Spatiotemporal variation in microplastics derived from polymer-coated fertilizer in an agricultural small river in Ishikawa Prefecture, Japan.

Marine plastic pollution has highlighted the need to address the disposal of plastic materials used in agricultural fields and prevent their runoff. To assess the status of microplastics derived from polymer-coated fertilizers (microcapsules), we investigated their seasonal and daily variations in a small agricultural river in Ishikawa Prefecture, Japan, throughout the irrigation period of April to October 2021 and 2022. We also investigated the relationship between microcapsule concentration and water quality. The mean microcapsule concentration over the study period ranged from 0.0 to 783.2 mg/m3 (median 18.8 mg/m3) and was positively correlated with total litter weight, but it was not correlated with common water quality parameters such as total nitrogen or suspended solids. Concentrations of microcapsules in river water showed distinct seasonal variations, being particularly high in late April and late May (median 55.5 mg/m3 in 2021, 62.6 mg/m3 in 2022) and almost undetectable thereafter. The timing of the increase in concentration coincided with the timing of the outflow from paddy fields, suggesting that microcapsules that flowed out of the paddy fields would reach the sea relatively quickly. The results of a tracer experiment supported this conclusion. Intensive observations revealed that microcapsule concentrations varied widely over time, with differences reaching a maximum of 110-fold (range 7.3-783.2 mg/m3) over a 3-day period. Daytime concentrations were higher than those at night, reflecting the fact that microcapsules are discharged from paddies by daytime operations such as puddling and surface drainage. Microcapsule concentrations in the river were not correlated with river discharge, making estimating their loading a future research challenge.

Model for projecting the generation of used disposable diapers in the era of depopulation and aging in Japan.

Japan has entered a period of depopulation and aging ahead of any other country. One concern in an aging population is increases in the generation of used disposable diapers. The use of disposable diapers, which are largely composed of plastic, can be an important issue as we work towards building a carbon-free society and break away from using fossil-derived plastics. This study aimed to develop a model to project the future generation of used disposable diapers in each municipality in Japan through 2045 and to identify the effects on municipal solid waste (MSW) management. We revealed the per capita generation of used disposable diapers, distinguishing disposable diaper products, urine and faeces in an online survey of 2000 respondents. The generation of used disposable diapers was estimated to increase in general, but the amount was projected to decrease in rural areas where the population of elderly people would decline. The proportion of used disposable diapers in combustible waste was projected to increase by 2045 in almost all municipalities of Mie Prefecture. Based on the scenario in which disposable diaper products would become lighter in the future because of technical improvements, we concluded that the impact of the decrease in the lower heating value (LHV) of used disposable diapers on the incineration process cannot be ignored in the future.

The input-output balance of microplastics derived from coated fertilizer in paddy fields and the timing of their discharge during the irrigation season.

Polymer-based microcapsules derived from coated fertilizers are not recovered after use. Therefore, they are a source of microplastics to the agricultural lands and coastal areas of Japan. In this study, we investigated the input-output balance of microcapsules in three paddy fields and the timing of microcapsule discharge from the fields with the aim of developing effective techniques to reduce microcapsule discharge. Microcapsules were discharged from the paddy fields primarily during puddling, when the weir plate was overflowed, and when surface drainage was implemented. About 50% of the total discharge during the irrigation period occurred during puddling, which is a process for leveling paddy fields. Therefore, contamination of the surrounding environment by microcapsules from paddy fields can be effectively reduced by preventing the release of microplastics from paddy fields during puddling. We also showed that the total microcapsule discharge cannot be controlled solely by irrigation water management, such as by adjusting the height of the weir plate. We found that about 0.067-0.076% of the total number of microcapsules accumulated in the soil of the paddy fields was discharged during the irrigation season in 2020. Furthermore, 70% of the microcapsules discharged from one field in 2020 had resided in the soil for at least two years. The use as fertilizer coatings of biodegradable polymers that would degrade completely in the soil within a few years could therefore substantially reduce the amount of microplastics released into the ocean from agricultural fields, and their development is thus urgently needed.

Accumulation of microcapsules derived from coated fertilizer in paddy fields.

