**5. Environmental effects and fate**

A complex network of interactions existing among the physical, chemical, and biological aspects of microplastics in an aquatic environment is shown in **Figure 3** [85]. The microplastic interfaces with pollutant chemicals and biofilms. In this system the plastic surface can be composed of pollutant chemical, biofilm, or biofilm contaminated with pollutant. With time the interactions of microorganisms and microplastics modify pollutant characteristics establishing how and why cells attach to plastic particles. The complexity of the relationship between plastic particles and microorganism attachment relies on factors influencing community development of biofilm and physical characteristics of microplastic particles.

**311**

as biofouling [90].

*The Importance of Biofilms to the Fate and Effects of Microplastics*

Plastics contaminating aquatic environments have been shown to hold various pollutant chemicals arising from the plastic manufacture and environmental pollution. Understanding of sorption and desorption of chemicals by plastics is pivotal to the evaluation of plastics, and their role is important to the environmental dynamics of these chemicals and as a vector of pollution and human health concerns [86]. The chemicals can be of inorganic and organic composition. Environmental microplastic pollution is an assembly of effects found in freshwater and marine conditions relating the complex interrelationship of physical processes, pollutant chemicals, and biota in the formation of biofilms. Sorption of chemicals and microbes to microplastic surfaces involves sorption of chemicals and biota directly to the plastic surface that may or may not be covered with other pollutant chemicals or biofilm. Direct sorption of chemicals to the plastic or biofilm covered plastic

The sorption of neutral chemicals to solids from a water phase requires partitioning of freely floating or partially dissolved organic chemical moieties from an aqueous phase to a plastic surface [87, 88]. Factors affecting the partitioning process are the magnitude of the sorption coefficient, temperature, pH, and other coexisting organic and inorganic constituents present in the water phase [89]. The environmental partitioning process is seldom if ever at equilibrium and non-equilibrium conditions describe the general status of environmental conditions. Stagnant or quiescent conditions in the environment may come the closest to equilibrium partitioning conditions. Non-equilibrium conditions in environmental aquatic systems arise from turbulent conditions ranging from flows through broken or incomplete flow paths found in freshwater streams, sea wave action, and wind and turbulent weather-related phenomena. Sorption properties are also related to phenomena such as the chemical/physical properties of the solid, the extent of physical degradation, biodegradation, and agglomerating processes such

Sorption is a physical process of the environment where chemicals are transferred from a fluid phase such as water and air to a solid phase [91]. The term "sorption" collectively refers to both absorption and adsorption which are components of the sorption process. Molecular penetration of a chemical and association within a solid phase matrix defines absorption [92]. Whereas, adsorption refers to a process

*DOI: http://dx.doi.org/10.5772/intechopen.92816*

*Microplastic formation and environmental degradation.*

**5.1 Sorption**

**Figure 3.**

surface may exhibit different effects.

*The Importance of Biofilms to the Fate and Effects of Microplastics DOI: http://dx.doi.org/10.5772/intechopen.92816*

**Figure 3.** *Microplastic formation and environmental degradation.*

### **5.1 Sorption**

*Bacterial Biofilms*

solid surface [77].

chemistry [80].

biofilm attachment [84].

**5. Environmental effects and fate**

biofilm and physical characteristics of microplastic particles.

microbial colonization and biofilm formation. The adhesion of individual bacteria to a surface-initiated biofilm formation is supported by a collection of factors arising

Bacteria communicate with one another using chemical signal molecules [75]. This process, termed quorum sensing, allows bacteria to monitor the environment to adjust community behavior at a population-wide scale in response to community changes in the number and species present [76]. The information conveyed by these molecules works to synchronize activities for a wide group of cells. This cell-to-cell communication is used by bacteria to coordinate population density-dependent changes in behavior. Quorum sensing involves the production of and response to diffusible or secreted signals, which can vary substantially across different types of bacteria and important to the first stage of encounter between a bacterium and a

Initial bacterial adhesion to a surface, bacterial mass transport, the role of substratum surface properties in initial adhesion and the transition from reversible to irreversible adhesion have been analyzed through a physiochemical lens to yield great insight. Surface thermodynamics and Derjaguin Landau Verwey Overbeek analyses can describe bacterial support using smooth, inert colloidal particles to estimate bacterial cells. A depiction of initial bacterial adhesion to surfaceprogrammed biofilm growth was found to have four major stages: bacterial mass transport towards a surface, reversible bacterial adhesion, conversion to irreversible adhesion, cell wall deformation, and associated developing properties [78]. The production of EPS can be surface-programmed [79]. Initial bacterial adhesion to surfaces and biofilm growth at the solid surface is driven by aspects of physico-

