Monofunctionalized cyclodextrin polymers for the removal of organic pollutants from water

Water is an important resource for domestic, industrial, agricultural and recreational purposes. The quality of water is however significantly deteriorating due to the accumulation of organic pollutants in aqueous systems. Conventional water treatment technologies fail to remove these contaminants to desirable levels. Recent studies have revealed that cyclodextrin nanoporous polymers are capable of absorbing pollutants from water to parts per billion levels. We have demonstrated that functionalised cyclodextrin polymers have enhanced absorption capacities for some organic pollutants. Here we report the synthesis of several insoluble monosubstituted cyclodextrin polymers or “nanosponges”. We show that these polymers have improved abilities in the absorption of p-nitrophenol and pentachlorophenol from aqueous solutions.     

Simultaneous sorption of aqueous phenanthrene and phosphate onto bentonites modified with AlCl3 and CTMAB

The purpose of this work is to synthesize a new type of bentonite sorbent that can simultaneously remove both organic compounds and phosphate from water. Inorganic-organic bentonites (Al-CTMAB-Bent) were synthesized by modifying bentonites with both AlCl₃ and cetyltrimethyl ammonium bromide (CTMAB). Simultaneous sorption of aqueous phenanthrene and phosphate onto Al-CTMAB-Bent was examined. Removal rates of phenanthrene and phosphate from water reached 96.3% and 90.2%, respectively, at their respective initial concentrations of 1 mg/L and 5 mg/L and the added amount of Al-CTMAB-Bent was 1.25 g/L. The residual turbidity of the Al-CTMAB-Bent suspension decreased 81.4% compared to that of organobentonite suspension after a 1 h settling time. Thus, inorganic-organic bentonite can be used to treat wastewater containing both organic pollutants and phosphate.     

Assessment of solid waste and dumpsite leachate and topsoil

Dumpsite leachate contains different hazardous substances, some of which threaten the environment. In this study, municipal solid waste, dumpsite leachate and topsoil from seven different dumpsites in Lagos and Ibadan, Nigeria were analysed using standard methods. The parameters analysed in the composite leachate samples collected are pH, solids, alkalinity, chloride, nitrate, sulfate, phosphate, biochemical oxygen demand, chemical oxygen demand turbidity, heavy metals (e.g. Zn, Pb, Co, Ni, Cd) and some persistent organic pollutants (e.g. polyaromatic hydrocarbons [PAHs] and polychlorinated biphenyls [PCBs]). Total organic carbon, heavy metals (e.g. Zn, Pb, Co, Ni, Cd) and organic pollutants (e.g. PAHs, PCBs) were analysed in the dumpsite topsoil and the control samples. The samples for heavy metal determination were digested using concentrated nitric acid and the digestate was analysed using atomic absorption spectrometry, whereas organic pollutants were extracted using cold extraction and quantified by gas chromatography-mass spectrometry (GC-MS). The study revealed that dumpsites in Ibadan have ～90% domestic and 10% industrial waste, whereas the figures for Lagos are 80% and 20%, respectively. In the leachate samples, concentrations of PAHs and PCBs ranged from 0.85 to 1.47 mg/L and 0.01 to 0.08 mg/L, respectively; the values were 0.94–2.79 mg/kg and 10.0–412 μg/kg in the topsoil. If not properly managed, dumpsite leachate can seep into groundwater and surface water via run-off, and can have adverse effects on human health and the entire ecosystem.     

Graphene quantum dots–eggshell nanocomposite to extract polycyclic aromatic hydrocarbons in water

In solid-phase extraction, the sorbent controls selectivity, affinity, and loading capacity. Many sorbents can be used, such as functionalized resin, naphthalene, activated carbon, molecular-imprinted polymers, and nanometer-sized materials. Here, we prepared a nanocomposite made of graphene quantum dots and eggshell to extract polycyclic aromatic hydrocarbons from aqueous solutions. We studied the effect of sample volume, solution pH, amount of nanosorbent, and sample loading flow rate on the extraction efficiency. We obtained a wide dynamic linear range from 0.1 to 200 ng m/L, good linearity with r ² higher than 0.99, and low-detection limits of 5–75 pg m/L. We measured PAH in spiked water samples.     

