Contamination Risk Assessment Research Articles

Health risk assessment of metal contamination in Malaysian rice (Oryza sativa): The impact of parboiling on toxic metal reduction prior to cooking

Health risk assessment of metal contamination in Malaysian rice (<i>Oryza sativa</i>): The impact of parboiling on toxic metal reduction prior to cooking

Multi-evidences investigation into spatiotemporal variety, sources tracing, and health risk assessment of surface water nitrogen contamination in China

A comprehensive understanding of nitrogen pollution status, especially the identification of sources and fate of nitrate is essential for effective water quality management at the local scale. However, the nitrogen contamination of surface water across China was poorly understood at the national scale. A dataset related to nitrogen was established based on 111 pieces of literature from 2000 to 2020 in this study. The spatiotemporal variability, source tracing, health risk assessment, and drivers of China's surface water nitrogen pollution were analyzed by integrating multiple methods. These results revealed a significant spatiotemporal heterogeneity in the nitrogen concentration of surface water across China. Spatially, the Haihe River Basin and Yellow River Basin were the basins where surface water was seriously contaminated by nitrogen in China, while the surface water of Southwest Basin was less affected. Temporally, significant differences were observed in the nitrogen content of surface water in the Songhua and Liaohe River Basin, Pearl River Basin, Southeast Basin, and Yellow River Basin. There were 1%, 1%, 12%, and 46% probability exceeding the unacceptable risk level (HI＞1) for children in the Songhua and Liaohe River Basin, Pearl River Basin, Haihe River Basin, and Yellow River Basin, respectively. The primary sources of surface water nitrate in China were found to be domestic sewage and manure (37.7%), soil nitrogen (31.7%), and chemical fertilizer (26.9%), with a limited contribution from atmospheric precipitation (3.7%). Human activities determined the current spatiotemporal distribution of nitrogen contamination in China as well as the future development trend. This research could provide scientifically reasonable recommendations for the containment of surface water nitrogen contamination in China and even globally.

Comprehensive monitoring of contamination and ecological-health risk assessment of potentially harmful elements in surface water of Maroon-Jarahi sub-basin of the Persian Gulf, Iran.

The increase in heavy metal concentration in water bodies due to rapid industrial and socio-economic development significantly threatens ecological and human health. This study evaluated metal pollution and related risks to ecology and human health in the Maroon-Jarahi river sub-basin in the Persian Gulf and Oman Sea basin, southwest Iran, using various indicators. A total of 70 water samples were taken from the sampling sites in the Maroon, Allah, and Jarahi sub-basins and analyzed for nine heavy metals. According to the results, the mean concentration of metals in the sampling locations across the entire sub-basin of Maroon-Jarahi was observed as follows Iron (528.22µg/L), zinc (292.62µg/L), manganese (56.47µg/L), copper (36.23µg/L), chromium (11.78µg/L), arsenic (7.09µg/L), lead (3.43µg/L), nickel (3.23µg/L), and cadmium (1.38µg/L). Most of the metals were detected at the highest concentration in the sub-basin of the Jarahi River. The Water Quality Index (WQI) index in the basin varied from 18.74 to 22.88, indicating well to excellent quality. However, the investigation of the pollution status at the monitoring stations, based on the classification of Degree of Contamination (CD) and Heavy Metal Pollution Index (HPI) indices, revealed that they are in the category of relatively high pollution (16 < CD < 32) to very high (32 ≤ CD), and in the low pollution category (HPI < 15) to high pollution (HPI < 30), respectively. According to the three sub-basins, the highest amount of WQI, HPI, and Cd was observed in the stations located in the sub-basins of the Jarahi River. The calculation of Heavy Metal Evaluation Index (HEI) also indicated that only 10% of the monitoring stations are in moderate pollution (10 < HEI < 20), while in other monitoring stations the HEI level is less than 10. The Potential ecological risk factors ( ) of an individual metal was obtained as follows: Cd (173.70) > As (131.99) > Zn (57.52) > Cu (55.39) > Ni (48.98) > Cr (21.57) > Pb (0.71), revealing that Cd and As are the main elements responsible for creating ecological risk in the studied area. The Maroon-Jarahi watershed included areas with ecological risks that ranged from low (PERI ≤ 150) to very high (PERI ≥ 600). HI and ILCR health indicators indicated that consumption and long-term contact with river water in the study area can cause potential risks to human health, especially children. Moreover, the findings, the highest level of pollution and health risk for both children and adults, considering both exposure routes, occurred in the Jarahi River sub-basin, suggesting that those who live in the vicinity of the Jarahi River are likely to face more adverse health effects. In addition, the findings of the evaluation of the relationship between land use patterns and water quality in the studied basin showed that agricultural lands acts as a main source of pollutants, but forest lands play an important role in the deposition of pollutants and the protection of water quality at the basin scale. In general, the results of pollution indicators, risk assessment, and statistical techniques suggest that the lower sub-basin, the Jarahi area, and the Shadegan wetland are the most polluted areas in the investigated sub-basin due to excessive discharge of agricultural runoff, industrialization, and rapid urbanization. Thus, special measures should be considered to reduce the risks of HMs pollution in the sub-basin of the Maroon-Jarahi watershed, especially its downstream and the impact of agricultural land use on water quality should be taken into consideration in basin management plans.

