Adsorption of cationic and anionic surfactants onto organic polymer resin Lewatit VPOC 1064 MD PH

The adsorption of a cationic (CTAB, cetyl trimethylammonium bromide) and an anionic surfactant (SLES, sodium dodecylethersulfate) from aqueous solution onto organic polymer resin (Lewatit VPOC 1064 MD PH) was studied. A series of batch experiments were performed to determine the sorption isotherms of surfactants to organic polymer resin. The experimental studies were analyzed by Langmuir and Freundlich isotherms. Furthermore, the isotherm parameters, average percentage errors (ε) of model data, and separation factor (R _L) were calculated. Other factors influencing the adsorption capacity (contact time, adsorbent amount, and initial surfactant concentration) were also discussed. The experimental data fitted very well to the Langmuir equilibrium model in the studied concentration range. The calculated R _L values showed that the adsorption of both surfactants were favorable. Among the surfactants, CTAB showed higher adsorption capacity onto organic polymer resin compared to SLES (Q ⁰ = 250 and 34.36 mg g⁻¹, respectively).     

Characterization and sources of PAHs in an urban river system in Beijing,China

Water samples from 20 locations on rivers in the Tongzhou District of Beijing were collected four times from July 2005 to March 2006. In addition, sediment samples were collected in July 2005. All samples were analyzed for 16 US Environmental Protection Agency (EPA) priority pollutants polycyclic aromatic hydrocarbons (PAHs). The concentration, distribution, seasonal variation, and sources of the 16 PAH compounds identified in the water samples, suspended particles, and surface sediments were then evaluated. The concentrations of PAHs in the water and suspended particle and surface sediment samples ranged from 87.3 to 1,890 ng l⁻¹, 1,330 to 27,700 ng g⁻¹, and 156 to 8,650 ng g⁻¹, respectively. These results demonstrated that rivers in the Tongzhou District of Beijing had a high level of PAH pollution, especially in the suspended particles. The highest and lowest concentrations of PAHs in the water samples were observed in summer and spring. However, the seasonal variations in the concentration of PAHs in the suspended particles were more complicated. The dominant compounds in the water, suspended particle, and surface sediment samples were two-, three- and four-ring PAH compounds, respectively. Ratio analysis illustrated that fuel-burning was the primary source of PAHs in the study area. Gasoline, diesel, coal, and coke oven sources were identified and the contributions of the different fuel-burning sources were then calculated using factor analysis and multiple linear regression. These analyses revealed that coal combustion, gasoline combustion plus coke oven emission, and diesel combustion accounted for 38.8%, 38.5%, and 22.7% of the PAHs in suspended particles, respectively.     

Field based speciation of arsenic in UK and Argentinean water samples

A field method is reported for the speciation of arsenic in water samples that is simple, rapid, safe to use beyond laboratory environments, and cost effective. The method utilises solid-phase extraction cartridges (SPE) in series for selective retention of arsenic species, followed by elution and measurement of eluted fractions by inductively coupled plasma mass spectrometry (ICP-MS) for “total” arsenic. The method is suitable for on-site separation and preservation of arsenic species from water. Mean percentage accuracies (n = 25) for synthetic solutions of arsenite (As^III), arsenate (As^V), monomethylarsonic acid (MA), and dimethylarsinic acid (DMA) containing 10 μg l⁻¹ As, were 98, 101, 94, and 105%, respectively. Data are presented to demonstrate the effect of pH and competing anions on the retention of the arsenic species. The cartridges were tested in the UK and Argentina at sites where arsenic was known to be present in surface and groundwaters, respectively, at elevated concentrations and under challenging matrix conditions. In Argentinean groundwater, 4–20% of speciated arsenic was present as MA and 20–73% as As^III. In UK surface waters, speciated arsenic was measured as 7–49% MA and 12–42% DMA. Comparative data from the field method using SPE cartridges and the laboratory method using liquid chromatography coupled to ICP-MS for all water samples provided a correlation of greater than 0.999 for As^III and DMA, 0.991 for MA, and 0.982 for As^V (P < 0.01).     

