Như đã được ghi nhận, nhiều chất gây ô nhiễm được tìm thấy trong môi trường của chúng tôi. Họ phát sinh từ nhiều nguồn, và tiếp xúc với những chất gây ô nhiễm có thể xảy ra thông qua các tuyến đường khác nhau. Ví dụ, trong không khí xung quanh trong khu vực đô thị, SO2, CO, NOx, và hút thuốc lá / lơ lửng các hạt, chì, và hydrocarbon chủ yếu được sản xuất từ than đá hay dầu cháy theo ngành nghề, nhà máy điện, và trong một số hộ gia đình. Các loại chất ô. | CHAPTER 3 Occurrence of Toxicants INTRODUCTION As has been noted numerous pollutants are found in our environment. They arise from many sources and exposure to these pollutants can occur through various routes. For example in the ambient air in urban areas SO2 CO NOx and smoke sus-pended particles lead and hydrocarbons are produced mainly from coal or heavy oil combustion by industries power plants and in some households. Various kinds of pollutants are also found in the indoor environment. Some examples include CO arising from incomplete combustion of fossil fuels and tobacco smoke Pb from paint used in old houses and formaldehyde from insulation and wood preservatives and adhesives. In this chapter we will discuss where and how certain toxicants may occur in our environment. Also included in our discussion is a brief review of several major pollution episodes disasters that took place in recent decades. VISIBLE SMOKE OR SMOG The presence of visible smoke or smog is a manifestation of air pollution. Smoke is the gaseous product of burning carbonaceous materials made visible by the presence of small particles of carbon. The brownish to blackish materials emitted from the stack of an inadequately controlled coal-burning industrial plant or from the chimney of a wood-burning home are examples. Wood burning has become a common practice in many American homes especially in winter. Burning wood in a well-insulated home however can lead to discomfort associated with indoor pollution. The problem associated with indoor air pollution is particularly serious in many villages in southern China where indoor combustion of coal as a means of cooking meals or drying vegetables is commonly practiced. 19 2001 by CRC Press LLC 20 ENVIRONMENTAL TOXICOLOGY Smog on the other hand is a fog made heavier and darker by smoke and chemical fumes. Smog is formed mainly as a result of photochemical reactions. In the presence of ultraviolet rays in sunlight nitrogen dioxide NO2 is .