Comprehensive analysis and risk assessment of Antibiotic contaminants, antibiotic-resistant bacteria, and resistance genes: Patterns, drivers, and implications in the Songliao Basin

The pervasive use of antibiotics has raised substantial environmental concerns, especially regarding their temporal and spatial distribution across diverse water systems. This study addressed the gap in comprehensive research on antibiotic contamination during different hydrological periods, focusing on the Jilin section of the Songliao Basin in Northeast China, an area with severe winter ice cover. The study examined the occurrence, distribution, influencing factors, and potential ecological risks of prevalent antibiotic contaminants. Findings revealed antibiotic concentrations ranging from 239.64 to 965.81 ng/L, with antibiotic resistance genes (ARGs) at 5.22 × 10−2 16S rRNA−1 and antibiotic-resistant bacteria (ARB) up to 5.76 log10 CFU/mL. Ecological risk assessments identified significant risks to algae from oxytetracycline, erythromycin, and amoxicillin. Redundancy analysis and co-occurrence networks with ordinary least squares (OLS) demonstrated that the dispersion of ARGs and ARB is significantly influenced by environmental factors such as total organic carbon (TOC), total phosphorus (TP), total nitrogen (TN), fluoride (F⁻), and nitrate (NO₃⁻). These elements, along with mobile genetic elements (MGEs), play crucial roles in ARG patterns (R2 = 0.94, p ≤ 0.01). This investigation offers foundational insights into antibiotic pollution dynamics in cold climates, supporting the development of targeted mitigation strategies for aquatic systems.

MMs (metals and metalloids) based 238U, 226Ra, 232Th,40 K contamination and health risk assessments in different surface soils near an uranium mine of Southeast China

MMs (metals and metalloids) based 238U, 226Ra, 232Th,40 K contamination and health risk assessments in different surface soils near an uranium mine of Southeast China

Source Identification Using Principal Component Analysis and Health Risk Assessment of Heavy Metals Contamination in PM2.5 Near an Industrial Area in Thailand

AbstractIndustrialization has led to a surge in air pollution-related problems, as particulate matter (PM) containing heavy metals poses significant health risks. Understanding airborne particle chemistry, particularly the presence of heavy metals, is vital for effective air quality management and health interventions. This study analysed heavy metal levels in PM2.5 across various sites near an industrial zone in Thailand, including areas near main roads, the industrial zone, as well as indoor and outdoor areas of childcare centres. The concentrations of ambient PM2.5 were found to exceed national standards and acceptable limits during the cool dry season, particularly in the industrial zone (46.4 µg/m3), followed by areas near main roads (41.0 µg/m3) and childcare centres (31.6 µg/m3). The impact of the indoor–outdoor relationship on PM2.5 concentration within childcare centres varied. During the cool dry season, Aluminium had the highest concentration, while lead (Pb) across all sites raised environmental concerns. Remarkably, indoor childcare centres showed higher Pb levels than industrial zones and areas near the main road. Principal Component Analysis revealed the distinct factors linked to specific metals, implying contributions from industrial and transportation sources. Lead isotopic analysis indicated potential associations between lead sources and industries like smelting and refining. During the cool dry season, non-carcinogenic risks were concerning (HI &gt; 1), especially near roads and industrial areas. Vulnerabilities were also observed in students and teachers within indoor childcare centres. This study underscores the importance of monitoring and reducing heavy metal pollution in PM2.5, especially in childcare centres near industrial zones, to preserve public health and regional air quality.

