Photocatalytic degradation of para-hydroxybenzoic acid: Relationship between substrate adsorption and photocatalytic degradation

Dark adsorption and photocatalytic degradation of para-hydroxybenzoic acid (PHBA) was studied in the presence of Degussa P-25 titanium dioxide photocatalyst under concentrated solar radiation. This work includes the study of the effect of pH, and of the presence of different anions and cations on dark adsorption and photocatalytic degradation (PCD) of PHBA on titanium dioxide. The results obtained clearly indicate that there is a link between the extent of adsorption of PHBA and its PCD. Conditions that favor greater adsorption of PHBA also favor a greater PCD. This points to the possibility that the mechanism of PCD involves a surface reaction between adsorbed PHBA and OH ° radical. Anions were generally found to have a detrimental effect on the photocatalytic degradation of PHBA. Cl^- caused the greatest decrease in the PCD followed by NO₃^-, HCO₃^- and SO₄^2-. Cations Cu²⁺ and Fe²⁺ were not found to assist the degradation of PHBA, possibly due to the anions associated with them.     

Assessment of temporal and spatial water quality in international Gomishan Lagoon,Iran, using multivariate analysis

Coastal lagoon ecosystems are vulnerable to eutrophication, which leads to the accumulation of nutrients from the surrounding watershed over the long term. However, there is a lack of information about methods that could accurate quantify this problem in rapidly developed countries. Therefore, various statistical methods such as cluster analysis (CA), principal component analysis (PCA), partial least square (PLS), principal component regression (PCR), and ordinary least squares regression (OLS) were used in this study to estimate total organic matter content in sediments (TOM) using other parameters such as temperature, dissolved oxygen (DO), pH, electrical conductivity (EC), nitrite (NO₂), nitrate (NO₃), biological oxygen demand (BOD), phosphate (PO₄), total phosphorus (TP), salinity, and water depth along a 3-km transect in the Gomishan Lagoon (Iran). Results indicated that nutrient concentration and the dissolved oxygen gradient were the most significant parameters in the lagoon water quality heterogeneity. Additionally, anoxia at the bottom of the lagoon in sediments and re-suspension of the sediments were the main factors affecting internal nutrient loading. To validate the models, R², RMSECV, and RPDCV were used. The PLS model was stronger than the other models. Also, classification analysis of the Gomishan Lagoon identified two hydrological zones: (i) a North Zone characterized by higher water exchange, higher dissolved oxygen and lower salinity and nutrients, and (ii) a Central and South Zone with high residence time, higher nutrient concentrations, lower dissolved oxygen, and higher salinity. A recommendation for the management of coastal lagoons, specifically the Gomishan Lagoon, to decrease or eliminate nutrient loadings is discussed and should be transferred to policy makers, the scientific community, and local inhabitants.     

Urinary 8-hydroxy-2'-deoxyguanosine in inhabitants chronically exposed to arsenic in groundwater in Cambodia

Arsenic concentrations in hair and urine, and urinary levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, were examined for inhabitants of the Mekong Basin in Kratie Province, Cambodia. Also, the arsenic levels of tube-well water were determined. Total arsenic concentrations in tube-well water ranged from <1 to 886 microg L(-1), and 44.8% of these exceeded the WHO drinking water guideline of 10 microg L(-1). Elevated levels of arsenic were observed in the human hair and urine, and also a significant positive correlation was observed between the concentrations in hair and urine. These results suggest that the inhabitants are chronically exposed to arsenic through drinking the tube-well water. Levels of urinary 8-OHdG were higher for the subjects with higher arsenic levels in hair and urine, suggesting that induction of oxidative DNA damage was caused by chronic exposure to arsenic in tube-well water for the inhabitants in Kratie Province. To our knowledge, this is the first report on the oxidative DNA damage caused by chronic exposure to arsenic in groundwater for the inhabitants in Cambodia.     

Assessment of the impact of landfill on groundwater quality: A case study of the Pirana site in western India

In present study focus has been given on estimating quality and toxicity of waste with respect to heavy metals and its impact on groundwater quality, using statistical and empirical relationships between different hydrochemical data, so that easy monitoring may be possible which in turn help the sustainable management of landfill site and municipal solid waste. Samples of solid waste, leachate and groundwater were analyzed to evaluate the impact of leachates on groundwater through the comparison of their hydrochemical nature. Results suggest the existence of an empirical relationship between some specific indicator parameters like heavy metals of all three above mentioned sample type. Further, K/Mg ratio also indicates three groundwater samples heavily impacted from leachate contamination. A good number of samples are also showing higher values for and Pb than that of World Health Organization (WHO) drinking water regulation. Predominance of Fe and Zn in both groundwater and solid waste samples may be due to metal plating industries in the area. Factor analysis is used as a tool to explain observed relation between numerous variables in term of simpler relation, which may help to deduce the strength of relation. Positive loading of most of the factors for heavy metal clearly shows landfill impact on ground water quality especially along the hydraulic gradient. Cluster analysis, further substantiates the impact of landfill. Two major groups of samples obtained from cluster analysis suggest that one group comprises samples that are severely under the influence of landfill and contaminated leachates along the groundwater flow direction while other assorted with samples without having such influence.     