Preparation of magnetic nanocomposite beads and optimizing the conditions for effective removal of U(VI) from aqueous solutions

Magnetic ion-imprinted polymers (IIPs) were prepared by precipitate polymerization and leached with HCl to remove uranium. Their ability to remove hexavalent uranium from wastewater effluents was studied. Batch adsorption studies to determine the optimum conditions of U(VI) removal were conducted at different levels of sample pH, sorbent amount, agitation time, and initial uranium concentration. It was observed that, under optimum conditions (i.e. pH 4, adsorbent amount of 50 mg, 45 min agitation time, and initial U(VI) concentration of 2 mg L^?1), the maximum removal of U(VI) cations was >98% and 80% for the magnetic IIP and the corresponding magnetic non-imprinted polymers (NIP), respectively. Langmuir and Freundlich isotherms were used to describe the adsorption of U(VI) onto magnetic IIP and NIP. The adsorption capacity of U(VI) was determined to be 1.06 and 0.85 mg g^?1 for the two isotherms, respectively. The order of selectivity was found to be U(VI) > Fe(III) > Pb(II). For six cycles of regeneration and reuse, the magnetic polymers maintained their stabilities with only a 4% loss in the extraction efficiency. The average extraction efficiencies of the magnetic polymers for the spiked acid mine drainage and sewage wastewater effluents were 71% and 58% for the magnetic IIP and NIP, respectively. From powder X-ray diffraction analysis, application of the Scherrer equation yielded magnetic nanoparticles of an average mean diameter of 11.9 nm. Thermo-gravimetric analysis revealed that the HCl-leached magnetic polymers had a magnetite residual weight of 5%.     

水生生物水质基准研究中轮虫、水螅、涡虫类受试生物的筛选

轮虫、水螅、涡虫是水生生态系统的重要生物类群。因其对水体污染较敏感,所以对水生生物基准研究有重要意义。依据我国生物区系资料及毒性数据丰度,筛选出8种代表性本土轮虫、水螅、涡虫类生物。参照美国水生生物基准技术指南,搜集、筛选了这8种代表性生物的急性毒性数据,通过数据分析,筛选出对各物种毒性最大的污染物,主要包括重金属、农药、有机锡化物、表面活性剂、吡啶胺类杀菌剂。分析污染物的物种敏感度分布,依据累积概率对代表性生物的物种敏感性进行分类,结果为:萼花臂尾轮虫(Brachionus calyciflorus)、绿水螅(Hydra viridissima)、普通水螅(Hydra vulgaris)对重金属铜的累积概率为6.5%、8.5%和10.4%,普通水螅(Hydra vulgaris)对重金属汞的累积概率为6.3%;龟甲轮虫(Keratella cochlearis)和四齿腔轮虫(Lecane quadridentata)对五氯酚钠的累积概率为5.1%和7.6%;褐水螅(Hydra oligactis)和绿水螅(Hydra viridissima)对三丁基氧化锡的累积概率为6.9%和13.8%,萼花臂尾轮虫(Brachionus calyciflorus)对氟啶胺的累积概率为6.7%,日本三角涡虫(Dugesia japonica)对四氯化碳、十二烷基苯磺酸钠的累积概率分别为6.7%和7.1%。上述结果表明:萼花臂尾轮虫、绿水螅对重金属铜敏感;普通水螅对重金属铜和汞敏感;龟甲轮虫和四齿腔轮虫对农药敏感;褐水螅和绿水螅对有机锡化物敏感;萼花臂尾轮虫对吡啶胺类杀菌剂敏感;日本三角涡虫对四氯化碳、表面活性剂敏感。这7种代表性生物可作为相关污染物的水生生物基准受试物种。     

Relationships Between Copper Species and Forms,Hydrographic and Biomass Parameters in the Taiwan Erhjin Chi Coastal Area

