Water Pollution

Water pollution is the contamination of water bodies (rivers, lakes, oceans, and groundwater) due to harmful substances like chemicals, plastics, sewage, and industrial waste, making it unsafe for human use, aquatic life, and the environment. It disrupts ecosystems, reduces water quality, and poses serious health hazards.

Types of impurities

Generally the types of Impurities which we can find in water includes: 

Organic Impurities and Nutrients

Impurities like human feces, animal waste, oils, urea, pesticides, herbicides, and decaying plant matter. These substances enter water bodies from sewage discharge, agricultural runoff, and industrial waste. 

• Phosphorus and nitrogen contained in these impurities are essential nutrients for microorganisms. When present in excessive amounts due to agricultural runoff, detergents, and sewage, they lead to oxygen depletion,  Promote algal blooms and fish kills.
• Further, Excessive amount of nutrition accelerates the amount of pathogents that can cause waterborne diseases like cholera and dysentery.

Pathogens: 

Pathogenic bacteria, viruses, fungi, and protozoa enter water from untreated sewage, animal waste, and contaminated surfaces. Microbial contamination causes serious diseases such as typhoid, cholera, hepatitis, and dysentery. Poor sanitation and unsafe drinking water increase the risk of outbreaks, especially in developing regions.

Inorganic Impurities: 

It consist of nitrates, phosphates, heavy metals (lead, mercury, arsenic, cadmium), and salts. These come from industrial effluents, fertilizers, and mining activities. For example:

• High levels of nitrates can cause Blue Baby Syndrome, 
• While heavy metals accumulate in the food chain, leading to toxicity and organ damage in humans and aquatic life.

We will study about these in detail in this chapter.

Impact of Water Pollution

Industrial discharge, agricultural runoff, and untreated sewage increase salinity, toxicity, and biological contamination in water bodies. This creates several health issues as discussed above. Water pollution leads to several other issues as mentioned below:

Environmental Issues 

• Depletion of Water Resources: Over-extraction of groundwater and drying of streams lead to water scarcity, desertification, and declining aquifer levels.
• Depletion of Aquatic Life: Water pollution, overfishing, habitat destruction, and reduced oxygen levels result in declining biodiversity and ecosystem imbalances.

Economic Impact: Water Poverty 

• Availability: Climate change, urbanization, and poor water management lead to severe water shortages.
• Accessibility: Water becomes unusable due to contamination with chemicals, heavy metals, and microbes.
• Affordability: Safe drinking water is expensive due to purification costs, making it inaccessible to low-income communities.

Social Problems: 

Water Disparity: Unequal distribution of water resources leads to regional and class-based inequalities, with some areas facing drought while others have excess supply.

Political Challenges such as Inter-State Water Disputes:

 Conflicts arise over shared rivers, reservoirs, and groundwater due to competing demands between states and nations, often leading to legal battles and tensions.

Water stress

Water stress occurs when the demand for water exceeds the available amount during a certain period or when poor quality restricts its use. World Bank indicates that by 2030 India’s per capita water availability may shrink to half, which will push the country into the ‘water scarce’ category from the existing ‘water stress’ category. It’s noteworthy that India is home to 16% of the World’s population however, it holds only about 4% of global freshwater. India achieved only 56.6% of the target by 2019 of fulfilling  SDG-6 –  “Clean water and sanitation for all by 2030”. As per the NITI Aayog’s Composite Water Management Index (2019), 75% of households in India do not have access to drinking water on their premises and India ranks 120th amongst 122 countries in the water quality index.

Understanding water Pollution 

The sources of River Pollution can be classified as:

1. Point Source
2. Non-Point Source

Point source: 

These are organized sources of pollution where the pollution load can be measured.  Where pollutants enter water-source from a single point. For example, Municipal nallah discharge into rivers and industrial waste discharge.

1. Untreated Sewage: Release of inadequately treated water or untreated sewage from areas not connected to the city’s sewerage network. It leads to eutrophication which depreciates the oxygen levels in water and kills all forms of aquatic life except the anaerobic micro-organisms. This further precipitates as frothing during the period. 
2. Heavy Metal Pollution: Mining, milling, plating and surface finishing industries are the main sources of heavy metal pollution and the concentration of such toxic metals has increased rapidly over the past few decades.
3. Pharma companies’ waste products: For example, a Researchers from IIT-D & National mission for clean Ganga (NMCG) found high concentration of pharmaceutical compounds/residues in sewage discharge in Yamuna. 

