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Article

The Geochemical and Environmental Characteristics of Trace Metals in Coastal Sediment Discharge off the Mailiao Industrial Zone of Central Western Taiwan

by 1,2,* and 1
1
Department of Marine Environmental Informatics, College of Marine Science and Resource, National Taiwan Ocean University, Keelung 202, Taiwan
2
Institute of Marine Biology, National Dong Hwa University, Pingtung 974, Taiwan
*
Author to whom correspondence should be addressed.
Water 2023, 15(2), 250; https://doi.org/10.3390/w15020250
Received: 17 November 2022 / Revised: 13 December 2022 / Accepted: 4 January 2023 / Published: 6 January 2023
(This article belongs to the Special Issue The Geochemical Behavior of Trace Elements in Inshore Environments)

Abstract

:
The geochemical fractions of trace metals in the coastal sediments of the central western Taiwan were examined, employing the Tessier sequential extraction method, and the metals contamination status of the analyzed sediments were also evaluated in the present study. Based on the metal fraction present in sediments, trace metals can be divided into three groups: (1) Al, Cr, Fe, Ni and Zn; (2) Cu and Pb and (3) Mn. In group (1) metal, the metals’ total concentrations were chiefly dominated by the residual fraction, exceeding 80% of the total concentration pool. In group (2) metal, the metals’ total concentrations were dominated by three labile fractions, carbonate, Fe-Mn oxides and organic, accounting for nearly 65% of the total pool, and the residual fraction contributed 35% of the total concentrations. Over 90% of Mn total concentrations were shared by three fractions, carbonate, Fe-Mn oxides and the residual fraction. The statistic results indicated that the total organic carbon contents in sediments played a more important role in influencing the metals contents in sediments. The contamination assessment results suggested that the Mailiao coastal sediments were minorly contaminated by trace metals. Lead should be paid more concerns because Pb total concentrations at some sediments exceeded the value (46.7 mg/kg) of effect range low, USA, and Pb was mainly present in the labile fraction.

