Portable EcoExposure™ Optical Assay Maintains Microplastic Detection Across Tannin-Rich Environmental and Beverage Matrices

Abstract 

Tannins and other polyphenols are common matrix components in environmental waters and certain consumer products. This technical note evaluates whether the EcoExposure™ smartphone-based optical assay maintains qualitative microplastic and nanoplastic detection capability across tannin-rich liquid matrices. Proof-of-concept testing was conducted using a range of tannin-containing beverages as controlled surrogate matrices (black tea, green tea, coffee, grape juice, cranberry juice, red wine, beer, and cola), supplemented by prior observations in dissolved organic matter-rich environmental waters. Qualitative optical differentiation between control and microplastic/nanoplastic-spiked samples remained observable across all matrices despite substantial variation in color, dissolved organic matter, and tannin content. These findings support the continued development of rapid, field-deployable optical methods for microplastic detection in diverse real-world matrices.

Table 1. Representative Tannin Matrices and Outcomes Between Control and Microplastic-Spiked Samples

Representative Matrix	Matrix Type	Qualitative Optical Differentiation Between Control and Microplastic-Spiked Sample Maintained
Filtered water	Reference	✓
DOM-rich lake water	Environmental	✓
DOM-rich pond water	Environmental	✓
Medium-roast coffee	High-tannin beverage	✓
Cabernet red wine	High-tannin fermented beverage	✓
Grape juice	Tannin-containing fruit juice	✓
Cranberry juice	Tannin-containing fruit juice	✓
Black tea	Tannin-containing tea	✓
Green tea	Tannin-containing tea	✓
Beer	Fermented beverage	✓
Cola	Colored beverage	✓

Introduction 

Tannins and other polyphenolic compounds are major components of natural organic matter in surface waters, lakes, rivers, and drinking water sources. Their presence influences water quality parameters and poses challenges in drinking water treatment, including color and taste issues as well as the formation of disinfection by-products upon reaction with chlorine and other disinfectants. Water utilities routinely monitor and attempt to remove NOM, including tannins, through coagulation, activated carbon, or other processes. 

Microplastics and nanoplastics have been detected in environmental waters worldwide, prompting interest in analytical methods that can perform reliably across matrices with varying natural organic matter composition. Tannins, in particular, can interact with particles and influence aggregation, settling, and optical properties. The objective of this technical note is to highlight tannins and NOM as important matrix considerations for microplastic detection and to discuss the potential role of rapid optical assays in addressing current monitoring limitations.

Natural organic matter, including tannins and other polyphenolic compounds, is a defining characteristic of many environmental waters. Because tannin concentrations vary considerably among watersheds, seasons, weather conditions, and source waters, they create highly variable optical and chemical backgrounds that analytical methods must accommodate.

In drinking water treatment, tannins increase coagulant demand, contribute to color and taste, influence floc formation, and serve as precursors to disinfection by-products. Beyond water treatment, tannins are also recognized as potential interferents in numerous analytical techniques due to their effects on optical measurements, particle interactions, and dissolved organic matter composition.

Consequently, one common question regarding rapid optical microplastic detection is whether elevated tannin concentrations interfere with assay performance.

Objective:

To evaluate whether the EcoExposure™ optical microplastic/nanoplastic assay maintains qualitative detection capability across representative tannin-rich liquid matrices.

Why Tannin-Rich Matrices Matter

Tannins occur naturally throughout environmental waters as components of dissolved organic matter generated from decomposing vegetation, wetlands, peatlands, forested watersheds, and seasonal runoff.

Because tannin concentrations vary substantially according to geography, season, watershed characteristics, and weather events, environmental samples frequently present diverse matrix conditions. Many drinking water utilities routinely monitor and manage tannins because they influence treatment performance through increased coagulant demand, altered flocculation behavior, and formation of disinfection by-products.

As a result, analytical methods intended for environmental deployment should ideally demonstrate compatibility across a broad range of tannin-rich conditions rather than only relatively clean laboratory waters.

Figure 1. Tannins in drinking water treatment: challenges and monitoring needs.

Figure 1. Conceptual overview of the role of tannins in drinking water systems. Tannins derived from decaying vegetation, forests, wetlands, peatlands, and seasonal leaf fall enter surface waters where they contribute to natural organic matter. Elevated tannin concentrations may increase coagulant demand, interfere with flocculation, contribute to sludge production, and serve as precursors to disinfection by-products during drinking water treatment. These operational challenges highlight the importance of analytical methods capable of maintaining performance across naturally variable tannin-rich matrices.

EcoExposure Evaluation Across Tannin-Rich Matrices

To intentionally challenge assay robustness under increasingly complex organic conditions, EcoExposure™ was evaluated using a diverse collection of tannin-rich surrogate matrices.

