Metal Contents and Pb Isotopes in the Surface Seawater of the Gulf of Prigi, Indonesia: Detection of Anthropogenic and Natural Sources

In order to investigate the anthropogenic and natural sources of metals in the Gulf of Prigi, Indonesia, it was analyzed their metal contents and Pb isotopes of surface seawater together with sediment, grouper fish, mosh, seaweed, soil, and sharp grass for protecting the environmental pollution of the study area. Samples were leached using a microwave digestion technique. Metal (Ca, Fe, Mn, Cu and Pb) concentrations and Pb, Pb and Pb in the leached solutions were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS). The level concentrations of Ca (491436 μg kg), Fe (12123 μg kg), Mn (37.2 μg kg), Cu (84.0 μg kg) and Pb (34.5 μg kg‐1) in the surface seawater were low compared with those of background seawater levels issued by World Health Organization (WHO). The range of Pb isotope ratios (Pb / Pb = 0.7966-0.9945 and Pb / Pb = 2.2600-2.8243) in surface seawater was higher in the plotted Pb growth curve suggesting unpolluted Pb reflected by natural sources such as mineral sources or lithogenic from marine sediment.


Introduction
Seawater is primaly used to inform the anthropogenic and natural sources of elements (including metals).Assessment of metal contents affected by physical, chemical and biological characteristics of surface seawater are vital substances as a major health controlling the living organism surrounding the sea.Variations of anthropogenic and natural sources are caused by mobilization of metal due to fresh water and pollutant from rivers, precipitation, and evaporation processes in the sea forming their geochemical fractions.[3][4][5][6] The status of seawater can be monitored using their level of metal contents in water, sediment, seaweed, coral reefs and then identified to investigate their source of metal contents using stable isotopes analysis, such as δ 11 B, δ 18 O, δ 13 C, δ 15 N and Pb isotope ratios ( 208 Pb / 206 Pb vs. 207 Pb / 206 Pb).The contaminant of [F -] in seawater is reflected by the F / Ca in non-symbiotic corals (Flabellum sp.). 3 Using the two stable isotopes (δ 11 B) with their composition, such as 10 B (ca. 20%) and 11 B (ca. 80%), provided the important information on the global geochemical cycle and metals mobility.The fractionations of 11 B released the dominant boron species of B(OH) 3 and B(OH) 4  -incorporating into marine carbonates (corals) which reflected the history of seawater records and level of pH associated with the coral growth.The pattern of two cyclic changes in δ 18 O and δ 13 C in coral aragonite indicates an annual change in seawater salinity. 7Stable