Cd2+ adsorption on alkaline-pretreated diatomaceous earth: equilibrium and thermodynamic studies

Naturally occurring diatomaceous earth was modified by alkaline pretreatment, and its effectiveness for Cd²⁺ removal from contaminated water was investigated. Batch experiments were carried out to determine Cd²⁺ adsorption capacity and the efficiency of the sorption process under different experimental conditions. Experimental data showed good fitting to Langmuir and Freundlich isotherms models. The Cd²⁺ maximum adsorption capacity was 0.058 mmol g⁻¹ for raw diatomite and increased to 0.195 mmol g⁻¹ for alkaline-pretreated diatomite with efficiency higher than 96% (diatomite dose 2.5 g L⁻¹, pH 6). Adsorption of Cd²⁺ to alkaline-pretreated diatomite increased as the temperature increased. Thermodynamic parameters were calculated to evaluate the feasibility of the adsorption process at different temperatures. The adsorption process was spontaneous and endothermic. The interaction between Cd²⁺ ions and diatomite surface was weak enough to be considered as physical sorption, confirmed by the low value of activation energy.     

Particle size distribution and pollutants in road-deposited sediments in different areas of Zhenjiang,China

An understanding of road-deposited sediment (RDS) characteristics on an impervious surface is essential to estimate pollutant washoff characteristics and to minimise the impacts of pollutants on the water environment. A total of 62 RDS samples were collected from four different land-use types (commercial, residential, intense traffic and riverside park) in Zhenjiang City, China. The samples were fractionated into seven grain-size classes and analysed for particle size distribution and concentrations of pollutants. The samples are found to consist predominantly of fine particles (60–80%, <250 μm). The maximum mean concentrations of zinc, lead and copper were 686.93, 589.19 and 158.16 mg/kg, respectively, with the highest metal concentrations found in samples from the intense traffic area. The maximum mean contents of organic matter (12.55%), nitrogen (6.31 mg/g) and phosphorus (5.15 mg/g) were found in samples from the commercial area. The concentrations of heavy metals were highest in the smallest particle size fraction analysed (63 μm). The organic matter and nitrogen content generally increased with decreasing particle sizes in the <500-μm particle size range. The results also revealed that most of the total nitrogen (TN) is attached to the finer sediments and that to effectively reduce TN loads in particulates, treatment facilities must be able to remove the finer particles (down to 125 μm for TN).     

Determination trace amounts of copper, nickel, cobalt and manganese ions in water samples after simultaneous separation and preconcentration

In the present article, a simple, rapid, sensitive and economical method has been developed for the simultaneous separation and preconcentration of the trace amounts of copper, nickel, cobalt and manganese in water samples by using modified XAD-4 resins. The sorption was quantitative in the pH range 6.0–9.0, whereas quantitative desorption occurred instantaneously with 5.0 mL of 2 M HNO₃, and selected elements have been determined by using flame atomic absorption spectrometry. Dynamic ranges were 0.04–3.5, 0.1–6.0, 0.04–4.5 and 0.04–4.0 μg/mL for copper, nickel, cobalt and manganese, respectively. The detection limits were 9.2, 28.6, 12.3 and 5.7 ng/mL for Cu(II), Ni(II), Co(II) and Mn(II), respectively. The effects of the experimental parameters, including the sample pH, eluent type, interference ions and breakthrough volume, were studied for separation and preconcentration of Cu(II), Ni(II), Co(II) and Mn(II) ions. Determination of these ions in standard samples confirmed that the proposed method has good accuracy. The proposed method was used for the determination of these ions in water samples.     

Synthesis and characterization of Fe-MCM-41 from rice husk silica by hydrothermal technique for arsenate adsorption

Rice husk (RH) agro-waste was used as a raw material for synthesizing mesoporous molecular sieves, MCM-41. The Fe-MCM-41 was prepared by the hydrothermal technique (HT), resulting in a higher surface area and crystallinity than when prepared under ambient conditions. In addition, a hexagonal structure was clearly seen with hydrothermal technique (HT) preparation. The adsorption of arsenate by HT-Fe-MCM-41 was investigated. The factors studied affecting arsenate adsorption capacity were ferric content in MCM-41, contact time, pH of solution, and initial arsenate concentration. It was found that HT-Fe-MCM-41 at the Si/Fe mole ratio of 10 gave the highest adsorption capacity. Arsenate adsorption reached equilibrium within 4 h. The adsorption capacity of HT-Fe-MCM-41 (Si/Fe = 10) was affected by the initial pH value and the initial arsenate concentration. The adsorption capacity was highest at pH 3 and decreased thereafter with increases in the pH of solution value. The Langmuir model fit the arsenate adsorption isotherm well. The maximum adsorption capacity for arsenate was 1,111 μg g⁻¹.     

