腐殖质的光化学降解及其对环境污染物环境行为的影响

腐殖质是地表环境中最重要的有机组分,也是生态环境中最主要的吸光物质之一,对环境污染物的形态、迁移、毒性和生物可利用性有着重要的影响。文章综述了腐殖质的结构特征和光化学降解反应过程和机理,指出腐殖质的光敏化和光化学降解过程对环境污染物的环境行为和归宿有重要的影响。通常,腐殖质的光敏化作用在低质量浓度下,尤其在一定铁离子的协同作用下可促进有机污染物的降解,但高质量浓度的腐殖质由于其本身的吸光作用以及参与自由基的竞争则抑制有机污染物的降解。腐殖质的光化学降解过程降低了环境体系的pH和腐殖质的分子量、破坏了腐殖质的芳环结构、改变了紫外和可见光区域的吸收等,导致其与重金属离子和有机污染物结合能力的下降,造成水体或颗粒态中游离的污染物质量浓度增加,对生态系统将造成更大的危害。目前对腐殖质和环境污染物本身的光化学降解机理已较为清晰,今后应加强对自然水体或土壤系统中腐殖质光化学降解的影响因素,腐殖质光化学降解过程中结构特性的变化机理,以及腐殖质的结构特性与环境污染物结合性质之间的构效关系等方面的研究。特别是随着平流层臭氧空洞的增加,增强了到达地球表面的紫外线强度,研究紫外线增强对腐殖质和有机污染物的降解以及对生态系统的影响可进一步深刻理解太阳光辐射对污染物环境行为和归宿的影响。     

Huminstoffe in Sedimentporenwässern ausgewählter Bundeswasserstraßen

Humic substances are an important component of organic carbon in natural waters. Their character and properties are determined by the sources and the processes of their origin. Humic substances are not exclusively refractory compounds, but they are involved in several transformation processes in the water. It is not possible to directly analyze humic substances, therefore several methods were applied for their characterization. The presented LC-OCD-technique is a size-exclusion-chromatography with online UV- and carbon detection. Carbon fractions, e.?g. humic substances were differentiated by their molecular size. The portion of humic substances in sediment porewaters of the rivers Elbe, Rhine, Danube, Oder, Müritz-Elde-Waterway was determined. With only a few exceptions it ranges from 50 to 67?% of the dissolved organic carbon. The high molecular weight fraction accounts for 10 to 34?%, and the fraction of the low molecular weight substances was from 7 to 37?%. The ratio between the spectral absorption coefficient (254?nm) and the organic carbon is called SUVA (L/mg × m) and is an inidicator of the proportion of unsaturated bonds in the humic substances. Both high molecular herbal components (e.?g. cellulose, lignin) and biological degradiation products (e.?g. amino acids, sugar) are involved in sediment porewater transformation and degradiation processes. This demonstrates the distribution of the dissolved organic carbon between the fractions.     

Arsenic in drinking water and mortality in the Southern Great Plain,Hungary

Arsenic distribution has been found in drinking waters. A connection between arsenic and other constituents of water was determined. Close positive correlation was found between arsenic and humic substances over most of the study area. In two smaller areas, there was no correlation between arsenic and humic substances. In these waters, the arsenic distribution is not controlled by organic matter, but by other factors which need further investigations.Examination of mortality in the populations consuming water containing levels of arsenic above and below that permitted did not show any significant differences in standardised mortality ratio (SMR) from all causes of death for both male and female. The SMR from the main causes of death — diseases of the circulatory system and neoplasms — shows controversial results for males and females.     

Arsenic species in the well water and sediments of the blackfoot disease area in Taiwan

The blackfoot disease (BFD) observed in southwestern Taiwan is due to drinking high arsenic concentrations in well water. This paper presents some results concerning the distributions of arsenic species in water and sediments collected in the BFD (well, river and coastal) area and the background (lake and ocean) area for comparison. The results show that the concentrations of arsenate (870 ± 26 ug/L) and arsenite (70.2 ± 2.6 ug/ L) in well waters, and the contents of arsenic (1640 ug/g) with high percentage of easily reducible (Fe and Mn oxides, 91.7%) and exchangeable and carbonate (4.6%) phases in well sediments were much higher than those in river, lake and coastal samples. Low arsenic (3.46–31.8 ug/g) with high percentages (73.8–97.3%) of detritus and minerals phase with low percentages (0.4–9.8%) of total carbonate and exchangeable phases were found in the river and coastal samples in the BFD area as well as the lake and ocean samples in background area. It might suggest that the higher concentrations of toxic As(III) in well water and arsenic with higher values of easily reducible, carbonate and exchangeable phases in the well sediments, combined with the higher values of dissolved organic carbon, humic and fulvic acids and aromatic carbon as well as the higher fluorescence indensity in the well water are the key factors to cause the BFD in Taiwan.     

