Lead is the chemical element with the atomic number 82 and the symbol Pb, which comes from its name in Latin (plumbum). It is a heavy metal known for its particular characteristics: it is very dense, with a soft structure and melts at low temperatures. The real color of lead is silvery-blue, but this is visible only when cut fresh. It quickly reacts with the air and turns grey. It is considered the heaviest stable element in the periodic table and the radioactive decay of heavier elements ends with three different isotopes of this common metal.
Lead has been known for a very long time because it can be extracted very easily, so it was mined in some parts of Asia since prehistoric times. The most important lead ore, galena, also has a content of silver. As a result, lead was available in large quantities during the Roman period, as a by-product. After the fall of the Roman Empire, lead production significantly decreased until late in the Industrial Revolution.
Lead was widely used for a long time, until the end of the 19th century when its toxic effects were discovered and it was removed from many applications. It is a neurotoxin that breaks the function of some critical enzymes and harms the nervous system. Lead also accumulates in time in bones and tissues and it can’t be eliminated. It is especially dangerous for children because it causes brain damage and personality issues and it can’t be cleansed from their bodies, even if the blood is purified.
Lead is a common element that can be found everywhere and it's part of the soil, water air and most household objects. However, exposure to toxic levels of lead was caused by human activities: the use of lead in the composition of home paint, its presence in gasoline and waste from various industrial processes. It used to be a widespread material used to manufacture common household objects, besides paint, plumbing items and pipes it was also found in ceramics, fuels, batteries, ammunition, cosmetics or solders. All of these objects were hazardous because of the toxic nature of this metal.
Many old industrial sites, for example abandoned smelters, can contaminate the nearby environment with high levels of lead. Lead is normally found in the soil, but only in amounts between 50 and 400 parts per million. However, locations close to former mines or smelting sites have a much higher concentration of lead and the soil can be heavily contaminated.
Lead can reach the air from industrial plants or the exhaust of vehicles. It will eventually fall to the ground and bind to various soil particles, but it can travel long distances in advance. Depending on the soil characteristics, lead can reach the level of the ground water and contaminate it as well.
Various activities that involve lead can cause exposure, not only the actual production of lead items but also recycling, removal or maintenance of old items made from this metal. The industrial sectors with the highest exposure risk are construction, transportation, manufacturing, repair and bulk trading.
The risk is especially high for construction workers who demolish or renovate old buildings where lead-based pigments have been used, since these can easily reach the air. Many other types of work require contact with objects made from lead or its alloys, especially the installation or removal of lead pipelines, maintenance of leaded glass, lead-based soldering or handling the panels used for radiation protection. Many common items also have a content of lead and it's easy for workers to come in contact with it: rechargeable batteries, plumbing parts, soldering materials, old lead bullets, leaded glass, radiators or various brass and bronze alloys that include this metal. Workers don’t have to produce these items; they are exposed by using them in any way, for example during repairs, maintenance or recycling.
Normal people are constantly exposed to the lead found in water, air or food; these amounts are low but can still be dangerous. Old lead-based paint that deteriorates is the main problem for kids who can have increased levels in their blood stream. Under the age of six, even small amounts of lead can cause serious cognitive issues. Lead is also toxic to the fetus, so pregnant women should avoid contact with this metal at all costs. Families of workers can also be exposed to high levels of lead since they can bring it home as dust on their shoes, clothes or other items.
This toxic metal can easily enter the body through ingestion or inhalation. While the amount of lead in the modern environment has decreased significantly, it remains a hazard. Some people have hobbies that use lead, while others inhale toxic fumes at work, in industrial facilities. Lead will first reach the lungs and then enter the blood stream, damaging various other internal organs. Metallic lead can't permeate the skin but it is easy to ingest or smoke it after touching objects or surfaces that have been contaminated. Once it accumulates inside the body, it can cause many serious symptoms like mental disorders, anemia, kidney conditions or digestive problems.
Lead has seen widespread use because of its excellent properties: it has a low melting point and is very ductile, so it is easily shaped or welded. In addition, it protects from both X and gamma rays due to its very high elemental density. Metallic silver and gold are soluble in lead and can be collected using it. However, lead is not good for structural uses because it is very soft and breaks very fast under stress.
This metal is very reactive in contact with air and quickly forms a coating of oxide when cut. This grey layer is actually a mix of the pure metal and lead monoxide, but it was believed for a long time to be Pb2O, or lead suboxide. This layer protects the rest of the metal from corroding further. Coating also explains why lead is able to resist hydrochloric or sulfuric acids, despite reacting with them. It forms a layer of chloride (PbCl2) or sulfate (PbSO4) that is not soluble, protecting the remaining metal from the reaction. Since it has a high chemical resistance, lead is widely use as cover for underwater or buried cables, as a roofing material, or in plumbing. It is also very well suited for recipients or conduits used in the transport of very reactive chemicals.
After lead was eliminated from many products due to its toxicity, it has remained a very important material in the production of batteries. It is also used to manufacture ammunition as well as many alloys such as type metal, pewter or solder. Lead sheets are a common element of heavy machinery, where they are needed as a protective shield in order to reduce vibration and noise. Lead has a high density and absorbs all types of short-wavelength radiation, so it is a very effective screen around nuclear plants and other places with high radiation, such as X-ray equipment or particle accelerators. Recipients for the transport of radioactive waste are also made from lead. The most common types of storage batteries are made from a combination of lead or its oxide and alloys with antimony or calcium.
Before 1900, lead had many additional uses in the United States and was found in ammunition, pipes, water supply lines, burial vault liners, ceramic glazes, leaded glass and crystal, paints and other coating types. After the First World War, the production of motorized vehicles exploded and the demand for lead surged, since it was used in the common batteries required to start engines, which contained lead and acid. The demand for lead also increased because it was a cheap gasoline additive and was required for radiation protection in the new generation of medical equipment.
In the middle of the 1980s, the use of lead in the United States decreased sharply since its toxic effects were recognized and strict environmental regulations demanded its replacement with alternative materials whenever possible. It was largely eliminated from plumbing, gasoline, coatings and soldering. While in the 1960s around one third of the lead produced in the world was used to manufacture lead-acid batteries, by the 2000s batteries remained the main consumers of lead, with around 88 percent of the total. It still has a number of other uses, as sheet lead, ammunition and some oxides needed for decorative glass or ceramic.