Bacterial adhesion is important to the fate and transport of plastics in aquatic environments. There has been no systematic investigation of bacterial adhesion to different types of plastics. A limited evaluation of short-term and long-term adhesion for different types of bacteria and four types of plastics, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC), was conducted [81]. The target physicochemical factors of surface charge, hydrophobicity/hydrophilicity, roughness, and plastic hardness were characterized. Surface hardness of the plastics was identified as a major factor dominating the adhesion of bacteria onto plastic surfaces in contrast to the other factors [82]. There were significant differences in bacterial cell adhesion for the types of plastics. The different plastic types influenced the bacterial adhesion due to intrinsic surface properties in both short- and long-term studies [83]. Generally, surface roughness, topography, surface free energy, surface charge, electrostatic interactions, and surface hydrophobicity are anticipated to be important to the process of

A complex network of interactions existing among the physical, chemical, and biological aspects of microplastics in an aquatic environment is shown in **Figure 3** [85]. The microplastic interfaces with pollutant chemicals and biofilms. In this system the plastic surface can be composed of pollutant chemical, biofilm, or biofilm contaminated with pollutant. With time the interactions of microorganisms and microplastics modify pollutant characteristics establishing how and why cells attach to plastic particles. The complexity of the relationship between plastic particles and microorganism attachment relies on factors influencing community development of

from initial adhesion to the growth of a mature biofilm [74].

**310**

Plastics contaminating aquatic environments have been shown to hold various pollutant chemicals arising from the plastic manufacture and environmental pollution. Understanding of sorption and desorption of chemicals by plastics is pivotal to the evaluation of plastics, and their role is important to the environmental dynamics of these chemicals and as a vector of pollution and human health concerns [86]. The chemicals can be of inorganic and organic composition. Environmental microplastic pollution is an assembly of effects found in freshwater and marine conditions relating the complex interrelationship of physical processes, pollutant chemicals, and biota in the formation of biofilms. Sorption of chemicals and microbes to microplastic surfaces involves sorption of chemicals and biota directly to the plastic surface that may or may not be covered with other pollutant chemicals or biofilm. Direct sorption of chemicals to the plastic or biofilm covered plastic surface may exhibit different effects.

The sorption of neutral chemicals to solids from a water phase requires partitioning of freely floating or partially dissolved organic chemical moieties from an aqueous phase to a plastic surface [87, 88]. Factors affecting the partitioning process are the magnitude of the sorption coefficient, temperature, pH, and other coexisting organic and inorganic constituents present in the water phase [89]. The environmental partitioning process is seldom if ever at equilibrium and non-equilibrium conditions describe the general status of environmental conditions. Stagnant or quiescent conditions in the environment may come the closest to equilibrium partitioning conditions. Non-equilibrium conditions in environmental aquatic systems arise from turbulent conditions ranging from flows through broken or incomplete flow paths found in freshwater streams, sea wave action, and wind and turbulent weather-related phenomena. Sorption properties are also related to phenomena such as the chemical/physical properties of the solid, the extent of physical degradation, biodegradation, and agglomerating processes such as biofouling [90].

Sorption is a physical process of the environment where chemicals are transferred from a fluid phase such as water and air to a solid phase [91]. The term "sorption" collectively refers to both absorption and adsorption which are components of the sorption process. Molecular penetration of a chemical and association within a solid phase matrix defines absorption [92]. Whereas, adsorption refers to a process

where molecules are confined at the interface between fluid and solid phases as an adherent physical form [93]. Sorption is directly related to properties of the solid, a chemical, and the surface-to-volume ratio of the solid which for microplastic particles is quite large [94]. Apart from surface area, plastics exhibit a range of properties and dimensions, implying the relevance of absorption and adsorption to understanding the importance to the understanding of microplastics' fate and effect. Physisorption or physical sorption occurs from noncovalent intermolecular interactions such as van der Waals interactions. The interaction forces of solids and chemicals though the noncovalent interactions and their combinations and physisorption are usually reversible. Generally, the sorption of materials and chemicals to environmental solids is by physisorption.

### **5.2 Chemicals**

Microplastics can sorb and accumulate both organic and inorganic contaminants detrimental to humans and ecosystem life when released to organisms that may ingest them [95]. Sorption is a major determinant for bioavailability and contributes to the effects of combined exposure to chemicals and microplastics related to the toxicity and bioaccumulation in humans and ecosystem flora. Neutral charged areas of the microplastic surface offer attractive settings for deposition of chemicals due to attractive hydrophobic forces. This is in contrast with hydrophilic or charged compounds that are attracted to the negative-charged areas on the microplastic surface through electrostatic interactions and aquatic media characteristics [94, 96]. Organic chemicals associated with microplastic debris are typically in the semi-volatile or non-volatile categories such as polychlorinated biphenyls and some organic pesticides [97, 98]. Inorganic chemical species are generally ionic. Fuel chemicals and other higher-boiling constituents can be found in the microplastic debris [88, 99–103]. Weathering can be significantly changed the composition containing volatile compounds.

