Water Pollution

What is mercury pollution?

Mercury is a persistent, bioaccumulative, toxic pollutant.

Mercury Properties

• Neurotoxicity.

• Liposolubility.

• Bioaccumulation.

• Biomagnification

How is mercury released into the environment?

- Disposal of items containing mercury, like batteries, thermometers, etc

- Chemical plants that produce chlorine using mercury electrodes

- Combustion of coal

Types of Chemical forms of Mercury

- Elemental mercury

- Inorganic mercury

- Organic mercury

Example of an Inorganic Mercury compound

Mercury Oxide

Example of an Organic Mercury compound

Methyl Mercury

Liquid (elemental) Mercury

- It is not easily absorbed through the skin or gut

- Vapours may be absorbed in the lungs if they are inhaled

Inorganic Mercury Compounds

- An example would be Mercury Oxide (HgO)

- They are absorbed moderately well in the gut

Organic Mercury Compounds

• Example: Methyl Mercury (CH₃Hg)

• Easily absorbed through the skin, by the gut, and as vapours if inhaled

Why are organic mercury compounds dangerous?

They are liposoluble, so can pass through cell membranes easily, including through the blood-brain barrier into the brain, where the impacts can be more serious.

It can also cross the placenta and harm unborn babies.

Also causes kidney damage.

Why are even low toxicity inorganic mercury compounds still having severe pollution impacts?

1) Relatively low toxicity inorganic mercury compounds enter anaerobic sediments in lakes or the sea

2) They may then be changed into organic compounds (such as methyl mercury) by anaerobic microbes.

3) The mercury then bioaccumulated and biomagnifies along food chains

4) It often reaches concentrations that are much higher than when it was released into the environment.

How to control mercury pollution?

• Replacing mercury thermometers with electronic thermometers

• Using reverse osmosis or activated carbon filters to remove mercury from effluents

• Ion exchange filters

• Disposal at high pH to reduce solubility

What are heavy metals?

Metals with toxic effects on the body, including lead and mercury.

Why are heavy metals dangerous?

Heavy metals inhibit enzyme function, especially the enzymes of the nervous system

What properties of heavy metals causes pollution?

- Liposolubility

- Synergism

- Solubility

Liposolubility of Heavy Metals

It means they can be stored in fat droplets in living cells, so that chronic exposure to small doses may eventually lead to toxic concentrations by bioaccumulation.

Passage along the food chain may lead to biomagnification

Synergism of Heavy Metals

They can cause more serious pollution if they act in conjunction with other pollutants. There is synergism between cadmium and zinc, affecting plant growth parameters and their oxidative stress.

Solubility of Heavy Metals

Heavy metals are more soluble at low pH. Therefore pollution caused by heavy metal wastes can be reduced by increasing the pH to reduce solubility.

2 types of Heavy Metals:

- Lead

- Mercury

Lead Properties

- Neurotoxicity

- Liposolubility

- Bioaccumulation

- Biomagnification

What does lead exposure lead to?

• Acute exposure to large doses may cause severe symptoms including brain damage, paralysis, and eventually death

• Very high doses can kill by causing liver and kidney failure

• These problems are only likely in industrial accidents and are prevented by good working practices, like wearing facemasks, using water sprays, or remote operations

Lead Controls

- Discontinued uses of: paint, petrol additives, lead pipes, solder for water pipes, lead fishing weights

- Waste storage at high pH

Discontinued uses of: solder for water pipes

• Water pipes used to be made of lead for like 4500 years.

• It then lead to lead being dissolved into water, and so people drinking it could suffer from chronic exposure.

• In the UK, most piping was replaced in the 20th century with copper pipes.

• Lead solder has been replaced with solder based on copper.

Discontinued uses of: lead based paint

• When lead based paint got dusty and crackly, it posed a much greater health risk, especially to children, who pick up particles under their fingernails and suck their fingers.

• Lead based paints were phased out in the 80s.

- Discontinued uses of: petrol additives

Anti knock agents (like tetra ethyl lead) were added to petrol to smooth the explosion of combustion and reduce engine wear.

However, lead particulates were released into the atmosphere, creating a public health threat.

Since the 80s, lead has been replaced with other chemicals such as benzene

Waste storage at high pH

Reduces lead solubility

What are the named pesticides?

• Organochlorines

• Organophosphates

• Pyrethroids

• Neonicotinoids

When were organochlorines introduced?

1940s

What are the properties of organochlorines?

• High toxicity

• High persistence

• High liposolubility

• Bioaccumulates and biomagnifies

What are the advantages of organochlorines?

They have high insect toxicity and low vertebrate toxicity.

They were initially used to control pests (like mosquitoes), then were used as an agricultural insecticide.

What are the disadvantages of organochlorine?

• High toxicity to insects led to the deaths of many non target insects (bees and butterflies)

• High persistence & high liposolubility, so less likely to be washed off fields.

• High liposolubility means its can cross the cell membrane. This allows DDT to bioaccumulate and biomagnify up the food chain.

