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Research on in-situ detection technology for marine biofouling based on photoacoustic signal excitation and detection
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Bacterial biofilms reduce the performance and efficiency of biomedical and industrial devices. The initial step in forming bacterial biofilms is the weak and reversible attachment of the bacterial cells onto the surface. This is followed by bond maturation and secretion of polymeric substances, which initiate irreversible biofilm formation, resulting in stable biofilms. This implies that understanding the initial reversible stage of the adhesion process is crucial to prevent bacterial biofilm formation. In this study, we analyzed the adhesion processes of E. coli on self-assembled monolayers (SAMs) with different terminal groups using optical microscopy and quartz crystal microbalance with energy dissipation (QCM-D) monitoring. We found that a considerable number of bacterial cells adhere to hydrophobic (methyl-terminated) and hydrophilic protein-adsorbing (amine- and carboxy-terminated) SAMs forming dense bacterial adlayers while attaching weakly to hydrophilic protein-resisting SAMs [oligo(ethylene glycol) (OEG) and sulfobetaine (SB)], forming sparse but dissipative bacterial adlayers. Moreover, we observed positive shifts in the resonant frequency for the hydrophilic protein-resisting SAMs at high overtone numbers, suggesting how bacterial cells cling to the surface using their appendages as explained by the coupled-resonator model. By exploiting the differences in the acoustic wave penetration depths at each overtone, we estimated the distance of the bacterial cell body from different surfaces. The estimated distances provide a possible explanation for why bacterial cells tend to attach firmly to some surfaces and weakly to others. This result is correlated to the strength of the bacterium-substratum bonds at the interface. Elucidating how the bacterial cells adhere to different surface chemistries can be a suitable guide in identifying surfaces with a more significant probability of contamination by bacterial biofilms and designing bacteria-resistant surfaces and coatings with excellent bacterial antifouling characteristics.
Photoacoustic imaging, an acoustic imaging modality with potentially optical resolution in an optical turbid medium, has attracted great attention. However, the convergence of wavefront optimization and raster scanning in computational photoacoustic imaging leads to the challenge of fast mapping, especially for a spatial resolution approaching acoustic deep-subwavelength regime. As a sparse sampling paradigm, compressive sensing has been applied in numerous fields to accelerate data acquisition without significant quality losses. In this work, we propose a dual-compressed approach for photoacoustic surface tomography which enables high-efficiency imaging with 3D spatial resolution unlimited by the acoustics in a turbid environment. The dual-compressed photoacoustic imaging with single-pixel detection, enabled by spatially optical modulation with synchronized temporally photoacoustic coding, allows decoding the fine optical information from the modulated acoustic signal even when the variance of original photoacoustic signals is weak. We perform a proof-of-principle numerical demonstration of dual-compressed photoacoustic imaging, that resolves acoustic sub-acoustic-wavelength details with a significantly reduced number of measurements, revealing the potential for dynamic imaging. The dual-compressed concept, which transforms unobtrusive spatial difference into spatiotemporal detectable information, can be generalized to other imaging modalities to realize efficient, high spatial resolution imaging.
Neuroimaging techniques can reveal complex brain functions associated with behaviors and emotions. However, most existing neuroimaging methods suffer from balancing tradeoffs among the temporal and spatial resolutions as well as the field of view (FOV). A high spatiotemporal resolution photoacoustic neuroimaging (PANI) technique with a wide FOV sufficient to cover the entire mouse cerebral cortex in transverse plane and measure fast neuronal dynamics is developed. Based on the experimental validations from both drug‐induced epilepsy and electrical stimulation in the mouse brain, PANI features the following capabilities: i) deriving functional information from the fluctuation of total hemoglobin (HbT) to identify the neural activity and connectivity of the mouse cortex; ii) integrating with other neurological recording methods such as electroencephalograph (EEG) to investigate the neurovascular coupling; and iii) revealing the interactive connectivity between distant brain regions under different physiological conditions. The special features of PANI offer a unique window on investigating the fast neural dynamics with a wide FOV at the capillary scale.