Risk assessment of metal contamination in wastewater drains of River Ghaggar in Punjab (India)

Risk assessment of metal contamination in wastewater drains of River Ghaggar in Punjab (India)

Health Risk Assessment of Metal Contamination in Four Green Leafy Vegetables from Various Open Markets in Benghazi

This study analysed aluminium, essential metals (chromium, manganese, iron, nickel, copper and zinc), and toxic metals (lead and cadmium) in green leafy vegetables (arugula, mint, parsley, and spinach) obtained from various markets in Benghazi city. A flame Atomic Absorption Spectrometer was used to determine the metal contents. Hazard quotient (HQ) and hazard index (HI) calculations were employed to assess non-carcinogenic and carcinogenic risks associated with the metals in the vegetables. Results showed that aluminium was detected in only 50% of the samples. All vegetable samples contained manganese, iron, copper and zinc within the ranges of 1.072-6.87mg, 26.71-298.4mg, 1.00-3.45mg and 3.61-9.33mg per 1kg of vegetable dry weight, respectively. Nickel and chromium were found in 33% and 50% of the samples, respectively. Cadmium and lead were present in all samples except for two spinach and two parsley samples. The levels of essential metals in the samples were below the maximum allowable limits set by FAO-WHO regulations. However, the contents of nickel, cadmium and lead in some vegetable samples exceeded the maximum limits. The metal contents in the collected vegetables were mostly lower than reported results from previous international studies. The HQ and HI values for the analysed metals were all below unity, suggesting that the consumption of these selected vegetables as part of a daily diet poses no threat to human health.

Dual biomarker traceability and ecological risk assessment of centennial organic contamination in South Dongting Lake

Enhanced anthropogenic activity strength has altered the watershed particulate transport and material cycle resulting in organic pollutant deposition changes in Dongting Lake associated with unclear ecological risk. In the present study, dual biomarkers i.e. n-alkanes and polycyclic aromatic hydrocarbon (PAHs) were applied in the 210Pb-dated sediment cores for traceability of centennial organic pollutants in the lake mouth area. The partial least squares path model and risk quotients method were used to explore the controlling pathways and ecological risk. The results show a range of sedimentary organic carbon (C), nitrogen (N), and phosphorus (P) was at 1.76–185.66, 0.97–89.80, and 0.01–0.97 g m−2 yr−1 with total reserves of 51.68, 18.44, and 0.27 t ha−1, respectively, over the past 179 years. The presence of PAHs rapidly increased by 2.47 fold from 535.60 ng g−1, while PAHs and carcinogenic PAHs (ΣCPAHs) burial fluxes increased by about 6 and 5 folds, respectively. Accompanied by anthropogenic activities and climate change, the exotic sources gradually becoming predominant. The n-alkane diagnostic ratios indicated a shift of organic matter (OM) from autotrophic bacteria, algae, and phytoplankton-derived sources to macrophyte and terrestrial plants. The exotic origins rose to approximately 73.61 %, while endogenous sources decreased to 26.39 %. The direct effects of anthropogenic activities and their indirect negative impacts on climate and sedimentary structure are the key ways for sediment material loading. The nutrient accumulation in sediments coincides with the lake's eutrophication history over the past decades. The ΣCPAHs accounted for about 89.37 ± 17.14 % of the total TEQ, reflecting a strong ecological risk. The contribution of anthropogenic activities such as fuel usage, fertilizer application, hard pavement coverage, and OM loss from the ecosystem to the sources of organic pollutants and their component types may be a focus of attention in the middle reaches of the Yangtze River plain lake.

Assessment of heavy metal contamination risk in dry fish from India: A comprehensive study

The widespread presence of heavy metal contaminants in aquatic ecosystems, and consequently in fish, has emerged as a paramount concern owing to the staple role of fish in the Indian diet. The present study addresses heavy metal contamination in dried fish consumed across India and its associated health risks. The objectives of this study were to determine the heavy metal concentrations in dried fish from different regions of India, assess daily heavy metal intake through dried fish consumption, and evaluate the carcinogenic and non-carcinogenic health risks associated with heavy metal exposure. Subsequently, 111 dried fish samples from Guwahati-Assam, Mumbai, Karad-Maharashtra, and Goa were analyzed for eight selected heavy metals using a validated inductively coupled plasma mass spectrometry method results indicated varying contamination levels across locations, with As being the most abundant heavy metal. In Maharashtra and Assam, the heavy metal load in dried fish was as follows: As > Cr > Ni > V > Cd > Pb > Co > Hg. For Goa, the order was As > Cr > Ni > V > Cd > Co > Pb > Hg. Dietary exposure assessments revealed varying levels of exposure between adults and children, with As and Cd posing higher risks to children. The Target Hazard Quotient (THQ) and Hazard Index (HI) values for all metals were within acceptable limit of one. Health risk assessments revealed generally low hazard levels for adults, but higher risks for children, particularly at higher percentiles. Furthermore, As was identified as posing a medium risk of cancer. In essence, this research emphasizes the necessity for strict monitoring and regulations with the aim of controlling health hazards related to heavy metal pollution in food sources.

