In this paper, several extreme learning machine (ELM) models, including standard extreme learning machine with sigmoid activation function (S-ELM), extreme learning machine with radial basis activation function (R-ELM), online sequential extreme learning machine (OS-ELM), and optimally pruned extreme learning machine (OP-ELM), are newly applied for predicting dissolved oxygen concentration with and without water quality variables as predictors. Firstly, using data from eight United States Geological Survey (USGS) stations located in different rivers basins, USA, the S-ELM, R-ELM, OS-ELM, and OP-ELM were compared against the measured dissolved oxygen (DO) using four water quality variables, water temperature, specific conductance, turbidity, and pH, as predictors. For each station, we used data measured at an hourly time step for a period of 4 years. The dataset was divided into a training set (70%) and a validation set (30%). We selected several combinations of the water quality variables as inputs for each ELM model and six different scenarios were compared. Secondly, an attempt was made to predict DO concentration without water quality variables. To achieve this goal, we used the year numbers, 2008, 2009, etc., month numbers from (1) to (12), day numbers from (1) to (31) and hour numbers from (00:00) to (24:00) as predictors. Thirdly, the best ELM models were trained using validation dataset and tested with the training dataset. The performances of the four ELM models were evaluated using four statistical indices: the coefficient of correlation (R), the Nash-Sutcliffe efficiency (NSE), the root mean squared error (RMSE), and the mean absolute error (MAE). Results obtained from the eight stations indicated that: (i) the best results were obtained by the S-ELM, R-ELM, OS-ELM, and OP-ELM models having four water quality variables as predictors; (ii) out of eight stations, the OP-ELM performed better than the other three ELM models at seven stations while the R-ELM performed the best at one station. The OS-ELM models performed the worst and provided the lowest accuracy; (iii) for predicting DO without water quality variables, the R-ELM performed the best at seven stations followed by the S-ELM in the second place and the OP-ELM performed the worst with low accuracy; (iv) for the final application where training ELM models with validation dataset and testing with training dataset, the OP-ELM provided the best accuracy using water quality variables and the R-ELM performed the best at all eight stations without water quality variables. Fourthly, and finally, we compared the results obtained from different ELM models with those obtained using multiple linear regression (MLR) and multilayer perceptron neural network (MLPNN). Results obtained using MLPNN and MLR models reveal that: (i) using water quality variables as predictors, the MLR performed the worst and provided the lowest accuracy in all stations; (ii) MLPNN was ranked in the second place at two stations, in the third place at four stations, and finally, in the fourth place at two stations, (iii) for predicting DO without water quality variables, MLPNN is ranked in the second place at five stations, and ranked in the third, fourth, and fifth places in the remaining three stations, while MLR was ranked in the last place with very low accuracy at all stations. Overall, the results suggest that the ELM is more effective than the MLPNN and MLR for modelling DO concentration in river ecosystems.

Solubility is a critical component of physicochemical characterisation of engineered nanomaterials (ENMs) and an important parameter in their risk assessments. Standard testing methodologies are needed to estimate the dissolution behaviour and biodurability (half-life) of ENMs in biological fluids. The effect of pH, particle size and crystal form on dissolution behaviour of zinc metal, ZnO and TiO₂ was investigated using a simple 2 h solubility assay at body temperature (37 °C) and two pH conditions (1.5 and 7) to approximately frame the pH range found in human body fluids. Time series dissolution experiments were then conducted to determine rate constants and half-lives. Dissolution characteristics of investigated ENMs were compared with those of their bulk analogues for both pH conditions. Two crystal forms of TiO₂ were considered: anatase and rutile. For all compounds studied, and at both pH conditions, the short solubility assays and the time series experiments consistently showed that biodurability of the bulk analogues was equal to or greater than biodurability of the corresponding nanomaterials. The results showed that particle size and crystal form of inorganic ENMs were important properties that influenced dissolution behaviour and biodurability. All ENMs and bulk analogues displayed significantly higher solubility at low pH than at neutral pH. In the context of classification and read-across approaches, the pH of the dissolution medium was the key parameter. The main implication is that pH and temperature should be specified in solubility testing when evaluating ENM dissolution in human body fluids, even for preliminary (tier 1) screening.

