Relationship between Potential Trace Elements Contamination in Sediment and Macrofauna in the Upper Gulf of Thailand

The relationship between heavy metal contamination in sediment and macrofauna in the upper Gulf of Thailand is presented as an indication of the environmental quality of coastal waters. This study aims to monitor five heavy metal elements (As, Cd, Mn, Ni, and Pb) between sediment and the sandworm (Perinereis quatrefagesi (P. quatrefagesi)). The geoaccumulation index (Igeo), enrichment factor (EF), and contamination factor (CF), including the pollution load index (PLI), were used for statistical analyses by one-way analysis of variance (ANOVA), and differences in the data were compared using the least significant difference (LSD) test. The sediment heavy metal concentrations were found to decrease (Al > Mn > Pb > Ni > Cd > As), and the quantity of heavy metal contamination in the sediment was not over the emergency point defined by the Pollution Control Department in Thailand. The Mn at the SH and SP points has Igeo > 0 but <1 and is considered not polluted to moderately polluted. The EF overall is <2 and is deficient in mineral enrichment. The CF of the Samut Sakhon (SH) and Samut Prakan (SP) sites had high Al and Mn values, indicating a low pollution level, but the PLI had an all-site average of 0.0215 ± 0.0252, which is <1. This indicates that the present areas are close to ideal and not polluted. To measure heavy metals in macrofauna, P. quatrefagesi was assessed, and concentrations were found to decrease (Mn > Ni > Cd > Pb > As). The Mn between sediment and the sandworm was directly correlated (r = 0.976; p < 0.01). The sandworm performs as a bioindicator for the quality of coastal sediment, specifically with Mn; thus, the result present at a baseline level may grow in the future if there is no control measure for defensive measures.


Introduction
Since the upper Tai Gulf connects to the central and eastern regions of Tailand, it has become a hub for industry and agriculture. However, the Tai Gulf is a semienclosed topical sea and serves as a boundary to Malaysia, Cambodia, and Vietnam [1]. Te upper zone of the Tai Gulf is connected to the industrial zone and major city and has similar characteristics to ก (Kor Kai is the 1 st Tai alphabet). Efectively, locals refer to this zone as "Auw Kor Kai" or "Kor Kai Bay," and its area encompasses seven provinces: Samut Sakhon, Samut Prakan, Samut Songkhram, Chachoengsao, Chonburi, and Rayong. Te major rivers of Tailand that empty into the upper Tai Gulf are the Chao Phraya, Mae Klong, Ta Chin, and Bang Pakong. However, the sandy beaches around the country's tropical regions encourage rapid urban development and tourism. Te upper zone of the Tai Gulf also has sandy beaches in the provinces of Chonburi, Rayong, and Phetchaburi and supported over 28 million visitors in 2016 [2,3]. Te sediment comprises the physical dynamics that accommodate and are used by biota, and it serves as a bioindicator of environmental quality [4]. Te primary principle of sustainable development is the protection of the environment from human activity, especially in developing countries [5], and one component of protecting the environment is monitoring environmental quality [6]. However, elemental contamination in sediment can also be a secondary source of water quality issues, such as environmental change, and determining the level of heavy metal contamination in sediment is a crucial component of risk evaluation and monitoring in aquatic environments. In the study, we used the geoaccumulation index (I geo ) and enrichment factor (EF) to measure the level of anthropogenic contaminant deposition in sediment and the pollution load index (PLI) to determine the pollutant's concentration in each individual sediment particle.
Macrofauna is an animal group ranging in size from 0.5 to 5 cm that inhabits soft sediment, sand, and mud, and they are associated with fragmentation and decomposition of organic matter as well as nutrient uptake from organic matter, which promotes growth and biofltration [7,8]. Furthermore, macrofauna is among the most suitable organisms for bioindicators and bioaccumulators in environmental monitoring studies as they use nutrients from the beach for maintenance and survival [9,10]. Tese nutrients act as specifc and appropriate biotic tools that can be used when monitoring environmental changes caused by toxic contamination in an area [11,12], especially for heavy elements that chronically contaminate the food chain. Nevertheless, this study investigates the macrofauna in the sediment of the upper Tai Gulf to assess whether its ratios of heavy metal absorption refect those of the environment, and the aim is to evaluate the relationship of heavy metal contamination between the beach sediment and macrofauna of the upper zone of the Tai Gulf. Tis research selected its environmental monitoring areas using literature reporting environmental contamination in the upper zone of the Gulf of Tailand and focused its survey on fve heavy metals (As, Cd, Mn, Ni, and Pb) in the sediment and macrofauna. Te macrofauna used in this research was the sandworm Perinereis quatrefagesi (P. quatrefagesi), which is distributed in the sediment around the upper Tai Gulf. P. quatrefagesi is responsible for the decomposition of aquatic animals on the coast, which makes it extremely appropriate for indicating the environmental quality [13][14][15] of the upper zone of the Tai Gulf. Tis article's presence aims to focus on monitoring elemental contamination in the upper zone of the Tai Gulf area, where there are industrial and agricultural zones with high vulnerability to pollution distribution in the environment, as well as the upper zone of the Tai Gulf being very important to the country's local fshery. Te fndings of this study suggest that environmental monitoring of sources of pollution will support the continuation of environmental protection policies in the future.

