Papers of the Month
Extramural
By Julie Leibach
Bottlenose dolphins ingest variety of tiny plastic particles
Plastic fragments found in bottlenose dolphins may have dietary and nondietary sources, NIEHS-funded researchers reported. The findings suggest new avenues for investigating plastic accumulation in aquatic organisms.
Plastic forms the bulk of debris affecting marine ecosystems. Earlier work documented plastic ingestion in wild bottlenose dolphins in Sarasota Bay, off Florida’s west coast. The researchers wondered if prey fish that consume microplastics, or tiny plastic pieces, could be a source of exposure to dolphins.
They collected 29 fish, representing four species, from Sarasota Bay and took samples from muscle and the gastrointestinal tract. During veterinary checkups, conducted through catch-and-release methods, the researchers also retrieved stomach content samples from seven dolphins. Back in the lab, they screened all samples for microplastics, analyzing properties such as color, shape, and texture.
Each dolphin sample contained at least one suspected plastic particle and often dozens. Nearly all fish also showed evidence of microplastic ingestion, with more particles appearing in samples from the gastrointestinal tract than from muscle. Plastic in the form of fibers and films appeared in fish and dolphin samples alike. By contrast, tire wear particles occurred in fish but not dolphins, and foam pieces were common among dolphins but absent in fish. Dolphins may ingest foam while playing with floating debris the team suggested.
The findings offer insight into the variety of plastic found in dolphins, but larger sample sizes are necessary to understand sources of exposure, according to the authors. Because dolphins and humans reside on similar levels of the food chain, the results may indicate seafood safety risks for people as well.
Citation: Hart LB, Dziobak M, Wells RS, Berens McCabe E, Conger E, Curtin T, Knight M, Weinstein J. 2023. Plastic, it’s what’s for dinner: a preliminary comparison of ingested particles in bottlenose dolphins and their prey. Oceans 4(4):409–422.
Exposure to nitrogen dioxide in air associated with Parkinson’s disease risk
Greater exposure to the air pollutant nitrogen dioxide (NO2) was associated with a higher risk of developing Parkinson’s disease, NIEHS-funded researchers found. The study, which centered on women, provides evidence that air quality can affect neural health.
Although Parkinson’s is the second-most common neurodegenerative disease in the U.S., its causes are largely unknown. Environmental exposures, acting alone or in concert with genetic factors, likely contribute to most cases. Studies suggest that air pollutants may play a role by traveling through the nasal passage, bypassing the brain’s protective barrier.
The researchers analyzed data on more than 47,000 women, ages 35-80, who participated in the NIEHS-funded Sister Study. They compared average levels of exposure to NO2 and particulate matter (PM2.5) from 2009 until the date of Parkinson’s diagnosis, last contact, death, or the study’s end in 2018. Through air pollution modeling, the team estimated NO2 and PM2.5 levels at each participant’s residence.
Parkinson’s risk increased with greater exposure to NO2. Further analysis suggested the association was stronger among women living in urban, small town, and rural areas — as opposed to women from suburban locations — and among women from under-resourced neighborhoods. Exposure to ambient PM2.5 was not linked to Parkinson’s risk, with the possible exception of participants from the Midwest. Certain chemicals tied to Midwestern agricultural activity may have contributed to this observation, the authors suggested.
The findings add to the limited body of research on connections between air pollution and Parkinson’s disease, according to the authors. Future work should probe the underlying mechanisms at play, they added.
Citation: Cao Z, Yuan Y, White AJ, Li C, Luo Z, D’Aloisio AA, Huang X, Kaufman JD, Sandler DP, Chen H. 2024. Air pollutants and risk of Parkinson's disease among women in the Sister Study. Environ Health Perspect 132(1):17001.
Natural materials can remove uranium and arsenic from water
A combination of limestone and a bone-like mineral called hydroxyapatite can remove arsenic and uranium from water, according to an NIEHS-funded study. Remediation strategies that use these natural materials could protect communities at risk of metal exposures.
