Edited by: Daniel Rittschof, Duke University, United States
Reviewed by: Eric Holm, Naval Surface Warfare Center Carderock Division, United States; Justin I. McDonald, Department of Primary Industries and Regional Development of Western Australia (DPIRD), Australia; Sonia Gorgula, Department of Agriculture and Water Resources, Australia
This article was submitted to Coastal Ocean Processes, a section of the journal Frontiers in Marine Science
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
The accumulation of aquatic organisms on the wetted surfaces of vessels (i.e., vessel biofouling) negatively impacts world-wide shipping through reductions in vessel performance and fuel efficiency, and increases in emissions. Vessel biofouling is also a potent mechanism for the introduction and spread of marine non-indigenous species. Guidance and regulations from the International Maritime Organization, New Zealand, and California have recently been adopted to address biosecurity risks, primarily through preventive management. However, appropriate reactive management measures may be necessary for some vessels. Vessel in-water cleaning or treatment (VICT) has been identified as an important tool to improve operating efficiency and to reduce biosecurity risks. VICT can be applied proactively [i.e., to prevent the occurrence of, or to remove, microfouling (i.e., slime) or prevent the occurrence of macrofouling organisms – large, distinct multicellular organisms visible to the human eye], or reactively (i.e., to remove macrofouling organisms). However, unmanaged VICT includes its own set of biosecurity and water quality risks. Regulatory policies and technical advice from California and New Zealand have been developed to manage these risks, but there are still knowledge gaps related to the efficacy of available technologies. Research efforts are underway to address these gaps in order to inform the regulatory and non-regulatory application of VICT.
Biofouling is the accumulation of aquatic organisms on immersed surfaces. Biofouling on maritime vessels is an ongoing burden for owners and operators (reviewed by
Vessel biofouling is also an important pathway for the human-mediated transport of marine non-indigenous species (NIS). For example, the biofouling pathway is a potential means of transfer for more than 80% of New Zealand’s and 60% of California’s marine and estuarine NIS (
While not all NIS have associated impacts, a subset of NIS have a broad range of impacts on the marine environment and the people reliant upon it (see
Because of the difficulty in predicting the impacts that marine NIS may have, a preventive approach has been identified as the most effective way to manage the biosecurity risks associated with vessel biofouling (
To minimize the risk of marine NIS transfers associated with the vessel biofouling pathway, guidelines (
Acronyms describing the different methods of in-water cleaning or treatment (VICT).
VICT | Vessel in-water cleaning or treatment |
PIT | Proactive in-water treatment |
PIC | Proactive in-water cleaning |
PICC | Proactive in-water cleaning and capture |
RIT | Reactive in-water treatment |
RIC | Reactive in-water cleaning |
RICC | Reactive in-water cleaning and capture |
There are two approaches to VICT:
Incidental amounts of macrofouling can establish on a vessel’s submerged surfaces even under best management practices (
Regardless of the approach (i.e., proactive or reactive), two types of environmental risk are identified that may require management (
Identification of biosecurity [B] and chemical contamination [C] risks associated with operation of reactive in-water cleaning and capture (RICC) systems [Adapted from
The release and environmental accumulation of chemical contaminants associated with antifouling coating systems; and
The release of marine NIS (as adults, larvae, or viable propagules) into new environments (
To provide regulators, vessel-related industries, and system operators with a scientific basis for the appropriate application of VICT, an understanding is needed of the risks associated with its application. This understanding requires a solid evidence-base from which to inform decision making (
This review provides a summary of the current knowledge regarding environmental risks and benefits of VICT technologies applied to external hull surfaces of commercial vessels (e.g., PIC, RIC). Also addressed are the technical obstacles related to the regulatory acceptance and responsible use of these tools to manage biosecurity and chemical contamination risk based on the experiences of New Zealand and California. In-water treatments (e.g., PIT, RIT) are not included in this manuscript, as efficacy of these methods has been recently reviewed by
Current cleaning and treatment approaches (
Summary of approaches to vessel in-water cleaning or treatment (VICT) of commercial vessels (
Cleaning | Remove material from the hull. | Manual removal (e.g., powered and non-powered hand-held tools). | PIC | RIC | PICC RICC |
Mechanical removal (e.g., brush-based, cutting head, and water jet-based systems, diver-operated carts, remotely operated vehicles (ROVs) and robots). | PIC | RIC | PICC RICC | ||
Treatment | Render the fouling non-viable. Subsequent vessel movement sloughs dead biofouling from the hull. | Surface-treatment (e.g., heat and ultrasonic). | PIT | RIT | N/A |
Shrouding* (e.g., encapsulation and enclosure). | N/A | N/A | N/A |
The management of biofouling on hulls and other immersed vessel surfaces is typically achieved by the application of antifouling systems, including antifouling coatings, to prevent or minimize the accumulation of organisms (
Non-biocidal coating systems have physical properties to impair attachment (e.g., silicone-based fouling release coatings) or allow regular or abrasive cleaning with minimal effect on the surface (e.g., hard coating systems that are mechanically resistant to damage).
