Written by Christine Salinas, Scott Warner and Tim Bradburne, who work for BBJ Group
By BBJ Group August 16, 2023
Written by Christine Salinas, Scott Warner and Tim Bradburne, who work for BBJ Group
Two of the most noteworthy and recently emerged persistent contaminants capturing the attention of regulatory bodies, environmental scientists, the media, and the public are microplastics (MPs) and per- and poly-fluoroalkyl substances (PFAS). These pervasive pollutants, some deem as “forever contaminants,” possess remarkable similarities, including persistence, bioaccumulative potential, and their ubiquitous existence. While their individual impact on the environment has been and continues to be extensively researched, their connection and interaction remain largely understudied1. In Part 1 of this two-part blog, we embark on a journey to unravel the complex and apparent synergistic dance between PFAS and MPs, highlighting some of the current regulatory actions and assessing a sustainable Conceptual Site Model (CSM) framework within a complex environmental system to help with further evaluating the complex relationship involving these two categories of anthropogenic constituents. Part 2 of the blog (to be published in September 2023) will focus on risk management and mitigation approaches.
You can access and download BBJ’s CSM E-book here.
Microplastics and PFAS may seem worlds apart, with one originating from our plastic-dominated society and the other arising from the usage and manufacturing of various industrial and consumer products, respectfully. Synthetic plastics were developed soon after the turn of the twentieth century with mass production generally occurring after World War II2. PFAS chemistry was developed in the late 1930s followed by widespread use for numerous products in manufacturing, defense, medical, and general consumer products increasing substantially in the 1950s3. While these constituents (and their many derivations) are intended for specific uses, their unintentional entry into different environmental and ecological systems became inevitable as life-cycle analyses were not part of the constituent's ultimate evaluation for use. Both categories of constituents, and their derivatives (that is, the chemical and physical transformations of the original constituents) can travel from their origin points through multiple transport mechanisms such as, but not limited to, soil deposition4, wind distribution of fugitive dust5, and leaching into subsurface and surface water environments6. Monitoring has also shown the constituents tend to accumulate within more developed areas (potentially leading to higher levels of contamination and exposure risks1), with both PFAS and MPs also detected at the highest elevations7 on Earth and broadly throughout the Earth’s seas and oceans8. It is also imperative to remember that improper disposal of anthropogenically generated waste9, such as in landfills or wastewater treatment facilities, can contribute to further dissemination and widespread existence1. When PFAS and MPs coexist in the environment, they create additional and sometimes synergistic conditions related to transport, fate, and transformations in the environment. Some of these conditions may also strengthen the persistence and increase the distribution of these constituents1 (Figure 1).
While the documented impacts of MPs and PFAS, individually, are becoming more widely known, their interaction remains enigmatic. As scientists delve into this collusion, many questions have arisen. Are MPs serving as carriers for PFAS, increasing their mobility and enhancing their potential to spread throughout ecosystems? Can the presence of PFAS in the environment alter the face and behavior of microplastics, affecting their distribution and potential harm?
Kang et al., in 20231 recently determined that PFAS and MPs can adsorb and sorb substances onto their surfaces. PFAS, being hydrophobic in nature, have an affinity for organic compounds like MPs. Another mechanism, electrostatic interaction, may also increase the interaction between the constituents as the charged functional groups of anionic, cationic, and zwitterionic PFAS can be drawn toward the charged surfaces of MPs1,10,11. When both PFAS and MPs have neutral charges on their surfaces, neutral electrostatic interactions can occur between them. The organofluorine molecule charge, as well as the length, structure, and MP surface chemistry, can affect the interaction between them. Other environmental factors, such as the presence of organic matter and pH can also influence the strength and nature of these interactions10,11.
For both types of interactions, PFAS may adhere to the surface of MPs, potentially amplifying each constituent’s concentration in the environment. The research into understanding how these interactions influence behavior and fate within the environment under varying in-situ conditions continues to be a primary interest1.
Figure 1- The overlap and interactions between MPs and PFAS; where the central yellow circle indicates the overlap and mechanisms of interaction and blue and purple circles encapsulate individual characteristics of MPs and PFAS, respectively. Modified from Kang et al., 20231.
Regulators strive to keep pace in an era of rapidly evolving information on the occurrence, distribution, risk, fate, migration, and risk potential of emerging contaminants. Analyzing risks associated with new industries, novel substances, and uncharted territories, they shoulder the burden of ensuring safety amidst uncertainties.
Regulatory action is the process through which authorities promote safeguards to public health and the environment. Each action requires a harmonious blend of science, legislation, and application with jurisdictions in different geographies often taking different tactics to implement regulatory guidance and action. Examples of the current actions being taken include, but are not limited to, the following:
Monitoring and tracking the presence of MPs and PFAS in the environment present unique challenges. The need for both constituents to utilize specific monitoring techniques and advanced analytical methods further compounds the limitations of cost and time consumption. Moreover, the pervasive presence of these constituents in various sources complicates the process of tracing and tracking their existence. Here are some notable variations among the methods used to detect these contaminants:
Microplastics:
PFAS:
The use of analytical methods to determine the extent of contamination is essential for developing effective CSMs, which in turn, are used to assess the risk and mitigation strategies.