Metal Contents and Pb Isotopes in the Surface Seawater of the Gulf of Prigi, Indonesia: Detection of Anthropogenic and Natural Sources
isotopes of δ 13 C and δ 15 C showed enrichment in muscle (0.5 and 1.3%), liver (1.3 and 1.0%), and whole fish tissues of brown-marbled groupers (Epinephelus fuscoguttatus). 8owever, the use of stable isotopes of δ 11 B, δ 18 O, δ 13 C and δ 15 N cannot distinguish anthropogenic and natural sources.To address this, previous studies have recommended using Pb isotope ratios ( 208 Pb / 206 Pb vs. 207 Pb / 206 Pb) as reflecting the anthropogenic and natural sources. 4,5,9,10he use of Pb stable isotope analysis in seawater is based on the premise that Pb isotopes are introduced as "fingerprints" of each anthropogenic or natural source of Pb, which can have unique isotopic ratio values.Pb has four main isotopes: 208 Pb (52%), 206 Pb (24%), 207 Pb (23%) and 204 Pb (1%), while radiogenic isotopes 206 Pb, 207 Pb and 208 Pb are produced as the decay of 238 U, 235 U and 232 Th, respectively.The 204 Pb is the only primordial stable isotope with a constant abundance on the Earth. 4The abundance of Pb isotopes in a sample strictly depends on the concentrations of primordial Pb, U and Th and the lengths of the closed system, i.e., half-lives (t 1/2 ) of the parent isotopes.The three radioactive isotopes 210 Pb (t 1/2 = 22 years), 212 Pb (t 1/2 = 10 h) and 214 Pb (t 1/2 = 26.8min) are commonly used in determining the history and sources of anthropogenic Pb inputs into the environment. 11,12urthermore, 210 Pb, for its convenient halftime, is widely used for dating of seawater, glacial ice, recent sediments and peat deposits. 13,14he isotopic composition of Pb is not significantly affected by physico-chemical fractionation processes.Pb isotopes provide an efficient tool for determining the sources and pathways of Pb pollution. 15,16The isotopic composition of Pb in the Earth (and especially in seawater) is commonly expressed as ratios 206 Pb / 204 Pb, 208 Pb / 206 Pb and 206 Pb / 207 Pb, with the latter being the most preferred since it can be determined precisely and the abundances of these isotopes are relatively vital.However, normalization to 204 Pb ( 206 Pb / 204 Pb, 208 Pb / 204 Pb) yields the largest variability between reservoirs.Furthermore, the abundance of 207 Pb has slightly changed with time compared to 206 Pb because most 235 U has already decayed, while 238 U still has a relatively high abundance on the earth and seawater. 17For example, while old Pb ores are generally characterized by low 206 Pb / 207 Pb ratios (1.06-1.10),more recent samples containing more radiogenic Pb (originating from U and Th decay) reflect higher 206 Pb / 207 Pb ratios (> 1.18). 18,19For the use of Pb isotopes to "track" the origin of contamination, the values of 206 Pb / 207 Pb, 207 Pb / 206 Pb and 208 Pb / 206 Pb are more commonly compared with the 204 Pb. 204 Pb does not change its value and is not of much interest as to distinguish between ratio values.The use of Pb isotope ratios have been studied in many sites for tracking the origin of contamination in plants, mammals, river sediment and ocean water. 4,5,10The growth curves of the Pb isotopes have been applied in many cases to address Pb pollution. 9The growth curve can be expressed using the ratios 208 Pb / 206 Pb against 207 Pb / 206 Pb, or 206 Pb / 207 Pb.Some researchers widely used 208 Pb / 206 Pb and 207 Pb / 206 Pb because the 206 Pb isotope is more abundant than 207 Pb and is therefore more suitable as a reference isotope.In addition, 208 Pb / 206 Pb and 207 Pb / 206 Pb are chosen for practical reasons including more frequent use of this previous research for similar locations and materials. 4,5,9,10he Gulf of Prigi, Indonesia, is one of the business centers for fisheries, recreation, and ecotourism on the southern coast of Java Island.The position of this Gulf is directly adjacent to the Indian Ocean, which has many coastal areas and the great potential for mobilization of metals and nutrients in seawater.All of anthropogenic and natural activities can contribute metals such as Ca, Fe, Mn, Cu and Pb in seawater.Those metals are essentially required for living organisms in specific concentration, but possibly produce high toxic effects in high concentrations.Some metals such as Pb, Zn, Cu, Fe and Mn are extremely toxic owing to their toxicity, persistent and bio-accumulative nature to induce multiple organ damage, even at lower levels of exposure.Because of activities in the Gulf of Prigi associated with environmental and health protections, the monitoring of metal contents in its surrounding seawater is quite imperative in order to investigate their sources.Here, we firstly report the level of metal contents and investigate the Pb isotopes in seawater associated with anthropogenic and natural sources in the Gulf of Prigi.In addition, we continue detecting their sources using the application of 208 Pb / 206 Pb vs. 207 Pb / 206 Pb with the modelling single stage one on the Pb growth curves.

