Microplastics: impacts on the environment and human health

Hundreds of millions of tons of plastics are produced each year. Millions of those tons enter our air, soil, and water as waste. As waste, some of this material–still many millions of tons–breaks down into smaller particles, or microplastics (< 5 mm in size); microplastics come from many sources including the manufacture of industrial products and the physical, chemical, and biological breakdown of larger pieces of plastic waste.

Microplastics decompose extremely slowly. As such, they can serve as long-lasting “reactive surfaces” that can contain and/or absorb antibiotics and also heavy metals, pesticides, and other toxic substances. Also, microplastics can be colonized by different microbial communities, and this combination of bacteria/microorganisms, antibiotics, and toxic substances can spread antibiotic resistance genes into normally non-pathogenic organisms and into new locations.

So, besides the visible negative impacts–to our land, water, and air and to aquatic and terrestrial animals–microplastics are a significant threat to human health.

Featured articles (these articles have been added to the Science Primary Literature database):

*Al-Jaibachi, R., Cuthbert, R. N., & Callaghan, A. (2018). Up and away: Ontogenic transference as a pathway for aerial dispersal of microplastics. Biology Letters, 14(9). [PDF] [Cited by]

Microplastics (MPs) are ubiquitous pollutants found in marine, freshwater and terrestrial ecosystems. With so many MPs in aquatic systems, it is inevitable that they will be ingested by aquatic organisms and be transferred up through the food chain. However, to date, no study has considered whether MPs can be transmitted by means of ontogenic transference, i.e. between life stages that use different habitats. Here, we determine whether fluorescent polystyrene beads could transfer between Culex mosquito life stages and, particularly, could move into the flying adult stage. We show for the first time that MPs can be transferred ontogenically from a feeding (larva) into a non-feeding (pupa) life stage and subsequently into the adult terrestrial life stage. However, transference is dependent on particle size, with smaller 2 µm MPs transferring readily into pupae and adult stages, while 15 µm MPs transferred at a significantly reduced rate. MPs appear to accumulate in the Malpighian tubule renal excretion system. The transfer of MPs to the adults represents a potential aerial pathway to contamination of new environments. Thus, any organism that feeds on terrestrial life phases of freshwater insects could be impacted by MPs found in aquatic ecosystems.”

*Allen, S., Deonie, A., Phoenix, V. R., Le Roux Gaël, Durántez Jiménez Pilar, Simonneau Anaëlle, . . . Didier, G. (2019). Atmospheric transport and deposition of microplastics in a remote mountain catchment. Nature Geoscience, 12(5), 339-344. [Cited by]

Plastic litter is an ever-increasing global issue and one of this generation’s key environmental challenges. Microplastics have reached oceans via river transport on a global scale. With the exception of two megacities, Paris (France) and Dongguan (China), there is a lack of information on atmospheric microplastic deposition or transport. Here we present the observations of atmospheric microplastic deposition in a remote, pristine mountain catchment (French Pyrenees). We analysed samples, taken over five months, that represent atmospheric wet and dry deposition and identified fibres up to ~750 µm long and fragments ≤300 µm as microplastics. We document relative daily counts of 249 fragments, 73 films and 44 fibres per square metre that deposited on the catchment. An air mass trajectory analysis shows microplastic transport through the atmosphere over a distance of up to 95 km. We suggest that microplastics can reach and affect remote, sparsely inhabited areas through atmospheric transport.”

*Anbumani, S., & Kakkar, P. (2018). Ecotoxicological effects of microplastics on biota: A review. Environmental Science and Pollution Research International, 25(15), 14373-14396. [Cited by]

“The ubiquitous presence of microplastics in the environment has drawn the attention of ecotoxicologists on its safety and toxicity. Sources of microplastics in the environment include disintegration of larger plastic items (secondary microplastics), personal care products like liquid soap, exfoliating scrubbers, and cleaning supplies etc. Indiscriminate usage of plastics and its poor waste disposal management pose serious concern on ecosystem quality at global level. The present review focused on the ecological impact of microplastics on biota at different trophic levels, its uptake, accumulation, and excretion etc., and its plausible mechanistic toxicity with risk assessment approaches. Existing scientific evidence shows that microplastics exposure triggers a wide variety of toxic insult from feeding disruption to reproductive performance, physical ingestion, disturbances in energy metabolism, changes in liver physiology, synergistic and/ or antagonistic action of other hydrophobic organic contaminants etc. from lower to higher trophics. Thus, microplastic accumulation and its associated adverse effects make it mandatory to go in for risk assessment and legislative action. Subsequent research priorities, agenda, and key issues to be addressed are also acknowledged in the present review.”

