Difficult chore and hard choices for parents
By Colleen Wood
Most cultivated rice grows submerged in paddy fields, primarily in South and Southeast Asia, although it is also grown in the United States and many other countries. These flooded fields provide a cool, fertile environment for a healthy crop, but that same environment also allows contamination from toxic heavy metals, including arsenic, cadmium, lead, and mercury.
At least some heavy metals appear to harm brain development and cognition; and have also been linked to ailments including lung disease, kidney disease, skin lesions, and cancer.
Heavy metal exposure is especially dangerous for infants because, compared to adults, they eat more food relative to their body weight and their diet is less varied. Babies are also particularly sensitive to the toxic effects of heavy metals because their bodies are still developing.
In February 2021, the U.S. House Oversight and Reform Subcommittee on Economic and Consumer Policy released a report on heavy metals in baby food produced by several of the country’s largest manufacturers. The 59-page document ended with a call for immediate action from the Food and Drug Administration.
Two months later, the FDA announced the Closer to Zero initiative, which uses an iterative approach to reduce heavy metal exposure among babies and children. The FDA issued draft guidance on lead in fruit and vegetable juice in April 2022 and in baby food more broadly in January 2023. Action plans for arsenic, cadmium, and mercury aren’t scheduled to be completed until 2024 at the earliest.
In the meantime, botanists, soil chemists, and plant geneticists — who have long worked to reduce heavy metals in the food supply — continue to look for potential solutions, from new land management practices to nano-sized fertilizers to genetic engineering. Not all of these technologies are available yet; however, even when they are, eliminating heavy metals entirely won’t be easy.
Still, some experts are optimistic about the possibilities. While “there is no single magic bullet that can address this problem,” said Om Parkash Dhankher, a professor of crop biotechnology at the University of Massachusetts Amherst, “there are lots of technologies and practices that farmers can use.”
Heavy metals are naturally present in the Earth’s crust and make their way into aquifers and rivers when water travels through underground rock formations and dissolves the toxic elements. Arsenic, for example, exists in high levels in the groundwater of the U.S., China, and India.
Agricultural practices have also contributed to heavy metal contamination. The U.S. has led the world in the use of arsenic for agriculture and industry, and while insecticides with lead and arsenic were banned in the 1980s, soil, paddy water, and rice grains still have detectable levels of the toxins.
These contaminants get sucked up by the roots of a rice plant, which absorb nutrients through proteins in their cell walls. According to Parkash, arsenic essentially “hijacks” these pathways. As the plant grows, arsenic travels from the roots into the leaves and grains.
Scientists including Parkash are looking for ways to stop arsenic from hijacking the plants to begin with. One approach is to apply more sulfur to paddy soils, which can bind to toxic metals and make them more difficult to absorb.
In recent years, Parkash and Jason White, who directs the Connecticut Agricultural Experiment Station, have been researching this process at a very small scale. Given how sulfur binds to toxic metals, Parkash and White have looked into ways that nanotechnology — which involves manipulating materials at the scale of billionths of a meter — could be used for soil remediation.
In a recent paper, they found that rice plants treated with both inorganic arsenic, the element’s more toxic form, and nanosulfur accumulated nearly a third less of the toxin in root tissue than plants exposed to inorganic arsenic alone.
Other alterations to a field can help, too. Wild plants like water spinach and water celery also slurp up nutrients and toxins, and scientists have studied intercropping rice paddies to help remove contaminants. When these aquatic vegetables are grown alongside rice, overall concentrations of arsenic in the soil decrease and the wild plants absorb the arsenic.
Certain species of bacteria can tolerate high levels of arsenic, lead, mercury, and cadmium, and some bacteria have been found to mitigate the toxic effects these heavy metals have on plants. Other microorganisms can reduce arsenic concentrations in crops. Scientists have also genetically engineered bacteria to produce a specific protein that boosts their ability to break down arsenic.
Some of these approaches have yet to be applied in large-scale interventions beyond the lab. “Scientists don’t even think about extension,” said Ganga Hettiarachchi, a soil and environmental chemistry scientist at Kansas State University, referring to a century-old partnership with the U.S. Department of Agriculture and land-grant universities to translate science for practical application in farms and food production.
When it comes to the newest research on soil and land management, Hettiarachchi worries that farmers might not be aware of how to apply the latest research. But she is optimistic: “I do see that it’s changing.”
Some research on heavy metals in rice can’t yet be applied in the field though. Genetic engineering of rice itself, to help the plant block heavy metals, has proven difficult, Shannon Pinson, a plant geneticist at the USDA’s Agricultural Research Service, told Undark.
There is no genetically modified rice in commercial production in the U.S., although Pinson said that the technology has been a useful research tool for understanding how plants take up heavy metals. For example, her research suggests arsenic accumulation is not controlled by a single gene, but rather many genes with individually small effects.
Not all rice varieties are the same, though, and some take up more arsenic and heavy metals than others. In a 2015 article, Pinson’s team examined 1,763 rice cultivars from around the world and compared concentrations of both organic and inorganic arsenic at different stages in the growing cycle.
The good news, according to Pinson, is that the genes responsible for limiting the uptake of both forms of arsenic are already present in U.S. cultivars. But that means that the plants are likely already reducing the arsenic as much as they can, she added, and it “will not be easy to find additional genes that would further reduce arsenic in U.S. rice varieties through traditional breeding.”
