Persistent toxic substances in soils and waters along an altitudinal gradient in the Laja River Basin, Central Southern Chile

In this study the levels and distribution of some persistent toxic substances (PTS) were investigated in soils, superficial water, and snow along an altitudinal gradient in the Laja River Basin (South Central Chile). The principal objective was to establish the basin's contamination status. The working hypothesis was that PTS levels and distribution in the basin are dependent on the degree of anthropogenic intervention. Fifteen PAHs, seven PCBs congeners, and three organochlorine pesticides were studied in superficial soil and water samples obtained along the altitudinal gradient and from a coastal reference station (Lleu-Lleu River). Soil samples were extracted using accelerated solvent extraction with acetone/cyclohexane (1:1) for PAHs and organochlorine compounds. Contaminants were extracted from water and snow samples by liquid-liquid extraction (LLE). PAH and organochlorine compound quantification was carried out by HPLC with fluorescence detection and GC-MS, respectively. PCBs in soils presented four different profiles in the altitudinal gradient, mainly determined by their chlorination degree; these profiles were not observed for the chlorinated pesticides. In general, the detected levels for the analyzed compounds were low for soils when compared with soil data from other remote areas of the world. Higher summation operator PAHs levels in soils were found in the station located at 227 masl (4243 ng g-1 TOC), in a forestry area and near a timber industry, where detected levels were up to eight times higher than the other sampling sites. In general, PAH levels and distribution seems to be dependent on local conditions. No pesticides were detected in surface waters. However, congeners of PCBs were detected in almost all sampling stations with the highest levels being found in Laja Lake waters, where 1.1 ng/l were observed. This concentration is two times higher than values reported for polluted lakes in the Northern Hemisphere. The presence of organochlorine compound in snow sampled at the highest elevation point of the basin is indicative of the transport and atmospheric deposition phenomena of alpha-HCH, gamma-HCH and PCB 52, with values being similar to the levels reported in Canadian snow samples. We conclude that environmental PTS substance levels are in general relatively low, although PAHs may be of concern in some areas of the basin.     

Organochlorine pesticide distribution in an organic production system for cow's milk in Chiapas,Mexico

The objective of this study was to evaluate the presence of organochlorine pesticides in samples of forage, soil, water, and milk in four units of an organic production system for cow´s milk (samples of forage, milk, soil, and water) in Tecpatan, Chiapas, Mexico. The organochlorine pesticides were extracted from forage, soil and water based on the USEPA (2005) guideline and from milk based on the IDF 1991 guideline. The pesticides were identified and quantified by gas chromatography with electron capture detector (CG-ECD). In general, the highest average concentration of total pesticides was found in the samples of milk and forage (311 ± 328 and 116.5 ±77 ng g^?1 respectively). Although, the production systems analyzed are organic, organochlorine pesticides were detected in all environmental samples (forage, soil, water, and organic milk). Although no values surpassed the defined limits of Mexican and International regulation it is advisable that a monitoring program of contaminants in these production systems is continued.     

Easy and fast extraction methods to determine organochlorine pesticides in sewage sludge,soil, and water samples based at low temperature

Organochlorine pesticides present in sewage sludge can contaminate soil and water when they are used as either fertilizer or agricultural soil conditioner. In this study, the technique solid–liquid extraction with low temperature purification was optimized and validated for determination of ten organochlorine pesticides in sewage sludge and soil samples. Liquid–liquid extraction with low temperature purification was also validated for the same compounds in water. Analyses were performed by gas chromatography-mass spectrometry operating in the selective ion monitoring mode. After optimization, the methods showed recoveries between 70% and 115% with relative standard deviation lower than 13% for all target analytes in the three matrices. The linearity was demonstrated in the range of 20 to 70 µg L^?1, 0.5 to 60 µg L^?1, and 3 to 13 µg L^?1, for sludge, soil, and acetonitrile, respectively. The limit of quantification ranged between 2 and 40 µg kg^?1, 1 and 6 µg kg^?1, and 0.5 µg L^?1 for sludge, soil, and water, respectively. The methods were used in the study of pesticide lixiviation carried out in a poly vinyl chlorine column filled with soil, which had its surface layer mixed with sludge. The results showed that pesticides are not leached into soil, part of them is adsorbed by the sewage sludge (4–40%), and most pesticides are lost by volatilization.     