The CSM plays a pivotal role in an environmental assessment as it is arguably the most essential organizational tool for creating a road map to characterize a site for contaminant sources, migration pathways, potential receptors, future scenarios, and risk mitigation (including remediation) strategies. Crafting an accurate and representative CSM is akin to assembling a jigsaw puzzle where misplaced pieces may lead to inaccurate results, but where missing pieces highlight uncertainty as a problem in knowing what an accurate picture looks like. Lack of clarity and lack of confidence in site characterization, whether for PFAS, MPs, or other constituents not only limits the number of alternatives available for mitigating a problem but could exacerbate the economic cost by leading to the selection of an overly conservative potential remedy that may be substantially overdesigned to accompany the high degree of uncertainty that describes a given contaminant problem. However, perfection is not the objective of the CSM, and in fact, its pursuit may be detrimental – but increased clarity and confidence, even if not complete, leads to better and more protective risk management outcomes.
Here are a few of the challenges when constructing a thorough CSM regarding MPs and PFAS:
Navigating through the intricacies of regulatory action and CSM development may seem like an arduous endeavor, but amidst challenges lies innovation.
Advanced analytical techniques, such as machine learning, are also emerging alongside these contaminants and they hold great promise in unlocking insights and data reservoirs. However, there are some components that still need to be addressed when forging a new CSM framework. Historically, remediation design processes have often overlooked the impacts of fluctuating climatic, hydrological, and biogeochemical characteristics and how the transient nature of these compartments influences contaminants such as MPs and PFAS. Developing a new CSM framework, to acknowledge the influence of anthropogenic stresses and processes (Figure 2) on the hydrobiogeochemical environment as it changes throughout time is key for a remedy to be resilient and durable23.
Figure 2 - Framework development of the PGBC site model that incorporates physical, chemical, and biological stress on phase transfers and reactions. CA and CB represent the chemical fate at the initial and next time steps, while ΣKAB is the sum of climatic influence integrated over time (Taken from Warner et al., 202323).
Check out how BBJ Group’s Jenna Chaffeur explains the integration of Mass Flux into a CSM framework.
Plastic is everywhere, and MPs, whether developed by intention or as a physical degradation part of larger plastic components are being described as ubiquitous in the environment. Factors such as UV radiation, mechanical abrasion, and microbial activity can reduce the size of the particles, but full degradation is elusive24.
PFAS are compounds that have exceptional chemical stability due to their C-F bond25, which also makes PFAS difficult to break down in the environment. However, certain environmental processes can partially transform via several mechanisms such as photolysis, hydrolysis, and biodegradation26.
As science is finding, while PFAS and MPs are different substances that have environmental impacts, their interactions with each other within the environment are creating additional complications regarding environmental health and protection. The degradation of MPs leads to the release of smaller particles, including nano plastics, which can carry PFAS compounds and contribute to further distribution and deposition1. Furthermore, PFAS undergo chemical transformations in the environment leading to the formation of more persistent compounds that can adhere to the microplastics and affect their toxicity, which creates dynamic and complex pollution ubiquitously1.
Constructing an accurate CSM framework that considers a transient environment requires careful consideration of numerous factors, including the individual impacts of MPs and PFAS and their synergistic effects. Anthropogenic stresses, such as the release of these substances into the environment, must be accounted for to accurately assess the risks they pose23. To identify how MPs and PFAS move throughout the environment, several steps can be taken to understand their pathways:
Creating a CSM framework to acknowledge the influence of anthropogenic behavior and processes on the hydrogeochemical environment as it changes through time21 will result in efficient risk management techniques and a remedial approach, which we will discuss in Part 2. Developing a CSM is inevitable as our comprehension of the intricate relationships between environmental contaminants and ecological systems advances.
2 Polymer History: Designed Monomers and Polymers: Vol 11, No 1 (tandfonline.com)
3 Historical and current usage of per‐ and polyfluoroalkyl substances (PFAS): A literature review - Gaines - 2023 - American Journal of Industrial Medicine - Wiley Online Library
4 https://www.sciencedirect.com/science/article/pii/S0048969721025158
5 https://www.sciencedirect.com/science/article/pii/S2468584421000817#bib15
8 https://link.springer.com/article/10.1007/s11356-023-28314-1
9 https://www.sciencedirect.com/science/article/pii/S0269749122000744
10 https://www.sciencedirect.com/science/article/pii/S2667010021000214
11 https://www.sciencedirect.com/science/article/abs/pii/S0039914018312451
12 https://www.epa.gov/sdwa/drinking-water-health-advisories-pfoa-and-pfos13 https://www.bclplaw.com/en-US/events-insights-news/pfas-update-state-soil-concentration-regulations-july-2023.html
14 https://echa.europa.eu/substance-information/-/substanceinfo/100.251.389
15 https://eur-lex.europa.eu/eli/dir/2019/904/oj
16 https://www.dcceew.gov.au/environment/protection/waste/plastics-and-packaging/plastic-microbeads
17 https://www.unep.org/resources/report/global-partnership-marine-litter
18 https://repository.library.noaa.gov/view/noaa/10296
19 https://www.epa.gov/system/files/documents/2021-09/method_1633_draft_aug-2021.pdf
22 https://chemrxiv.org/engage/chemrxiv/article-details/640e7b92e53eff1af309157d
24 https://www.sciencedirect.com/science/article/pii/S0269749122003736
25 https://www.sciencedirect.com/science/article/pii/S0960852421015650
26 https://www.sciencedirect.com/science/article/pii/S2213343722000744
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