Luís Pinto da Silva

Abstract Urban parks are essential to sustainable cities, providing climate regulation, supporting biodiversity, and offering vital spaces for recreation and overall well-being. At the same time, their soils can act as long-term reservoirs for persistent organic pollutants (POPs), reflecting decades of atmospheric deposition, diffuse urban emissions, and historical land-use practices. This review synthesises current knowledge on the occurrence, sources, and environmental behaviour of priority POPs, including OCPs, PCBs, PCDD/Fs, PBDEs, PFAS, and PAHs, in the soils of urban parks and gardens worldwide. Evidence from multiple regions reveals consistent patterns: urban parks accumulate complex mixtures of legacy and emerging contaminants, reflecting both historical inputs and ongoing urban activities. These contaminants primarily contribute to scenarios of chronic, low-level exposure through the ingestion of soil and dust, inhalation of resuspended particles, dermal contact, and, in some cases, dietary intake when food is cultivated in contaminated park soils. While such exposure pathways have been associated with a range of adverse health outcomes in toxicological and epidemiological studies, the presence of POPs in park soils does not imply that urban parks represent hazardous environments. Instead, it emphasises the importance of proportionate, evidence-based assessments within spaces that yield substantial net benefits to public health. Despite growing research interest, significant gaps remain, including limited understanding of mixture toxicity, insufficient data on temporal trends, a lack of harmonised monitoring strategies, and the absence of exposure scenarios specifically tailored to recreational soils. This review also examines major international and European regulatory frameworks and soil-quality guideline approaches relevant to urban and recreational soils, identifying mismatches between scientific evidence and regulatory practice. By integrating perspectives from environmental chemistry, toxicology, urban ecology, and policy, this review highlights the importance of targeted monitoring and context-specific management strategies to ensure that urban parks remain safe, healthy, and equitable components of increasingly complex urban landscapes.

Abstract The presence of emerging organic contaminants in water and effluents, including antibiotics, poses significant environmental and health risks. Moreover, while photocatalysis is a promising approach for their removal, the inefficient utilization of natural sunlight by common photocatalysts limits its large-scale use. This work demonstrates the enhanced sunlight-driven photodegradation of the antibiotic Ciprofloxacin (CIP) using a nanocomposite composed of carbon dots (CDs) and TiO2 (NC50:50). The CDs were obtained from corn stover, a major agricultural waste product. Initial testing was performed under artificial solar radiation: CIP was virtually fully degraded within 20 min, with a rate constant of 0.2372 min(-1) and a 217% enhancement of catalytic activity over commercial TiO2. Validation under real-world irradiation conditions was subsequently made by performing photocatalytic assays under natural sunlight on different days under diverse meteorological conditions. The performance of NC50:50 was retained, degrading CIP within 30 min under natural conditions. Notably, while degradation by-products were identified under both artificial and natural sunlight, they were subsequently photodegraded by the nanocomposite under these conditions. This enhanced performance was attributed to a combination of effects resulting from CDs' incorporation, namely, improved absorption of visible light, enhanced charge separation, and increased specific surface area. Furthermore, the addition of CDs resulted in changes in the reactive species generation profile, which can alter the available degradation pathways. Thus, this study provides insight that can be useful for strategies aimed at the rational design of sunlight-active TiO2-based photocatalysts with tunable surface reactivity.

Abstract While heteroatom doping is widely used to enhance the fluorescence of carbon dots, the actual mechanism underlying this claimed enhancement remains unclear. Herein, we report a systematic comparison between nitrogen-doped carbon dots (N-CDs) and nitrogen/sulfur co-doped carbon dots (N,S-CDs) synthesized hydrothermally, with ethylenediamine and sodium thiosulfate as the N- and S-dopants, respectively. Contrary to expectations, the inclusion of the S-precursor significantly reduced the quantum yield by 63%, from 35.9% to 13.2%, while leaving the emission profile and response largely unchanged. Characterization assays revealed that S-doping in N,S-CDs was residual, whereas the surface oxygen content increased markedly, indicating surface oxidation. The data suggest that sodium thiosulfate acted not as a dopant but overall as an oxidant, generating oxygen-based surface defects that introduced nonradiative recombination pathways. Thus, our findings show that co-doping with this S-precursor can decrease the quantum yield by promoting surface oxidation and the effective formation of more oxidized N-CDs, rather than heteroatom incorporation and production of co-doped CDs. This decreasing effect on the quantum yield was also observed when using thiourea as the S-precursor. Future work should include the study of other common S-precursors. In conclusion, our research shows that specific heteroatom-based precursors can alter the optical characteristics of CDs through redox/surface-modification effects instead of actual compositional doping, and thus, claims based on heteroatom doping may need closer examination.

Abstract <jats:p>Persistent organic pollutants accumulate in urban soils, yet information on the occurrence, spatial variability and human health implications of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) remains limited, particularly in Portugal. Surface soils were collected from six urban and peri-urban green spaces across the Porto Metropolitan Area, encompassing contrasting land-use histories and anthropogenic settings. Seventeen sampling locations were analysed for the 17 WHO-priority PCDD/F congeners and the 12 dioxin-like PCB congeners. The total number of 2005 toxic equivalents (TEQs) was determined, and screening-level human health risks were evaluated for adults considering incidental soil ingestion, dermal contact and inhalation of resuspended soil particles. PCDD/Fs and dl-PCBs were detected at all sampling locations, with total TEQ concentrations ranging from 1.91 to 330.9 ng TEQ kg⁻¹ dry weight. PCDD/Fs accounted for most of the overall toxicity. The majority of the samples under analysis can be considered representative of the urban background level in Porto, at 2.51 ± 0.54 ng TEQ kg⁻¹ dw. TEQ concentrations at most sites were consistent with diffuse urban background levels reported internationally, whereas one informal urban allotment constituted a distinct contamination hotspot. This spatial pattern was reflected in the risk assessment. Non-carcinogenic and carcinogenic risks remained below widely accepted screening thresholds at all locations except the hotspot, where children exhibited a hazard index (HI) of 1.50 and an incremental lifetime cancer risk (ILCR) of 1.17 × 10⁻⁵. Incidental soil ingestion was the predominant exposure pathway; dermal contact contributed modestly, and inhalation contributed negligibly. Sensitivity analysis demonstrated that these conclusions were robust to alternative assumptions about soil ingestion. These findings suggest that historical land use is a major determinant of site-specific PCDD/F and dl-PCB contamination and associated human health risks in urban green spaces. Incorporating land-use history into urban soil assessments could improve contamination hotspot identification and strengthen environmental monitoring and risk management strategies.</jats:p>

Abstract TiO2 nanoparticles are promising photocatalysts due to their oxidizing strength and inertness. However, their inability to efficiently absorb visible light limits industrial applications that could use sunlight. The addition of carbon dots to TiO2 has been recently shown to have the potential to address this issue by enhancing the visible light-driven photocatalytic efficiency of the resulting nanocomposites. However, concrete data on their sustainable development and fabrication is lacking. Herein, we performed a life cycle assessment (LCA) study to understand the environmental impacts of different TiO2-carbon dots nanocomposites with enhanced visible light-driven photocatalytic activity. It was found that the nanocomposites with the highest photocatalytic activity were the ones whose synthesis was associated with lower environmental impacts. Furthermore, the carbon dots generally have little to moderate contributions to most impact categories, except for marine eutrophication. Finally, the most critical parameter was found to be the source of TiO2 for the nanocomposites.