Acute and chronic effects of innovative antifouling nanostructured biocides on a tropical marine microcrustacean

Adults of Sun Coral Tubastraea coccinea (Lesson 1829) Are Resistant to New Antifouling Biocides

Biocides used in antifouling (AF) paints, such as 4,5-dichlorine-2-n-octyl-4-isothiazole-3-one (DCOIT), can gradually leach into the environment. Some AF compounds can persist in the marine environment and cause harmful effects to non-target organisms. Nanoengineered materials, such as mesoporous silica nanocapsules (SiNCs) containing AF compounds, have been developed to control their release rate and reduce their toxicity to aquatic organisms. This study aimed to evaluate the acute toxicity of new nanoengineered materials, SiNC-DCOIT and a silver-coated form (SiNC-DCOIT-Ag), as well as the free form of DCOIT and empty nanocapsules (SiNCs), on the sun coral Tubastraea coccinea. T. coccinea is an invasive species and can be an alternative test organism for evaluating the risks to native species, as most native corals are currently threatened. The colonies were collected from the Alcatrazes Archipelago, SP, Brazil, and acclimatized to laboratory conditions. They were exposed for 96 h to different concentrations of the tested substances: 3.33, 10, 33, and 100 µg L-1 of free DCOIT; 500, 1000, 2000, and 4000 µg L-1 of SiNC; and 74.1, 222.2, 666.7, and 2000 µg L-1 of SiNC-DCOIT and SiNC-DCOIT-Ag. The test chambers consisted of 500 mL flasks containing the test solutions, and the tests were maintained under constant aeration, a constant temperature of 23 ± 2 °C, and photoperiod of 12 h:12 h (light/dark). At the end of the experiments, no lethal effect was observed; however, some sublethal effects were noticeable, such as the exposure of the skeleton in most of the concentrations and replicates, except for the controls, and embrittlement at higher concentrations. Adults of T. coccinea were considered slightly sensitive to the tested substances. This resistance may indicate a greater capacity for proliferation in the species, which is favored in substrates containing antifouling paints, to the detriment of the native species.

Water and sediment toxicity and hazard assessment of DCOIT towards neotropical marine organisms

DCOIT is an effective antifouling biocide, which presence in the environment and toxicity towards non-target species has been generating great concern. This study evaluated the waterborne toxicity of DCOIT on marine invertebrates (i.e., survival of brine shrimp Artemia sp., larval development of the sea urchin Echinometra lucunter and the mussel Perna perna), as well as DCOIT-spiked-sediment toxicity on the fecundity rate of the copepod Nitrocra sp. And the mortality of the amphipod Tiburonella viscana. The data outcomes were used to calculate environmental hazards and risks, which were compared to their corresponding values obtained from temperate regions. Waterborne toxicity can be summarized as follows: Artemia sp. (LC_50-48h = 163 (135-169) μg/L), E. lucunter (EC_50-36h = 33.9 (17-65) μg/L), and P. perna (EC_50-48h = 8.3 (7-9) μg/L). For whole-sediment toxicity, metrics were calculated for T. viscana (LC_50-10d = 0.5 (0.1-2.6) μg/g) and Nitrocra sp, (EC_50-10d = 200 (10-480) μg/kg). The DCOIT hazard was assessed for both tropical and non-tropical pelagic organisms. The predicted no-effect concentration (PNEC) for tropical species (0.19 μg/L) was 1.7-fold lower than that for non-tropical organisms (0.34 μg/L). In whole-sediment exposures, DCOIT presented a PNEC of 0.97 μg/kg, and the risk quotients (RQs) were >1 for areas with constant input of DCOIT such as ports ship/boatyards, marinas, and maritime traffic zones of Korea, Japan, Spain, Malaysia, Indonesia, Vietnam, and Brazil. The presented data are important for supporting the establishment of policies and regulations for booster biocides worldwide.

Chronic toxic effects of polystyrene micro-plastics, DCOIT and their combination on marine Chlorella sp

Polystyrene (PS) is one of the most dangerous polymers, mainly because of the mutagenic or carcinogenic risk of the monomers used to produce it. Sea-Nine 211 is a commercial antifouling agent; its active ingredient is the biocide 4,5-dichloro-2-octyl-4-isothiazolinone-3-one (DCOIT). Micro- and nano-plastics have different synergistic effects on marine organisms together with organic pollutants. To understand the toxic effects of DCOIT and PS alone and in combination, marine Chlorella sp was selected as the experimental organism. The exposure concentration of DCOIT was set at 50 μg/L, and that of PS was set at 10 μg/L. The results show that all exposed groups promoted the growth of marine Chlorella sp in the late stage of exposure, and the recovery time of marine Chlorella sp in the exposed group containing PS was earlier. Changing trend of chlorophyll a was consistent with the growth trend. On the 15th day of exposure, the gene expression of the photosynthesis system in the combined exposed group showed a significant difference, and the cells produced oxidative stress. Scanning electron microscope observation shows the algae adhered to each other. The volume of algae cells in DCOIT and PS exposed groups decreased, and the internal structure of algae cells in each exposed group was damaged.

