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Comprehensive Guide to Water Filtration Media and Contaminant Removal

Comprehensive Guide to Water Filtration Media and Contaminant Removal

Water filtration is the process of removing unwanted substances from water by passing it through media that trap contaminants while allowing water to flow through. This guide focuses exclusively on water filtration technologies, the media they employ, and the specific contaminants they target.

Mechanical Filtration Media

Sediment Filters

Materials: Polypropylene, polyester, cotton, pleated paper

Contaminants Removed:

  • Sediment, dirt, rust particles
  • Sand and silt
  • Suspended solids
  • Large particulates (>5 microns)
  • Applications: Pre-filtration in water systems, well water treatment, residential water filtration
  • Ratings: Typically measured in microns (1-100 microns)

Microfilters & Ultrafilters

Materials: Ceramic, hollow fiber membranes, polymer sheets

Contaminants Removed:

  • Fine particles (0.1-10 microns)
  • Bacteria (E. coli, Salmonella)
  • Protozoan cysts (Giardia, Cryptosporidium)
  • Algae and some viruses
  • Applications: Point-of-use water treatment, backpacking water filters
  • Mechanism: Physical straining, size exclusion

Chemical Filtration Media

Activated Carbon

Materials: Coconut shell, wood, coal, processed to create a highly porous structure

Contaminants Removed:

  • Chlorine and chloramines
  • Volatile organic compounds (VOCs)
  • Pesticides and herbicides
  • Industrial solvents (TCE, PCE)
  • Odors and unpleasant tastes
  • Some pharmaceuticals
  • PFAS (partially, especially with specialized carbon)
  • Disinfection byproducts (THMs, HAAs)
  • Applications: Drinking water filters, under-sink systems, refrigerator filters
  • Mechanism: Adsorption (contaminants bind to the carbon surface)
  • Types:
    • Activated Carbon (GAC)
    • Carbon block
    • Catalytic carbon (enhanced for chloramine removal)

Ion Exchange Resins

Materials: Synthetic polymers with charged functional groups

Contaminants Removed:

  • Cation Exchange: Calcium, magnesium (water hardness), heavy metals (lead, copper, cadmium)
  • Anion Exchange: Nitrates, sulfates, arsenic, fluoride, perchlorate, chromium-6
  • Mixed Bed: Combined removal of both positive and negative ions
  • Applications: Water softeners, deionization systems, selective contaminant removal
  • Regeneration: Using salt (NaCl) for cation resins, caustic soda for anion resins

Zeolites

Materials: Natural or synthetic aluminosilicate minerals with porous structure

Contaminants Removed:

  • Ammonia
  • Heavy metals
  • Radioactive isotopes (especially cesium and strontium)
  • Some organic compounds
  • Applications: Specialized water treatment, industrial wastewater treatment
  • Types: Clinoptilolite, chabazite, mordenite, synthetic zeolites

Biological Filtration Media

Biofilters

Materials: Ceramic rings, plastic biomedia, lava rock, sponges

Contaminants Removed:

  • Ammonia (converted to nitrite, then nitrate)
  • Organic waste compounds
  • Some pharmaceuticals and pesticides
  • Applications: Aquariums, ecological water treatment, constructed wetlands
  • Mechanism: Hosts beneficial bacteria (Nitrosomonas, Nitrobacter) that break down waste compounds

Membrane Filtration

Reverse Osmosis (RO) Membranes

Materials: Thin-film composite (typically polyamide)

Contaminants Removed:

  • Dissolved salts and minerals (sodium, chloride)
  • Heavy metals (lead, mercury, arsenic)
  • Fluoride
  • Nitrates
  • PFAS (per- and polyfluoroalkyl substances)
  • Most bacteria and viruses
  • Many pharmaceutical compounds
  • Microplastics
  • Applications: Drinking water purification, desalination
  • Limitations: Wastes water, removes beneficial minerals, requires pre-filtration

Nanofiltration Membranes

Materials: Modified polymer membranes

Contaminants Removed:

  • Divalent ions (calcium, magnesium)
  • Larger molecules (>200-400 Daltons)
  • Some pesticides and herbicides
  • Color compounds
  • Hardness
  • Most pharmaceutical compounds
  • Applications: Water softening, selective contaminant removal
  • Advantages: Lower pressure requirements than RO, higher flow rates

Ultrafiltration Membranes

Materials: Polymer hollow fibers or sheets

Contaminants Removed:

  • Bacteria and protozoa
  • Colloids and suspended solids
  • High molecular weight organics
  • Proteins and macromolecules
  • Microplastics
  • Applications: Whole-house filtration, commercial water treatment
  • Pore size: Typically 0.01-0.1 microns

Microfiltration Membranes

Materials: Polyvinylidene fluoride (PVDF), polysulfone, ceramics

Contaminants Removed:

  • Bacteria
  • Large particles
  • Suspended solids
  • Some viruses when attached to larger particles
  • Applications: Pre-treatment for RO, clarification
  • Pore size: Typically 0.1-10 microns

Specialized Water Filtration Media

KDF (Kinetic Degradation Fluxion)

Materials: High-purity copper-zinc granules

Contaminants Removed:

  • Chlorine
  • Heavy metals (lead, mercury, arsenic)
  • Iron, hydrogen sulfide
  • Algae and fungi
  • Applications: Shower filters, whole-house systems, pre-treatment for RO
  • Mechanism: Redox reactions

Bone Char

Materials: Charred animal bones

Contaminants Removed:

  • Fluoride
  • Lead and other heavy metals
  • Some organic contaminants
  • Applications: Defluoridation of water
  • Mechanism: Adsorption and ion exchange

Greensand

Materials: Glauconite mineral coated with manganese oxide

Contaminants Removed:

  • Iron and manganese
  • Hydrogen sulfide
  • Radium
  • Applications: Well water treatment, municipal water
  • Regeneration: Potassium permanganate

Activated Alumina

Materials: Porous aluminum oxide

Contaminants Removed:

  • Fluoride
  • Arsenic
  • Selenium
  • Applications: Specialized water treatment for specific contaminants
  • Limitations: Narrow pH range for optimal performance

Birm

Materials: Lightweight manganese dioxide coated media

Contaminants Removed:

  • Iron
  • Manganese (at higher pH levels)
  • Applications: Well water treatment
  • Mechanism: Catalytic oxidation of dissolved metals

Disinfection Methods

UV Treatment

Materials: UV-C lamps with quartz sleeves

Contaminants Removed:

  • Bacteria
  • Viruses
  • Protozoa
  • Other microorganisms
  • Applications: Point-of-entry disinfection, bottling plants
  • Mechanism: DNA/RNA damage that prevents reproduction
  • Limitations: No residual protection, requires clear water

Chlorination Media

Materials: Calcium hypochlorite, sodium hypochlorite, chlorine tablets

Contaminants Removed:

  • Bacteria
  • Viruses
  • Some protozoa
  • Applications: Municipal water treatment, emergency water disinfection
  • Mechanism: Oxidation of cellular structures
  • Byproducts: Creates disinfection byproducts (DBPs) like trihalomethanes (THMs)

Multi-Stage Filtration Systems

Point-of-Use (POU) Combination Systems

  • Sediment pre-filter (5-10 micron)
  • Activated carbon block
  • Optional specialized media (KDF, bone char)