1. Introduction

The Mailiao Industrial Zone (MIZ) was constructed on the artificial land located at the Yulin county in the central western Taiwan. The MIZ was constructed from 1991 by the ministry of economic affair, Taiwan, and finished in 1994. The MIZ was approximately 2255 hectares. The constructed purpose of the MIZ is to provide an industrial zone for serving the Formosa Petrochemical Corporation (FPC), Formosa Plastic Industrial Group and some chemical industrial companies. Currently, more than 60 industries are located at this MIZ and the annual production value of the MIZ is approximately 50 billion US dollars. The MIZ has 10 wastewater treatment plants and the treated wastewater, ca. 8–9 × 104 m3/d, is discharged into the inshore environment after mixing with the cooling seawater, ca. 13 × 106 m3/d, through a diversion dike (https://www.fpg.com.tw, accessed on 1 August 2022). The cooling seawater is pumped from the harbor of the MIZ to maintain the manufactory’s normal operation. In order to protect the marine ecology of the coastal area around the MIZ, the authority of MIZ has the obligation to seasonally investigate the water quality and ecology of the inshore environment around the MIZ and submits the survey report to the Environmental Protection Administration (EPA), Taiwan, and is open to the public (https://www.epa.gov.tw/DisplayFile, accessed on 1 August 2022)
The Mailiao coastal seawater is not only impacted by the wastewater discharge from the MIZ but is also influenced by the discharges of the Choshui River and the New Huwei River. The Choshui River and the New Huwei River are located at the north and south of the MIZ coast, respectively. The Choshui River is the longest river (186 km) in Taiwan and its catchment area is approximate 3157 km2. The annual mean discharge flow and sediment flux in the past 30 years are approximately 61 km3/y and 60 Mt/y, respectively [1]. The Chinese meaning of the Choshui River is the turbid water. It is indicated that the western coastal rivers in Taiwan deliver an average of ~80 Mt of fluvial sediments annually to the Taiwan Strait, half of which comes from the Choshui River [2]. The monthly average river flow rates of the Choshui River during the years 2012–2017 ranged from 2.50–1005.07 m3/s [3], and all the data are shown in Figure 1a which indicates that the higher river flow rate generally occurs from April to June due to the southern Asian monsoon climate. In addition, Taiwan Island is located along the so-called “Typhoon Alley” in the northwestern Pacific. Thus, the episodically extremely heavy precipitation may occur during July to September when a typhoon is coming. The monthly average particle flux of the Choshui River is not available and only the discrete date of particle flux is recorded [3]. The values ranged from 39.92–8,402,324 ton/day during the years 2016–2017 and the recorded data are also plotted in Figure 1b. The river flow rate against the particle flux recorded in the same day during the years 2016–2017 is plotted in Figure 1c which clearly shows that the particle flux positively correlated well with the flow rate, suggesting that the river flow rate dominantly determines the particle flux in the Choshui River. Abundant sand and mud from this river are deposited along the Mailiao coast due to the northward and southward tidal flow along the coast [4].
The New Huwei River is a relatively small river, and no river flow rate is recorded in this river [3]. However, this river is a pollutant source, especially for nutrients, because many activities, including rice farming, aquaculture and pig farms, are conducted along the river sides and the wastewaters are discharged into the river through small canals, meaning that the river has severe eutrophication and pollutes the water quality of the inshore environment, particularly after heavy rainfall which flushes a large amount of the pollutants into the inshore environment [5]. Nevertheless, the seasonal investigation report did not show many anomalous values and the seawater quality around the MIZ coast generally obeyed the seawater quality criteria of EPA, Taiwan. A few exceptions of dissolved ammonium and total phosphate, exceeding the seawater quality criteria, were occasionally reported. In addition, Cr and Ni concentrations of the Mailiao coastal sediments frequently exceeded the effective range-low (ERL) biological effect guideline value (Cr, 81 mg/kg; Ni, 20.9 mg/kg, [6]) (http://www.epa.gov.tw/np.asp?ctNode=32970&mp=epa, accessed on 1 August 2022). However, the seasonally monitoring project carried out by the authority of MIZ generally focuses on total concentrations of trace metal in the Mailiao coastal sediments. The national survey of the water quality of the Taiwanese rivers carried out by EPA, Taiwan, generally focuses on the dissolved phases and occasionally investigates the compositions of river sediments. The survey results of total concentrations of trace metals in sediments of the Choshui River and the New Huwei River during the 2015-year and 2019-year survey, respectively, are shown in Figure 1d,e (https://Sed.epa.gov.tw/Sediments_Public/Query, accessed on 1 December 2022). The concentrations of trace metals in sediments of the Choshui River and the New Huwei River during these investigations were generally much lower than the effect range low (ERL) value, EPA USA, with the exception of Ni concentration, which ranged from 17.3–20.6 mg/kg in the Choshui River and 21.5–35.7 mg/kg in the New Huwei River. The Ni ERL value, EPA USA, is 20.9 mg/kg. The concentrations of trace metals in sediments of the New Huwei River were generally higher than those of the Choshui River, as shown in Figure 1d,e. This result suggests that the New Huwei River contains more pollutants than the Choshui River, as mentioned above.
It is indicated that marine organisms tend to utilize more the labile fraction than the residual fraction of trace metals in marine sediments, because the residual fraction of trace metals is mainly present in the crystal lattice and has very strong bonding [7,8]. Thus, from the geochemical view and understanding the bioavailability, toxicity and mobility of trace metals in marine sediment, it is probably more important to know the metals’ speciation than the metals’ total concentrations in the marine sediment [9,10,11,12]. Briefly, from view of the chemical resistance, the metals speciation in marine sediment can be simply divided into the labile and the residual fractions [9,10]. The labile fraction is considered the easier dissolution and mobilization under environmental conditions such as pH and redox potential, change, the benthic organism interference, and during the diagenetic process under the sediment burial processes [9,10,11]. Many analytical methods have been developed to quantify the metal species in marine sediment ([11], and references cited therein). Thus, in order to distinguish the geochemical fractions and contamination status of trace metals in the Mailiao coastal sediments, the present study pioneeringly employed the sequential extraction method published by Tessier et al. [12] to identify the trace metal speciation in the Mailiao coastal sediment. In addition, three typically environmental indices, namely the enrichment factor, geo-accumulation index and risk assessment code, were applied to evaluate the trace metal contamination status of the Mailiao coastal sediments.

