The spice sellers’ secret

A hunt for the sources of lead poisoning in Bangladesh

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The rural areas of Bangladesh are quilted with verdant rice paddies nestled between glittering, blue river tributaries. Women wrapped in fuchsia, pomegranate-red and tangerine-orange saris walk among tan-and-brown cows. Market stalls are piled high with multicolored produce and spices. It is a country of vibrant colors.

This is where Jenna Forsyth landed in 2015, during the first summer of her PhD program with the Emmett Interdisciplinary Program in Environment and Resources at Stanford University. Armed with data that showed surprisingly high levels of lead in pregnant women in rural Bangladesh, her mission was to figure out where it was coming from and how to get rid of it.

At the start, there weren’t any obvious answers. There were no lead-belching factories in the area. Leaded gasoline had been banned for years. And it couldn’t be lead-based paint because few residents could afford to paint their homes. Her adviser thought the source could be lead-arsenate pesticides, but after spending days wading in muddy rice paddies, she ruled that out. She had hit a scientific dead end.

Undaunted, she returned to Stanford University and joined an interdisciplinary team of researchers to look at the problem anew. Ultimately, using old-fashioned detective work and high-tech chemical analysis, the team identified the source and joined government officials in getting the lead out. Now, they hope to use the same approach to reduce lead exposure throughout the world.

A heavy metal

Forsyth’s main PhD adviser was Stephen Luby, MD, an epidemiologist who had been tackling the global lead problem since the early 1990s. His work began in Pakistan, where his research contributed to banning leaded gasoline in that country. But after he read a study (Bergkvist et al., 2010, in Environmental Research) about unexpectedly high levels of lead in pregnant women in rural Bangladesh, he knew his work wasn’t done.

“There is no safe level for lead exposure,” said Luby, a Stanford School of Medicine professor of medicine and the director of research for the Stanford Center for Innovation in Global Health. Early in his career, Luby spent eight years focused on improving public health in Bangladesh, so this was personal.

Lead is a toxic heavy metal that can seriously damage reproductive, neurological and cardiovascular systems. Exposure to it is a global problem, with an estimated 1 in 3 children with blood lead levels at or above 5 micrograms per deciliter, the level considered unacceptable by the World Health Organization. (In October 2021, the U.S. Centers for Disease Control and Prevention lowered this level to 3.5 micrograms per deciliter.)

“There is no safe level for lead exposure.”

Stephen Luby, MD, director of research for the Stanford Center for Innovation in Global Health

Between 24 million and 46 million children and teenagers in Bangladesh are estimated to have lead levels above this threshold, the fourth highest number in this age group behind India, Nigeria and Pakistan. Lead poisoning has lifelong, irreversible effects on the cognitive abilities of children, and the social and economic impacts to a country can be devastating.

Children with blood lead levels above 5 micrograms per deciliter may score 3 to 5 points lower on intelligence tests than unaffected peers, limiting their potential. In addition, preschool lead exposure is often associated with juvenile delinquency, violence and crime. In Bangladesh alone, the lower IQ levels caused by lead poisoning are estimated to cost $16 billion annually in lost lifetime productivity, 6% of gross domestic product.

After Forsyth returned from Bangladesh, she reviewed her disappointing findings with Luby. But she had a hunch. She’d recently read a lead study from that region (Gleason et al., 2014 in Journal of Environmental and Public Health) hypothesizing turmeric as a potential source of lead. Could it be the powdery, orange-yellow spice that permeates daily life in Bangladesh? Turmeric is used in curries, as a clothing dye, in cosmetics, in medicines and as an insect repellent. Luby was skeptical, but he let her run with it. “Show me the evidence,” he said.

So, she analyzed 17 turmeric samples from her Bangladesh trip, and one had exceedingly high levels of lead and chromium. It was a start, and like any good medical detective, she began gathering more clues.

The golden spice

Forsyth is an environmental scientist with wanderlust. She’s spent nearly 15 years studying health problems in Bangladesh, Kenya, Tanzania, Costa Rica and Australia, looking for ways to reduce contaminants in air, water, soil and food.