Contaminants Removed:

  • Sediment
  • Chlorine
  • VOCs
  • Lead
  • Heavy metals
  • Taste and odor

Under-Sink Reverse Osmosis Systems

  • Sediment pre-filter
  • Carbon pre-filter
  • RO membrane
  • Post-filter carbon
  • Optional remineralization

Contaminants Removed:

  • Nearly all contaminants including dissolved solids, heavy metals, and fluoride

Whole-House Treatment Systems

  • Sediment pre-filter
  • Carbon filtration
  • Optional UV disinfection

Contaminants Removed:

  • Sediment
  • Chlorine
  • Some VOCs

Emerging Water Filtration Technologies

Graphene Filters

Materials: Single-atom thick carbon sheets

Contaminants Removed:

  • Dissolved salts
  • Heavy metals
  • Organic contaminants
  • Bacteria and viruses

Advantages:

  • High flow rates
  • Lower energy requirements than RO

Electrochemical Filtration

Materials: Conductive carbon materials with applied voltage

Contaminants Removed:

  • Heavy metals
  • Microorganisms
  • Organic contaminants
  • Applications: Point-of-use water treatment

Advantages:

  • Regenerable in place
  • Selective removal

Magnetic Nanoparticles

Materials: Iron oxide nanoparticles with functional coatings

Contaminants Removed:

  • Heavy metals
  • Radionuclides
  • Specific targeted contaminants
  • Applications: Groundwater remediation

Advantages: Retrievable and reusable

Filter Selection Considerations

Water Quality Factors

  • Source water analysis
  • Primary contaminants of concern
  • pH and hardness levels
  • Presence of oxidizers (chlorine)

Performance Metrics

  • Flow rate capacity
  • Pressure requirements
  • Contaminant reduction percentages
  • Certification to NSF/ANSI standards

Practical Considerations

  • Installation requirements
  • Maintenance needs
  • Filter replacement frequency
  • Cost of ownership

Effective water filtration relies on selecting appropriate media for the specific contaminants present in your water supply. Many filtration systems combine multiple media types to address a range of contaminants. Understanding the capabilities and limitations of each filtration medium is essential for designing effective treatment systems that provide the desired level of purification while considering factors like cost, maintenance requirements, and environmental impact.

Regular water testing and proper maintenance of filtration systems are crucial for ensuring continued protection against water contaminants.

Contaminants

Chlorine

Chlorine is commonly used in water treatment but can be considered a contaminant for several reasons: Chlorine is added to public water supplies primarily as a disinfectant to kill harmful bacteria, viruses, and parasites. This practice has been crucial in preventing waterborne diseases like cholera and typhoid fever.

Health Concerns:

Formation of disinfection byproducts (DBPs) like trihalomethanes (THMs) and haloacetic acids when chlorine reacts with organic matter

These DBPs have been linked to increased risks of cancer, reproductive problems, and other health issues with long-term exposure

Can cause respiratory irritation when chlorine gas evaporates from hot water

Imparts a distinct chemical taste and smell to water

Many people find chlorinated water unpleasant to drink

Environmental Impact:

Chlorinated water discharged into natural water bodies can harm aquatic ecosystems

Toxic to fish, amphibians, and other aquatic organisms

Other issues:

Can damage rubber seals in plumbing fixtures over time

May interfere with certain industrial processes or home brewing

Methods for Removing Chlorine

Activated Carbon Filtration: Most common and effective method

Reverse Osmosis Systems: Removes chlorine along with other impurities

Ultraviolet Light: Can break down chlorine compounds

Chemical Neutralization: Using substances like sodium thiosulfate

Evaporation: Letting water stand uncovered (takes 24+ hours)

Boiling: Accelerates the evaporation process

While there are legitimate reasons to remove chlorine from drinking water, it’s important to note that the disinfection benefits of chlorine have saved countless lives by preventing waterborne disease. The decision to remove chlorine should consider the source water quality and ensure that proper alternative disinfection is in place if needed. This is why it’s important to leave the chlorine until you’re ready to use it.

THMs

THMs, or Trihalomethanes, are a group of chemical compounds that form as disinfection byproducts (DBPs) when chlorine or other disinfectants used to treat drinking water react with naturally occurring organic matter in the water.

The main THMs that concern water quality include:

  • Chloroform (the most common THM)
  • Bromodichloromethane
  • Dibromochloromethane
  • Bromoform

These compounds form when chlorine used for disinfection reacts with organic material like decaying vegetation, algae, or other natural organic matter present in the source water. The reaction typically occurs during the water treatment process.

Health concerns associated with THMs include:

  • Potential increased risk of certain cancers with long-term exposure
  • Possible reproductive issues including increased risk of miscarriage and birth defects
  • Potential liver, kidney, and central nervous system effects

The EPA regulates THMs under the Safe Drinking Water Act, setting a maximum contaminant level (MCL) of 80 parts per billion (ppb) for total THMs in drinking water systems. Water utilities must regularly test and report THM levels and take corrective action if levels exceed regulatory limits.

To reduce THM formation, water treatment facilities may:

  • Use Activated carbon in the filtration process.
  • Remove organic matter before disinfection.
  • Use alternative disinfection methods like UV light or ozone.

Arsenic

Arsenic is a naturally occurring element that poses serious health risks when present in drinking water. It’s considered one of the most significant water contaminants globally.

Sources of Arsenic in Water

Natural Sources:
  • Weathering and erosion of arsenic-containing rocks and minerals
  • Geothermal activity releasing arsenic into groundwater
  • Areas with volcanic bedrock often have higher arsenic levels
Anthropogenic (Human) Sources:
  • Mining operations and mine drainage
  • Metal processing facilities
  • Agricultural use of arsenic-containing pesticides (historically)
  • Wood preservatives (primarily before 2004)
  • Industrial waste discharge

Health Impacts

Arsenic is particularly concerning because it:

  • Is a known carcinogen linked to multiple types of cancer (bladder,lung, skin, kidney, liver, prostate)
  • Causes arsenicosis (arsenic poisoning) with symptoms including:
    • Skin lesions, hyperpigmentation, and keratosis
    • Cardiovascular disease
    • Peripheral neuropathy
    • Diabetes
  • Has no taste, color, or odor in water (undetectable without testing)
  • Bioaccumulates in the body over time
  • Causes developmental issues in children, including reduced cognitive function
  • Has effects that may appear only after years of exposure to low levels

Regulatory Standards

The WHO and EPA have established maximum contaminant levels for arsenic in drinking water:

  • EPA standard: 10 ppb (parts per billion)
  • WHO guideline: 10 ppb
  • Many experts recommend even lower levels (≤5 ppb) for optimal safety

Removal Methods

Arsenic is difficult to remove from water. Effective methods include:

  • Oxidation followed by filtration
  • Coagulation/filtration processes
  • Reverse osmosis systems
  • Ion exchange technology
  • Activated alumina adsorption

Copper

Copper is an essential micronutrient that becomes problematic at elevated concentrations in drinking water. Unlike arsenic, which is toxic at any level, copper has a more nuanced status as a water contaminant.

