Based on the application of sediment microbial fuel cell (SMFC) in the bioremediation of sediment, this study used the sediment microbial fuel cell technology as the leading reactor. Modification of anode carbon felts (CF) by synthesis of PANI/MnO₂ composited to improve the electrical performance of the sediment microbial fuel cell. This study investigated the degradation effects, degradation pathways of the specific contaminant enrofloxacin and microbial community structure in sediment microbial fuel cell systems. The results showed that the sediment microbial fuel cell system with modified anode carbon felt (PANI-MnO₂/CF) prepared by in-situ chemical polymerization had the best power production performance. The maximum output voltage was 602 mV and the maximum power density was 165.09 mW m⁻². The low concentrations of enrofloxacin (12.81 ng g⁻¹) were effectively degraded by the sediment microbial fuel cell system with a removal rate of 59.52%.

As reservoirs for pollutants transported via the Yangtze and Yellow Rivers, the Bohai Sea (BS) and Yellow Sea (YS) play an important role in transporting microplastics (MPs) to the Pacific Ocean. The fate, sources and mass budget of MPs in the BS and the YS were investigated by Pearson correlation, principal component analysis-multilinear regression analysis (PCA-MRLA) and a mass balance model to sedimentary MPs data. Average MP abundances were 137 and 119 items kg⁻¹ in the Bohai and Yellow Seas, respectively. MPs <1000 μm exhibited similar distribution patterns to total organic carbon and fine-grained sediments, while MPs >1000 μm were confined in the BS and exhibited a strong positive correlation with chlorophyll-a and polyethylene terephthalate, suggesting that larger MPs might deposit faster due to biofouling or when comprised of high density polymers. PCA-MLRA analysis indicated land-based inputs (packing materials, textile material and daily commodities) were dominant in the BS, while maritime activities (fishing and mariculture) were the main source of MPs in the YS. The mass balance model revealed that the total MP input and output to the BS and the YS was 3396.92 t yr⁻¹ and 3814.81 t yr⁻¹, respectively. The major input pathway of MPs to the BS and the YS were river discharge and air deposition, respectively. Notably, 94% of MPs in the BS and the YS were deposited to sediments. This study revealed that BS and YS sediments play an important role in preventing MPs from being further transported to the Pacific Ocean, thus more attention should be paid to local ecological risk assessment.

The distinct spatial variability in microplastic concentrations between marine regions and habitats calls for a better understanding about the transport pathways of this omnipresent pollutant in the marine environment. This study provides empirical evidence that a sessile filter feeder, the Blue mussel M. edulis, accelerates microplastic deposition by aggregating them into sinking particulate faeces and pseudofaeces. After settling to the seafloor, the bioturbation of benthic fauna quickly buries these microplastics. Collectively, these results suggest that if such biologically-mediated benthic-pelagic coupling would be integrated into hydrodynamic transport models, the spatial variability and source-sink dynamics of microplastics would be better understood. It is proposed that microplastic pollution is monitored through sampling that takes into account faeces and pseudofaeces underneath filter feeders. The implications of this detrital pathway for microplastic transfer to the seafloor, and the role of shellfish mariculture in this process, are discussed. Studies that consider filter feeders and benthic communities from other regions, and during different seasons, are needed to validate the proposed biological pump mechanism across space and time.

Freshwater cyanobacteria produce highly toxic secondary metabolites, which can be transported downstream by rivers and waterways into the sea. Estuarine and coastal aquaculture sites exposed to toxic cyanobacteria raise concerns that shellfish may accumulate and transfer cyanotoxins in the food web. This study aims to describe the competitive pattern of uptake and depuration of a wide range of microcystins (MC-LR, MC-LF, MC-LW, MC-LY, [Asp3]-MC-LR/[Dha7]-MC-LR, MC-HilR) and nodularins (NOD cyclic and linear) within the common blue mussel Mytilus edulis exposed to a combined culture of Microcystis aeruginosa and Nodularia spumigena into the coastal environment.Different distribution profiles of MCs/NODs in the experimental system were observed. The majority of MCs/NODs were present intracellularly which is representative of healthy cyanobacterial cultures, with MC-LR and NOD the most abundant analogues. Higher removal rate was observed for NOD (≈96%) compared to MCs (≈50%) from the water phase. Accumulation of toxins in M. edulis was fast, reaching up to 3.4 μg/g shellfish tissue four days after the end of the 3-days exposure period, with NOD (1.72 μg/g) and MC-LR (0.74 μg/g) as the dominant toxins, followed by MC-LF (0.35 μg/g) and MC-LW (0.31 μg/g). Following the end of the exposure period depuration was incomplete after 27 days (0.49 μg/g of MCs/NODs). MCs/NODs were also present in faecal material and extrapallial fluid after 24 h of exposure with MCs the main contributors to the total cyanotoxin load in faecal material and NOD in the extrapallial fluid. Maximum concentration of MCs/NODs accumulated in a typical portion of mussels (20 mussels, ≈4 g each) was beyond greater the acute, seasonal and lifetime tolerable daily intake. Even after 27 days of depuration, consuming mussels harvested during even short term harmful algae blooms in close proximity to shellfish beds might carry a high health risk, highlighting the need for testing.