When she was growing up in Logan, Utah, she loved mysteries. Early on, she decided to become a detective, and for her eighth-grade science fair project she went undercover to swab bathroom doorknobs at local restaurants, culturing bacterial samples to evaluate sanitation levels.

This love of evidence-driven puzzles set her on a course to carry on her detective work and, after studying biology as an undergraduate, then earning a master’s in environmental engineering and global health at the University of Washington, she contacted Luby. He recruited her as a PhD candidate, and she joined his initiative to reduce lead exposure in pregnant women, along with icddr,b, a global nonprofit in Bangladesh formerly known as International Centre for Diarrheal Disease Research, Bangladesh.

Back in Bangladesh, Forsyth and the team began a deep dive into the workings of the turmeric supply chain. They interviewed the stakeholders in the production, consumption and regulation of turmeric. They went to mills, wholesalers and spice markets, all the while collecting samples of turmeric, colorants, dust and soil in little baggies for analysis.

To mask flawed turmeric, some processors began dusting the roots with lead chromate — an orange-yellow industrial pigment used to color plastics and furniture.

Turmeric, a member of the ginger family, is made from the rootstalks, aka rhizomes, of Curcuma longa. At the end of the growing season, farmers let the knee-high, leafy green tops dry out, then use hoes to dig up the rhizomes. Next workers, typically women, painstakingly remove dirt clods and break off the feeder roots. Then the naked rhizomes are washed, steamed and laid out to dry for a few weeks.

After drying, the rhizomes are polished to remove dirt and the skins, revealing the yellow inner root. This is done manually or, in larger operations, by placing the rhizomes in rotating drums made of an abrasive wire mesh. Next, the rhizomes are cut, crushed and ground into a powder.

Color matters to turmeric purchasers, and turmeric that is more vibrantly yellow typically sells for higher prices. The Stanford University team learned that this color-linked perception of quality may have started in the 1980s, when a flood interrupted the drying process, turning rhizomes brown and moldy.

To mask flawed turmeric, some processors began dusting the roots with lead chromate — an orange-yellow industrial pigment used to color plastics and furniture. From the interviews, Forsyth learned that this coloration step continued for four decades after the flood and that most processors weren’t aware that the pigments were toxic. But, with Forsyth’s help, this would soon change.

Bring on the ray guns

As a child, Scott Fendorf, PhD, the Terry Huffington Professor and senior associate dean for integrative initiatives in the Stanford Doerr School of Sustainability, liked playing in the dirt. Fortunately for science, his parents encouraged this obsession, and today, he is a leading expert in soil chemistry.

Fendorf was one of Forsyth’s PhD thesis advisers and was the first expert she consulted when she returned from Bangladesh with baggies full of spice, dust and dirt.

Sitting in his cozy office, overgrown with houseplants thriving on enriched soil, Forsyth presented Fendorf with her challenges: How could she figure out where the lead poisoning was coming from? Was it in food, pesticides, lead-soldered cans, silt from local water supplies, or impurities in the clay/ash pellets that many pregnant women chewed to alleviate mineral cravings? And what technology could be applied to verify that lead  from a given source was poisoning the Bangladeshis?

Fendorf explained that a metal like lead can be composed of unique mixes of elemental isotopes that vary according to the source. These location-specific ratios can sometimes be used to pinpoint a lead source in the same way detectives use fingerprints to identify criminals. Analyze the lead isotope ratio in a blood sample to see if it matches one of the lead sources; if it does, bingo, you’ve found the culprit.

But he warned that this approach doesn’t always work, so they enlisted Katharine Maher, PhD, professor of Earth System Science, and Karrie Weaver, technical director at the SIGMA Shared Lab at the Stanford Doerr School of Sustainability, to evaluate how useful the analysis could be for this application.