Adsorption of vanadate(V) on Fe(III)/Cr(III) hydroxide waste

Adsorption of vanadate(V) from aqueous solution onto industrial solid ‘waste’ Fe(III)/Cr(III) hydroxide was investigated. HCl treated Fe(III)/Cr(III) hydroxide was found to be more efficient for the removal of vanadate(V) compared to untreated adsorbent. The adsorption follows second-order kinetics. Langmuir and Freundlich isotherms have been studied. The Langmuir adsorption capacity (Q ₀) of the treated and untreated adsorbents was found to be 11.43 and 4.67 mg g⁻¹, respectively. Thermodynamic parameters showed that the adsorption process was spontaneous and endothermic in the temperature range 32–60°C. Maximum adsorption was found at system pH 4.0. The adsorption mechanism was predominantly ion exchange. Effect of other anions such as phosphate, selenite, molybdate, nitrate, chloride, and sulfate on adsorption of vanadium has been examined.     

Solid phase extraction and preconcentration of cobalt in mineral waters with PAR-loaded Amberlite XAD-7 and flame atomic absorption spectrometry

A simple, sensitive, accurate, and selective method for determination of ultratrace levels of Co is modified. The method is based on preconcentration of Co on the PAR-loaded Amberlite XAD-7 at pH 2.0 ± 0.2 for contact time as low as 45 min. The adsorbed cobalt was eluted with concentrated nitric acid and measured by flame atomic absorption spectrometry. Recoveries up to 90% were achieved. The optimized preconcentration method was applied to cobalt determination in natural mineral waters. The detection limit was found to be 0.1 ng mL⁻¹. The relative standard deviation was found to be 13% for 600 mL of 2.0 ng mL⁻¹, for 10 replicate preconcentration procedures. Cobalt concentrations in the studied water samples were found to be in the ranges of 0.5–3.5 ng mL⁻¹.     

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.     

Automated method for the determination of total arsenic and selenium in natural and drinking water by HG-AAS

A multicommutated flow system was designed and evaluated for the determination of total arsenic and selenium by Hydride Generation Atomic Absorption Spectrometry (HG-AAS). It was applied to the determination of arsenic and selenium in samples of natural and drinking water. Detection limits were 0.46 and 0.08 μg l⁻¹ for arsenic and selenium, respectively; sampling frequency was 120 samples h⁻¹ for arsenic and 160 samples h⁻¹ for selenium. Linear ranges found were 1.54–10 μg l⁻¹ (R = 0.999) for arsenic and 0.27–27 μg l⁻¹ (R = 0.999) for selenium. Accuracy was evaluated by spiking various water samples and using a reference material. Recoveries were in the range 95–116%. Analytical precision (s _r (%), n = 10) was 6% for both elements. Compared with the Standard Methods, APHA, 3114B manual method, the system consumes at least 10 times less sample per determination, and the quantities of acid and reducing agent used are significantly lower with a reduction in the generation of pollutants and waste. As an additional advantage, the system is very fast, efficient and environmentally friendly for monitoring total arsenic and selenium levels in waters.     

