Contaminants In Polluted Water: What's Lurking Beneath?

Water pollution is the contamination of water bodies, including lakes, rivers, oceans, and groundwater, with harmful substances, often due to human activities. These contaminants can be divided into four main categories: sewage discharges, industrial activities, agricultural activities, and urban runoff. Sewage pollution, for example, can introduce disease-causing microorganisms into water bodies, posing a direct threat to public health. Industrial activities can release toxic chemicals such as lead, mercury, and chromium into water sources. Agricultural practices can contribute pollutants like pesticides, fertilizers, and animal waste. Urban runoff, including stormwater, can carry various contaminants, including motor fuels, oils, and plastic waste, into water bodies. These pollutants have far-reaching consequences, including the degradation of aquatic ecosystems, the spread of water-borne diseases, and the contamination of drinking water sources, highlighting the urgent need for collective action to address this pressing environmental issue.

Sewage and wastewater

Sources of Sewage and Wastewater

Composition of Sewage and Wastewater

The composition of sewage and wastewater can vary depending on the sources, but they typically contain a mixture of water, human waste, used water from bathrooms, food preparation wastes, laundry wastewater, soaps, detergents, and other waste products of normal living. Sewage and wastewater can also contain inorganic minerals, metals, and compounds, such as sodium, potassium, calcium, magnesium, copper, lead, nickel, and zinc. These substances can originate from industrial and commercial sources, stormwater, and inflow and infiltration from cracked pipes.

Treatment of Sewage and Wastewater

The treatment of sewage and wastewater is essential to remove potential pollutants and disease-causing agents. Primary treatment methods can remove large solid debris, floating matter, and settleable matter. Secondary treatment methods, such as the OxyMem Membrane Aerated Biofilm Reactor, use microorganisms to break down organic pollutants. However, it is important to note that not all sewage and wastewater are treated adequately. Developing countries, for example, treat only an average of 4.2% of their sewage, leading to the release of untreated sewage into the environment.

Impact of Sewage and Wastewater on Pollution

Industrial activities

One of the primary sources of industrial water pollution is the release of toxic substances and chemicals during manufacturing and other industrial processes. These toxic substances can include heavy metals such as copper, lead, cadmium, zinc, nickel, arsenic, and mercury. For instance, the electroplating process in the metal processing industry results in highly polluted water containing these heavy metals. Petroleum products, used as fuel or lubricating oil, are another common pollutant produced during plastic manufacturing. Hazardous wastes, which are highly flammable and corrosive, are often generated during construction, demolition, manufacturing, and waste treatment processes.

Additionally, industrial wastewater can contain a range of harmful chemicals, such as asbestos, sulfur, mercury, lead, nitrates, phosphates, dyes, pesticides, acids, benzene, and volatile organic compounds. The pharmaceutical industry, for example, produces wastewater contaminated with active pharmaceutical ingredients, such as antibiotics (e.g. sulphamide, penicillin) and hormones (e.g. cyproterone acetate, letrozole). Inorganic chemical plants are some of the biggest industrial dischargers of toxic pollution, releasing pollutants like nitrogen, cyanide, chromium, nickel, and lead into waterways.

The release of untreated or inadequately treated industrial wastewater has severe environmental and health consequences. It can lead to the contamination of freshwater systems, making the water unsafe for human consumption and disrupting aquatic ecosystems. For instance, high levels of nitrogen in the water can cause algal blooms that deplete oxygen levels, leading to fish kills. Certain chemicals, such as asbestos, pose health risks, including increased chances of developing mesothelioma.

While some regions, like Europe, have implemented strict regulations to control industrial water pollution, many other parts of the world lack comprehensive policies. The absence or inadequate enforcement of regulations allows industries to bypass laws and continue polluting water sources.

Agricultural activities

Agriculture is a major cause of water pollution, accounting for 70% of water withdrawals worldwide. Farms discharge large quantities of agrochemicals, organic matter, drug residues, sediments, and saline drainage into water bodies. This includes pesticides and fertilizers, which can contaminate both groundwater and surface water. The use of pesticides and fertilizers has led to increased soil erosion, salinity, and sediment loads in water.

Another issue is the use of untreated wastewater in agriculture, which can lead to the accumulation of microbiological and chemical pollutants in crops, livestock products, and soil and water resources. This can have severe health impacts on exposed food consumers and farm workers and may also exacerbate antimicrobial resistance.

Agricultural runoff is a significant contributor to water pollution, impacting rivers, streams, lakes, and wetlands. This runoff includes pollutants such as soil erosion, nutrient loss, bacteria from livestock manure, and pesticides, which can enter local streams, rivers, and groundwater. Increased levels of nitrogen and phosphorus from fertilizer and manure can stimulate algal blooms, leading to hypoxic conditions that are harmful to aquatic life.

To mitigate these issues, various conservation practices can be implemented, such as using drip irrigation to control the amount of pesticides and nutrients added to irrigation water, and storing livestock manure in protected areas to minimize runoff risks.

Urban runoff

One of the most significant effects of urban runoff is on ephemeral streams, which are watercourses that typically have little to no water during dry weather. Urbanisation causes these streams to have an unnatural year-round streamflow, which harms the surrounding vegetation, wildlife, and stream bed. The runoff rushes down the stream channel, causing severe erosion and increasing sediment loads, while also carrying a range of pollutants, including trash, excessive silt, and other wastes. This can pose moderate to severe health hazards and negatively impact the natural features of the waterway, such as meanders and sandbars.

The sources of pollution in urban runoff are diverse and include vehicular transportation-related activities, atmospheric deposition, and metallic building envelopes. Roads and parking lots are major sources of polycyclic aromatic hydrocarbons (PAHs), which are byproducts of gasoline and other fossil fuel combustion. They also contribute to the presence of heavy metals such as nickel, copper, zinc, cadmium, and lead in stormwater. Roof runoff is another significant source, as it introduces high levels of synthetic organic compounds and zinc from galvanised gutters.

Improper fertiliser use on residential lawns, parks, and golf courses can also lead to increased levels of nitrates and phosphorus in urban runoff. Eroding soils and poorly maintained construction sites further contribute to the problem by increasing sedimentation in runoff. Additionally, irrigation practices, such as overwatering with sprinklers, can produce runoff that carries accumulated pollutants to streams, resulting in higher pollutant concentrations than would occur during regional precipitation events.

The consequences of urban runoff extend beyond the immediate impact on ephemeral streams. It contributes to the deterioration of surface water quality, increases temperatures in streams (harming fish and other organisms), and can lead to urban flooding. Most municipal storm sewer systems discharge untreated stormwater into natural water bodies, and this excess water can also intrude into people's properties, causing repetitive and costly issues for communities.

Oil spills

The transportation and transfer of oil pose a significant risk of spills, with each transfer between ocean tankers, pipelines, trains, and trucks increasing the likelihood of an accident. Intense industrial operations and the use of supertankers capable of transporting large volumes of oil further elevate the chances of spills. Oil spills can also occur during routine maintenance, such as bilge pumping, and from non-point sources like industrial and domestic runoff, including spills in fuel depots, oil leaks in vehicles, and improper disposal of paint or oil.

The cleanup and recovery process after an oil spill is challenging and time-consuming, often taking weeks, months, or even years. It depends on factors like the type of oil, water temperature, and the nature of the shorelines and beaches affected. Physical cleanup methods include the use of floating booms, skimmers, sorbents, and burning. Booms act as physical barriers to contain the oil and prevent it from spreading, while skimmers and sorbents help remove oil from the water surface. Burning the oil can effectively remove it, but it also releases nitrogen and sulphur, contributing to acid rain and additional pollution.

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