Non-point Source

These are non-measurable sources of pollution entering into rivers generally from all locations. For example, agricultural run-off, acid rain, storm-water drainage etc.

1. Agricultural – irrigation discharge into the field is polluted with fertilizer and pesticide waste. This too leads to an increase in eutrophication as well as increased toxicity.
2. Bathing at ghats: Generally, these are spread all across the Indian rivers.
3. Solid waste dumping: It is more near the habitations and minimal in the forested areas.

Impact of reduced flow in the river

In the recent times, the amount of flow in the rivers have drastically reduced. The lower Quantum of flow also reduces the river’s capacity to ‘absorb’ pollution. This is happening due to the following reasons: 

1. Diversion of river’s flow for multiple uses like irrigation, power generation, industrial use and domestic use. For example, the flow of river Yamuna has drastically reduced in Delhi reducing its capacity
2. Groundwater extraction also decreases the flow of water in the river.
3. Occupation of the wetlands: Which had always been an integral part of the river system which helps in the sequestration of the pollutants.
4. Climate change: This reduces the volume of freshwater stored in glaciers.

This exacerbates the amount of pollution in water.

Impact of water pollution:

Pathogens: 

Pathogens are Disease-causing bacteria and other organisms that enter water through domestic sewage & animal excreta. 

For example, Human excreta contains Bacteria, namely Escherichia Coli and Streptococcus faecalis. It is a good indicator of the amount of pathogenic microorganisms in water. These can cause gastro intestinal diseases.

This is the most serious factor in water pollution.

Organic wastes: 

Sewerage, Leaves, grass, trash etc. act as a nutrition for the Pathogens (harmful micro-organisms) 3 Parameters that are used to measure the level of Organic Pollution in water:

1. Dissolved Oxygen (DO): DO comes from either photosynthesis of under-water plants or it is diffused from atmosphere.
   • Bacteria decomposes organic matter & consume DO.  Even moderate amt. of organic matter deplete oxygen. Concentration of DO is very important for aquatic life. If below 6ppm growth of fish gets inhibited. 
   • During night photosynthesis stops, plants continue to respire: reduction of DO.
   • In cold water: DO can reach concentration up to 10ppm (O in air is 200,000ppm). 
2. Anaerobic bacteria: When all O consumed by aerobic bacteria to decompose. Anaerobic bacteria (without oxygen) start breaking down organic waste & produce foul smell: harmful to human health.
   • E-Coli: Escherichia Coliform Bacteria: is a non-pathogenic bacteria faecal coliform group, which indicates the bacteria growth in water. 
3. Biological Oxygen Demand (BOD): Oxygen reqd. to break down organic matter present to certain volume of sample.: Used to measure amount of Organic matter present in water in terms of how much O will be reqd to break it biologically.
   • Clean water has BOD = 5ppm or less.
   • Highly polluted water can have more than 17ppm.
4. Other: Phytoplankton growth within water also cause water pollution. These are biodegradable.

Eutrophication and Algal bloom

(nutrient enrichment; decomposers (saprophytes) use dissolve oxygen; Ecosystem dies), man-made eutrophication (use of fertilizers).  Ministry of Earth Sciences and National Oceanic and Atmospheric Administration (U.S.A) are jointly working on a research collaboration programme which, among others, would understand formation mechanisms of ‘Harmful Algal Blooms’ (HABs):  Cyanobacterial blooms are sometimes also called algal blooms. Most blooms, in fact, are beneficial because the tiny plants are food for animals in the ocean. In fact, they are the major source of energy that fuels the ocean food web. They occur when optimal conditions occur: Nutrient enrichment: Nitrates and Phosphates. Water temperature: Warm Water. Anoxia Condition: Dead Algae are decomposed by Anaerobic bacteria. They consume all the Diffused Oxygen (DO). This degrades aquatic ecosystem and caused the death of all its organisms. HABs: occur when colonies of algae—simple plants that live in the sea and freshwater—grow out of control while producing toxic or harmful effects on people, fish, shellfish, marine mammals, and birds.  While many people call these blooms ‘red tides,’ scientists prefer the term harmful algal bloom. The human illnesses caused by HABs, though rare, can be debilitating or even fatal. A small%age of algae, however, produce powerful toxins that can kill fish, shellfish, mammals, and birds, and may directly or indirectly cause illness in people. They produce neurotoxins and Hepatotoxins. This kills higher forms of life. Zooplankton. HABs also include blooms of non-toxic species that have harmful effects on marine ecosystems. The Produce Aesrosolized air near coasts.  They can be of different colours and sometimes can also occur at low concentration when water is transparent.

