Wastewater treatment plants (WWTPs) play a pivotal role in removal of microplastics (MPs) particles before the waste streams are discharged into aquatic environments. Indiscriminate disposal of the effluent and untreated wastewater not only contribute to accumulation of MP in the marine environment, but they can also act as a carrier for various hydrophobic compounds and contributors of pollutants that leach from them via natural degradation. In this assessment, we have summarized the MP concentrations in influent and effluent streams, and provide quantification of the discharges from these WWTPs. Almost 50% of the global wastewater influent of 3,562,082 × 10⁵ m³ remains untreated. Some conservative estimates indicate that treated effluent disposal can add around 1.47 × 10¹⁵ MPs annually, whereas the discharge of untreated effluent is likely to add a staggering 3.85 × 10¹⁶ MPs annually to the aquatic environments. The efficiency of MP removal in wastewater treatment plants varies between 88 and 99.9%, indicating the potential of capturing the majority of the MP from escaping into the freshwater and marine environment. Based on WWTP removal efficiencies for MPs, calculations suggest that if all the globally produced wastewater was treated prior to release, a reduction of over 90% of the current amount of MP inputs into the aquatic environment could be achieved. From the number of studies conducted and assessments made on MPs in waste streams, it is obvious the methodologies followed were quite different, and the use of acids and heating are likely to deteriorate the MPs, emphasizing the need to develop harmonized protocols for microplastic assessment in wastewater treatment plants.

Bioaccumulation of organochlorine pesticides (OCPs) in red, green, and brown seaweeds from the Gulf of Mannar was investigated using gas chromatography–mass spectrometry (GC–MS). The concentration of OCPs in all the seaweeds was in the order of endosulfan > endrin > HCH > DDT > aldrin > heptachlor > methoxychlor. The concentrations of HCH, endrin, endosulfan, and DDT in Sargassum wightii and Gelidiella acerosa, and HCH and endosulfan in Gracilaria verrucosa were above the limits prescribed by the European Commission. However, in Ulva lactuca, except for endosulfan, all other OCPs were below the permissible level. The bioaccumulation of OCPs in seaweeds was in the order of S. wightii > G. acerosa > Gracilaria verrucosa > U. lactuca. The results of comparative analysis of the levels of the investigated pesticides against the standard human health risk assessment revealed that pesticide exposure from seaweeds is hazardous to human health and the marine environment of the Gulf of Mannar.

An innovative multiple regression analysis was used to evaluate metal/metalloid contamination in the surface sediments of a coastal lagoon. The concentrations of metals/metalloids were represented as a function of geochemical characteristics of the sediments (fine fraction, concentrations of organic carbon, Ca, Al, Mn) and distances between sampling points. The effect of distances on the concentrations were negligible for Li, Co, Ni, Ba, V, Cr, and only geochemical variables specific for each element explained its spatial variation. The concentrations of As, Cu, Zn and Pb were influenced by both geochemical and geographical distance variables, the latter representing the anthropogenic influence and the extent of transport of contaminants away from the upstream source. Enrichment of the sediment with Ba, As, Co, Cr and V was determined mainly by enrichment with Mn. The proposed approach is supplementary to the traditional utilization of enrichment factors, and is better suited for systems with anthropogenic influence.

This study identifies the impact of river sediments on coastal ecosystems in the southwestern coastal region of Korea. Surface sediments were analyzed for their spatial distributions of organic matter, nutrients, and heavy metal concentrations. Furthermore, pollutants were identified according to the pollution load index (PLI) and potential ecological risk index (RI). Concentrations did not show serious pollution levels compared to generalized guidelines; however, some sites exceeded the PLI pollution standard, and were also identified as potential ecological risks. Through cluster analyses the sediment sites were classified into three groups: rivers with relatively high concentrations of organic matter and nutrients, rivers affected largely by artificial heavy metal pollution, and rivers with low levels of pollution by organic matter, nutrients, and heavy metals. It is evident that continuous monitoring and management are required to prevent major pollution from industrial complexes, agriculture, and commercial activities in the regions near these rivers.

The Persian Gulf, the most important marine ecosystem, and its islands are negatively impacted by development and pollution. Different types of pollution, especially heavy metals in these habitats, may create risks to birds, influencing reproductive performance, survival, and behaviors.Heavy metals (Cd, Pb, Cr) were analyzed in two long-lived and top food web–level sea birds, Lesser (Thalasseus bengalensis) and Greater Crested Tern (Thalasseus bergii). The research was carried out during 2018 on Nakhiloo Island, located in Dayyer-Nakhiloo Marine National Park, northeastern Persian Gulf, Iran. The nests were selected randomly, and 40 eggs of colonially-nesting terns (20 eggs T. bengalensis and 20 eggs T. bergii; a single egg per nest) were collected. The concentration of heavy metals in eggshells and egg contents was studied to investigate whether bioaccumulation varies between the eggshells and egg contents and also varies in both species. There were significant differences in the amounts of Cd between eggshell and egg content in the Greater and Lesser Crested Tern. This difference was not significant in the concentrations of Pb between the eggshell and egg content in the Tern species. Concentration of Cr did not appear to accumulate in the egg content and was below detection limit. There were significant differences in the concentrations of Cd in the eggshells and egg content between the Greater and Lesser Crested Tern. The results serve to improve understanding and to evaluate the dynamics of heavy metals in eggshells and egg content in various avian species.

