Fluorene degradation by Rhodococcus sp. A2-3 isolated from hydrocarbon contaminated sediment of the Pearl River estuary, China.

The pollution of polycyclic aromatic hydrocarbons was serious in sediments of the Pearl River estuary, China. A fluorene-degrading bacterium, strain A2-3, was isolated from hydrocarbon contaminated sediment of this estuary and identified as Rhodococcus sp. based on the analyses of 16S rRNA gene sequence and morphology. Rhodococcus sp. A2-3 can take naphthalene, p-Teropheny, fluorene, pyrene, salicylic acid, citric acid, acetic acid, diethyletheranhydrous, methanol or 4,4'-dibromodiphenyl ether as sole carbon source. 100% of 100 mg/L fluorene or 89% of 400 mg/L fluorene was removed in 7 days by strain A2-3 at 30 °C and pH 7.5. The strain A2-3 showed a high degradation efficiency of fluorene when pH values ranged from 5.5 to 8.5. The proposed pathway of fluorene catabolism by strain A2-3 was initially attacked by 3,4 dioxygenation. Our results suggested Rhodococcus sp. A2-3 can degrade PAHs under aerobic conditions and can function in bioremediation, particularly for weakly acid environment.

Mercury methylation-related microbes and genes in the sediments of the Pearl River Estuary and the South China Sea.

Methylmercury (MeHg) is a toxicant that mainly originates from in situ microbial methylation of inorganic mercury (Hg) in the environment and poses a severe health risk to the public. However, the characteristics of the Hg-methylating microbial community and its relationship with MeHg production in various environments remain to be understood. In the present study, Hg-methylating microbial communities and genes (hgcAB cluster) in the sediments of the Pearl River (PR), Pearl River Estuary (PRE) and South China Sea (SCS) were investigated at a large spatial scale using high-throughput sequencing-based approaches. The results showed that sulfur-reducing bacteria (SRB) and iron-reducing bacteria (IRB) were consistently the dominant microbial strains responsible for the methylation of inorganic Hg in all three regions investigated. The abundance and diversity of Hg-methylating communities and genes were both found to be higher in the PR sediments compared to that in the PRE and SCS sediments, and in good agreement with the spatial distribution of MeHg. Furthermore, a significant correlation was observed between the MeHg concentration and the abundance of both hgcA and hgcB genes in the sediments of the PR, PRE and SCS regions. Overall, the present study suggested that there was the presence of a close link between MeHg and Hg-methylating communities or genes in the ambient aquatic environment, which could be used to reflect the potential of in situ MeHg production.

Distribution and sources of the polycyclic aromatic hydrocarbons in the sediments of the Pearl River estuary, China.

The Pearl River delta, one of the most prosperous economically region in China, has experienced significant contaminant inputs. However, the dynamics of pollutants in the Pearl River estuary and the adjacent coastal areas are still unclear at present. In the paper, distribution and sources of polycyclic aromatic hydrocarbons (PAHs) were investigated in the surface sediments of the Pearl River estuary. The total PAHs concentrations ranged from 126.08 to 3828.58 ng/g with a mean value of 563.52 ng/g, whereas the highest PAHs were observed in Guangzhou channel. Among the U.S. Environmental Protection Agency's 16 priority PAHs, PAHs with 3-4 rings exhibited relative higher levels. A positive relationship was found between PAHs and total organic carbon. The source analysis further showed that the major sources of PAHs in the Pearl River estuary were originated from the pyrolytic inputs, reflecting a mixed energy structure such as wood, coal and petroleum combustion. In summary, although PAHs in Lingding Bay and the adjacent coastal areas of the Pearl River estuary exhibited a relatively low pollution level, the relatively high pollution level of PAHs in Guangzhou channel will be attended.

Variation of phytoplankton community structure from the Pearl River estuary to South China Sea.