 

Chemical Pollutants:

• Water Soluble Inorganic Chemicals incl.:
  • Heavy metals: Cd, Hg, Ni etc. Body can’t excrete them: they are dangerous. 
    • Over a tolerance limit, they damage kidneys, CNS, liver etc.
  • Acids from mine drainage & salts from many different sources including raw salt used to melt snow in colder climates (Na/Ca Cl): water soluble chemical pollutants.
• Organic Chemicals: Manufactured
  • Petroleum products (For example, oil spills), 
  • Pesticides (drift down from sprays via run-off), 
  • Boom-infested water inhibits the growth of other living organisms. Process: nutrient-enriched water bodies support a dense phytoplankton population: kill animal life by depriving it of O & result in subsequent loss of biodiversity: Eutrophication. 
  • Various industrial chemicals; For example, polychlorinated biphenyls (PCBs): used as cleansing solvents in detergents and fertilizers are suspected to be Carcinogenic. Nowadays most detergents are biodegradable. However, they too can create problems like water salination. 

• Bacteria responsible for degrading biodegradable detergent feed on it & grow rapidly. Use O.
• Fertilizers contain P: enhances the chances of Algae growth in water: profuse growth covers water surfaces & reduces O conc.: Leads to anaerobic conditions, commonly with accumulation of obnoxious decay & animal death.

International Standard for Drinking Water: 

• Fluoride: ion conc. 
  • Its deficiency is harmful: causes tooth decay etc. 
  • F– make enamel harder by converting hydroxyapatite to much harder fluorapatite. Soluble fluoride (often added): 1ppm or 1mg/l. 

3(Ca3(PO4)2.Ca(OH)2 → 3(Ca3(PO4)2.CaF2

• F– conc above 2ppm causes brown mottling of teeth, and excess fluoride (over 10ppm) causes harmful effects on bones & teeth (reported in Rajasthan).

• Lead: When lead pipes are used for transportation. [Leaching]
  • Upper limit: 50ppb(billion) – can damage the kidney, liver, and reproductive system.
• Sulphate: Excess (>500ppm) causes a laxative effect, otherwise harmless.
• Nitrate: Max limit: 50 ppm. Excess can cause disease: 
  • Methemoglobinemia (‘blue baby’ syndrome): Cardiovascular defects; Symptom: Blue tips of fingers.
• Others:

Waste-water Treatment: 

Treatment of water involves four essential processes: Bar screen for coarse waste: pebbles, sticks etc.

1. Grit Chamber (inorganic suspended particles) & sand removal tank.
2. Skimmer: Solid waste (such as faeces) settles in a large tank sloped towards the middle. Removed by scrapper. The skimmer removes floatable solids like oil & grease. = Clarified water.
   • Sludge decomposed by anaerobic bacteria in a separate tank = Biogas = Fuel or electricity.
3. For Organic waste: Now acted upon by Aerobic bacteria by pumping air. After several hours suspended microbes settle at the bottom of the tank as activated sludge (97% water). Water is removed from the top. Treated water has a very low level of organic material.
   • Activated sludge is removed by sand-drying beds or machines. This can be used as manure in the soil.

• On-site sewage disposal system: Septic tanks, chemical toilets, composting pits.

Further treatment may involve: Aeration, Filtration, Chlorination; Treatment Plant:

Chlorination:

Chlorination is the process of adding chlorine to drinking water to disinfect it and kill germs. Different processes can be used to achieve safe levels of chlorine in drinking water. Chlorine is available as:

1.  compressed elemental gas, 
2. sodium hypochlorite solution (NaOCl) or solid calcium hypochlorite (Ca(OCl).

This makes it easier to apply as a disinfectant in medical areas, next to its use as a bleach. When bleaching powder dissolves, it reacts with water to underchloric acid (HOCl) and hypochlorite ions (OCl–). Chlorine kills pathogens such as bacteria and viruses by breaking the chemical bonds in their molecules.