Biocidal coating systems prevent the attachment and growth of biofouling organisms through the release of biocides, such as copper and zinc compounds. Copper is the most commonly used biocide, however, co-biocides are often incorporated into coating systems to ensure efficacy over a range of species (
Conducted appropriately, PIC that is consistent with most antifouling system manufacturer’s recommendations may result in discharges that meet local standards or requirements (
Using the model,
The total quantity of copper released into the environment during the
Reactive in-water cleaning methods, including abrasive brush systems and high-pressure water jets, may abrade biocidal antifouling coatings resulting in contaminant release into the surrounding marine environment (
A range of factors influence the nature of discharges associated with RIC and RICC. These include the type(s) and age of the antifouling coating systems cleaned, the submerged areas cleaned, the amount and type of biofouling present, the method of in-water cleaning, and the hydrodynamic environment (
Independently derived and publicly available data on the release of contaminants associated with RIC and RICC on actual vessels are scarce. Mean total copper concentrations in samples taken from the discharge plume from the Submerged Cleaning and Maintenance Platform (SCAMP) during the cleaning of three US Navy vessels ranged from 1.57 to 2.62 mg/L. The mean range of the dissolved copper fraction was 66 to 146 μg/L. The mass of copper released was estimated to be 4.8 g/m2 of surface cleaned (
The effluent treatment system consisted of a particulate filter followed by a weir tank, which discharged through a filter cartridge array consisting of a 100 μm stainless steel mesh screen, two 10 μm filter cartridges in series, and a 5 μm filter cartridge. Effluent then entered a pressure vessel containing 2,000 pounds of organoclay (modified zeolite).
Treatment through the system, including two passes through the pressure vessel, reduced both the total and dissolved copper concentration in the effluent to less than 100 μg/L. The concentration of total and dissolved zinc was reduced to approximately 600 μg/L. The pressure vessel containing organoclay removed approximately 80% of the dissolved copper and approximately 25% of the dissolved zinc from the cleaning effluent (
The
Using the MAMPEC model,
While PIC is likely to release significant amounts of microbial material and microscopic stages of macrofouling species into the marine environment, the biosecurity risk of proactive cleaning is widely viewed as acceptable, as it is currently not possible to manage vessel biofouling below the level of a slime layer (
The effects of PIC and PICC on antifouling coatings is also important with respect to assessing the overall minimization of biosecurity risk (
From a biosecurity perspective, if PIC or PICC is permitted, it will be necessary to ensure with a high level of certainty that there are no specific biosecurity risks associated with the vessel (i.e., only a slime layer is being removed). Factors such as voyage history, cleaning history, and a pre-inspection of the areas to be cleaned may be considered prior to deployment (
Reactive in-water cleaning systems can facilitate the release (e.g., stress-induced spawning, larval release, or non-capture of fragments) and establishment of marine NIS (
While RICC systems are being developed to mitigate the biosecurity risks associated with this activity (
Cleaning efficacy is generally lower with harder types of fouling (e.g., calcareous or shell-forming species) and greater fouling extent (
While effluent treatment is a key component of a biosecure RICC system, it needs to be practically achievable.