The Pearl River is located in the northern part of South China Sea. The environment of the Pearl River estuary (PRE) is significantly impacted by nutrients from anthropogenic activities. Along the anthropogenic pollution gradient from the PRE to South China Sea, the phylogenetic diversity and biomass of phytoplankton was examined in relation to physic-chemical variables. The richness of rbcL gene was higher in the open sea than the estuary, while the concentration of chlorophyll a (Chl a) was higher in the estuary than in the open sea. The cluster analysis of the sequences data resulted in seven phytoplankton community types and the dominant species of phytoplankton changed from Cryptophytes and Diatoms to Prymnesiophytes and Diatoms along the gradient. The community structure of phytoplankton was shaped by nutrients and salinity. The phytoplankton biomass was significantly positively affected by phosphorus, nitrite and ammonium (P < 0.01) but negatively by salinity (P < 0.05); the phytoplankton diversity was highly positively affected by salinity (P < 0.05) but negatively by silicate and nitrate (P < 0.01; P < 0.05, respectively). Anthropogenic activities played a critical role in the phytoplankton distribution and biomass of the study area. Further research is necessary to reveal the influence mechanism of environmental factors on the phytoplankton.

Saltwater intrusion regulates the distribution and partitioning of heavy metals in water in a dynamic estuary, South China.

The mixing processes of fresh-salt water in estuarine and coastal regions have a substantial impact on the characteristics of heavy metals. A study was conducted in the Pearl River Estuary (PRE), located in South China, to examine the distribution and partitioning of heavy metals and the factors that influence their presence. Results showed that the hydrodynamic force, caused by the landward intrusion of the salt wedge, was the major contributor to the aggregation of heavy metals in the northern and western PRE. Conversely, metals were diffused seaward at lower concentrations along the plume flow in surface water. The study found that some metals, including Fe, Mn, Zn and Pb, were significantly higher in surface water than in bottom water in eastern waters, but the reverse was true in the southern offshore area, where limited mixing hindered the vertical transfer of metals in the water column. The partitioning coefficients (KD) of metals varied, with Fe exhibiting the highest KD (1038 ± 1093 L/g), followed by Zn (579 ± 482 L/g) and Mn (216 ± 224). The highest KD values of metals in surface water were observed in the west coast, while the highest KD in bottom water was found in eastern areas. Furthermore, re-suspension of sediment and the mixing of seawater and freshwater offshore, caused by seawater intrusion, resulted in the partitioning of Cu, Ni and Zn towards particulate phases in offshore waters. This study provides valuable insights into the migration and transformation of heavy metals in dynamic estuaries influenced by the interaction of freshwater and saltwater and highlights the importance of continued research in this field.

Polymeric carbohydrates utilization separates microbiomes into niches: insights into the diversity of microbial carbohydrate-active enzymes in the inner shelf of the Pearl River Estuary, China.

Polymeric carbohydrates are abundant and their recycling by microbes is a key process of the ocean carbon cycle. A deeper analysis of carbohydrate-active enzymes (CAZymes) can offer a window into the mechanisms of microbial communities to degrade carbohydrates in the ocean. In this study, metagenomic genes encoding microbial CAZymes and sugar transporter systems were predicted to assess the microbial glycan niches and functional potentials of glycan utilization in the inner shelf of the Pearl River Estuary (PRE). The CAZymes gene compositions were significantly different between in free-living (0.2-3 µm, FL) and particle-associated (>3 µm, PA) bacteria of the water column and between water and surface sediments, reflecting glycan niche separation on size fraction and selective degradation in depth. Proteobacteria and Bacteroidota had the highest abundance and glycan niche width of CAZymes genes, respectively. At the genus level, Alteromonas (Gammaproteobacteria) exhibited the greatest abundance and glycan niche width of CAZymes genes and were marked by a high abundance of periplasmic transporter protein TonB and members of the major facilitator superfamily (MFS). The increasing contribution of genes encoding CAZymes and transporters for Alteromonas in bottom water contrasted to surface water and their metabolism are tightly related with particulate carbohydrates (pectin, alginate, starch, lignin-cellulose, chitin, and peptidoglycan) rather than on the utilization of ambient-water DOC. Candidatus Pelagibacter (Alphaproteobacteria) had a narrow glycan niche and was primarily preferred for nitrogen-containing carbohydrates, while their abundant sugar ABC (ATP binding cassette) transporter supported the scavenging mode for carbohydrate assimilation. Planctomycetota, Verrucomicrobiota, and Bacteroidota had similar potential glycan niches in the consumption of the main component of transparent exopolymer particles (sulfated fucose and rhamnose containing polysaccharide and sulfated-N-glycan), developing considerable niche overlap among these taxa. The most abundant CAZymes and transporter genes as well as the widest glycan niche in the abundant bacterial taxa implied their potential key roles on the organic carbon utilization, and the high degree of glycan niches separation and polysaccharide composition importantly influenced bacterial communities in the coastal waters of PRE. These findings expand the current understanding of the organic carbon biotransformation, underlying the size-fractionated glycan niche separation near the estuarine system.