As emerging pollutants, the occurrence and risks of organophosphate esters (OPEs) in mariculture farms should be concerned; however, information is limited. Beibu Gulf is one of the essential mariculture zones in China. This study aimed to investigate the occurrence of OPEs in mariculture farms of the Beibu Gulf, their phase distribution and bioaccumulation among sediment, organisms (shrimp, crab, and oyster), water, and feed. Human exposure to OPEs through seafood consumption was also assessed. The total concentrations of the 11 target OPEs (∑₁₁OPEs) in the water samples ranged 32.9–227 ng L⁻¹. It was significantly higher in water from the culture ponds (mean 122 ng L⁻¹) than in water from the estuaries and nearshore areas (mean 51.1 ng L⁻¹) (nonparametric test, p < 0.05). ∑₁₁OPEs in the feeds averaged 46.0 (range 21.7–84.5) ng g⁻¹ dw, which is similar to the level in the organism samples (mean 55.5, range 21.3–138 ng g⁻¹ dw) and 4.4 times higher than that in the sediment (mean 10.9, range 35–22.1 ng g⁻¹ dw). The ∑₁₁OPEs released from the feeds to the culture ponds was estimated to be 49 μg m⁻² per three-month period. In the aquaculture ponds, the sediment-water distribution coefficient (log KOC), and the bioaccumulation factors from the water (log BWAFs) or the feed (log BFAFs) to the organisms, depend linearly on the hydrophobicity (log KOW) of OPEs. The log BWAFs and log BFAFs increased with increasing log KOW within the log KOW range of 1–7. The human exposure to OPEs through consumption of shrimp, crab, and oysters from the mariculture farms does not pose a health risk at present.

Microplastic pollution in estuarine and coastal environments has recently been characterised in several countries but few researchers have addressed the influence of different forms of coastal zone use on the distribution of microplastic. Here, microplastic particles were sampled in Hangzhou Bay, which is heavily influenced by a range of human activities, and their abundance, size, and polymer type characterised. The abundance of microplastics was 0.14 ± 0.12 items/m³ in water, 84.3 ± 56.6 items/kg dry weight of sediment, and between 0.25 ± 0.14 and 1.4 ± 0.37 items/individual in biota. These results show that Hangzhou Bay has a low level of microplastic contamination compared to other coastal systems in China, although abundance was spatially variable within the bay; relatively higher microplastic abundances were found in the southern area of the bay, which has adjacent industrial and urban land-use zones, while lower abundances were observed in the central and northern bay areas where mariculture, fisheries, and mineral and energy industries are most common. The relatively low microplastic abundance observed in the biota samples is consistent with the generally low values for the seawater and sediment samples. Pellets were the most common of four particle-shape classes (fibres, fragments, films, and pellets) in surface seawater, while fibres were most abundant in sediment and biota. Smaller-sized microplastics (<1.0 mm) were dominant in all samples. Microplastics in the surface seawater were dominated by low-density polypropylene and polyethylene particles, while rayon was dominant in the sediment and biota samples. Our results demonstrate that regional variability in anthropogenic activity and land-use are important controls on the spatial pattern of microplastic pollution in Hangzhou Bay.

The abuse of antibiotics has caused the propagation of antibiotic resistance genes (ARGs) in aquaculture systems. Although the recirculating systems have been considered as a promising approach for preventing the coastal water pollution of antibiotics and ARG, rare information is available on the distribution and proliferation of ARGs in the recirculating mariculture system. This study firstly investigated the proliferation of ARGs in coastal recirculating mariculture systems. Ten subtypes of ARGs including tet (tetB, tetG, tetX), sul (sul1, sul2), qnr (qnrA, qnrB, qnrS), and erm (ermF, ermT) were detected. The absolute abundances of the ARGs detected in the mariculture farm were more than 1 × 10⁴ copies/mL. The sulfonamide resistance genes (sul1 and sul2) were the most abundant ARGs with the abundance of 3.5 × 10⁷–6.5 × 10¹⁰ copies/mL. No obvious correlation existed between the antibiotics and ARGs. Some bacteria were positively correlated with two or more ARGs to indicate the occurrence of multidrug resistance. The fluidized-bed biofilter for wastewater treatment in the recirculating system was the main breeding ground for ARGs while the UV sterilization process could reduce the ARGs. The highest flux of ARGs (6.5 × 10²¹ copies/d) indicated that the discharge of feces and residual baits was the main gateway for ARGs in the recirculating mariculture system to enter the environments.