Sodium chlorate (NaClO₃) is a widely used non-selective herbicide. It is also generated as a byproduct during disinfection of drinking water by chlorine dioxide. In the present work, the effects of NaClO₃ on human erythrocytes were studied under in vitro conditions. Incubation of erythrocytes with different concentrations of NaClO₃ at 37 °C for 90 min resulted in significant hemolysis. Cell lysates were prepared from NaClO₃-treated and untreated (control) erythrocytes and assayed for various biochemical parameters. Methemoglobin levels were significantly increased and methemoglobin reductase activity was reduced upon NaClO₃ treatment. There was a significant increase in protein oxidation and lipid peroxidation with a decrease in reduced glutathione and total sulfhydryl content. This suggests the induction of oxidative stress in erythrocytes upon exposure to NaClO₃. The occurrence of oxidative stress was confirmed by significantly increased generation of reactive oxygen species and lowered antioxidant response of the cells. NaClO₃ treatment also increased nitric oxide levels showing induction of nitrosative stress. The activities of major antioxidant and membrane-bound and metabolic enzymes were significantly altered upon incubation of erythrocytes with NaClO₃. The erythrocytes became more osmotically fragile while electron microscopic images showed gross morphological alterations in NaClO₃-treated cells. These results show that NaClO₃ induces oxidative stress in human erythrocytes, which results in extensive membrane damage and lowers the antioxidant response.

Personal exposure to PM₂.₅ associated with heavy metals were investigated at and around the same road by cycling, walking, taxi and bus in Tianjin, China. One trip on each mode was undertaken during 4 h of both morning and evening peak hours. Results of one-way analysis of variance (ANOVA) to compare mean concentrations of PM₂.₅ and each metal measured by four modes, the enrichment level of heavy metals in four modes and the carcinogenic, non-carcinogenic risk and probabilistic estimation of health risks of metals (Cr, Ni, Cu, Zn and Pb). Arithmetic means of PM₂.₅ personal exposure were 323.66, 313.37, 214.84 and 160.71 μg/m³ for cycling, walking, bus and taxi, which resulted from the difference of source (vehicle exhaust and road dust) of exposure to PM₂.₅. Na has the highest concentration, followed by Al, Ca, K, Fe, Mg, Zn, Ni, Pb, Cu and Cr. The higher Na concentrations were observed in Tianjin in light of its major sea salt influence. The concentrations of Ca, Mg, Fe and Zn in four modes followed different orders, while other metals have no significant difference between four modes. Enrichment factors of metals in PM₂.₅ showed that some metals are enriched, ranging from contaminated to extremely contaminated, for example, Ni, Cu, Zn, Pb, Na and Cr. Others are barely enriched such as Ca, K, Mg and Fe. It illustrated the former is mainly effected by anthropogenic activates and the source of latter comes from crust. From the results of non-carcinogenic and carcinogenic risks of metals, the intake of metals with inhalation for 4 h by four modes did not pose a significant potential chronic-toxic risk and was an acceptable or tolerable risk at present. But uncertainty analysis of health risks showed there were 4.05 and 6.87% probability that make carcinogenic risk values to exceed 10⁻⁴ when male choose walking/cycling to work. Commuters’ rush hour exposures were significantly influenced by mode of transport. We suggest that future work should focus on further research between heavy metals in PM₂.₅ exposure and its specific epidemiology effects.

To further treat the reclaimed municipal wastewater and rehabilitate the aquatic ecosystem of polluted urban rivers, an 18.5-km field-scale ecological restoration project was constructed along Jialu River, a polluted urban river which receives only reclaimed municipal wastewater from Zhengzhou City without natural upland water dilution. This study investigated the potential efficiency of water quality improvement, as well as genotoxicity and cytotoxicity reduction along the ecological restoration project of this polluted urban river. Results showed that the chemical oxygen demand (COD) and ammonia nitrogen (NH₃-N) of the reclaimed municipal effluent were reduced by more than 45 and 70%, respectively, meeting the Chinese surface water environmental quality standard level IV, while the total phosphorus and metal concentrations had no significant reduction along the restoration project, and Pb concentrations in all river water samples exceeded permissible limit in drinking water set by WHO (2006) and China (GB5749-2006). The in vitro SOS/umu assay showed 4-nitroquinoline-1-oxide equivalent (4-NQO-EQ) values of reclaimed municipal wastewater of 0.69 ± 0.05 μg/L in April and 0.68 ± 0.06 μg/L in December, respectively, indicating the presence of genotoxic compounds. The results of 8-hydroxy-2′-deoxyguanosine (8-OHdG) and hepatic cell apoptosis in zebrafish after a chorionic long-term (21 days) in vivo exposure also demonstrated that the reclaimed municipal wastewater caused significant DNA oxidative damage and cytotoxicity. After the ecological purification of 18.5-km field-scale restoration project, the genotoxicity assessed by in vitro assay was negligible, while the DNA oxidative damage and cytotoxicity in exposed fish were still significantly elevated. The mechanisms of DNA oxidative damage and cytotoxicity caused by the reclaimed municipal wastewater need further study.