Plasmonic vapor nanobubbles are currently considered for a wide variety of applications ranging from solar energy harvesting and photoacoustic imaging to nanoparticle-assisted cancer therapy. Yet, due to their small size and unstable nature, their generation and consequences remain difficult to characterize. Here, building on a phase-field model, we report on the existence of strong pressure waves that are emitted when vapor nanobubbles first form around a laser-heated nanoparticle immersed in water and subsequently after bubble rebound. These effects are strongest when the fluid is locally brought high in its supercritical state, which may be realized with a short laser pulse. Because of the greatly out-of-equilibrium nature of nanobubble generation, the waves combine a high-pressure peak with a fast pressure rising time and propagate in water over micron distances, opening the way to induce spatially and temporally localized damage. Discussing the consequences on biological cell membranes, we conclude that acoustic-mediated perforation is more efficient than nanobubble expansion to breach the membrane. Our findings should serve as a guide for optimizing the thermoacoustic conversion efficiency of plasmonic vapor nanobubbles.
The present work highlights that the laser diode, acting as an ultrasonic source by photoacoustic effect, can be successfully employed for defect detection in mechanical components; the performed investigation specifically involves a railway axle with cracks on the body and fillets, respectively 13 mm-deep and 2 mm-deep. To ease the inspection process, a methodology for amplification of the ultrasound is introduced which is based on the appropriate choice of the TTL signal modulating the diode; amplification is achieved by constructive interference between two ultrasonic signals: the first is induced by the dilation resulting from the laser ignition, the second conversely derives from the contraction obtained when the laser is powered off. The proposed amplification methodology allows ultrasonic energy to be focused in a narrow range of frequencies, promoting the use of traditional detection devices like narrowband probes. The developed inspection system, which takes advantage of a 20 W source, enables the identification of the ultrasonic pattern and defect detection regardless of the application of post-processing techniques on the acquired signals: allowing for excitation of high-amplitude ultrasound without directly contacting the component, the laser diode represents a suitable source for the non-destructive inspection of the axle while it rotates (i.e., during operation). Thanks to the cost reduction achieved in comparison with the use of more traditional pulsed lasers, the diode lends itself to large-scale application in the field of non-destructive testing on mechanical structures.
The deep ocean below 200 m water depth is the least observed, but largest habitat on our planet by volume and area. Over 150 years of exploration has revealed that this dynamic system provides critical climate regulation, houses a wealth of energy, mineral, and biological resources, and represents a vast repository of biological diversity. A long history of deep-ocean exploration and observation led to the initial concept for the Deep-Ocean Observing Strategy (DOOS), under the auspices of the Global Ocean Observing System (GOOS). Here we discuss the scientific need for globally integrated deep-ocean observing, its status, and the key scientific questions and societal mandates driving observing requirements over the next decade. We consider the Essential Ocean Variables (EOVs) needed to address deep-ocean challenges within the physical, biogeochemical, and biological/ecosystem sciences according to the Framework for Ocean Observing (FOO), and map these onto scientific questions. Opportunities for new and expanded synergies among deep-ocean stakeholders are discussed, including academic-industry partnerships with the oil and gas, mining, cable and fishing industries, the ocean exploration and mapping community, and biodiversity conservation initiatives. Future deep-ocean observing will benefit from the greater integration across traditional disciplines and sectors, achieved through demonstration projects and facilitated reuse and repurposing of existing deep-sea data efforts. We highlight examples of existing and emerging deep-sea methods and technologies, noting key challenges associated with data volume, preservation, standardization, and accessibility. Emerging technologies relevant to deep-ocean sustainability and the blue economy include novel genomics approaches, imaging technologies, and ultra-deep hydrographic measurements. Capacity building will be necessary to integrate capabilities into programs and projects at a global scale. Progress can be facilitated by Open Science and Findable, Accessible, Interoperable, Reusable (FAIR) data principles and converge on agreed to data standards, practices, vocabularies, and registries. We envision expansion of the deep-ocean observing community to embrace the participation of academia, industry, NGOs, national governments, international governmental organizations, and the public at large in order to unlock critical knowledge contained in the deep ocean over coming decades, and to realize the mutual benefits of thoughtful deep-ocean observing for all elements of a sustainable ocean.