Te Sample Collection Areas.
After 1958, Tailand developed from an agricultural country to an industrial one by opening the public sector and investing in the country. From 1986−1991, the country developed the industrial sector so quickly that Tailand was designated as a newly industrialized country (NIC) of Asia [16]. Presently, the industrial and service sectors represent the majority of the gross domestic product (GDP) of the country [17]. Concurrently, rural areas are being urbanized, which increasingly afects residential areas in the economic zones, and the populations of high-density cities are growing, which is characteristic of urbanization in the country [18]. Te sediment may contain some elemental residue, afecting pollutant levels in the environment.
Te sediments around the upper zone of the Tai Gulf have collected during the day from 10 : 00 AM to 3 Figure 1. A quadrate was used to create a margin area on the foor and collect sediment at a depth of 0-5 cm, or about 100-200 g, in the red graphic of the quadrate. However, the sample shall have a weight of about 1.3 kilograms per station and be a homogeneous mixture prior to collection in a polypropylene bag.

Sediment and Macrofauna Collection and Extraction.
Te sediment was collected from the same sample collection points and mixed homogeneously. Sediment samples weighed approximately 5 kg at each site. Te microfauna sample collection was conducted within 0.04 m 2 of the quadrat sampler at depths of 0-5 cm using mattock plastic. Twenty samples were collected at each site to ensure the collection of P. quatrefagesi, and samples were soaked and stored in absolute ethanol before analysis in laboratories. However, successful sample collection of microfauna only occurred at three sites in this study: SH, CH, and SP.
Te sediment samples were dried in a hot air oven at 105°C for 168 h until dry. Tey were then ground using a mortar and pestle. Net no 20 sifted soil was selected for extraction and used in ICP-OES analysis. For this, 2 g of each soil sample was mixed with concentrated hydrofuoric acid (HF), concentrated perchloric acid (HClO 4 ), and concentrated nitric acid (HNO 3 ) at a 1 : 1 : 1 ratio, totaling 20 mL. Extractions occurred at 500°C in a SpeedDigester K-425 BUCHI (Switzerland) until dry. Each residue was rinsed with 1% HNO 3 and sieved through flter paper. Te supernatant was transferred to a 50 mL volumetric fask, and 1% HNO 3 was added for continued inductively coupled plasma (ICP) analysis in a PlasmaQuant 9100 series (Germany).
For the sandworm heavy metal analysis, 1 g of wet weight was soaked in 10 mL of concentrated HNO 3 in a beaker for 24 h. After initial digestion, concentrated HF, HClO 4 , and HNO 3 were added in a 1 : 1 : 1 ratio, totaling 10 mL. Extractions were performed at 500°C in a SpeedDigester K-425 BUCHI (Switzerland) until dry. Each residue was rinsed with 1% HNO 3 and sieved through flter paper. Te supernatant was transferred to a 20 mL volumetric fask, and 1% HNO 3 was added for ICP analysis in a PlasmaQuant 9100 series (Germany), and the sample was compared with the ICP multielement standard solution of the AccuStandard (USA).