Contamination, speciation, and health risk assessment of arsenic in leafy vegetables in Ambagarh Chowki (India).

Green leafy vegetables are essential for a balanced diet, providing vital nutrients for overall well-being. However, concerns arise due to contamination with toxic substances, such as arsenic, posing risks to food safety and human health. This study analyzes inorganic (iAs), monomethyl (MMA), and dimethyl arsenic (DMA) in specific leafy vegetables (Amaranthus tricolor L., Corchorus olitorius L., Cordia myxa L., Hibiscus sabdariffa L., Ipomoea batatas (L.) Lam., Moringa oleifera Lam., and Spinacia oleracea L.) grown in the heavily polluted Ambagarh Chouki region, Chhattisgarh, India. Concentrations of DMA, MMA, and iAs ranged from 0 to 155, 0 to 7, and 131 to 3579mg·kg-1, respectively. The health quotient (HQ) for iAs ranged between 0.37 and 3.78, with an average value of 2.58 ± 1.08.

Assessment of Heavy Metal Contamination and Health Risks in "Snow Cover-Soil Cover-Vegetation System" of Urban and Rural Gardens of an Industrial City in Kazakhstan.

This article investigates the extent of heavy metal pollution in both urban and rural gardens in Pavlodar, which cultivate potatoes and tomatoes. As a city of industrialization, Pavlodar is exposed to emissions from industrial enterprises, transport and stove heating. The city also has the highest incidence of environmental diseases among the population. This study examines the accumulation of heavy metals and metalloid in the snow, their migration into the soil and their accumulation in plants, and assesses the non-cancer and cancer health risks of consuming these vegetables. The results show that the concentrations of trace elements in the solid phase of snow decrease in the following order: Fe (26,000) > Mn (592.5) > Cr (371.3) > Zn (338.8) > Pb (161.9) > Cu (142.5) > Ni (30.9) > As (15.1) > Co (12.1) > Cd (2.6). In soils, the concentrations of elements decrease in the following order: Mn (22,125) > Fe (20,375) > Zn (246.9) > Cr (109.5) > Cu (39.3) > Pb (25.6) > Ni (22.4) > As (9) > Co (6.6) > Cd (0.2). In urban gardens, the snow pollution coefficient was the highest. In rural gardens, the contamination index varied from 0.3 (Cr) to 5.3 (Cd). Magnesium in the soil exceeds the maximum allowable concentration (MPC) by 28.6-35.7 times, and zinc by 1.6-10.9 times. Only zinc and copper exceed the MPC for vegetables. Nickel in potatoes exceeds MPC by a factor of 6 and in tomatoes by a factor of 4.4. The cobalt content in tomatoes exceeds the background value by 2.2 times, with a maximum value of 5.3 times. The risk assessment showed that the non-carcinogenic and carcinogenic risks associated with potato and tomato consumption were low. However, these risks are higher in urban areas than in rural areas.

Occurrence and Environmental Risk Assessment of Contaminants of Emerging Concern in Brazilian Surface Waters.

We investigated the occurrence and the environmental risk of eight contaminants of emerging concern (CECs; acetaminophen, naproxen, diclofenac, methylparaben, 17β-estradiol, sulfathiazole, sulfadimethoxine, and sulfamethazine) in three Brazilian water bodies, namely, the Monjolinho River Basin (São Paulo State), the Mogi Guaçu River (São Paulo State), and the Itapecuru River (Maranhão State) in three sampling campaigns. The CECs were only quantified in surface water samples collected at the Monjolinho River Basin. Acetaminophen, naproxen, and methylparaben were detected in the range of <200 to 575.9 ng L-1, <200 to 224.7 ng L-1, and <200 to 303.6 ng L-1, respectively. The detection frequencies of the three measured compounds were between 33% and 67%. The highest concentrations of CECs were associated with intense urbanization and untreated sewage discharge. Furthermore, CEC concentrations were significantly correlated with total organic carbon, electrical conductivity, and dissolved oxygen levels, suggesting that domestic pollution from urban areas is an important source in the distribution of CECs in the Monjolinho River Basin. The environmental risk assessment indicated a high risk for acetaminophen (risk quotient [RQ] values between 2.1 and 5.8), a medium risk for naproxen (RQs between 0.6 and 0.7), and a low risk for methylparaben (RQs < 0.1) to the freshwater biota of the Monjolinho River Basin. Our findings show potential threats of CECs in Brazilian water bodies, especially in vulnerable areas, and reinforce the need for improvements in environmental regulations to include monitoring and control of these compounds in aquatic systems. Environ Toxicol Chem 2024;00:1-12. © 2024 SETAC.