For the optoacoustic communication from in-air platforms to submerged apparatus, a method based on speech recognition and variable laser-pulse repetition rates is proposed, which realizes character encoding and transmission for speech. Firstly, the theories and spectrum characteristics of the laser-generated underwater sound are analyzed; and moreover character conversion and encoding for speech as well as the pattern of codes for laser modulation is studied; lastly experiments to verify the system design are carried out. Results show that the optoacoustic system, where laser modulation is controlled by speech-to-character baseband codes, is beneficial to improve flexibility in receiving location for underwater targets as well as real-time performance in information transmission. In the overwater transmitter, a pulse laser is controlled to radiate by speech signals with several repetition rates randomly selected in the range of one to fifty Hz, and then in the underwater receiver laser pulse repetition rate and data can be acquired by the preamble and information codes of the corresponding laser-generated sound. When the energy of the laser pulse is appropriate, real-time transmission for speaker-independent speech can be realized in that way, which solves the problem of underwater bandwidth resource and provides a technical approach for the air-sea communication.
These days, many marine autonomous environment monitoring networks are set up in the world. These systems take advantage of existing superstructures such as offshore platforms, lightships, piers, breakwaters or are placed on specially designed buoys or underwater oceanographic structures. These systems commonly use various sensors to measure parameters such as dissolved oxygen, turbidity, conductivity, pH or fluorescence. Emphasis has to be put on the long term quality of measurements, yet sensors may face very short-term biofouling effects. Biofouling can disrupt the quality of the measurements, sometimes in less than a week.
Many techniques to prevent biofouling on instrumentation are listed and studied by researchers and manufacturers. Very few of them are implemented on instruments and of those very few have been tested in situ on oceanographic sensors for deployment of at least one or two months.
This paper presents a review of techniques used to protect against biofouling of in situ sensors and will give a short list and description of promising techniques.
Adhesion of marine fouling organisms on artificial surfaces such as ship hulls causes many problems, including extra energy
consumption, high maintenance costs, and increased corrosion. Therefore, marine antifouling is an important issue. In this
review, physical and biochemical developments in the field of marine biofouling, which involves biofilm formation and macro-organism
settlement, are discussed. The major antifouling technologies based on traditional chemical methods, biological methods, and
physical methods are presented. The chemical methods include self-polishing types such as tributyltin (TBT) self-polishing
copolymer coatings, which despite its good performance has been banned since 2008 because of its serious environmental impact.
Therefore, other methods have been encouraged. These include coatings with copper compounds and biocide boosters to replace
the TBT coatings. Biological extracts of secreted metabolites and enzymes are anticipated to act as antifoulants. Physical
methods such as modification of surface topography, hydrophobic properties, and charge potential have also been considered
to prevent biofouling. In this review, most of the current antifouling technologies are discussed. It is proposed that the
physical antifouling technologies will be the ultimate antifouling solution, because of their broad-spectrum effectiveness
and zero toxicity.
Keywordsbiofouling–antifouling technology–biofilm–adhesion mechanism
Development of microbial biofilms and the recruitment of propagules on the surfaces of man-made structures in the marine environment cause serious problems for the navies and for marine industries around the world. Current antifouling technology is based on the application of toxic substances that can be harmful to the natural environment. For this reason and the global ban of tributyl tin (TBT), there is a need for the development of "environmentally-friendly" antifoulants. Marine microbes are promising potential sources of non-toxic or less-toxic antifouling compounds as they can produce substances that inhibit not only the attachment and/or growth of microorganisms but also the settlement of invertebrate larvae and macroalgal spores. However, so far only few antilarval settlement compounds have been isolated and identified from bacteria. In this review knowledge about antifouling compounds produced by marine bacteria and diatoms are summarised and evaluated and future research directions are highlighted.
A theoretical formulation of photoacoustic (PA) imaging with a line-focus beam (LFB) for surface and undersurface simulated defect was performed. Equivalence between 2D surface defect photoacoustic tomography (PAT) and X-ray CT was derived. PAT imaging experiment was carried out A second harmonics of a LD-pumped YAG laser was used as a LFB. The laser power was 45mW. The length and width of a laser beam on a specimen was 25 mm times 0.65mm The measured area was 27mm x 27mm, while the reconstructed area was 18mm x 18mm. 64 times 64 resolution image was reconstructed from the rotation and translation scanning. Reconstructed PA image agreed with the PA image obtained with a point-focus PA imaging. The frequency dependence of thermally diffused image agreed well with the theoretical prediction (thermal diffusion length is inversely proportional to the square root of modulation frequency) Under surface PAT image was obtained by a thermal wave diffraction formula, and the simulated image agreed well with the experimental data.