Determination of organochlorine pesticide residue in sediment and water from the Densu river basin, Ghana

The distribution of organochlorine pesticides in the aquatic ecosystem from the Densu river revealed varying levels of concentration in water and the sediment samples. Three locations were sampled along the river to evaluate the levels of organochlorine pesticide residue in the river. Sediment and surface water samples were extracted by soxhlet and liquid-liquid extraction respectively and analyzed using Gas Chromatograph coupled with electron capture detector. The detectable organochlorine pesticides were gamma-hexachlorocyclohexane (HCH), delta-hexachlorocyclohexane, heptachlor, aldrin and dieldrin. The other pesticides that were investigated are gamma-chlordane, alpha endosulfan, endosulfan sulfate, p,p′-DDT and its metabolite p,p′-DDE, methoxychlor, endrin and its metabolite endrin aldehyde and endrin ketone. The order of increasing frequency of detection of samples was higher in sediment than water. In sediment, the mean concentration ranged from 0.030 μg kg⁻¹ dry weight (endrin) to 10.98 μg kg⁻¹ dry weight (aldrin). The highest detected concentration of organochlorine in water was endosulfan sulfate with mean concentration of 0.185 μg L⁻¹. Analysis of variance indicated significant differences for most organochlorine pesticide residue in the sediment sampled from the various locations. Some of the levels of organochlorine pesticides detected in water were relatively high compared to guideline values set by World Health Organization and Australia and thus could be harmful if the trend is not checked.     

ASE提取GPC净化双塔双柱气相色谱法测定土壤中有机氯农药

对土壤中8种有机氯农药(α-HCH、β-HCH、γ-HCH、δ-HCH、p,p’-DDE、p,p’-DDD、o,p’-DDT、p,p’-DDT)进行了分析,使用加速溶剂萃取(ASE)仪对土壤样品中的目标组分进行萃取、凝胶渗透色谱(GPC)仪对萃取液净化、双塔双柱同时进样分析,采用双电子捕获检测器(ECD)同时定性定量测定。结果表明,该方法检测效果较好,8种有机氯农药的回收率在81.3%～88.6%,相对标准偏差为3.9%～5.7%,检出限为0.18～0.37μg/kg。与传统的方法相比,该方法操作简便、重复性好,定性定量更准确。     

Residues of organochlorine and organophosphorus pesticides in sugarcane crop soils and river water

The presence of residual organochlorine and organophosphorus pesticides was evaluated at different periods of sugarcane cultivation in agricultural soil and water samples from the town of Tlaltizapan, which is located in the state of Morelos in Mexico, to determine the presence and persistence of these compounds and their possible effects on the region. The compounds p,p′-DDE, p,p′-DDD (metabolites of p,p′-DDT), γ-HCH and heptachlor were found in more of 95% of the sampling zones in the three monitoring periods performed along 2 years. The highest concentration detected (129.6 μg/kg _{dry soil}) was for α-HCH, but its frequency of detection was ～5%. The low detection frequency of α-HCH and the high concentration values of γ-HCH indicate the repeated use of technical-grade HCH and Lindane (γ-HCH) in the region. Among the organophosphorus pesticides, ethyl parathion was the compound with the highest soil concentration, at ～2000 μg/kg_{dry soil}, during the initial monitoring. However, this compound was detected in the second monitoring with a concentration of ～4 μg/kg_{dry soil}, but it was not detected in the third, indicating that is was not accumulated in the environment. The heptachlor was the compound most commonly found in all water samples, within a range of 0.45–1.25 ng/L. The presence of this organochlorine compound in the water samples indicated a possible migration from the soil to water bodies due to soil erosion. The presence of organophosphorus compounds was not detected in the water samples, which could be attributed to the moderate persistence of these compounds and their consequent degradation before arriving at the water bodies.     

