In vitro digestion of microplastics in human digestive system: Insights into particle morphological changes and chemical leaching.

Despite the well-reported occurrences and established pathways for microplastics (MPs) ingestion by humans, the eventual fate of these particles in the human gastrointestinal system is poorly understood. The present study tries to gain a better understanding of the fate of four common food-borne MPs, i.e. Polystyrene (PS), Polypropylene (PP), Low-density Polyethylene (LDPE), and Nylon, in a simulated in vitro human digestive system. Firstly, the changes in the physicochemical properties of 20-210 µm sized MPs as well as the leaching of chemicals were monitored using fluorescence microscopy, FTIR, and LC-QTOF-MS. Thereafter, the mass loss and morphological alterations in 3-4 mm sized MPs were observed after removing the organic matter. The interaction of PS and PP MPs with duodenal and bile juices manifested in a corona formation. The increase in surface roughness in PP MPs aligned with MP-enzyme dehydrogenation reactions and the addition of NO groups. A few fragments ranging from 30 to 250 µm, with negligible mass loss, were released during the MP digestion process. In addition, the leaching of compounds, e.g. capsi-amide, butanamide, and other plasticizers and monomers was also observed from MPs during digestion, and which may have the potential to accumulate and get absorbed by the digestive organs, and to subsequently impart toxic effects.

Long-term presence of microplastics in aerobic and anaerobic sequential batch reactors: Effect on treatment, microbial diversity, and microplastics morphology.

Sewage treatment plants (STPs) are identified as the significant sink and source of microplastics (MPs) in aquatic bodies and terrestrial systems. A major fraction of MPs gets retained in STPs for a longer duration, and their potentiality for secondary MPs generation and additives leaching remain under investigated. Therefore, this study focussed on the effect of long-term exposure of aerobic and anaerobic biological sewage treatment units on MPs, along with the effect of MPs on treatment efficiency and microbial consortium. A mixture of polyvinyl chloride, polystyrene, and nylon MPs at 262 MPs/L was spiked in the aerobic and anaerobic sequential batch reactors (SBRs) for 120 days at the start of study. The study revealed a release of noteworthy fraction of secondary MPs into the reactors from spiked MPs. At the end of 120th day, the presence of secondary generated MPs was estimated as 1000 ± 71 MPs/L and 650±141 MPs/L in aerobic and anaerobic SBRs respectively. Most of the observed secondary MPs were of size < 300 µm. Leaching of additives, i.e. cyclohexylamine, cyclotetradecane, octadecanol, pipericine etc., into the SBR effluents were also observed. The depuration capacities of the reactors were not affected with the presence of MPs during the study. While the microbial diversity and abundance were negatively impacted in aerobic SBRs, no such impacts were observed in anaerobic SBRs due to MPs. These results do suggest such exposures to potentially cause secondary MPs and chemical pollution in receiving matrices for the treated effluent, as well as effect on the native microbial community.

A unified modelling framework for type I (discrete) settling and rising of microplastics in primary sedimentation tanks.

Sewage treatment plants (STPs) are considered as a significant source of microplastic pollution into the terrestrial and aquatic environment. Existing observations suggest that primary treatment accounts for major microplastics removal in STPs, though with high variability due to the complex nature of the polymer compositions, abundance, and sizes in the incoming sewage. Here, we develop a unified modelling framework to simulate the Type I (or discrete) settling or rising behaviour of microplastics to predict their eventual fate in Primary Sedimentation Tank (PST). The model was developed as per the conventional design protocol for PST involving Stokes equation and modifications as per flow regime for settling of nylon and polystyrene microplastics. It was subsequently validated with independent column experiments for both settling (nylon and polystyrene) and rising (low-density polyethylene and polypropylene) microplastics in different size ranges. The validated model was then applied for multiple realistic scenarios of polymer compositions, relative abundance, and size distributions in the incoming sewage. The model predicts removals ranging from 12% to 94% for a mixture of microplastics in the size fraction 0-500 µm. Model simulations also suggest better microplastics removal with the integration of skimming in PST, and optimization of surface overflow velocity.

Estimation of microplastic exposure via the composite sampling of drinking water, respirable air, and cooked food from Mumbai, India.

Despite the established presence of microplastics in consumable products and inhalable air and the associated health hazards, the actual extent of human exposure to microplastics is currently unknown. We estimated exposure to microplastics through 24-h composite sampling of drinking water, cooked food, and respirable air. Daily average exposures of 382 ± 205, 594 ± 269, and 1036 ± 493 particles per person were observed through drinking water, air, and food, respectively. Our estimates suggest an average daily exposure of 2012 ± 598 microplastic particles per person via these dominant routes. Considering the variety of common consumer plastics, the plastic intake was calculated to be 122.25 ± 177.38 to 202.80 ± 294.25 mg per person per day. Food ingestion was observed to be the major pathway, with fragments as the dominant particle type, followed by fibers and spherical beads. The major polymers identified in the food samples were polyethylene terephthalate, polystyrene, polynorbornene, nylon, polychloroprene, and copolymer polyacrylamide. These results provide a realistic estimate of urban exposure to microplastics and may be helpful in their risk characterization.

Contamination of Household Open Wells in an Urban Area of Trivandrum, Kerala State, India: A Spatial Analysis of Health Risk Using Geographic Information System.

OBJECTIVE: To assess the sanitary condition and water quality of household wells and to depict it spatially using Geographic Information System (GIS) in an urban area of Trivandrum, Kerala state, India. STUDY DESIGN: A community-based cross-sectional census-type study. METHODS: Study was conducted in an urban area of Trivandrum. All households (n = 449) residing in a 1.05 km2 area were enrolled in the study. Structured questionnaire and Differential Global Positioning System (DGPS) device were used for data collection. Water samples taken were analyzed in an accredited laboratory. RESULTS: Most of the wells were in an intermediate-high contamination risk state, with more than 77% of wells having a septic tank within 7.5 m radius. Coliform contamination was prevalent in 73% of wells, and the groundwater was predominantly acidic with a mean of 5.4, rendering it unfit for drinking. The well chlorination and cleaning practices were inadequate, which were significantly associated with coliform contamination apart from a closely located septic tank. However, water purification practices like boiling were practiced widely in the area. CONCLUSION: Despite the presence of wells with high risk of contamination and inadequate chlorination practices, the apparent rarity of Water-borne diseases in the area may be attributed to the widespread boiling and water purification practices at the consumption level by the households. GIS technology proves useful in picking environmental determinants like polluting sources near the well and to plan control activities.