Toxic metals and sources of metal Pollution:

The term ‘‘heavy metal’’ refers to any metal and metalloid element that has a relatively high density ranging from 3.5 to 7 g/cm3 and is toxic or poisonous at low concentrations.

• Report: Toxic metals in Indian rivers 2018 by Central Water Commission.
  • The report has highlighted that 42 rivers in India have at least two toxic heavy metals in quantities beyond the permissible limit.
  • Ganga was found to be polluted with five heavy metals—chromium, copper, nickel, lead and iron.

Sources: 

• Mining, milling, 
• Plating and surface finishing industries are the main sources of heavy metal pollution and the concentration of such toxic metals has increased rapidly over the past few decades.

Impact of Heavy metal toxicity;

Primary metals considered to be toxic are lead, arsenic, copper, cadmium, mercury and nickel.

• Health impacts of toxic metals: Heavy metals pose a serious threat to humans and the environment because of their toxicity, 
• Environmental impacts: non-biodegradability and bioaccumulation and may result in reduction of species diversity.

Corrective measures: 

• Controlling runoff pollution such as agriculture runoff, urban runoff and runoff from livestock farms through afforestation, sustainable agriculture practices and using wastewater for irrigation etc.
• Using Green remediation techniques such as Phytoextraction for soils and wetlands contaminated with toxic metals. e.g. – Water hyacinth is used for cleansing polluted water by absorbing pollutants, especially chromium.

<trstyle=”background-color: #ffc027; ” >FluorideAluminium melting, glass, phosphate fertilizer, brick manufacturing and coal-based thermal plantsDecay in the tooth (Dental Fluorosis), also affects the Kidney, lever, Brain and Thyroid (an endocrine mechanism)

<trstyle=”background-color: #fff2cc; “>ChromiumMining, electroplating, tanneries & textiles, Copper Mining, pesticides, Lead Paint, batteries, pesticides, automobile emissions, burning of coalPresent in small Quantities.

Metal	Source	Impact on health
Arsenic	Pesticides, fungicides, metal smelters	Kidney and lung malfunction, diseases of the blood vessels (Blackfoot disease) and reproductive disorders.
Cadmium	Welding, electroplating, pesticides, fertilizers, batteries, nuclear plants	Carcinogenic: Can lead to cancers of skeletal, urinary, reproductive, cardiovascular, central & peripheral nervous, and respiratory systems.  Itai-Itai disease: softening of bones and kidney failure
Mercury	Pesticides, batteries, paper industries	Minamata Disease – Neurological disorders. It is stored in the fat tissues and the Brain is mostly made up of fat.
Nickel	Electroplating, zinc base coating, battery industries	Can cause dermatitis if consumed in large quantities.
Zinc	Refineries, brass manufacturing, metal plating, immersion of painted idols	Present in small Quantities.
Manganese	Welding, fuel addition, ferro manganese production	Present in small quantities.
Lead (airborne)	Burning of petroleum and coal (airborne)	Brain & Kidney damage; Anaemia & weakness. Symptoms may include abdominal pain, constipation, headaches, irritability, memory problems, infertility, and tingling in the hands and feet.

Biological disaster of Yamuna: 

• Najafgarh Drain drains out all sewage of Delhi and Gurugram into Yamuna. It was in the past known as River Sahibi, whose catchment is now encroached, reducing its capacity to drain and is now a toxic stream.
• The Problem of Froth: The foam has been visible for more than a decade. But, by all accounts, it has been covering a greater expanse of the river in the past five years. Possible Reasons for Froth: 
  • Untreated Sewage: It precipitates frothing. During the period when the river’s flow is lean, it is not able to wash off this detritus. 
  • Pollution by Paper and Sugar mills: The Delhi government has accused sugar and paper mills in places like Meerut and Shamli of releasing untreated wastewater into the Hindon Canal at the Yamuna Barrage. 
  • Lower flow: The Haryana government has also been criticised for squeezing the river’s flow to the capital. 
  • According to an NGT committee report of 2018, the 22 km stretch of the Yamuna from Badarpur to Okhla — about 2% of the river’s total length — accounts for 75% of the river’s pollution. 
• Pharmaceutical waste products in rivers: Researchers from IIT-D & National Mission for Clean Ganga collected water samples from 6 years across a 25km river stretch during 3 different seasons. The highest concentration of pharmaceutical compounds/residues was located downstream at Wazirabad at the point where Najafgarh Drain meets river Yamuna.
  • Reasons – Mainly Excretion of drugs: Our body doesn’t use the entire quantity of the drug we take, most of it is excreted and ends up in aquatic systems via domestic sewage.
  • Impact: 
    • Ibuprofen & Paracetamol are found in the highest concentration. 
    • Impact of Ibuprofen: Studies have shown that even small concentrations of ibuprofen could cause an antagonistic effect on aquatic organisms. Further, ibuprofen exposure could increase cyanobacterial growth in the water.
    • Caffeine was found in high concentration in most of the sites.

