Ships transport about 80 percent of world trade and transfer approximately three to five billion tons of ballast water internationally every year. Due to the likely presence of pollutants, the ballast water discharged by ships can have negative effects on aquatic ecosystems. This study was conducted on 10 ships that entered the Bushehr port to determine the effectiveness of the ballast water exchange method and also to specify the contents of heavy metals (Ni, Cd, Pb and Cu) in the water and sediment of the ships’ ballast tanks. The samples were collected from January 2017 to July 2018 during a cold and a hot season. The results indicate the values of heavy metals in the samples in this order: Ni> Cu > Pb > Cd. The heavy metals concentrations in the sediment samples did not exceed the standard of the National Oceanic and Atmospheric Administration (NOAA). Whereas, Cu and Ni in all water samples and Cd in samples 2 and 7 exceeded the NOAA quality standard value. A correlation analysis of the metals showed that the sources of heavy metals vary in water and sediment samples, except for Pb and Cu in sediment samples which a positively significant relationship were observed. The results also revealed that the ballast water exchange method cannot by itself be effective and an efficient management together with continuous monitoring seems to be essential to prevent pollution of the ballast tanks of the ships entering the Bushehr port.

High phosphorus (P) load and consequent algal bloom are critical issues because of their harmful effects to aquatic ecosystems. The organic phosphorus (Po) cycling and hydrolyzation pathway in the sediments of a hypereutrophic lake area with high algae biomass were investigated using stable isotopes (δ¹³C and δ¹⁵N) along with C/N ratios, a sequential extraction procedure, ³¹P NMR spectrum, and alkaline phosphatase activity (APA) was measured simultaneously. C/N ratios lower than 10 combined with lighter δ¹³C (−23.5 to −25.2‰) and δ¹⁵N values (3.7–9.5‰) indicated that endogenous algal debris contributed to the predominant proportions of P-containing organic matter in the sediments. Sequential extraction results showed that Po fractions decreased as nonlabile Po > moderately labile Po > biomass-Po. Decreasing humic-associated Po (HA-Po) in sediments downward suggested the degradation of high-molecular-weight Po compounds on the geological time scale to low-molecular-weight Po including fulvic-associated Po (FA-Po), which is an important source of labile Po in the sediment. An analysis of the solution ³¹P NMR spectrum analysis showed that important Po compound groups decreased in the order of orthophosphate monoesters > DNA-Po > phospholipids. The significant correlation indicated that orthophosphate monoesters were the predominant components of HA-Po. Rapid hydrolysis of labile orthophosphate diesters further facilitated the accumulation of orthophosphate monoesters in the sediments. Additionally, the simultaneously upward increasing trend demonstrated that APA accelerated the mineralization of Po into dissolved reactive phosphorus (DRP), which might feed back to eutrophication in algae-dominant lakes. The significantly low half-life time (T₁/₂) for important Po compound groups indicated faster metabolism processes, including hydrolysis and mineralization, in hypereutrophic lakes with high algae biomass. These findings provided improved insights for better understanding of the origin and cycling processes as well as management of Po in hypereutrophic lakes.

Environmental emissions of perfluoroalkyl acids (PFAAs) often contaminate aquatic ecosystems and accumulate in the species therein. This can represent an exposure pathway for human populations where seafood is consumed. Concentrations of PFAAs in water breathing animals may be a function of many different factors, however, little is known about how these different factors impact contaminant accumulation in estuarine and marine species. This study explores the relationships between PFAA accumulation and two key variables, animal size and sediment concentrations, for a number of important seafood species. Sixty Dusky Flathead (Platycephalus fuscus), 58 Mulloway (Argyrosomus japonicus) and 53 Giant Mud Crab (Scylla serrata) were tested for perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorohexane sulfonate (PFHxS) in edible tissues, and the concentrations compared with animal size and sediment concentrations at the location of capture. PFAAs showed a high degree of variation among species, and PFOA and PFHxS were only common in Giant Mud Crab. Log-transformed PFOS concentrations in all three species showed negative correlations with animal size (weight). There was limited evidence for relationships between PFOS muscle tissue concentration and sediment PFOS concentration. The patterns observed are potentially explained by changes in trophic position, relative growth rate, consumption rate and metabolic rate, throughout the species life history. The results contrast with observations for other persistent organic pollutants, whereby larger individuals tend to carry greater contaminant loads. Future work is required to establish whether these patterns are evident for PFAAs in other species and contaminant sources.

Atrazine contamination is of great concern due to its widespread occurrence in shallow lakes. Here, the distribution and degradation of atrazine in acidic and alkaline lake systems were investigated. Meanwhile, the bacterial communities in different sediments and the effects of environmental factors on atrazine-degrading bacteria were evaluated. In the lake systems without plants, atrazine levels in sediment interstitial water reached peak concentrations on the 4th d. More than 90% of atrazine was then degraded in all sediment interstitial water by day 30. Meanwhile, the degradation rate of atrazine in alkaline sediments was faster than that in acidic sediments. Values of hydroxylated metabolites in the acidic lake sediments tended to be greater. Moreover, the amounts of Proteobacteria, Actinobacteria, Firmicute, Nitrospinae, Aminicenantes, Ignavibacteriae and Saccharibacteria in acidic Tangxunhu Lake sediments were significantly different from alkaline Honghu Lake sediments, while the amounts of Cyanobacteria and Saccharibacteria in sediments treated with atrazine were significantly greater than those in sediments without atrazine (P < 0.05). Notably, pH was the most relevant environmental factor in the quantitative variation of atrazine-degrading bacteria, including in Clostridium-sensu-stricto, Pseudomonas, Comamonas and Rhodobacter. The Mantel test results indicated that the degradation of atrazine in different sediments was mainly affected by the sediment physicochemical properties rather than by the addition of atrazine and the cultivation of hydrophytes.

