Recent research has documented microplastic particles (< 5 mm in diameter) in ocean habitats worldwide and in the Laurentian Great Lakes. Microplastic interacts with biota, including microorganisms, ...in these habitats, raising concerns about its ecological effects. Rivers may transport microplastic to marine habitats and the Great Lakes, but data on microplastic in rivers is limited. In a highly urbanized river in Chicago, Illinois, USA, we measured concentrations of microplastic that met or exceeded those measured in oceans and the Great Lakes, and we demonstrated that wastewater treatment plant effluent was a point source of microplastic. Results from high-throughput sequencing showed that bacterial assemblages colonizing microplastic within the river were less diverse and were significantly different in taxonomic composition compared to those from the water column and suspended organic matter. Several taxa that include plastic decomposing organisms and pathogens were more abundant on microplastic. These results demonstrate that microplastic in rivers are a distinct microbial habitat and may be a novel vector for the downstream transport of unique bacterial assemblages. In addition, this study suggests that urban rivers are an overlooked and potentially significant component of the global microplastic life cycle.
Microplastics are ubiquitous contaminants in aquatic habitats globally, and wastewater treatment plants (WWTPs) are point sources of microplastics. Within aquatic habitats microplastics are colonized ...by microbial biofilms, which can include pathogenic taxa and taxa associated with plastic breakdown. Microplastics enter WWTPs in sewage and exit in sludge or effluent, but the role that WWTPs play in establishing or modifying microplastic bacterial assemblages is unknown. We analyzed microplastics and associated biofilms in raw sewage, effluent water, and sludge from two WWTPs. Both plants retained >99% of influent microplastics in sludge, and sludge microplastics showed higher bacterial species richness and higher abundance of taxa associated with bioflocculation (e.g. Xanthomonas) than influent microplastics, suggesting that colonization of microplastics within the WWTP may play a role in retention. Microplastics in WWTP effluent included significantly lower abundances of some potentially pathogenic bacterial taxa (e.g. Campylobacteraceae) compared to influent microplastics; however, other potentially pathogenic taxa (e.g. Acinetobacter) remained abundant on effluent microplastics, and several taxa linked to plastic breakdown (e.g. Klebsiella, Pseudomonas, and Sphingomonas) were significantly more abundant on effluent compared to influent microplastics. These results indicate that diverse bacterial assemblages colonize microplastics within sewage and that WWTPs can play a significant role in modifying the microplastic-associated assemblages, which may affect the fate of microplastics within the WWTPs and the environment.
Microplastic (particles < 5 mm) pollution dynamics are well documented in oceans and increasingly studied in freshwater. We used a watershed-scale approach to examine spatial and temporal patterns in ...microplastic concentrations in the Gallatin River watershed (Montana, USA). At 72 sites, trained volunteers collected ∼1-L grab samples at 4 seasons per year over 2 years (n = 714 samples). Microplastics were found in 57% of the samples (mean = 1.2 particles L−1). The majority of particles were fibers (80%), 0.1–1.5 mm long. Chemical identification determined 93% of particles measured by μFT-IR were synthetic or semi-synthetic materials. Microplastic concentration differed significantly among dates, but showed no longitudinal pattern or relationship to land-use among subwatersheds. At two sites with gaging stations, microplastic was negatively related to discharge when compared across dates. This suggests stormwater is not a source of microplastic in this watershed, but instead dilutes microplastic inputs from other sources. We conclude that microplastic sources are diverse, and measurements of microplastic deposition, resuspension, and transport may be needed to clarify the role of land-use patterns on microplastic pollution. This large scale, citizen science based approach provides a model for future analysis which can further expand microplastic collection at the watershed scale.
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•Watershed-scale approach examines spatial and temporal microplastic concentration.•Trained volunteers (citizen scientists) collected 714 1L grab samples over 2 years.•No longitudinal pattern found between microplastic concentration and land-use.•Microfibers dominant type of microplastics discovered.•High flow periods may dilute microplastic inputs from point sources.