Geoaccumulation Index (I geo ), Enrichment Factor (EF), and Contamination Factor (CF).
Te geoaccumulation index (I geo ) was originally formulated by Muller [19] and is a quantitative measure of pollution in aquatic sediment [20]. It was developed through an understanding of the lithogenic efect. I geo was derived using the following formula: where C n is the measured concentration of an element in the sediment and B n is the background value of the element. Te interpreted values of I geo are <0 � not polluted, 0-1 � not polluted to moderately polluted, 1-2 � moderately polluted, 2-3 � moderately to strongly polluted, 3-4 � strongly polluted, 4-5 � strongly to extremely polluted, and >5 � extremely polluted. Te enrichment factor (EF) was derived by the following formula: where (C/RE) sample is the concentration (C) of an element to a reference element (RE) in the samples, and (C/ RE) background is the concentration (C) of an element to a reference element (RE) present in the background. Aluminum (Al) was used as the reference element, as it is a major component of clay, and the interpreted values of EF are <2 � defciency to mineral enrichment, 2−5 � moderate enrichment, 5−20 � signifcant enrichment, 20−40 � very high enrichment, and >40�extremely high enrichment. Te concentration factor (CF) is approximated as the ratio of the observed concentration of an element in the sample (C i ) to the background level of the same element (Cb). Te concentration factors were calculated as follows: Te interpreted values of CF are <1 � low pollution level, 1−3 � moderate pollution level, 3−6 � considerable pollution level, and >6 � very high pollution level.
Te background element values for the I geo , EF, and CF calculations were formulated from the references for As and Ni [21], Al and Pb [22], Cd [23], and Mn [24].
After calculating the concentration factors, they were used to calculate the pollution load index (PLI), which demonstrates the general contamination level [25]. Te formula for PLI is as follows: where CF is the contamination factor of the elements and n is the number of observed elements. Te interpreted values of PLI are 0 � perfection, <1 � baseline level, and >1 � polluted.

Statistical Analysis.
Data were analyzed using a one-way analysis of variance (ANOVA), and the diferences in the datasets were compared using the least signifcant diference (LSD) test with a p value of <0.05. Correlations of data were assessed using Pearson's r correlation coefcient (p < 0.05). All analyses were conducted using Statistical Package for the Social Science (SPSS) v.22.