Alternatives to filtration include effluent treatment via heat, biocides, or ultra-violet (UV) light to render propagules within the effluent non-viable, or direct disposal into municipal sewerage with secondary treatment (
Reactive in-water cleaning and RICC systems can physically damage antifouling coating systems or accelerate their biocide release rates, shortening the overall service life. Rapid re-fouling of such coatings subsequently increases the biosecurity risk for future recipient ports and reduces vessel operating efficiency (
Approvals from the relevant authorities are often required to ensure that biosecurity and chemical contamination risks are being managed prior to undertaking VICT.
In New Zealand, discharges associated with VICT are governed by different legislative regimes including, but not limited to: the Resource Management Act 1991 (Ministry for the Environment; Department of Conservation), Biosecurity Act 1993 [Ministry for Primary Industries (MPIs)], Maritime Transport Act 1994 (Maritime New Zealand), and the Hazardous Substance and New Organisms Act 1996 (Environmental Protection Authority). Local government (i.e., Regional Councils and Unitary Authorities) also have responsibilities under the Resource Management Act and the Biosecurity Act. This makes for a complex regulatory management regime which may present unnecessary practical barriers for vessel and VICT operators to achieve compliance (Trecia Smith, Personal Communication, September 2018, Ministry for Primary Industries, New Zealand).
To ensure the biosecurity risks associated with VICT are managed, MPI has commissioned research to inform the development of performance criteria and evaluation methods for RICC systems (
The regulation of VICT in California falls under multiple jurisdictions. Water quality and chemical contamination risks are currently regulated under the U.S. Clean Water Act’s (CWA) National Pollutant Discharge Elimination System (NPDES), the California Toxics Rule, and applicable water quality control plans including, but not limited to, the California Porter-Cologne Water Quality Control Act, the Clean Coast Act, the California Ocean Plan, the California Environmental Quality Act, and the Marine Managed Areas Improvement Act. Traditional PIC, RIC, and RIT systems (i.e., systems that do not include capture and effluent treatment) are all covered and permitted under the U.S. Environmental Protection Agency’s Vessel General Permit for Discharges Incidental to the Normal Operation of a Vessel (VGP), under authority of the CWA. California’s State Water Resources Control Board has added requirements to the VGP, essentially prohibiting VICT of copper-containing antifouling coating systems within waterbodies that have been listed by the U.S. Environmental Protection Agency through the CWA Section 303(d) (see
Proactive and reactive in-water cleaning and capture systems (i.e., PICC, RICC), however, produce a new discharge (i.e., effluent from the RICC filtration or treatment system) that may not be covered by the VGP. In these cases, vendors of PICC and RICC systems may be required to obtain individual NPDES permits or comply with general NPDES permits to operate in specific waterbodies, with discharge limits that vary depending on the level of existing copper impairment in that waterbody. The San Francisco Bay Regional Water Quality Control Board has issued an in-water vessel hull cleaning best management practices document that describes system configuration and discharge limits for allowable PICC and RICC operations within the San Francisco Bay (see
The current regulatory regime governed by the NPDES program and the VGP will change over the next 4 years, as the U.S. Environmental Protection Agency and the U.S. Coast Guard develop and implement new regulations required by the Vessel Incidental Discharge Act (VIDA) enacted in December 2018. The VIDA regulations will supersede and replace the requirements set through the VGP and will presumably cover PIC and RIC operations. However, uncertainty still exists about whether the VIDA regulations will also apply to PICC and RICC systems, as the VIDA narrowly applies to “discharges incidental to the normal operation of vessels,” essentially the same discharges that are currently covered by the VGP.