Revisiting Odum (1956) Hoellein, Timothy J.; Bruesewitz, Denise A.; Richardson, David C.
Limnology and oceanography,
November 2013, Volume:
58, Issue:
6
Journal Article
Peer reviewed
Open access
H. T. Odum’s influential Limnology and Oceanography 1956 publication compared gross primary production (GPP) and ecosystem respiration (ER) among aquatic ecosystems. Few syntheses of aquatic ...ecosystem metabolism have been completed since. We used Odum’s conceptual framework to compare GPP and ER from open-water diel oxygen curves in lakes, wetlands, estuaries, and streams (n = 350). We also documented environmental drivers of metabolism among ecosystems. GPP and ER were strongly related in lakes and estuaries, but weakly related in streams and wetlands. GPP and ER were highest in estuaries, and GPP : ER was lowest in streams. Differences in the magnitude and variability of metabolism among ecosystems were attributable to landscape and water-column factors. Watershed size and phosphorus (P) concentrations were positively related to GPP and ER across all ecosystems. Considered independently, lake and estuary GPP were driven by P concentrations. In contrast, land-use and canopy cover drove stream metabolism, not nutrient concentrations. Results confirmed the classic paradigm that estuaries are the most productive aquatic ecosystem; however, our synthesis showed that relative to streams and estuaries, there was higher variation in lake GPP and ER than previously documented. Results will be valuable for management, restoration, and carbon budgets, which incorporate metabolism measurements at both the catchment and landscape scales. As metabolism datasets grow, future syntheses will address challenges including seasonality, sensor deployment time and location, hydrology, and variation in analytical conventions by discipline. Ongoing technological and computational advancements, combined with increased communication among subdisciplines, should also expand insights generated by subsequent metabolism syntheses.
The “plastic cycle” Hoellein, Timothy J; Rochman, Chelsea M
Frontiers in ecology and the environment,
04/2021, Volume:
19, Issue:
3
Journal Article
Peer reviewed
Open access
Research on plastics in global ecosystems is rapidly evolving. Oceans have been the primary focus of studies to date, whereas rivers are generally considered little more than conduits of plastics to ...marine ecosystems. Within a watershed, however, plastics of all sizes are retained, transformed, and even extracted via freshwater use or litter cleanup. As such, plastic litter in terrestrial and freshwater ecosystems is an important but underappreciated component of global plastic pollution. To gain a holistic perspective, we developed a conceptual model that synthesizes all sources, fluxes, and fates for plastics in a watershed, including containment (ie disposed in landfill), non-containment (ie persists as environmental pollution), mineralization, export to oceans, atmospheric interactions, and freshwater extraction. We used this model of the “plastic cycle” to illustrate which components have received the most scientific attention and to reveal overlooked pathways. Our main objective is for this framework to inform future research, offer a new perspective to adapt management across diverse waste governance scenarios, and improve global models of plastic litter.
Abstract
The ecological dynamics of microplastic (<5 mm) are well documented in marine ecosystems, but the sources, abundance, and ecological role of microplastic in rivers are unknown and likely to ...be substantial. Microplastic fibers (e.g., synthetic fabrics) and pellets (e.g., abrasives in personal care products) are abundant in wastewater treatment plant (
WWTP
) effluent, and can serve as a point source of microplastic in rivers. The buoyancy, hydrophobic surface, and long transport distance of microplastic make it a novel substrate for the selection and dispersal of unique microbial assemblages. We measured microplastic concentration and bacterial assemblage composition on microplastic and natural surfaces upstream and downstream of
WWTP
effluent sites at nine rivers in Illinois, United States. Microplastic concentration was higher downstream of
WWTP
effluent outfall sites in all but two rivers. Pellets, fibers, and fragments were the dominant microplastic types, and polymers were identified as polypropylene, polyethylene, and polystyrene. Mean microplastic flux was 1,338,757 pieces per day, although the flux was highly variable among nine sites (min = 15,520 per day, max = 4,721,709 per day). High‐throughput sequencing of 16S
rRNA
genes showed bacterial assemblage composition was significantly different among microplastic, seston, and water column substrates. Microplastic bacterial assemblages had lower taxon richness, diversity, and evenness than those on other substrates, and microplastic selected for taxa that may degrade plastic polymers (e.g.,
Pseudomonas
) and those representing common human intestinal pathogens (e.g.,
Arcobacter
). Effluent from
WWTP
s in rivers is an important component of the global plastic “life cycle,” and microplastic serves as a novel substrate that selects and transports distinct bacterial assemblages in urban rivers. Rates of microplastic deposition, consumption by stream biota, and the metabolic capacity of microplastic biofilms in rivers are unknown and merit further research.