One challenge in tinkering with soil chemistry and plant genetics is blocking arsenic can affect the way a plant takes up other nutrients. “There is a balance between this, a tradeoff between the required nutrients and these toxic elements,” Parkash said. “It's a very complex system.”
The tradeoff between nutrients and heavy metals plays out beyond the paddy field, and when it comes to setting rules around food, exposure to toxins is not the only consideration.
In recent guidance for arsenic in infant rice cereal, and for lead in baby food more broadly, the FDA notes that strict limits may not be possible for manufacturers. Pinson told Undark that although it is possible to produce rice with relatively low levels of arsenic, supply chain realities make it difficult to achieve low levels in rice-based baby foods, in part because sellers merge grains from multiple truckloads from different farms into single bins, making low-arsenic rice difficult to trace.
The manufacturing process can also increase concentrations in baby food products that make it on the shelf. The February 2021 Economic and Consumer Policy Subcommittee report found that, at least in tests from of one company’s products, inorganic arsenic levels were 28 to 93 percent higher in the finished products compared to ingredients.
The report points to high levels of arsenic in additives — like vitamin mixes and spices — as the cause of the spike pre- and post-manufacturing.
If food companies can’t meet limits on heavy metals in their products, Elisabeth Davis, a spokesperson for the FDA, told Undark that there could be unintended economic consequences for consumers.
This includes, she continued, “limiting access to foods that have significant nutritional benefits by making them unavailable or unaffordable for many families, or unintentionally increasing the presence of one environmental contaminant when foods are reformulated to reduce the presence of another.”
In March 2016, the FDA released a risk assessment that compared economic impacts and the lifetime risk of cancer at various potential guidance levels for arsenic. The risk assessment compared the effect of different parts per billion (ppb) limits — which is not a unit of mass, but a description of a ratio.
For example, adding about half of a teaspoon of salt to an Olympic-size swimming pool would make it 1 ppb salt. While a 100-ppb limit could lead to anywhere from a 4 to 93 percent loss of rice in the food supply, the FDA calculated that a 75-ppb limit could lead to a 14 to 99 percent loss.
The FDA’s risk assessment estimated the average lifetime risk of cancer at different levels of infant rice consumption at various limits of inorganic arsenic. For white rice infant cereal, a limit of 100 parts per billion would reduce the risk of cancer by almost 19 percent, whereas limits of 75 and 50 ppb were calculated to reduce risk by 41 and 79 percent, respectively.
The hazard models the report’s authors used are a standard approach, but experts told Undark that the science of calculating health risks around heavy metal contamination is complex.
While it is quite straightforward to calculate exposure from water, when it comes to food, White, from the Connecticut Agricultural Experiment Station said: “There isn't a formula right now that could be used to actually calculate something like that.”
In the end, the FDA recommended inorganic arsenic limits at 100 parts per billion, which it first proposed in draft guidance in April 2016 and finalized in August 2020. This is more lenient than the 10 ppb proposed by national lawmakers in the Baby Food Safety Act, a bill that has stalled in Congress since March 2021.
The act would align the inorganic arsenic limits in food with the U.S. Environmental Protection Agency’s standard for drinking water, though the 100-ppb limit in food is below the voluntary standards set by the leading international food standards body, the Codex Alimentarius.
Like all of the FDA’s guidelines on food limits, 100 parts per billion of arsenic in infant rice cereal is just a recommendation, not a legal requirement. But some evidence suggests the change might be working. The FDA points to a slight downward trend in average concentrations of arsenic in infant rice cereal since it first issued the draft guidance.
However, recent investigations by Consumer Reports and the advocacy group Healthy Babies Bright Futures suggest that at least some baby food in stores across the U.S. contains more than 100 ppb of arsenic — four of seven infant rice cereals that were tested exceeded the FDA’s limit.
The February 2021 report, along with a follow-up report issued that September, showed that several companies set internal limits on arsenic above the FDA’s guidance. And some companies found that arsenic levels in infant cereal still surpassed their higher limits.
“Baby food manufacturers hold a special position of public trust. Consumers believe that they would not sell unsafe products. Consumers also believe that the federal government would not knowingly permit the sale of unsafe baby food,” the report read. Baby food manufacturers and federal regulators had “broken the faith.”
Despite evidence of arsenic in infant rice cereal above 100 ppb, there was no FDA-mandated recall. Instead, some companies voluntarily pulled products from the shelves. In June 2021, Beech-Nut announced it was leaving the market for rice cereal entirely.
Potential sources of exposure to heavy metals go far beyond the products covered by Closer to Zero. The FDA has no standards for heavy metals in foods beyond the action level for arsenic in infant rice cereal and two draft guidance levels for lead in juice and baby food more broadly.
And while processed foods can be systematically tested for heavy metals, Hettiarachchi’s research has shown that even individual and community gardens can also be contaminated, meaning that the risk of exposure remains even with homemade food.
As for the FDA efforts on reducing heavy metal exposure so far, “it’s good, and I fully support getting closer to zero,” Hettiarachchi said. “But at the same time, I think we have to do much better.”
Colleen Wood is a writer and educator based in New York City. Her work has appeared in The Diplomat, Foreign Policy, New Lines Magazine, and The Washington Post, among other outlets. Find her on Twitter @colleenwood_.
This article was originally published on Undark. Read the original article.
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