Community assembly patterns and processes of microbiome responses to habitats and Mytilopsis sallei invasion in the tidal zones of the Pearl River Estuary.

The sustainability of estuarine ecosystem functions depends on the stabilization of microbial ecological processes. However, due to the unique and variable habitat characteristics of estuarine areas, in-depth studies on ecological processes such as the spatial distribution and assembly patterns of microbial community structure are lacking. As methods to elucidate this structure, we used 16S rDNA, 18S rDNA and ITS sequencing technologies to study the composition, diversity, spatial pattern and aggregation mechanism of the bacterial, protist and fungal communities in the tidal zones of the Pearl River Estuary (PRETZ). The abundance of bacterial communities was much higher than that of protists and fungi, and the spatial pattern was obvious in PRETZ. The application of neutral and null models revealed the assembly process of three microbial communities dominated by stochastic processes. Among the stochastic processes, undominated processes (64.03 %, 62.45 %, and 59.29 %) were the most critical processes in the assembly of bacterial, fungal and protist communities. Meanwhile, environmental variables, geographic locations, and biological factors were associated with the composition and assembly of bacterial, protist, and fungal communities. Among the environmental variables, dissolved oxygen and salinity were the main predictors that jointly affected the differences in the community structure of the three microorganisms, and geographic location was the second predictor affecting the community structure of the three microorganisms and had a more pronounced effect on the diversity and network structure of the bacterial and fungal communities. However, biological factors exerted a weaker effect on the microbial community structure than spatial factors and only affected bacteria and protists; the invasive species Mytilopsis sallei only affected the process of protist community assembly. In addition, environmental variables affected the relative importance of stochastic processes. In summary, the formation of microbial communities in the PRETZ was affected by random processes, environmental variables, geographic location, and invasive species.

Spatial and temporal change of tetrabromobisphenol A and hexabromocyclododecane in mangrove sediments from the Pearl River Estuary, South China.

Spatial and temporal trends of tetrabromobisphenol (TBBPA) and hexabromocyclododecane (HBCD) in mangrove sediments from the Pearl River Estuary (PRE) in South China were evaluated. Concentrations of TBBPA and HBCD in mangrove sediments ranged from 0.23 to 13.3 and 0.36 to 54.7 ng g-1 dry weight. The highest TBBPA concentration was seen in Guangzhou mangrove wetland near a dockyard and a ferry terminal where TBBPA is utilized in the coatings for the shipbuilding industry. The rapid development of building might elucidate the higher concentrations of HBCD in Shenzhen mangrove sediments. γ-HBCD and α-HBCD was the two main diastereoisomer of HBCD in mangrove sediments with contributions of 56.1 % and 34.0 %. Sediments from the three PRE mangrove ecosystems were selectively enriched for (-)-γ-HBCD. TBBPA concentrations in mangrove sediments from Guangzhou rose during 2012-2015 and declined from 2015 to 2021. HBCD concentrations in the PRE mangrove sediments exhibited an increasing trend from 2012 to 2021.

Bioaccumulation and translocation of organophosphate esters in a Mangrove Nature Reserve from the Pearl River Estuary, South China.

Little is known about the distribution and bioaccumulation of organophosphate esters (OPEs) in mangrove ecosystems. In this study, water, sediments, plants and animals were collected from Qi'ao Island Mangrove Nature Reserve to investigate the levels, bioaccumulation and biomagnification of OPEs. Concentrations of ΣOPEs in the mangrove plant Sonneratia apetala (an exotic species) were greater than those in Kandelia obovata (a native species). Translocation factors of OPEs in the two mangrove tree species were greater than 1, indicating that OPEs were mainly absorbed in aboveground tissues. Concentrations of OPEs in mangrove trees and animals were negatively correlated with their log Kow, suggesting that accumulation of OPEs in mangrove biota was influenced by hydrophobicity. A significant difference for concentrations of ΣOPEs was found among the eight mangrove animal species. Concentrations of ΣOPEs in mangrove animals were related with lipid contents, feeding habits and Kow of OPEs. Biota-sediment accumulation factor of OPEs was larger than 1, suggesting that bioaccumulation of OPEs occurred in mangrove animals. The targeted OPEs except isodecyl diphenyl phosphate were not biomagnified in mangrove animals. This study highlights bioaccumulation of OPEs in mangrove biota and suggests further concern about the ecological risk of OPEs to mangrove biota.