Characterization of dissolved organic carbon and Humic substances in the well water of the Blackfoot disease area in Taiwan

Since the early 1960s, many investigators have reported that blackfoot disease, a peripheral vascular disease, observed in southwestern Taiwan is due to drinking the higher arsenic concentration in well water. However, recent studies indicated that the relationship with blackfoot disease is not only with arsenic but also humic substances. This paper presents some results concerning the characterization (such as fluorescence, elemental composition, molecular weight and carbon distribution) of humic substances isolated from the Fuhsing well water of the blackfoot disease area. For comparison, the dissolved organic carbon (DOC) and humic substances in the normal well water from Chiuying and the Nanwan coastal water were also analyzed. In general, in the well water of the blackfoot disease area, extremely high concentrations of DOC (18.5mg/L) and fulvic acid (7.54mg/L) with high fluorescence intensity (59.1, equivalent to 0.0282uM quinine sulfate solution) and high percentages (over 50%) of low molecular weights of less than 1,000 were obtained compared with those of normal waters. C‐13 Nuclear magnetic resonance spectroscopy showed a high content (37.2%) of aromatic carbon. These higher concentrations of DOC and fulvic acid with the higher content of aromatic carbon in well water might be one of the key factors causing the blackfoot disease in Taiwan.     

Species of Trace Metals, Organic Residues and Humic Substances in Sediments From the Taiwan Erhjin River and Coastal Areas

Total organic carbon, humic substances, and the species of trace metals (including Cu, Zn, Pb, Cd, Cr, Mn and Fe) in six and seven phases, such as bioexchangeable (P1), skeletal (carbonates, P2), easily reducible (Fe and Mn oxides, P3), moderately reducible (crystalline Mn oxides, P4), organic matters with sulphides (P5), and detritus with minerals (P6) as well as organic with humic substances (PB4) and organic residues (PB6), were analyzed in sediments from the Taiwan Erhjin coastal (including river and estuarine) area, where places we found the copper pollution. Results indicate that higher percentages of P1 and P2 for copper, zinc, lead, cadmium and manganese in samples collected in March and September of 1990 were much higher than those in P3-P6. High percentages of chromium and iron in samples respectively collected in March and September of 1990 were found in P6. for the seven phase analysis, higher percentages of copper species in PB4 and PB6 as well as iron species in PB7 were observed. On the other hand, purified humic acid with the high contents of manganese and iron in humic acid as well as purified fulvic acids were generally found at the upstream stations; and low values at coastal stations. However, extremely high copper (as high as 1750μg g^-1, dry weight in fulvic acid and 820μg g^-1 in humic acid) and lead (821μg g^-1 in humic acid) concentrations with relatively high manganese and iron concentrations were observed in humic substances from the station near the copper recycling area. Comparing the results obtained from the Antarctic Ocean sediments with those from the Taiwan Erhjin Chi coastal sediments, the human impacts on the latter are evaluated.     

Strong adsorption of DNA molecules on humic acids

Analysing soil microbial communities is often hampered by DNA adsorption on soil organic compounds such as humic acids. However the role of humic acids in DNA adsorption and stability in soils remains controversial. To characterize DNA–humic acid interactions, we studied DNA adsorption on two commercially available humic acids and a soil humic acid extracted from an Andosol. Desorption of the adsorbed DNA using 4 different solutions—distilled water, 0.1 M NaCl, 0.1 M sodium phosphate buffer (pH 6.0), and 1% sodium dodecyl sulfate solution—was also studied to understand the mechanism of DNA adsorption on humic acids. Here, we show that humic acids play an important role in DNA adsorption to soils. DNA molecules were adsorbed on the humic acids, with adsorption increasing proportionally with the DNA concentrations in the solution. The adsorption on all humic acid samples was fitted with Freundlich equation, and the parameters obtained from the equation indicated a high affinity between the humic acids and DNA molecules. The total amount of DNA desorbed by the 4 solutions was less than 2% of the total DNA adsorbed on all the humic acids. The results demonstrate that DNA molecules are able to bind strongly to humic acids by ligand binding, hydrophobic interaction, aggregation, or precipitation.     

