While the Earth’s crust naturally contains lead, it does not impact the general population’s health. On the other hand, anthropogenic activities cause high levels of lead contamination. The public health impacts of lead pollution are grave — particularly among children.
The relationship between increased blood lead levels in children and decrements in intelligence quotient (IQ) has been observed following lead exposure even at a level as low as 1 µg/dL. For adults, studies have found a relationship between blood lead level and increased risk of cardiovascular morbidity and mortality even at low levels.
One of the greatest historical sources of lead exposure was the use of tetraethyl lead in petrol at the beginning of the 20th century. It was estimated that resulted in the dispersion of at least 9 million tonnes of lead into the environment.
The United States was the first country to ban leaded petrol in 1975. Shortly after that, the decision to phase-out leaded petrol went global. In the 1980s and 1990s, other high-income countries such as Sweden and Germany also enforced the phase-outs.
All thanks to this decision, the average level of lead in the blood for people up to 74 years in the USA decreased by 78% between 1976 and 1991. Researchers observed similar decreases in other high-income countries.
But developing countries implemented the phase-outs and eliminated leaded petrol from being used in automobiles only by the end of 2005.
Despite this, the average blood lead levels in the general population of low-income and middle-income countries are still substantially higher than that in developed countries. In a new study published in Lancet Planet Health, a team of researchers investigated the leading sources of lead exposure in 49 developing countries.
Bret Ericson from Macquarie University, Sydney, and colleagues found that 632 million children in 34 developing countries were estimated to have a blood lead level exceeding the US Centers for Disease Control’s reference value of 5 µg/dL.
“The contrast between developing countries and high-income countries is stark. In the USA, for example, 2017 CDC National Childhood Blood Lead Surveillance Data showed that less than 2% of children (aged 0–5 years) had blood lead levels exceeding 5 μg/dL,” the researchers observed.
They further analyzed that the four major sources of lead exposure in developing countries are informal lead-acid battery recycling and manufacture, metal mining and processing, electronic waste, and the use of lead as a food adulterant, primarily in spices.
“This finding is troubling, particularly because research continues to show the adverse effects of lead at progressively decreasing amounts of exposure,” they wrote.
To delve deeper into how general populations in developing countries are routinely exposed to high levels of lead, the team of researchers conducted a systemic review of 520 studies that reported blood lead levels among individuals in 49 countries. These studies included 100,34,55 individuals residing in different low-income and middle-income countries. The studies were published between Jan 1, 2010, and Oct 31, 2019.
Studies that comprised at least 30 participants were reviewed for inclusion if they contained blood lead level data from human populations residing in any low-income and middle-income country. Another criterion for selecting prior studies was that the data was collected from 2005 onwards.
The highest number of studies (149) that were included in the analysis were from China. The other countries that had sufficient data on their populations’ blood lead levels were Mexico, India, Bangladesh, Brazil, Egypt, Iran, Nigeria, Pakistan, South Africa, Thailand, Turkey, Ethiopia, Sudan, Sri Lanka, Nepal, Palestine, Russia, Vietnam, and Myanmar, among others.
Children in Palestine and Pakistan had the highest blood lead concentrations at 9·30 µg/dL and 9.27µg/d respectively — almost twice as high as the US Centers for Disease Control’s reference value of 5 µg/dL.
The other countries where children were also exposed to high levels of lead pollution were Cameroon (blood lead level of 8.70 µg/d), Egypt (8.24 µg/d), Senegal (8.22 µg/d), Serbia (7.80 µg/d), and Nigeria (7.67 µg/d).
Of the 1·30 billion children (aged 0–14 years) living in the 34 low-income and middle-income countries with adequate data on background blood lead levels in children, approximately 413 million children (31·7%) of the 1.30 billion were estimated to have a blood lead level above 10 µg/dL.
Whereas adults living in Pakistan and Egypt had the highest concentrations of blood lead level at 11.36 µg/dL and 10.36 µg/dL, respectively.
The team of researchers further wrote that analyzing the published values of blood lead level in developing countries had three important findings:
- There is a paucity of rigorous data on lead exposure in the general populations of low-income and middle-income countries (LMICs). In the 137 countries classified as LMICs by the World Bank, only 44 countries had adequate data on background blood lead levels for adults and even fewer (34 countries) for children
- The figures of children’s blood lead levels might be underestimates of global LMIC exposure because they represent only 34 of 137 LMIC countries
- While lead-based paints used in residential areas are a source of lead exposure in the USA, they do not appear to be a major source of lead exposure in LMICs