2. Materials and Methods

2.1. Study Area

Twenty-two surface sediment samples along the Mailiao coast in the central Taiwan were seasonally collected on 6 January, 14 April, 13 July and 17 November, respectively, in 2017 by employing a fishing boat. The surficial sediment samples were collected using a grabber and placed in clean plastic bags. Samples were immediately placed in a cooler box on board and sent back to the laboratory as soon as possible. The sampling stations along the Mailiao coast are shown in Figure 2. Stations 1–5 and stations 15–17 were located outside of the Choshui River and the New Huwei River estuarine mouths, respectively. Stations 9–14 resided outside of the wastewater discharge point of the MIZ. As mentioned above, the Mailiao coastal seawater is impacted by three discharges from the Choshui River, the New Huwei River and the treated wastewater from the MIZ. The impact from the two rivers is dependent upon the river discharges, which vary significantly throughout the dry and rainy seasons, as shown in Figure 1a. The influence of the treated wastewater discharge from the MIZ was fairly stable because the discharge volume varied minorly, and the major component of the treated wastewater was the cooling seawater.
As well as the impacts from the three water discharges, the seawater quality of the inshore environment may be altered by tidal currents, Asian monsoons and the Earth’s rotation [13,14]. The tidal range in the central west Taiwan coast is generally >4 m, belonging to the macro-tide. The large tidal current generates strong tidal currents flowing northward along the shelf coast during flood periods and moving to the south during ebb periods [5]. In addition, the coastal current around the Taiwan Island is significantly modulated by East-Asian monsoons. The southwest monsoon blows from the South China Sea and generally occurs from May to September. The rainy season around the Taiwan Island occurs at the end of May, extending to mid-June, and the tropical typhoon occasionally hits the Taiwan Island during these months, as mentioned above. The northeasterly monsoon prevails from October to March, usually peaking in December and January, which brings strong wind and dust from the Mongolian Plain [15]. Thus, the sediment resuspension in the Mailiao coastal water is frequently observed in the winter season because the strong wind induces the strong current [16].

2.2. Analytical Methods

When the collected samples were sent back to the laboratory, the samples were further processes and determined the metals fractions according to the Tessier’s five-step sequential extraction method [12], the total organic carbon (TOC) and the grain size. The detailed analytical procedure of TOC and grain size can be found elsewhere [17,18]. The measurement of grain size in the sediment samples was divided into four fractions: medium sand (MS, >177 μm); fine sand (FS, 125–177 μm); very fine sand (VFS, 63–125 μm) and mud (<63 μm). The trace metal fractions in the sediment were analyzed by the Tessier’s method which chemically divides the trace metals into five fractions: exchangeable, hereafter refers to as fraction 1 (F1); bound to carbonate (F2); bound to Fe-Mn oxides (F3); bound to organic (F4) and residual (F5). The metal fractions, chemical treatment and the possible reaction mechanisms of the Tessier’s method can be referred to the literature [12,19,20]. The MESS-3 reference material was employed to seek the analytical quality of the trace metal fraction determination. Table 1 shows the results of the analytical accuracy, defining the measured metals total concentrations to the certified value. The analytical accuracy of the most trace metals generally ranged from 82–110%, with the exception of Al of which the value was approximately 69%. The analytical accuracy of the MESS-3 reference material analyzed in the present study was consistent with the previous studies, which indicated that lithological characteristics of marine sediment reference materials (MSRM) may have been responsible for the relatively lower accuracy of Al in the MSRM analyzed by sequential extraction method [19,20].