The first incident of green oysters (Crassostrea gigas) was reported in Taiwan in the Charting coastal area in January, 1986 and mortality was reported three months later. the cause of the greened oysters was identified as copper pollution. the copper content of the green oysters was extremely high - 2100 ppm, 2225 ppm, and 4400 ppm dry weight, in January, 1986, February 1987, and January 1989, respectively. in this paper we summarize the seasonal and regional distributions of copper species (complexed by inorganic and organic ligands, labile and non-labile, polar and non-polar) and forms (dissolved and particulate) and the hydrographic and biomass parameters (mainly particulate organic carbon, chloropyll -α, adenosine triphosphate and primary production) in sea water in the Erhjin Chi coastal area. in general, high concentrations of particulate material (0.24 to 724 ppb) and non-labile organic copper (0.03 to 21.5 ppb) were observed. Low values of polar organic copper (<0.02 to 16.5 ppb) indicated that non-polar organic complexes (0.3 to 20.4 ppb) from man-made organic pollutants were the major complexes in the area studied. On the basis of this data, the cause of greening and mortality in oysters is evaluated in relation to the bioavailable copper (sum of particulate and labile copper) and copper assimilative capacity (detoxicant). Finally, the correlations between the species and forms of copper, hydrographic and biomass parameters are also discussed.     

Equilibrium,kinetics and thermodynamics of hexavalent chromium biosorption on pristine and zinc chloride activated Senna siamea seed pods

Hexavalent chromium contamination in water is an issue of huge concern due to its use at a high scale, toxicity and non-biodegradability. Biosorption is a cost effective and unconventional strategy for the elimination of Cr(VI). Here, a novel biosorbent Senna siamea seed pod biomass and its chemically activated form have been investigated for the elimination of hexavalent chromium from aqueous solution. The biosorbent was characterized by using BET, FTIR, FESEM-EDX and TGA techniques. Parameters controlling the biosorption process were optimized as pH 2.0, temperature 30°C, initial Cr(VI) concentration 500?mg/L, biosorbent dose 0.5?g/L. Optimized contact time was 210 and 180 min for pristine biomass and activated carbon, respectively. Langmuir isotherm correlated well with experimental data revealing that the biosorption occurred in monolayer pattern. Maximum biosorption capacity calculated by Langmuir biosorption isotherm was 119.18 and 139.86?mg/g for S. siamea pristine biomass and activated carbon, respectively. Pseudo-second order kinetic model correlated well with experimental data. Thermodynamic studies suggested that the biosorption process occurs in a non-spontaneous, stable and endothermic manner. These interesting findings on Cr(VI) biosorption by S. siamea seed pod biomass and S. siamea zinc chloride activated carbon vouches for its potential application as an unconventional biosorbent.     

Removal of high concentrations of polycyclic aromatic hydrocarbons from contaminated soil by biodiesel

Solubilizing experiments were carried out to evaluate the ability of biodiesel to remove polycyclic aromatic hydrocarbons (PAHs) from highly contaminated manufactured gas plant (MGP) and PAHs spiked soils with hydroxypropyl-β-cyclodextrin (HPCD) and tween 80 as comparisons. Biodiesel displayed the highest solubilities of phenanthrene (420.7 mg·L^-1), pyrene (541.0 mg·L^-1), and benzo(a)pyrene (436.3 mg·L^-1). These corresponded to several fold increases relative to 10% HPCD and tween 80. Biodiesel showed a good efficiency for PAH removal from the spiked and MGP soils for both low molecular weight and high molecular weight PAHs at high concentrations. Biodiesel was the best agent for PAH removal from the spiked soils as compared with HPCD and tween 80; as over 77.9% of individual PAH were removed by biodiesel. Tween 80 also showed comparable capability with biodiesel for PAH solubilization at a concentration of 10% for the spiked soils. Biodiesel solubilized a wider range of PAHs as compared to HPCD and tween 80 for the MPG soils. At PAH concentrations of 229.6 and 996.9 mg·kg^-1, biodiesel showed obvious advantage over the 10% HPCD and tween 80, because it removed higher than 80% of total PAH. In this study, a significant difference between PAH removals from the spiked and field MGP soils was observed; PAH removals from the MGP soil by HPCD and tween 80 were much lower than those from the spiked soil. These results demonstrate that the potential for utilizing biodiesel for remediation of highly PAH-contaminated soil has been established.     

活化过氧乙酸技术去除水体有机污染物研究进展

过氧乙酸(peracetic acid,PAA)是一种广谱、高效、环保型消毒剂.近年来,基于活化过氧乙酸的高级氧化技术由于适用pH范围广、产生毒副产物少及具备一定剩余消毒能力等优点在水体有机污染物去除方面受到了越来越多的关注.本文介绍了PAA的性质,综述了活化PAA技术去除水体有机污染物的基本原理及研究现状,分析了活化PAA技术去除有机污染物的主要影响因素(pH及水质组分).最后提出了该技术目前面临的问题及未来发展方向,以期为开发可实际应用于饮用水/污水深度处理的活化PAA技术提供借鉴.     