Representative matrices included:

• Black tea

• Green tea

• Coffee

• Cranberry juice

• Grape juice

• Red wine

• Beer

• Cola

Although these beverages are not intended to replicate environmental waters directly, they provide practical, reproducible systems spanning a wide range of dissolved organic matter, color, and polyphenol composition. They therefore serve as useful challenge matrices for evaluating optical assay robustness before broader environmental deployment.

Figure 2. Representative tannin-rich matrices evaluated using the EcoExposure™ optical microplastic and nanoplastic assay.

Figure 2. Representative environmental and beverage matrices spanning increasing organic matrix complexity evaluated using the EcoExposure™ smartphone-based optical microplastic and nanoplastic assay. Matrices include filtered water, tap water, hard water, tannin-containing beverages (tea, coffee, fruit juice, beer, and wine), and dissolved organic matter-rich environmental waters (lake water, pond water, and saltwater). Despite increasing dissolved organic matter, polyphenol, and tannin content, qualitative optical differentiation between control and microplastic/nanoplastic-spiked samples was maintained across the representative matrices evaluated.

Results

Across all tannin-rich matrices evaluated, EcoExposure™ maintained qualitative optical differentiation between control and microplastic/nanoplastic-spiked samples.

Despite substantial differences in:

• color,

• optical background,

• dissolved organic matter,

• tannin concentration,

• and matrix composition,

qualitative optical differences remained observable.

Response kinetics varied among matrices, indicating that tannins and other dissolved organic compounds may influence the rate at which optical changes develop. However, these matrix effects did not prevent qualitative differentiation between control and microplastic-containing samples.

These observations extend previous proof-of-concept studies demonstrating EcoExposure™ performance in dissolved organic matter-rich lakes, ponds, and other environmental waters.

Relevance to Environmental Monitoring

The present findings suggest that tannins should not necessarily be viewed solely as analytical interferents.

Instead, tannin-rich matrices provide practical challenge systems for evaluating assay robustness under realistic environmental conditions.

Demonstrating qualitative detection across diverse tannin-rich matrices is particularly relevant because natural organic matter is ubiquitous in environmental waters and varies substantially over space and time. Methods capable of operating across these matrix conditions are likely to be more broadly applicable to decentralized environmental monitoring.

For drinking water utilities, environmental researchers, and field monitoring programs, matrix robustness may reduce concerns regarding naturally occurring tannin variability during rapid optical screening.

Conclusions

The principal finding of this technical note is that the EcoExposure™ optical microplastic and nanoplastic assay maintained qualitative optical differentiation between control and microplastic/nanoplastic-spiked samples across a diverse collection of tannin-rich liquid matrices.

This included representative beverage matrices intentionally selected to challenge assay robustness as well as previous proof-of-concept observations in dissolved organic matter-rich environmental waters.

Although tannins are frequently considered potential interferents in environmental and analytical measurements, the present observations suggest that EcoExposure™ remains compatible with substantial variation in tannin content and organic matrix complexity.

These findings support continued development of EcoExposure™ as a rapid, field-deployable optical platform for microplastic and nanoplastic detection across diverse environmental and consumer-product matrices.

This paper is also available at: https://doi.org/10.5281/zenodo.21253330

Representative References Sillanpää, M. et al. (2018). Removal of natural organic matter in drinking water treatment by coagulation: A comprehensive review. Chemosphere.

Matilainen, A. et al. (2010). Natural organic matter removal by coagulation during drinking water treatment: A review. Advances in Colloid and Interface Science.

Crittenden, J.C. et al. (2012). MWH's Water Treatment: Principles and Design (textbook — good for general coagulation challenges).

Zazouli MA, Kalankesh LR. Removal of precursors and disinfection by-products (DBPs) by membrane filtration from water; a review. J Environ Health Sci Eng. 2017 Dec 8;15:25. doi: 10.1186/s40201-017-0285-z. PMID: 29234499; PMCID: PMC5721515.

Appendix:Appendix Figure S1. Major natural sources of tannins in environmental waters.

Appendix Figure S1. Major natural sources contributing tannins and natural organic matter to environmental waters. Forests, wetlands, peatlands, decaying vegetation, soil leaching, storm runoff, and agricultural landscapes contribute varying amounts of dissolved organic matter to streams, rivers, lakes, and reservoirs. These natural processes create geographically diverse matrix conditions that analytical methods may encounter during environmental monitoring.

Appendix Figure S2. Seasonal variation of tannins in surface waters.

Appendix Figure S2. Conceptual illustration of seasonal variation in tannin concentrations within surface waters. Tannin loading is influenced by seasonal vegetation cycles, storm runoff, and hydrologic conditions, with elevated concentrations commonly occurring following autumn leaf fall and major rainfall events. This natural variability contributes to changing dissolved organic matter conditions throughout the year and underscores the value of analytical methods capable of operating across diverse environmental matrices.