Water pollution by industries and its effects

A change in the chemical, physical, biological, and radiological quality of water that is injurious to its uses. The term "water pollution" generally refersto human-induced changes to water quality. Thus, the dischargeof toxic chemicals from industries or the release of human or livestock waste into a nearby water body is considered pollution.The contamination of ground water of water bodies like rivers, lakes, wetlands, estuaries, and oceans can threaten the health ofhumans and aquatic life. Sources of water pollution may be divided into two categories. (i) Point-source pollution, in which contaminants are discharged from a discrete location. Sewage outfalls and oil spills are examples of point-source pollution. (ii) Non-point-source ordiffuse pollution, referring to all of the other discharges that deliver contaminants to water bodies. Acid rain and unconfined runoff from agricultural or urban areas falls under this category.The principal contaminants of water include toxic chemicals, nutrients, biodegradable organics, and bacterial & viral pathogens. Water pollution can affect human health when pollutants enter the body either via skin exposure or through the direct consumption of contaminated drinking water and contaminated food. Prime pollutants, including DDT and polychlorinated biphenyls (PCBs), persist in the natural environment and bioaccumulation occurs in the tissues of aquatic organisms. These prolonged and persistent organic pollutants are transferredup the food chain and they can reach levels of concern in fish species that are eaten by humans. Moreover, bacteria and viral pathogens can pose a public health risk for those who drink contaminated water or eat raw shellfish from polluted water bodies.Contaminants have a significant impact on aquatic ecosystems. Enrichment of water bodies with nutrients (principally nitrogen and phosphorus) can result in thegrowth of algae and other aquaticplants that shade or clog streams.If wastewater containing biodegradable organic matter is discharged into a stream with inadequate dissolved oxygen, thewater downstream of the point ofdischarge will become anaerobic and will be turbid and dark. Settleable solids will be deposited on the streambed, andanaerobic decomposition will occur. Over the reach of stream where the dissolved-oxygen concentration is zero, a zone of putrefaction will occur with the production of hydrogen sulfide (H2S), ammonia (NH3), and other odorous gases. Because many fish species require a minimum of 4–5 mg of dissolved oxygen per liter of water, they will be unable to survive in this portion of the stream.Direct exposures to toxic chemicals are also a health concern for individual aquatic plants and animals. Chemicals such as pesticides are frequently transported to lakes and rivers via runoff, and they can have harmful effects on aquatic life. Toxic chemicals have been shownto reduce the growth, survival, reproductive output, and disease resistance of exposed organisms. These effects can have important consequences for the viability of aquatic populations and communities.