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Jetzt kostenlos anmeldenWhat does the term 'heavy metals' mean to you? You might think of headbanging concerts and iconic rock songs. But in a scientific sense, the term heavy metals refers to metallic elements with a high density.
Their high density gives them useful properties in construction and manufacturing, but has been associated with toxicity.
Want to know more about heavy metals, but don't have time to mine through useless information? Take a look at this article to learn about its characteristics, the formation, and more!
Let's begin with a definition.
The term heavy metal refers to a metallic chemical element with a high density that is toxic or poisonous at low concentrations.
Some elements classed as heavy metals are actually metalloids – elements that have properties of both metals and non-metals.
At high concentrations, heavy metals pollute the environment.
Examples of heavy metals include mercury, Lead, and cadmium.
Heavy metals are naturally occurring elements in Earth's crust. Some heavy metals are essential to maintain health and metabolism of the body. Heavy metals enter our bodies through food, water, or air.
Ingesting very high concentrations of heavy metals can Lead to toxicity and associated health problems.
Lead poisoning is estimated to have caused of 30% of global intellectual disability.
Natural phenomena, such as weathering and volcanic eruptions, can contribute to the formation of heavy metal Pollution. Alternatively, heavy metal pollution can result from anthropogenic sources, such as:
Industrial waste
Mining and smelting processes
Agricultural use of metals
Processing plants
Burning fossil fuels
Nuclear power stations
As their name implies, heavy metals are dense elements. Heaviness is suggested to be associated with toxicity.
Other characteristics include:
Lustre: the surface of heavy metals have a gentle sheen.
Ductility: heavy metals can undergo changes in their physical form without breaking.
Malleability: the shape of heavy metals can be easily distorted under compression.
Conductivity: heavy metals can effectively conduct heat and electricity.
In trace amounts, heavy metals have important biochemical and physiological functions in living organisms. Copper and zinc in particular are very useful in the body.
Copper and Zinc
Copper is used alongside iron to form red blood cells. It helps to maintain healthy bones, nerves, and immune function. Copper nutritional deficiencies are associated with high cholesterol and high blood pressure.
Zinc aids the immune system, metabolism function, wound healing, and DNA synthesis. Zinc nutritional deficiencies are associated with lethargy, poor wound healing, and immune problems.
High-protein foods are excellent sources of copper and zinc. Make sure that your diet contains adequate amounts of meat, shellfish, nuts, seeds, and legumes.
Heavy metals are also important due to their tendency to bioaccumulate.
Bioaccumulation is the increase in concentration of a chemical in a biological organism over time.
Chemicals accumulate in living organisms when they are taken up and stored faster than they can be metabolised or excreted.
Bioaccumulation is associated with biomagnification.
Biomagnification is the process by which chemicals are passed from one trophic level to another, thus increasing in concentration.
The bioaccumulation and biomagnification tendencies of toxic heavy metals can cause health issues in living organisms, including humans.
Now, we're going to look at some common heavy metals, their anthropogenic sources, and the health problems that they can cause in humans.
Heavy Metal | Anthropogenic Sources | Health Problems | Complications |
Mercury |
| Symptoms of mercury poisoning are primarily neurological, often impacting development. | Complications include brain damage, kidney damage, and circulatory failure. |
Cadmium |
| Exposure to cadmium causes flu-like symptoms. | Complications include coughing, anaemia, irreversible kidney damage, and an increased risk of cancer. |
Arsenic |
| Symptoms of arsenic poisoning include vomiting, abdominal pain, and diarrhoea. | Complications include pigmentation, skin lesions, and an increased risk of cancer. |
Chromium |
| Chromium poisoning can affect cardiovascular, respiratory, renal, digestive, and neurological systems. | Complications lead to fatal problems in a variety of different organ systems. |
Thallium |
| Exposure to thallium causes fever, delirium, and coma. | Complications have been associated with psychotic behaviour, and issues with skin, bones, and organs. |
Lead |
| Exposure to lead causes symptoms such as pain, anaemia, and organ damage. | Complications are neurological; poisoning at a young age may disrupt cognitive development and lead to intellectual disabilities. |
Copper |
| Symptoms of copper toxicity include stomach pain, fatigue, and nausea. | Complications can lead to organ failure, brain damage, and death. |
Nickel |
| Ingestion of nickel causes nausea, vomiting, and diarrhoea. | Complications include death and an increased risk of cancer. |
Zinc |
| Symptoms of zinc toxicity include nausea, vomiting, and fatigue. | Complications include dyspnoea (laboured breathing) and gastrointestinal problems. |
Heavy metal Pollution is typically dispersed (spread over a wide area) through wind, water, and soil.