  This produced levels that were toxic to predatory vertebrates at the top of the food chain like herons and otters (basically it killed a bunch of top predators)

Why was the bioaccumulation and biomagnification of organochlorines bad?

It produced levels that were toxic to predatory vertebrates at the top of the food chain (like herons and otters)

Are organochlorines banned?

Yes

What are the properties of organophosphates?

• Low persistence

• Low liposolubility

• High water solubility

• High toxicity

What are the advantages of organophosphates?

The low persistence and liposolubility mean they don’t bioaccumulate.

What are the disadvantages of organophosphates?

• High mammalian toxicity

• They are neurotoxins and inactivate the enzyme acetylcholinesterase so nerve function is damaged. It was used in WW2 as a weapon

Why is high mammalian toxicity of organophosphates bad?

Farmworkers can be at risk of acute exposure to doses, possibly causing death

What does chronic exposure to organophosphates lead to?

ADHD, Alzheimer’s

What are the properties of pyrethroids?

• Low persistence

• Not liposoluble / do not bioaccumulate / biomagnify

• High specificity / high insect toxicity / low mammal toxicity

• Insoluble in water / low mobility

• Not carcinogenic

Why is the low persistence of pyrethroids good?

It means pyrethroids don’t remain in the environment for a long time, as it degrades quickly

What are the properties of neonicotinoids?

• High specificity/ high insect toxicity / lower vertebrate toxicity

• Relatively persistent

• Water soluble

What are the advantages of neonicotinoids?

• High insect toxicity

• Lower vertebrate toxicity as they cannot cross the cell membrane and blood-brain barrier since they aren’t liposoluble

• Neonicotinoids are broken down rapidly in the presence of sunlight and soil microbes.

What are the disadvantages of neonicotinoids?

• Neonicotinoids are neurotoxins and inhibit the action of the neurotransmitter acetylcholine

• Relatively persistent

• Water soluble.

Why is neonicotinoids being water soluble bad?

• They can leach into rivers and cause harms to fish.

• Leaching into water bodies can cause toxicity if consumed.

• Leaching allows the dispersal of lower concentrations

What do neonicotinoids do to bees?

Their use has been linked to the decline of many bee populations.

They are very toxic to bees

Since they have neurotoxic effects, they reduce the bees’ ability to navigate. Also reduces their immunity to disease.

When does neonicotinoid's impact on non targeted species appear to be increased?

By a synergist action with some fungicides that may be present at the same time.

Long term impacts of neonicotinoids

Some research suggests that neonicotinoids may build up in aquifers, which may cause issues in the future.

What is the most widely used pesticide?

Neonicotinoids

What are the named controls of pesticides?

• Restrictions on use

• Use of non-persistent pesticides

• Use of more specific pesticides

• Use of systemic pesticides

• Application timing

Restrictions on use

Some pesticides have been banned, or their use has been restricted where they could cause problems.

Examples of restricted pesticides

Use of organochlorines is banned in most countries (though DDT can be used in some countries for malaria control)

Use of non-persistent pesticides

Non-persistent pesticides will break down rapidly and won’t become concentrated or travel long distances after application

Example of low persistent pesticides

Organophosphates are less persistent than organochlorine

Use of more specific pesticides

Pyrethroid and organochlorine insecticides are both toxic to insects but pyrethroids are less toxic to mammals

Use of systemic pesticides

They are absorbed by the crop and translocated within it.

They do not need to be sprayed onto all surfaces, are not washed off after they have been absorbed, and will protect new growth.

What is the issue with systemic pesticides?

As the systemic pesticides are present within the plant tissue, they may be eaten by humans if they are still present when the crop is eaten.

Application timing

• Spraying on not windy days results in less spray drifting to surrounding habitats.

• Spraying at night or when crops are not in flower will reduce impact on bees

• Newer spraying techniques use smaller droplets to produce a more even coverage which reduces the amount required

The food samples collected were individually wrapped before being sent for analysis of pesticide levels.

Why is this less important for samples containing systemic pesticides than contact pesticides?

Systemic pesticides will be retained within the food

Suggest why pesticide residue levels in samples of a single type of food may show high variability.

Different amounts of pesticides applied because:

• Types of pest may vary

• Seasonal changes. A species life cycle affect abundance, and therefore different application rates are used

• Different application methods

• Number of predators vary

Variation after application because:

• Rainfall

• Time before harvest

• Storage method

Food items are collected and analysed for pesticide residues throughout the year.

Suggest other factors that may be considered when selecting food items for testing to ensure that the pesticide residue levels are representative.

• Large sample size

• Random locations

• Samples from different regions

• Large range of food items tested

• Large range of food from different outlets (suppliers, like supermarkets, wholesalers)

What is acid mine drainage?

Acidic water exiting from a subsurface mine, and it is very detrimental to aquatic ecosystems

Sources

Spoil heaps

What reactions occur in spoil heaps that contribute to acid mine drainage?

Small amounts of sulfide ores and oxygen react in the spaces between waste particles.

What substances are formed from those reactions?