The role of exposure time on wetland sediment-bound phosphorus (P) biogeochemical behavior is studied in Lake Poyang after the operation of the Three Gorges Dam (TGD). The multiple P compounds primarily include orth–P (88.3%), mono–P (8.9%), DNA–P (2.1%), and pyro–P (0.8%) in the exposed sediments. A significant decreasing trend of orth–P occurred after the operation of the Three Gorges Dam (TGD), with the mean concentration decreasing from 175.9 to 142.5 mg kg⁻¹ from 2007 to 2012 (ANOVA: P < 0.05), whereas the temporal change in biogenic P showed great variability. The plant distribution pattern and the increase in plant biomass due to decreased water levels might be the reason that caused variations in the P species. Furthermore, the content of orth–P, mono–P, DNA–P, and pyro–P showed increasing trends as sediment exposure time increased. However, the enzyme hydrolysis rate of DNA–P decreased with exposure time and may cause the bioavailability of biogenic P to decrease. Despite the fact that the bioavailability of biogenic P might decline in the short term, the favorable environmental conditions for P release in sediment rewetting processes, together with the increase in orth–P and biogenic P due to extended exposure time, indicate that these large additions of P would enter the overlying water and cause water quality decline once the sediment is submerged underwater during the next wet season. An environmental process analysis showed that the increased exposure time induced sediment environmental conditions changes that played an important role in the biogeochemical cycle of P and may be an important way of P replenishment in Lake Poyang. The results of this study help provide a better understanding of the role of sediment drying/wetting cycles in nutrient biogeochemical behavior and fates in wetland ecosystems.

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.

Dissolved phosphate (Pᵢ) can be released during resuspended sediments exposed to sunlight. However, the significance of this phenomenon in the process of eutrophication is not clear. In this study, the behavior of photo-induced Pᵢ release during sediment resuspension in shallow lakes with the different trophic states was investigated. The amount of photo-induced Pᵢ release in the sediment resuspension from Lake Liangzi, Lake Dong, Lake Tangxun and Lake Longyang in China was 0.013, 0.019, 0.032, and 0.048 mg/L, respectively, and increased as the trophic states of the lakes increased. The results of phosphorus speciation analysis showed that the phosphate monoester in the particulate phosphorus is the organic phosphorus species participated in the photochemical reaction. The steady-state concentration of hydroxyl radical (OH) in the sediment resuspension also increased along with the trophic states of lakes increased and dissolved organic matter (DOM), nitrate, and Fe³⁺ presented in sediment resuspension were the main photosensitizers for OH production. All these results indicate that the increase of trophic states of lakes leads to the accumulation of organic phosphorus and OH, resulting in more dissolved phosphate photo-released, which accelerate the eutrophication process in a form of positive feedback.

Microplastic (MPs) pollution in the aquatic and terrestrial environments has caught many attentions in the scientific literatures. Currently, no information is available about MPs pollution in Caspian Sea, the largest lake in the world. This study indicates the first report on the MPs pollution in the sediments of the southern Caspian coastal zones, northern Iran. Density separation method was conducted on 17 surficial sediments. The combination of observation techniques including SEM-EDS analysis, polarized light microscopy and Raman micro-spectroscopy were used to identify MPs. The abundance and size of microplastics in the samples ranged between 25 and 330 items/kg and 250–500 μm, respectively. Fibers constituted the most common MPs shape and polystyrene (PS) and polyethylene (PE) were major polymer types in the samples. The distribution of MPs in the study area reflected a patchy and irregular spatial pattern implying that the higher MPs concentration are near mouth of permanent rivers and in the regions with higher level of the fishing and tourism activities. The results showed the wide occurrence of MPs in the sediments of the world’s largest lake which extend the knowledge on MPs pollution in the marine system. We also recommend further research on microplastics in different compartments of Caspian Sea to inform policy discussions and the development of appropriate management responses.

In this study, the Songgang River (SR) was selected as a typical tributary that is heavily polluted by rapid urbanization and industrialization. The polycyclic aromatic hydrocarbon (PAH) distribution at five representative sampling sites from different urban functional areas was studied. The chemical and physical properties and spatial and vertical distribution of PAHs in sediments were investigated. PAH source identification and the ecological risks of the sediments were evaluated. The results suggested that the industrial zone and dense residential and commercial areas were the most contaminated areas of the SR, as the chemical and physical properties of total organic carbon content in sediments was the highest at the dense residential and commercial areas (0.1–4.5%); however, the acid volatile sulfide, total nitrogen, and total phosphorus contents were the highest in the industrial zone, with ranges of 700.0–1618.4 mg/kg dw, 22.4–3543.9 mg/kg dw, and 82.3–4550.7 mg/kg dw, respectively. The spatial distribution of residual PAHs in the sediment cores showed a wide variation among different urban functional areas, and the vertical characterization (0–300 cm) depicted a significant decreasing trend with depth and with an abrupt increase at 180 cm. The concentration of ∑16 PAHs ranged from 208.7 to 7709.8 ng/g dw, with the highest concentrations obtained in the industrial zone. The low molecular weight-PAHs (153–6720 ng/g dw) were predominant in the sediments. Furthermore, there were combined sources (biomass burning: 40.3%; fossil fuel combustion: 25.5%; mixed source: 21.5%; oil pollution: 12.7%) and a long term accumulation effect, with anthropogenic activities and industrial pollution as the major contributing sources. The concentrations of Nap, Acy, Ace, Flu, and Ant exceeded the lower limit of the sediment quality criteria, and higher toxic equivalent concentration values of the total carcinogenic PAHs were observed nearby the midstream of the SR, which may cause adverse biological effects and implies a need for regular monitoring.