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Alternatives to Organochlorine Insecticides
Organophosphate Insecticides
• Strongly active against a wide variety of species
• Break down rapidly in the environment
• Exhibit high acute toxicity to verterbrates as well as
insects
- Exception: Malathion, LD50 =1200 mg/kg
• Mechanism of action: Cholinesterase inhibitor
Dichlorvos
(a phosphate)
Parathion
(a phosphorothioate)
Malathion
(a phosphorodithioate)
Some Considerations:
• Choice of appropriate type of pesticide for a given
application:
 Stability, solubility, toxicity
 Natural vs. synthetic
• Use of pheromones or hormones where feasible
• Biological control (via predators, parasites
pathogens; examples: Bacillus thuringiensis (BT) or
Entomophaga maimaiga for the gypsy moth)
• Using farming methods that do not provide favorable
conditions for pests
• Using resistant plant strains; genetic engineering
• Using physical methods to reduce pest population
(e.g., traps)
• Keeping new species from entering an area
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)
Formed as an impurity in the synthesis of
2,4-dichlorophenoxyacetic acid (2,4-D) and
2,4,5-trichlorophenoxyacetic acid (2,4,5-T):
2,4-D
Which are mimics for
the plant growth
hormone:
2,4,5-T
Indoleacetic acid
Effective on broad-leafed plants, but not
harmful to grasses.
Also formed in the postcombustion zones of
incinerators directly from carbon or chlorinated
phenols, via reactions catalyzed by fly ash (metal
salts).
Toxicity?
•Listed as “known to be a human carcinogen” in January,
2001 by the U.S. National Toxicity Program.
•Oil contaminated with some dioxins was applied to a horse
arena in Missouri. As little as 32g dioxins per kg soil
was sufficient to kill birds, cats, dogs and horses that
used the arena. Reactions in humans were far less
severe: One child developed a variety of skin lesions.
•Toxicity in mammals occurs through binding of Ah (aryl
hydrocarbon receptor; affects translocation.
•Exhibits antiestrogenic activity; may cause endometriosis.
Table 8-4
Variation in TCDD Toxicity
Animal
Guinea pig
Mink
Rat
Monkey
Rabbit
Mouse
Dog
Hamster
LD50 (mg/kg)
0.6-2.5
4
22-330
<70
115-275
114-280
>100-<3000
1150-5000
Source: Adapted from D.J. Hanson, Dioxin toxicity:
New studies prompt debate, regulatory action, Chem.
Eng. News, p. 8, Aug. 12, 1991.
Bailey, Clark, Ferris, Krause and Strong, “Chemistry of the Environment,” second
edition (San Diego: Academic Press) 2002.
Bailey, Clark, Ferris, Krause and Strong, “Chemistry of the Environment,” second
edition (San Diego: Academic Press) 2002.