Distribution, origin and fate of chromium in soils in Guanajuato, Mexico

Total, hexavalent and trivalent chromium were determined in surface and 30-cm depth soil samples from a highly chromium-polluted area in Guanajuato state, central México. Four samples were also analyzed by a sequential extraction procedure. Nearly 0.9 km(2) out of the 8 km(2) area sampled was polluted with chromium, at concentrations up to 12960 mg kg(-1), mostly as Cr(III). Concentrations of Cr(VI) were lower than 0.5 mg kg(-1) in most sampled points, with the exception of one, where the concentration was found to be 65.14 mg kg(-1). Chromiumcontaining dust from a chromate factory accounted for most of the contamination. The highest concentrations of hexavalent chromium in soil, were in the bottom sediments of an abandoned water reservoir used to store polluted water from a well, before use of the water in the factory process. Tannery wastes, dust from a sanitary landfill of chromate compounds and the transport of chromium products are the sources of chromium at other sites. Chromium is fixed preferentially in the hydrous Fe and Mn oxides in the more polluted soils. Less polluted soils have a high proportion of chromium associated with the sulfide and organic fraction. Cr(III) is retained preferentially in the superficial soil layer. Variations in the physical characteristics of the soil, relative abundance of the various soil components and characteristics of the contaminant source, give rise to differences in chromium soil concentrations with depth.     

Determination of organochlorine and organophosphorus pesticide residues in low moisture, nonfatty products using a solid phase extraction cleanup and gas chromatography

A multiresidue solid-phase extraction (SPE) method for the isolation and subsequent gas chromatographic determination of organochlorine and organophosphorus pesticide residues in low-moisture, nonfatty products is described. Residues are extracted from samples with an acetonitrile/water mixture. Cleanup of the extract is performed using graphitized carbon black and anion exchange SPE columns, and analysis is performed by gas chromatography with Hall electrolytic conductivity and flame photometric detection. Recovery data was obtained by fortifying corn, oats and wheat with pesticides. The average recoveries were 79-123% for eight organochlorine and 51-122% for 28 organophosphorus pesticide residues. The limit of quantitation for chlorpyriphos was 0.05 ppm using the Hall electrolytic conductivity detector and < 0.005 ppm using the flame photometric detector.     

Evaluation of HCH isomers and metabolites in soils, leachates, river water and sediments of a highly contaminated area

In this work we evaluate the contamination caused by HCH residues in the soil, leachates, river water and sediments of an industrial estate of the NW of Spain. We study the distribution of the isomers in the different matrices, analysing 37 soil samples, collected in eight points at several depths, six natural leachates, four river water samples and three river sediments. Soil and leachate samples present very high levels of HCH isomers, higher than the established by legislation, and some pesticides were also detected in the analysed river water whereas no pesticides were detected in the river sediments. The distribution of isomers was different depending on the matrix analysed. Some natural degradation products and also other organochlorine pesticides were detected in the samples analysed.     

Determination of organochlorine and organophosphorus pesticide residues in low moisture,nonfatty products using a solid phase extraction cleanup and gas chromatography

Abstract

A multiresidue solid‐phase extraction (SPE) method for the isolation and subsequent gas Chromatographie determination of organochlorine and organophosphorus pesticide residues in low‐moisture, nonfatty products is described. Residues are extracted from samples with an acetonitrile/water mixture. Cleanup of the extract is performed using graphitized carbon black and anion exchange SPE columns, and analysis is performed by gas chromatography with Hall electrolytic conductivity and flame photometric detection. Recovery data was obtained by fortifying corn, oats and wheat with pesticides. The average recoveries were 79–123% for eight organochlorine and 51–122% for 28 organophosphorus pesticide residues. The limit of quantitation for chlorpyriphos was 0.05 ppm using the Hall electrolytic conductivity detector and <0.005 ppm using the flame photometric detector.     

Microtox testing of pentachlorophenol in soil extracts and quantification by capillary electrochromatography (CEC)--a rapid screening approach for contaminated land

An approach to rapid soil testing which involved the use of simple solvent extraction methods was developed. The analytes of interest were priority pollutants of low water solubility which could not be readily removed from the soil using water. Direct toxicity testing of the soil samples by Microtox showed a high background toxicity which prevented realistic toxicity data from being obtained for the contaminants present. A range of different extraction solutions was used in an attempt to extract the contaminants while eliminating the matrix effects of the soil. It was necessary that the solvents selected for extraction of the soil samples were not of significant toxicity, as this could potentially mask the toxic effects of any compounds extracted from the soil. The extraction efficiencies of solvent systems were evaluated using pentachlorophenol (PCP) as a model compound of known toxicity in the Microtox assay. A rapid and cost-effective method was developed in order to determine the amount of PCP recovered from the soil by the extraction solvents employed. This method consisted of a solid phase extraction (SPE) step followed by quantification using capillary electrochromatography (CEC). Recoveries were greater when a higher proportion of organic solvent (methanol) was used in the extraction process, and lowest when water was used. An extraction based on water could provide information on the potential for leaching of contaminants from the soil into nearby water bodies in an environmental setting. An organic solvent extraction method could indicate how much toxicity soil-dependent organisms might be exposed to through ingestion. Extraction based on 50% (v/v) methanol in water was considered to be the most suitable overall extraction solution for soil screening, given that this permitted extraction of the water-insoluble compound PCP at a level which was clearly toxic in the Microtox assay while also retaining the capability to extract water-soluble contaminants.     