Biofouling is a major issue for many industries including shipping, oil, and gas and can lead to accelerated corrosion, particularly for structures and components in and around salt water. Many efforts are undertaken to lessen its impact and financial losses. One of the promising methodologies is application of antibiofouling coatings to minimize biofouling, and the best results were observed with a superhydrophobic coating. Ample literature reviews on superhydrophobic coating have shown biofouling inhibition on the surface due to high wetting angles similar to the phenomenon on a lotus leaf. The hydrophobic coating can be deposited using multiple techniques such as electroless plating, chemical vapor deposition (CVD), sol–gel, and electrodeposition. In this review, an effort has been made to encompass such experimental work under a single domain and compare the effectiveness of each coating. In addition, mechanical properties and surface characteristics such as wetting angle, surface energy, and morphology were also discussed for various types of polymeric coating. Similarly, the application of nanoparticles such as ZnO, SiO2, TiO2, and CeO2 was found to improve the substrate's mechanical properties, the durability of coatings, improvement in wear properties, adhesion, interlaminar cohesion, and increased wetting angle and above all, improve superhydrophobicity. These improvements are compared for various nanoparticle integrated coatings. In addition, other novel approaches to prevent marine biofouling by various polymer-based coatings such as superhydrophobic, foul-release, and foul-resistant coatings are discussed in this paper.
Surgery represents the mainstream therapeutic modality in oncology. Aggressive radical surgery to achieve no residual tumor would improve survival, which is mainly affected by vascular involvement and accuracy of judging the negative margin of tumor resection. However, there is currently no intraoperative tool that can simultaneously perform microscopic analysis of the peritumoral vasculature in vivo and the surgical margin pathology of the tumor ex vivo, which leads to the randomness of one-time complete resection of the tumor, and the patient may have to undergo secondary surgery. To address this critical need, we developed a 532/266 nm dual-wavelength photoacoustic (PA) microscopy imaging (532/266-PAI) system that enables both in vivo tumor regional vascular involvement analysis and pathological margin assessment of fresh ex vivo tumor samples. A mammary tumor animal model was established to mimic the process of tumor resection, from in vivo imaging vascular involvement of tumor to intraoperative judgment of negative tumor margins. It is proved that the 532/266-PAI technology can identify the tumor vascular involvement through vascular visualization, determine the surgical plan, and then judge whether the tumor is completely removed through ultraviolet PA (UPA) tumor pathological imaging. Re-excision and secondary margin evaluation are performed when margin positive is diagnosed in the intraoperation UPA imaging. The 266/532-PAI technique has great potential for complete tumor resection in surgical navigation.
An all-optical off-beam quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor employing double-pass acoustic microresonators was proposed and experimentally investigated. An optical fiber Fabry–Perot interferometric sensor with quadrature point self-stabilization was employed for the detection of quartz prong vibration. A commercial quartz tuning fork with a resonant frequency of 30.72 kHz was employed as an acoustic transducer. Water vapor as the catalyst was added for improving the vibrational energy transfer. The minimum detection limit of ∼2.41 ppmv was obtained with a 1 s averaging time, which corresponded to a normalized noise equivalent absorption coefficient of 7.76×10⁻⁸cm ⁻¹⋅W⋅Hz−1/2 at the methane absorption line of 6046.95 cm ⁻¹ with an optimized modulation depth of 0.172 cm ⁻¹. The detection sensitivity was enhanced by a factor of ∼1.48 in comparison to the off-beam QEPAS employing a single-pass microresonator. An Allan deviation analysis indicated that the ultimate detection limit for the QEPAS-based sensor was ∼0.288 ppmv at the optimum averaging time of ∼125 s.