Characteristics of nutrients and heavy metals and potential influence of their benthic fluxes in the Pearl River Estuary, South China.

Nutrient and heavy metal concentrations in porewater/overlying water and their benthic fluxes were investigated to study their accumulation and transport at the sediment-water interface and the influences of sediment in the Pearl River Estuary, China. Results revealed that distribution of nutrients and metals reflected the effects of terrestrial inputs and some physicochemical processes. Benthic fluxes also suggested that nutrients and heavy metals Pb, Zn and Cd diffused from sediment to overlying water, but not for As, Co, Cr, Fe, Mn and Ni. Exchange capacities showed that 106-108 mol nutrients and 105-107 g Pb, Zn and Cd released from sediment to overlying water annually, indicating their potential ecological threat. However, 105-109 g metals As, Co, Cr, Fe, Mn and Ni were deposited annually, which may reduce the pollution pressure caused by anthropogenic activities. This study will provide references for the potential influence of benthic fluxes on estuarine environment globally.

A multi-stable isotopic constraint on water column oxygen sinks in the Pearl River Estuary, South China.

Bottom water oxygen depletion is a central concern in estuaries and coastal oceans worldwide. However, a mechanistic understanding and quantitative diagnosis of different oxygen-consuming processes are less clear. In this study, a multi-stable isotope approach is developed to delineate the role of oxygen respiration and nitrification contributing to total oxygen consumption in the Pearl River Estuary (PRE), a large eutrophic estuary in south China. The approach highly couples with analysis of the carbon isotope composition of dissolved inorganic carbon (δ13C-DIC) and with stable nitrogen isotope analysis in ammonium (δ15N-NH4+) and nitrate (δ15N-NO3-). In all seasons, relatively low DO concentrations were observed in the upper reach and, to some extent, in the outer estuary during summer, while high concentrations of DO were found in the transition zone between the inner and outer estuary. On the basis of isotopic differentiation, our data reveal that much more depleted δ13C-DIC is coincident with DIC additions and low oxygen in the upper reach and inner estuary during most seasons. This is most likely a consequence of organic carbon (OC) degradation via aerobic respiration. Based on the carbon isotopic mass balance of DIC and the stoichiometry ratio of -ΔDO/ΔDIC, we found that the OC degradation dominates the total oxygen consumption in the upper reach, as well as in the inner estuary during summer (48.3%-93.5%). In addition, nitrification is another key process in contributing to total oxygen loss in the upper reach, as supported by the well-coupled variations of δ15N of NH4+ and NO3- and apparent oxygen utilization (AOU). Using the formerly determined N isotopic fractionation and observed δ15N variation, we estimated that nitrification could account for 35.3%-44.1% and 28.5%-31.6% of the total oxygen consumption in the upper reach during winter and summer, respectively, while its contribution to total oxygen loss is minor in the inner and outer estuary. Overall, this study demonstrates the potential of the multi-stable isotopic approach to assess oxygen sink partitioning in large human-perturbed estuaries.

Bioaccumulation and biomagnification of short-chain chlorinated paraffins in marine organisms from the Pearl River Estuary, South China.