In vitro tungsten bioaccessibility in Chinese residential soils: Implications for human health risk assessments and soil screening level derivation

Tungsten (W) contamination presents emerging environmental challenges, necessitating the need to establish soil screening levels (SSLs), especially for residential soils. This study assessed the health exposure risk and derived national and regional residential SSLs for W in Chinese residential soils, incorporating machine-learning prediction of in-vitro soil W bioaccessibility. We analyzed 204 residential soil samples collected across 24 provinces, recording a wide range of W concentrations (0.01–3063.2 mg/kg). Synchrotron-based X-ray fluorescence spectroscopy, chemical extractions, and random forest modeling indicated that the key determinants of soil W bioaccessibility were soil pH, cation exchange capacity, organic matter, and clay contents. Monte Carlo simulations demonstrated that soil W contamination predominantly results in noncarcinogenic health risks to residents via oral exposure, especially in mining-affected regions. A national residential SSL (NRSSL) of 35.5 mg/kg and regional residential SSLs (RRSSLs) of 34.5–49.2 mg/kg were established. Incorporating predicted bioaccessibility increased the NRSSL to 73.8 mg/kg and the RRSSLs to 69.8–112.5 mg/kg. Southern China, which is rich in W ore, exhibited lower RRSSLs, underscoring a need for enhanced safety management. Our framework and findings provide a robust scientific foundation for future soil contamination risk assessment studies, and we present customized SSLs that can guide targeted W risk control strategies.

Mapping Arsenic Contamination and Health Risk Assessment of Arsenic in Agricultural Soils of Eastern India

Mapping Arsenic Contamination and Health Risk Assessment of Arsenic in Agricultural Soils of Eastern India

Heavy metal contamination and human health risk assessment in the soils grown field crops in Antalya, Türkiye

ABSTRACT Soil pollution results from heavy metals has become a severe environmental concern. Heavy metals pose a risk to human health by entering the food chain. The aim of this study was to determine the concentrations, sources and potential ecological and human health risks of heavy metals in soils which grown field crops in Antalya, Turkey. Soil samples were collected at depths of 0–30 cm from 292 fields and concentrations of cadmium (Cd), lead (Pb), nickel (Ni), chromium (Cr), cobalt (Co), iron (Fe), manganese (Mn), copper (Cu) and zinc (Zn) were determined. The mean concentrations of total Cd, Pb, Ni, Cr, Co, Fe, Mn, Cu and Zn were 4.73, 68.67, 152.74, 98.52, 24.77, 28098, 823, 42.72 and 62.85 mg kg−1, respectively. These results showed that the average concentrations of Cd, Pb, Ni, Cr, Co, Cu and Mn exceeded the Upper continental crust average. Enrichment factor (EF), geo-accumulation index (I geo) and contamination factor (CF) values of soils indicate serious enrichment for Cd. Principal component analyses (PCA) indicated that Co, Cr and Ni was lithogenic origins, but Fe and Pb concentrations were determined by lithological and anthropogenic sources. Hazard index (HI) values of heavy metals were < 1, suggesting that non-carcinogenic health risks to adult residents. In addition, the total carcinogenic risk (TCR) values except for Cr, suggesting that carcinogenic risks for residents were not expected. The results showed that children were more sensitive to the non-carcinogenic and carcinogenic effects of heavy metals.