Species of Trace Metals,Organic Residues and Humic Substances in Sediments From the Taiwan Erhjin River and Coastal Areas

Abstract

Total organic carbon, humic substances, and the species of trace metals (including Cu, Zn, Pb, Cd, Cr, Mn and Fe) in six and seven phases, such as bioexchangeable (P1), skeletal (carbonates, P2), easily reducible (Fe and Mn oxides, P3), moderately reducible (crystalline Mn oxides, P4), organic matters with sulphides (P5), and detritus with minerals (P6) as well as organic with humic substances (PB4) and organic residues (PB6), were analyzed in sediments from the Taiwan Erhjin coastal (including river and estuarine) area, where places we found the copper pollution. Results indicate that higher percentages of P1 and P2 for copper, zinc, lead, cadmium and manganese in samples collected in March and September of 1990 were much higher than those in P3-P6. High percentages of chromium and iron in samples respectively collected in March and September of 1990 were found in P6. for the seven phase analysis, higher percentages of copper species in PB4 and PB6 as well as iron species in PB7 were observed. On the other hand, purified humic acid with the high contents of manganese and iron in humic acid as well as purified fulvic acids were generally found at the upstream stations; and low values at coastal stations. However, extremely high copper (as high as 1750μg g^?1, dry weight in fulvic acid and 820μg g^?1 in humic acid) and lead (821μg g^?1 in humic acid) concentrations with relatively high manganese and iron concentrations were observed in humic substances from the station near the copper recycling area. Comparing the results obtained from the Antarctic Ocean sediments with those from the Taiwan Erhjin Chi coastal sediments, the human impacts on the latter are evaluated.     

Investigations of some trace elements in the Bay of Lim

Sea water was collected at several stations in the Bay of Lim at a depth of one meter below the surface, and before analysis, was filtered with 0.45-μm Millipore filters. Shallow water sediments were collected at the same locations. Humic acids used in this work were separated from near-shore sediments taken from various saline waters of the Bay of Lim. The prepared humic acids were then analysed for their elementary composition and also for positions of their hydrolytic products to obtain more data on how and to which characteristic part, the trace elements were related. The hydrolysis of humic acids was done by chemical methods in order to obtain four main components: amino acids, sugars, phenols and condensed benzene core. Neutron activation analysis was used for trace element analysis in evaporated portions of filtered sea water, sediments, soil, living organisms, humic acids and their hydrolytic products. This work was undertaken to obtain more data on the organic matter present in sediments and in seagrass flats, and also to collect more data on trace elements that are associated with typical and representative samples for the Bay of Lim. Analyses of trace elements associated with either humic acids or their hydrolytic products were performed with the purpose of gaining evidence as to which part of humic acids metals are bound. Humic acids or their decomposition products play an important role in the distribution and availability of a number of essential or nonessential trace elements. Results of this work indicate that humic acids influence the process of redistribution of trace elements in the investigated local coastal area.     

Isolation and Chemical Characterization of Dissolved and Colloidal Organic Matter

An overview of the methods used for the isolation and characterization of organic matter in natural waters is presented. Commonly used techniques for the concentration and isolation of organic matter from water, such as preparative chromatography, ultrafiltration and reverse osmosis, and the methods used to analyze the organic matter obtained by these methods are reviewed. the development of methods to obtain organic matter that is associated with fractions of the dissolved organic carbon other than humic substances, such as organic bases, hydrophilic organic acids and colloidal organic matter are discussed. Methods specifically used to study dissolved organic nitrogen and dissolved organic phosphorous are also discussed.     

Biozide in Gebäudefassaden – ökotoxikologische Effekte, Auswaschung und Belastungsabschätzung für Gewässer