Mariculture activities including enclosure, raft and cage cultures employ a variety of plastic gear such as fishing nets, buoyant material and net cages. The plastic gear poses a potential source of microplastics to the coastal environment, but relevant data on the impacts of mariculture are still limited. To this end, a semi-enclosed narrow bay (i.e., Xiangshan Bay, China) with a long-term mariculture history was investigated to assess how mariculture activities affect microplastics in seawater and sediment. The results indicated that mariculture-derived microplastics accounted for approximately 55.7% and 36.8% of the microplastics in seawater and sediment, respectively. The average microplastic abundances of seawater and sediment were 8.9 ± 4.7 (mean ± SD, n = 18) items/m³ seawater and 1739 ± 2153 (n = 18) items/kg sediment, respectively. The types of mariculture-derived microplastics included polyethylene (PE) foam, PE nets, PE film, polypropylene (PP) rope, polystyrene (PS) foam and rubber. PE foam had the highest proportion (38.6%) in the seawater samples. High usage rates and the porous structure of PE foam led to the high abundance. The average microplastic sizes of seawater and sediment are 1.54 ± 1.53 mm and 1.33 ± 1.69 mm, respectively. The spatial variations in the abundance and size of microplastics implied that the mariculture-derived microplastics in Xiangshan Bay were transported along the Bay to the open sea. The results of this study indicate that mariculture activity can be a significant source of microplastics. Further research is required to investigate how the high microplastic abundance in mariculture zone affects marine organisms, especially cultured seafood.

During chlorine disinfection process, reactions between the disinfectant and 17β-estradiol (E2) lead to the formation of halogenated disinfection byproducts (DBPs) which can be a risk to both ecosystem and human health. The degradation and transformation products of E2 in sodium hypochlorite (NaClO) disinfection processes of different water samples were investigated. The reaction kinetics research showed that the degradation rates of E2 were considerably dependent on the initial pH value and the types of water samples. In fresh water, synthetic marine aquaculture water and seawater, the reaction rate constant was 0.133 min−1, 2.067 min−1 and 2.592 min−1, respectively. The reasons for the above phenomena may be due to the different concentrations of bromide ions (Br−) in these three water samples which could promote the reaction between NaClO and E2. Furthermore, Br− could also cause the formation of brominated DBPs (Br-DBPs). The main DBPs, reaction centers and conceivable reaction pathways were explored. Seven halogenated DBPs have been observed including three chlorinated DBPs (Cl-DBPs) and four Br-DBPs. The active sites of E2 were found to be the pentabasic cyclic ring and the ortho position of the phenol moiety as well as C9-C10 position. The identified Cl/Br-DBPs were also confirmed in actual marine aquaculture water from a shrimp pond. The comparison of bio-concentration factors (BCF) values based on calculation of EPI-suite showed that the toxicities of the Br-DBPs were stronger than that of their chloride analogues. The absorbable organic halogens (AOX) analysis also suggested that the DBPs produced in the marine aquaculture water were more toxic than that in the fresh water system.

At the Pearl River Estuary of southern China, mercury and its environmental problems have long been a great concern. This study investigated the distribution and speciation of mercury compounds that are significantly influenced by the increasing content of humic acid (HA, a model natural organic matter) in this region. The inorganic mercury and methyl mercury, being adsorbed and converted at different HA levels, were studied in sediments and surface water at both mariculture and their reference sites. In mariculture sediments with higher HA content (up to 4.5%), more mercury were adsorbed at different compound levels, promoting the methylation and accumulation of mercury (P < 0.05) at the sediment-water interface. Seasonal shift in environmental temperature might control the HA content, subsequently favouring mercury methylation (maximum 1.75 ± 0.08 mg L−1 d−1) under warm weather conditions. In reference sites received less HA wastes, lower adsorption capacity and methylation rate were observed for mercury in sediments and surface water. Our work points to the significant roles of HA on mercury distribution and speciation both spatially and seasonally, thus addressing the impacts of mariculture activities on estuary eco-system.