Many living things, including humans, need micro quantities of certain essential minerals for good health. The list includes iron, copper, zinc, manganese, magnesium, calcium, phosphorus, sodium, chloride, potassium, iodine and others. Lead is conspicuously absent. In fact, health authorities around the world have been revising their RDI for lead downwards for decades and in many places, it has reached '0'. In other words, health authorities now believe there is no safe level (intake or exposure) for lead because it only takes minute quantities to cause health problems. Children are particularly susceptible.
Lead is a cumulative toxin. It builds up in the body over time, causing a range of non-specific, not particularly unique symptoms
as it accumulates. More severe symptoms may not appear until the build up approaches acute levels. This is probably why the health problems associated with lead were widely ignored for so long. It was far more expedient to lay the blame elsewhere, with other health disorders that produce similar symptoms, particularly as much of the literature until the 20th century was predominantly circumstantial.
How Lead Works As A Toxin
When lead is ingested, the body mistakes it for calcium. Calcium is essential for 4 main groups of functions:
- Bone growth and density
- Neural communication
- Muscle contractions
- Blood clotting activation
Whilst lead might 'look' like calcium to the body, it obviously isn't calcium and can't carry out the functions assigned to calcium. So when it starts replacing calcium in the body, those functions stop getting done properly, or don't get done at all. The result is a slow, insidious breakdown of vital systems within the body.
- The brain stops receiving and sending messages because there are no longer enough calcium ions to keep its synapses firing.
- The blood-brain barrier may also be compromised, allowing damaging substances to penetrate brain tissue with long-term consequences.
- In young and very young brains, brain development is obstructed because the lead interferes with synapse pruning. Evidence is increasingly showing that very often those young brains never fully recover, leading to a range of intellectual disabilities.
- Nerve cells are destroyed.
- Muscle function is impaired.
- It can cross the placental barrier in pregnant women and damage the foetus, particularly its brain.
Lead doesn't stop there though. It's responsible for a whole host of other issues besides those associated with calcium.
- It contributes to DNA damage.
- It interferes with the body's antioxidant defence mechanisms, causing oxidative stress (a build up of free radicals aka reactive oxygen species (ROS) faster than the body can neutralise them).
- It alters erythrocytic membrane and fatty acid structure, reducing their lifespan and causing a corresponding drop in red blood cell count (ie anaemia).
- It interferes with heme synthesis; heme is the component in haemoglobin (a protein in red blood cells) that binds to oxygen and allows it to be carried around the body. Heme is also found in myoglobin, a similar protein to haemoglobin found in skeletal muscle tissue.
- It damages vessels in the kidney, causing renal problems like gout and hyperuricemia.
- It increases the risk of hypertension and stroke.
- It damages sperm and lowers sperm count, even at low levels.
- It affects the immune system, also even at low levels.
Unfortunately, most of these things happen slowly and often by the time the effects are noticeable, the worst damage is already done.
Normal Or Typical – Just How Much Lead Should We Have In Our Bodies
In many developed countries, the average blood lead level (BLL) has declined sharply since the phase out of leaded fuel and paints, and now sits at or just below 5 µg/dL or 0.24 µmol/L (5 micrograms per decilitre). Up to 10 µg/dL is considered typical, whilst 10 to 25 µg/dL indicates recurrent lead exposure. At 80 µg/dL levels, treatment for lead toxicity may be required and anything over that is probably going to cause some serious health problems, even death, if left untreated. However, the official advice is to seek treatment at any level of toxicity if symptoms appear 1.
Now compare these figures to the 0.01 to 0.02 µg/dL found in ancient bones prior to anthropogenic deposition of lead into the atmosphere. Whilst we can't be certain that these would have been the widespread 'norm' for BLLs in ancient humans per se, it does provide a clue that before we started disturbing previously inert lead ores, our likely typical BLL (and thus our 'norm' as a species) was some 250 to 500 times lower than what is considered a 'safe' BLL today.
Disturbingly, during the decades of leaded petrol a BLL of 80 µg/dL was widely accepted as 'normal' for humans!
It's Not As If We Weren't Warned About Lead Toxicity
The connection between lead and ill health is not a modern medical discovery. There are recorded observations dating back at least to Hippocrates about a range of mysterious illnesses that plagued those who were habitually exposed to lead. In 370 BC he documented stomach problems in a metalworker who was likely working with lead, and suspected that a type of gout was linked to food and wine, although he didn't associate it with lead. The gout subsequently became rife throughout Roman society, particularly amongst the upper classes, courtesy of the enormous amount of lead in their food and wine.
The Romans coined a name for the gout because its symptoms were similar to the character attributes of Saturn, the gloomy, sluggish Roman God of agriculture and civilisation. They called it Saturnine Gout, and today we know this to be a "form of gout in which the causative role of lead can clearly be proven"2. Saturnine Gout was also common amongst the wealthy throughout the Middle Ages. By then it was known to be associated with lead but was considered a bit of a 'badge of success', something you got when you'd made it in life and could indulge in its 'richness'. The industrial and working classes though took a completely different view when it seeped into their lives.