Short-chain chlorinated paraffins (SCCPs) are a series of new persistent organic pollutants, posing a risk of significant adverse effects to biota. Increasing attention has been paid to SCCP pollution in China as large amounts of chlorinated paraffin (CP) products containing SCCPs have been produced and used there. However, knowledge of the bioaccumulation of SCCPs in marine organisms from the Pearl River Estuary (PRE), Southern China, is still scarce. In this study, SCCP concentrations were measured in seawater, sediments, and marine organisms from the PRE. SCCP concentrations ranged from 180 to 460 ng/L in seawater, from 180 to 620 ng/g dry weight (dw) in sediments, and from 870 to 36,000 ng/g lipid weight (lw) in marine biota samples. C10-11 SCCPs were the predominant homologues in all the samples, with an average abundance of 68% in seawater, 57% in sediments, and 56-77% in marine organisms. However, chlorine patterns of SCCPs in seawater, sediments, and marine organisms were different. Cl8-10 SCCPs dominated in sediments, whereas Cl5-7 SCCPs were the predominant SCCP homologues in water and most organism species. The logarithm bioaccumulation factors (BAFs) of SCCPs ranged from 1.6 to 3.0, and increased significantly with the increase of Kow values for most marine biota species, indicating that Kow was the major factor controlling the bioaccumulation of SCCPs and that SCCPs with higher lipophilicity were more prone to being bioaccumulated from water. Opposite to that observed for log BAFs, biota-sediment accumulation factors of specific SCCPs (range: 0.01-30) decreased significantly with the increase of Kow values. The biomagnification factor of total SCCPs for oyster-mangrove crab was 2.40, implying the potential biomagnification of SCCPs for benthos in the PRE.

Response of Bacterial Metabolic Activity to the River Discharge in the Pearl River Estuary: Implication for CO2 Degassing Fluxes.

Bacterial production (BP), respiration (BR) and growth efficiency (BGE) were simultaneously determined along an environmental gradient in the Pearl River Estuary (PRE) in the wet season (May 2015) and the dry season (January 2016), in order to examine bacterial responses to the riverine dissolved organic carbon (DOC) in the PRE. The Pearl River discharge delivered labile dissolved organic matters (DOM) with low DOC:DON ratio, resulting in a clear gradient in DOC concentrations and DOC:DON ratios. BP (3.93-144 µg C L-1 d-1) was more variable than BR (64.6-567 µg C L-1 d-1) in terms of the percentage, along an environmental gradient in the PRE. In response to riverine DOC input, BP and the cell-specific BP increased; in contrast, the cell-specific bacterial respiration declined, likely because labile riverine DOC mitigated energetic cost for cell maintenance. Consequently, an increase in bacterial respiration was less than expected. Our findings implied that the input of highly bioavailable riverine DOC altered the carbon portioning between anabolic and catabolic pathways, consequently decreasing the fraction of DOC that bacterioplankton utilized for bacterial respiration. This might be one of the underlying mechanisms for the low CO2 degassing in the PRE receiving large amounts of sewage DOC.

Organophosphorus flame retardants in mangrove sediments from the Pearl River Estuary, South China.

Forty-eight surface sediments were collected from three mangrove wetlands in the Pearl River Estuary (PRE) of South China to investigate the distribution of organophosphorus flame retardants (OPFRs) and the relationship between OPFRs and microbial community structure determined by phospholipid fatty acid. Concentrations of ΣOPFRs in mangrove sediments of the PRE ranged from 13.2 to 377.1 ng g-1 dry weight. Levels of ΣOPFRs in mangrove sediments from Shenzhen and Guangzhou were significantly higher than those from Zhuhai, indicating that OPFRs were linked to industrialization and urbanization. Tris(chloropropyl)phosphate was the predominant profile of OPFRs in mangrove sediments from Shenzhen (38.9%) and Guangzhou (35.0%), while the composition profile of OPFRs in mangrove sediments from Zhuhai was dominated by tris(2-chloroethyl) phosphate (25.5%). The mass inventories of OPFRs in the mangrove sediments of Guangzhou, Zhuhai and Shenzhen were 439.5, 133.5 and 662.3 ng cm-2, respectively. Redundancy analysis revealed that OPFRs induced a shift in the structure of mangrove sediment microbial community and the variations were significantly correlated with tris(1,3-dichloro-2-propyl)phosphate and tris(2-butoxyethyl) phosphate.

Short-chain chlorinated paraffins in marine organisms from the Pearl River Estuary in South China: Residue levels and interspecies differences.