*Arias-Andres, M., Klümper, U., Rojas-Jimenez, K., & Grossart, H. (2018). Microplastic pollution increases gene exchange in aquatic ecosystems. Environmental Pollution, 237, 253-261. [PDF] [Cited by]

Spread of antibiotic resistance through microplastics can affect aquatic ecology and evolution, but also human health.

Pollution by microplastics in aquatic ecosystems is accumulating at an unprecedented scale, emerging as a new surface for biofilm formation and gene exchange. In this study, we determined the permissiveness of aquatic bacteria towards a model antibiotic resistance plasmid, comparing communities that form biofilms on microplastics vs. those that are free-living. We used an exogenous and red-fluorescent E. coli donor strain to introduce the green-fluorescent broad-host-range plasmid pKJK5 which encodes for trimethoprim resistance. We demonstrate an increased frequency of plasmid transfer in bacteria associated with microplastics compared to bacteria that are free-living or in natural aggregates. Moreover, comparison of communities grown on polycarbonate filters showed that increased gene exchange occurs in a broad range of phylogenetically-diverse bacteria. Our results indicate horizontal gene transfer in this habitat could distinctly affect the ecology of aquatic microbial communities on a global scale. The spread of antibiotic resistance through microplastics could also have profound consequences for the evolution of aquatic bacteria and poses a neglected hazard for human health.”

*Imran, M., Das, K. R., & Naik, M. M. (2019). Co-selection of multi-antibiotic resistance in bacterial pathogens in metal and microplastic contaminated environments: An emerging health threat. Chemosphere, 215, 846-857. [Cited by]

Misuse/over use of antibiotics increases the threats to human health since this is a main reason behind evolution of antibiotic resistant bacterial pathogens. However, metals such as mercury, lead, zinc, copper and cadmium are accumulating to critical concentration in the environment and triggering co-selection of antibiotic resistance in bacteria. The co-selection of metal driven antibiotic resistance in bacteria is achieved through co-resistance or cross resistance. Metal driven antibiotic resistant determinants evolved in bacteria and present on same mobile genetic elements are horizontally transferred to distantly related bacterial human pathogens. Additionally, in marine environment persistent pollutants like microplastics is recognized as a vector for the proliferation of metal/antibiotics and human pathogens. Recently published research confirmed that horizontal gene transfer between phylogenetically distinct microbes present on microplastics is much faster than free living microbes. Therefore, microplastics act as an emerging hotspot for metal driven co-selection of multidrug resistant human pathogens and pose serious threat to humans which do recreational activities in marine environment and ingest marine derived foods. Therefore, marine environment co-polluted with metal, antibiotics, human pathogens and microplastics pose an emerging health threat globally.”

*Wetherbee, G. A., Baldwin, A. K., & Ranville, J. F. (2019). It is raining plastic (No. 2019-1048). US Geological Survey. [PDF] [Cited by]

“Atmospheric deposition samples were collected using the National Atmospheric Deposition Program / National Trends Network (NADP/NTN) at 6 sites in the Denver-Boulder urban corridor and 2 adjacent sites in the Colorado Front Range. Weekly wet-only atmospheric deposition samples collected at these sites during winter-summer of 2017 were filtered (0.45 micrometers, polyethersulfone) to obtain particulates washed from the atmosphere (washout). Plastics were identified on over 90 percent of the filters. The plastic materials are mostly fibers that are only visible with magnification (~40X). Fibers were present in a variety of colors; the most frequently observed color was blue followed by red > silver > purple > green > yellow > other colors. Plastic particles such as beads and shards were also observed with magnification. More plastic fibers were observed in samples from urban sites than from isolated, montane sites. However, frequent observation of plastic fibers in washout samples from the isolated Loch Vale site in Rocky Mountain National Park (elevation 3,159 meters) suggests that wet-deposition of plastic is ubiquitous and not just an urban condition. The mass of plastic in even the most concentrated samples was not large enough to weigh or reliably estimate. Developing a routine capability to calculate plastic wet-deposition loads is not possible with current technology. Counting plastic fibers under a microscope and multiplying the counts by a mean mass per fiber might be possible, but it is tedious, expensive, and has large inherent error. A means to estimate the recovery of the plastic materials from the NADP samples is needed. However, saving the NADP filters for subsequent analysis would make a washout deposition network possible with very little added expense, and methods could be developed to more accurately estimate plastic loads using the NTN. It is unclear how these plastic materials are accumulating and being assimilated in the environment and biota. Moreover, the potential effects of these materials on biota is not understood.”

Questions? Please let me know (engelk@grinnell.edu).

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