Turmeric is an orange-yellow spice used in curries, as a clothing dye, in cosmetics, in medicines and as an insect repellent. Close to 50% of Bangladesh’s population is employed in agriculture, and turmeric is an important cash crop and export. (Photography by Timothy Archibald)

The SIGMA, or Stanford Isotopic and Geochemical Measurement and Analysis, lab is home to several state-of-the-art devices — inductively coupled plasma mass spectrometers — that can analyze the precise elemental components of just about any material, from water, soil and tissues, to dinosaur bones. How do these mass spectrometers work? A sample is placed into a chamber where hot argon plasma breaks down a substance into its elemental components. Then the components are stripped of impurities, separated and analyzed by molecular weight and identified by custom software.

As a first step, Forsyth and Weaver characterized the unique isotope ratios for each Bangladeshi lead source — and they lucked out. The lead-isotope fingerprints varied enough to identify specific sources. After the techs analyzed the blood samples collected during their first trip to Bangladesh, there was a clear signal — the blood-borne lead was coming from the turmeric and the industrial pigments used to color it.

Next, the team had to figure out how to quickly identify tainted product in real time in the field; sending samples to a lab for analysis was too expensive and time-consuming to be practical.

For this, Alandra Lopez, Fendorf’s PhD student at the time, showed Forsyth a bright yellow plastic device that looked like a toy ray gun. It was a handheld X-ray fluorescent analyzer. Their lab used it for identifying toxins in the soil, and Lopez was tasked with developing a test methodology and training protocol for its use in turmeric testing.

Then Forsyth bought one for the team for roughly $40,000, and they went back to Bangladesh, armed and ready.

The sting

Gathering scientific evidence in a foreign country to fix a public health problem is one thing. Getting the country to act on it is another. This is where Luby’s deep understanding and love of the Bangladeshi culture came in handy.

“It’s a profoundly hospitable culture, committed to education, with people who really want to make the country better,” said Luby.

Bangladesh is one of the most densely populated countries in the world, surrounded by India to the west, north and east, and Myanmar to the southeast. Its soil is fertile, enriched by frequent flooding of the Ganges and Brahmaputra river systems. Close to 50% of Bangladesh’s population is employed in agriculture, and turmeric is an important cash crop and export.

The government was highly motivated to do something about the lead problem, and Luby made sure that its Department of Agricultural Authority officials were partners in designing and implementing the lead study from the beginning.

“It’s a profoundly hospitable culture, committed to education, with people who really want to make the country better.”

Luby, a Stanford School of Medicine professor of medicine

In July 2017, three years into her PhD research, Forsyth and the team shared their stunning findings: Turmeric mixed with lead-chromate pigments contained lead levels up to 500 times the Bangladesh legal limit of 2.5 micrograms per gram, making it the most likely cause of the lead poisonings.

Their presentation was attended by 21 governmental and non-governmental organizations, including Bangladesh’s Food Safety Authority. Participants were alarmed, and word quickly spread to the highest levels of the government.

From September through December 2019, the Stanford University/icddr,b team and public health officials launched a get-the-lead-out plan, beginning with an effort to inform manufacturers and consumers about the adverse health effects of lead-based pigments. News releases were published, face-to-face meetings were held with key businesspeople, and 50,000 educational posters went up in the markets and public spaces.

The government declared that turmeric adulteration was a prosecutable violation, and Bangladesh Prime Minister Sheikh Hasina discussed the problem on national TV. Then, the Stanford University researchers collected blood samples from workers at one of the larger processors to illustrate how the lead was not only poisoning consumers but also their employees.

Finally, the officials revealed the most important part of the plan to the Stanford University team — a sting operation.

Dusted and busted

Food Safety authority representatives, flanked by soldiers in camouflage uniforms, magenta berets and guns slung over their shoulders, strode down the center of a busy street market in Dhaka, the capital city. The crowds parted.

Men riding three-wheeled rickshaws pulled over. Street vendors stopped stirring their aromatic curries. The spice sellers wearing parti-colored lungi skirts fell silent. Some curious merchants, sitting atop stacks of potatoes, ginger, onions and garlic, jumped down to follow the entourage.