Perchlorate contamination of groundwater from fireworks manufacturing area in South India

Perchlorate contamination was investigated in groundwater and surface water from Sivakasi and Madurai in the Tamil Nadu State of South India. Sensitive determination of perchlorate (LOQ?=?0.005 μg/L) was achieved by large-volume (500 μL) injection ion chromatography coupled with tandem mass spectrometry. Concentrations of perchlorate were <0.005–7,690 μg/L in groundwater (n?=?60), <0.005–30.2 μg/L in surface water (n?=?11), and 0.063–0.393 μg/L in tap water (n?=?3). Levels in groundwater were significantly higher in the fireworks factory area than in the other locations, indicating that the fireworks and safety match industries are principal sources of perchlorate pollution. This is the first study that reports the contamination status of perchlorate in this area and reveals firework manufacture to be the pollution source. Since perchlorate levels in 17 out of 57 groundwater samples from Sivakasi, and none from Madurai, exceeded the drinking water guideline level proposed by USEPA (15 μg/L), further investigation on human health is warranted.     

Persistent organochlorines in human breast milk from major metropolitan cities in India

The present study was carried out to understand the current contamination status of organochlorine compounds (OCs) in human breast milk from three metropolitan cities in India (New Delhi, Mumbai and Kolkata). Among the OCs analyzed, DDTs were predominant followed by HCHs and PCBs. CHLs and HCB levels were much lower. Contamination patterns were different in human milk found in our previous study in Chennai, a metropolitan city in southern India, indicating region specific exposure routes and variable sources. In comparison with previous data, levels of DDTs and HCHs generally declined with time, implying the effect of various bans and restrictions on their usage. No association between concentrations of OCs and demographic characteristics such as parity and age of mothers was observed which might be due to narrow range of mother's age. Estimated daily intake shows that some infants are exposed to OCs to a greater extent, particularly HCHs than the guideline standard.     

Contamination status of arsenic and other trace elements in drinking water and residents from Tarkwa, a historic mining township in Ghana

This study was conducted to assess the contamination status of 22 trace elements, especially As in water and residents in Tarkwa, a historic mining town in Ghana. Drinking water and human urine samples were collected from Tarkwa in addition to control samples taken from Accra, the capital of Ghana in March, 2004. Concentrations of As and Mn in some drinking water samples from Tarkwa were found above the WHO drinking water guidelines posing a potential health risk for the people. A potential health risk of As and Mn is a concern for the people consuming the contaminated water in this area. No significant difference of As concentrations in human urine between mining town (Tarkwa) and control site (Accra) was observed. Although As concentrations in drinking water in Tarkwa were low, urinary As levels were comparable to those reported in highly As-affected areas in the world. These results suggest the presence of other sources of As contamination in Ghana. This is the first study on multi-elemental contamination in drinking water and human from a mining town in Ghana.     

Mercury in hair and blood from residents of Phnom Penh (Cambodia) and possible effect on serum hormone levels

High concentration of mercury (Hg) in hair has been reported for Cambodians. To confirm the Hg contamination occurring through intake, Hg concentrations were determined in both hair and blood of residents (n=20) from Phnom Penh, Cambodia. Mercury concentrations in the hair and blood were 0.69-190microg g(-1) dry wt and 5.2-58microg l(-1), respectively, which were lower than those from Hg contaminated or high fish intake regions, but were higher than those from non-contaminated regions. Some female subjects had hair and blood Hg levels exceeding the threshold values for neurotoxic effects. Interestingly, serum estrone and estradiol levels were positively correlated with blood Hg level for both males and females, indicating possible induction of female hormones by Hg exposure in Cambodians.     

Electrochemical destruction of p-chlorophenol and p-nitrophenol -- Influence of surfactants and anode materials

The electrochemical oxidative removal of p-chlorophenol and p-nitrophenol was studied by cyclic voltammetry (CV) and constant current electrolysis on commercially available graphite and titanium substrate insoluble anodes (TSIA). The effect of cationic cetyl trimethylammonium bromide (CTAB), anionic sodium dodecyl sulphate (SDS) and non-ionic polyoxyethylene(23)lauryl ether (Brij-35) surfactants, which prevent adherent film formation on the electrode surface were also studied. CV experiments indicate that p-chlorophenol exhibits a relatively higher tendency for film formation on graphite and that sodium chloride is a better medium for the destruction of phenols. The electrochemical oxidation of phenols under galvanostatic conditions in chloride medium with CTAB enhanced the detoxification process with significantly lower fouling effects on TSIA. The surfactants, however, did not improve phenol removal on graphite under identical experimental conditions. A charge of 2.5F per mol was found to be sufficient to achieve 44-48% removal of phenol on both the electrodes in the absence of the surfactants. A 55-65% removal was achieved in the presence of the cationic surfactant on the TSIA electrode. Phenol was removed as a low molecular weight polymer (MW approximately 4450).