2.3. Trace Metals Contamination Assessment

For protecting the coastal environment and sustaining the marine ecology, many countries in the world have set the sediment quality guidelines (SQGs) to evaluate the contamination and pollution status of the marine sediments in the last three decades [8,21,22]. The metals concentrations in marine sediments may vary significantly, depending on the grain size, bulk minerals and heavy mineral fractionation [9] and may markedly differ from different areas worldwide [23]. Thus, in order to more fairly assess the metal contamination and pollution status in marine sediments, many methods have been developed to compensate the metal concentrations variations induced by grain size, bulk minerals and heavy mineral fractionation [9,24,25,26,27]. The commonly employed methods include the enrichment factor (EF), geo-accumulation index (Igeo), individual contamination factor and potential ecological risk assessment code (RAC). The detailed descriptions of these three assessment methods can be found elsewhere [23,27,28]. The present study also employed these three methods to examine the contamination/pollution status of trace metals in the Mailiao coastal sediments.

3. Results

3.1. Grain Size (GS) and TOC

The grain size and TOC content in surface sediments of the Mailiao coast obtained during the four surveys ranged between 11–463 μm and 0.12–0.52%, respectively, and all the data obtained at each station are plotted in Figure 3. The sediment GS at the same stations observed in the different surveys generally varied minorly, except at stations 1, 18, and 22 which exhibited significantly differences from the different surveys. The TOC contents in surface sediments at the studied stations generally fell in the range of 0.1–0.3%, but a relatively higher concentration, ranging within 0.4–0.5%, was observed at stations 15–16 which were located inside the Mailiao industrial harbor. The sediment GS at these two stations was the finest among the studied stations and was generally <30 μm. The TOC contents in marine sediment generally inversely correlated with the GS because the finer GS had the larger surface area [9,29]. However, Figure 3c shows the plots of GS against the TOC content in all data and both parameters seem not to inversely correlate well, suggesting that the GS influencing the TOC content in the analyzed sediment samples was not so significant. This interpretation will be addressed more in the following section.
The percentages of the four fractions of GS in sediment at each station are plotted in Figure 4 which indicates that the percentage variations of the GS fractions in the different surveys were not so obvious, except for the third season survey (13 July 2017). Basically, the sediments at stations 1–14 were commonly dominated by the fine sand (125–177 μm) and very fine sand (63–125 μm), except in the third season survey. Whereas the sediments at some stations, such as stations 1, 5, and 6, were occasionally governed by medium sand (MS, >177 μm). The sediments at stations 15–22 seemed to be dominated by very fine sand (63–125 μm) and mud (<63 μm). In the third season survey, the sediments at some stations of stations 1–14 seemed to be dominated by very fine sand and mud, which was contrast to the other surveys. Vice versa, the sediments at stations 15–22, except stations 16 and 19, were dominated by medium sand and fine sand during the third season survey.