Biosecurity risks are managed in California by the State Lands Commission (the Commission) under the Marine Invasive Species Act. Commission staff are working cooperatively with regional counterparts (in nearby coastal states) through the Coastal Committee of the Western Regional Panel on Aquatic Nuisance Species to develop a consistent set of requirements to minimize biosecurity risks. These regionally consistent requirements would then be used by the local Regional Water Quality Control Boards agencies issuing NPDES permits, in concert with their own water quality requirements, to evaluate permit applications (see
There is a paucity of robust and independently generated data to inform the assessment of biosecurity and chemical contamination risk arising from VICT using currently available technologies. This lack of reliable data has created significant uncertainty regarding approvals for VICT use (
Transparent and robust system evaluations conducted by appropriately qualified independent providers have the potential to facilitate the generation of VICT system data that has wide regulatory applicability, thus decreasing stakeholder costs and regulatory burden. As an appropriate analog, the accepted approach for the approval of ballast water management systems relies on aligned analytical and evaluation procedures and reporting of results (
Ministry for Primary Industries and the Commission have recently contributed funds and resources toward research programs aimed at providing protocol development for, and independent evaluations of, reactive in-water cleaning and capture (RICC) and proactive in-water cleaning (PIC) systems (
Vessel based evaluation using the full VICT system (e.g., cleaning head, effluent treatment system);
VICT system evaluations should be a simulation of the intended use of the system (e.g., systems designed to remove hard fouling should be evaluated on hard fouling at the peak coverage of intended use; systems should be evaluated on different vessel surfaces as applicable to their intended use);
VICT system evaluations should be conducted and supervised by appropriately qualified and approved, independent scientists (i.e., evaluation conduct and reporting should be objective and not be subject to bias);
All evaluation failures should be reported (i.e., reporting should be transparent).
Ministry for Primary Industries has also recently commissioned research to help strengthen New Zealand’s approach to manage VICT across the various regulatory regimes (
In addition to New Zealand and California, the Australian Government is endeavoring to create nationally consistent standards for VICT (
Vessel in-water cleaning or treatment regulatory authorities may include in their considerations the importance of marine stewardship at both domestic and international levels. For example, broad and inflexible prohibition of VICT is likely to reduce the incentive to develop environmentally acceptable technologies and encourages cleaning in locations where environmental considerations may be lower (
Vessel biofouling is not evenly distributed across the surface of a hull. Areas that are protected from a constant or uniform water flow, or susceptible to wear or damage of the antifouling coating tend to accumulate a higher biomass of organisms (
Given the difficulty of accessing niche areas relative to the general hull, there is little research, and thus much uncertainty, with respect to the efficacy of VICT for internal seawater systems (
Vessel in-water cleaning or treatment has significant benefits as a tool to optimize vessel efficiency and curb emissions. However, considerable uncertainty exists with respect to the management of environmental risks associated with VICT technologies. Although the goals of some of the more recent technologies includes the minimization of biosecurity and chemical contamination risks, hastening the use of these tools before they have been properly evaluated may result in unacceptable risk to core values. Therefore, data generated to enable system approval should be subject to appropriate validation. Ongoing or recently completed research programs (see
The following actions would further facilitate the development of VICT technologies and our understanding of their associated risks (if any):
Identification and process mapping of relevant legislation and regulatory regimes responsible for approvals, application of consenting conditions, and ongoing monitoring within jurisdictions;
Setting of practical and feasible performance criteria, particularly for reactive systems, that minimize biosecurity and chemical contamination risks, as applicable;
Development of robust and transparent procedures for independent system evaluation and reporting;
Development of an agreed approach for system approvals within and across jurisdictions, as possible.
Both authors contributed equally to the development of this manuscript.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Nicole Dobroski, Justin Wood, and Julisa Portugal (California State Lands Commission), Mario Tamburri (University of Maryland Center for Environmental Science), and Abraham Growcott, Christine Reed, Sudharma Leelawardana, Daniel Kluza, Trecia Smith, Tanayaz Patil, and Steve Hathaway (Ministry for Primary Industries) reviewed the draft versions of the manuscript. The input of the three reviewers greatly improved this manuscript.