Rivers are a major pathway for plastics between lands and the ocean. At the land-ocean interface, estuaries make the transfer dynamic of plastics complex and nonlinear. That is why very little is known about this dynamic. In this respect, a specific marker (i.e. Microlax packaging) showing date-prints was systematically investigated in different riverbanks of the Seine estuary to identify the share of “old” and “recent” litter transiting through the estuary toward the ocean. Up to 70% of Microlax were “old” plastic items probably related to the meandering dynamic of the river over large time and space scales, and hydrodynamic conditions (tides) at smaller scales. This contributes together to increase the residence time of plastics into the estuary up to decades with almost endless transport, deposit and remobilization cycles. Consequently, the Seine estuary may function as a “microplastic factory” resulting from the fragmentation of macroplastics into microplastics well before they reach the ocean.

The present work was undertaken to assess the impact of trace element concentration and the status of potential ecological risk in the reef sediments of the Vembar group of islands, Gulf of Mannar Marine National Park, India. Totally, 114 reef sediments (surface) were collected from the Vembar group of islands (Nallathanni Island – 36 samples; Upputhanni Island – 48 samples; Puluvinichalli Island-30 samples). The reef sediments are enriched with sand-sized calcareous particles. The calcium carbonate percentage (CaCO₃) was primarily controlled by the distribution of coral colonies and available lithogenic grains. The pollution load index (PLI) reveals that the majority of the sediments fall under the unpolluted category. Moreover, the potential ecological risk (PERI) and sediment pollution index (SPI) reveals that the Vembar group of islands fall under the low ecological risk category.

Red tide has always been an environmental issue with global concern. A Noctiluca scintillans red tide and a Mesodinium red tide occurred successively in Yantai nearshore, China, where is usually oligotrophic, in October 2019. Currents, phytoplankton community composition and nutrients were analyzed to access the driving factors of the red tides. The maximum N. scintillans and Mesodiniium abundance reached 124.92 ± 236.84 × 10³ cells/L and 1157.52 ± 1294.16 × 10³ cells/L respectively. The fast growth of N. scintillans was due to increasing abundance of phytoplankton. The currents were crucial to the assembly and dispersal of red tides. The red tides significantly redistributed the nutrients in the red tide patches and regulated the dominant species in phytoplankton community. Our study illuminates the influence of physical-biochemical coupling processes on red tides, and suggests that ocean dynamics such as currents and tidal factors deserve more attention when considering the ecosystem health problems of coastal zones.

This paper presents an incubation experiment with sediment cores from the Changjiang Estuary Mud Area (CEMA) to quantify the release of nutrients due to simulated resuspension. The results show that except for nitrate (NO₃⁻-N), phosphate (PO₄³⁻-P), ammonium (NH₄⁺-N), nitrite (NO₂⁻-N) and silicate (SiO₃²⁻-Si) were released from the sediment to the overlying water, primarily due to desorption (P), dissolution (SiO₃²⁻-Si) and mineralization (NH₄⁺-N) with only minor direct contributions from the sediment pore water. The significant release of nutrients by resuspension and subsequent processes can alleviate the phosphorus and silicon limitation in water bodies, enhance the growth of phytoplankton, and thus promote the oxygen consumption and ultimately lead to hypoxia. The results of this study are highly relevant for many coastal areas in other parts of the world with large amounts of stored organic matter and nutrients in sediments and frequent perturbation by storm events.

This study aims to evaluate the expression of biomarkers of oxidative stress (LPO, GPx, AtCh, SOD) in mussels (Mytilus galloprovincialis) following the exposure to suspensions of microparticles irregular shaped fibres of Polyethylene terephthalate of different sizes (small 5–60 μm, S-PET; medium 61–499 μm, M-PET; large 500–3000 μm, L-PET) at a single dose of 0.1 g/L. Mussels were tested under two different starting pH conditions of marine water: standard (8.0) and acidified (7.5). The results obtained from this study show that: i) PET microplastics are able to induce biochemical stress in mussels; ii) among the biomarkers tested, LPO and GPx were more effective in detecting the stress induced by microplastic in both initial pH conditions; iii) the expression of biomarkers was influenced by the size of the microparticle. In particular, greater effects were associated with the largest PET particle tested (0.5–3.0 mm); iv) regarding the effect of pH, in experiments starting from 7.5 pH the animals showed a lower biomarker expression than those starting from 8.0 pH.