Microplastics (particles <5 mm) are commonly found in aquatic organisms across taxonomic groups and ecosystems. However, the egestion rate of microplastics from aquatic organisms and how egestion ...rates compare to other rates of microplastic movement in the environment are sparsely documented.
We fed microplastic fibres to round gobies (Neogobius melanostomus), an abundant, invasive species in the Laurentian Great Lakes. We conducted two trials where round gobies were fed microplastic‐containing food either a single time (1 day) or every day over 7 days.
There was no difference in microplastic egestion rates from the 1 day or 7 day feeding trials, suggesting no impact of duration of exposure on egestion (exponential decay rate = −0.055 ±0.016 SE and −0.040 ±0.007 SE, respectively). Turnover time of microplastics (i.e., average time from ingestion to egestion) in the gut ranged from 18.2 to 25.0 hr, similar to published values for other freshwater taxa.
We also measured microplastics in the digestive tracts of round gobies collected directly from Lake Michigan, U.S.A. Using published values for round goby density and microplastic concentration at the study sites, we calculated areal egestion rate by round gobies (no. particles m–2 day–1), and compared it to riverine microplastic export (no. particles m–2 day–1). Both area‐based rates were of the same order of magnitude, suggesting that round goby egestion could be an important, and potentially overlooked component of microplastic dynamics at the ecosystem scale.
Animal egestion is well‐known as a major component of nutrient and carbon cycling. However, direct measurements of microplastic fluxes in the environment that include animal egestion rates are uncommon. An ecosystem ecology approach is needed to meet the emerging challenge of generating microplastic budgets for freshwater environments and elsewhere, thereby informing management and mitigation of plastic pollution at a global scale.
Rivers are a major source of microplastic particles (<5 mm) to oceans, but empirical measurements of microplastic movement in freshwater ecosystems are rare. The hard, buoyant surface of microplastic ...is a novel habitat that selects for unique microbial assemblages in rivers, especially downstream of wastewater treatment plant (WWTP) point sources. We measured microplastic in surface water and benthic habitats 50 m upstream and 50, 305, 1115, and 1900 m downstream of the effluent outfall from a large WWTP in an urban river. We used high-throughput sequencing to measure bacterial assemblages on microplastic from surface and benthic habitats and compared them to bacterial assemblages from seston, water, and sediment. Concentrations of total microplastic and microplastic types (fragment, pellet) in surface water did not change with distance downstream of the WWTP. Thus, microplastic transport showed no net deposition or resuspension. Microplastic concentrations were much higher in the benthic zone than surface water. Benthic deposition appears to be a plastic sink over longer time scales, but subsequent studies are needed to resolve microplastic transport dynamics by particle type, size, and habitat. Composition of microplastic-attached bacterial assemblages differed from that of assemblages in water, seston, and sediment and supports domestic wastewater as a point source of microplastic (e.g., gastrointestinal taxa). Shifts in microplastic assemblages with distance from the WWTP suggest succession toward a ‘stream-like’ bacterial assemblage. Future studies are required to quantify the metabolic capacity of microplastic-associated bacteria. Estimates of transport distance, microplastic storage, and microbial interactions are critical to include lotic ecosystems in accountings of global plastic budgets.
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