tailieunhanh - The Environmental Life Cycle Costing - Chapter 5

Nó được biết đến rộng rãi rằng nhiều yếu tố có thể ảnh hưởng đến độc tính xenobiotic. Trong chương này, chúng tôi sẽ kiểm tra một số trong số này, bao gồm các tính chất hóa lý của chất độc, liều lượng hoặc nồng độ, chế độ và thời gian tiếp xúc, yếu tố môi trường, tương tác, và các yếu tố sinh học và dinh dưỡng. | CHAPTER 5 Factors Affecting Xenobiotic Action INTRODUCTION It is widely known that many factors can affect xenobiotic toxicity. In this chapter we will examine some of these including physicochemical properties of toxicants dose or concentration mode and duration of exposure environmental factors interaction and biological and nutritional factors. PHYSICOCHEMICAL PROPERTIES Physical and chemical characteristics of a pollutant such as whether it is solid liquid or gas whether it is soluble in water or in lipid whether of organic or inorganic material ionized or nonionized etc. can affect the ultimate toxicity of the pollutant in question. For instance a nonionized substance may be more toxic than an ionized or charged counterpart because the nonionized species can pass through the membrane more easily than the ionized species and thus be more readily absorbed and elicit its toxic action. DOSE CONCENTRATION Dose or concentration of any toxicant to which an organism is exposed is often the most important factor affecting the toxicity. Once a pollutant gains entry into a living organism and reaches a certain target site it may exhibit an injurious action. For this reason any factors capable of modifying internal concentrations of the toxicant can alter the toxicity. The effect of the pollutant then is a function of its 47 2001 by CRC Press LLC 48 ENVIRONMENTAL TOXICOLOGY 120 -I 80 - c ỌỊ 2 60 - CL 40 - 100 - Radicle length Invertase activity 20 - 0 -I-------------- ------------ ------ 0 1 NaF mM Figure Effect of NaF on radicle growth and invertase activity in mung bean seedlings. concentration at the locus of its action. A pollutant may either depress or stimulate normal metabolic function. Generally minute amounts of a pollutant may stimulate the metabolic function of an organism whereas large doses can impede or destroy its activity. For example a recent epidemiological study showed that in the area of Kuitan a city in western China many residents