Lead is a naturally occurring toxic metal found in the Earth’s crust. Its widespread use has resulted in extensive environmental contamination, human exposure and significant public health problems in many parts of the world. Important sources of environmental contamination include mining, smelting, manufacturing and recycling activities, and, in some countries, the continued use of leaded paint and leaded aviation fuel. More than three quarters of global lead consumption is for the manufacture of lead-acid batteries for motor vehicles. Lead is, however, also used in many other products, for example pigments, paints, solder, stained glass, lead crystal glassware, ammunition, ceramic glazes, jewellery, toys and some cosmetics and traditional medicines. Drinking water delivered through lead pipes or pipes joined with lead solder may contain lead. Much of the lead in global commerce is now obtained from recycling. Young children are particularly vulnerable to the toxic effects of lead and can suffer profound and permanent adverse health impacts, particularly on the development of the brain and nervous system. Lead also causes long-term harm in adults, including increased risk of high blood pressure and kidney damage. Exposure of pregnant women to high levels of lead can cause miscarriage, stillbirth, premature birth and low birth weight. Sources and routes of exposurePeople can become exposed to lead through occupational and environmental sources. This mainly results from:
An additional source of exposure is the use of certain types of traditional medicines and cosmetics. High levels of lead have, for example, been reported in certain types of kohl, as well as in some traditional medicines used in countries such as India, Mexico and Viet Nam. Consumers should therefore take care only to buy and use regulated products. Young children are particularly vulnerable to lead poisoning because they absorb 4–5 times as much ingested lead as adults from a given source. Moreover, children’s innate curiosity and their age-appropriate hand-to-mouth behaviour result in their mouthing and swallowing lead-containing or lead-coated objects, such as contaminated soil or dust and flakes from decaying lead-containing paint. This route of exposure is magnified in children with a psychological disorder called pica (persistent and compulsive cravings to eat non-food items), who may pick away at and eat leaded paint from walls, door frames and furniture. Exposure to lead-contaminated soil and dust resulting from battery recycling and mining has caused mass lead poisoning and multiple deaths in young children in Nigeria, Senegal and other countries. Once lead enters the body, it is distributed to organs such as the brain, kidneys, liver and bones. The body stores lead in the teeth and bones, where it accumulates over time. Lead stored in bone may be released into the blood during pregnancy, thus exposing the fetus. Undernourished children are more susceptible to lead because their bodies absorb more lead if other nutrients, such as calcium or iron, are lacking. Children at highest risk are the very young (including the developing fetus) and the economically disadvantaged. Health effects in childrenLead exposure can have serious consequences for the health of children. At high levels of exposure lead attacks the brain and central nervous system, causing coma, convulsions and even death. Children who survive severe lead poisoning may be left with intellectual disability and behavioural disorders. At lower levels of exposure that cause no obvious symptoms, lead is now known to produce a spectrum of injury across multiple body systems. In particular, lead can affect children’s brain development, resulting in reduced intelligence quotient (IQ), behavioural changes such as reduced attention span and increased antisocial behaviour, and reduced educational attainment. Lead exposure also causes anaemia, hypertension, renal impairment, immunotoxicity and toxicity to the reproductive organs. The neurological and behavioural effects of lead are believed to be irreversible. There is no known safe blood lead concentration; even blood lead concentrations as low as 5 µg/dL may be associated with decreased intelligence in children, behavioural difficulties and learning problems. As lead exposure increases, the range and severity of symptoms and effects also increase. Encouragingly, the successful phasing out of leaded gasoline in most countries, together with other lead control measures, has resulted in a significant decline in population-level blood lead concentrations. As of July 2021, leaded fuel for cars and lorries is no longer sold anywhere in the world (1). However, more needs to be done to phase out of lead paint: so far, only 41% of countries have introduced legally binding controls on lead paint (2). Burden of diseaseThe Institute for Health Metrics and Evaluation (IHME) estimated that in 2019, lead exposure accounted for 900 000 deaths and 21.7 million years of healthy life lost (disability-adjusted life years, or DALYs) worldwide due to long-term effects on health. The highest burden was in low- and middle-income countries. IHME also estimated that in 2019, lead exposure accounted for 62.5% of the global burden of developmental intellectual disability whose cause is not obvious, 8.2% of the global burden of hypertensive heart disease, 7.2% of the global burden of the ischaemic heart disease and 5.65% of the global burden of stroke (3). WHO responseWHO has identified lead as one of 10 chemicals of major public health concern needing action by Member States to protect the health of workers, children and women of reproductive age. WHO has made available through its website a range of information on lead, including information for policy-makers, technical guidance and advocacy materials. WHO has also developed guidelines on clinical management of lead exposure and is preparing guidelines on prevention of lead exposure, which will provide policy-makers, public health authorities and health professionals with evidence-based guidance on the measures that they can take to protect the health of children and adults from lead exposure. Since leaded paint is a continuing source of exposure in many countries, WHO has joined with the United Nations Environment Programme to form the Global Alliance to Eliminate Lead Paint. WHO is also a partner in a project funded by the Global Environment Facility that aims to support at least 40 countries in enacting legally binding controls on lead paint (4). The phasing out of lead paint by 2020 is one of the priority actions for governments included in the WHO Road map to enhance health sector engagement in the Strategic Approach to International Chemicals Management towards the 2020 goal and beyond. (1) End of leaded fuel use a “milestone for multilateralism” press release End of leaded fuel use a “milestone for multilateralism” press release; 2021 (2) Global Health Observatory: Regulations and controls on lead paint. Geneva: World Health Organization; 2021(3) Institute for Health Metrics and Evaluation (IHME). GBD Compare. Seattle, WA: IHME, University of Washington; 2019.(4) SAICM GEF Project - Lead in Paint Component
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What refers to the range of plasma levels that are present when a drug is effective without producing toxic effects?
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