Te Quantity of Heavy Metals in the Sediment of the Tai
Gulf. Te heavy metal content in the sediment of the upper Tai Gulf was mainly composed of Al, and the average concentration of Al in the samples was 15,642 ± 2,020 mg/ kg dry weight. Te heavy metal concentrations of the samples exhibited the following pattern: Al > Mn > Pb > Ni > Cd > As. Te sediment concentrations of heavy metals in the upper Tai Gulf are presented in Table 1. Te concentration of Al was higher at SH (55,358 ± 802 mg/kg) and SP (12,337 ± 770 mg/kg), but not signifcantly higher at all the sample collection sites. Te average sediment As concentration was 0.0612 ± 0.0225, and the As concentration was signifcantly higher at the PB site than at the SS collection site (p < 0.05). Te Pb concentrations at the SH, CH, and SP collection sites were not signifcantly diferent but were signifcantly higher than those at the PB and SS sites (p < 0.05). Te Cd concentration was high at the SP site and signifcantly diferent (p < 0.05) from the SH, CH, and PB collection sites. Te Mn and Ni concentrations were signifcantly higher at the SP site (p < 0.05) than at the SH, CH, PB, and SS collection sites. Te concentrations of heavy metals in the sediment of the upper Tai Gulf stand were compared to the emergency points of contamination. In using the scale of land use for agriculture and residential areas by the Pollution Control Department [26], reported metal concentrations are Cd < 67 mg/kg, Mn < 1.7 g/kg, Ni 140.4 mg/kg, Pb < 400 mg/kg, and As < 3.9 mg/kg. Tus, the averages of heavy metals in this series do not exceed the standard for any element. Te amount of Al between study sites, however, is not statistically signifcant, but there are differences in the volume because the nature of the sediment component varies depending on the site. For example, the PB and SS sites have a majority of sand components, whereas the SH, CH, and SP sites almost exclusively have alluvial soil components, which has an impact on the number of elements in the area.   Table 2, which aligns with Tongra-ar et al. [27], who presented the geoaccumulation indices (I geo ) of Cd and Ni at values below 0. However, in this study, Mn in the SH and SP collection sites had high I geo values over 0 but <1 (0.1873 and 0.5936, respectively). Tis indicates that SH and SP are not polluted or moderately polluted with Mn. Te Al at SH was 0.6376 ± 0.0062, which means that the area was not polluted to moderately polluted with AL. Te I geo of Al at SH was signifcantly diferent (p < 0.05) from those at the CH, SP, PB, and SS sites. Te I geo of As showed no signifcant diferences among any study sites. Mn and Ni I geo values showed signifcant diferences among all study sites (p < 0.05). Pb I geo values between the PB and SS sites were not signifcantly diferent, but the two sites were signifcantly diferent (p < 0.05) from the SH, CH, and SP sites. Nevertheless, the I geo of the sediment of the Tai Gulf indicates that the area is mostly not polluted, and some areas are experiencing light to moderate contamination [28].
Te EF values in the upper Tai Gulf area are lower than 2, meaning that the sediment has a defciency in mineral enrichment (Table 2). Te EFs of As, Pb, and Cd between the PB and SS sites were not signifcantly diferent, but the EFs of As, Pb, and Cd at the PB and SS sites were signifcantly diferent (p < 0.05) compared to those at the SH, CH, and SP sites. Te EF of Mn at the SS site was signifcantly higher (p < 0.05) than that at all other study sites. Te EF of Ni at the SS site was signifcantly higher (p < 0.05) than that at the SH, CH, and SP sites but was not signifcantly diferent from that at the PB site. Te EF values of the upper Gulf of Tailand indicate low coastal heavy metal contamination. Two sample sites had CF values >1: Al (6.512 ± 0.0943, considerable pollution) and Mn (1.539 ± 0.0166, moderate pollution) at SH, and Mn (3.923 ± 0.0263, considerable pollution) and Al (1.451 ± 0.0906, moderate pollution) at SP.
Te three analyses illustrate the sediment quality of the upper Gulf of Tailand. Te SH and SP collection sites present Al and Mn as ranging from high to overrecommended levels to no pollution. Terefore, PLI is important to use when conducting holistic environmental monitoring of coastal areas in the Gulf of Tailand. Te average PLI of all sites in this study was 0.0215 ± 0.0252, which is <1, and indicates that the areas are ideal and not polluted [29,30]. Te PLI values of the SH and SP collection sites were signifcantly diferent (p < 0.05) from all other sites, as shown in Table 3.

P. quatrefagesi in Sediment.
Macrofauna is used as bioindicators of coastal environments, as they indicate environmental quality. Te sandworm P. quatrefagesi is a bioindicator of acute pollution conditions for heavy metals [31,32]. Te sandworms in this study were collected from three sites: SH, CH, and SP. Te features and characteristics of the sandworms from the study sites are presented in Figure 2. As concentrations were signifcantly higher in worms from the SP collection site (p < 0.05) than in those from the SH and CH sites, the Pb and Cd contamination in the sandworms from the SH and SP collection sites were signifcantly diferent (p < 0.05) compared to the CH site. Te Mn concentrations in the worms were signifcantly diferent (SP > SH > CH, p < 0.05), and the Ni concentrations in sandworms from all study sites were not signifcantly diferent. Te sandworm heavy metal concentrations are presented in Table 4. P. quatrefagesi is the optimal bioindicator for copper, manganese, lead, and cadmium [33,34]. Te sandworm is the primary way heavy metals are introduced into the food chain, as they efciently absorb heavy metals from the environment [35,36].

Correlation between Heavy Metals in Sediment and P. quatrefagesi.
Te correlation between sample location and heavy metals in sediment and sandworms was evaluated using Pearson's r correlation coefcient. Positive correlations were detected in the sediment for manganese (r � 0.710; p < 0.05), lead (r � 0.691; p < 0.05), and cadmium (r � 0.671; p < 0.05), and arsenic was positively correlated between sample location and sandworm (r � 0.671; p < 0.05). Cadmium heavy metal contamination between sediment and the sandworm was signifcantly positively correlated (r � 0.969; p < 0.01); similar correlations were also seen with lead and manganese in the sandworm (r � 0.993; p < 0.01). Lead in the sandworm and manganese in the sediment were signifcantly positively correlated (r � 0.970; p < 0.01), and lead in the sandworm and cadmium in the sandworm were also signifcantly positively correlated (r � 0.954; p < 0.01). Lead in the sandworm and nickel in the sediment were signifcantly positively correlated (r � 0.916; p < 0.01). Te correlations of the other components are presented in Table 5.

