Antifouling paint additives in surface sediments were investigated in Okpo Harbor and Onsan Harbor, South Korea, two harbors characterized by contrasting dominant anthropogenic activities. Okpo Harbor is a shipbuilding-oriented harbor with a large shipyard, whereas Onsan Harbor represents a multi-use industrial harbor. Organotin compounds were detected at substantial levels in both harbors; however, their spatial distributions and compositional characteristics differed markedly. Okpo Harbor exhibited relatively low mean concentrations, with distinct inner-harbor hotspots dominated by tributyltin, suggesting relatively fresh TBT inputs or remobilization of TBT-containing legacy residues associated with shipyard activities. In contrast, Onsan Harbor showed higher mean concentrations and broader spatial variability, with monobutyltin predominating, reflecting aged residues derived from advanced degradation of historical TBT inputs. Booster biocides were enriched in inner-harbor areas of Okpo Harbor, likely associated with hull coating and repair activities, whereas concentrations in Onsan Harbor were generally lower and spatially restricted. Potentially toxic elements were elevated in zones influenced by ship repair in Okpo Harbor and by adjacent industrial complexes in Onsan Harbor, consistent with surrounding land-use characteristics. Ecological risks were generally low, with TBT-driven risks localized in inner Okpo Harbor and medium-high mERM-Q values, driven by Zn and Pb, at two industrial sites in Onsan Harbor. These findings highlight the importance of harbor-specific management strategies that consider dominant anthropogenic activities and local environmental conditions.
Heavy metal contamination in coastal marine sediments poses significant ecological and public health risks, necessitating the development of efficient and reliable monitoring methods. This study developed a simple, high-throughput approach for monitoring heavy metal pollution in wet sediments using field portable X-ray fluorescence (pXRF) spectrometry. To enhance field applicability, we optimized sample thickness, acquisition time, and centrifugation-based pretreatment to minimize moisture–induced variability. After centrifugation, moisture content in marine sediments decreased from 30.5 to 62.8% to 24.4–35.3%, enabling more consistent pXRF measurements. Moisture correction improved measurement accuracy, while empirical calibration approaches including site-specific and site-integrated calibration further enhanced analytical performance. Site-specific calibration yielded the highest accuracy in previously characterized areas, whereas site-integrated calibration proved effective for contamination assessment in areas without prior study data. Application of the optimized approach to major South Korean harbors successfully identified contamination hotspots associated with industrial discharge and shipbuilding activities. These results suggest that pXRF, when combined with optimized pretreatment and calibration strategies, is a practical and effective tool for rapid screening and spatial mapping of heavy metal contamination in coastal marine sediments.
Developing efficient and durable oxygen evolution reaction (OER) electrocatalysts is essential for sustainable hydrogen production through water electrolysis. Herein, pristine NiO nanoparticles and NiO–S composites containing 10 wt% (NiO@S1) and 20 wt% sulfur (NiO@S2) were prepared through hydrothermal synthesis, solid-state mixing, and thermal treatment. XRD refinement confirmed that the cubic NiO structure was retained after sulfur addition, while FTIR, EDS, XPS, and EPR analyses revealed sulfur-related surface interactions, electronic redistribution, and defect-rich environments. The optimized NiO@S1 electrode exhibited the best OER activity in 1 M KOH, requiring an overpotential of 330 mV to reach 50 mA cm−2 and displaying an apparent Tafel slope of 138.7 mV dec−1. It also provided the largest electrochemically active surface area of 125 cm2 and the lowest charge-transfer resistance of 0.40 Ω. Periodic LSV and EIS measurements conducted at 1-h intervals during 25 h chronoamperometry demonstrated better activity retention and smaller resistance growth for NiO@S1 than for NiO and NiO@S2. Moreover, NiO@S1 sustained OER operation for 225 h under strongly alkaline operating conditions with limited morphological deterioration. These findings demonstrate that moderate sulfur loading produces favorable surface and interfacial characteristics, whereas excessive sulfur loading obstructs active sites and compromises structural and electrochemical stability.