Ricinus communis L. (castor bean or castor oil plant) was found growing on metal-contaminated sites (4) of peri-urban Greater Hyderabad comprises of erstwhile industrial areas viz Bollaram, Patancheru, Bharatnagar, and Kattedan industrial areas. During 2013–2017, about 60 research papers have appeared focusing the role of castor bean in phytoremediation of co-contaminated soils, co-generation of biomaterials, and environmental cleanup, as bioenergy crop and sustainable development. The present study is focused on its use as a multipurpose phytoremediation crop for phytostabilization and revegetation of waste disposed peri-urban contaminated soils. To determine the plant tolerance level, metal accumulation, chlorophyll, protein, proline, lipid peroxidation, oil content, and soil properties were characterized. It was noticed that the castor plant and soils have high concentration of metals such as cadmium (Cd), lead (Pb), iron (Fe), manganese (Mn), and zinc (Zn). The soils have high phosphorous (P), adequate nitrogen (N), and low concentration of potassium (K). Iron (Fe) concentrations ranged from1672±50.91 to 2166±155.78 mg kg⁻¹ in the soil. The trend of metal accumulation Fe>Zn>Mn>Pb>Cd was found in different plant parts at polluted sites. The translocation of Cd and Pb showed values more than one in industrial areas viz Bollaram, Kattedan, and Bharatnagar indicating the plants resistance to metal toxicity. Chlorophyll and protein content reduced while proline and malondialdehyde increased due to its tolerance level under metal exposure. The content of ricinoleic acid was higher, and the fatty acids composition of polluted areas was almost similar to that of the control area. Thus, R. communis L. can be employed for reclamation of heavy metal contaminated soils.

The rate of degradation of enrofloxacin in broiler chicken manure has been characterised. Its degradation was investigated in manure excreted by broiler chickens in an intensively reared chicken facility; further, the degradation also followed after transfer of the excreta into the natural environment occurred. The effect of enrofloxacin and its degradation products on cucumber and tomato was also investigated. Enrofloxacin degradation was shown to take place within the rearing facility and also continuing after the manure was transferred into the environment. The rates of enrofloxacin degradation and the degree of degradation product formation in the manure heap incubated in the environment were condition specific, both variables depending on the manure sampling depth. The degradation half-lives ranged from 12.7 to 38.1 days for enrofloxacin and from 1.2 to 8.2 days for the main metabolite ciprofloxacin. Only the cucumber showed signs of toxicity when incubated with the composted manure immediately after transfer into field occurred (t = 0). No toxic effects to plants were observed when manure from the last incubation day (60th) of the field study and manure from the last incubation day of the laboratory degradation study were applied. The degradation study under field conditions showed that enrofloxacin and its degradation products degrade fast in the environment. Additionally, the toxic effects to plants decrease with the incubation time of manure containing enrofloxacin residuals.

A large complex water quality data set of a polluted river, the Tay Ninh River, was evaluated to identify its water quality problems, to assess spatial variation, to determine the main pollution sources, and to detect relationships between parameters. This river is highly polluted with organic substances, nutrients, and total iron. An important problem of the river is the inhibition of the nitrification. For the evaluation, different statistical techniques including cluster analysis (CA), discriminant analysis (DA), and principal component analysis (PCA) were applied. CA clustered 10 water quality stations into three groups corresponding to extreme, high, and moderate pollution. DA used only seven parameters to differentiate the defined clusters. The PCA resulted in four principal components. The first PC is related to conductivity, NH₄-N, PO₄-P, and TP and determines nutrient pollution. The second PC represents the organic pollution. The iron pollution is illustrated in the third PC having strong positive loadings for TSS and total Fe. The fourth PC explains the dependence of DO on the nitrate production. The nitrification inhibition was further investigated by PCA. The results showed a clear negative correlation between DO and NH₄-N and a positive correlation between DO and NO₃-N. The influence of pH on the NH₄-N oxidation could not be detected by PCA because of the very low nitrification rate due to the constantly low pH of the river and because of the effect of wastewater discharge with very high NH₄-N concentrations. The results are deepening the understanding of the governing water quality processes and hence to manage the river basins sustainably.