There is limited information available on the bioaccumulation of short-chain chlorinated paraffins (SCCPs), a complicated group of persistent organic pollutants (POPs) candidates listed in the Stockholm Convention, in estuarine ecosystem. This study analyzed SCCPs in marine organisms (five fish and six invertebrates) from the Pearl River Estuary in South China. The concentrations of total SCCPs ranged from 210 to 21,000 ng · g(-1) lipid weight, with relatively higher levels in benthic invertebrates (shrimp, crabs and bivalves) than in non-benthic species (pelagic and mesopelagic fish and squid). SCCPs were biomagnified from prey fish (tapertail anchovy, Coilia mystus) to predator fish (Bombay duck, Harpadon nehereus), and the biomagnification factors (BMFs) of SCCP congeners ranged from 1.1 (C10H16Cl6) to 3.4 (C13H18Cl10). Species-specific homologue group patterns were also observed, with significantly lower proportions of C10 congeners in the shrimp, bivalves and Bombay duck than in the other species.

Bioaccumulation and biomagnification of halogenated organic pollutants in mangrove biota from the Pearl River Estuary, South China.

Four biota species were collected from mangrove ecosystems of the Pearl River Estuary to investigate the bioaccumulation and biomagnification of polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), polybrominated diphenyl ethers (PBDEs), dechlorane plus (DP), and decabromodiphenyl ethane (DBDPE). Concentrations of ΣPCBs, ΣDDTs, ΣPBDEs, DP, DBDPE and anti-Cl11-DP (the dechlorination product of anti-DP) in mangrove biota ranged from 32.1-466, 153-3819, 3.88-59.8, 0.18-6.88, not detected (nd)-30.6 and nd-2.65 ng/g lipid weight, respectively. Daggertooth pike conger (Muraenesox cinereus) had higher concentrations of contaminants than the other three biota species. Significant positive relationship between anti-Cl11-DP and anti-DP levels was observed in mangrove biota. DDTs were the predominant HOPs in all biota species, followed by PCBs and PBDEs. All the target compounds exhibited biomagnification, with biomagnification factors greater than 1 in the studied feeding relationships. Food web magnification was found for ΣPCBs, ΣDDTs, ΣPBDEs and DP, with trophic magnification factors of 2.76, 2.61, 2.20 and 2.31, respectively.

Brominated flame retardants in mangrove sediments of the Pearl River Estuary, South China: spatial distribution, temporal trend and mass inventory.

Sediments were collected from three mangrove wetlands in the Pearl River Estuary (PRE) of South China to investigate spatial and temporal distributions of polybrominated diphenyl ethers (PBDEs), decabromodiphenyl ethane (DBDPE) and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE). Concentrations of ΣPBDEs, DBDPE and BTBPE in mangrove sediments of the PRE ranged from 1.25-206, 0.364-34.9, and not detected-0.794 ng g(-1) dry weight, respectively. The highest concentrations of ΣPBDEs, DBDPE and BTBPE were found at the mangrove wetland from Shenzhen, followed by Zhuhai and Guangzhou, showing the dependence on the proximity to urban areas. PBDEs were the predominant brominated flame retardants (BFRs) in mangrove sediments. The concentrations of ΣPBDEs, DBDPE and BTBPE in sediment cores showed an increasing trend from the bottom to top layers, reflecting the increasing usage of these BFRs. The inventories of ΣPBDEs, DBDPE and BTBPE in mangrove sediments were 1962, 245, and 4.10 ng cm(-2), respectively. This is the first study to report the occurrence of DBDPE and BTBPE in mangrove ecosystems.

Determination of eight pharmaceuticals in an aqueous sample using automated derivatization solid-phase microextraction combined with gas chromatography-mass spectrometry.

An automated aqueous derivatization solid-phase microextraction (SPME) coupled with a gas chromatography/mass spectrometry (GC/MS) method was developed for simultaneous determination of eight pharmaceuticals in water samples. Dimethyl sulfate and tetrabutylammonium hydrogen sulfate were selected as derivatization and activation reagents for the esterification reaction. An experimental design approach, central composition design (CCD), was employed to investigate and optimize the operative factors influencing the extraction efficiency, including extraction time, extraction temperature and ionic strength. The other parameters such as type of fiber coating, pH and derivatization conditions were also evaluated. SPME was finally carried out in headspace mode at 80°C for 60min with the presence of 3.00g Na2SO4, using a home-made 44µm PDMS fiber. Wide linear ranges and low limits of detection (0.06-1.24ng L(-1)) were obtained under the optimized conditions. The relative standard deviations (RSDs) and recoveries ranged from 0.5% to 12.3% and 85% to 110%, respectively. The proposed method was successfully applied to the analysis of the real surface water samples from the Pearl River Estuary.