Reevaluation of microplastics identification based on Neuston net survey data

Influence of monsoon seasonality and tidal cycle on microplastics presence and distribution in the Upper Gulf of Thailand

Southeast Asian countries are recognized as significant contributors to the discharge of abundant plastic waste into the ocean. In this study, we conducted neuston net surveys on Si Chang Island of the Gulf of Thailand, a coral reef conservation area, to determine the presence of microplastic (MP) pollution. The survey, conducted during the wet (southwesterly monsoon), transition, and dry seasons (northeasterly monsoon), revealed that the MP abundance was in the range of 0.02-42.46 particles m-3. The precipitation, wind, and current direction induced by monsoons influenced the abundance and distribution of MP, presenting a significant seasonality. The cluster analysis for colors and polymer types of MPs suggested that the origin of plastic particles is diverse. Based on our results, a proposal for the generation, sources, and pathways for MPs in the Gulf of Thailand is presented: 1) plastic wastes exposed to strong UV light during the dry season get fragmented around the river, and 2) heavy rains wash away the particles during the wet season. This proposal is applicable to tropical regions, including the Gulf of Thailand. Therefore, this paper concluded that ocean currents induced by monsoons and the unique climate, resulting in the generation of MPs on land, increase MP presence and distribution in the ocean surrounding Southeast Asia countries. Furthermore, coral reef ecosystems can be particularly threatened by MPs in these areas. So, an increase in MP monitoring on coral ecosystems from Thailand and the world is highly recommended.

Accessing the intrinsic factors of carbonyl index of microplastics: Physical and spectral properties, baseline correction, calculation methods, and their interdependence

Carbonyl index (CI) is a measure of the degradation status of microplastics. While many studies address environmental factors of microplastic degradation, intrinsic factors like physical properties, spectral properties, baseline correction, and CI calculation methods are less explored. This research focused on these aspects using surface seawater samples. We found that color and shape have limited dependence on particle size or signal-to-noise ratio (SNR). Baseline correction can significantly alter CI values, with the direction of the shift depending on the methods used. Additionally, most CI values before and after baseline correction and those calculated using different methods tend to be strongly correlated. Using the selected CI calculation methods, we found that CI values varied significantly by shape and color. CI's relation to the similarity between the sample and its pristine form suggests an alternative degradation measure. Our findings emphasize the need for standardized CI calculation methods.

Comparative evaluation of the carbonyl index of microplastics around the Japan coast

The carbonyl index (CI) of polyethylene and polypropylene microplastics (MPs) (2950 particles) collected in coastal waters around Japan was investigated. The CI of MPs was calculated by the specified area under band technique. The mean MP CI in all samples (regardless of shape and color) was 0.69 ± 0.34 and 0.70 ± 0.34 for polyethylene and polypropylene, respectively, and there was no significant difference in the color or shape of the MPs. The polyethylene, white, and fragment MPs CI was negatively (p < 0.05) correlated with the major length of the MPs. Large MPs with relatively little deterioration were distributed along the west coast of the Sea of Japan, whereas small MPs were distributed along the east coast. Our findings of this gradual change in the deterioration of MPs, based on geographical distribution, are in accordance with literature CI-size and MP degradation hypotheses.

Contamination of sea surface water offshore the Tokai region and Tokyo Bay in Japan by small microplastics

A nested double neuston net was prepared and used to collect samples from the surface of coastal waters around Japan to obtain information about the properties of both small microplastics (SMPs; <350 μm) and large microplastics (LMPs; >350 μm). The SMP concentrations ranged from 1000 to 5900 pieces m^-3 in the open ocean and averaged approximately 3000 pieces m^-3 in the inner part of Tokyo Bay. The SMP concentrations were around 20-60 times greater than the LMP concentrations. By analyzing the seawater, we obtained a microplastic size distribution that spanned 50-5000 μm. The LMPs mainly comprised packaging-related plastics, such as polyethylene (PE) and polypropylene, while the SMPs were dominated by paint-related plastics. SMPs derived from packaging materials (e.g., PE) may have gradually sank down from the sea surface when they were smaller than 600 μm.