Just over 100 years after Hippocrates noted mysterious illnesses in metal workers and gout in people who drank and ate a lot, a fellow Greek by the name of Nikander of Colophon produced what may be the first description of lead poisoning symptoms when he described lead-caused anaemia and colic.
In 14 BC, Roman architect Marcus Vitruvius Pollio warned in his book De Architecture
using lead pipes for transporting water was not a good idea. He had noticed that many workers who worked regularly with lead suffered from pale complexions and other illnesses. He wrote "the lead receives the current of air, the fumes from it occupy the members of the body, and burning them thereupon, rob the limbs of the virtues of the blood. Therefore, it seems that water should not be brought in lead pipes if we desire it to be wholesome.
" He was ignored.
Pliny the Elder (AD 23/24 – 79), author of Naturalis Historia, although initially a staunch advocate of using lead or lead lined pots to produce wine and grape juice because it tasted better, nevertheless complained when eventually 'genuine, unadulterated wine' was no longer available. He had noted that 'excessive' consumption of 'corrected' wine often caused a type of paralysis of the hands. 'Corrected' means that additives like sapa, a preservative / sweetener made of reduced grape juice that had been boiled down in lead pots, had been added to improve flavour. He also wrote that "red-lead is a deadly poison and should not be used medicinally" and that "lead acetate is a deadly poison". He was ignored.
A contemporary of Pliny's, Pedanius Dioscorides (40 – 90 AD) Greek physician and author of De materia medica
linked lead exposure to delirium, paralysis, swelling and intestinal issues. He noted that "Lead makes the mind give wa
y" and that wine that had been 'corrected' with sapa was "most hurtful to the nerves
." "The drinking of litharge causes oppression of the stomach, belly and intestines, with intense griping pains; ... it suppresses the urine, while the body swells and acquires an unsightly leaden hue.
" He too was ignored.
In fact, historians now believe a large proportion of Roman society likely suffered from lead poisoning. Certainly the upper echelons, with their particular fondness for lead in all its various forms and the financial means to obtain it in large enough quantities, would have been prime candidates for lead toxicity. Julius Caesar and Caesar Augustus for instance were both found wanting when it came to heir producing. Julius only ever had one son, and Augustus had none. Given that low fertility is a known symptom of lead poisoning, it's a plausible explanation for their situation. Other Roman emperors including Claudius, Nero, and Caligula were also famously afflicted with health problems that hindsight tells us were probably the result of lead poisoning. Some authorities have even suggested that it may have contributed to the Empire's eventual downfall, although this is probably stretching things. As the popular saying goes - all good things must come to an end, eventually.
Lead wasn't just a problem for the wealthy in Roman society. There are documented accounts of health disorders amongst the metal working community and those who habitually worked with lead products (builders, plumbers and the like). This indicates lead toxicity was a common issue within these sectors of the Roman population too. It was probably rife amongst the mineworkers who dug the stuff up at the Empire's many lead / silver mines as well, but as most of them were slaves their illnesses and deaths didn't attract a great deal of attention.
The Evidence For The Case Against Lead Accumulates
As the centuries rolled on, reports of wine drinkers with stomach issues and paralysis in mineworkers who were exposed to lead increased. From the vantage of hindsight though, and given how much lead was floating around in society, lead toxicity was undoubtedly causing severe illness and death in all levels of society.
One famous case in point is Beethoven, who reportedly had a range of health problems including digestive and abdominal issues, depression, and irritability. None of the doctors he visited, and there were at least 30 of them from all accounts, could pinpoint a cause or causes, much less offer a cure. Debates about his ill health and subsequent untimely death at 57 are long standing but a 2000 report into his death may have finally settled the matter. It mentions chemical evidence that points the finger squarely at lead poisoning….
And Just Keeps On Accumulating
Noted figures like Benjamin Franklin also chimed in, citing their own personal experience with the health issues associated with lead use – he had been working with lead printing equipment and found his hands developed a tendency to freeze up on him. From his past knowledge of the problems attributed to lead, he knew enough to quit that job before it killed him! Yet, despite this growing body of literature linking the metal to serious and widespread health problems, there remained a general reluctance to do anything about it. As Ben noted in a letter written to a friend in 1786 "You will observe with Concern how long a useful Truth may be known, and exist, before it is generally receiv'd and practis'd on." One wonders what he would have thought had he been able to foretell that it would be nearly 200 years before it was seriously 'practis'd on'.
However, all the lead we'd ever used paled into insignificance in the 20th century!
This was when we lifted our lead use, and pollution, to a whole new level, and it shows in atmospheric lead contamination profiles3. We dusted off a lead compound developed in Europe in the mid 1850's that was so toxic it had never been used for anything in the decades since its development, and added it to a product that most of the world's population would eventually come into contact with. That compound was of course tetraethyl lead, or TEL for short, and the product we created with it was leaded petrol, the lifeblood of the vast majority of motor vehicles that graced the world's highways and byways for over half a century.