 Solutions to treat Yamuna

• We need more studies in this field.
• Asita Project: It’s a Yamuna River Front Development Project, that aims to restore, revive and rejuvenate the river’s floodplains and make them accessible to the people of Delhi.
  • Reviving the Ecosystem by creating a wetland, to store the flood waters and to improve the groundwater recharge which will eventually result in the flourishing of biodiversity in the floodplains. 
  • NMCG is monitoring the development of the project.

Sujalam 2.0 campaign: 

• Launched by: Union Ministry of Jal Shakti, for greywater management on World Water Day, 2022.

• Theme: ‘Groundwater: making the invisible visible’. 
• Objective:  to manage greywater through people’s participation. 
  • Plan to mobilize communities, institutions like panchayats, schools, and Anganwadi to undertake greywater management. 
  • Greywater can be best managed where it is generated and turns into a major management and infrastructure challenge if it is allowed to accumulate and stagnate. 
• Funding:  sourced from SBM-G Phase II or through 15th Finance Commission tied-grants or MGNREGS or through convergence of all.

Groundwater Contamination

Arsenic Contamination: 

Arsenic (As) is an odourless and tasteless metalloid widely distributed in the earth’s crust. It exists in two forms:

• Inorganic form.
• If carbon is attached, then the arsenic compound is an organic compound.

• Report on Groundwater Arsenic Contamination in India by CGWB:
  • 21 states across the country have pockets with arsenic levels higher than the Bureau of Indian Standards (BIS) stipulated permissible limit of 0.01 milligram per litre (mg/l).
  • The states along the Ganga-Brahmaputra-Meghna (GBM) river basin UP, Bihar, Jharkhand, West Bengal and Assam are the worst affected.
  • Arsenic contamination in groundwater has penetrated the food chain.

Sources of arsenic contamination

• It is naturally present at high levels in the groundwater of a number of countries. Weathering of rocks and minerals comprising sand, silt and clay, followed by leaching and runoff.
• Anthropogenic activities like intense exploitation of groundwater, application of fertilizers, burning of coal and leaching of metals from coal-ash tailings.

Acceptable Limit: 

WHO recommended the current limit of arsenic in drinking water is 10 μg/L.

• It is one of WHO’s 10 chemicals of major public health concern.

Consequences of arsenic contamination

• Arsenic contamination results in kidney and lung, diseases of the blood vessels (Blackfoot disease) and reproductive disorders.
  • In utero and early childhood, exposure has been linked to negative impacts on cognitive development and increased deaths in young adults.
  • Inorganic arsenic is a known human carcinogen — it is this form of arsenic that is linked with increased risks of cancer such as skin cancer, skin lesions, cancers of the bladder,
  • It has also been associated with cardiovascular disease and diabetes. 
• Regular extraction of groundwater for irrigation deposits arsenic in soil and consequently its uptake by the crops. Also, paddy farms flooded with contaminated water eventually caused the accumulation of arsenic in the food crops.
• Rice husk used as fodder for livestock, exposes them to the impacts of arsenic contamination. 
  • This leads to potential risks for humans when they consume cattle-based food products.
• Biomagnification: concentration of Arsenic at higher trophic levels in the food chain is possible. Affecting food: A recent publication by the Jadavpur University, has revealed a rise in arsenic contamination of paddy plants from groundwater in West Bengal. It eventually causes photo-accumulation of arsenic in the food crops, especially in the leaves, which can emanate from contaminated water sprayed on them.