The aim of this study was to assess the historical trends of metal concentrations in coastal sediments in the vicinity of an inactive mining area, find background values and contamination levels of metals around the Karaburun peninsula, and then search for other sources of mercury in marine sediment cores using multivariate statistical analysis and report the potential ecological risks from that metal contamination. Surface sediment samples were taken from seven stations. Water depths were less than 20 m (coastal area) at stations KB07 and KB08. The depths at stations KB01, KB02, and KB03 were between 20 and 40 m, and stations KB05 and KB06 were more than 40 m (open area). In surface sediments at depths between 20 and 40 m, Mo, Cu, Pb, Zn, Ni, Co, Fe, Cd, Ti, Zr, Sn, As, Y, and Hg levels revealed higher contamination factors (Cf) compared to those of the coastal and open areas. Also, sediment samples were taken for historical records at stations KB01 and KB02 for 2012. Metal concentrations of Cu, Zn, Ni, Co, As, Sb, Cr, Ba, Ti, Al, and Hg in the sediment core samples were significantly higher during the Holocene (~5700 BC to 2000 B.C.) and Medieval Warm periods (~1000 A.D. to 1400 A.D.) and tended to decrease towards the Little Ice Age (2200 B.C. to the birth of Jesus Christ). Background concentration of Hg in sediment was found as 1.67 μg/g around the Karaburun peninsula. Average EF values higher than 20 were identified for As, Hg, Sb, and Ca. Ni and Hg levels were found above the PEL values. It was determined that the accumulation effect of Hg coming from the mafic rocks due to erosion in the marine environment was higher than that of Hg coming from the mine. The factor analyses showed an association between Hg, Ni, and Co. This reveals the importance of the contribution of mafic rocks reaching the marine environment by wave erosion. According to the factor analyses, high concentrations of Pb, Zn, Cd, As, Sb, Ba, Ti, and Zr were detected in the lithogenic sources.

Trace elements in the atmosphere could provide information about regional atmospheric pollution. This study presented a whole year of precipitation observation data regarding the concentrations of trace metals (e.g., Cr, Ni, Cu, Mn, Cd, Mo, Pb, Sb, Ti, and Zn), and a TEM-EDX (transmission electron microscope-energy dispersive X-ray spectrometer) analysis from June 2014 to September 2015 at a remote alpine glacier basin in Northwest China, the Laohugou (LHG) basin (4200 m a.s.l.), to determine the regional scale of atmospheric conditions and chemical processing in the free troposphere in the region. The results of the concentrations of trace metals showed that, although the concentrations generally were lower compared with that of surrounding rural areas (and cities), they showed an obviously higher concentration and higher EFs in winter (DJF) and a relatively lower concentration and lower EFs in summer (JJA) and autumn (SON), implying clearly enhanced winter pollution of the regional atmosphere in Northwest China. The TEM observed residue in precipitation that was mainly composed of types of dust, salt-dust, BC-fly ash-soot, and organic particles in precipitation, which also showed remarked seasonal change, showing an especially high ratio of BC-soot-fly ash particles in winter precipitation compared with that of other seasons (while organic particles were higher in the summer), indicating significant increased anthropogenic particles in the winter atmosphere. The source of increased winter anthropogenic pollutants mainly originated from emissions from coal combustion, e.g., the regional winter heating supply for residents and cement factories in urban and rural regions of Northwest China. Moderate Resolution Imaging Spectroradiometer (MODIS) atmospheric optical depth (AOD) also showed a significant influence of regional atmospheric pollutant emissions over the region in winter. In total, this work indicated that the atmospheric environment in western Qilian Mountains also showed enhanced anthropogenic pollution in winter, probably mainly caused by regional fossil fuel combustion.