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Lead: Meaning
What is lead?
Lead is a soft post-transitional metal.
Lead has a bright, silvery appearance with a hint of blue. It tarnishes upon contact with moist air.
What is a post-transitional metal? Well, like most metals, post-transitional elements are malleable, ductile and relatively dense. However, their lower melting and boiling points separate these metals from the rest.
Lead occurs naturally within the Earth's crust, often combining with oxygen and sulfur.
Properties of Lead
Lead's key properties as a metal include:
A low melting point
Workability
Corrosion resistance
Poor electrical conduction
High toxicity
Toxicity Properties
Lead has high toxicity. Even just 5 µg/dL of lead in the bloodstream can cause lead poisoning. Symptoms of lead poisoning include fatigue and pain. In children, it can lead to developmental delays and learning difficulties.
Neurotoxicity
Lead toxicity typically affects the CNS.
CNS refers to the central nervous system, which comprises the brain and spinal cord.
Lead neurotoxicity occurs when lead exposure alters normal CNS activity, causing damage. Symptoms can be immediate or delayed.
Liposolubility
Lead is liposoluble, meaning that it can dissolve in fats. This property allows it to enter organs such as the brain and the liver.
Liposolubility isn't lead's only fat-related trait. High levels of lead in the bloodstream can cause an excess of adipose tissue, leading to obesity. The suspected cause is lead-altering gene methylation, affecting genes related to the body's metabolism.
Methylation is the addition of a methyl group (CH3). Its addition can negatively affect how molecules act in the body.
This symptom can even be passed down to unborn children; maternal lead exposure has been associated with a higher intergenerational risk of obesity.
Bioaccumulation
Lead can build up in the bodies of animals, including humans. Over time, this can lead to lead poisoning. Unlike many pollutants, lead is not subject to biomagnification.
Biomagnification is the increasing concentration of a pollutant along the food chain.
Lead is mostly stored in the bones, which reduces the risk of lead transmission to other animals in the food chain.
Natural Sources of Lead in the Environment
Lead occurs naturally in soils, at low rates of 10 to 50 mg/kg. Lead tends to accumulate in the upper layers of soil, closest to the surface, where it is held very tightly by particles of clay and organic matter.
Small amounts of lead in the soil can be transferred to plants – but not always. Lead availability to plants depends on how tightly it is held by soil particles and its solubility.
In neutral soils (around pH 6.5), the lead is held tightly by the soil, and it has low solubility. It is not easily taken up by plants.
In acidic soils (around pH 5) lead is held less tightly, and is more soluble, so it can be taken up by plants.
If lead is taken up by plants, it has the potential to be passed to any animals (including humans) who eat the plants.
Don't worry, natural levels of lead do not pose any harm. Only soils contaminated with lead from artificial sources can present a risk.
Uses of Lead
Lead has been widely used since Roman times due to its corrosion resistance and workability.
Since discovering its toxicity, lead has been discontinued from a range of products:
Pipes (including solders)
Paint and glazes
Insecticides
Hair dyes
Petrol additive
Radiators
When storing or disposing of waste lead, the lead is kept at a high pH to reduce solubility and toxicity.
However, lead is still used in a few products. Despite its toxicity, it has some unique and useful properties.
Car batteries often contain lead. These batteries perform better at lower temperatures than other kinds of battery. Furthermore, they're a cost-effective method for storing enough energy to start a vehicle.
Lead's high density and ability to absorb vibrations make it an excellent shield against harmful radiation. As a result, lead is used in X-ray machines and nuclear reactors.
High density lead linings are commonly used in the storage of corrosive liquids.
Lead Pollution in the Environment
Because of lead's widespread use for centuries, lead pollution is a significant environmental problem.
Soils can become contaminated with lead pollution from manufacturing processes, mining, burning materials containing lead, or water runoff. Water itself can become contaminated if it travels through a source of lead, such as pipes.
A notable domestic source of lead pollution is paint chips from old lead-based paint. Furthermore, some countries use lead in traditional medicine and cosmetics, such as Kohl.
Kohl is a dark-coloured eye cosmetic, often made by grinding galena (lead sulfide).
Effects of Lead Pollution on the Environment
Once the environment has experienced lead pollution and contamination, it can have a range of negative effects on plants, animals, and humans.
Plants
Excess lead in the soil can cause a number of toxicity symptoms in plants, including stunted growth and chlorosis.
Chlorosis is the loss of a plant's green colouration, generally caused by micronutrient deficiencies.
Lead can inhibit photosynthesis, disrupt water and mineral balances, impact seedling development, and alter the plant's hormones.
At very high lead concentrations of 10000 to 40000 mg/kg, lead can affect the soil community, killing bacteria and fungi. Many of these microorganisms have mutualistic relationships with plants.
A symbiotic relationship is a close ecological relationship between individuals of two different species. In a mutualistic symbiotic relationship, both species benefit.