The second near infrared photoacoustic imaging (NIR-II PAI) and photothermal therapy (NIR-II PTT) have attracted wide interest in cancer theranostics because of maximum permission exposure (MPE), deep penetration, and lower scattering and background noise compared to NIR-I counterparts; however, it is imperative to develop biocompatible nanomaterials having NIR-II response. By utilizing multivalent Au-S coordination bonds, we constructed a zwitterionic polypeptide nanocomposite of PMC@AuNP with a suitable size of 48 ± 2 nm, which possessed a strong and broad absorbance at 650-1100 nm and an excellent photothermal conversion efficiency of 49.5%. In vitro biological studies demonstrated that NIR-II PTT within MPE was more effective than NIR-I PTT beyond MPE. Along with X-ray computed tomography and photothermal imaging functions, PMC@AuNP in vivo presented unique NIR-I/II PAI with 2.6-5.9 times signal enhancement compared to the contrast. By single dose and NIR-II irradiation (1064 nm, 1 W cm-2, 10 min), NIR-II PTT within MPE completely eradicated MCF-7 tumors without tissue damage and tumor recurrence within 24 days, inducing a better antitumor efficacy than NIR-I PTT beyond MPE. Importantly, this study provides an innovative method for the fabrication of biocompatible zwitterionic polypeptide nanocomposites with unique NIR-I/II PAI and NIR-II PTT attributes, thus holding great potential for precise cancer theranostics and further clinical transitions.
This paper presents an alternative to conventional antifouling methods through the projection of ultraviolet (UV) irradiation onto submerged surfaces.
Tests carried out establish that UV irradiation can effectively prevent biofouling growth on a small scale using commercially available technology with low cost. The demonstration for antifouling purposes also indicates the potential for ultraviolet irradiation to be applied to many different surfaces and diverse applications across the maritime industry.
It is demonstrated that intermittent UV can achieve successful antifouling results on submerged surfaces. This significantly increases the design versatility for this antifouling approach, without the need for constant UV exposure there is inherently greater design flexibility for such applications. This suggests the possibility of in-situ UV antifouling systems which can be deployed when vessels are stationary.
UV intensity measurements carried out suggest manufacturing variability exists between light emitting diodes (LEDs) of the same specification. The large variation in light intensity observed indicates that devices may perform below the indicated manufacturer's specifications and this could have a detrimental effect on antifouling performance.
Results indicate that minor shadowing from direct UV irradiation exposure can impede antifouling performance. Tests indicate prolonged UV LED exposure is likely to result in the photo-degradation of polymer based materials.
These days, many marine autonomous environment monitoring networks are set up in the world. Such systems take advantage of existing superstructures such as offshore platforms, lightships, piers, breakwaters or are placed on specially designed buoys or deep sea fix stations. The major goal of these equipments is to provide in real time reliable measurements without costly frequent maintenance. These autonomous monitoring systems are affected by a well-known phenomenon in seawater condition, called biofouling. Consequently, such systems without efficient biofouling protection are hopeless. This protection must be applied to the sensors and to the underwater communication equipments based on acoustic technologies. This paper presents the results obtained in laboratory and at sea, with various instruments, protected by a localised chlorine generation system. Two other major protection techniques, wipers and copper shutters, are presented as well.
Significance and impact of the study:
In this study, ultrasonic acoustic vibration is presented as a chemical-free, ecologically friendly alternative to conventional methods for the perturbation of microbial attachment to submerged surfaces. The results indicate the potential of an ultrasonic antibiofouling method for the disruption of microbial biofilms on marine sensor housings, which is typically a principle limiting factor in their long-term operation in the oceans. With increasing deployment of scientific apparatus in aquatic environments, including further offshore and for longer duration, the identification and evaluation of novel antifouling strategies that do not employ hazardous chemicals are widely sought.
Firstly, strategic demands of ocean exploration technologies and equipments in four aspects are analyzed, including ocean exploitation and economic growth, maritime rights and interests maintenance and maritime security, construction of ocean ecological civilization and marine scientific progress. Secondly, the current situation of ocean exploration technologies and equipments is reviewed, and development tendency is pointed out. Lastly, according to status of ocean exploration technologies and equipments in China, existing problems are presented, and advices and measures are proposed.
An experimental investigation was made of the optoacoustic effect in water aerosols interacting
with CO2 laser pulses. Saturation of the optoacoustic signal was observed when
the energy density exceeded 5 J/cm2. This was attributed to a change in the particle size
distribution of the aerosol during a laser pulse.
