除草剂毒理学

Herbicide Toxicology
Part I: Introduction, definition Factors affecting its activity Absorption and Translocation Herbicide Metabolism Part II: Mode of Action
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b). Translocation in plants
• Phloem translocated herbicides that move downward and suppress root and rhizome (根茎) growth, as well as top growth, provide the best perennial weed control. 2,4-D is example of systemic herbicides that will translocate in the phloem and provide good, long-term control of certain perennial weeds.
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1. Factors affecting herbicide activity
• Environment also influences herbicide efficacy by affecting plant growth. Plants are generally most susceptible to postemergence herbicides when actively growing. Extreme environmental conditions that slow plant growth and thicken leaf cuticles often increase plant tolerance to a herbicide.
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b). Translocation in plants
• Contact herbicides are not translocated. Contact herbicides generally are ineffective for long-term perennial weed control. • Systemic herbicides can be translocated to other parts of the plant either in the xylem(木质部) or the phloem
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Part I
Introduction
A herbicide is a pesticide used to kill unwanted plants. Herbicides are chemicals that inhibit or interrupt normal plant growth and development. Weedicide
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1. Factors affecting herbicide activity
• 1). Soil texture : • Herbicide adsorption is greater in finetextured soils high in organic matter than in coarse-textured soils low in organic matter. Thus, a lower proportion of herbicide is available in the fine-textured soils, so a higher herbicide application rate is required to provide the same level of weed control as in a coarse-textured soil.
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b). Translocation in plants
• The apoplastic(非原生质体) system constitutes the total continuum of intercellular spaces, cell walls, and mature xylem; it is considered to be nonliving. • Apoplasticly mobile herbicides, which are absorbed by the roots, follow the same pathway as water.
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b). Translocation in plants
• The symplastic(共质体) system constitutes the total continuum of protoplasm throughout the plant, including the cytoplasm of each cell, their interconnecting plasmodesma(胞 间连丝), and the phloem(韧皮部), it is considered to be living.
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2. Absorption and Translocation
• A) Foliar absorption: • cuticle wax (lipophilic): no-polar • Cuticle • cutin(角质,hydrophilic): polar • Pectin(胶质): hydrophilic
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Translocation
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b). Translocation in plants
• Herbicides can be translocated in the xylem, the phloem, or both. Herbicides translocated only in the xylem are most effective as soilapplied or early postemergence treatments because translocation is only upward. Atrazine (莠去津) is a good example of a herbicide that is translocated only in the xylem.
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Part I
Introduction
2006年，生产农药130万吨（折100%）， 同比增长20%。其中杀虫剂50万吨，占39%； 杀菌剂11万吨，占9%；除草剂39万吨，占 30%。
50 45 40 35 30 2
除草剂
杀虫剂
Part I
Introduction
• 2006年我国进口农药4.3万吨,用汇2.1亿 美元; 出口农药保守估计39.8万吨,创外汇 10.4亿美元. 其中: • 除草剂出口22.3万吨(创外汇5.3亿美元), 占出口的56%,占除草剂产量的57.6%.
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Part I
Introduction
• Selectivity : The herbicide’s ability to kill certain plants without injuring others is called selectivity. Selective herbicide Non-selective herbicide Contact herbicide Systemic herbicide
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1. Factors affecting herbicide activity
• Water molecules compete with herbicide molecules for adsorption sites on soil particles and organic matter. Therefore, herbicide adsorption is highest under dry soil conditions, and lowest in moist soils. Consequently, weed control is generally best with moist soil conditions because more herbicide is available for plant uptake in the soil solution or gaseous phase.
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3. Herbicide Metabolism
• Metabolism is one of the most important ways a plant can escape the toxic effects of a herbicide. Herbicide-tolerant plants often have the ability to metabolize or break down the chemical to nonactive compounds before it can build up to toxic levels at the site of action.
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b). Translocation in plants
• Symplastically mobile herbicides, which are absorbed by the leaves, move along with the photosynthate(光 合作用产物) via the same pathway. • Phloem: injured by herbicide
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1. Factors affecting herbicide activity
• 2).Soil moisture • Soil moisture is important because it influences herbicide adsorption to soils. Therefore, the herbicide is unavailable for plant uptake. Adsorption occurs when herbicide molecules adhere to soil particles and organic matter. While adsorbed, herbicide molecules are unavailable for absorption by plants.