Sources of Copper in Water

  1. Plumbing Infrastructure:
    • Corrosion of copper pipes and fixtures
    • Leaching from brass fittings (which contain copper)
    • More pronounced in water with low pH (acidic) or high carbonate levels
  2. Natural Sources:
    • Weathering of copper-bearing rocks and minerals
    • Natural deposits in soil that interact with groundwater
  3. Industrial Sources:
    • Mining operations and mine drainage
    • Electronics manufacturing
    • Agricultural runoff (copper-based fungicides)
    • Industrial waste discharge

Health Impacts

Copper has a dual nature when it comes to human health:

At Normal Levels:
  • Essential for blood cell formation and iron metabolism
  • Supports nerve function and immune system health
  • Required for collagen formation
At Elevated Levels:
  • Causes gastrointestinal distress (nausea, vomiting, diarrhea, abdominal cramps)
  • Metallic taste in the mouth
  • Blue-green staining of plumbing fixtures and laundry
  • Can cause liver and kidney damage with long-term exposure
  • Particularly problematic for individuals with Wilson’s disease

Regulatory Standards

  • EPA Maximum Contaminant Level Goal: 1.3 mg/L (1,300 ppb)
  • EPA “Action Level”: 1.3 mg/L (requires water systems to take steps when exceeded)
  • WHO guideline: 2 mg/L

Detection Signs

Unlike many contaminants, copper often provides noticeable indicators:

  • Blue-green stains in sinks, tubs, and on fixtures
  • Metallic taste in water
  • Green corrosion on pipes and fittings

Removal Methods

  1. Water Treatment:
    • Activated carbon filtration
    • Reverse osmosis systems
    • Ion exchange
    • Distillation
  3. Source Control:
    • Adjusting water pH (less acidic water is less corrosive)
    • Adding corrosion inhibitors to water supply
    • Replacing copper plumbing with PEX or other alternatives
    • Running cold water for 30-60 seconds before using for consumption

Environmental Impact

While copper is toxic to humans at high concentrations, it’s even more toxic to aquatic life, particularly:

  • Fish
  • Invertebrates
  • Algae (at very low concentrations)

This makes copper pollution in natural waterways especially concerning from an ecological perspective.

The unique aspect of copper contamination is that it’s often introduced after water leaves treatment facilities, making point-of-use testing and treatment particularly important for this contaminant.

Mercury

Mercury and Water Contamination

Mercury contamination in water is a significant environmental and public health concern.

Sources of Mercury Contamination

Mercury enters water systems through both natural and human-caused pathways:

  • Industrial activities: Coal-fired power plants, mining operations (especially gold mining), and certain manufacturing processes
  • Medical and electronic waste: Improper disposal of products containing mercury
  • Natural sources: Volcanic activity, weathering of mercury-containing rocks
  • Historical pollution: Legacy contamination from past industrial activities
  • Artisanal gold mining: A major source globally, particularly in developing countries

Chemical Forms and Behavior

Mercury exists in water in different forms:

  • Elemental mercury: Metallic form that can evaporate and travel through air
  • Inorganic mercury compounds: Various salts and minerals
  • Methylmercury: The most dangerous form, created when microorganisms in water convert inorganic mercury to organic mercury

The transformation to methylmercury is particularly concerning because:

  • It bioaccumulates in aquatic food chains
  • It’s highly toxic to humans and wildlife
  • It can cross the blood-brain barrier and placental barrier

Health Effects

Mercury exposure from contaminated water and fish can cause:

  • Neurological damage and developmental issues
  • Kidney damage
  • Impaired cognitive function
  • Cardiovascular problems
  • Reproductive issues
  • In severe cases, paralysis, coma, and death
  • Developing fetuses and young children are particularly vulnerable.

Detection and Monitoring

Water systems are monitored for mercury using:

  • Specialized laboratory testing
  • Continuous monitoring systems in high-risk areas
  • Fish tissue sampling programs
  • Sediment analysis

Methods to address mercury contamination include:

  • Chemical precipitation and coagulation
  • Adsorption using activated carbon
  • Membrane filtration
  • Bioremediation approaches
  • Phytoremediation (using plants to extract contaminants)

Regulations and Standards

Many regulatory bodies have established limits for mercury in drinking water:

  • The WHO guideline value is 0.006 mg/L (6 ppb)
  • The US EPA maximum contaminant level is 0.002 mg/L (2 ppb)

Phosphorus

Phosphorus and Water Contamination

Phosphorus contamination in water is a major environmental concern with significant ecological impacts. Here’s a comprehensive overview:

Sources of Phosphorus Contamination

Phosphorus enters water systems through several pathways:

  • Agricultural runoff: Fertilizers, manure from livestock operations
  • Urban/suburban runoff: Lawn fertilizers, pet waste, detergents
  • Industrial discharges: Food processing, manufacturing facilities
  • Municipal wastewater: Human waste and phosphate-containing products
  • Erosion: Natural weathering of phosphorus-containing rocks and soils

Environmental Impact

Excess phosphorus in water bodies causes:

  • Eutrophication: Accelerated growth of algae and aquatic plants
  • Harmful algal blooms (HABs): Toxic cyanobacteria that harm wildlife and humans
  • Oxygen depletion: As algae die and decompose, they consume oxygen
  • Dead zones: Areas where oxygen levels are too low to support aquatic life
  • Biodiversity loss: Reduction in fish and other aquatic species

Chemical Behavior

Phosphorus exists in water in different forms:

  • Orthophosphate: The most bioavailable form that plants can use directly
  • Polyphosphates: Chains of phosphate molecules
  • Organic phosphorus: Bound to organic matter
  • Particulate phosphorus: Attached to soil particles

Unlike many contaminants, phosphorus typically doesn’t directly harm human health at levels found in water systems.

Detection and Monitoring

Water is monitored for phosphorus through:

  • Regular water quality testing in lakes, rivers, and streams
  • Satellite monitoring of algal blooms
  • Continuous monitoring systems in critical watersheds
  • Sediment analysis

Remediation and Management

Methods to address phosphorus contamination include:

  • Prevention strategies:
    • Precision agriculture and nutrient management
    • Buffer zones along waterways
    • Improved wastewater treatment
    • Stormwater management practices
  • In-water treatments:
    • Aluminum or iron salts to bind phosphorus
    • Aeration systems
    • Dredging phosphorus-rich sediments
    • Phosphorus-binding materials

Fluoride

Fluoride as a Water Contaminant

Fluoride in water presents a unique case as it can be both beneficial and harmful depending on concentration levels. Here’s a comprehensive overview:

Sources of Fluoride in Water

Fluoride enters water systems through various pathways:

  • Natural geological sources: Weathering of fluoride-containing minerals (fluorite, apatite)
  • Industrial processes: Aluminum production, phosphate fertilizer manufacturing, semiconductor production
  • Intentional addition: Water fluoridation for dental health benefits
  • Coal burning: Releases fluoride compounds that can enter water through air deposition
  • Mining activities: Especially phosphate mining

Health Effects

The health impacts of fluoride vary significantly with concentration:

  • Beneficial effects (0.7-1.2 mg/L):
    • Strengthens tooth enamel
    • Reduces dental caries (cavities)
    • Supports bone development
  • Harmful effects (above 1.5-4 mg/L):
    • Dental fluorosis: Discoloration and pitting of teeth
    • Skeletal fluorosis: Joint pain, stiffness, and bone structure alterations
    • Potential neurological effects at very high exposures
    • Possible thyroid function impacts