Metal oxides and oxides of sulfur

What do metal oxides and sulfur oxides do?

They dissolve in drainage water, producing sulfuric acid.

What is the term for drainage water containing sulfuric acid from spoil heaps?

Acid mine drainage

Effects

- The acidic solutions that leach out of the spoil heap have low pH

- Acid mine drainage leads to increased solubility and mobilisation of toxic metals

A change in river pH

It moves the pH of the river water outside of the species' range of tolerance

How does a change in river pH affect enzymes in organisms?

It can denature enzymes, preventing them from performing functions like digestion.

What impact does a change in river pH have on soil health?

It reduces soil health, causes nutrient leaching, and kills detritivores and microorganisms.

How does a change in river pH affect species with calcium-based exoskeletons?

It dissolves calcium based exoskeletons, affecting species like freshwater crayfish

How can drainage mine water acidity be controlled?

By passing it through crushed limestone, neutralising the acidity.

What additional benefit does passing drainage water through crushed limestone provide?

It reduces the solubility of many toxic metals.

What happens to metals in mine water after treatment with crushed limestone?

Since their solubility is reduced, the solid metal precipitate deposits can then be filtered out and removed using techniques such as reverse osmosis.

How are wetland plants used in mine water control?

Wetland plants are often used for bioremediation to help treat mine water.

What are organic nutrients?

Carbohydrates, lipids, proteins

Sources

Many processes involving animal and plant products produce liquid effluents. These effluents contain organic nutrients

What kinda processes involving animals and plant products we talkin' 'bout here?

• Sewage works

• Manure disposal

• Paper mills

• Food processing plants

Effects

- Deoxygenation

- Pathogens

Deoxygenation

• Untreated organic nutrients flow into rivers, providing food for microorganisms. Aerobic digestion from these microorganisms deoxygenates the water and may kill aerobic organisms such as fish

• Microorganisms can also cover the river. This prevents light reaching normal water plants and all of photosynthesis is inhibited

Pathogens

Sewage can contain pathogens from infected people

If other people come into contact with these pathogens, either directly or through contaminated food or water, the disease can spread

Diseases spread include cholera, typhoid, and dysentery

Controls

- Pre treatment

- Primary treatment

- Secondary treatment

- Tertiary treatment

- Anaerobic sludge digestion

Why is it important to treat organic effluents?

To prevent deoxygenation of water

Sewage treatment works

• Each sewage treatment works is designed to treat specific effluent it receives to a satisfactory standard

• The fluids can then be discharged without causing unacceptable pollution

• A high standard may be required in more sensitive environments or where it is more urban

Pre treatment

The removal of solid objects, such as paper, plastic

Pre treatment methods:

Screens

Grit traps

Pre treatment methods - Screens

Metal grills or sieves used to trap floating and suspended items such as plastic and paper items. These are then treated by incineration or disposed of in a landfill site

Pre treatment methods - Grit traps

The channel widens out so that the effluent flows more slowly, and the kinetic energy lowers until it’s not enough to carry the grit along, and the grit drops to the bottom.

The grit can later be removed from the tank and then disposed of in a landfill site

Primary treatment

The separation of most organic solids from fluids

Primary treatment methods:

Primary sedimentation

Primary treatment methods - Primary Sedimentation

• The effluent is left to stand in large tanks, where the faecal solids sink to the bottom so that they can be removed and treated separately

• 95% of the organic matter is removed from the fluid effluent

• The risk of deoxygenation in the water body is greatly reduced

Secondary treatment

The digestion and breakdown of the remaining organic matter in the fluids

Secondary treatment methods:

- Aeration tanks

- Secondary Sedimentation

- Filter beds

Secondary treatment methods - Aeration tanks

The remaining organic matter in the fluid effluent is broken down by bacteria

Shortage of oxygen can be a limiting factor as it slows down this aerobic process

To prevent this happening, large amounts of air are mixed in by paddle wheels, or air stones

Secondary treatment methods - Secondary sedimentation

The effluent from the aeration tanks contain suspended bacteria

It is collected in the secondary sedimentation tank, and returned to the aeration tank as activated sludge

The clear effluent is then discharged into a river.

• This isn't great as it could contain some dissolved inorganic nutrients and could cause cultural eutrophication.

Secondary treatment methods - Filter beds (Alternative to aeration tanks)

Rotating arms spray the liquid effluent over gravel.

The surface area is maximised for microbes (bacteria, fungi, algae, invertebrates) that digest organic matter.

Some bacteria denitrify nitrates, reducing eutrophication.

Tertiary treatment

Additional treatment to remove phosphates or bacteria

Tertiary treatment methods:

- Phosphate removal

- Bacterial microfilters

Tertiary treatment methods - Phosphate removal

Phosphates are removed by adding Fe₂(SO₄)₃, forming insoluble FePO₄.

This can be used as an agricultural fertiliser.

Tertiary treatment methods - Bacterial microfilters

Effluent is strained through micro-strainers, and remaining bacteria are killed by UV light or sterilising chemicals like chlorine.