Sample collection and pretreatment for analysis
A total of 24 samples of surface seawater were collected from the southern part of the Gulf of Prigi, from January to July 2017 (Figure 1, Table 1).
In order to investigate the source of anthropogenic and natural sources, we also collected the sediment, grouper fish, moss, seaweed, soil, and sharp grass surrounding the gulf.All samples were collected in the surroundings of the floating home, which is located in the middle of the Gulf of Prigi.During seawater sampling, temperature (T), pH, electrical conductivity (EC), and turbidity were measured at several sites (samples SW1 up to SW24) using water quality checker (WQC) 22A.Salinity of surface seawater was measured by salinometer Atago S-28E.Sulfate concentrations in seawater  were determined by colorimetry.Chemical oxygen demand (COD) was measured using dichromate reflux technique standard method.Dissolved oxygen (DO) and biological oxygen demand (BOD) in seawater were determined by the Winkler method.The chlorophyll a was determined by spectroscopic method at 32 spot locations (SP1 to SP32) for detecting natural sources and then mapping using the Surfer 10.0 software 20 (Figure 2).For seawater analysis, the chromatography column was prepared before sample digestion.The column was attached by glass wool at the end of column prior to filling the slurry (1 g Chelex-100 resin containing 100-200 mesh Na form in NH 4 OH solution).The filled resin column was conditioned at pH 7 using CH 3 COONH 4 to convert the active sites of the resin into ammonium form for reducing the potential interference of the salt matrix in seawater analysis. 21After exiting the resin, 7 mL of the sample in a 120 mL Teflonperfluoroalkoxy (PFA) microwave digestion vessel were digested using a closed microwave oven system (CEM MARS 6).We used ultrapure grade HNO 3 (69%, specific gravity 1.42, Fluka) for digesting cycles at 10-15 min and then analyzing for Ca, Fe, Mn, Cu, and Pb using inductively coupled plasma mass spectrometry (ICP-MS).
The accuracy of the method was confirmed by analyzing certified reference materials (LGC-6187 and BCR-141R), revealing good agreement (recoveries = 81-122%) between the certified and the measured values. 22ediment, grouper fish, moss, seaweed, soil, and sharp grass samples were dried in an oven at ca. 70 o C until they were completely dried (approximately 12 h).The dried samples were kept in a clean plastic, then ground and homogenized in an agate mortar and sifted through a polyethylene sieve of less than ca.50 μm.All plastic, hair, wood, and paper were removed from samples.Finally, the fine-grained fraction samples were also kept enclosed in a clean plastic bag to prevent contamination.We used the total leaching metal contents for these samples using microwave digestion, 6 as follows: 10.0-11.0mg of dry sediment, grouper fish, moss, seaweed, soil, and sharp grass samples were leached with 1 mL of HNO 3 (15.3M) in 7 mL vials, subjected to continuous shaking for 24 h, put in a sonic bath for 30 min and centrifuged for 10 min, respectively.The supernatant solution was then put in a sonic bath for 30 min and then centrifuged at 100 rpm for 10 min.After the resultant residue was heated to 110 o C, 3 drops of HF and 3 drops of HNO 3 (15.3M) were added, and it was heated again until dry.Then the residue was dissolved and diluted with 1 mL 1% HNO 3 five times.The total leached supernatant and residue samples were finally mixed and poured into a 7 mL polyethylene tube for ICP-MS analysis.

ICP-MS analysis
Total concentrations of Ca, Fe, Mn, Cu, Fe and Pb isotopes in leached solutions of seawater, sediment, grouper fish, moss, seaweed, soil, and sharp grass samples were analyzed by ICP-MS (NexION 300, PerkinElmer).The concentrations of ICP-MS-68B standard solution A were set to be 0.25, 0.50, 0.75, 1, 10 and 100 μg L -1 .The sample uptake rate of ICP-MS was ca.0.1 mL min -1 adjusted by micro flow perfluoro-alkoxy (PFA) nebulizer.The operation for integration was 3 s per mass and radio frequency (RF) power was 1.3 kW, while reflected power was smaller than 1.0 W. The flow rates of the plasma and nebulizer gas (argon) were 16.0 and 1.0 L min -1 , respectively.
All samples were counted three times per run.The concentration of metals was determined using a calibration method with correlation coefficient (r 2 ) ranging from 0.99 to 1.00.Analyses in the leached solutions were converted and calculated on a dry weight basis.The detection limits of Ca, Fe, Mn, Cu, and Pb were found to be 0.10, 0.10, 0.10, 0.68, and 0.30 g mL -1 , respectively.The precision of the method was evaluated by standard certified reference material of coastal seawater (CASS-4) and the results varied between 0.7 and 1.3% (relative standard deviation; RSD) (n = 5). 23

