CHEMISTRYoftheENVIRONMENT（环境化学课件3）.ppt

Figures 4.2 and 4.3 show that POTW transfers have been cut by factors of five and nine for benzene and chromium, respectively, two chemicals that are known to cause cancer. (The discharges to surface waters have been cut less, because they were relatively small to begin with.) Nonpoint sources represent a much harder problem. They include emissions from transport vehicles, agricultural runoff, which can carry excess nutrients, pesticides, and silt(淤泥) into streams and ground waters, and urban runoff, which can carry toxic metals and organics through storm drains into sewage treatment plants, or directly into rivers and lakes (see Figure 14.4). The progress made in controlling point sources of pollution has drawn attention to nonpoint sources, which account for an increasing fraction of the total pollutant load. For example, the relative contribution to the cadmium (Cd) load to the Rhine River from point and nonpoint sources changed dramatically between the mid 1970s and mid 1980s (see Figure 4.5). 2. Nonpoint source of pollution While most of the Cd came from point sources in the 1970s, this is no longer the case, thanks to industrial controls. Now the greater share of Cd derives from nonpoint sources from urban and agricultural runoff (Cd is a contaminant in urban dust as well as in phosphate fertilizer). As discussed above, nonpoint sources are responsible for the overfertilization of lakes and bays. Section 2 Water Body Pollution 1. Water body pollution and its self-purification Definition Physical self-purification Chemical self-purification Biological self-purification 2. Pollutants in water body ?(1) Pathogenic pollutant For instance, Virus, germina, parasite Schistosomiasis, cholera, dysentery, hepatitis In 1848 and 1854, ten thousands people died of cholera because of water pollution in England. In 1892, 750 people died of cholera in Germen. Characteristic of pathogenic pollutant： Big quantity wide distributing long life fast reproduction drug-fa