Global Context

Fluoride contamination varies worldwide:

  • Naturally high concentrations in parts of India, China, Africa, and the Middle East
  • The “fluoride belt” stretches from Syria through Jordan, Egypt, Libya, Algeria, Sudan, and Kenya
  • An estimated 200 million people globally are exposed to excessive fluoride

Detection and Monitoring

Fluoride in water is monitored using:

  • Ion-selective electrode methods
  • Colorimetric methods
  • Ion chromatography
  • Regular testing in municipal water systems

Treatment and Remediation

Methods to remove excess fluoride include:

  • Adsorption: Using activated alumina, bone char, or clay
  • Membrane processes: Reverse osmosis, nanofiltration
  • Precipitation methods: Adding calcium and phosphate compounds
  • Ion exchange: Using specially designed resins
  • Electrodialysis: Electric current to separate ions

Regulations and Guidelines

Major regulatory standards include:

  • WHO guideline value: 1.5 mg/L
  • US EPA maximum contaminant level: 4 mg/L (with a secondary standard of 2 mg/L)
  • European Union standard: 1.5 mg/L

Water Fluoridation Controversy

The practice of adding fluoride to water supplies has been controversial:

  • Proponents cite significant dental health benefits, especially for disadvantaged populations
  • Critics raise concerns about personal choice, potential health effects, and appropriate delivery methods
  • Many countries have adopted fluoridation while others have rejected it

Chromium

Chromium is a transition metal that can exist in several oxidation states, but in water, it is primarily found as trivalent chromium (Cr³⁺) and hexavalent chromium (Cr⁶⁺). These two species differ significantly in their chemical behavior, environmental mobility, toxicity, and bioavailability.

Sources of Chromium in Water

Chromium contamination in water can arise from both natural sources and anthropogenic (human-made) activities:

Natural Sources:
  • Weathering of chromium-containing rocks (e.g., chromite, FeCr₂O₄)
  • Volcanic activity
  • Forest fires
Anthropogenic Sources:
  • Electroplating and metal finishing industries
  • Leather tanning (using chromium sulfate)
  • Wood preservation (chromated copper arsenate)
  • Pigment and dye production
  • Mining and ore refining
  • Improper disposal of industrial waste

Chromium Speciation in Water

Trivalent Chromium (Cr³⁺):
  • Typically less soluble and less mobile in the environment.
  • Forms stable complexes with organic matter and precipitates as Cr(OH)₃.
  • Considered an essential micronutrient in trace amounts for humans and animals (involved in glucose metabolism).
  • Low toxicity.
Hexavalent Chromium (Cr⁶⁺):
  • Highly soluble in water as chromate (CrO₄²⁻), dichromate (Cr₂O₇²⁻), or hydrogen chromate (HCrO₄⁻), depending on pH.
  • Extremely toxic, carcinogenic, and mutagenic.
  • Not essential to human health.
  • High mobility in aqueous environments due to its solubility and weak adsorption to soils and sediments.

Environmental Chemistry and Behavior

Redox Transformations:
  • Chromium speciation is highly dependent on redox conditions and pH
  • Under oxidizing and alkaline conditions: Cr⁶⁺ is stable
  • Under reducing and acidic to neutral conditions: Cr⁶⁺ can be reduced to Cr³⁺
  • Microorganisms and organic matter in sediments can mediate these redox transformations
Mobility:
  • Cr⁶⁺ is more mobile and can leach into groundwater
  • Cr³⁺ tends to adsorb to soil particles or form insoluble hydroxides

Toxicology

Hexavalent Chromium (Cr⁶⁺):
  • Carcinogenic via inhalation and ingestion (classified as Group 1 by IARC)
  • Causes oxidative stress, DNA damage, and apoptosis
  • Acute exposure: Nausea, vomiting, diarrhea, and abdominal pain
  • Chronic exposure: Kidney and liver damage, skin ulcers, and increased risk of cancer (especially stomach and lung)
Trivalent Chromium (Cr³⁺):
  • Low toxicity due to poor absorption
  • Acts as a dietary trace element, though its essentiality is debated

Regulatory Standards

World Health Organization (WHO):
  • Maximum allowable concentration of total chromium in drinking water: 0.05 mg/L (50 µg/L)
U.S. Environmental Protection Agency (EPA):
  • Maximum contaminant level (MCL) for total chromium (includes both Cr³⁺ and Cr⁶⁺): 0.1 mg/L (100 µg/L)
  • No separate federal MCL for Cr⁶⁺, though some states (e.g., California) have proposed stricter limits

Analytical Detection Methods

  • ICP-MS (Inductively Coupled Plasma Mass Spectrometry) – highly sensitive for total chromium
  • AAS (Atomic Absorption Spectroscopy) – for specific speciation with pre-treatment
  • Ion Chromatography (IC) with UV detection – for Cr⁶⁺
  • Colorimetric methods (e.g., diphenylcarbazide method for Cr⁶⁺)

Remediation and Treatment Technologies

For Hexavalent Chromium:
  • Chemical Reduction: Cr⁶⁺ → Cr³⁺ using reducing agents (e.g., ferrous sulfate, sulfur dioxide, sodium metabisulfite), followed by precipitation
  • Ion Exchange: Removes chromate ions using anion-exchange resins
  • Adsorption: Activated carbon, iron oxides, or bioadsorbents like chitosan and modified clays
  • Reverse Osmosis: Effective but energy-intensive
  • Bioremediation: Certain bacteria (e.g., Pseudomonas, Bacillus) can reduce Cr⁶⁺ to Cr³⁺

Cyanuric Acid

Cyanuric acid (CYA), also known as 1,3,5-triazine-2,4,6-triol, is an organic compound commonly associated with swimming pool chemistry, but it can also appear as a water contaminant under certain environmental and industrial conditions.

Chemical Structure and Properties

  • Molecular Formula: C₃H₃N₃O₃
  • Molecular Weight: 129.07 g/mol
  • Structure: A symmetrical triazine ring substituted with three hydroxyl groups.

Physical Properties:

  • White, odorless solid
  • Melting point: ~330°C (decomposes)
  • Slightly soluble in cold water (more soluble in hot water)
  • pKa values: ~6.9, 11.4, and 13.5 – indicates weakly acidic behavior

Sources of Cyanuric Acid in Water

Anthropogenic Sources:
  • Swimming pools: Used as a chlorine stabilizer (prevents UV degradation of free chlorine)
  • Disinfectants: Present in chlorinated isocyanurates (e.g., trichloroisocyanuric acid, dichloroisocyanuric acid)
  • Industrial effluents: From plastic and resin manufacturing
  • Agriculture: Degradation product of herbicides (e.g., atrazine, simazine)
  • Fire retardants and bleach alternatives: Decomposition products can include CYA
Natural Sources:
  • Cyanuric acid is not naturally occurring in significant concentrations in the environment but may arise through biodegradation of man-made nitrogen-containing organics

Environmental Fate and Behavior

Solubility and Mobility:
  • Cyanuric acid is moderately soluble in water but forms strong hydrogen bonds, leading to low volatility
  • It is relatively stable in aquatic environments due to the robustness of the triazine ring
  • Not strongly adsorbed to soil or sediment, so it has potential for leaching into groundwater
Persistence:
  • Biodegradation occurs, but slowly
  • Certain bacteria (e.g., Pseudomonas spp., Arthrobacter spp.) can degrade CYA using cyanuric acid hydrolase to produce ammonia and carbon dioxide