Index of pollutant (anthropogenic) and natural assessment of metal in seawater Pollution load index (PLI)
We modified the PLI to assess the metal contents data in seawater using the background values. 24The mathematical equation using PLI can be written as follows: (1) where 4 is the number of measured metal contents in seawater collected from the study area.The terms , , , indicate the highest concentration of measured metals for each site per their metal background (b).Polluted sample (anthropogenic) is indicated by PLI value > 1, while unpolluted (natural) is specified by PLI < 1. 5,25 Index of the non-carcinogenic/chronic risk (hazard quotient, HQ) The HQ is measured to estimate the non-carcinogenic or chronic risk of seawater in the Gulf of Prigi.If the value of HQ is lower than 1, it is assumed to be safe, whereas HQ greater than 1 indicates chronic risk. 5,26,27The HQ is expressed by applying the following equation: where average daily dose (ADD) is defined here as ADD = Cm × IR / BW.Cm, IR and BW are the measured concentration of metal in seawater samples, the water ingestion rate (2 L day -1 ) and the average Indonesian's body weight (65 kg), respectively.The reference dose (RfD) is the data of the oral toxicity reference dose values. 28The value of RfD is given as follows: Fe = 0.07 mg kg -1 day -1 , Mn = 1.4 × 10 -1 mg kg -1 day -1 , Cu = 3.7 × 10 -2 mg kg -1 day -1 , and Pb = 3.6 × 10 -2 mg kg -1 day -1 .