Potential fluoride contamination in the drinking water of Marks Nagar,Unnao district,Uttar Pradesh,India

This study was conducted in the summer season (May, 2007). The fluoride concentration along with other physico-chemical parameters in ground water samples was determined in Marks Nagar of Unnao district, Uttar Pradesh (India), since it is the only source of drinking water for the villagers. The fluoride concentration in the water varied from 0.8 to 13.9 mgl⁻¹ with a mean of 4.02 mgl⁻¹. The correlation analysis revealed that fluoride had a positive correlation with pH, CO₃, HCO₃, and sodium adsorption ratio (SAR), whereas a negative correlation with Ca and Mg was found. A soil profile was also dug in the area to assess depth-wise fluoride content in the soil. The soil samples and underneath calcium carbonate (CaCO₃) concretion were analyzed for fluoride content. The percent of soluble fluoride to total fluoride in the soil varied from 25.15 to 4.76% down the soil profile. The soluble fluoride was found to decrease with the increase in the clay content in the soil. The total leachable fluoride in CaCO₃ concretions was found to be 6.08%. It was inferred from this study that the soil and underneath layer of CaCO₃ concretions may be the potential source of fluoride contamination in the shallow drinking water sources of the area.     

Chemistry of inorganic arsenic in soils: kinetics of arsenic adsorption–desorption

The influence of ionic strength, index cations and competing anions on arsenate (As^V) adsorption–desorption kinetics was studied in an Alfisol soil. A flow-through reactor system similar to that developed by Carski and Sparks (Soil Sci Soc Am J 49:1114–1116, 1985) was constructed for the experiments. Arsenate adsorption kinetics for all the treatments were initially fast with 58–91% of As^V adsorbed in the first 15 min. Beyond 15 min, As^V adsorption continued at a slower rate for the observation period of the experiments. Changes in the solution composition had differing effects on the cumulative amount of As^V adsorbed by the soil. Ionic strength and different index cations had little effect on the amount of As^V adsorbed, while the presence of phosphate decreased the amount of As^V adsorbed from 169 to 89 and 177 to 115 g As^V μg⁻¹ in 0.03 M sodium nitrate and 0.01 M calcium nitrate, respectively. Considerably less As^V was desorbed than was adsorbed, with only between 2 to 17% of the adsorbed As^V desorbed. The presence of phosphate increased the amount of As^V desorbed by 17%, but other changes in the solution ionic strength or index cation had little effect on the amount of As^V desorbed.     

The effects of soil properties on the turbidity of catchment soils from the Yongdam dam basin in Korea

Environmental concerns have been raised that suspended solids in turbid water adversely affect human health, and that their removal increases in the cost of water treatment. The Yongdam dam reservoir, located in the southwestern region of Korea, is severely affected by inflowing turbid water after storms. In this study, soil samples were collected from 37 sites in the Yongdam upstream basin to investigate mineralogical and environmental factors associated with the turbidity potential of soils in water environments. Turbidity potential was estimated by measuring the turbidity of soil-suspension solutions after settling for 24 h. The mineralogy of the soils was dominated by four minerals—quartz, microcline, albite, and muscovite—with lesser amounts of hornblende, chlorite, kaolinite, illite, and mixed layer illite. The quartz content was the most variable of the soil mineralogy among the collected samples. Principal-components analysis (PCA) was used to examine relationships between turbidity potential and other soil properties. The variables considered in the PCA included turbidity potential, quartz content, albite content, mean size of soil particles, clay content, clay mineral content, zeta potential, conductivity, and pH of the soil-suspension solution. The first two components of the PCA explained 52% of the overall variation of the selected variables. The first component was possibly explained by physical properties such as the size of the soil particles; the second was correlated with chemical properties of the soils, for example dissolution and extent of weathering. Closer examination of the PCA results revealed that the quartz content of the soils was negatively correlated with their turbidity potential. A linear correlation (r = 0.63) was obtained between measured turbidity potential and that predicted using multiple regression analysis based on the content of clay-sized particles, clay minerals, and quartz, and the conductivity of the soil-suspension solution.     

Spectrophotometric determination of trifluralin in commercial formulations and agricultural samples using factorial design

A simple spectrophotometric method was developed for determination of trifluralin in commercial formulation and food samples. The method was based on the hydrolysis of trifluralin with sodium hydroxide to form 2,6-dinitro-4-trifluoromethylaniline. The resultant aniline group was diazotized with nitrate in acidic media and the diazotized product was coupled with β-naphthol to form red colored product having λ_max 550 nm. The reaction conditions were optimized for hydrolysis as well as for the diazotization reaction. The Beer’s law was obeyed over the range of 0.2–17 μg mL⁻¹ with molar absorptivity of 1.5 × 10⁴ L mol⁻¹ cm⁻¹. The relative standard deviation was found to be 3.6%. A two level factorial design of 2³ was used for optimization of all parameters. The influence of different factors and their interactions on the final azo dye formation were also studied from these factorial designs. The method has been applied successfully for the analysis of commercial formulations and agricultural samples. The recovery for the determination of trifluralin was found to be in the range 95–97%.     

