Underwater hidden microplastic hotspots: Historical ocean dumping sites

Deciphering the seasonal dynamics of microplastic morphotypes and associated co-contaminants along the northwest coast of India

In the present study, the northwest coast of India, bordering the Arabian Sea, was selected to evaluate the microplastic (MP) abundance. This is the first study to emphasize the effects of different seasons on MP distribution. The collected MPs were dried, segregated, and evaluated based on their morphotype, size, color, and polymer type. A total of 1756.6, 7326.6, and 202 particles/kg of sand were estimated in the pre-monsoon, monsoon and post-monsoon seasons, respectively, with a dominance of polypropylene (PP) type of plastic in the pre-monsoon and high-density polyethylene (HDPE) in monsoon and post-monsoon seasons. HDPE and PP collected MPs during the monsoon season were further characterized for associated contaminants. Metal absorbance was detected using SEM-EDX mapping and ICP-MS. The presence of organic compounds (OCs) was analyzed using GC-MS. MPs exhibit distinct associations with metals, among which the HDPE pellet morphotype exhibits a higher range of metal adsorption. Total 61 different OCs were associated with MPs. The HDPE pellets contained the highest amounts of hydrophobic organic compounds. PP pellets were found to contain triglycerides, fatty aldehydes, and alkaloids, along with HOCs. Among morphotypes, pellet forms of MPs were found to adsorb more contaminants. These co-contaminants infiltrate the study area through sewage runoff and shoreline debris deposition, subsequently interacting with MPs. Furthermore, the MP diversity was studied by employing the MP diversity integrated index, which suggests that most of the MP diversity was observed in the pre-monsoon period. The pollution load index employed an MP risk assessment, which presented a low degree of MP contamination. In contrast, the polymer hazard index was calculated as 21650.3 in post-monsoon, placing the area under the extreme danger category. It is evident from the data that the types of MP is more important than their number. Thus, MP morphotypes have importance in the adsorption of co-contaminants.

Microplastic-induced inhibition of cell adhesion and toxicity evaluation using human dermal fibroblast-derived spheroids

Nanoplastics and microplastics (MPs) can significantly affect marine ecosystems and pose potential risks to human health. Although adverse effects stemming from direct exposure to MPs have been demonstrated at the cellular level in animal models, the potential toxicity of these materials in the human body remains uncertain. In this study, we investigated the three-dimensional (3D) behavior of dermal-derived cells exposed to MPs using artificially manufactured spherical primary polystyrene (PS) particles. To explore these effects, we used cellular spheroids as a 3D cell culture model, examined the size-dependent penetration of PS-MPs, and observed morphological alterations in the spheroids. Furthermore, we assessed changes in physiological activities, including reactive oxygen species, adenosine triphosphate, and lactate dehydrogenase, to elucidate the potential intra- and extracellular toxic reactions to PS-MPs. Additionally, our examination of cell-cell junctions and the extracellular matrix (ECM), along with analysis of the regulators involved in their decreased integrity, revealed negatively influenced changes in expression. This exposure study using spheroid models provides new insights into the potential toxicity of short-term exposure to MPs under conditions that closely resemble in vivo systems.

Applying new regional background concentration criteria to assess heavy metal contamination in deep-sea sediments at an ocean dumping site, Republic of Korea

It is crucial to establish appropriate background concentrations to discern heavy metal pollution in the marine environment. In this study, we analyzed heavy metals in deep-sea sediment cores to determine regional background concentrations at the East-Sea Byeong Ocean dumping site. The vertical profiles of heavy metals were categorized into three groups based on their contamination characteristics, and regional background levels for 12 metals were determined using pre-1900 averages. The enrichment factor, contamination factor, and pollution load index, calculated using regional background concentrations, indicated significant contamination by Cr, Co, Cu, Zn, Cd, Hg, and Pb during the ocean dumping period. These results differ from those obtained using global average concentrations. This underscores the importance of considering regional characteristics to minimize the risk of misinterpreting anthropogenic impacts. The approach based on local information is considered useful when sediment quality guidelines are absent or inapplicable.