Mycorrhizal fungi form mutualistic relationships with plants. The fungi increase the root area, helping plants to access essential nutrients and vitamins. In return, plants provide the fungi with carbohydrates.
If lead poisoning disrupts the soil community, it can have severe effects on plant growth and nutrient cycling.
Humans
Lead can enter the human body by consuming contaminated food and water, or inhaling dust or fumes that contain lead. Once in the body, it's stored in the bones and blood, giving rise to a range of unpleasant symptoms. Large doses of lead can cause pain, weakness, headaches, memory loss, anaemia, organ damage, and even death.
Unborn Babies
Lead exposure can cause miscarriage and stillbirths in pregnant women. Alternatively, it can cross the placenta and cause damage to the unborn baby's nervous system.
Children
Children are at significant risk of irreversible long-term effects of lead poisoning. In particular, lead influences brain development and reduces IQ and attention span, whilst increasing antisocial behaviour and risk of psychiatric problems in later life.
It's estimated that 62.5% of unknown development and intellectual disabilities were caused by lead exposure.
Additionally, children are more likely to ingest lead than adults. Young children regularly put objects in their mouth. Eating sweet-tasting lead paint chips is a common cause of lead poisoning in children.
Lead-based paint chips are often eaten by small children, and can easily contaminate soils. Unsplash
1 in 3 children worldwide have significant levels of lead poisoning, causing 1 million deaths annually. Furthermore, the intellectual disabilities it causes has led to an estimated $1 trillion loss of income for low and middle income countries. That's approximately 6% of their GDP. Scientists have also observed a link between lead exposure and violent crime.
The charity Lead Exposure Elimination Project (LEEP) aims to reduce lead poisoning around the globe. 59% of countries have no regulation on lead paint, so LEEP is pushing for regulations to restrict the production, importation, and sales of leaded petrol and paint. The charity focus on targeted research, government advocacy, industry outreach, and follow-up studies.
I hope that this article has explained what lead is and why it poses a risk for you. This highly toxic metal can contaminate the environment, leading to lead poisoning if ingested. Lead poisoning is a particular problem for children, who may experience irreversible health and developmental problems.
Lead - Key takeaways
- Lead is a soft post-transitional metal. Small amounts of lead occur naturally in the soil. It's a corrosion-resistant, workable, soft metal with a low melting point.
- These properties meant that it was used in pipes, paints, and fuels for centuries. Its widespread use has resulted in environmental contamination and pollution.
- Excess lead in the soil can inhibit normal plant function, leading to stunted growth and chlorosis. High concentrations of lead can kill symbiotic microorganisms in the soil, impacting plant growth and nutrient cycling.
- Lead is a highly toxic metal. If ingested, even in tiny amounts, it can cause lead poisoning. The lead molecules can enter organs, affect the CNS, and accumulate in the bones.
- Children are especially at risk for lead poisoning; they are more likely to ingest lead, and it can cause irreversible developmental delays and intellectual disabilities.
1. Dr Lucia Coulter, Medicine, nonprofit entrepreneurship, and lead, Lead Exposure Elimination Project, 2022
2. Guoying Wang, Association Between Maternal Exposure to Lead, Maternal Folate Status, and Intergenerational Risk of Childhood Overweight and Obesity, JAMA Network Open, 2019
3. Honglin Sun, Lead Exposure Induces Weight Gain in Adult Rats, Accompanied by DNA Hypermethylation, PLoS One, 2017
4. K. M. Wade, Lead, PlantProbs, 2019
5. Nuclear-Power, Lead – Melting Point – Boiling Point, 2021
6. Richard Stehouwer, Lead in Residential Soils: Sources, Testing, and Reducing Exposure,
Penn State Extension, 2010
7. Subhendu Datta, Influence of some abiotic environmental factors on acute toxicity of inorganic lead to Cyprinus carpio var Communis (Linn.) and Catla catla (Ham.) in simulated toxic aquatic environment, Toxicological & Environmental Chemistry, 2003
8. World Health Organisation, Lead poisoning, 2021
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Frequently Asked Questions about Lead
What is lead?
Lead is a soft, grey, post-transitional metal.
How to prevent lead pollution in the environment?
Lead pollution in the environment can be prevented by removing and disposing of potential contaminants such as old pipes or lead-based paint.
How does lead get into the environment?
Lead enters the environment by manufacturing processes, mining, burning lead-based materials, or water runoff.
How does lead in water affect the environment?
Lead in water can contaminate soils, affecting plants and soil microbial communities.
What are the uses of lead?
Lead is used in car batteries, diving weight belts, storing corrosive liquids, radiation protection, and some solders.
What are the 5 physical properties of lead?
Lead’s physical properties are a low melting point, workability, corrosion resistance, poor electrical conduction, and high toxicity.
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