Hydrogeological characteristics and water chemistry in a coastal aquifer of Korea: implications for land subsidence.

Land subsidence is the gradual or sudden dropping of the ground surface developed by increasing the total stress. Most studies have discussed the relationship between land subsidence with groundwater level. However, there is a lack of discussion on groundwater environmental changes after occurring land subsidence. This study aimed to evaluate the hydrogeological and water chemistry characteristics of construction sites with land subsidence. Land subsidence in the Yangyang coastal area occurred suddenly on August 3, 2022, when the retaining wall of the construction collapsed. The groundwater level was measured three times, and water samples were collected twice between August 5, 2022, and September 5, 2022, for laboratory analysis. After land subsidence occurred, the average groundwater level was - 19.91 m ground level (GL) on August 9, 2022, and finally decreased to - 19.21 m GL on September 05, 2022. The groundwater levels surrounding the construction site gradually increased for a month. The electrical conductivity value measured at the monitoring wells ranged from 89 to 7800 µS/cm, and four wells exceeded the measurement limit near the groundwater leaked points. The highest mixing ratio of leaked water samples, collected on August 9, 2022, was 27.6%. Furthermore, the fresh groundwater-saltwater interface depth was estimated to be above the construction bottom. Although groundwater levels recovered, the groundwater quality continuously is affected by saltwater. This finding could contribute to understanding the hydrogeological characteristics surrounding construction sites with land subsidence and provide insight into the hydrochemical evolution process during declined groundwater levels in coastal aquifers.

Microplastic contamination in groundwater of rural area, eastern part of Korea.

Microplastics (MPs) are emerging contaminants in agricultural regions owing to the widespread use of plastics in farming activities. Groundwater has a vital role in farming activities, and it can be contaminated by MPs, fragmented from plastic products used in agricultural activities. Following an appropriate sampling protocol, this study investigated the distribution of MPs in shallow to deep aquifers (well depths: 3-120 m) and cave water of an agricultural region in Korea. Our investigation found that MPs contamination can penetrate up to the deep bedrock aquifer. The abundance of MPs was lower during the wet season (0.014-0.554 particles/L) than during the dry season (0.042-1.026 particles/L), which may be attributed to the dilution effect of precipitation in the groundwater. The abundance of MPs increased as the MPs size decreased at all sampling points, and size ranges were 20.3-869.6 and 20.3-673.0 µm in the dry and wet seasons, respectively. Our findings showed lower MPs abundance compared to previous studies, and we inferred that it might be due to differences in groundwater sampling volume, low agricultural intensity, and the non-application of sludge fertilizers. Our findings suggest that repeated and long-term investigations are needed to identify better the factors that influence the results of MPs distribution in groundwater, including sampling methods and hydrogeological and hydrological conditions.

Microplastic contamination in groundwater on a volcanic Jeju Island of Korea.

Microplastic (MPs) contamination in groundwater has received massive attention since plastic waste has been released directly into the environment. This study investigates MPs contamination in groundwater on the Jeju volcanic Island, Korea. To the best of our knowledge, this is the first study to identify MPs in groundwater from volcanic islands. A total of 21 sites were sampled for groundwater wells and springs in July and September (2021). Sampling was performed without cross-contamination through quality assurance and quality control. The results showed that MPs abundance ranged from 0.006 to 0.192 particles/L in groundwater samples. Additionally, MPs were detected in deep groundwater wells where the groundwater level was 143 m below ground surface. Eight MPs polymer types, including polypropylene, polyethylene, polyethylene terephthalate, polyvinyl chloride, polystyrene, polyamide, acrylonitrile butadiene styrene, and polyurethane, were detected using Micro-Fourier Transform Infrared Spectroscopy (µ-FT-IR). Most of the detected MPs size ranged from 20 to 100 µm, accounting for 95% of the total. Fragments and fiber shaped MPs were detected, with the majority of them being fragmented in groundwater samples. The concentrations of MPs and major ions in groundwater showed a positive correlation. A negative correlation was observed between MPs concentration and topographic elevation (r = -0.59, p = 0.01). The source of MPs contamination is most likely attributed to agricultural activities, such as plastic mulching and greenhouses, which account for most of the land use in the study area. In this study, MPs entered the aquifer through the soil at the surface and seeped through cracks in fractured rock on basalt with sealed groundwater wells. This study takes 500 L of samples to prevent sample bias, reveal plastic contamination in groundwater, and indicating the characteristics and sources of contaminated plastics.

Microplastics in soil and freshwater: Understanding sources, distribution, potential impacts, and regulations for management.

Plastic debris is a complex and persistent environmental contaminant that has received a high amount of attention in the last few years. Understanding the sources, transport, fate, occurrence, and health risks of microplastics (MPs) in the environment is essential as millions of tons of plastic are manufactured and released into the environment. There is a high possibility that MPs will accumulate and retain within continental environments and have effects on the environment and human health. This review elucidates the outcomes of studies related to the prevalence, transport, fate, and health risks of MPs in soil and freshwater environments. The review shows that the sources of MPs are diverse and extensive and their occurrence, transport, fate, and health risks in the environment are affected by their physico-chemical characteristics and by natural factors. Implemented legislation or regulatory plans to reduce MPs contamination of the environment have been reviewed in this study. Moreover, management options are presented.

Good field practice and hydrogeological knowledge are essential to determine reliable concentrations of microplastics in groundwater.

There are some weaknesses in the methodology of original paper "Informal landfill contributes to the pollution of microplastic in the surrounding environment" published in Environmental Pollution. We commented on the groundwater sampling procedure that affect the calculated concentrations of microplastics in groundwater. Important information related to the description of sampling wells, informal landfill, and the exact description of sample collection method are missing. In addition, significant data related to the groundwater like water level, flow direction, and velocity have been skipped, which are fundamental in groundwater related studies. There should be a clear diagram of landfill location and sampling wells in the landfill, for appropriate understanding of microplastics (MPs) pollution in surrounding environment of a landfill.

Human health implications, risk assessment and remediation of As-contaminated water: A critical review.

Arsenic (As) is a naturally occurring metalloid and Class-A human carcinogen. Exposure to As via direct intake of As-contaminated water or ingestion of As-contaminated edible crops is considered a life threatening problem around the globe. Arsenic-laced drinking water has affected the lives of over 200 million people in 105 countries worldwide. Limited data are available on various health risk assessment models/frameworks used to predict carcinogenic and non-carcinogenic health effects caused by As-contaminated water. Therefore, this discussion highlights the need for future research focusing on human health risk assessment of individual As species (both organic and inorganic) present in As-contaminated water. Various conventional and latest technologies for remediation of As-contaminated water are also reviewed along with a discussion of the fate of As-loaded waste and sludge.