Toxicology and Health Impacts

Toxicity Profile:
  • Low acute toxicity in mammals (oral LD₅₀ in rats: >5000 mg/kg)
  • Not classified as carcinogenic, mutagenic, or teratogenic
  • Can cause gastrointestinal irritation at high doses
  • In combination with melamine, CYA can form insoluble crystals that may precipitate in kidneys, leading to renal failure – this interaction was implicated in the 2007 pet food contamination incident
Ecotoxicology:
  • Generally low toxicity to aquatic organisms, but chronic exposure data is limited
  • Synergistic effects with chlorine degradation products may pose additional risks

Detection and Analysis

Analytical Methods:
  • Spectrophotometry (e.g., Melamine-CYA complexation colorimetric assays)
  • High-performance liquid chromatography (HPLC) with UV or MS detection
  • Ion chromatography
  • Gas chromatography-mass spectrometry (GC-MS) after derivatization

Regulatory Guidelines and Standards

  • U.S. EPA: No federal drinking water Maximum Contaminant Level (MCL) established
  • WHO: No guideline values for CYA in drinking water
  • Swimming Pool Guidelines:
    • Recommended range: 30–50 mg/L
    • Upper limit: ~100 ppm – higher concentrations reduce chlorine effectiveness
  • Cyanuric acid in public water supplies is not generally regulated unless introduced through unusual sources

Environmental and Public Health Concerns

Swimming Pools and Recreational Water:
  • Excess CYA levels can bind free chlorine, reducing disinfection power and allowing microbial survival.
  • Can lead to “chlorine lock”, where chlorine is present but not bioavailable.
Industrial Spills or Improper Disposal:
  • Contaminated wastewater can introduce CYA into local surface or groundwater sources
  • Long environmental persistence and potential degradation into nitrogen-rich byproducts can impact nitrogen cycling and eutrophication in aquatic systems
Interaction with Other Contaminants:
  • In combination with melamine, it poses a risk of nephrotoxicity through the formation of insoluble complexes
  • Also relevant in wastewater reuse and greywater systems where breakdown products may accumulate

Treatment and Removal

Conventional Methods:
  • Not effectively removed by standard drinking water treatment (e.g., coagulation, sedimentation, filtration)
  • Activated carbon: Limited effectiveness
Advanced Treatment:
  • Advanced oxidation processes (AOPs): Some degradation via ozone or UV/H₂O₂
  • Biological treatment:
    • Bioreactors with cyanuric acid-degrading bacteria show promise
    • Natural attenuation in soils over time
Pool Water Treatment:
  • Partial draining and dilution is the most common method for reducing high CYA concentrations in swimming pools
  • Specialized enzymatic additives containing CYA hydrolase are also available

Lead

Lead (Pb) is a heavy metal and a well-known toxic water contaminant. It poses significant risks to human health, especially in children, and persists in the environment without degradation. Lead contamination in water is primarily due to corrosion of plumbing systems and industrial pollution.

Chemical and Physical Properties

  • Atomic Number: 82
  • Atomic Weight: 207.2 g/mol
  • Oxidation States: +2 (Pb²⁺, dominant in water), +4
  • Solubility: Poorly soluble in water as metallic lead, but Pb²⁺ ions and lead salts are soluble to varying degrees
  • pH Sensitivity: Lead solubility increases in acidic and soft (low mineral content) water

Sources of Lead in Water

Anthropogenic Sources:
  • Lead pipes and plumbing (primary source in developed countries)
    • Lead service lines (LSLs)
    • Lead solder in copper pipes
    • Brass or bronze fixtures containing lead
  • Industrial discharge
    • Battery manufacturing
    • Mining and smelting
    • Paint and pigment production
    • Ceramics and glass industries
  • Atmospheric deposition from leaded gasoline (historically), waste incineration, and mining activities
  • Contaminated soil runoff
Natural Sources:
  • Weathering of galena (PbS) and other lead-containing minerals, though less significant than anthropogenic sources

Chemistry of Lead in Water

Speciation:

In aqueous environments, lead primarily exists as:

  • Pb²⁺ (free ion, soluble, highly bioavailable)
  • Complexes with inorganic ligands:
    • Carbonates (e.g., PbCO₃, Pb(CO₃)₂²⁻)
    • Hydroxides (e.g., Pb(OH)₂, amphoteric behavior)
    • Chlorides, nitrates, sulfates
  • Organic complexes with humic and fulvic acids in natural waters
Solubility and Mobility:
  • Lead solubility is influenced by pH, alkalinity, redox potential, and presence of complexing agents
  • Low pH and soft water enhance lead dissolution
  • In high pH environments, lead can precipitate as Pb(OH)₂ or PbCO₃

Toxicological Profile

Human Health Effects:
  • No safe level of lead exposure, especially for children
  • Lead mimics calcium and accumulates in bones, teeth, and soft tissues
Acute Exposure:
  • Abdominal pain, vomiting, constipation, fatigue, encephalopathy (at high doses)
Chronic Exposure:
  • Neurotoxicity: Lowered IQ, attention deficits, behavioral problems (especially in children)
  • Nephrotoxicity: Kidney damage
  • Cardiovascular effects: Hypertension, arterial stiffness
  • Reproductive toxicity: Reduced fertility, miscarriage, preterm birth
  • Anemia: Inhibits enzymes in heme synthesis pathway
Children and Pregnant Women:
  • Most vulnerable populations
  • Lead can cross the placental barrier and affect fetal development
Environmental Effects
  • Toxic to aquatic life even at low concentrations
  • Accumulates in sediments and benthic organisms
  • Bioaccumulation in the food chain
  • Can affect enzyme activity, reproduction, and growth in fish and invertebrates
Regulatory Standards
Organization Maximum Contaminant Level (MCL) for Lead
U.S. EPA 0.015 mg/L (action level, not a health-based MCL)
WHO 0.01 mg/L (10 µg/L)
EU 0.01 mg/L

The U.S. EPA’s Lead and Copper Rule (LCR) requires action if more than 10% of tap water samples exceed 15 µg/L.

Detection and Analytical Methods

  • Inductively Coupled Plasma Mass Spectrometry (ICP-MS) – highly sensitive
  • Graphite Furnace Atomic Absorption Spectrometry (GFAAS) – widely used
  • Anodic Stripping Voltammetry (ASV) – field-portable, sensitive
  • X-ray Fluorescence (XRF) – for solids or rapid screening

Water Treatment and Remediation

Corrosion Control:
  • Orthophosphate addition – forms insoluble lead phosphate scale inside pipes
  • pH/alkalinity adjustment – reduces lead solubility
Point-of-Use (POU) Systems:
  • Activated carbon filters – limited effectiveness
  • Reverse osmosis (RO) – effective for dissolved lead
  • Ion exchange resins – selective for Pb²⁺
Source Replacement:
  • Lead service line replacement is the only permanent solution
Environmental Remediation:
  • Sediment dredging in contaminated water bodies
  • Soil stabilization using phosphate amendments or encapsulation

Summary of Lead Behavior in Water

Property Characteristics
Mobility Moderate; increases in acidic, soft water
Toxicity High, especially for children
Persistence Does not degrade; accumulates in environment
Bioavailability High in ionic form
Treatment Difficulty Challenging; requires multiple approaches

Radon

Overview

Radon (Rn-222) is a radioactive noble gas formed from the radioactive decay of radium-226, itself a decay product of uranium-238. It is colorless, odorless, and chemically inert, but radioactively active and potentially hazardous when inhaled or ingested.