Background, aim and scope Sources of organic micropollutants occuring in surface waters are often unknown. Regarding environmental risk assessments for surface waters, construction materials have as till now, not been given much consideration, although biocides used as preservatives are known to reach urban storm water runoff. The study focused on biocides for facades coatings and aimed (1) to determine ecotoxicological effect values, (2) to quantify the leaching behaviour and (3) to assess the environmental risk for surface waters using a dynamic transport model. Materials and methods Eight biocides used in resin based facade coatings were investigated. Some biocides are substances known as pesticides for agricultural purposes like diuron, carbendazim and terbutryn. Ecotoxicological effect values for aquatic organisms were determined for every biocide. Leaching of four biocides from a render under UV-irradiation has been investigated in the laboratory including the influence of varying temperatures. Using 80 irrigation intervals over 28 days, facade runoff was sampled and followed by biocide chemical analysis. The total losses were calculated based on the concentration patterns. These data were used for modelling the transport of cybutryn from facades to surface waters. Biocide specific effect values and leaching characteristics have been taken into consideration. Results Acute and chronic effect values as well as predicted no effect concentrations for the investigated biocides indicate their high potential to affect aquatic organisms. The leaching of four biocides (diuron, terbutryn, cybutryn, carbendazim) from the facade render under the experimental conditions delivers high concentrations in the beginning followed by an exponential decrease. Rising temperature increased the concentration of biocides in the runoff. The total losses were between 7?% and 29?% depending on the substances. More than half of the losses occur in the runoff within the first 15 min of runoff from a 60 min irrigation cycle. The modelling result for cybutryn underlines its high environmental risk for small surface waters. Discussion The leaching of the biocides, their potential ecotoxic effects and persistence show clearly that the environmental risk for surface waters and soils seems to be high for certain biocides; whereas for others the risk seems to be significantly lower. With respect water quality criteria, polluted facades runoff has to be diluted before runoff can enter the discharge. Diuron and carbendazim are however also used as pesticides and preservatives for other materials and cybutryn is also used as an antifouling agent. All pathways have to be evaluated in order to identify relevant sources and to act more efficiently with respect to water and soil protection. Conclusions Concentrations with high environmental risk are expected at new facades, especially at facades with thermal insulation. With the given low predicted no effect concentrations in a range of a few ng/L and large amounts of biocides applied in paints and renders, the environmental risk for common biocides used in facade coatings has to be investigated in laboratory and field scale. It seems plausible that source control measures as the most efficient and sustainable precautionary principle need to be evaluated. Recommendations and perspectives Biocides and additives applied in construction materials have to be taken into consideration as relevant sources when evaluating the quality of storm water runoff, discharge into urban areas and the impact to soil and surface waters. A sustainable construction material management and storm water management are required. It is expected that ongoing laboratory and field studies with exterior paints, renders and flat sheets for waterproofing containing biocides and additives will give further insight into their environmental impact.     

Isolation and Chemical Characterization of Dissolved and Colloidal Organic Matter

An overview of the methods used for the isolation and characterization of organic matter in natural waters is presented. Commonly used techniques for the concentration and isolation of organic matter from water, such as preparative chromatography, ultrafiltration and reverse osmosis, and the methods used to analyze the organic matter obtained by these methods are reviewed. the development of methods to obtain organic matter that is associated with fractions of the dissolved organic carbon other than humic substances, such as organic bases, hydrophilic organic acids and colloidal organic matter are discussed. Methods specifically used to study dissolved organic nitrogen and dissolved organic phosphorous are also discussed.     

First determination of Cu adsorption on soil humin

Humic substances are heterogeneous mixtures of organic compounds occurring in huge amounts mainly in waters, soils, sediments and organic wastes. They are formed during the decay of living organisms. They play a very important role in many environmental processes including carbon sequestration, water cleaning and retention, soil erosion, fertility and pollutant retention. However, due to their complex nature, humic substances are still poorly characterized and much less known than living matter. Humin is the most insoluble and, in turn, the least understood fraction of humic substances. To our knowledge, no information is currently available on the adsorption and desorption behaviors of metal ions on soil humin. Here, we report the adsorption and desorption properties of Cu(II) on humin and humic acids isolated from a forest soil in northeast China using the batch equilibration method. Solid-state ¹³C cross-polarization magic angle spinning nuclear magnetic resonance (¹³C CPMAS NMR) spectroscopy was used to characterize and compare the chemical structures of humin and humic acid. The batch experiments’ results show that humin has a lower adsorption capacity and higher adsorption reversibility for Cu(II) than humic acid. The adsorption isotherms well fitted both the Langmuir and Freundlich equations. Humin, therefore, plays an important role in controlling the fate, transport and bioavailability of Cu(II) in the environment. The ¹³C CPMAS NMR spectra showed that compared with humic acid, humin was higher in alkyl C, carbohydrate C and phenolic C and was lower in methoxyl C, aryl C and carbonyl C. These findings mean that humin was less alkylated, more aliphatic and more hydrophobic.     

