The lowdown on lead

By Carrie Garavan and Frank Houghton*

Concern about lead and its effects on human health is considerable and it is perhaps one of the most studied public health topics of all time. 

Although most, if not all adults are aware of the dangers of lead (Pb) poisoning, it is often in a rather broad and non-specific sense. Frequently there is complacency about this issue which underestimates both the level of exposure to Pb that people may experience, as well as the often unseen and yet extremely negative consequences.

A recent global recall of a significant number of popular children’s toys because of their Pb content and the recent water contamination in Galway has focused attention on this issue and it is opportune to explore this topic in more depth.

Pb is ubiquitous in the environment and is detectable in all phases of the inert environment such as air, water and soil as well as in most biological systems. It is one of man’s mans most valuable commodities and is mined and processed in over sixty countries worldwide with approximately 2 million tonnes per year being produced in Europe.

It has been know since ancient times that exposure to Pb can have serious consequences for health. It has been described as the most important toxic hazard in the development of civilisation. Exposure of human populations to lead toxicity was considered relatively low until the arrival of the industrial revolution of the 1920s and 1930s and large-scale mining.

The occupational threats of working with Pb have long been recognised with certain occupations being at particular risk to Pb exposure. Other non-occupational sources of Pb exposure include Pb dust, batteries, ceramics, and certain hobbies.

Although Pb has been banned from paint and petrol for some years now, it remains a constant in our environment. The main avenues of Pb uptake among humans are via ingestion and inhalation (and rarely by skin exposure).

Given improvements in legislation that have reduced Pb in pollutants, it would be easy to be complacent on this issue. Today, in many parts of the world, Pb toxicity from paint represents a major source of exposure for children.

Children ingest dust and soil contaminated with Pb from paint which flakes or chalks as it ages or is disturbed during home maintenance or renovation.  Similarly, many older homes may still have Pb pipes, and plumbing in newer homes may include Pb solder.

Pb poisoning is an environmental disease that is the result of human activities. Sub-clinical Pb toxicity is defined by a whole blood concentration greater than or equal to 10 micrograms per decilitre (µg/dL).

Children and adults are susceptible to health effects from Pb exposure, but the exposure pathways and effects are somewhat different. Although many body systems can be severely affected by high chronic and acute Pb exposure, Pb is a hazard mainly not because of the moderate or low exposure but the chronic exposure that can affect the developing nervous system of young children in more elusive and detrimental ways. 

The recent decades have seen a continual reduction in what are deemed ‘safe’ levels of blood lead levels.  Evidence of health impacts at lower levels of exposure continue to emerge in the research literature. However, it is important to note that there is no evidence to date that contradicts the suspicion that there may be no threshold below which Pb does not exert a toxic effect.

Despite the progressive medical and scientific understanding of the effects of Pb, there remain limitations in clarity of diagnosis of Pb toxicity at low exposure levels. Effects are variable and do not have a consistent behavioural signature. The health effects of Pb have been widely studied with the result that more is probably known about Pb health effects than those of any other non-carcinogenic environmental contaminant.

Pb is not distributed homogeneously in the human body and blood Pb concentration reflects only recent exposure. Pb serves no useful purpose in the human body, and its presence in the body can result in toxic effects, regardless of exposure pathway.

Pb toxicity causes haematological, gastrointestinal, and neurological dysfunction in adults and children. Severe or prolonged exposure may also cause chronic kidney disease, high blood pressure, and reproductive impairment.

Less severe exposure to Pb has been implicated in poor pregnancy outcomes, impaired neurobehavioral development, reduced stature in young children, and higher blood pressure in adults.

Children are particularly susceptible to the toxic effects of lead due to increased absorption and increased hand to mouth contact. Pb poisoning is usually asymptomatic with the result that most cases go undiagnosed and untreated.

The public health implications of low Pb exposure in children will continue to provoke widespread concern in many countries worldwide. Considerable progress has been made in many countries in reducing population exposure to environmental Pb largely as a result of regulatory control.

Despite, regulations and mandatory testing, pockets of vulnerability remain in exposure to Pb paintwork in old homes, a significant route of exposure particularly for young children.

Basic precautions against Pb exposure include showering and changing after occupational or hobby exposure thus avoiding bringing contaminated clothing into the home. Clothes exposed to Pb dust should be laundered separately.

Where there is concern about Pb in water (which is a particular problem as when dissolved in water Pb is tasteless, colourless and odourless), only cold water should be used for cooking and drinking and the tap should be let run for 15-30 seconds.

Diets high in calcium and iron also help prevent Pb absorption.  Diets lacking in protein, vitamin C and zinc may also increase blood-lead levels.

Where Pb dust is an issue, cleaning children’s toys regularly, particularly those of young infants is advised. In such environments wet disposable dusting and moping and vacuum cleaning are advised as well as teaching children regular hand-washing.

In Pb dust-polluted environments, particular care is needed with infants to try and avoid pica (eating non-food items, particularly soil or paint chippings), and it is advisable that children play on grass rather than bare soil areas outdoors.

Educating parents and caregivers about the common sources of Pb such as paint, contaminated soil and dust, minimises exposure to Pb. It is important to include discussions on nutrition and the importance of dietary iron in any primary prevention educational programme.

Despite improved protection measures Pb remains a threat in human environments. Recent recalls of children’s toys continue to highlight the need for strict surveillance, communication and action on the issue of PB exposure.

Particular attention must continue to be exercised around the issue of Pb via occupational exposure, individuals with associated hobbies, polluted industrial and extraction sites, and older industrial and residential premises (where Pb pipes and peeling Pb paint may be an issue).

One of the major threats caused by Pb may result from complacency about the issue in an era of tighter environmental controls, and a lack of familiarity with exposure sources and their potential impacts.

*Carrie Garavan is EPA Senior Research
Fellow-Environment and Health,
at the University of Limerick
and Frank Houghton is a
Health Geographer and Lecturer
at Limerick Institute of Technology

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