Results and Discussion
Chemical-physical parameters and metal contents of surface seawater (SW samples) Analytical results of SW1-SW24 at the study site are listed in Table 1.Water temperature at different sites varied from 29.9-30.6 o C during the day on the sampling date (January-June 2017), while air temperature was ca. 30 o C. According to the East Java meteorological observatory, water temperature of seawater in the Gulf of Prigi ranged from 29-30 o C during the last 10 years.Our temperature data implies that the observation was performed on one of the hottest days in the year, whereby it has a large influence on climate and weather surrounding the region of East Java.The high temperature of seawater was possibly affected by the interaction between atmosphere and the Indian Ocean.
Seawater salinity of SW1-SW24 ranged from 32.0-36.0psu (practical salinity units) and it increased with elevating surface water temperature (Table 1).The high salinity of SW1-SW24 (34.0-36.0psu), except for SW18, SW20, SW21 and SW22, was possibly governed by the high evaporation of surface water in the Gulf of Prigi at day time.The salinity of oceanic water ranged from 33.6-34.1 psu, 29 which is comparatively lower than our observation (32.0-36.0psu).The salinity of seawater above 30.0psu may increase the tolerance of corals against the high temperature effects and cover by high light intensity. 29he DO, specific conductance (EC), pH, COD, turbidity, sulfate, and BOD values in SW1-SW24 ranged from 6.50-8.50mg L -1 , 1.40-44.8mS m -1 , 6.30-6.80mg L -1 , 35-7582 mg L -1 , 0.11-1.55nephelometric turbidity units (NTU), 9.20-75.9mg L -1 , and not detected-19.5mg L -1 , respectively (Table 1).DO contents of SW1-SW24 were higher than the average of saturation state of seawater 70-87%. 29DO value above 6.50 mg L -1 indicates no water pollution. 24The high contents of DO in SW1-SW17 suggest that the condition of seawater in the Gulf of Prigi may provide enough oxygen for respiration and decomposition of organic matters in seawater.Therefore, the floating home at the SW1-SW17 possibly can be used as the media of natural sources for increasing the fish, coral, lobster, and shrimp productivities.
EC in SW reflects the competition of ionic composition in seawater, e.g., when Ca 2+ , Fe 3+ , Mn 2+ , Cu 2+ , and Pb 2+ ions competed with SO 4 2-ion (Table 1, Figure 3).All values of EC in SW, except for SW1, SW2, SW4, SW11 and SW18, were found in the range of typical drinking water (5-50 mS m -1 ). 24EC of SW1, SW2, SW4, SW11 and SW18 were recorded at ca. 5 mS m -1 related with the average of EC of seawater in the world's oceans. 30The data can be used as a typical way to monitor and treat in low quality water (e.g., water rich with sodium, boron and fluorides) as well as in high quality irrigation water (e.g., adequately fertilized water with appropriate nutrient concentrations and ratios).EC is related to pH values in seawater.The measured pH at SW1-SW24 tended to be relatively stable within the range of 6-7.The pH in SW probably was affected by acid solutions such as H 2 CO 3 , HNO 3 , H 2 SO 4 , and H 3 PO 4 using cation exchange reactions and C, H, O, N, and S or biogeochemical cycles in surface seawater.
The COD values of SW1-SW5, SW11 and SW17 are categorized as very low (below 2100 mg L -1 ) (Table 1). 31e suggest that the index reflected no water pollution by organics due to high seawater quality discharge from river runoff.Such lower value of COD in seawater indicates the little oxygen required for the chemical oxidation of organic matter.We used K 2 Cr 2 O 7 as the strong chemical oxidant for COD test.The possible chemical reaction can be written as follows: For the case of turbidity, all values in SW1-SW24 were recorded below 1 NTU, except for SW8 (1.55 NTU).It might be caused by a wide variety of suspended particles and the effect of ocean turbidity through the Indian Ocean currents.Such low turbidity in SW1-SW24 might support the photosynthesis process.The acceptable and permissible limits of turbidity in water are 1 and 5, respectively. 30One of the parameters to influence turbidity is sulfate content in seawater.SW1-SW24 contained sulfate ions and most of these ions are also slightly soluble in seawater.Sources of sulfate ions were possibly produced by oxidation process of their ores, such as CaSO 4 , PbSO 4 and Fe 2 (SO 4 ) 3 or by products of industrial waste associated with river runoff.All of the sulfate values in SW were found in the range of the values in desirable limit (200 mg L -1 ) and permissible limit (400 mg L -1 ) in natural water.Moreover, the BOD values in SW1-SW24 were found below 10 mg L -1 , except for those in SW3, SW10, and SW11.BOD value less than 10 mg L -1 are categorized as low contamination. 24The low of BOD values may also suggest that the biodegradability of dissolved organic matter slightly occurred in SW. 32 In order to investigate the ecological characteristics of seawater in the Gulf of Prigi, we report the distribution of chlorophyll a along the sampling points (Figure 2).As shown in Figure 2, concentrations of chlorophyll a were found to vary between 0.90-2.34mg m -3 from sea surface to Indian Ocean in ca.18.5 m.
