous (and restricted use) with an
oral LD50 less than or equal to 1.0 mg/kg of body weight

Category II: moderately toxic and have an oral LD50 less
than or equal to 500 mg/kg

Category III: generally nontoxic and have an oral LD50
less than or equal to 15,000 mg/kg
31

Organochlorine Insecticides

chlorinated hydrocarbon: e.g. DDT (was banned in 1977)
and dieldrin

There use was ceased since decades because they
were found to be neurotoxicants and cause acute effects
by interfering with the transmission of nerve impulses
32

Organophosphorus Insecticides (OPs)

phosphoric acid esters or thiophosphoric acid esters

E.g. parathion and malathion (the least toxic one)

inhibit acetylcholinesterase resulting in accumulation of
acetylcholine especially in peripheral neurons

Generally are nonpersistent in the environment (only few
hours to several months)
33

Organophosphorus Insecticides (OPs)

some OP compounds have been associated with
delayed neurotoxicity, known as organophosphorus-
induced delayed neuropathy

bilateral paralysis of the distal muscles, predominantly of the
lower extremities, occurring some 7 to 10 days following
ingestion
34

Carbamate Insecticides

esters of N-methyl carbamic acid (H2NCOOH)

Acetylcholinesterase inhibition

Inhibition more rapidly reversed than with OPs
compounds

Generally are nonpersistent in the environment (only few
hours to several months)
35

New Insecticide Classes

applied at low dosages and are extremely effective but
are relatively nontoxic to humans

E.g. fiproles and fipronil
36

Rodenticides

E.g. warfarin

warfarin inhibits the synthesis of vitamin K-dependent
clotting factors, which include Factors II, VII, IX, and X,
and the anticoagulant proteins C and S

potent toxicant with an oral LD50 of 3.0 mg/kg

As the rats navigate through narrow passages, they
bruise themselves, developing small hemorrhages

Warfarin prevents the blood from clotting, and the
animals bleed to death in about a week

Toxicity in humans is treated with vitamin K, and if the
poisoning is severe, blood transfusions as a treatment
37

TOXINS

A toxicant is any chemical, of natural or synthetic origin,
capable of causing a deleterious effect on a living
organism

A toxin is a toxicant that is produced by a living organism
and is not used as a synonym for toxicant—all toxins are
toxicants, but not all toxicants are toxins

Toxins may be of animals, plants, insects, or microbes
origin

Toxins are generally metabolic products that have
evolved as defense mechanisms for the purpose of
repelling or killing predators or pathogens
38

Microbial Toxins

high molecular weight and have antigenic properties

E.g. tetanus toxin, botulinus toxin, and diphtheria toxin