Water pollution affects man’s health, recreational use of water and sense of beauty. The spread of water-carried disease is of great concern. In highly developed countries in particular, emphasis has changed from concern over bacterial disease to concern over water-carried viral(病毒性的) disease. Viral hepatitis(肝炎), for example, has been found to occur more frequently in cities whose water supplies have comparatively high levels of water impurity. Poisonous chemicals found in streams that are ultimately used for water supplies also create an important public health problem. It is clear that poisonous chemicals must be excluded from water, but more and more chemicals from new pesticides(杀虫剂), fertilizers, and other new products have been found in water. Since the public health importance of these chemicals is not yet fully known, they are of increasing concern. The chemicals from fertilizers are also finding their way into water supplies from pollution.
As man’s desire for water-based recreation increases, greater demands are placed on the quality of the water. The water must not only but be attractive in appearance but also meet certain other conditions. Sports such as swimming involve direct contact with water, and so water standards are raised higher.
The range of water quality necessary for industrial processes varies greatly with the intended use of the water. The water used in steel mills, foe example, must have a lower chloride(氧化物)level than that accepted for drinking water. Cooling water can often be of comparatively low sanitary(卫生的)quality. A large part of the water used in the paper-making industry an be of relatively low quality in some aspects, but must contain little iron and carbon dioxide.
67. The chemicals from pesticides and fertilizers found in water are of increasing concern because_________.
A. their importance to man’s health has not been completely known
B. they may cause groundwater pollution
C.
D. they can find their way into water supplies for farmers they are important factors contributing to the spread of disease
68. According to the passage, water-based recreation demands that_________.
A.
The water contain a higher level of oxygen