Sunday the 20th October 2013 marked the beginning of the International Lead Poisoning Prevention Week, an initiative coined by the Global Alliance to Eliminate Lead Paints, the World Health Organization and the United States Environmental Protection Authority. This year's theme is "Lead Free Kids for a Healthy Future", with the focus aimed squarely on the global manufacture and use of lead paint and its impacts on childhood health. This is a timely theme as the debate surrounding industry compensation to replace lead paint in homes still rages in the United States.
Impacts of Childhood Lead Exposure
Lead contamination is particularly concerning for young children. Lead's neurotoxicity impacts parts of the brain responsible for learning and behaviour. Young children are often at the greatest risk of lead exposure due to their exploratory learning habits which include consumption of soil through pica. Lead paint is a major contributor to increased blood lead levels. Some other sources include leaded petrol, atmospheric particulate and soil deposits (often from mining/smelting). Home renovations, resulting in disturbance of lead paint, can increase a child's blood lead level by as much as 17% compared to children in non-renovating households.
Preventing lead exposure at each development stage is critically important for mitigating the burden of disease generated by this heavy metal. Children prenatally exposed to low (<5.0 µg/dL) blood lead concentrations have delayed neurological development at ages 12, 24 and 36 months. Lead is stored in blood, soft tissues, bones and teeth. Lead retained in bones and teeth can slowly leach back into the blood over time. Typically a child's blood lead level will increase significantly during the ages of 18 to 36 months as the child becomes more mobile but has deficient personal hygiene capabilities. As a child develops personal hygiene practices, blood lead levels have a tendency to decrease.
Lead exposure during early childhood has significant impacts on learning and brain development. A study in the United States identified an overall accumulated 6.9 IQ point deficit in children, compared to standard age-based expected outcomes of the Wechsler Intelligence Scale, with blood lead levels in the range of 2.4 to 30.0 µg/dL. The greatest IQ point deficit (3.9 IQ points) was seen among children with 2.4 to 10.0 µg/dL blood lead. A follow up investigation examining the individuals from the Cincinnati Lead Cohort Study showed that those children with lifetime mean blood lead levels of 20.0 µg/dL were likely to have on average a 7.0 IQ point deficit compared to those children with a lifetime mean blood lead level of 10.0 µg/dL.
Children with elevated blood lead concentrations have been shown to engage in greater criminal activity in their later lives. The research shows a strong correlation between increased prenatal and childhood blood lead concentrations and the number of arrests within the Cincinnati area 19 to 24 years after the study population birth. Similar research in Australia, where a 21 year time lag has been placed on data relating to a cohort of children exposed to lead at a young age, shows a strong correlation between lead exposure and criminal activities later in life.
Debate surrounds the 'safe' level of lead exposure for children. Currently Australia has a 10.0 µg/dL investigation threshold for blood lead in humans. Research on the impacts of lead on children's health suggests that the investigation threshold for blood lead should be reduced to <1.0 µg/dL. It is well established that the most significant adverse health impacts occur in children within the lowest exposure thresholds. All of the current research points to the message that there is no safe level of lead in the blood.
Is Focusing on Lead Paint Enough to Reduce the Burden of Disease?
While the attention of the International Lead Poisoning Prevention Week is on lead in paint, we must ask ourselves, given the low levels of exposure which result in detrimental development, if focusing on this one exposure pathway is enough to combat the global burden of disease from lead contamination? Zamfara State in Northern Nigeria, where one of the world's largest lead contamination events is having devastating impacts on childhood mortality rates, with an estimated 734 children having died from lead exposure, is caused by the dust generated during artisanal gold mining practices. In 7 Asian countries (Bangladesh, India, Indonesia, Kazakhstan, Pakistan, Philippines and Thailand) it is predicted that 189,725 children between 0 and 4 years are exposed to lead contamination, from living near hazardous waste sites, sufficient to generate noticeable IQ deficits. Lead acid battery recycling also contributes to the human toll of lead contamination, for in 2008 18 children died from exposure to lead in Thiaroye Sur Mer, Dakar. Finally, the amateur recycling of electronic waste(e-waste) in many parts of Asia is contributing to elevated blood lead levels of workers and their children.
Leaded petrol is often recognised as the largest contributor to lead contamination, other research suggests that the lead acid battery recycling industry and smelting are the largest contributors to global lead contamination. Lead paint is a good place to start but there is much more that needs to be done in order to substantially reduce the burden of disease created by childhood lead exposure.
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