Khan M. G. Mostofa

Arsenic poisoning in groundwater: Health risk and geochemical sources in Bangladesh

Of the 2508 water samples analyzed in 10 districts of Bangladesh, 51%, on an average, contained arsenic levels of 0.05 to 2.50 mg/l. 95% of nail, 96% of hair, and 94% of urine samples contained arsenic above the normal level. Approximately 3.58 million people out of a total of 17.92 million who are drinking water containing arsenic levels >0.20 mg/l are potentially exposed to high risk of health hazard. Eight thousand and five hundred arsenic patients are identified; they are suffering from various skin lesions, gangrene in leg, skin, lung, bladder, liver, and renal cancer. A big portion of the total population is highly vulnerable to various internal cancers. Lowest arsenic concentration in drinking water producing dermatological disease is found to be 0.103 mg/l. However, the exposure time to develop arsenicosis varies from case to case reflecting its dependence on arsenic level in drinking water and food, nutritional status, genetic variant of human being, and compounding factors. This study has determined the high intensity of fluorescent humic substances in drinking water containing elevated concentrations of arsenic and very low concentrations of heavy metals. The synergistic/antagonistic effect of fluorescent compounds present in drinking water may aggravate the toxicity of arsenic. Geochemical study suggests that arsenic may be released from both reductive dissolution of Fe and Mn (oxy)hydroxide and microbial oxidation of organic matter.

Complexation between Hg(II) and biofilm extracellular polymeric substances: An application of fluorescence spectroscopy

The three-dimensional excitation emission matrix (EEM) fluorescence spectroscopy was employed to investigate the interaction of extracellular polymeric substances (EPS) from natural biofilm with Hg(II). The EEM spectra demonstrated that EPS with molecular weight over 14 kDa had two protein-like fluorescence peaks. The fluorescence intensity at both peaks was strongly dependent on the solution pH in the absence and presence of Hg(II), with the maximal fluorescence intensity at neutral pH. Fluorescence of both protein-like peaks was significantly quenched by Hg(II). The values of conditional stability constants (log K(a)=3.28-4.48) derived from modified Stern-Volmer equation are approximate to those for humic substances and dissolved organic matter (DOM), indicating that fluorescent components in EPS have strong binding capacity for Hg(II). Our findings suggest that EPS from biofilm is a class of important organic ligands for complexation with Hg(II) and may significantly affect the chemical forms, mobility, bioavailability and ecotoxicity of heavy metals in the aquatic environment.

Three-dimensional fluorescence as a tool for investigating the dynamics of dissolved organic matter in the Lake Biwa watershed

Quantitative and qualitative characterizations of dissolved organic matter (DOM) were carried out at the watershed level in central Japan by measuring dissolved organic carbon (DOC) concentration and the three-dimensional excitation–emission matrix (3-D EEM). DOC concentration was low (mean 37 ± 19 µM C) in the upstream waters, whereas, in general, it increased toward the downstream areas (mean 92 ± 47 µM C). Significant variations in DOC concentration were detected among rivers and channels. DOC concentration in the epilimnion of Lake Biwa increased during the summer period and decreased during the winter period. The lake hypolimnion has lower DOC concentration (mean 87 ± 7 µM C) compared with the epilimnion (107 ± 15 µM C). Fulvic acid (FA)-like substances in the DOM were directly characterized by 3-D EEM. The fluorescence peak for upstream DOM was found in regions with longer wavelengths (excitation/emission 386 ± 6/476 ± 5 nm) compared with downstream and lake DOM (351 ± 12/446 ± 15 nm and 341 ± 6/434 ± 6 nm, respectively). The DOC concentration is correlated with fluorescence peak intensity of FA-like substances in DOM in river waters. Such a relationship was not found in lake DOM. A blueshift of the fluorescence peak from upstream to lake DOM was observed. A decrease in fluorescence intensities was also detected during the summer period. These results may suggest that the degradation of FA-like substances in DOM occurs from natural solar irradiation. Protein-like fluorescence was significantly detected in the lake epilimnion during the summer period. A linear relationship between DOC concentration and protein-like fluorescence indicated that an autochthonous input of DOM gave rise to the increase in DOC concentration in the lake epilimnion during the summer. These results may suggest that the 3-D EEM can be used as a tool for the investigation of DOM dynamics at the watershed level with concurrent measurement of DOC concentration and the fluorescence properties of fulvic acid-like and protein-like substances.

Spatial and temporal variations and factors controlling the concentrations of hydrogen peroxide and organic peroxides in rivers

Environmental context. Hydrogen peroxide (H2O2) and organic peroxides (ROOH) are ubiquitously present in natural waters and primarily essential for several redox reactions. This study examines the effects of various dissolved organic substances on the formation of H2O2 and ROOH and their relationship with different water quality parameters in two Japanese rivers. This study suggests that fulvic acid is primarily responsible for production of H2O2 and ROOH in river waters. Abstract. Hydrogen peroxide (H2O2) and organic peroxides (ROOH) were examined in water samples collected from the upstream and downstream sites of two Japanese rivers (the Kurose and the Ohta). H2O2 concentrations during monthly measurements varied between 6 and 213 nM in the Kurose River and 33 and 188 nM in the Ohta River. ROOH varied between 0 and 73 nM in the Kurose River and 1 and 80 nM in the Ohta. Concentrations of peroxides were higher during the summer months than in winter. H2O2 concentrations correlated well with the measured content of dissolved organic carbon and/or the fluorescence intensity of the fluorescent dissolved organic matter (FDOM) in the water from these rivers, which suggested that the dissolved organic matter and FDOM are the major sources of H2O2. Further characterisation of FDOM components by excitation emission matrix spectroscopy and parallel factor (PARAFAC) analysis indicated that fulvic acid is a dominant source of H2O2 in river waters, which accounted for 23–70% of H2O2 production in the Ohta River, 25–61% in the upstream and 28–63% in the downstream waters of the Kurose River, respectively. A fluorescent whitening agent and its photoproduct (4-biphenyl carboxaldehyde) together contributed 3–7% of H2O2 production in the downstream waters of the Kurose River. Tryptophan-like substances were a minor source of H2O2 (<1%) in both rivers. An increase in the H2O2 concentration was observed in the diurnal samples collected at noon compared with the samples collected during the period before sunrise and after sunset, thus indicating that H2O2 was produced photochemically. This study demonstrates that H2O2 and ROOH are produced mainly from the photodegradation of FDOMs, such as fulvic acid.