Japanese agriculture uses large amounts of plastics. Fertilizer-containing plastic microcapsules with a diameter of 2-5 mm ("coated fertilizer") are not recovered after use, and after diffusion of the fertilizer components these microcapsules are found in large quantities, not only on agricultural land but also along the coast of Japan. Here, we investigated the accumulation of microcapsules derived from coated fertilizer in 19 paddy fields. Microcapsules were detected in all of the paddy fields surveyed, at concentrations in the range of 6-369 mg/kg (mean 144 mg/kg)-much higher than the concentrations of microplastics in farmlands in other countries. There was no difference in mean microcapsule concentration between sampling sites with continuous rice cultivation and those with crop rotation, but that of a paddy field that had never received coated fertilizer was significantly lower. Examination of the spatial distribution of microcapsules in one paddy field showed that there was a hot spot with a high concentration near the drainage outlet. This was likely due to the strong influence of irrigation water flowing from the water inlet to the drainage outlet. The amount of microcapsules accumulated in Japanese paddy fields, as estimated from our results, and the amount applied to the fields, as estimated from the statistics, were almost equivalent. Therefore, most of the microcapsules that have already been applied to paddy fields may continue to accumulate. The impact of these high concentrations of microcapsules on the soil environment needs to be assessed.

The role of coated fertilizer used in paddy fields as a source of microplastics in the marine environment.

Fixed-point and multi-point field survey was conducted to determine the actual contamination of the Japanese coast by microcapsules derived from coated fertilizers. The results indicated that the amount of microcapsules increased during the irrigation season (9423-74,869 pieces/m2) and decreased in the non-irrigation season (77-1471 pieces/m2). Microcapsules accounted for 90% of all microplastics sampled during the irrigation season. The lack of correlation between the area of agricultural land in the watershed and the microcapsule density on the coast suggested that the density of microcapsules on the coast was not only dependent on the total load to the ocean, but also on topographic and meteorological conditions. More than 90% of the microcapsules collected from the shoreline were made of polyethylene. Scanning electron microscopic observation of the surface of the microcapsules revealed that portions of the microcapsules were removed as secondary microplastics in the process of migration to the ocean.

Bicarbonate and unsaturated fatty acids enhance capsular polysaccharide synthesis gene expression in oral streptococci, Streptococcus anginosus.

We recently reported on the capsular polysaccharide (CP) synthesis (cps) genes of the oral streptococci, Streptococcus anginosus. In this study, we investigate the effects of carbon dioxide (CO2), bicarbonate (HCO3-) and unsaturated fatty acids (UFAs) on CP synthesis of S. anginosus. We found that CP production increased when bacteria were exposed to high concentrations of CO2. This increase was similarly observed in the presence of sodium bicarbonate (NaHCO3) under atmospheric condition. Since ectopic expression of carbonic anhydrase, which converts CO2 to HCO3-, eliminated the requirement for CO2 in CP production and growth of S. anginosus lacking this enzyme, it seemed that HCO3- is an essential factor for CP production. Furthermore, UFAs also stimulated the CP production. Promoter-reporter assay and quantitative reverse transcription polymerase chain reaction (RT-qPCR) analysis confirmed that stimulation of CP production occurs at the transcription level. The results of the promoter assays suggest that the expression and stimulation of cps genes by HCO3- or UFAs require the cpsA gene, which is located in the first position of the cps operon. With respect to the relationship between HCO3-and UFAs, HCO3- may stimulate UFA synthesis pathway at transcription level. Therefore, it is possible that UFAs are definitive signals for the CP production in S. anginosus.

Guaiacol oxidation activity of herbivorous land crabs, Chiromantes haematocheir and Chiromantes dehaani.

The land crabs, Chiromantes haematocheir (Akate-gani) and Chiromantes dehaani (Kurobenkei-gani) inhabit seaside forests in Japan. The crabs mainly consume plant material and its detritus. Therefore, they are expected to possess the ability to degrade the major components of biomass, cellulose and lignin in order to digest plant materials. In this study, we analyzed biomass-degrading activities of the land crabs, especially guaiacol oxidation activity, which seems to be related to lignin degradation. Cellulase activity was detected from almost all gut samples including the stomach, midgut gland and intestine of all dissected crabs. Conversely, high guaiacol oxidation activity was detected in the midgut gland of all C. dehaani and several female C. haematocheir crabs. This is consistent with a previous study showing that female crabs were more herbivorous than male crabs were and observation that C. dehaani crabs are more herbivorous than C. haematocheir. Guaiacol oxidation activity might play an important role in the herbivorous behavior of land crabs.