The range of concentrations of chlorophyll a were 1.45-1.54mg m -3 , observed for SW1-SW3, SW12, SW13, SW20 and SW21.For SW8-SW10 and SW16-SW19 it was detected between 1.69-1.78and 1.55-1.63mg m -3 , respectively, while SW4-SW7, SW14, SW15, and SW22-SW24 were found to be 1.63-1.70mg m -3 .The concentration of chlorophyll a measured in this research is the same range of chlorophyll a concentrations at the surface seawater as in the previous study. 33,34The variability of chlorophyll a-enriched reflected the good ecological conditions of marine systems in the Gulf of Prigi and such variability was possibly affected by the changes in the physical and chemical characteristics of the marine environment, such as terrestrial runoff, mass corals bleaching, temperature, wind stress and the Indian Ocean Dipole (IOD).Seasonal and inter-annual variability of phytoplankton biomass in the eastern part of the gulf, which is influenced by mixing of fresh water discharges (estuary) with Indian Ocean, may also contribute to the high distribution of chlorophyll a concentrations in the Gulf of Prigi.][37] The abundance of chlorophyll in seawater governs the invasion of populations of grouper fish.Our observations of enriched chlorophyll in seawater indicates the Gulf of Prigi tends to be a natural source and provides nutrient for marine organisms.Therefore, it is significantly required to conduct permanent and serious effort of protect this natural source from anthropogenic inputs which may cause the pollution in the water bodies of the gulf.
The concentrations of Ca, Fe, and Mn ranged from 243917-504518, 1181-2270, and not detected-44.8μg kg -1 , respectively, and those of Cu and Pb ranged from 41.2-99.2 and 6.00-35.2μg kg -1 , respectively.As listed in Table 2 and shown in Figure 3, the highest Ca concentration (491436 μg kg -1 ) was found in SW6.In SW1-SW24, the averages of Ca concentrations were recorded as multifold higher than the respective permissible limit set by WHO. 24a enrichment in seawater suggests the possible leaching of Ca and its dissolution at low pH in surface seawater from coral skeletons or aragonite (CaCO 3 ) surrounding the Gulf of Prigi.Input of acids to leach CaCO 3 caused the pollutant input through river, contributing HNO 3 , H 2 SO 4 (including H 2 S), H 3 PO 4 and other organic acids.In addition, the source of mineral and organic acids was emitted by rock weathering process surrounding rivers, agricultural activities, fertilizer use, livestock, sewage treatment plant, and soil dust.The chemical reaction can be written as folows: Table 2. Metal contents and isotopic Pb of surface seawater samples and their related materials in the Gulf of Prigi Sample Ca / (μg kg -1 ) Fe / (μg kg -1 ) Mn / (μg kg -1 ) Cu / (μg kg -1 ) Pb / (μg kg -1 ) 206 Pb / (μg kg -1 ) 207 Pb / (μg kg -1 ) 208 Pb / (μg kg -1 ) SW1   Sample Ca / (μg kg -1 ) Fe / (μg kg -1 ) Mn / (μg kg -1 ) Cu / (μg kg -1 ) Pb / (μg kg -1 ) 206 Pb / (μg kg -1 ) 207 Pb / (μg kg -1 ) 208 Pb / (μg kg -1 ) The highest average of Fe concentration (1213 μg kg -1 ) was found in SW2 with the overall concentrations ranging from 1203-1218 μg kg -1 .Fe concentrations of the study area (SW1-SW24) were shown to be extremely higher than their permissible level. 24The source of Fe was possibly leached from the Fe oxide/hydroxide in the mineral sediment of seawater as nodules and crusts.Concomitantly, the concentration of Fe 2+ or Fe 3+ increases with decreasing pH.The chemical reaction is written as: The highest Mn concentration (44.8 μg kg -1 ) was noticed in SW18.As listed in Table 2 and Figure 3, all of the seawater samples (SW1-SW24) show lower concentrations of Mn than the permissible value (400 μg kg -1 ). 24Mn concentrations in the study area were also found to be lower than those reported previously 27 in the surface water and sub-surface water samples of Bucha and surrounding areas of Mohammad agency, northern Pakistan.Mn was possibly deposited near the seafloor and then removed by weathering.As shown in Figure 3, the pattern of the concentrations of Mn and Cu are relatively similar, except for SW10.For SW10, located at the end area of sampling sites close to Indian Ocean, the lowest conentration of Mn maybe affected by the high dissolution of MnO 2 to the ocean.The highest average concentration of Cu (84.0 μg kg -1 ) was noticed in SW19.At the SW1-SW24 sampling sites, Cu contents are lower in comparison to their respective permissible limit set by WHO (2000 μg kg -1 ). 24The low levels of Cu suggest that they were originated most likely from natural occurrence.The source of Cu comes from the cobalt-bearing mineral, such as chalcopyrite, bornite and chalcocite. 38,39The high mean concentration of Pb (up to 34.5 μg kg -1 ) at SW24 exceeded the background value of WHO (10.0 μg kg -1 ). 24However, the Pb concentrations of surface seawater samples at SW1-SW24 were close to the standard Pb value by WHO, 24 except for SW18-SW21, and SW24 (Table 2 and Figure 3).Additionally, the Pb and Ca in SW1-SW24 show a similar pattern, indicating the cooperation with sulfate ionic in surface seawater.
There is a correlation between total Pb content with 206 Pb, 207 Pb, and 208 Pb.The correlation coefficients of total Pb content vs. 206 Pb, 207 Pb, and 208 Pb were 0.9961, 0.9947, and 0.9981, respectively.The similar pattern plots among 206 Pb, 207 Pb, and 208 Pb suggest the source of Pb in surface seawater initiated from the decay of parent rock, such as 238 U, 235 U, and 237 Th.The natural sources of U and Th cooperating with Pb isotopes were generally from stones and mineral sources in sediment around the Gulf of Prigi.Our results reflect the evolution of U-Th-Pb isotope system in the leached sedimentary rock, which provides for evaluation of the sources of the Pb isotope composition of the seawater.The data in parentheses indicate the number of seawater sample.PLI: pollution load index; b: metal (Fe, Mn, Cu or Pb) content in the background reference; ADD: dose-response data; RfD: reference dose; HQ: hazard quotient.