Photobiogeochemistry of Organic Matter

Hydrogen Peroxide and Organic Peroxides.- Hydroxyl Radical and Other Free Radical Species.- Dissolved Organic Matter Degradation.- Chromophoric or Colored Dissolved Organic Matter.- Fluorescent Dissolved Organic Matter.- Photosynthesis.- Chlorophyll.- Biogeochemical Complexion of Dissolved Organic Matter with Trace Elements.- Impacts of Global Warming on Biogeochemical Cycles.

Distribution and characteristics of molecular size fractions of freshwater-dissolved organic matter in watershed environments: its implication to degradation

Distributions of molecular size and fluorescence properties of dissolved organic matter (DOM) in the Lake Biwa and Lake Baikal watersheds were investigated using the cross-flow ultrafiltration technique and three-dimensional fluorescence measurements. From the fluorescence properties, protein-like substances were usually found in the 0.1 μm-GF/F fraction (the Durapore membrane retentate of the GF/F filtrate) of the lake DOM. The results indicated autochthonous production of protein-like organic-matters in the lake environment. Fulvic acid (FA)-like components were composed of two fractions with respect to fluorescence properties and molecular size. Two FA-like fluorescence peaks, which showed different fluorescence peak positions in the excitation-emission matrix (EEM), were partly fractionated by the molecular size of 5000 daltons (5 kDa). The FA-like fluorescence peak position of the <5-kDa fraction was observed at the shorter wavelength region compared with that of the fraction between 5 kDa and 0.1 μm (5 kDa20.1 μm fraction). A blue shift of the FA-like fluorescence peak position as well as a decrease in the molecular size of the DOM was observed in lake samples. The relative contribution of the <5 kDa fraction to the DOC concentration was high in lake waters (68%–79%) compared with river waters (44%–68%), suggesting characteristic changes in molecular size between riverine and lacustrine DOM. DOM of the 5 kDa–0.1 μm fraction was relatively higher in river waters than in lake waters. These findings coincided with in situ distributions of the fluorescence properties and molecular size of DOM found in both stream and lake environments. These results indicate that FA-like substances from forested watersheds are decomposed qualitatively and quantitatively in the river-lake environment by photochemical and biological processes.

Sources, factors, mechanisms and possible solutions to pollutants in marine ecosystems.

Algal toxins or red-tide toxins produced during algal blooms are naturally-derived toxic emerging contaminants (ECs) that may kill organisms, including humans, through contaminated fish or seafood. Other ECs produced either naturally or anthropogenically ultimately flow into marine waters. Pharmaceuticals are also an important pollution source, mostly due to overproduction and incorrect disposal. Ship breaking and recycle industries (SBRIs) can also release various pollutants and substantially deteriorate habitats and marine biodiversity. Overfishing is significantly increasing due to the global food crisis, caused by an increasing world population. Organic matter (OM) pollution and global warming (GW) are key factors that exacerbate these challenges (e.g. algal blooms), to which acidification in marine waters should be added as well. Sources, factors, mechanisms and possible remedial measures of these challenges to marine ecosystems are discussed, including their eventual impact on all forms of life including humans.

Dissolved Organic Matter in Natural Waters

Organic matter (OM) in water is composed of two major fractions: dissolved and non-dissolved, defined on the basis of the isolation technique using filters (0.1–0.7 μm). Dissolved organic matter (DOM) is the fraction of organic substances that passes the filter, while particulate organic matter (POM) remains on the filter (Danielsson 1982; Kennedy et al. 1974; Liu et al. 2007; Mostofa et al. 2009a). DOM is generally originated from three major sources: (i) allochthonous Dissolved Organic Matter in Natural Waters

Fluorescent Dissolved Organic Matter in Natural Waters

Dissolved organic matter (DOM), of allochthonous and autochthonous origin, is a heterogeneous mixture of organic compounds, with molecular weights ranging from less than 100 to over 300,000 Da in natural waters. The DOM components are involved into key biogeochemical processes such as global carbon cycle, nutrient dynamics, photosynthesis, biological activity and finally as energy sources in the aquatic environments. Among the DOM components, only a limited fraction of organic compounds show fluorescence properties. These compounds are termed the fluorescent DOM (FDOM). In the pioneering works conducted by Kalle and Duursma, the fluorescence of terrestrial humic substances served as a tracer of soil organic matter in freshwater and seawater environments. The fluorescence of humic substances has then been used to distinguish the mixing of river water with seawater as well as their sources.

Complexation of Dissolved Organic Matter with Trace Metal Ions in Natural Waters

Complexation of the metal ions (M) with dissolved organic matter (DOM), i.e. M-DOM formation is of fundamental importance in metal ion chemistry and can control the occurrence of free toxic metals, the transport or migration of metals, acid–base balance and solubility in water, occurrence of the photo-Fenton reaction in surface water, biological effects, the bioavailability and toxicity to organisms in water, sediment and soil environments.