tailieunhanh - Introduction to ENVIRONMENTAL TOXICOLOGY Impacts of Chemicals Upon Ecological Systems - CHAPTER 6

Các yếu tố Sửa đổi Hoạt động của chất độc Cũng như có một số lượng lớn các chất ô nhiễm trong môi trường của chúng tôi, vì vậy có nhiều yếu tố ảnh hưởng đến độc tính của các chất gây ô nhiễm. Các yếu tố chính ảnh hưởng đến độc tính chất gây ô nhiễm bao gồm các tính chất hóa lý của chất ô nhiễm, thời gian phơi sáng, các yếu tố môi trường, tương tác, các yếu tố sinh học, và các yếu tố dinh dưỡng. Các thông số thay đổi hành động độc hại của một. | CHAPTER 6 Factors Modifying the Activity of Toxicants Just as there are a large number of pollutants in our environment so are there many factors that affect the toxicity of these pollutants. The major factors affecting pollutant toxicity include physicochemical properties of pollutants exposure time environmental factors interaction biological factors and nutritional factors. The parameters that modify the toxic action of a compound are examined in this chapter. PHYSICOCHEMICAL PROPERTIES OF POLLUTANTS Characteristics such as whether a pollutant is solid liquid or gas whether the pollutant is soluble in water or in lipid organic or inorganic material ionized or nonionized etc. can affect the ultimate toxicity of the pollutant. For example since membranes are more permeable to a nonionized than an ionized substance a nonionized substance will generally have a higher toxicity than an ionized substance. One of the most important factors affecting pollutant toxicity is the concentration of the pollutant in question. Even a generally highly toxic substance may not be very injurious to a living organism if its concentrations remain very low. On the other hand a common pollutant such as carbon monoxide can become extremely dangerous if its concentrations in the environment are high. As mentioned earlier exposure to high levels of pollutants often results in acute effects while exposure to low concentrations may result in chronic effects. Once a pollutant gains entry into a living organism and reaches a certain target site it may exhibit an action. The effect of the pollutant then is a function of its concentration at the locus of its action. For this reason any factors capable of modifying internal concentration of the chemical agent can alter the toxicity. TIME AND MODE OF EXPOSURE Exposure time is another important determinant of toxic effects. Normally one can expect that for the same pollutant the longer the exposure time the more detrimental the effects. Also .