Water Pollutants: Understanding The Four Major Contaminants

Water pollution is a pressing issue that affects our planet's water sources, including rivers, lakes, oceans, and groundwater. The four main categories of water pollutants are pathogens, inorganic compounds, organic materials, and macroscopic pollutants. These contaminants can originate from various sources, such as sewage discharges, industrial activities, agricultural practices, and urban runoff. Pathogens, such as bacteria, viruses, and protozoa, can cause waterborne diseases like cholera and typhoid. Inorganic compounds, including heavy metals and toxic chemicals, can have severe health impacts on humans and other organisms. Organic materials, such as MTBE, can lead to serious illnesses, while macroscopic pollutants like plastic waste and trash are visible and directly harm aquatic ecosystems.

Four Major Water Pollutants and Their Characteristics

Industrial activities

The quality and quantity of wastewater generated by industries depends on the type of industry. For example, non-biodegradable waste such as heavy metals, pesticides, and plastics may be produced by some industries, while biodegradable compounds such as paper, leather, and wool may be produced by others. Industrial wastewater can be toxic, reactive, carcinogenic, or ignitable. It can also contain total organic carbon (TOC), nitrogen, and phosphorus, which are key parameters of overall pollution in water releases.

Many industrial sites produce waste in the form of toxic chemicals and pollutants, and not all have proper waste management systems in place. As a result, industrial waste is sometimes dumped into nearby freshwater systems, polluting the water and causing potential harm to human health and the environment. Industrial waste can also make its way into rivers, streams, and other bodies of water that lead to the sea.

In Europe, industrial emissions to water have decreased since 2010, with significant reductions in heavy metal emissions. This is due in part to European policy and improved pollution abatement technology. However, data gaps make it difficult to fully assess the contribution of industry to overall water pollution in Europe.

Agricultural activities

Agriculture is the leading cause of water degradation worldwide, accounting for 70% of water consumption. It is also the single largest contributor of non-point-source pollution to surface water and groundwater.

The Food and Agriculture Organization of the United Nations (FAO) recognizes agriculture as both a cause and victim of water pollution. With the increasing demand for agricultural commodities, farmers are turning to non-conventional water sources, such as wastewater, which can contain high levels of nutrients, including untreated sewage. The unsafe use of these alternative water sources can lead to the accumulation of microbiological and chemical pollutants in crops, livestock products, and water resources, with potential severe health impacts on consumers and farm workers.

In addition to the direct discharge of pollutants into water bodies, agricultural practices can also contribute to water pollution through soil erosion, increased salinity, and excessive use or misuse of agricultural inputs, such as fertilizers. Irrigation practices have also been linked to increased malaria incidence in the tropics. Furthermore, the intensification of agriculture has resulted in increased soil erosion, salinity, and sediment loads in water bodies.

To address these issues, the FAO works closely with countries and organizations to monitor, control, and mitigate pollution loads from agricultural activities. The organization takes a multidimensional approach to ensure that socio-economic, health, environmental, and food safety concerns are addressed. Implementing the right policies and incentives can encourage more sustainable and healthy dietary choices, reducing the demand for food and, consequently, the environmental impacts of agriculture.

Urban runoff

Sources of urban runoff pollution include vehicular transportation, atmospheric deposition, and metallic building envelopes. The pollutants from these sources can have various biological impacts, including bioaccumulation, reduced recruitment of anadromous species, algal blooms, the transfer of human pathogens, and interference with recreational activities. For example, during the “First Flush," the first major rainstorm of the winter season, high concentrations of pollutants can cause stress for aquatic organisms.

To address urban runoff, various strategies have been outlined in the Urban Runoff Action Plan, which is implemented by staff from agencies, local cities, counties, and the MBNMS. These strategies include increasing public education and outreach to inform citizens about urban runoff, water quality, and watershed issues. Additionally, there is a focus on improving technical training for city and county public works staff to prevent urban runoff pollution and adopt guidelines such as the California Environmental Quality Act (CEQA).

The successful implementation of pollution mitigation tools and source controls requires a comprehensive understanding of the sources of urban runoff pollution. While research efforts have been made to document specific sources and pollutants, a complete overview of all contributing sources is still missing. However, with the collaboration of multiple entities and the continuous advancement of clean manufacturing and pollution control technologies, effective measures can be taken to mitigate urban runoff and improve water quality.

Sewage discharges

Sewage discharge is one of the four main sources of water pollution, alongside industrial activities, agricultural activities, and urban stormwater runoff. Sewage typically consists of 99.9% water and 0.1% solids, including a mixture of bacteria, solids, toxic chemicals, and other pollutants. When sewers overflow during storms, sanitary sewer overflows or combined sewer overflows can occur, resulting in water pollution from untreated sewage.

Sewage contamination is a global issue, with large areas (thousands of square kilometres) affected by high levels of sewage contamination. These contamination hotspots often overlap with coral reefs, salt marshes, and fish-rich river systems, threatening biodiversity and ecosystem health. Sewage discharge can alter the environmental conditions of rivers, leading to changes in the microbial community and a decrease in species richness and diversity.

Untreated sewage contains high levels of nutrients, pathogens, endocrine disruptors, heavy metals, and pharmaceuticals, which can have detrimental effects on both human and ecological systems. Waterborne diseases, such as cholera, giardia, and typhoid, are commonly associated with untreated or poorly treated sewage. The presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has also been detected in wastewater, indicating a potential risk of transmission through the water used for swimming, boating, and fishing.

In addition to the health risks, sewage discharges can also impact aquatic life. Estrogenic chemicals found in wastewater treatment effluents can disrupt the endocrine functioning of riverine fish, causing permanent alterations to their reproductive, immune, and respiratory systems. Sewage contamination also facilitates the growth of pathogenic bacteria, such as Vibrio, which can cause diseases in fishes, such as vibriosis.

To address the issue of sewage discharges, new sewage management solutions are being developed, including waste-free toilets and resource recovery to generate fuel and drinking water. However, more innovation is needed, and conservationists must collaborate with the human health sector to effectively tackle this global issue.

Plastic waste

The issue is not limited to the visible plastic waste that blights our beaches and rivers; it is the microscopic pieces that pose the most significant threat. These tiny pieces of plastic, smaller than a grain of rice, are ingested by aquatic animals, causing entanglement, ingestion, and suffocation. They are also absorbed by terrestrial and aquatic plants, which pass them up the food chain to consumer animals and humans. Microplastics have now been found in human blood and can be passed from mothers to their unborn children through the placenta.

The majority of plastic waste in the ocean, a staggering 94%, has sunk to the seafloor. In the North Pacific, a gyre, or swirling whirlpool of ocean currents, collects plastic debris. It is estimated to be twice the size of France and is predicted to double in size over the next ten years if plastic waste continues to be mismanaged. This mismanagement is caused by the properties of plastic that make it so useful—its durability, lightweight nature, and low-cost production.

The accumulation of plastic in water systems is a global environmental threat. It affects the health of both humans and animals, blocks waterways, and causes hygienic problems. It is also linked to endocrine disruption and some cancers, becoming more potent as they move up the food chain. While the recycling of plastic waste is improving, the absolute amount of plastic pollution continues to increase due to the sheer volume of plastic being produced and disposed of.

To combat this issue, it is essential to focus on the management of plastic waste on land before it reaches rivers and estuaries. Local actions to reduce plastic inputs in urban coastal areas can effectively decrease plastic export to the oceans. Monitoring plastic in rivers, even by simple means such as counting floating objects, can help track plastic transport and confirm the success of measures to reduce plastic pollution.

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