Photodegradation of chromophoric dissolved organic matters in the water of Lake Dianchi,China

Water samples were taken from Lake Dianchi, on the Yungui Plateau of southwest China, and experiments were conducted to simulate the photochemical degradation characteristic of chromophoric dissolved organic matter (CDOM) in the lake water. Three groups of experiments under different light conditions: ultraviolet (UV) light, visible light, and dark, were done and variations of fluorescence properties, UV absorbance, and dissolved organic carbon (DOC) concentrations during the experiments were analyzed to study the photodegradation process of CDOM with time. The result showed that light irradiation led to significant photochemical degradation of CDOM, resulting in changes in florescent properties, absorbance losses, decreases in aromaticity and average molecular weight, as well as decline in DOC concentration in the water. It was also observed that UV irradiation had greater effect than visible light did. However, various fluorophores had different sensitivities to the same irradiation condition, that is, protein-like fluorophore at the low excitation wavelengths is more sensitive to UV irradiation than the other fluorophores, and is more readily to undergo photo-degradation. In addition, visible light irradiation did not have significant impact on DOC in the water, with DOC concentration decrease by 5.57% –59.9% during the experiment time. These results may provide new knowledge on the environment behavior of CDOM in the water of Lake Dianchi.     

微塑料与有机污染物的相互作用研究进展

微塑料(粒径小于5 mm的塑料)作为海洋中一种新型的污染物正受到越来越多的关注。微塑料在全球多个海域均有检出,根据其来源分为原生微塑料和次生微塑料。原生微塑料由人工直接制造所得,常见于日常生活用品中;次生微塑料由大块塑料制品长期风化、磨损和光解形成。塑料自身含有多种有机添加剂,不断向环境中释放,污染海洋环境;微塑料表面还可吸附有机污染物,此吸附作用受两者的物理化学性质和环境条件影响,吸附污染物后的微塑料生物毒性增强。另外,聚合物复合光催化材料可加快有机污染物如染料的光降解反应速率,因而微塑料可能会促进有机污染物的光解。针对目前微塑料对有机物光降解的贡献、机理鲜见研究的问题,未来应加强以下3方面的研究:(1)微塑料对不同有机污染物光降解是否存在影响?(2)微塑料类型、尺寸以及反应条件对有机污染物光降解如何影响?(3)微塑料对有机污染物光降解影响的内在机制是什么?     

水中天然含氮有机物的形成、迁移转化及分布

天然含氮有机物是水环境中的重要组成部分,其在天然水体中的形态及分布对环境质量有显著影响.本文围绕水中天然含氮有机物在氮循环中的地位、迁移转化以及其在国内主要水域中的分布情况,对天然含氮有机物的研究现状进行了梳理.我国不同水域中溶解性含氮有机物(DON)浓度相差较大;其中水体中DON浓度一般在1.0 mg·L^-1以下;沉积物中DON浓度通常为几十至几百mg·kg^-1.水体DON以分子量<1 kDa的有机物为主,主要成分是尿素、氨基酸等物质.沉积物DON以分子量<1 kDa和>30 kDa的有机物为主,其中前者主要由芳构化程度较高的氨基酸等小分子有机物构成,后者以腐殖质类为主.水体中部分胺类物质本身具有一定毒性,游离氨基酸等DON还是卤乙腈、卤代酰胺、卤代硝基甲烷、卤化氰和亚硝胺等含氮消毒副产物的重要前体物.由于水体中许多含氮有机物具有生物可利用性,有机氮可能是引起水体富营养化的重要原因之一.     

High amounts of free aromatic amino acids in the protein-like fluorescence of water-dissolved organic matter

Fluorescence spectroscopy is widely used to study water pollution. The fluorescence of water natural organic matter can be classified into two groups: the protein-like fluorescence originating from aromatic amino acids and the humic fluorescence originating from humic substances. Actually, the precise molecular origin of the protein-like fluorescence is unknown because this fluorescence may be caused by either free amino acids, peptides or proteins. Therefore, we studied the molecular origin of the protein-like fluorescence of Suwannee River natural organic matter and fractions A, B and C + D obtained by size exclusion chromatography/polyacrylamide gel electrophoresis. Fractions were analyzed by reversed-phase high-performance liquid chromatography. The electrophoretic mobilities of fractions varied in the order C + D > B > A and the molecular size in the opposite order. Our results show that the protein-like fluorescence is almost exclusively located in high molecular size fraction A and medium molecular size fraction B. Retention times and fluorescence emission spectra of authentic free aromatic amino acids tyrosine and tryptophan were identical with the retention times and emission spectra of several chromatographic peaks of fractions A and B. More than 50 % of the protein-like fluorescence is due to free aromatic amino acids incorporated in water natural organic matter.     