"Smart" nanosensors for early detection of corrosion: Environmental behavior and effects on marine organisms

Corrosion is an environmental and economic global problem. "Smart" or stimuli-responsive colorimetric nanosensors for maritime coatings have been proposed as an asset to overcome the limitations of the current monitoring techniques by changing color in the presence of triggers associated with the early stages of corrosion. Layered double hydroxides (Zn-Al LDH; Mg-Al LDH) and silica mesoporous nanocapsules (SiNC) were used as precursor nanocarriers of active compounds: hexacyanoferrate ions ([Fe(CN)₆]^3-) and phenolphthalein (PhPh), respectively. Additionally, the safer-by-design principles were employed to optimize the nanosensors in an eco-friendly perspective (e.g., regular vs. warm-washed SiNC-PhPh; immobilization using different carriers: Zn-Al LDH-[Fe(CN)₆]^3- vs. Mg-Al LDH-[Fe(CN)₆]^3-). Therefore, the present study aims to assess the environmental behavior in saltwater and the toxic effects of the nanosensors, their nanocarriers, and the active compounds on the marine microalgae Tetraselmis chuii and the crustacean Artemia salina. Briefly, tested compounds exhibited no acute toxic effects towards A. salina (NOEC = 100 mg/L), apart from SiNC-PhPh (LC₅₀ = 2.96 mg/L) while tested active compounds and nanosensors caused significant growth inhibition on T. chuii (lowest IC₅₀ = 0.40 mg/L for SiNC-PhPh). The effects of [Fe(CN)₆]^3- were similar regardless of the nanocarrier choice. Regarding SiNC-PhPh, its toxicity can be decreased at least twice by simply reinforcing the nanocapsules washing, which contributes to the removal (at least partially) of the surfactants residues. Thus, implementing safe-by-design strategies in the early stages of research proved to be critical, although further progress is still needed towards the development of truly eco-friendly nanosensors.

Toxicity of innovative antifouling additives on an early life stage of the oyster Crassostrea gigas: short- and long-term exposure effects

Recent advances in nanotechnology have allowed the encapsulation of hazardous antifouling (AF) biocides in silica mesoporous nanocapsules (SiNC) reducing their short-term toxicity. However, the chronic effects of such novel nanoadditives remain understudied. The present study aimed to assess short- and long-term sub-lethal effects of soluble forms (DCOIT and Ag) and nanostructured forms (SiNC-DCOIT and SiNC-DCOIT-Ag) of two AF biocides and the "empty" nanocapsule (SiNC) on juveniles of Crassostrea gigas after 96 h and 14 days of exposure. Juvenile oysters exposed for a short period to free DCOIT and AgNO₃ presented worse physiological status comparing with those exposed to the nanostructured forms. The long-term exposure to DCOIT and Ag⁺ caused an extensive biochemical impairment comparing with the tested nanomaterials, which included oxidative damage, activation of the antioxidant defense system, and neurotransmission impairment. Despite the negative effects mostly observed on the health condition index and AChE, the encapsulation of the abovementioned AF biocides into SiNC seems to be a technological advantage towards the development of AF nanoadditives with lower long-term toxicity comparing with the soluble forms of such biocides.

Can the toxicity of polyethylene microplastics and engineered nanoclays on flatfish (Solea senegalensis) be influenced by the presence of each other?

Microplastics and nanomaterials are applied in a myriad of commercial and industrial applications. When leaked to natural environments, such small particles might threaten living organisms' health, particularly when considering their potential combination that remains poorly investigated. This study investigated the physiological and biochemical effects of polyethylene (PE; 64-125 μm in size, 0.1, 1.0, and 10.0 mg·L^-1) single and combined with an engineered nanomaterial applied in antifouling coatings, the copper-aluminium layered double hydroxides (Cu-Al LDH; 0.33, 1.0, and 3.33 mg·L^-1) in the flatfish Solea senegalensis larvae (8 dph) after 3 h exposure, in a full factorial design. Particles ingestion, histopathology, and biochemical biomarkers were assessed. Fish larvae presented <1 PE particles in their gut, independently of their concentration in the medium. The histological health index showed minimal pathological alterations at PE combined exposure, with a higher value observed at 1 mg LDH·L^-1 × 0.1 mg PE·L^-1. Gut deformity and increased antioxidant defences (catalase), neurotransmission (acetylcholinesterase), and aerobic energy production (electron transport system) were observed at PE ≥ 1.0 mg·L^-1. No oxidative damage (lipid peroxidation) or alterations in the detoxification capacity (glutathione-S-transferase) was observed on single and combined exposures. PE, combined or not with Cu-Al LDH, does not seem to compromise larvae's homeostasis considering levels reported so far in the marine and aquaculture environments. However, harsh effects are expected with MP contamination rise, as projections suggest.