Occurrence of PAHs, PCBs and organochlorine pesticides in the Tonghui River of Beijing, China

Tonghui River, a typical river in Beijing, People's Republic of China, was studied for its water and sediment quality, by determining the levels of 16 polycyclic aromatic hydrocarbons (PAHs), 12 polychlorinated biphenyls (PCBs) and 18 organochlorine pesticides in water and sediment samples. Total PAHs, PCBs and organochlorine pesticides concentrations in water varied from 192.5 to 2651 ng/l, 31.58-344.9 ng/l and 134.9-3788 ng/l, respectively. The total PAHs, PCBs and organochlorine pesticides concentrations in surficial sediments were 127-928 ng/g, 0.78-8.47 ng/g and 1.79-13.98 ng/g dry weight, respectively. The results showed that the concentration of these selected organic pollutants in sediment was higher than those in surface water. It may be due to the fact that organic hydrophobic pollutants tend to stay in the sediments. The PAHs were dominated by 2-, 3-ring components in water samples and by 3- and 4-ring compounds in sediment. For organochlorines, alpha-HCH, delta-HCH, Heptachlor, Endosulfan II, DDT are the major organochlorine pesticides in water while Heptachlor, Dieldrin and DDE composed of 95% of total organochlorine pesticides in sediment. For HCHs (HCHs=alpha-HCH+beta-HCH+gamma-HCH+delta-HCH), the predominance of alpha-HCH of total HCHs were clearly observed in water and sediment. PCB18, PCB31 and PCB52 were predominant in water, on average these compounds collectively accounted for 67% of total PCBs. But in sediment, the predominant compounds were PCB28, PCB31 and PCB153, which accounted for 71% of total PCBs in sediment. The levels of micro pollutants in our study areas were compared with other studies.     

Application of a novel cold activated carbon fiber-solid phase microextraction for analysis of organochlorine pesticides in soil

A novel and simple analytical procedure using cold activated carbon fiber-solid phase microextraction (CACF-SPME) was applied to determine organochlorine pesticides (OCs) in soil samples. The pesticides in this study consist of α -, β -, γ -, and δ -hexachlorocyclohexane (HCH). By heating the sample while cooling the fiber, the developed method not only provides better performance in terms of sensitivity, linearity and recovery but also offers shorter adsorption procedure than that of traditional headspace-solid phase microextraction (HS-SPME). The experimental conditions such as the amount of water, adsorption time and adsorption temperature were optimized. Matrix effects were investigated with different types of soils. We concluded that using the standard addition method was required for quantification purposes. The limits of detection obtained using the proposed method range from 0.01 to 0.05 ng/g, and the recoveries for CACF-SPME are in the range of 80.01% to 89.68% with relative standard deviation (RSDs) better than 8.60%. The proposed method was further applied to determine OCs in real agricultural soil. The results are in good agreement with those obtained using traditional ultrasonic extraction. The research demonstrates the suitability of the CACF-SPME for the analysis of OCs in soil.     

Application of a novel cold activated carbon fiber-solid phase microextraction for analysis of organochlorine pesticides in soil

A novel and simple analytical procedure using cold activated carbon fiber-solid phase microextraction (CACF-SPME) was applied to determine organochlorine pesticides (OCs) in soil samples. The pesticides in this study consist of alpha -, beta -, gamma -, and delta -hexachlorocyclohexane (HCH). By heating the sample while cooling the fiber, the developed method not only provides better performance in terms of sensitivity, linearity and recovery but also offers shorter adsorption procedure than that of traditional headspace-solid phase microextraction (HS-SPME). The experimental conditions such as the amount of water, adsorption time and adsorption temperature were optimized. Matrix effects were investigated with different types of soils. We concluded that using the standard addition method was required for quantification purposes. The limits of detection obtained using the proposed method range from 0.01 to 0.05 ng/g, and the recoveries for CACF-SPME are in the range of 80.01% to 89.68% with relative standard deviation (RSDs) better than 8.60%. The proposed method was further applied to determine OCs in real agricultural soil. The results are in good agreement with those obtained using traditional ultrasonic extraction. The research demonstrates the suitability of the CACF-SPME for the analysis of OCs in soil.     