Photosensitivity sources of dissolved organic matter from wastewater treatment plants and their mediation effect on 17α-ethinylestradiol photodegradation

● EE2 photodegradation behavior in the presence of four WWTPs’ DOM was explored. ● The ³DOM* played a major role in the EE2 photodegradation mediated by WWTPs’ DOM. ● The A²/O process DOM contained more aromatic and oxygen-containing substances. ● Possible photosensitivity sources of DOM in the A²/O process were proposed. Dissolved organic matter (DOM) from each treatment process of wastewater treatment plants (WWTPs) contains abundant photosensitive substances, which could significantly affect the photodegradation of 17α-ethinylestradiol (EE2). Nevertheless, information about EE2 photodegradation behavior mediated by DOM from diverse WWTPs and the photosensitivity sources of such DOM are inadequate. This study explored the photodegradation behavior of EE2 mediated by four typical WWTPs’ DOM solutions and investigated the photosensitivity sources of DOM in the anaerobic-anoxic-oxic (A²/O) process. The parallel factor analysis identified three varying fluorescing components of these DOM, tryptophan-like substances or protein-like substances, microbial humus-like substances, and humic-like components. The photodegradation rate constants of EE2 were positively associated with the humification degree of DOM (P < 0.05). The triplet state substances were responsible for the degradation of EE2. DOM extracted from the A²/O process, especially in the secondary treatment process had the fastest EE2 photodegradation rate compared to that of the other three processes. Four types of components (water-soluble organic matter (WSOM), extracellular polymeric substance, humic acid, and fulvic acid) were separated from the A²/O process DOM. WSOM had the highest promotion effect on EE2 photodegradation. Fulvic acid-like components and humic acid-like organic compounds in WSOM were speculated to be important photosensitivity substances that can generate triplet state substances. This research explored the physicochemical properties and photosensitive sources of DOM in WWTPs, and explained the fate of estrogens photodegradation in natural waters.     

Distribution and behaviour of polycyclic aromatic hydrocarbons in subtropical river estuary,Okinawa, Japan

Surface water samples were collected along the salinity gradient of Manko estuary in Okinawa, Japan, between January and November 2012, to examine spatial and temporal variability in the distribution, composition, behaviour, and sources of particulate polycyclic aromatic hydrocarbons (PAHs). Concentrations of total particulate PAHs ranged from 169.7?ng?g^?1 at riverine station (N1) in November 2012 to 922?ng?g^?1 at another riverine station (K3) in May 2012. Based on observed environmental behaviour, particularly relationships to organic matter, the PAHs appear divisible into two groups: group I (low molecular weight) PAHs were characterised by low particles affinity and strong correlations with a pool of autochthonous organic matter (e.g. high concentrations of polyunsaturated fatty acids), reflecting processes controlling their delivery to the estuary; and, in contrast, group II (high molecular weight) PAHs were characterised by high particles affinity and exhibited estuarine distribution primarily controlled by suspended solid load and inputs from terrigenous sources through river inflows. This relationship, coupled with isomer ratios indicative of combined mixed sources from petroleum and petroleum combustions, indicates that terrestrial run-off is the dominant mode of delivery of particulate PAHs in the estuary. The relationships between distinct groups of PAHs and lipid biomarkers demonstrated in this study suggest that very specific pools of particulate organic matter, as opposed to concentrations of particulate organic carbon alone, can be important in the transport and fate of hydrophobic contaminants.     

Photoreactivity of humic substances: relationship between fluorescence and singlet oxygen production

Humic substances are natural compounds abundantly present in the environment. They play a significant role in the natural attenuation of pollution in surface water due to their capacity to generate reactive species upon solar light excitation. Finding physico chemical parameters related to this property would be of a great help in the prediction studies of the organic pollutants fate. In this work, we investigated relationships between the ability of the humic substances to produce singlet oxygen and their fluorescence properties. For this, a series of sixteen humic acids, fulvic acids, and water-extractable organic matter from soils were studied. The steady-state singlet oxygen concentrations in the irradiated humic substances solutions were measured by monitoring the loss of furfuryl alcohol added as a singlet oxygen scavenger. The emission spectra of the sixteen samples were also recorded. Values of the steady-state singlet oxygen concentrations and the emission intensities showed significant variations among the humic samples and a parallel increase. Thus, here we demonstrate that the rate of singlet oxygen production and the emission intensity of the humic samples are correlated, the best correlation being obtained for emission wavelengths between 500 and 580 nm. This correlation which was never reported until now can be used to estimate the singlet oxygen-production capacity of the humic substances based on their fluorescent properties.