Sorption evaluations can identify the chemicals with higher affinity to microplastics under a variety of environmental conditions. Bench scale sorption studies permit the evaluation of the mass balance for a specific chemical or chemical mixtures. The distribution of chemicals in an environment contaminated with microplastics can be estimated from experimentally determined sorption capacities. Toxicity parallels sorption data, but greater sorption to microplastics does not necessarily lead to higher toxicity or bioaccumulation of a pollutant chemical.

### **5.3 Buoyancy and aggregation**

Biofilm formation at the surface of microplastics may lead to density changes of particles that alter the specific gravity for the mass of microplastic debris [104]. Mineral detritus when incorporated in microplastic debris will increase the density which leads to sinking. Biofilm distribution and bioavailability are expected to be adjusted in response to the buoyancy of microplastics [105]. Biofouling causes changes in the buoyancy of microplastics and, with increasing specific gravity, leads to descension in the water column to a depth of comparable density. Microplastic sampling in the water column can lead to an underestimation of quantities since turbulence leads to vertical mixing.

Aggregate debris formation can be enhanced by biofilm formation on microplastic surfaces commonly expected in situations where diverse bacterial communities colonize the microplastic surfaces. Aggregation has been confirmed by experiment as a factor leading to the apparent removal of microplastics from the surface layer of the marine ecosystems [106].

**313**

*The Importance of Biofilms to the Fate and Effects of Microplastics*

Microplastics aggregate rapidly with biogenic particles found in the marine environment [107]. The incorporation of organic material is accelerated through gross aggregate formation. It is anticipated that natural aggregation dynamics will influence particle size distribution and the export rates of organic matter which

Significant abiotic and biotic conditions exist to show that plastics are vulnerable to these forces found in the environment. Plastic weathering contributes to structural defects and size reduction but incomplete decay. Chemical and physical degradation processes contribute to the overall weathering process. Plastics are composed of a wide variety of chemical structure features that degrade in a spectrum of kinetics under biotic and abiotic conditions. Biodegradation of plastics under aerobic conditions forms new products during the degradation path leading potentially to mineralization forming process end-products such as CO2, H2O, or CH4 depending on the terminal electron acceptor [108]. Oxygen is the terminal electron acceptor for the aerobic degradation process. Aerobic conditions lead to the formation of CO2 and H2O in addition to the cellular biomass of microorganisms during the degradation of the plastic forms. When sulfidogenic conditions are encountered, plastic biodegradation can lead to the formation of CO2 and H2O. Polymer degradation accomplished under anaerobic conditions produces organic acids, H2O, CO2, and CH4. The aerobic process has been found to be more efficient than anaerobic conditions. The anaerobic process produces less energy due to the absence of O2, serving the electron acceptor, which is more efficient in

initial effects of biodegradation are encountered. The biodegradation rate is directly related to the composition of the plastic. The increase of microbial-colonized surface area leads to faster biodegradation rates assuming all other environmental conditions to be equal [110]. Microorganisms can break organic chemicals into simpler chemical forms through biochemical transformation. Plastic biodegradation is a process in which any change in the polymer structure occurs through the structure altering action of microbial enzymes leading to plastic property changes in the form of molecular weight reduction, mechanical strength changes, and surface properties. A more complete understanding of plastic daughter products of environmental degradation is required to more thoroughly understand the effectiveness of envi-

A wide spectrum of pathogenic microorganisms exists and some form biofilms with microplastics in aquatic environments [111]. Freshwater ecosystem analysis has the formation of biofilms on microplastic substrates by a selected grouping of human pathogens utilizing high-throughput sequencing of 16S rRNA that had distinctive community structures [112]. Opportunistic human pathogens such as *Pseudomonas monteillii*, *Pseudomonas mendocina*, and a plant pathogen *Pseudomonas syringae* were detected forming a microplastic biofilm. The opportunistic pathogens were enriched in a biofilm, and the microplastic biofilm exhibited a unique microbial community structure. Distinctive antibiotic resistance genes were detected in the microplastic biofilm. It appears that microplastic surfaces are novel microbial niches and may serve as a vector for antibiotic resistance genetic traits and pathogens in freshwater bodies, engendering environmental risk and exerting adverse

[109]. The exposed surface of plastics is where the

may mirror the similar processes of freshwater and marine ecosystems.

*DOI: http://dx.doi.org/10.5772/intechopen.92816*

**5.4 Plastic biodegradation**

comparison to CO2 and SO4

ronmental plastic degradation.

impacts on human health [113].

*5.4.1 Human health and pathogenicity*

−2

Microplastics aggregate rapidly with biogenic particles found in the marine environment [107]. The incorporation of organic material is accelerated through gross aggregate formation. It is anticipated that natural aggregation dynamics will influence particle size distribution and the export rates of organic matter which may mirror the similar processes of freshwater and marine ecosystems.