Factor Analysis of Heavy Metal Components of Macrofauna and Sediment.
Te factor analysis of the parameters of the 11 components (heavy metals, sediment, and sandworms) was performed using principal component analysis (PCA). Te components found that three PCs had an eigenvalue >1 and explained 88.89% of the cumulative variance in the dataset (  Figure 3). Te location was the most important contributor, for which the highest factor load was 0.9394. Location was followed by the primary loading factor, cadmium in sediment (0.8449), and in PC2, the three components were lead in sandworms, cadmium in sandworms, and nickel in sediment. In PC3, arsenic in sediment was found to be an important factor. Te PC distributions are presented in Figure 3.

Quality of Sediment around the Upper Gulf of Tailand.
Te results of the PCA found that location afects the level of heavy metals in sediment and macrofauna. Tis is also demonstrated by the PLI results, which indicate that the locations of this study are close to ideal. Tis shows that the coast of the upper zone of the Gulf of Tailand has good environmental quality. However, PLI analysis for surveying environmental quality is only one method for monitoring the environment [37], and it is important in long-term coastal environmental assessments and risk evaluations to use other indicators in conjunction with PLI analysis [38,39]. Furthermore, in this study, the EF of all components and all areas was <2, which indicates a defciency in mineral enrichment. Additionally, I geo and CF signify no Al or Mn pollution, and Al is the major element of this soil, which is readily absorbed by bottom sediments in the form of metastable compounds [40]. Mn is a product of anthropogenic activity and street dust and is an infuential indicator of coastal environmental quality [41,42]. Its existence is an indicator of human activity on land, which afects the quantity and type of heavy metals in sediment [43,44].

Performance of Sandworms as Bioindicators for Heavy
Metals. Te PCA and PC2 results showed that Pb and Cd had high loadings in macrofauna (0.9852 and 0.9654) and were important factors for this analysis. Te sandworm (Perinereis spp.) is the optimal macrofauna to be collected  and used to detect Zn, Cu, Pb, and Cd in the sediment [45,46]. However, in the heavy metal concentration correlation analyses, only Mn was shown to be directly correlated between sediment and macrofauna (r � 0.976; p < 0.01). Mn concentration in Perinereis spp. is indicative of human activity, which may afect sediment and cause chronic or acute pollution conditions [32]. Te ability of polystyrene microplastics to contaminate seawater and sediment is also linked to bioaccumulation within Perinereis spp. [47].

Conclusion
Te sediment heavy metal concentrations were found to decrease (Al > Mn > Pb > Ni > Cd > As), and the quantity of heavy metal contamination in the sediment was not over the emergency point defned by the Pollution Control Department in Tailand. Mn at the SH and SP collection sites had an I geo , which is considered not polluted to moderately polluted and represents a gray area where there is the possibility of pollutants increasing to a crisis point if defensive measures are not taken in the future. Te EF overall was defcient in mineral enrichment. Te CF of the SH and SP sites had high Al and Mn values, indicating a low pollution level, but the PLI had an all-site perfection level. However, Al is a major component of parent soil sediment in the central region, although Mn levels are rising due to intense trafc and transit that includes industrial zones. Tis indicates that the present areas are close to ideal and not polluted, but the present result at a baseline level may increase in the future if no defensive measures or controls are taken. To measure heavy metals in macrofauna, P. quatrefagesi was assessed, and concentrations were found to decrease (Mn > Ni > Cd > Pb > As). Te Mn between the sediment and the sandworm was directly correlated. Te sandworm contributes as a bioindicator for the quality of coastal sediment, particularly when Mn is present. However, sediment and macrofauna are important instruments for measuring and monitoring the environmental conditions associated with pollution in the estuarine and Gulf of Tailand ecosystems around the upper zone of the Gulf of Tailand.

Data Availability
All the data generated and analyzed during the current study are included in this published article and are available from the corresponding author upon request.

Conflicts of Interest
Te authors declare that they have no conficts of interest.

Authors' Contributions
Pakjirat Singhaboot and Kun Silprasit designed the research methodology. Arin Ngamniyom collected samples. Patarapong Kroeksakul planned the project and was the main writer of the manuscript. basis for weighing the public interest and individual interest in