Effects of nanostructure antifouling biocides towards a coral species in the context of global changes

Biofouling prevention is one of the biggest challenges faced by the maritime industry, but antifouling agents commonly impact marine ecosystems. Advances in antifouling technology include the use of nanomaterials. Herein we test an antifouling nano-additive based on the encapsulation of the biocide 4,5-dichloro-2-octyl-4-isothiazolin-3-one (DCOIT) in engineered silica nanocontainers (SiNC). The work aims to assess the biochemical and physiological effects on the symbiotic coral Sarcophyton cf. glaucum caused by (1) thermal stress and (2) DCOIT exposure (free or nanoencapsulated forms), in a climate change scenario. Accordingly, the following hypotheses were addressed: (H1) ocean warming can cause toxicity on S. cf. glaucum; (H2) the nanoencapsulation process decreases DCOIT toxicity towards this species; (H3) the biocide toxicity, free or encapsulated forms, can be affected by ocean warming. Coral fragments were exposed for seven days to DCOIT in both free and encapsulated forms, SiNC and negative controls, under two water temperature regimes (26 °C and 30.5 °C). Coral polyp behavior and photosynthetic efficiency were determined in the holobiont, while biochemical markers were assessed individually in the endosymbiont and coral host. Results showed transient coral polyp retraction and diminished photosynthetic efficiency in the presence of heat stress or free DCOIT, with effects being magnified in the presence of both stressors. The activity of catalase and glutathione-S-transferase were modulated by temperature in each partner of the symbiosis. The shifts in enzymatic activity were more pronounced in the presence of free DCOIT, but to a lower extent for encapsulated DCOIT. Increased levels of oxidative damage were detected under heat conditions. The findings highlight the physiological constrains elicited by the increase of seawater temperature to symbiotic corals and demonstrate that DCOIT toxicity can be minimized through encapsulation in SiNC. The presence of both stressors magnifies toxicity and confirm that ocean warming enhances the vulnerability of tropical photosynthetic corals to local stressors.

Functional nanomaterials, synergisms, and biomimicry for environmentally benign marine antifouling technology

Marine biofouling remains one of the key challenges for maritime industries, both for seafaring and stationary structures. Currently used biocide-based approaches suffer from significant drawbacks, coming at a significant cost to the environment into which the biocides are released, whereas novel environmentally friendly approaches are often difficult to translate from lab bench to commercial scale. In this article, current biocide-based strategies and their adverse environmental effects are briefly outlined, showing significant gaps that could be addressed through advanced materials engineering. Current research towards the use of natural antifouling products and strategies based on physio-chemical properties is then reviewed, focusing on the recent progress and promising novel developments in the field of environmentally benign marine antifouling technologies based on advanced nanocomposites, synergistic effects and biomimetic approaches are discussed and their benefits and potential drawbacks are compared to existing techniques.

Nautical Tourism in Marine Protected Areas (MPAs): Evaluating an Impact of Copper Emission from Antifouling Coating

Copper (Cu) has a narrow range between optimal concentrations as a micronutrient critical for phytoplankton growth and concentrations potentially toxic to living organisms. This sensitivity indicates an ecosystem vulnerability that threatens not only nature but also human health due to bioaccumulation. An important source of elevated Cu concentrations in coastal environments are biocides used as antifouling protection on ships. A pilot study conducted in the Marine Protected Area (MPA) of the Krka Estuary (Croatia) over a period of 16 months investigated the relationship between ship traffic and Cu concentrations. The aim was to contribute to more informed environmental management by assessing the associated risks. In the study presented here, Cu concentrations were monitored, analyzed, and correlated with vessel traffic. Observations revealed that the seasonal increase in maritime traffic caused by nautical tourism was associated with an increase in Cu concentrations of more than five times, posing a toxicity risk to the environment. In order to understand the distribution of copper emissions, a mapping of maritime traffic was carried out by counting transits, radar imagery, and drone photography. This approach has proven sufficient to identify the potential risks to the marine environment and human health, thus providing an effective assessment tool for marine stakeholders.