Occurrence in Water

  • Radon can dissolve into groundwater as it moves through uranium- and radium-rich rocks, particularly granite, shale, and phosphate-bearing formations.
  • More common in private wells tapping deep aquifers; not usually present in surface waters due to volatilization.

Health Effects

  • Primary risk: Inhalation of radon gas released from water during activities like showering, cooking, and laundry.
  • Radon decays to short-lived radioactive progeny (e.g., polonium-218, polonium-214), which emit alpha particles that damage lung tissue.
  • Associated with lung cancer – second leading cause after smoking.
  • Ingestion risk: Less significant, but internal organ exposure (e.g., stomach) is still a concern.

Regulation and Guidelines

Agency Recommended Limit
U.S. EPA (proposed) 300–4,000 pCi/L (action levels)
WHO No formal guideline, but risk-based evaluation

Detection and Treatment

  • Detection: Liquid scintillation counting, gamma spectroscopy
  • Treatment:
    • Aeration systems (effective at removing >99%)
    • Activated Carbon (GAC) filters (less preferred due to radioactive buildup in media)

Radium

Overview

Radium (Ra) is a naturally occurring radioactive metal in Group 2 of the periodic table. The most common isotopes in water are Ra-226 and Ra-228.

Occurrence in Water

  • Found in groundwater due to dissolution from uranium and thorium ores.
  • High concentrations in aquifers rich in granite, phosphate rocks, or shale.
  • Tends to adsorb weakly to sediments, making it mobile in water.

Health Effects

  • Radiological hazard: Emits alpha, beta, and gamma radiation.
  • Mimics calcium: Incorporated into bones, leading to bone cancer, leukemia, and other disorders.
  • Long-term ingestion increases risk of skeletal damage and hematological malignancies.

Regulation and Guidelines

Agency MCL (Maximum Contaminant Level)
U.S. EPA 5 pCi/L (combined Ra-226 and Ra-228)
WHO 1 Bq/L (27 pCi/L) for Ra-226

Detection and Treatment

  • Detection: Alpha spectrometry, gamma spectroscopy, liquid scintillation counting
  • Treatment:
    • Ion exchange resins
    • Lime softening
    • Reverse osmosis
    • Co-precipitation with barium sulfate

Hydrogen Sulfide

Overview

Hydrogen sulfide (H₂S) is a colorless, toxic, flammable gas with a characteristic “rotten egg” odor. It forms naturally through anaerobic bacterial activity, particularly sulfate-reducing bacteria (SRB) that convert sulfates to H₂S.

Occurrence in Water

  • Common in anaerobic groundwater (e.g., deep wells, confined aquifers)
  • Produced in swamps, sewers, oil fields, and geothermal springs
  • May be released from decaying organic matter or metal sulfide minerals

Health Effects

  • At low concentrations (e.g., <1 ppm in water), mainly a nuisance due to odor and taste.
  • At higher concentrations (inhalation), H₂S can:
    • Irritate eyes and respiratory tract
    • Suppress cellular respiration
    • Cause asphyxiation at extreme levels
  • Can corrode pipes and plumbing fixtures

Regulation and Guidelines

  • No specific MCL by the U.S. EPA (considered a secondary contaminant for aesthetics)
  • WHO recommends that water with >0.05 mg/L of H₂S be considered unacceptable for drinking

Detection and Treatment

  • Detection: Odor threshold (~0.0005 ppm in air), sulfide ion-selective electrodes, colorimetric kits
  • Treatment:
  • Aeration (oxidizes H₂S to elemental sulfur or sulfate)
  • Activated carbon filtration
  • Chlorination followed by filtration (H₂S → sulfur or sulfate)
  • Oxidizing agents: Hydrogen peroxide, potassium permanganate

Uranium

Overview

Uranium (U) is a naturally radioactive heavy metal, found in soil, rocks, and groundwater. Its most common oxidation state in water is Uranium(VI) as the uranyl ion (UO₂²⁺). Uranium contamination is both a chemical and radiological hazard.

Occurrence in Water

  • Naturally present in areas with granite, shale, and phosphate rocks
  • Released from mining, uranium milling, nuclear fuel processing
  • Can also enter water from fertilizers and coal combustion waste

Health Effects

  • Chemical toxicity: Primary concern is damage to the kidneys (nephrotoxicity) due to heavy metal properties
  • Radiological risk: Alpha radiation from uranium isotopes (e.g., U-238, U-234), but less significant than chemical effects
  • Long-term ingestion can lead to renal tubular damage

Regulation and Guidelines

Agency MCL
U.S. EPA 30 µg/L (0.03 mg/L)
WHO 30 µg/L

Detection and Treatment

  • Detection: ICP-MS, laser fluorescence spectroscopy
  • Treatment:
    • Anion exchange
    • Reverse osmosis
    • Coagulation/filtration
    • Adsorption on iron oxides or activated alumina

Nitrite

Overview

Nitrite (NO₂⁻) is an intermediate in the nitrogen cycle, typically formed by microbial oxidation of ammonia and reduction of nitrate. It is highly reactive and toxic in water.

Occurrence in Water

  • Formed during nitrification and denitrification
  • Found in:
  • Septic system leakage
  • Agricultural runoff
  • Poorly aerated waters
  • Chloraminated drinking water systems (incomplete disinfection)

Health Effects

  • Reacts with hemoglobin to form methemoglobin, reducing oxygen transport
  • Can cause methemoglobinemia (“blue baby syndrome”) in infants
  • Linked to blood and vascular system disorders

Regulation and Guidelines

Agency MCL
U.S. EPA 1 mg/L as N (≈3.3 mg/L as NO₂⁻)
WHO 0.2 mg/L as NO₂⁻

Detection and Treatment

  • Detection: Spectrophotometry, ion chromatography
  • Treatment:
    • Biological denitrification
    • Ion exchange
    • Reverse osmosis
    • Chemical oxidation (to nitrate)

Nitrate

Overview

Nitrate (NO₃⁻) is a stable, highly soluble anion and a major nutrient in ecosystems, but in excess it is a significant contaminant, especially in drinking water.

Occurrence in Water

  • Common sources:
    • Fertilizer runoff
    • Sewage and septic systems
    • Animal feedlots
    • Decomposing organic matter
  • Can leach into groundwater due to its high solubility and mobility

Health Effects

  • Also causes methemoglobinemia in infants
  • Long-term exposure suspected of links to thyroid dysfunction, diabetes, and potential carcinogenic effects via N-nitroso compound formation

Regulation and Guidelines

Agency MCL
U.S. EPA 10 mg/L as N (≈45 mg/L as NO₃⁻)
WHO 50 mg/L as NO₃⁻

Detection and Treatment

  • Detection: UV spectroscopy, ion chromatography
  • Treatment:
  • Ion exchange
  • Biological denitrification
  • Reverse osmosis
  • Electrodialysis

Sulfite

Overview

Sulfite (SO₃²⁻) is a reduced sulfur oxyanion, often used as a preservative, disinfectant, or oxygen scavenger in industrial water systems. It is rarely found naturally in surface or groundwater.