Accumulation of cadmium and bioenergetics in the mussel Mytilus edulis

Accumulation rates of cadmium, the amount of food ingested and assimilated, the amount of oxygen consumed and changes in dry flesh weight have been measured in Mytilus edulis L. exposed to 0, 10 and 100 ppb cadmium for 17 d in aquaria with seawater flowing continously and at constant algal concentration. The accumulation rates were linear at 10 and 100 ppb, amounting to 0.58 and 8.89 ppm d^-1, respectively. Body loads up to 150 ppm caused no effects on either clearance, ingestion, assimilation, respiration, or growth. High net growth efficiencies between 55–59% were obtained, indicating near optimal experimental conditions. It is suggested that the setup and experimental procedure provide an excellent tool in the study of accumulation and sublethal effects of environmental pollutants in suspension feeding bivalves.     

Evaluation and quantification of genotoxicity of urban waters by using Vicia faba bioassays

The ecotoxic effect of pollutants in the water environment has become a hot topic of research. Because of the genotoxicity describing the composite deleterious action of the toxicants in water, the Vicia faba root-tip cell micronucleus (MN) test was applied for genotoxicity assessment of organic and inorganic substances in four rivers, two lakes and effluent flows from two wastewater treatment plants in Xi’an, China. Results showed that the lowest MN frequency was between 2.0‰ and 3.0‰. However, the highest MN frequency of the water samples was as high as 30.0–34.0‰. The results well reflected that the seriously polluted river with high chemical oxygen demand and total organic carbon showed high genotoxicity, and also indicated the genotoxic impact of urban discharge on the surface waters and the ability of urban water bodies to absorb the impact. In addition, there were significant correlations between the genotoxicity expressed by MN rate and Cr⁶⁺ (5–80?mg/L) and phenol concentrations (2–40?mg/L). The genotoxicity of the urban water could be quantified as equivalent Cr⁶⁺ or phenol concentrations and which might be used as a set of quantitative indicators of the water genotoxicity.     

Effects of metal pollution in the monosodium glutamate production effluent on full exploitation and biological treatment

Monosodium glutamate (MSG) effluent was sampled from three MSG mills and 21 metal elements were measured with a inductively coupled plasma (ICP) Spectrometer. The total metal concentration of each MSG wastewater sample was 19192, 3190 and 3161 mg/L respectively. Compared with the water quality standard issued by the Chinese Government and the World Health Organization (WHO), some values were found to exceed the standards. The 24hr‐LC₅₀, 48hr‐LC₅₀, 72hr‐LC₅₀ and 96hr‐LC₅₀ to the fish Ctenopharyngodon idellus were 6.9%, 3.2%, 2.5% and 1.4% MSG wastewater individually. The specific growth rate for photosynthetic bacteria (PSB) Rhodopseudomonas sphaeroides was inhibited by the metals in MSG wastewater. Therefor the MSG wastewater should not be discharged into drinking, irrigation and fishery water systems, moreover it cannot be treated by general biological processes efficiently. How to develop an effective biotechnique for the utilization of organic pollutants in MSG effluent will also be discussed in this paper.     

Antioxidant enzyme activities of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> in response to nonylphenols and degradation of nonylphenols by <Emphasis Type="Italic">M. aeruginosa</Emphasis>

The aim of this study was to examine the effects of chemical nonylphenols (NPs) on the antioxidant system of Microcystis aeruginosa strains. The degradation and sorption of NPs by M. aeruginosa were also evaluated. High concentrations of NPs (1 and 2 mg/l) were found to cause increases in superoxidase dismutase (SOD) and glutathione-S-transferase (GST) activities and in glutathione (GSH) levels. These results suggest that toxic stress manifested by elevated SOD and GST levels and GSH contents may be responsible for the toxicity of NPs to M. aeruginosa and that the algal cells could improve their antioxidant and detoxification ability through the enhancement of enzymatic and nonenzymatic prevention substances. The observed elevations in GSH levels and GST activities were relatively higher than those in SOD activities, indicating that GSH and GST contributed more in eliminating toxic effects than SOD. Low concentrations of NPs (0.05–0.2 mg/l) enhanced cell growth and decreased GST activity in algal cells of M. aeruginosa, suggesting that NPs may have acted as a protecting factor, such as an antioxidant. The larger portion of the NPs (>60%) disappeared after 12 days of incubation, indicating the strong ability of M. aeruginosa to degrade the moderate persistent NP compounds. The sorption ratio of M. aeruginosa after a 12-day exposure to low nominal concentrations of NPs (0.02–0.5 mg/l) was relatively high (>30%). The fact that M. aeruginosa effectively resisted the toxic effects of NPs and strongly degraded these pollutants indicate that M. aeruginosa cells have a strong ability to adapt to variations in environmental conditions and that low and moderate concentrations of organic compounds may favor its survival. Further studies are needed to provide detailed information on the fate of persistent organic pollutants and the survival of algae and to determine the possible role of organic pollutants in the occurrence of water blooms in eutrophic lakes.     

