Papers of the Month
By Julie Leibach
For oysters, microplastic uptake and purging depend on contaminant size and shape
Accumulation and elimination of plastic litter in eastern oysters depends on contaminant size and shape, according to research funded by NIEHS. The team also found that holding oysters in a water tank so they can purge contaminants — a process called depuration — is effective at removing many, but not all, particles.
Because oysters filter nutrients from surrounding water, they can consume tiny pieces of plastic-containing debris called microplastics. People who eat the shellfish could also be at risk of exposure.
The researchers exposed groups of oysters to microscopic polyethylene fibers, nylon fragments, or crumb rubber — like what flakes off tires — for one, two, and four days. A subset of exposed oysters depurated over the same number of days. Using a mathematical modeling approach called toxicokinetics, the team analyzed contaminant uptake and elimination.
They found that microplastic size and shape were associated with different modes of accumulation. For polyethylene fibers and nylon fragments, buildup occurred in a nonlinear fashion, with more fibers than fragments accumulating in oysters. By contrast, crumb rubber accumulated steadily, at a faster rate and in higher amounts than fragments and fibers. The result suggested that shellfish were more efficient at capturing crumb rubber, perhaps for texture reasons, according to the authors.
Patterns of depuration suggested that oysters purged some contaminants immediately but cycled others through the body before elimination. The process cut particle loads by only 68%, at most, over 44 hours (the recommended industry minimum), according to the authors. However, the team also found that crumb rubber depuration did not substantially improve even after 96 hours.
Gaining more insight into how oysters expunge microplastics is critical for informing decisions about depuration time in shellfish intended for eating, the authors added.
Citation: Weinstein JE, Ertel BM, Gray AD. 2022. Accumulation and depuration of microplastic fibers, fragments, and tire particles in the eastern oyster, Crassostrea virginica: a toxicokinetic approach. Environ Pollut 308:119681.
Gut microbiome associated with arsenic metabolism in infants
Microbes in the human digestive system may complement a person’s ability to metabolize arsenic, particularly in the first few weeks of life, according to a study funded partly by NIEHS. The association appears to be stronger for infants delivered by caesarean, the team found.
The human gut microbiome — the collection of microorganisms in the digestive tract — includes species capable of breaking down arsenic. Because the ability to detoxify and excrete contaminants is less mature in infants, changes in microbiome composition could affect their susceptibility to arsenic exposure.
The researchers leveraged data on 222 infants who participated in the New Hampshire Birth Cohort Study, which was established to investigate the effects of environmental exposures on pregnant women and their children. Specifically, the team analyzed stool samples for the presence of bacterial genes involved in arsenic metabolism and urine samples for associated metabolic byproducts. Then they compared results for 6-week-old infants and 1-year-old babies. The team also examined whether associations were stronger in infants born via caesarean.
They found associations between urinary arsenic levels and abundance of arsenic-metabolizing genes in the gut microbiome. Associations were stronger in 6-week-old infants compared to 1-year-olds — particularly those delivered by caesarean. The finding suggested that bacterial transmission through vaginal birth may confer protection from arsenic exposure during a vulnerable window of time, noted the researchers.
Overall, the results indicated that certain bacterial genes complement human metabolism of arsenic, highlighting a potential therapeutic approach for babies at risk of exposure, according to the authors.
Citation: Laue HE, Moroishi Y, Palys TJ, Jackson BP, Madan JC, Karagas MR.. 2022. Contribution of gut bacteria to arsenic metabolism in the first year of life in a prospective birth cohort. Environ Res 214(Pt 4):114099.
Early-life exposure to flame retardants could affect bone health
Exposure to organophosphate esters (OPEs) — which are found in flame retardants, plastics, and personal care products — during early development may be associated with changes in adolescent bone health, according to an NIEHS-funded study. Those changes may depend on sex and exposure period.
Bone development starts during gestation, and rates of bone mineral accrual peak at about age 12 in females and age 14 in males. This study is the first to evaluate connections between early-life OPE exposure and bone health in humans, the authors noted.
The team followed 223 mother-child pairs enrolled in the Health Outcomes and Measures of the Environment (HOME) Study. They assessed urinary concentrations of four OPE metabolites, or byproducts, in urine samples collected from pregnant women and their children at ages 1, 2, 3, 5, and 8 years. After the kids turned 12, the researchers examined bone health through x-ray imaging and calculated bone mineral content and density at several skeletal sites.
Associations between OPE exposure and measures of bone health were specific to skeletal site, sex, and exposure period. For example, higher levels of two urinary OPE metabolites during gestation and in 8-year-olds were associated with higher bone density scores. The reverse was true for ages 1, 2, 3, and 5 years. Those patterns were stronger among males than females. Across OPEs, associations were generally strongest at the hip skeletal region. Sex differences were most apparent at the spine.
Future studies assessing bone-related health problems, such as fracture and osteoporosis, could help contextualize the potential long-term health implications of early exposure to OPEs, the authors noted.
Citation: Kuiper JR, Vuong AM, Lanphear BP, Calafat AM, Ospina M, Cecil KM, Xu Y, Yolton K, Kalkwarf HJ, Braun JM, Chen A, Buckley JP. 2022. Early life organophosphate ester exposures and bone health at age 12 years: The Health Outcomes and Measures of the Environment (HOME) Study. Sci Total Environ 851(Pt 2):158246.
Alligators exposed to elevated levels of PFAS show signs of immune disruption
American alligators living in North Carolina’s Cape Fear River had elevated levels of per- and polyfluoroalkyl substances (PFAS) in their blood and associated signs of immune dysfunction, according to an NIEHS-funded study. The findings suggest that American alligators could help scientists understand the consequences of long-term exposure to PFAS mixtures, the authors noted.
Water sampling has revealed high levels of PFAS in the Cape Fear River, an important drinking water source for hundreds of thousands of North Carolinians. However, the public health and environmental effects of long-term exposure to the contamination are unclear.
For their study, the researchers sampled blood from 75 adult and juvenile alligators — 49 from the Cape Fear River basin and 26 from neighboring Lake Waccamaw, which served as a basis for comparison. The team detected an average of 10 PFAS in Cape Fear River alligators and an average of five PFAS in Lake Waccamaw alligators. In addition, levels of PFAS were higher in Cape Fear River alligators than in the reference population.
In adult alligators, higher PFAS concentrations were associated with greater lysozyme activity, a measure of immune response to disease-causing agents. In addition, several Cape Fear River alligators revealed unhealed wounds and skin lesions reminiscent of certain autoimmune disorders in humans. Moreover, the team measured higher levels of biological markers and gene expression associated with human autoimmune diseases in Cape Fear River alligators relative to Lake Waccamaw alligators.
Heightened immune activity among Cape Fear River alligators could stem from PFAS exposure, according to the authors. Alligators may serve as sentinels for autoimmune hazards caused by chemical pollutants, they added.
Citation: Guillette TC, Jackson TW, Guillette M, McCord J, Belcher SM. 2022. Blood concentrations of per- and polyfluoroalkyl substances are associated with autoimmune-like effects in American alligators from Wilmington, North Carolina. Front Toxicol 4:1010185.