Methods to tackle Arsenic contamination

• Treatment technologies based on oxidation, co-precipitation, adsorption, ion exchange and membrane process have been developed for the removal of arsenic from contaminated water.
• Removal technologies:
  • Lime softening is a water treatment process that uses CaOH, or limewater.
  • Iron co–precipitation implies that Arsenic is precipitated using an Iron-based substrate.
• Innovative technologies, such as permeable reactive barriers, phytoremediation, biological treatment and electro-kinetic treatment are also being used to treat arsenic-contaminated water and soil.
• Precautions during Rainwater harvesting and recharging of groundwater table to avoid the depletion in the groundwater level and check the leaching of metals into groundwater.

 Uranium Contamination: 

A small concentration of Natural Uranium makes the water weakly radioactive, but the radioactivity remains so because of its long physical half-life (4.468 billion years for uranium-238).

• The biological half-life (half-life in the human body) for uranium is about 15 days.
• It is a naturally occurring element found in low levels within all rock, soil, and water. This is the highest-numbered element to be found naturally in significant quantities on Earth. 
• It is considered to be more plentiful than Antimony, Beryllium, Cadmium, Gold, Mercury, Silver or Tungsten and is as abundant as tin, arsenic or molybdenum.

Recently, a new study by researchers has found widespread uranium contamination in groundwater from aquifers in 16 Indian states.

• Mostly located in: Rajasthan and parts of Punjab, Haryana and Gujarat

• Most of the wells tested in Rajasthan and Gujarat had more uranium than the WHO’s recommended limit of 30 μg/L.

Primary Source of Uranium Contamination

• It is naturally contained in aquifer rocks. Oxidation conditions enhance the extracted uranium’s solubility in water. This when interacts with other chemicals in the groundwater, such as bicarbonate, which can further enhance its solubility.
  • Granite, in the Himalayan range, may have slowly leached to release U in Indian states. 
• Anthropogenic factors such as overexploitation of groundwater for agricultural irrigation and nitrate pollution due to overuse of nitrogenous fertilizers may further enhance uranium mobilization.

Problems

• No limit is prescribed for Uranium in BIS Drinking Water Specifications which makes quality monitoring of the water table impossible. Some of the major contaminants that are monitored under the specification include: Cadmium, Cyanide, Mercury, Lead, Arsenic, Chromium etc.
• Uranium in drinking water raises concerns because of chemical toxicity, chronic kidney problems etc.

Way Forward: 

• Revision of the current water quality monitoring program in India.
• Evaluation of human health risks in areas of high uranium prevalence.
• Development of adequate remediation technologies.
• Including a uranium standard in the Bureau of Indian Standards’ Drinking Water Specification based on uranium’s kidney-harming effects.
• Establishing monitoring systems to identify at-risk areas, and exploring new ways to prevent or treat uranium contamination.

What is water pollution and what are its primary causes?

Water pollution is the contamination of water bodies (rivers, lakes, groundwater, oceans) by harmful substances like sewage, chemicals, plastics, and industrial waste, making it unsafe for human consumption, aquatic life, and the environment.
Primary causes include untreated sewage, agricultural runoff, industrial effluents, and dumping of solid waste.

What are the main types of water impurities and their impacts?

Organic Impurities: Human and animal waste, pesticides – promote microbial growth, cause diseases like cholera and dysentery.
Inorganic Impurities: Heavy metals (lead, mercury, arsenic), nitrates – cause diseases like blue baby syndrome, cancer, kidney and nervous disorders.
Pathogens: Bacteria and viruses from sewage – lead to typhoid, hepatitis, and gastrointestinal illnesses

What is BOD and how is it related to water pollution?

Biological Oxygen Demand (BOD) measures the amount of oxygen needed by microbes to decompose organic matter in water.
Higher BOD indicates more pollution.
Clean water has BOD ≤ 5 ppm; polluted water has BOD > 17 ppm.
Low oxygen levels (DO < 6 ppm) harm aquatic life and encourage anaerobic bacteria, producing foul smells.

What is eutrophication and how does it affect aquatic ecosystems?

Eutrophication is excessive nutrient enrichment (especially nitrogen & phosphorus) in water bodies, often from fertilizers and sewage.
It causes:
Algal blooms (HABs)
Oxygen depletion
Death of aquatic organisms
Ecosystem collapse

What are Harmful Algal Blooms (HABs)?

HABs are rapid growths of algae that produce neurotoxins and hepatotoxins, affecting humans and marine life.
Often caused by nutrient pollution and warm water.
Lead to dead zones, fish kills, and human health issues through aerosolized toxins near coasts.