Adsorptive separation of phosphate oxyanion from aqueous solution using an inorganic adsorbent

Phosphate removal from aqueous solution was explored using granular ferric hydroxide (GFH) as an inorganic adsorbent. Adsorption, desorption and kinetic studies were conducted on laboratory scale to evaluate the performance of GFH as an adsorbent for low concentrations of phosphate solution. The effect of pH on adsorption was investigated, and phosphate uptake was shown to decrease with an increase in solution pH, with maximum removal seen to occur at pH 3. The experimental data best fit the Temkin isotherm at both pH 3 and 4. Uptake of phosphate by GFH follows second-order kinetics, with the small particle range (76–200 μm) removing phosphate from the solution more rapidly than the larger particle range (710–850 μm). The kinetic results suggest that intra-particle diffusion is an important factor in phosphate adsorption onto GFH. Thermodynamic parameters (ΔG°, ΔH°, ΔS°) were evaluated, and the results indicated that the adsorption process was endothermic and spontaneous. This study demonstrates that GFH has potential to be used as a cost-effective adsorbent for phosphate removal from aqueous solution.     

Sorption and bioavailability of arsenic in selected Bangladesh soils

The bioavailability of arsenic (As) in the soil environment is largely governed by its adsorption–desorption reactions with soil constituents. We have investigated the sorption–desorption behaviour of As in four typical Bangladeshi soils subjected to irrigation with As-contaminated groundwater. The total As content of soils (160 samples) from the Laksham district ranged from <0.03 to approximately 43 mg kg⁻¹. Despite the low total soil As content, the concentration of As in the pore water of soils freshly irrigated with As-contaminated groundwater ranged from 0.01 to 0.1 mg l⁻¹. However, when these soils were allowed to dry, the concentration of As released in the pore water decreased to undetectable levels. Remoistening of soils to field moisture over a 10-day period resulted in a significant (up to 0.06 mg l⁻¹) release of As in the pore water of soils containing >10 mg As kg⁻¹ soil, indicating the potential availability of As. In soils containing <5 mg As kg⁻¹, As was not detected in the pore water. A comparison of Bangladeshi soils with strongly weathered long-term As-contaminated soils from Queensland, Australia showed a much greater release of As in water extracts from the Australian soils. However, this was attributed to the much higher loading of As in these Australian soils. The correlation of pore water As with other inorganic ions (P, S) showed a strongly significant (P < 0.001) relationship with P, although there was no significant relationship between As and other inorganic cations, such as Fe and Mn. Batch sorption studies showed an appreciable capacity for both As^V and As^III sorption, with As^V being retained in much greater concentrations than As^III.     

Chemistry and adsorption-desorption properties of manganese oxides deposited in Forehill Water Treatment Plant,Grampian, Scotland

Manganese oxide coatings on sand particles within filtration beds from a water treatment plant in Grampian, Scotland were examined to determine their control on metal mobility. This study first sought to characterise the oxides, notably their mineralogy and metal content, to provide a foundation for studies on the adsorption of dissolved metals from the treated water by the oxides. The oxides were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and analysed by flame atomic absorption spectrophotometry (AAS). These techniques showed the oxide coatings were amorphous but uniformly distributed over each sand grain. The oxides were selectively removed from the sand grains prior to analysis by AAS using a hydroxylamine hydrochloride selective leaching method. The compositional range of the extracts was 100–150 mg L⁻¹ Mn; 30–55 mg L⁻¹ Fe; 17–56 mg L⁻¹ Ca; 4.6–7.0 mg L⁻¹ Ni; 4.6–6.8 mg L⁻¹ Zn and 1.3–5.7 mg L⁻¹ Mg. When these results are expressed as mg of metal per mg of Mn, the metal content of the oxides is remarkably uniform: 0.25–0.37 mg Fe; 0.14–0.35 mg Ca; 0.035–0.042 mg Ni; 0.035–0.040 mg Zn; 0.01–0.04 mg Mg. The greatest metal concentrations were consistently found in the upper 3 cm of the filtration bed, and these decrease with increasing depth. After the beds are cleaned a more uniform distribution of metals occurs throughout the bed. The metals taken up by the manganese coating are retained over a wide pH range with the exception of Ca and Mg which desorb to a significant extent. The percentage of calcium and magnesium lost from the coating ranges from 30–94%, the amount being dependent on the final pH of the solution. The presence of manganese oxide in the filtration beds appears to be advantageous in terms of removal of transition metals from the treated water.     

