The Hidden Threats of Biofouling and Microbiologically Influenced Corrosion—Implications for Coatings Science and Sustainable Infrastructure

Biofouling and microbiologically influenced corrosion (MIC) pose profound allied threats, both visible and invisible, across global industrial and societal infrastructures, encompassing both stationary and mobile systems, such as maritime shipping, aquaculture, offshore and onshore energy platforms, desalination and wastewater treatment and distribution systems.

Both processes often begin imperceptibly, with early-stage microbial adhesion and biofilm formation that the naked eye cannot readily detect. In the case of biofouling, these microscopic communities progressively develop into visible macrofouling layers, such as algae, barnacles, and other organisms, that impair surface performance [1]. MIC, however, remains largely invisible throughout its progression, as microbial activity accelerates chemical and electrochemical corrosion within hidden microenvironments, leading to material degradation that typically becomes evident only after significant damage has occurred. In other words, biofouling evolves from invisible microbial colonization to visible surface overgrowth, whereas MIC is a biologically driven corrosion process that often continues unseen [2]. Together, these processes compromise the integrity, performance, and service life of critical materials, posing significant risks to industrial operations and essential infrastructure, while challenging the long-term sustainability of related activities.

The persistence of these biological processes translates into profound economic, environmental, and strategic costs that extend far beyond routine maintenance. Marine transportation, a sector particularly affected by biofouling, incurs substantial annual costs estimated at around USD 150 billion, and is associated with increased hull drag, fuel consumption, shipping delays, hull degradation, and intensified maintenance [3,4].

These losses, however, represent only a portion of the broader material degradation burden. Corrosion in general, including MIC, accounts for roughly 3%–4% of each nation’s gross domestic product (GDP), with global costs estimated at around USD 2.5 trillion [5,6,7] and MIC alone contributing to up to 20% of these costs in various systems [8,9], or even up to a severe contributor to pipeline integrity failures, with internal MIC implicated in up to 40% of corrosion-related incidents in certain pipeline systems [10].

This subtle nature of biofouling and MIC increases the risk of unexpected failures. Real-world incidents illustrate these risks: in 2006, a pipeline in Alaska’s Prudhoe Bay ruptured, which was associated with MIC issues, releasing over 267,000 gallons of crude oil, disrupting production for weeks, and incurring tens to hundreds of millions of dollars in remediation and fines [11]. Although catastrophic failures of marine infrastructure are rarely attributed only to MIC, the truth is that these are usually related to biothreats, as microbial biofilms and biofouling contribute to localized structural degradation and operational issues. These biofilms accelerate corrosion, promoting pitting, surface deterioration, and reducing the mechanical resistance of infrastructures. Biofouling, on the other hand, further exacerbates degradation by altering surface chemistry and increasing stress [1]. Technical reports by Hill [12] and Hill et al. [13] showed how microbial biofilms in ballast tanks, bilges, and fuel systems accelerate pitting and localized corrosion, weaken protective coatings, and create oxygen and concentration cells that intensify metal degradation. Microbial contamination of marine fuels, including FAME-derived biodiesel and conventional distillates, further promotes biofilm formation in tanks and pipelines, clogging filters and impairing fuel handling systems. Without proactive monitoring, regular inspection, and targeted remediation and preventive measurements, such as biocide treatment, mechanical cleaning, or protective coatings, microbial activity can compromise vessel integrity, shorten service life, and cause substantial economic, environmental, and safety burdens.

The importance of biofouling and MIC management is undeniable in safeguarding maritime infrastructure and the sustainability of industrial activities. Throughout the history of control measures, the balance between effective surface protective strategies and environmental safety has not been achieved. This became clear and raised serious global concerns since the revolutionary generation of antifouling coating protection in the 1960s, marked by the appearance of tributyltin (TBT)-release-based coatings in the marine industry, which further triggered several restrictions on the use of potentially less toxic biocidal substitutes (BPR-Biocidal Products Regulation (EU) No 528/2012). Breaking this barrier is challenging, but efforts are being made, particularly on one of the most suitable strategies for aquatic applications, coatings.

Coatings that inhibit microbial adhesion, impede corrosive processes, and extend service life are essential elements of a broader strategy to safeguard industrial assets, protect ecosystems, and promote sustainable development. Research and development that integrates advanced analytical techniques, biologically informed surface engineering, and environmentally responsible antifouling and anticorrosion solutions are crucial in confronting these complex challenges.

New potential strategies inspired by nature observation have been emerging. Special interest has been given to approaches focused on a hybrid concept, which combines multiple physicochemical defensive mechanisms, mimicking surface features and substances found in organisms and plants. This learning from nature has enhanced the ability to design and tailor chemical and physical surface properties, such as surface energy, wettability, morphology, and physicochemical resistance, allowing coatings to actively adapt to environmental conditions, including temperature, pH, light, biota, and mechanical damage, thereby enabling long-term efficiency. Some examples of these inspired approaches, and only to mention a few, include nano- and micro-topographies [14,15], zwitterionic polymers [16], self-assembled monolayers [17], and non-release biocidal foul-release coatings [18], which aim to confer multifunctionality into a coating relying on non-toxic mechanisms. Some other recent approaches, which reinforce new potential directions, include the use of bioactive natural metabolites [19,20] and bioactive ionic liquids in coatings [21], exploring synergetic antifouling effects by combining different material classes (e.g., organic + inorganic) [22] or even bind them through chemical functionalization approaches (e.g., functionalised nanomaterials) [23,24].

Nevertheless, we are still far from overcoming the complex challenges of biofouling and related processes such as MIC, and, most certainly, we will not be able to mitigate them fully. Instead, we should reinforce our knowledge of their interactions with surfaces and the surrounding environment to learn how to coexist with them. This is because we will always face dynamic challenges in a constantly changing environment. The primary challenge is the complexity of biofouling itself. It involves enormous biodiversity, governed by several key environmental parameters (e.g., temperature, daylight irradiation, nutrient levels, flow rates), which vary seasonally and spatially. A deeper understanding of these biotic communities, particularly the mechanisms involved in biofouling settlement, will undoubtedly help in designing suitable protective coatings.

Another significant and recognized challenge is global warming. Its effects on temperature, together with the increased freshwater inputs, will drive changes in ecosystems. Such disruptions may require a complete reformulation of current diagnostic and monitoring methodologies, as well as coating technologies, since many were originally designed for specific conditions that may no longer exist. In this context, AI, machine learning, and digital twin tools will play a key role, providing data-driven models that can accelerate the development of protective technologies by reducing costs and time required for optimization.

It will not be an easy task to readapt to such emergent challenges. Success will require cooperative effort between researchers and the industry. Nevertheless, the ongoing intensive efforts and the pursuit of innovative strategies have provided promising technologies that encourage the search for new findings to overcome these hidden biothreats.