Occurrence in Water

  • Added during:
    • Food processing
    • Boiler feed water treatment
    • Pulp and paper manufacturing
  • Occasionally formed from microbial sulfur reduction or chemical processes

Health Effects

  • Can cause allergic reactions or asthma attacks in sensitive individuals
  • Toxic at high concentrations: may interfere with cellular respiration
  • Generally not a widespread environmental concern unless industrial misuse occurs

Regulation and Guidelines

  • No EPA MCL; regulated in food more than water
  • WHO has no specific drinking water guideline

Detection and Treatment

  • Detection: Colorimetric assays (e.g., pararosaniline), titration
  • Treatment:
    • Oxidation to sulfate (e.g., with chlorine, oxygen)
    • Aeration
    • Activated carbon filtration

Sulfate

Overview

Sulfate (SO₄²⁻) is a naturally occurring ion formed through oxidation of sulfide minerals and organic sulfur. It is non-volatile, chemically stable, and common in natural waters.

Occurrence in Water

  • Found in:
    • Groundwater from gypsum (CaSO₄) or anhydrite
    • Industrial effluents (mining, tanneries, paper mills)
    • Atmospheric deposition from fossil fuel combustion
  • Not typically hazardous in moderate amounts

Health Effects

  • High concentrations (>500 mg/L) may cause:
    • Laxative effect (especially in non-acclimated individuals)
    • Dehydration
    • Unpleasant taste
  • Not known to be carcinogenic or systemically toxic

Regulation and Guidelines

Agency Secondary Standard (non-enforcable)
U.S. EPA 250 mg/L (aesthetic concern)
WHO 500 mg/L

Detection and Treatment

  • Detection: Gravimetric analysis, ion chromatography
  • Treatment:
    • Reverse osmosis
    • Ion exchange
    • Lime softening (for CaSO4)

Bromine

Overview

Bromine (Br2) is a halogen similar to chlorine but more reactive in some contexts. In water, bromine is typically introduced as a disinfectant or can form disinfection byproducts (DBPs) such as bromate (BrO₃⁻) when reacting with ozone.

Occurrence in Water

  • Naturally present in seawater and brackish groundwater
  • Used in pool disinfection, industrial cooling towers
  • Bromide (Br⁻) is naturally occurring, and ozonation or chlorination can oxidize it to bromate

Health Effects

  • Elemental bromine (Br2) is corrosive and irritating
  • Bromate is a probable human carcinogen (Group 2B, IARC)
  • Chronic exposure may cause:
    • Kidney effects
    • Central nervous system toxicity (at high doses)
    • Carcinogenicity (animal evidence)

Regulation and Guidelines

Agency MCL for Bromate
U.S. EPA 0.010 mg/L (10 µg/L)
WHO 0.010 mg/L

Detection and Treatment

  • Detection: Ion chromatography, UV absorbance
  • Treatment:
    • Minimize bromide in source water
    • Control ozonation conditions
    • Activated carbon, reverse osmosis

Zinc

Overview

Zinc (Zn²⁺) is an essential trace element for humans but can become problematic in water at high concentrations, mostly due to aesthetic concerns (taste, color, corrosion).

Occurrence in Water

  • Natural weathering of zinc ores (e.g., sphalerite – ZnS)
  • Industrial sources: galvanized pipes, brass fittings, mining runoff
  • Present in some corrosion control chemicals

Health Effects

  • Nutritionally essential in small amounts
  • High doses (>3–5 mg/L) can cause:
    • Metallic taste
    • Stomach cramps, nausea, vomiting
  • Low toxicity relative to other metals

Regulation and Guidelines

Agency Secondary Standard (non-enforcable)
U.S. EPA 5.0 mg/L
WHO 3.0 mg/L

Detection and Treatment

  • Detection: Atomic absorption spectroscopy (AAS), ICP-MS
  • Treatment:
    • Ion exchange
    • Reverse osmosis
    • Lime softening

Sodium Chloride (NaCl)

Overview

Sodium chloride (NaCl) is common table salt. While not toxic at low levels, elevated concentrations in water can lead to taste, corrosion, and health issues in specific populations.

Occurrence in Water

  • Natural mineral deposits, rock salt (halite)
  • Road de-icing runoff
  • Water softeners
  • Seawater intrusion into groundwater

Health Effects

  • High sodium can contribute to hypertension in sensitive individuals
  • High chloride causes:
    • Salty taste
    • Corrosion of plumbing and appliances

Regulation and Guidelines

Agency Recommend Levels (non-enforceable)
U.S. EPA 250 mg/L (chloride)
WHO No health-based limit; <200 mg/L (aesthetic)

Detection and Treatment

  • Detection: Ion chromatography, conductivity
  • Treatment:
    • Reverse osmosis
    • Electrodialysis
    • Distillation

Manganese

Overview

Manganese (Mn) is a naturally occurring metal in soil and rocks. While essential in trace amounts, excess manganese in drinking water is a neurotoxicant and can cause aesthetic problems.

Occurrence in Water

  • Present in groundwater, especially under reducing conditions
  • Common in deep wells, mining regions, or iron-rich aquifers

Health Effects

  • Excess intake may cause:
    • Neurological effects (especially in infants and children)
    • Parkinsonian symptoms with chronic exposure
  • Stains laundry, plumbing, and water fixtures
  • Can promote biofilm growth in pipes

Regulation and Guidelines

Agency MCL / Secondary Standard
U.S. EPA 0.05 mg/L (aesthetic); Health Advisory: 0.3 mg/L
WHO 0.1 mg/L

Detection and Treatment

  • Detection: Colorimetric methods, AAS, ICP-OES
  • Treatment:
  • Oxidation–filtration (e.g., chlorine, permanganate)
  • Greensand filtration
  • Reverse osmosis

Aluminum

Overview

Aluminum (Al³⁺) is the most abundant metal in the Earth’s crust. It is used in water treatment as a coagulant (aluminum sulfate – alum). While not highly toxic, it is a concern for neurological health and aesthetic quality.

Occurrence in Water

  • Alum-treated water supplies
  • Leaching from acidic soils or bauxite-rich formations
  • Industrial discharge

Health Effects

  • High levels (>0.2 mg/L) linked to:
    • Possible neurological issues (suspected link to Alzheimer’s, though evidence is inconclusive)
    • Bone and kidney damage at extremely high exposure
  • Causes discoloration, turbidity, and metallic taste

Regulation and Guidelines

Agency Guideline (non-enforceable
U.S. EPA 0.05–0.2 mg/L (secondary standard)
WHO 0.2 mg/L (operational)

Detection and Treatment

  • Detection: AAS, ICP-OES, colorimetry
  • Treatment:
    • pH adjustment and filtration
    • Ion exchange
    • Reverse osmosis</li>

Iron

Overview

Iron (Fe) is a common element in Earth’s crust, and it occurs in two oxidation states in water:

  • Ferrous (Fe²⁺): Soluble, colorless
  • Ferric (Fe³⁺): Insoluble, forms rust-colored precipitates

Occurrence in Water

  • Naturally present in groundwater, especially anaerobic aquifers
  • Can also be introduced from corroding iron pipes
  • Promotes biofilm and iron bacteria growth in plumbing

Health Effects

  • Not toxic at typical concentrations
  • High levels cause:
  • Metallic taste
  • Staining of laundry and plumbing
  • Support of bacterial slime formation

Regulation and Guidelines

Agency Guidance Level
U.S. EPA 20 mg/L (health advisory for sensitive populations)
WHO 200 mg/L (aesthetic only)

Detection and Treatment

  • Detection: Colorimetry, AAS, ICP-OES
  • Treatment:
    • Aeration + filtration
    • Oxidizing agents (chlorine, ozone, permanganate)
    • Ion exchange
    • Greensand filters

Sodium

Overview

Sodium (Na⁺) is a naturally occurring element and an essential nutrient but can be a concern in drinking water at elevated levels, especially for individuals with hypertension or sodium-sensitive conditions.

