Higher blood lead level in pregnant women: What could be the source?

Higher blood lead levels among pregnant women in rural Bangladesh, identified by a recent icddr,b study in collaboration with Stanford University, USA, raise concerns as to what causes the excess levels.

Lead exposure over time results in lead deposit in the bones and it may be released in the blood during pregnancy. Photo: Rabiul Hasan / icddr,b

Surprisingly, rather than evidence of a single source causing the elevated lead levels in pregnant women, the study identified multiple possible sources of lead exposure from the environment and food sources, says Professor Stephen P. Luby, senior author of the study and professor of medicine at Stanford University.

Findings published in Environmental Research analysed blood lead levels (BLL) among 430 pregnant women and found one third of them had elevated BLL greater than 5 micrograms per deciliter (DL) while 6 percent of them had more than 10 micrograms per DL. One sample was found at 29.1 micrograms per DL, which is 6 times greater than threshold noted by the Center for Disease Control and Prevention (CDC).

“Compared to women with low blood lead levels, women with the highest blood lead levels were more likely to be exposed to consuming food from lead-soldered metal food containers (cans), consuming food from agricultural fields where herbicide and pesticides have been used and consuming ground rice,” says Mr Sarker Masud Parvez, co-author of the study and research investigator at icddr,b.

Since women with higher BLL were more likely to have been exposed to possible lead sources in the environment, the researchers examined soil, 382 agrochemical samples including herbicides and pesticides and 127 ground and unground rice samples.  

Of the food and agrochemical samples analysed, seven out of 17 turmeric powder samples had excess lead than the tolerable limit at 2.5 micrograms per gram, designated by Bangladesh Standards and Testing Institution (BSTI). One unpackaged and unbranded sample contained over 265 microgram/gram lead.

Some food may contain excess lead but food is not the only source. Photo: GMB Akash / icddr,b

Elevated BLL in pregnant women is a cause for public health concern. It is a threat for mothers and their developing fetus as well as for the newborn as lead deposits in the mother’s body are released in blood and subsequently into breast milk, according to CDC. Lead exposure in pregnancy interferes with children’s brain development. In adults, lead exposure increases the risk of heart and brain disease.


Where is the lead coming from?

Since women with higher BLL were more likely to consume food from lead-soldered food cans, the researchers examined 28 cans which the women had used to store dry food such as puffed rice and turmeric.

“It is possible that food stored in these cans absorbs lead from the soldered seams, depending on the chemical composition of the food, especially liquid,” says Ms Jenna E. Forsyth, a doctoral researcher at Stanford University and first author of the study.

An image of one of the lead-soldered cans that previously held cooking oil; (middle) lead solder visible as designated by the arrow; (right) representative images of three can seams taken at Stanford's linear accelerator SLAC showing a cross-section of a can with lead solder (green) at seams facing the inside of the can and iron composing the can's walls (red). The elemental contribution of Pb and Fe in the cans was visualized through X-ray absorption at the respective elemental absorption edges of Pb L(III)-edge at 13035 eV and Fe K-edge 7112 eV. Photo/Graphic: Researchers / original study

However, the women reported storing only solid food such as puffed rice. Since these cans are old and rusty, it is possible that old and rusted oxidised particles flake off into puffed rice and then inadvertently consumed, read the study.

Since there was insignificant lead level in the soil, rice and agrochemical samples analysed, the study notes that currently banned agrochemicals (herbicide and pesticide) may have contributed to lead exposure in the past.

“Lead exposure over time results in lead deposit in the bones and it may be released in the blood during pregnancy,” mentions Dr Rubhana Raqib, co-author of the study and senior scientist and head of immunobiology, nutrition and toxicology laboratory at icddr,b.

Therefore, it cannot be ruled out that exposure to lead for these women could have taken place over a decade prior to sample collection, notes the study. Some of the banned agrochemicals are often rebranded with other names and may be a source of occasional contamination which is yet to be proven.

However, the tangible evidence of lead in some turmeric samples issues a warrant to investigate this further to ascertain possible sources of lead contamination.

The study was supported by Stanford University's Woods Institute, USAID, Stanford's Emmett Interdisciplinary Program in Environment and Resources, Stanford's Center for South Asia, and the Bill and Melinda Gates Foundation.

Muhamamd Zahir Hassan Nabil