Pb isotope ratios of seawater from the Gulf of Prigi Pb isotope ratios growth curve for detection of sources of Pb mines Pb isotope ratios can be used to reflect time-dependent decay process and provide information on the age of material associated with Pb content.The modelling growth curve of the Pb is produced by plotting on the line of Pb ore mined in the world.In order to apply the modelling of growth curve of Pb isotope ratios in seawater of the Gulf of Prigi, we calculated the data of Pb isotopes references from various mines around the world, in combination with the age of the different ore Pb published previously (Table 3 and Figure 5). 40As listed in Table 4, the third column from the right indicates the geological age of the ore Pb contents.Using a single-stage model of Russell and Reynolds, 40 we predict the value of Pb isotope ratios for different ages according to the decay of unstable U and Th into the stable end-product Pb isotopes. 238U decays comprise 14 steps to produce 206 Pb as the stable end-product, with half-life of 4.468 × 10 9 years. 235U decays to 207 Pb and 232 Th decays to 208 Pb with half-lives of 0.7038 × 10 9 and 14.010 × 10 9 years, respectively. 204Pb is the only naturally-occurring stable isotope of Pb that is not radiogenic, thus its abundance does not change over time.The decay constants used are λ = 0.155125 × 10 -9 year -1 , λ' = 0.98485 × 10 -9 year -1 , λ'' = 0.49475 × 10 -10 year -1 , and α = 238 U / 235 U (present) = 137.88.We used the following values using the new decay constants and the corrected Pb isotope ratios of Table 4: a = 18.465 ± 0.074, b = 15.642 ± 0.010 and c = 38.057± 0.095, whereas V = 0.066413 ± 0.00085 and W = 36.058± 0.132.We chose the time for every 0.1 × 10 9 years from present day to 1.5 × 10 9 years in order to produce the lead growth curve according with the range value of Pb isotope ratios of seawater in the Gulf of Prigi.The calculated Pb isotope ratios are listed in Table 5.
As mentioned above, 204 Pb is not a radiogenic isotope and it has therefore become more common to convert the ratios 207 Pb / 206 Pb and 208 Pb / 206 Pb in the Pb isotope ratio calculation.The calculated 208 Pb / 206 Pb and 207 Pb / 206 Pb ratios as a function of time (Table 5) are plotted in Figure 5.The growth curve shows the calculated values, where the end of curve at lower values to the left represents the present day.The line of growth curve was calculated and made from the values of Pb isotope ratios of the Pb ores in the world (Table 5 and Figure 5).As shown in Figure 4, we finally normalized from the predicted line calculations in the Pb growth curve.This Figure can be used to monitor the value of Pb isotope ratios in seawater of the Gulf of Prigi for detecting their originating mine sources.
Pb isotope ratios in the samples of the Gulf of Prigi In order to investigate the anthropogenic and natural sources, we detected and treated calculation of Pb isotope ratios in seawater of the Gulf of Prigi.Seawater samples (SW1-SW24) as a group show a wide range in 207 Pb / 206 Pb (2.2600-2.8243)and 208 Pb / 206 Pb (0.7966-0.9945) (Table 6).Figure 5 shows the patterns and variations of Pb isotope ratios from SW1 to SW24.The SW1-SW24 samples extend from the typical Pb-polluted growth curve.These results indicate that source of unpolluted Pb in seawater of the Gulf of Prigi may be originated from natural sources including fresh water and mineral resources in sediment of the Gulf of Prigi.
Pb isotope ratios in our natural samples group, such as sediment, grouper fish, moss, seaweed, soil, and sharp grass, were investigated to understand their relation with seawater of the Gulf of Prigi.As listed in Table 6, the range of their Pb isotope ratios ( 207 Pb / 206 Pb = 0.4033-0.9667and 208 Pb / 206 Pb = 2.1918-2.2253)were also higher in the plotted Pb growth curve (Figure 5).Pb isotope ratios of seawater for SW24 agreed well to that in the natural samples group, except for the Pb isotope ratios of seaweed ( 207 Pb / 206 Pb = 0.4033 ± 0.176 and 208 Pb / 206 Pb = 0.4033 ± 0.0293).This result shows that Pb in seawater could contribute and transport to the grouper fish, moss, soil, and sharp grass and might also be affected by coastal sediment of Prigi (Figure 5).
In order to detect anthropogenic sources, Pb isotope ratios in seawater were plotted in the Pb growth curve, indicating Pb ore mined in the world.As shown in Figure 5, we also plotted the Pb isotope ratios of Broken Hill mine ( 207 Pb / 206 Pb = 0.952 and 208 Pb / 206 Pb = 2.2182) and Mississipi Valley ( 207 Pb / 206 Pb = 0.820 and 208 Pb / 206 Pb = 2.0172) ores  in the additive of gasoline to increase the octane ratio of fuel.Their Pb isotopic compositions of ores in leaded gasoline presents a wide range of Pb isotope ratios and exhibit different ranges compared to those of seawater (Figure 5).Pb isotope ratios of soil were also chosen as one of anthropogenic sources in order to detect its fingerprint in seawater.The Pb leached from agricultural soil may contribute in the seawater (Figure 1).
The Pb isotope of soil at Prigi was closer to seawater (SW-24) comparing with that in soil pollution.This result indicates that the Pb isotope ratios of soil pollution did not agree well with that of seawater.In order to detect the sources of atmospheric pollution input in seawater, we added the value of Pb isotope ratios of municipal solid waste incinerator.The municipal solid waste incinerator was well known as the source of pollution in seawater of the Gulf of Thailand and other countries. 5,15,43The range of Pb isotope ratios in the incinerator fly ash ( 207 Pb / 206 Pb = 0.867-0.870and 208 Pb / 206 Pb = 2.200-2.120)was very far from the Pb isotope ratios in seawater.
Table 5 and Figure 5 also show the value of Pb isotope ratios of geologic material such as galena (PbS).The range of Pb isotope ratios of galena ( 207 Pb / 206 Pb = 2.091-2.118and 208 Pb / 206 Pb = 0.8394 ± 0.8654) falls completely within that of seawater.These results indicated that the leaded gasoline, soil pollution, incinerator fly ash, and galena did not contribute to the concentrations of Pb that were present in seawater.