Occurrence in Water

  • Natural sources: Weathering of rocks, saltwater intrusion
  • Human activities:
    • Road salt runoff
    • Water softeners (ion exchange with NaCl)
    • Industrial effluents

Health Effects

  • Generally safe for most people
  • At-risk groups: Those with high blood pressure, kidney disease, or heart conditions
  • May contribute to hypertension if consumed in excess

Regulation and Guidelines

Agency Guidance Level
U.S. EPA 20 mg/L (health advisory for sensitive populations)
WHO 200 mg/L (aesthetic only)

Detection and Treatment

  • Detection: Flame photometry, AAS, ICP-OES
  • Treatment:
  • Reverse osmosis
  • Distillation
  • Electrodialysis

Hardness

Overview

Water hardness refers to the concentration of calcium (Ca²⁺) and magnesium (Mg²⁺) ions. It affects water’s ability to lather with soap and contributes to scale formation in pipes.

Occurrence in Water

  • Results from the dissolution of limestone (CaCO3) and dolomite (CaMg(CO3)2)
  • Common in groundwater and hard rock aquifers

Health Effects

  • Not a health risk
  • May provide beneficial minerals (calcium, magnesium)
  • Aesthetic and operational problems:
    • Soap inefficiency
    • Boiler scaling
    • Skin dryness

Classification

Hardness (mg/L as CaCO3) Classification
0–60/td> Soft
61–120 Moderately hard
121–180 Hard
>180 Very hard

Treatment

  • HydroFLOW
  • Ion exchange (water softeners)
  • Reverse osmosis

Benzene

Overview

Benzene (C6H6) is a volatile organic compound (VOC), known for being a carcinogenic industrial solvent and component of petroleum products.

Occurrence in Water

  • Leaks from underground fuel storage tanks
  • Petroleum refining, chemical plants
  • Cigarette smoke and automobile emissions may contribute to atmospheric deposition

Health Effects

  • Group 1 carcinogen (IARC) – linked to leukemia
  • Other effects:
    • Bone marrow suppression
    • Immune system depression
    • Anemia

Regulation and Guidelines

Agency MCL
U.S. EPA 0.005 mg/L
WHO 0.01 mg/L

Detection and Treatment

  • Detection: GC-MS, purge-and-trap methods
  • Treatment:
  • Activated Carbon
  • Air stripping
  • Reverse osmosis

Toluene

Overview

Toluene (C6H5CH3) is a solvent derived from crude oil, used in the manufacture of paints, thinners, and adhesives.

Occurrence in Water

  • Industrial discharges
  • Fuel spills and underground tank leaks
  • Degradation of petroleum hydrocarbons

Health Effects

  • Short-term: Dizziness, nausea, fatigue
  • Long-term: Liver and kidney damage, neurological effects
  • Not classified as a human carcinogen

Regulation and Guidelines

Agency MCL
U.S. EPA 1.0 mg/L
WHO 0,7 mg/L

Detection and Treatment

  • Detection: GC-MS
  • Treatment:
  • Air stripping
  • Activated carbon
  • Bioremediation

Xylene

Overview

Xylene (C6H4(CH3)2) refers to three isomers (ortho-, meta-, para-) and is used as a solvent in the rubber, paint, and leather industries.

Occurrence in Water

  • Petroleum contamination
  • Industrial discharge
  • Improper disposal of paints and solvents

Health Effects

  • Neurological effects (dizziness, confusion)
  • Liver and kidney damage
  • Not considered a significant carcinogen

Regulation and Guidelines

Agency MCL
U.S. EPA 10 mg/L
WHO 0.5 mg/L

Detection and Treatment

  • Detection: GC-MS
  • Treatment:
    • Air stripping
    • Activated carbon filtration
    • Advanced oxidation

PFAS (Per- and Polyfluoroalkyl Substances)

Overview

PFAS are a group of synthetic chemicals used for their water, grease, and heat resistance. They include PFOA, PFOS, and GenX. Often called “forever chemicals” due to their environmental persistence.

Occurrence in Water

  • Firefighting foams (AFFF)
  • Industrial discharge
  • Landfills
  • Non-stick cookware, textiles, food packaging

Health Effects

  • Linked to:
    • Thyroid disruption
    • Immune suppression
    • Cancer (kidney, testicular)
    • Liver damage
    • Developmental effects in fetuses and children

Regulation and Guidelines

Agency Limit
U.S. EPA (2023 Proposed) 4 ng/L for PFOA and PFOS
WHO 100 ng/L (PFOS), 100 ng/L (PFOA)

Detection and Treatment

  • Detection: LC-MS/MS
  • Treatment:
  • Activated Carbon
  • Anion exchange resins
  • High-pressure nanofiltration or reverse osmosis

Pesticides / Herbicides

Overview

These include a variety of synthetic organic compounds used in agriculture to control weeds, insects, and fungi. Common types: atrazine, glyphosate, 2,4-D, alachlor.

Occurrence in Water

  • Agricultural runoff
  • Leaching from fields to groundwater
  • Improper application or disposal

Health Effects

  • Varies by compound:
    • Hormonal disruption
    • Neurotoxicity
    • Carcinogenicity (e.g., atrazine, alachlor)
    • Reproductive effects

Regulation and Guidelines

Compound EPA MCL
Atrazine 0.003 mg/L
Glyphosate 0.7 mg/L
2,4-D 0.07 mg/L

Detection and Treatment

  • Detection: GC-MS, LC-MS/MS
  • Treatment:
    • Activated carbon
    • Advanced oxidation
    • Membrane filtration

VOCs (Volatile Organic Compounds)

Overview

VOCs are carbon-containing chemicals that easily evaporate into the air. Common VOCs in water include benzene, chloroform, trichloroethylene (TCE), and tetrachloroethylene (PCE)

Occurrence in Water

  • Industrial solvents
  • Gasoline and dry-cleaning operations
  • Leaching from landfills and chemical spills

Health Effects

  • Many are carcinogenic or neurotoxic
  • Long-term exposure linked to:
    • Liver and kidney damage
    • Central nervous system effects
    • Cancer (especially liver and blood cancers)

Regulation and Guidelines

  • Multiple VOCs are regulated individually by the EPA
    • Benzene: 0.005 mg/L
    • TCE: 0.005 mg/L
    • PCE: 0.005 mg/L

Detection and Treatment

  • Detection: Purge-and-trap GC-MS
  • Treatment:
    • Air stripping
    • Activated Carbon
    • Advanced oxidation processes