Depth profiles of microplastics in sediments from inland water to coast and their influential factors

Microplastics, plastic particles with a size smaller than 5 mm, are widely observed in the global environments and pose a growing threat as they accumulate and affect the environments in numerous ways. These particles can be transported from inland water to coast and disperse from surface water to deep sediments, especially the latter, while knowledge of the hidden microplastics in sediment layers is still lacking. Understanding the characteristics and behavior of microplastics in deep sediments from inland water to coast is crucial for estimating the present and future global plastic budget from land to seas. Herein, present knowledge of microplastic sedimentation from inland water to coast is reviewed, with a focus on the physical characteristics of microplastics and environmental factors that affect sedimentation. The abundance, shape, composition, and timeline of microplastics in sediment layers in rivers, floodplains, lakes, estuaries and coastal wetlands are presented. The abundance of microplastics in sediment layers varies across sites and may exhibit opposite trends along depth, and generally the proportion of relatively small microplastics increases with depth, while less is known about the vertical trends in the shape and composition of microplastics. Timeline of microplastics is generally linked to the sedimentation rate, which varies from millimeters to centimeters per year in the reviewed studies. The spatiotemporal characteristics of microplastic sedimentation depend on the settling and erosion of microplastics, which are determined by two aspects, microplastic characteristics and environmental factors. The former aspect includes size, shape and density influenced by aggregation and biofouling, and the latter includes dynamic forces, topographic features, bioturbation and human activities. The comprehensive review of these factors highlights the needs to further quantify the characteristics of microplastic sedimentation and explore the role of these factors in microplastic sedimentation on various spatiotemporal scales.

High salinity promotes the photoaging of polystyrene microplastics with humic acid in seawater

The photoaging of microplastics (MPs) accumulated in the sea can be influenced by humic acid (HA). However, the role of salinity cannot be ignored, as it may potentially disrupt the interaction between MPs and HA, thereby altering the photoaging of MPs. Herein, this study investigated how salinity influences the effect of humic acid (HA, derived from lignite) on the photoaging of polystyrene microplastics (PS MPs) in artificial and natural seawater. The results revealed that HA promoted the photoaging of PS MPs under both low (5 PSU) and high salinity (35 PSU) in light conditions (L), reflected in the formation of fragments, the production of oxygen-containing functional groups (OH, CO, and OCO), and the increase in hydrophilicity of PS MPs. Furthermore, high salinity promoted the photoaging of PS MPs with HA more significantly, as evidenced by the similar indicators and the order of oxygen/carbon atom ratio (O/C): L-HA-High (0.15) > L-HA-Low (0.10) > Unaged (0.02). Interestingly, due to the reduction of electrostatic repulsion, the adsorption of HA on photoaged PS MPs in natural and artificial high salinity seawater was 1.77 mg/g and 0.39 mg/g, respectively, which was significantly higher than those PS MPs photoaged in the low salinity seawater. Furthermore, the electron spin resonance (ESR) results confirmed that more hydroxyl radicals (OH) were generated after adsorbing HA under high salinity conditions, thus promoting the fragmentation and oxidation of PS MPs. Overall, our findings highlight the crucial role of salinity in influencing the photoaging of MPs with HA and help to assess the marine risk of MPs accurately.

Spatial distribution and historical trend of microplastic pollution in sediments from enclosed bays of South Korea

Seafloor sediments are an important sink for microplastics (MPs), and the vertical profile of MP accumulation in a sediment core represents historical pollution trends. In this study, MP (20-5000 μm) pollution in surface sediments of urban, aquaculture, and environmental preservation sites in South Korea was evaluated, and the historical trend was investigated using age-dated core sediments from the urban and aquaculture sites. The abundance of MPs ranked in the order of urban, aquaculture, and environmental preservation sites. Polymer types were more diverse at the urban site compared to other sites, and expanded polystyrene was dominant in the aquaculture site. An increase in MP pollution and polymer types was observed from bottom to top of cores, and historical trends of MP pollution reflect local influences. Our results indicate that the characteristics of MPs are determined by human activities, and MP pollution should be addressed according to the characteristics of each site.