Conclusions
In the Gulf of Prigi, the majority of physico-chemical parameters including temperature, salinity, DO, EC, pH, COD, turbidity, sulfate, BOD, chlorophyll a and metal contents of Ca, Fe, Mn, Cu, Pb isotopes in surface seawater samples were found within the permissible limits set by WHO.The relationship between total content of Pb and their Pb isotopes showed that the Gulf of Prigi receives contributions from natural sources reflected from parent rock such as U and Th.The investigation of 208 Pb / 206 Pb and 207 Pb / 206 Pb falls completely with the Pb growth curve and anthropogenic sources corresponding to the predominant unpollution by natural-leached Pb from marine sediment.This study, by investigating surface seawater from the Gulf of Prigi, revealed that this gulf is a potential dwelling for opening and increasing the productivities of fish, shrimp, corals, lobster and associated marine products for the public welfare.The use of Pb isotopes in seawater of the Gulf of Prigi is an effective approach for environmental monitoring associated with its interaction with Indian Ocean.

Figure 1 .
Figure 1.Map showing sampling locations of surface seawater in the middle of the Gulf of Prigi.

Figure 2 .
Figure 2. Map of chlorophyll a distributions in the Gulf of Prigi.

Figure 3 .
Figure 3. Distributions of metal contents of surface seawater in the sampling locations in the Gulf of Prigi.

Figure 5 .
Figure5.Pb isotope ratios of seawater, sediment, grouper fish, moss, soil, seaweed and sword grass including natural and anthropogenic sources in the Gulf of Prigi.The line shows the Pb growth curve.40

Table 2 .
Metal contents and isotopic Pb of surface seawater samples and their related materials in the Gulf of Prigi (cont.)

Table 2 .
Metal contents and isotopic Pb of surface seawater samples and their related materials in the Gulf of Prigi (cont.)

Table 3 .
PLI and HQ assessments of metals in seawater

Table 4 .
Ore lead isotope ratios and geological ages a Not included in calculations for the growth curve development.-: geological age of present day.

Table 5 .
Calculated Pb isotope ratio development, using single-stage model 1