Heavy metals are non-biodegradable, so they continue to persist in the environment. Thus, heavy metal pollution requires remediation.
In the UK, heavy metal pollution is studied using a monitoring network, which consists of 15 rural sites around the UK. It measures the deposition and background concentrations of heavy metals, by analysing rainwater and atmospheric particulates. The metal concentrations are combined with meteorological data to calculate deposition, and build deposition maps of the UK.
This monitoring network is used to predict heavy metal mobility, and inform monitoring programmes. The, vulnerable members of the public are identified and informed about the risk of heavy metal pollution.
We've learned that heavy metal pollution is non-biodegradable and can lead to severe health problems if ingested in large amounts. So, it's important to limit heavy metal pollution.
It's a form of bioremediation, suitable for a variety of contaminants, including:
Metals
Explosives
Oil
Phytoremediation is a technique that uses plants to clean up contaminated environments.
Fibre crops are grown in Soils contaminated by heavy metal ions.
Edible crops are not used for this process, for fear that toxic ions may enter the food chain.
As they grow, fibre crops extract the heavy metal ions from the Soils by storing them in their roots, stems, or leaves. They can convert the ions into less harmful chemicals within the plant or root zone, where they are released into the air as gases, or transferred to soil microbes who break them down.
Phytoremediation is a slow, but effective process. However, phytoremediation techniques work best where contaminant levels are low. Otherwise, high concentrations may limit plant growth.
Polymers are widely used to remove heavy metal ions from wastewater. The metal ions adhere to the polymer, which has a high surface area.
Adsorption is the process by which a solid holds molecules of a gas, liquid, or solute as a thin film.
Not to be confused with absorption!
The adsorption process is cheap, highly available, and environmentally friendly. Polymers have a high removal capacity, and cannot be damaged by high concentrations of heavy metal ions.
EcoBond® is a chemical additive that converts heavy metals in soils and sediments to insoluble minerals. Thus, it permanently stabilises the harmful ions, limiting leaching and its associated ecological problems. EcoBond® products are made of hybrid elastimeric bond (HEB) polymers. It works by drawing in moisture, eliminating off-gassing.
The EcoBond® additive can be used from -37ºC to 60ºC, and even underwater!
A common cause of heavy metals in agricultural soil is agrochemicals and inorganic fertilisers. This can be limited by:
Growing plants with lower transfer factors (preventing metals from spreading into edible parts of the crop)
Applying organic soil amendments to decrease metal accumulation
Crop rotation
Planting crops for phytoremediation
I hope that this article has explained heavy metals for you. Remember that they are dense, toxic metals that can cause a variety of health problems. Control strategies for heavy metal pollution include phytoremediation and adsorption using polymers.
1. Nixalite of America Inc., Eco Bond, 2013
2. UK Centre for Ecology & Hydrology, Introduction to Heavy Metal Monitoring, 2022
3. World Health Organization, Lead Poisoning, 2022
Heavy metals are metallic chemical elements with a high density that are toxic or poisonous at low concentrations.
Examples of heavy metals include mercury, cadmium, arsenic, chromium, thallium, lead, copper, nickel, and zinc.
Natural phenomena contribute to the formation of heavy metal pollution. Anthropogenic sources include industry, mining, agriculture, processing plants, and power generation.
Heavy metal ions can be formed by weathering, volcanic eruptions, or anthropogenic sources.
Heavy metals have biochemical and physiological functions in living organisms. However, they can rapidly bioaccumulate, affecting health. The physical properties of heavy metals (e.g. density, ductility, malleability) make them useful.
Flashcards in Heavy Metals45
Start learningWhat is lead?
Lead is a soft post-transitional metal.
What is a major property of post-transitional metals?
Post-transitional metals have lower melting and boiling points than other metals.
When does lead neurotoxicity occur?
Lead neurotoxicity occurs when lead exposure alters normal CNS activity, causing damage.
Define liposoluble.
If a substance is liposoluble, it can dissolve in fats.
Where does lead accumulate in the body?
Lead accumulates in the bones.
Lead cannot be taken up by plants in acidic soils.
False
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