Pollution of local water sources by metals associated with hard rock mining is a major concern among Native American communities in the western U.S. Remediation methods that use accessible materials could help reduce exposures in under-resourced areas. Research has shown that natural limestone and hydroxyapatite can react with dissolved metals to remove the contaminants from solution.
The researchers sought to design a process for simultaneously removing uranium and arsenic from water. They dissolved arsenic and uranium in water under acidic and basic conditions to mimic groundwater and surface water near mining sites. Then, they added either limestone or a combination of limestone, phosphate, and calcium. Phosphate and calcium are necessary for the formation of hydroxyapatite.
At high acidity, limestone alone removed nearly all uranium and arsenic from solution, mainly through precipitation, or formation of solids. By contrast, uranium and arsenic remained mostly dissolved at neutral acidity. Meanwhile, adding calcium and phosphate to the limestone solution resulted in rapid removal of more than 90% of uranium through precipitation, regardless of acidity. Increasing calcium and phosphate concentrations under basic conditions resulted in nearly complete arsenic removal from the solution. Imaging analysis confirmed that hydroxyapatite had formed and bound to most of the arsenic.
The results indicate that materials such as limestone and hydroxyapatite could be an accessible remediation strategy for Tribal communities affected by a legacy of mining. Future studies should investigate how naturally occurring minerals perform under realistic environmental conditions, according to the authors.
Citation: Meza I, Hua H, Gagnon K, Mulchandani A, Gonzalez-Estrella J, Burns PC, Ali AS, Spilde M, Peterson E, Lichtner P, Cerrato JM. 2023. Removal of aqueous uranyl and arsenate mixtures after reaction with limestone, PO43-, and Ca2. Environ Sci Technol 57(49):20881–20892.
New model could help predict algal toxin buildup in marine food webs
Researchers funded by NIEHS have developed a conceptual model to predict algal toxin buildup in marine food webs. The framework could complement efforts to monitor seafood sources for potential contamination.
Ciguatera is a type of seafood poisoning caused by ciguatoxins, harmful chemicals produced by marine algae in the group Gambierdiscus. Monitoring seafood for ciguatoxin contamination is difficult because mere traces of the chemicals can make people sick but are hard to detect. A model of toxin infiltration into the food web could help forecast ciguatera outbreaks.
To build their model, the researchers integrated data on Gambierdiscus growth and toxicity, as well as on the feeding preferences and behavior of seaweed-eating fish. They collected samples of algae from eight sites around the Florida Keys and the Virgin Islands, recording water temperature at each location. Next, they analyzed the samples for Gambierdiscus, measuring cell density and estimating toxin levels. Drawing on published studies, the team gathered information on the type and amount of seaweed that coral reef fish consume monthly. Then, they assessed their model’s ability to simulate ciguatoxin uptake by reef fish.
Model outputs suggested a lack of alignment among the parameters, indicating that one parameter may not necessarily predict another. For example, algal cell densities were not correlated with estimates of ciguatoxin buildup in fish, perhaps because highly toxic strains of Gambierdiscus skewed the relationship. By contrast, toxin levels in algal samples were generally correlated with toxin accumulation in fish. In addition, in one case where all model parameters aligned, the model predicted a major toxin infusion into reef fish, indicating a possible ciguatera outbreak.
Future studies should target specific species of seaweed for measuring ciguatoxin levels and adjust for species across sites and seasons, according to the authors. Ultimately, ciguatoxin modeling could be incorporated into other monitoring programs, such as seafood screening, to shape strategic responses to potential ciguatera outbreaks.
Citation: Parsons ML, Richlen ML, Smith TB, Anderson DM, Abram AL, Erdner DL, Robertson A. 2024. CiguaMOD I: a conceptual model of ciguatoxin loading in the Greater Caribbean Region. Harmful Algae 131:102561.
(Julie Leibach is a senior science writer at MDB, Inc., a contractor for the NIEHS Division of Extramural Research and Training.)