Pesticide pollution remains severe after cleanup of a stockpile of obsolete pesticides at Vikuge, Tanzania

High levels of DDT residues and hexachlorocyclohexanes (HCHs) were found in soil, well water, and surface water around a collapsed pesticide storage shed at Vikuge Farm, Tanzania. Residues of DDT and HCHs were found at three soil depths down to 50 cm. Surface soil samples contained up to 28% total DDT and 6% total HCH residues. Water samples had concentrations of up to 30 microg L(-1) of organochlorine pesticides. Other compounds detected were aldrin, azinphos-methyl, carbosulfan, gamma-chlordane, chlorprofam, heptachlor, hexazinone, metamitron, metazachlor, pendimethalin, and thiabendazole. Although the visible remains of pesticides have been removed, the remaining soil is itself hazardous waste and poses a risk to the environment and the inhabitants of the surrounding villages. These findings show the necessity to follow up the environmental situation at former storage sites of obsolete stocks of pesticides, and that the environmental problems are not necessarily solved by removing the visible remains.     

Measurement of pollution levels of organochlorine and organophosphorus pesticides in water, soil, sediment, and shrimp to identify possible impacts on shrimp production at Jiquilisco Bay

This study aims to identify levels of several organochlorine and organophosphorus compounds in shrimp-raising areas of coastal El Salvador, to assess potential impacts on shrimp growth and survival that hamper the sustainability of aquaculture in the region. The paper reports the current levels of γ-HCH, 4,4'-DDT, 4,4'-DDE, 4,4'-DDD, endrin, dieldrin, heptachlor, parathion, methyl parathion, and etoprophos in soils (depth 20 cm), sediments (depth 5 cm), shrimp (Penaeus sp.), and water of three rearing ponds and also in the sediment (depth 5 cm) and water surrounding those ponds in Jiquilisco Bay. Sampling was carried out during the dry (January-March) and rainy (June-August) seasons of 2008. The presence of pesticides in the samples of water, shrimp, and sediment at shrimp ponds was not detected in either season; however, in soil samples (depth 20 cm) taken from these ponds, heptachlor, endrin, dieldrin, 4,4'-DDD, and 4,4'-DDT were identified at concentrations below the method limit of quantification (LOQ), and 4,4'-DDE was found in a concentration falling in the range from 3.85 to 19.61 ng/g. In samples of water taken at the bay water intakes to the rearing ponds, we observed dieldrin concentrations in the range between 0.085 ng/mL and 0.182 ng/mL during the dry season. In the samples of sediments taken in the surrounding areas of shrimp ponds, we found-for both seasons-that in 60 % of the samples, 4,4'-DDE was present in concentrations ranging from 3.75 ng/g to 30.97 ng/g. Additionally, in the rainy season, we observed heptachlor in sediment at concentrations below the method quantification limit. It was concluded that organochlorine compounds from pesticides are still present in Jiquilisco Bay, trapped in deep sediment, even though they have been banned since the 1980s. These were not detected in shrimp tissue, surface water, and shallow sediment in rearing ponds, and hence, we do not believe their presence has any major impact on shrimp production in sampled areas.     

Mobility of arsenic, cadmium and zinc in a multi-element contaminated soil profile assessed by in-situ soil pore water sampling, column leaching and sequential extraction

Three methods for predicting element mobility in soils have been applied to an iron-rich soil, contaminated with arsenic, cadmium and zinc. Soils were collected from 0 to 30 cm, 30 to 70 cm and 70 to 100 cm depths in the field and soil pore water was collected at different depths from an adjacent 100 cm deep trench. Sequential extraction and a column leaching test in the laboratory were compared to element concentrations in pore water sampled directly from the field. Arsenic showed low extractability, low leachability and occurred at low concentrations in pore water samples. Cadmium and zinc were more labile and present in higher concentrations in pore water, increasing with soil depth. Pore water sampling gave the best indication of short term element mobility when field conditions were taken into account, but further extraction and leaching procedures produced a fuller picture of element dynamics, revealing highly labile Cd deep in the soil profile.     