UVR-induced photoinhibition of summer marine phytoplankton communities from Patagonia

During austral summer 2006, experiments were carried out to evaluate the effects of ultraviolet radiation (UVR, 280–400 nm) on carbon fixation of natural phytoplankton assemblages from Patagonia (Argentina). Surface water samples were collected (ca. 100 m offshore) at mid morning using an acid-cleaned (1 N HCl) dark container. The short-term impact of UVR (measured as radiocarbon incorporation) was immediately assessed by exposing samples to three artificial illumination treatments: PAR (400–700 nm), PAR + UV-A (320–700 nm), and PAR + UV-A + UV-B (280–700 nm). Pico-nanoplankton characterized the assemblages, and taxon-specific pigment fingerprinting combined with CHEMTAX and supplemented with microscopic observations showed varied proportions of diatoms, chlorophytes, and cyanobacteria throughout January–February 2006. Photosynthetic efficiency, as assessed through assimilation numbers, was high [between 4.4 and 10.4 μg C (μg chl-a)⁻¹ h⁻¹], and it was probably favored by the supply of inorganic nutrients from the Chubut River. UVR-induced photoinhibition appeared to be related to the taxonomic composition: in general, higher photoinhibition was observed when diatoms dominated, whereas this was lower when samples were dominated by chlorophytes. Our data suggest that xanthophyll pigments might have provided only limited protection in these already highlighted acclimated assemblages.     

Residues of fluoroquinolones in marine aquaculture environment of the Pearl River Delta, South China

Concentrations and distributions of selected fluoroquinolones (norfloxacin, ciprofloxacin and enrofloxacin) in water, sediments and nine kinds of fish species collected from 6 sites in two marine aquaculture regions of the Pearl River Delta, China, were analyzed by using high-performance liquid chromatography with fluorescence detector (HPLC). The results showed that the concentrations of ciprofloxacin and enrofloxacin were below the limits of quantification (LOQ) in all water samples except for norfloxacin. Norfloxacin and ciprofloxacin concentrations ranged from 1.88 to 11.20 ng g⁻¹ dry wt, 0.76–2.42 ng g⁻¹ dry wt in sediments collected from the Dapeng’ao region (sites 1–3) and ranged from 2.31 to 4.75 ng g⁻¹ dry wt, 1.26–1.76 ng g⁻¹ dry wt in sediments collected from the Hailing Island region (sites 4–6), respectively. However, no enrofloxacin was found in all sediment samples. The three fluoroquinolones (FQs) were detected in all fish samples, and the concentrations were higher in liver tissues than those in muscle tissues. The levels of norfloxacin were higher than ciprofloxacin and enrofloxacin in both liver and muscle tissues. Among the nine marine fish species, Siganus fuscescens from Hailing Island had a significantly high level of norfloxacin in liver tissue (254.58 ng g⁻¹ wet wt), followed by Sparus macrocephalus (133.15 ng g⁻¹ wet wt) from Dapeng’ao, and the lowest value was Lutianus argentimaculatus (5.18 ng g⁻¹ wet wt) from Hailing Island. The obtained results of FQs in present study do not represent a risk to the human health in Guangdong coastal area, based on the maximum residue limits (MRLs) established by Chinese Government and the acceptable daily intake (ADI) recommended by the Food and Agriculture Organization and World Health Organization (FAO/WHO).