The spice SWAT team visited six turmeric sellers’ stalls. At each, a Stanford University-trained technician pressed the nose of the X-ray fluorescent analyzer into dusty yellow bags of turmeric roots. After a minute or so, the tech could tell whether the root stalks were lead dusted. If they were, law enforcement officials moved in to confiscate and destroy the bags of tainted product.

“It was law enforcement theater.”

Jenna Forsyth, PhD, a research scientist with the Stanford School of Medicine

Because the government is understaffed in food safety enforcement and has a slow judicial process, officials opted for a shock-and-awe approach to punishment. Mobile court officials followed the SWAT team and, as soon as a violation was confirmed, they issued on-the-spot fines in the equivalent of $9,288 in U.S. currency, about three years of an average Bangladeshi’s salary.

To amplify the message, the whole sting operation was filmed by a Jamuna Television news crew and broadcast across the nation.

“It was law enforcement theater,” Forsyth said. But she admitted it was a highly effective way of informing dirty turmeric producers and sellers, “You’re being watched.”

After the intervention, the team went back to the study sites to measure changes in lead levels in the turmeric supply chain, and they were amazed at the effectiveness of the campaign. At the markets, incidence of adulterated spice plunged from 47% in September 2019, to 5% in the first quarter of 2020, to no detectable lead in 2021. Evidence of lead-chromate pigment in the processing mills dropped from 30% in 2017 to 0% in 2021. And 16 months after the intervention, lead levels in the blood of sample test subjects dropped by a median of 30%.

Getting the lead out

Back at his office overlooking Stanford University’s engineering quad, Luby multitasks in front of five computer displays. It gives visitors the impression that his ambitions for tackling our most challenging public health issues are much bigger than can be managed on one or two screens.

Luby grew up in Omaha, Nebraska, raised by an OB/GYN father and a nurse mother. As an undergrad, he immersed himself in philosophy, history and political science at Creighton University, a Jesuit school that emphasizes social justice. He went on to get a medical degree, then studied epidemiology and preventive medicine, eventually serving as the head of the U.S. Centers for Disease Control and Prevention agency in Bangladesh.

During college, Luby never thought he’d become a scientist, but his unique mix of compassion, determination and scientific rigor is making a significant dent in the global lead problem.

“Americans generally think we’ve solved the lead problem, but this is fundamentally not true,” said Luby. “There are 800 million children in the world with lead blood levels greater than recommended standards, and many will go on to suffer permanent brain damage. One million adults die every year because of exposure to lead.”

“In Dhaka, we found this important cohort of young children, 2- to 4-year-olds, who have wildly high levels of lead poisoning.”

Forsyth, whose research is now focused on finding other sources of lead contamination in Bangladesh

He emphasized that lead-dusted turmeric isn’t just a Southeast Asian problem. Worldwide, turmeric is more popular than ever as an ingredient in teas, curries, anti-inflammatory supplements and coloring for processed foods like macaroni and cheese, yogurt, and ice cream. And while the major spice companies that sell it in the U.S. have good quality control procedures, a lot of turmeric is brought in by less conscientious importers, he said.

Luby is now looking at using the playbook that worked in Bangladesh — evidence gathering, education, media coverage and law enforcement — to see if it can be applied to other countries.

Meanwhile, Forsyth and the lead team are still hunting down other lead sources in Bangladesh.

“In Dhaka, we found this important cohort of young children, 2- to 4-year-olds, who have wildly high levels of lead poisoning,” she said.

And like any good detective, she’s keeping an open mind about possible culprits.

“Right now, we’re exploring lead sources in battery recycling dumps, metal factories, and in pots and pans.”

Looking back on the project to date, Forsyth reflected on the most important lesson she’s learned: “Lead is pervasive in our environment, and the toxic effects are profound. This is why we need to keep working this puzzle.”

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Kris Newby

Kris Newby is a freelance science writer. Contact her at

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