The other standout lead-loaded contribution to environmental contamination and lead poisoning was lead paint. Lead made paint more durable and longer lasting so it was slapped on everything from household walls to children's toys and equipment. Within a very short space of time, childhood mental disorders, IQ problems and various other health issues started to escalate. The first documented cases of lead toxicity in children were in 1892 and the source of the lead was ultimately confirmed as lead from house paint in 1904. From there, the evidence snowballed and today it's estimated that some "600,000 new cases of intellectual disability occurs among children every year4" courtesy of exposure to lead paint in their surroundings.
By the end of the 20th century, lead was being phased out of both petrol and lead as new laws came into play requiring that a) motor vehicle manufacturers reduce tailpipe emissions, and b) paint manufacturers reduce or eliminate the lead in their products.
In the case of motor vehicles, the catalytic converters fitted to new vehicles to ensure compliance with new emissions laws couldn't handle leaded fuel. In short, it wrecked them! Oil companies had to come up with an alternative type of additive, and eventually they realised their only option was to replace TEL altogether. Originally, they opted for petroleum-based additives like Methyl Tertiary Butyl Ether (MTBE) and, when that proved to be a problem with water pollution, the BTEX Complex. Subsequent health issues arising from BTEX products forced yet another change and so, 100 years after it was originally used to fuel motor vehicles, ethanol made a triumphant come back. Ah, the irony ……..
Today most of the unleaded fuel sold around the world contains ethanol as the octane booster, commonly in a 10/90 ratio with petroleum. (Officially) about the only type of leaded fuel still available in most countries is Avgas, a leaded fuel designed for piston or spark ignition petrol engine aircraft. Even so, the amount of lead in Avgas has been reduced, with most refineries claiming the bulk of the Avgas they produce contains the bare minimum of TEL required to meet aircraft performance safety standards. Turbine powered aircraft, which includes passenger jets, don't use leaded fuel. The aviation industry globally is working towards eliminating leaded aviation fuels altogether but it's an expensive exercise with some significant hurdles to overcome (many of them involving convoluted red tape). According to some sources 5
, you may still find leaded petrol available in some countries for off-road use ie farm machinery, off-road vehicles, marine engines and racing cars.
Leaded paint went through similar phase out stages, and today in many countries the legislated maximum amount of lead allowed is 0.1% or less. There are also regulations now in some countries about the amount of lead that can be present in dust on floors and window sills. These are designed to reduce the risk of children coming into contact with lead from old leaded paints because "Since the phase-out of leaded petrol, lead paint has been one of the largest sources of exposure to lead in children" 4.
Lead Toxicity And Other Species
Lead poisoning is estimated to kill a million wildfowl a year in Europe and cause sub-lethal poisoning in another ≥3 million.6
Lead poison is also a serious issue for species other than humans and will remain so for a very long time, particularly whilst there is still ongoing environmental lead contamination. In addition to what is already there, other sources of lead contamination continue. Spent lead shot that gets into lakes and river systems for instance is picked up by water birds and water dependent species that forage for food along the bottoms of these systems 7 8. It can also move higher up the food chain as predators eat lead contaminated prey / carcasses. A number of countries have now banned lead ammunition for hunting waterfowl and other water species.
Likewise, lead fishing weights that come off fishing nets and lines pose a significant threat to marine and fresh water species 8. As with lead ammunition, some countries have banned the use of lead in fishing equipment as well.
On land, carcasses of animals and birds that have been killed with lead shot / lead bullets can be eaten by other species, notably birds of prey and other scavengers. If they also consume fragments of lead in the carcass, it can lead to lead poisoning. The California condor for example is a critically endangered bird of prey that lives with ever-present danger of being poisoned in this way. For those that live in the Grand Canyon, lead poisoning is in fact the most common cause of death. For this reason, it is now illegal to use lead ammunition in the condor's native ranges.
Domestic livestock and pets are also susceptible to lead poisoning 9
. If these animals are part of the human food chain ie dairy and meat animals, then the poisoning will get passed along. Just as concerning is the fact that if these animals are able to get access to enough lead to poison them, it's highly likely their owners can too.
Whilst globally governments have done a lot of work to reduce the effects of lead with respect to human health, there is still a lot more work to be done yet around environmental contamination. The biggest issue is not what we're still producing in terms of lead products because that is now far more regulated (lead now has the highest recycling rate of any metal), but what remains in the environment courtesy of ill-advised decisions made a century ago. Granted, lead pollution has been around since we learned how to extract it from ore but the levels were manageable until the 20th century. Lead doesn't disintegrate so what has been pumped into the environment is now out there permanently until or unless some major clean up operations are implemented.
- Understanding the Link Between Lead Toxicity and ADHD
- Saturnine gout - ScienceDirect
- History of Atmospheric Lead Deposition Since 12,370 14C yr BP from a Peat Bog, Jura Mountains, Switzerland
- Lead Contamination
- How Leaded Gas Came to Be and Why We Don't Miss It
- Effects of lead from ammunition on birds and other wildlife: A review and update
- Sanderson, Glen C. and Frank C. Bellrose. 1986. A Review of the Problem of Lead Poisoning in Waterfowl. Illinois Natural History Survey, Champaign, Illinois. Special Publication 4. 34pp.
- The ecotoxicology of lead shot and lead fishing weights
- Metabolism and toxicity of cadmium, mercury, and lead in animals: a review