Distribution and characteristics of microplastics in sediment at representative dredged material ocean dumping sites, China

Dredged material ocean dumping activities are likely an important source of microplastics (MPs) in coastal areas but have received little attention globally. In this study, we investigated the spatiotemporal distribution and characteristics of MPs in sediments at eight dredged material dumping sites of China. MPs were separated from sediment through density flotation, and polymer types were identified using μ-FTIR. The results showed that the average MP abundance was 112.82 ± 109.68 items/kg d.w. The MPs were more abundant at nearshore dumping sites than at distant dumping sites. Dumping activities may be the main contributor of MPs to Site BD1, the farthest dumping site from shore, but only a minor source of MPs at the other dumping sites. The characteristics of MPs were dominated by transparent PET fibers <1 mm. Overall, sediments at the dumping sites exhibited relatively low to moderate concentrations of MPs in comparison to most other coastal sediments.

Microplastics transport in a low-inflow estuary at the entrance of the Gulf of California

Microplastics (MPs) are recognized as a global emergent pollution impact, which can affect all food chains. Estimating MPs transport pathways in coastal ecosystems is needed to assess their likely effects. Here, we studied MPs accumulation and transport pathways in the Estero de Urias lagoon system (low-inflow estuary) using field data and a 3D particle model. Field results showed that the MPs present similar abundances throughout the study area during the dry and rainy seasons. Model simulations indicated that i) morphology and tidal currents caused the MPs discharged in the lagoon to remain inside, and ii) wind-induced currents caused the MPs in the coastal area to be transported to the southwest. These transport processes may be responsible for homogenizing MPs concentrations through the studied area. In addition, model simulations suggested that EUL-dense waters can export MPs from the coastal area to the sea bottom.

Warming and microplastic pollution shape the carbon and nitrogen cycles of algae

Oceans absorb most excess heat from anthropogenic activities, leading to ocean warming. Moreover, microplastic pollution from anthropogenic activities is serious in marine environments and is accessible to various organisms. However, the combined effects of environmentally realistic ocean warming and microplastic pollution (OW+MP) on dominant marine species phytoplankton and related biochemical cycles are unclear. We investigated the combined effects on the dominant genera of diatoms (Chaetoceros gracilis, C. gracilis) over 100 generations. As a biological adjustment strategy, the growth rates of C. gracilis were nonsignificantly changed by OW+MP, body size decreased, and the chlorophyll a (Chl a) content and photosynthetic efficiency significantly decreased by 32.5% and 10.86%, respectively. The OW+MP condition inhibited carbon and nitrogen assimilation and sequestration capacity and allocated carbon into flexible forms of carbohydrates instead of proteins. Furthermore, the decrease in Si:C and Si:N ratios affected carbon transport to both the mesopelagic layer and deep ocean. Integrated transcriptomics and metabolomics showed that OW+MP disturbed ribosome and nitrogen metabolism. Given the rising concurrence of warming and MP pollution, the changes in metabolism suggest that the covariation in carbon, nitrogen and silicon biochemical cycles and the hidden influence on biodiversity and food web changes in the ocean should be reconsidered.

Long-term deposition records of microplastics in a plateau lake under the influence of multiple natural and anthropogenic factors

Microplastic accumulation in the lake aquatic environment has attracted worldwide attention, but the long-term deposition characteristics and influencing factors of microplastics are not clear. Hence, we attempted to analyze the factors that influence the accumulation of microplastics during the process of natural environmental change and social development through the method of the sedimentological approach. In this investigation, the chronological sequence of sediment core was set up based on lead-210 composition to study microplastic accumulation rates in a plateau lake, Jianhu Lake. For the first time, the records of microplastic deposition were analyzed combined with multiple anthropogenic and natural factors, including 4 natural and 17 social factors to reveal the influence of natural processes and social development on microplastic abundances. The results showed that sediments were highly contaminated by microplastics, and the mean abundance of microplastics in the sediment cores of Jianhu Lake was 924 ± 427 particles/kg, and showed a gradually increasing trend from the bottom (25 to 30 cm) to surface layer (0 to 5 cm). Blue and black were the main colors of microplastics, and the average proportion of wirelike microplastics was 63 %. Additionally, the polymer type of microplastic was mainly rayon, the surface morphology of different polymer types was disparate, and various elements enriched on the surface of microplastics were also detected. In the past 70 years, the deposition rate of microplastics in Jianhu Lake maintained the trend of continuous growth, and the abundance of microplastics is projected to be 448 to 3017 and 513 to 3670 particles/kg by 2035 and 2050, respectively. What is more, there are significant correlations among multiple natural and anthropogenic factors and microplastic deposition, as well as microplastic polymer species.