Comparison of Three Extraction Methods for 17 β-Estradiol in Sand,Bentonite, and Organic-Rich Silt Loam

Extraction is an important procedure for samples that contain soil because other compounds in soil may affect analysis of estrogens. This study was conducted to evaluate three different extraction methods for 17β-estradiol in soil. Sand, bentonite, and organic-rich silt loam were spiked with 1 mg kg^{? 1} of 17β-estradiol as a model compound of estrogens. 17β-estradiol and its metabolites, estrone and estriol, were extracted using (i) a modified Bligh and Dyer extraction, (ii) a pressurized fluid extraction, and (iii) a diethyl ether extraction, and measured by liquid chromatography tandem mass spectrometry. There were significant differences in the extraction efficiency for 17β-estradiol among the extraction methods and the soils: the efficiencies ranged from 10% to 97%. Overall, the diethyl ether extraction method had the largest efficiency of 17β-estradiol with 45% and 57% for bentonite and silt loam, respectively. Transformation of 17β-estradiol to estrone and estriol in the different extraction methods was less than 3.6% during the extraction procedures. This study underlined the importance of sample preparation for estrogen analysis in soil samples.     

Detection and quantification of chlordecone in contaminated soils from the French West Indies by GC-MS using the 13C10-chlordecone stable isotope as a tracer

Chlordecone is an organochlorine insecticide that has been widely used to control banana weevil in the French West Indies. As a result of this intense use, up to 20,000 ha are contaminated by this insecticide in the French West Indies, and this causes environmental damage and health problems. A scenario of exposure was drawn by French authorities, based on land usage records. Many efforts have been made to monitor the occurrence of chlordecone and its main metabolites using different analytical methods, including GC, GC/MS, LC/MS, and NIRS. Although these different methods allow for the detection and quantification of chlordecone from soils, none of them estimate the bottleneck caused by extraction of this organochlorine from soils with high adsorption ability. In this study, we used ¹³C₁₀-chlordecone as a tracer to estimate chlordecone extraction yield and to quantify chlordecone in soil extracts based on the ¹³C/¹²C isotope dilution. We report the optimization of ¹³C₁₀-chlordecone extraction from an Andosol. The method was found to be linear from 0.118 to 43 mg kg^?1 in the Andosol, with an instrumental detection limit estimated at 8.84 μg kg^?1. This method showed that chlordecone ranged from 35.4 down to 0.18 mg kg^?1 in Andosol, Nitisol, Ferralsol, and Fluvisol soil types. Traces of the metabolite β-monohydrochlordecone were detected in the Andosol, Nitisol, and Ferralsol soil samples. This last result indicates that this method could be useful to monitor the fate of chlordecone in soils of the French West Indies.     

Effects of environmental factors on organochlorine pesticide residues in soils of the Guanting Reservoir area, China

Topsoil samples from 56 sites around the Guanting Reservoir, China, were measured for HCH and DDT concentrations. The total soil HCH content (including alpha-, beta-, gamma-, and delta-isomers) in these soil samples ranged from 0 to 7.33 ng x g(-1), with a mean of 0.69 ng x g(-1). These levels were considerably lower than those of the total DDT soil contents (including pp'-DDE, pp'-DDD, op'-DDT, and pp'-DDT), which ranged from 0 to 76.01 ng x g(-1), with a mean of 9.46 ng x g(-1). DDT was also found to be the major pollutant in the soil samples, accounting for approximately 93% of the total organochlorine pesticide (OCP) contents. Several environmental factors including land use, soil texture, soil taxonomy, and microbial biomass were considered to be responsible for the OCP levels observed. The data provide some insight into the effects of environmental conditions such as soil formation, agricultural cultivation, nutrient enrichment, and other anthropogenic activities on the degradation of OCPs in soils. Although the OCP residues currently are below the maximum limits set for use on agricultural land in China, and only rarely would such levels pose significant ecological concern, OCPs are highly persistent in soil and bioaccumulative. The data provided in this study are considered crucial for reservoir remediation, especially since the Guanting Reservoir will serve as one of the main drinking water sources for Beijing in the foreseeable future.