River Pollution: Understanding The Main Causes

Water pollution is a pressing issue that jeopardizes the health of millions of people and ecosystems around the world. Rivers, being a source of freshwater, are particularly vulnerable to pollution. While some water pollution occurs naturally, such as when mercury filters from the Earth's crust, the leading cause is human activity. Rivers absorb contaminants from farms, factories, cities, and other industrial sites, including toxic chemicals, waste, and plastic. These pollutants are carried by streams and rivers into our bays and estuaries, eventually reaching the sea.

Industrial waste

The production of all kinds of industrial goods generates wastewater that can be contaminated with toxic substances. For example, the metal processing industry produces wastewater containing lubricants, mainly mineral oils, which cause a high COD value. In electroplating, it is highly polluted active baths, contaminated by heavy metals such as zinc, nickel, copper or cadmium. Other types of industrial wastewater include petroleum products, hazardous wastes, and sediments.

In some areas of the world, industrial wastewater is discharged untreated into nearby public waters. This is particularly common in emerging countries such as China, India, Africa, or South America, where the number of industrial plants has only recently begun to grow. Even in countries with environmental policies in place, the implementation and monitoring of legislation can be inconsistent, leading to the illegal discharge of wastewater from industries into rivers and lakes.

The discharge of residual pollution into public waters has serious consequences. Many of the hazardous substances from industry are difficult to biodegrade and therefore accumulate in water sediments. This can lead to fish, crustaceans and other creatures becoming ill and dying, reducing biodiversity. Polluted water from rivers and the contaminants from water sediments can also enter the groundwater, affecting drinking water supplies.

Agricultural waste

Agriculture is a major contributor to river pollution. Farms discharge large quantities of agrochemicals, organic matter, drug residues, sediments, and saline drainage into water bodies. In the US, agriculture is the main source of pollution in rivers and streams, the second-largest source in wetlands, and the third in lakes. In China, agriculture is responsible for a large share of surface-water pollution and is almost exclusively responsible for groundwater pollution by nitrogen.

Agricultural pollution poses risks to aquatic ecosystems, human health, and productive activities. For example, high levels of nitrates in water can cause "blue baby syndrome", a potentially fatal illness in infants. In Organization for Economic Co-operation and Development (OECD) countries, the environmental and social costs of water pollution caused by agriculture are estimated to exceed billions of dollars annually.

Farmers apply nutrients to their fields in the form of chemical fertilizers and animal manure, which provide crops with the nitrogen and phosphorus necessary for growth. However, when these nutrients are not fully utilized by the plants, they can be washed from the fields into waterways during rain or snowmelt and can also leach through the soil into groundwater over time. This excess nitrogen and phosphorus can cause eutrophication of water bodies, leading to hypoxia ("dead zones") and a decrease in aquatic life.

Another source of agricultural pollution is veterinary medicines, which have emerged as a new class of pollutants in recent years. Antibiotics, vaccines, and growth promoters move from farms through water to ecosystems and drinking water sources. Fish excreta and uneaten feeds from aquaculture also contribute to water pollution, along with the increased use of antibiotics, fungicides, and anti-fouling agents, which may pollute downstream ecosystems.

To mitigate the impacts of agricultural pollution, farmers can implement practices such as managing livestock access to streams by installing fences to block animal access, thus preventing excess nutrients from entering the water. Collaboration between farmers, state governments, conservation groups, and community organizations is vital to reducing nutrient pollution in water and air.

Oil spills

Oil is a fossil fuel composed of the liquid remains of ancient plants and animals. It is found below ground or beneath the ocean floor in reservoirs and is extracted through drilling and pumping. Oil spills can occur during the transportation of oil from these reservoirs to processing plants via pipes, ships, trucks, or trains.

The effects of oil spills in rivers can be devastating. Oil reduces the oxygen supply in the water, endangers marine life and ecosystems, and makes drinking water unsafe. Cleanup efforts can be challenging, and even with advanced technologies, it is nearly impossible to remove 100% of the spilled oil. Additionally, cleanup methods must be carefully chosen to avoid causing further harm to sensitive habitats.

To address oil spills in rivers, responders employ various techniques, including the use of vacuum devices to remove submerged oil and skimming to collect oil from the water surface. The movement of oil spills in freshwater systems is also modelled using tools like the GNOME spill trajectory model, which helps contingency planners and field responders minimize ecological impacts.

Sewage and wastewater treatment

Sewage treatment plants are considered a "point source" of pollution, as they release treated sewage into water bodies. However, the problem arises when the treatment processes are inadequate or ineffective, leading to the discharge of partially treated or untreated sewage. This is particularly prevalent in less developed countries, where the percentage of untreated wastewater can exceed 95%.

Wastewater from various human activities, such as industrial processes, agriculture, and domestic use, contains a range of contaminants. These can include chemicals, pesticides, fertilizers, and organic waste. When this wastewater is not properly treated before being released into rivers, it introduces these pollutants into the water, degrading water quality.

One of the significant concerns with sewage and wastewater treatment is the presence of pathogens and microorganisms. Untreated or partially treated sewage can contain harmful bacteria, viruses, and parasites, such as those causing typhoid, cholera, and giardia. These pathogens can contaminate river water, leading to waterborne diseases and posing a significant risk to public health.

Additionally, sewage and wastewater can contain high levels of nutrients, particularly nitrates and phosphates, from fertilizers and organic matter. While these nutrients are essential for plant growth, excessive amounts can lead to eutrophication and the formation of "dead zones" in rivers and coastal areas. These dead zones have extremely low oxygen levels, making them uninhabitable for aquatic life, thus disrupting the natural functioning of ecosystems.

Urban and transport runoff

Urban areas, with their dense populations and extensive infrastructure, generate significant amounts of runoff. This runoff collects pollutants from a variety of sources, including atmospheric deposition, vehicular transportation-related activities, and metallic building materials. The vehicular transportation sector, in particular, is a major contributor to pollution in urban runoff. As vehicles emit pollutants and deposit them onto roads and other surfaces, the runoff carries these contaminants into nearby water bodies.

The impact of urban runoff on river pollution is exacerbated by the increased volume and velocity of stormwater. In natural landscapes, rainfall would seep into the ground, recharging aquifers and reducing the amount of surface runoff. However, in urban areas with extensive impervious surfaces, the water has nowhere to go but into storm drains, resulting in increased runoff volumes. This increased volume can lead to flooding and further contribute to the pollution of rivers and other water bodies.

Additionally, the contamination of rivers through urban and transport runoff has significant economic, environmental, and health implications. Economically, communities may face higher costs for managing increased water volumes and treating polluted water. Environmentally, river pollution can lead to the destruction of marine life and ecosystems, as well as a reduction in oxygen supply within the water environment. Moreover, the presence of harmful chemicals and bacteria in the water can have detrimental health effects on humans, causing illnesses and even deaths.

Mitigating urban and transport runoff pollution requires a comprehensive understanding of its sources and the implementation of effective pollution control measures. While advancements in clean manufacturing and pollution control technologies have been made, the constant introduction of new chemicals and substances into the environment presents ongoing challenges. To address these challenges, source controls have been identified as effective tools for mitigating pollution, but a complete overview of all contributing sources is still lacking and requires further research.

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