制药废水的可生物降解性与生物毒性研究

制药废水有机物含量高,难生物降解成分多,有些成分可抑制污泥活性或具有生物毒性.以某制药企业维生素生产的7个工段(W1 ～ W7)的排放废水为研究对象,用摇瓶试验评价了各工段废水的可生物降解性能,用瓦勃氏呼吸仪测试了各工段废水对污泥活性的抑制作用,用发光菌急性毒性试验评价了各工段废水经好氧生物处理前后的生物毒性变化.研究...     

Improved sample preparation and GC–MS analysis of priority organic pollutants

Mass spectrometry is a major tool for analysing organic pollutants. However, scientists often complain about laborious sample preparation. The development of new commercial high-resolution mass spectrometers gives a chance to improve simultaneously speed, reliability, and sensitivity of the analysis. Here, we used the time-of-flight high-resolution mass spectrometer Pegasus GC-HRT to identify and quantify 55 priority organic pollutants in water samples. This mass spectrometer has a high resolution of 50,000, a high mass accuracy of about 1 ppm and a very high acquisition rate of up to 200 full mass range spectra per second. 1 mL water samples were extracted with 1 mL dichloromethane. Results show that the sample preparation and analysis are achieved 30 times faster, requiring 1,000 times less water and 350 times less solvent than the classic 8270 method of the United States Environmental Protection Agency. The detection limit is 1 μg/L. The quantification limit is 10 μg/L. Our procedure, named accelerated water sample preparation, is simpler, faster, cheaper, safer and more reliable than 8270 Method.     

Steam activation,characterisation and adsorption studies of activated carbon from maize tassels

In this paper, steam-produced activated carbon (STAC) from maize tassel (MT) was evaluated for its ability to remove basic dye (methylene blue MB) from aqueous solution in a batch adsorption process. The equilibrium experiments were conducted in the range of 50–300 mg/L initial MB concentrations at 30°C, for effect of pH, adsorbent dosage and contact time. The experimental data were analysed by Langmuir, Freundlich and Temkin isotherm models of adsorption. Freundlich adsorption isotherm was found to have highest value of R²(R²=0.97) compared to other models of Langmuir and Temkin having (0.96 and 0.95 respectively). STAC has a high adsorptive capacity for MB dye (200 mg/g) and also showed favourable adsorption for the dye with the separation factor (R_L<1) for the dye-activated carbon system. The kinetic data obtained were analysed using pseudo first-order kinetic equation and pseudo second-order kinetic equation. The experimental data fitted well into pseudo second-order kinetic equation, as demonstrated by the high value of R².     

An improved activated carbon method to quantify dichlorodiphenyltrichloroethane (DDT) in surface water

Currently, South Africa is designing a strategy for surface water protection involving organic contaminants such as dichlorodiphenyltrichloroethane (DDT), which is currently used for malaria control in mosquito-infested areas. Here, we demonstrate the successful use of an improved activated carbon technique using dichloromethane instead of chloroform, and slower leaching rate of 15 mL/min to quantify DDT and its metabolites in surface water. The recovery tests for 2,4′DDT, 2,4′DDD, 2,4′DDE, and 4,4′DDT, 4,4′DDD, 4,4′DDE ranged from 75 to 84% and 87 to 96%, respectively (DDE: dichlorodiphenyldichloroethylene, DDD: dichlorodiphenyldichloroethane). The main advantages of this technique over conventional liquid–liquid extractions are reduced amount of organic solvent, little sample preparation, and larger sample throughput. Because activated charcoal is fairly cheap, the technique can be routinely used to quantify and monitor DDT and its metabolites in surface water samples.     