Micro‐ and nano‐plastic loads in fish and macroinvertebrates in a tropical river

Abstract This study examines microplastic contamination in river macroinvertebrates and fish within a rapidly urbanising tropical catchment, and provides data on the quantity of microplastics ingested by various taxonomic and functional feeding groups. We employed both a widely used low‐resolution visual inspection method, capable of identifying microplastics ranging from 0.1 to 5 mm, and a novel automated method specifically designed to identify smaller plastics in the nano size range, from 0.004 to 0.1 mm. Analysis using the low‐resolution method indicated that a significant portion of fish (95%) and macroinvertebrates (44%) contained larger microplastics. The composition of microplastic within the animals differed from that in river water and on the river bed: microplastics in the water and on the bed were predominantly fibres (98% and 92% respectively), whereas the animals exhibited a more even mix of fibres (c. 35%), fragments (c. 43%), and film (c. 22%). Microplastic loads in aquatic organisms correlated with feeding group and body size, although patterns were not always consistent. Larger individuals generally contained more microplastic, especially among macroinvertebrates, but this trend was not observed uniformly among fish species. Additionally, differences in body loads among macroinvertebrate taxa and feeding groups varied depending on whether loads were expressed per individual or per unit weight. Use of the high‐resolution enumeration method revealed a substantially higher microplastic count compared to the low‐resolution method, highlighting the potential underestimation of contamination levels by the latter. The study underscores the non‐random uptake of microplastics by aquatic biota, influenced by feeding mode, and stresses the necessity of high‐resolution sample processing for accurate quantification of contamination levels and risk assessment for smaller organisms.

Regional Assessment of Groundwater Contamination Risk from Crude Oil Spillages in the Niger Delta: A Novel Application of the Source-Pathway-Receptor Model

AbstractOnshore oil spills are known for their disastrous environmental impacts and potential to cause lasting damage to underlying groundwater. The Niger Delta is particularly vulnerable to widespread spillages linked to extensive oil exploration, transportation, and theft-related incidents. This research employed a geospatial approach in formulating risk equations, based on the source-pathway-receptor (S-P-R) model using multiple openly available data sets, to assess groundwater contamination risk in the Niger Delta Region (NDR), Nigeria. To develop the overall risk equation, the study combined fourteen thematic data layers including the volume of oil spilled, type of spill, slope, elevation, proximity to spill site, pipeline, oil wells and streams, drainage density, mean annual precipitation and population density. These layers were integrated into source potency, pathway transmissivity, and receptor susceptibility. The NDR was systematically categorized into low, moderate, and high groundwater risk zones. The delineation revealed that high-risk zones predominantly span the central areas, extending from southeast to northwest, effectively encircled by regions of low to medium risk located in both the northern and southern extents of the delta. The efficacy of the risk model was corroborated by existing knowledge. Moderate to high-risk zones were found to be in about 16% of the NDR, revealing previously unknown areas of risk. This spatial configuration underscores a significant gradient in contamination risk across the NDR, with the central corridor emerging as a critical focus for groundwater protection and remediation efforts. In line with UN Sustainable Development Goal (SDG) #6, this study recommends targeted strategies to ensure clean water provision in these identified high-risk areas. By leveraging the S-P-R model within this complex and sensitive ecological area, this research both advances environmental risk assessment and sets a precedent for future large-scale environmental risk assessments utilizing open-source data.

Assessment of spatiotemporal risks for nationwide groundwater nitrate contamination

National assessments of groundwater contamination risks are crucial for sustaining high-quality groundwater supplies. However, traditional methods often treat groundwater contamination risk as a steady-state indicator without considering spatiotemporal variation in risk, both geographically and over time, caused by anthropogenic and climatic factors. In this work, XGBoost, a tree-based algorithm, was applied to comprehensively analyze the drivers of groundwater contamination from nitrate, using data on 13 physical features (as used by the index-based ranking method DRASTIC) and 30 anthropogenic features from 1985 to 2010 in the contiguous United States (CONUS). The results indicate that physical features controlling the transport processes, particularly those affecting contaminant travel time from land surface to groundwater (depth to water table and transmissivity), were the dominant factors for nitrate contamination in groundwater. This was followed by features representing the potential nitrogen loading. Positive correlations between most features and the nitrogen loading time (year) were found, suggesting their growing influence on contamination risk. Based on the drivers identified for nitrate concentrations exceeding 10 mg/L in groundwater and their varying temporal contributions, this study proposes a reformulated index-based method for contamination risk assessment. With this method, an overall accuracy of around 70 % was achieved based on the validation data set. The predicted high-risk areas are mainly intensive irrigation regions, such as the High Plains, northern Midwest, and Central Valley. This new approach contributes to a more accurate and effective assessment of the contamination risks of groundwater on a regional and national scale under temporally varying environmental conditions.

Microplastic Contamination and Ecological Risk Assessment in Tropical Riverine Surface Water of Selangor River Basin, Malaysia

Microplastic Contamination and Ecological Risk Assessment in Tropical Riverine Surface Water of Selangor River Basin, Malaysia