A sound source excited through the irradiation of a water surface with a powerful laser pulse is called an optoacoustic (OA) source. This phenomenon makes possible the remote control of submerged oceanographic devices (buoys) directly from a flying vehicle equipped with a pulse laser. The principal factors are analyzed (i.e., reverberation, ambient noise, etc.) which influence the efficiency of OA digital data transfer. The gap between the two neighboring laser pulses is the only parameter of signal that allows the transmitting of data through this remote technique. This makes different versions of pulse?position modulation preferable. Algorithms for processing detected signals are described. The optoacoustic communication system was tested at the White Sea. A CO2 laser on board a research vessel was used to launch an OA source. The acoustic signal level of about 10? Pa at a 1?m depth was achieved within the frequency band of up to 100 kHz. Test data messages at a rate of 2 bits per second for laser pulse repetition rate of about 0.5 Hz were transmitted along an experimental vessel?to?vessel 480?m line. The OA technique works well for devices submerged to depths of 2000 m and possibly more. [Work supported by RFBR.]
Optoacoustic imaging is a new technique with unusual features. It allows not only optical imaging, but also imaging of thermal structures on and in the sample. With optical radiation, images are produced from sample depths exceeding the optical penetration depth by several orders of magnitude. The resolution of, at present, about 7μm reveals microscopic structures. With simple image processing techniques information can be obtained from certain sample layers, and background structure can be suppressed.
The rediationless absorption of light propagating in optical fibres induces both stress waves and thermal waves in the fibre medium. Detection of such waves is termed the optoacoustic effect. Successful detection in optical fibres is easily obscured by scattered light impinging on the detector. We have obtained a signal of 2 mV on a piezoceramic transducer attached to a commercial step-index optical fibre after passage of a 1 J ruby laser light pulse along the fibre axis. No signal was, however, produced when the transducer was not in contact with the fibre. Similar results were obtained using chopped cw laser radiation but then more care had to be taken since the transducers used had a measureable sensitivity to the low frequency chopped radiation emitted perpendicular to the optical fibre axis.
In medical optoacoustics (photoacoustics), absorbing structures, such as blood vessels, hidden inside scattering media are illuminated with short laser pulses resulting in the generation of thermoelastic pressure transients. This initial three-dimensional (3D) acoustic pressure distribution, which exactly resembles the absorption distribution, was imaged into a water container with a 4f acoustic lens system. An optical dark-field stereo imaging system using a 30 ns flash illumination light was used to capture a snapshot of the pressure-induced refraction index changes in the water container at a predetermined time after the original laser pulse. The imaging system works at 20 Hz frame rate and was designed toward a theoretical resolution of 50 μm. The proposed method directly provides 3D images of absorbing structures without the need of computational reconstruction algorithms.
Photoacoustic imaging also called optoacoustic or thermoacoustic imaging has the potential to image animal or human organs, such as the breast and the brain, with simultaneous high contrast and high spatial resolution. This article provides an overview of the rapidly expanding field of photoacoustic imaging for biomedical applications. Imaging techniques, including depth profiling in layered media, scanning tomography with focused ultrasonic transducers, image forming with an acoustic lens, and computed tomography with unfocused transducers, are introduced. Special emphasis is placed on computed tomography, including reconstruction algorithms, spatial resolution, and related recent experiments. Promising biomedical applications are discussed throughout the text, including 1 tomographic imaging of the skin and other superficial organs by laser-induced photoacoustic microscopy, which offers the critical advantages, over current high-resolution optical imaging modalities, of deeper imaging depth and higher absorption contrasts, 2 breast cancer detection by near-infrared light or radio-frequency–wave-induced photoacoustic imaging, which has important potential for early detection, and 3 small animal imaging by laser-induced photoacoustic imaging, which measures unique optical absorption contrasts related to important biochemical information and provides better resolution in deep tissues than optical imaging. © 2006 American Institute of Physics.
The imminent ban of environmentally harmful tributyltin (TBT)-based paint products has been the cause of a major change in the antifouling paint industry. In the past decade, several tin-free products have reached the commercial market, and claimed their effectiveness as regards the prevention of marine biofouling on ships in an environmentally friendly manner. The main objective of this review is to describe these products in as much detail as possible based on the knowledge available in the open literature. This knowledge has been supplemented by means of performance data provided, upon request, by some of the paint-producing companies. An exhaustive review of the historical development of antifouling systems and a detailed characterisation of sea water are also included. The need for studies on the behaviour of chemically active paints under different sea water conditions is emphasised. In addition, the most common booster biocides used to replace TBT-containing compounds are listed and described. It must be stressed that there is still a lack of knowledge of their potential environmental side effects.