Fabrication of highly efficient Bi2WO6/CuS composite for visible-light photocatalytic removal of organic pollutants and Cr(VI) from wastewater

• A novel Bi₂WO₆/CuS composite was fabricated by a facile solvothermal method. • This composite efficiently removed organic pollutants and Cr(VI) by photocatalysis. • The DOM could promoted synchronous removal of organic pollutants and Cr(VI). • This composite could be applied at a wide pH range in photocatalytic reactions. • Possible photocatalytic mechanisms of organic pollutants and Cr(VI) were proposed. A visible-light-driven Bi₂WO₆/CuS p-n heterojunction was fabricated using an easy solvothermal method. The Bi₂WO₆/CuS exhibited high photocatalytic activity in a mixed system containing rhodamine B (RhB), tetracycline hydrochloride (TCH), and Cr (VI) under natural conditions. Approximately 98.8% of the RhB (10 mg/L), 87.6% of the TCH (10 mg/L) and 95.1% of the Cr(VI) (15 mg/L) were simultaneously removed from a mixed solution within 105 min. The removal efficiencies of TCH and Cr(VI) increased by 12.9% and 20.4%, respectively, in the mixed solution, compared with the single solutions. This is mainly ascribed to the simultaneous consumption electrons and holes, which increases the amount of excited electrons/holes and enhances the separation efficiency of photogenerated electrons and holes. Bi₂WO₆/CuS can be applied over a wide pH range (2–6) with strong photocatalytic activity for RhB, TCH and Cr(VI). Coexisiting dissolved organic matter in the solution significantly promoted the removal of TCH (from 74.7% to 87.2%) and Cr(VI) (from 75.7% to 99.9%) because it accelerated the separation of electrons and holes by consuming holes as an electron acceptor. Removal mechanisms of RhB, TCH, and Cr(VI) were proposed, Bi₂WO₆/CuS was formed into a p-n heterojunction to efficiently separate and transfer photoelectrons and holes so as to drive photocatalytic reactions. Specifically, when reducing pollutants (e.g., TCH) and oxidizing pollutants (e.g., Cr(VI)) coexist in wastewater, the p-n heterojunction in Bi₂WO₆/CuS acts as a “bridge” to shorten the electron transport and thus simultaneously increase the removal efficiencies of both types of pollutants.     

Identification of Anthropogenic Organic Contamination Associated with the Sediments of a Hypereutropic Tropical Lake, Venezuela

The concentrations of organic carbon (Corg), inorganic carbon (Cinorg), organic nitrogen (Norg) and total aromatic (Arom_T) were determined in 25 samples of bottom sediments from the Lake Valencia, Venezuela, as a contribution to the knowledge about pollution by organic compounds in tropical lakes. Results demonstrate that the Corg and Norg concentrations do not show the pollution indexes by themselves. This is a consequence of the masking effect of naturally derived organic matter from the decay of algae and organisms in the water column and terrestrial plants, which are transported to the lake. Nevertheless, the Arom_T concentrations and the normalised Arom_T (normalized to organic carbon) make it possible to detect organic matter of anthropogenic origin, in the Arom_T levels are about nine times higher than those natural. The variation in the band intensity of the IRFT spectra for some functional groups present in the saturate and aromatic hydrocarbon fractions gives an indication of anthropogenic contribution for some zones of the lake. With the ¹H NMR spectra it was not possible to differentiate a natural source from an anthropogenic one in the lake. Naturally occurring organic compounds (eicosane, pentacosane, and hexacosane) were detected with GC technique in the saturated hydrocarbon fraction. The presence of an unresolved complex mixture (UCM) in the GC chromatograms indicates pollution by branched and cyclic hydrocarbons. These compounds are probably produced by the incomplete combustion of oil products. Potentially toxic organic compounds such as anthracene, phenanthrene and chrysene were found in the aromatic hydrocarbon fraction, which despite presenting low concentrations (ppb order) accumulate in the lake sediments along with the natural source organic matter. The main access paths of organic pollutants to the lake are the rivers which cross the two urban and industrial areas (Maracay and Valencia cities). The mixture of polluted sediments with bottom natural sediments and the autochthonous contribution of organic matter mitigate the pollution levels progressively towards the center of the lake.