3.2. Trace Metals

The metals total concentrations range and the percentage range of each metal fraction obtained at all the stations during the four surveys are shown in Table 2. The five-fraction concentrations of trace metals in surface sediments at the studied stations during the four surveys are plotted in Figure 5, Figure 6, Figure 7 and Figure 8. It seemed that the metals’ total concentrations slightly differed from the different surveys, and concentrations found at stations 1–12 were generally lower than those at stations 13–22. The SQGs, effects range low (ERL), of the US EPA [6] was used to quickly examine the contamination status of trace metals at all the stations. The examined results indicated that the metals’ total concentrations, except Ni and Pb, were generally lower than the ERL values. In contrast, all the Ni total concentrations and Pb concentrations at some stations were higher than the ERL values. The detailed interpretations of the contamination status of trace metals in the Mailiao coast is described below.
Based on the metal species present in the Mailiao coastal sediments, the trace metals can be divided into three groups: (1) Al, Cr, Fe, Ni and Zn; (2) Cu and Pb and (3) Mn. Table 2 and Figure 9, Figure 10, Figure 11 and Figure 12 show that the total concentrations of trace metals in group (1) were chiefly dominated by the residual fraction (F5). The F5 of Al and Fe, and of Cr, Ni, as well as Zn, averagely exceeded 91–98% and 70–80% of their total concentrations, respectively, during the four surveys. In this group, the importance of the other fractions differed from the different metals. For Fe, the Fe-Mn oxides (F3) species played the second important fraction and occupied approximately 8% of their total concentrations. The contributions of the other three fractions to the total concentrations were relatively minor and generally <2%. The Fe-Mn oxides (F3) fraction of Ni and Zn also ranked the second important fraction and accounted for an average of 12% and 16% of their total concentrations, respectively. The contribution of the carbonate (F2) plus the organic (F4) fraction nearly equalized to the Fe-Mn oxides (F3) fraction. In contrast, the contribution of F3 to the Cr total concentrations was insignificant. Instead, the contribution of carbonate (F2) fraction nearly equalized to the organic (F4) fraction, and each fraction occupied, on average, approximately 8% of Cr total concentrations.
The residual fractions of Cu and Pb also dominated their total concentrations. However, the predominance was reduced to approximate 35% of their total concentrations. The plus contributions of the three fractions, F2, F3 and F4, accounted for nearly 65% of their total concentrations. The concentrations of these three fractions of Pb nearly equalized. The Cu total concentrations were mainly dominated by F4 and F3, and the F2 fraction was generally < 9% of the Cu total concentrations. The group (3) metal, Mn behaved significantly different from the other metals. The Mn total concentrations were dominated by three fractions, carbonate (F2, 26–51%, average 37%), Fe-Mn oxides (F3, 21–41%, av. 28%) and the residual (F5, 16–38%, av. 27%). The plus concentrations of these three fractions exceeded 90% of Mn total concentrations. In addition, the exchangeable (F1) species occupied approximately 3% of the total concentrations, which was the highest among the studies of the metals. The contribution of F1 species to total concentrations of the other metals was generally insignificant (<0.1%), except Mn, Cu and Ni, as shown in Table 2. Finally, Figure 9, Figure 10, Figure 11 and Figure 12 show that the variations of metal fraction differing from the different surveys were not marked, except Cu and Pb. The organic fraction of Cu and Pb obviously varied during the different surveys.

3.3. Trace Metals Contamination Assessment

The value ranges of the three assessmental indices obtained during the four surveys are also tabulated in Table 2 and the values obtained at each station are plotted in Figure 13, Figure 14 and Figure 15. Figure 13 shows that the EF values of Cr, Fe, Ni, Pb and Zn generally ranged from 1–3, and the values of Cu and Mn approached 1. Whereas the EF values of Pb at stations 10, 11 and 16 during the second season survey exceeded 4. Figure 13 suggests that the studied stations were not or minorly contaminated by trace metals. Figure 14 indicates that the Igeo values of the most trace metals, except Ni and Pb, were generally less than 0. Whereas some values of Cr, Fe and Zn at a few stations ranged from 0–1. Most of the Igeo values of Ni and Pb ranged between 0–1. The result of Figure 14 suggests that the studied stations were practically uncontaminated to moderately contaminated by trace metals. The assessed results of both normalized methods agreed fairly well. Figure 15 shows the RAC percentages of the studied metals which can be divided into four groups: (1) Fe, <10%, low risk to marine organisms; (2) Cr, Ni and Zn, 10–30%, medium risk to marine organisms; (3) Cu and Pb, 30–50%, high risk to marine organisms and (4) Mn, >50%, very high risk to marine organisms. Such a result did not parallel well with the results of the enrichment factor and the geo-accumulation index. The comprehensive evaluation of the contamination status of trace metals in the studied area will be further discussed in the following section.

4. Discussion

4.1. Grain Size and TOC

The temporal variations of the sediment GS suggest that the Mailiao inshore environment was rather hydrodynamic, especially in the north coast, adjacent to the Choshui river’s estuarine mouth. As mentioned above, the Choshui River is very turbid, and the average annual concentration of suspended particulate matter (SPM) can reach up to 11,000 mg/L, which ranks the second highest around the world [30]. Figure 1b shows that the SPM concentrations in the Choshui River water can vary between three orders of magnitude during the different river flow discharge. Previous study has employed the instruments equipped with an array of optical backscatter sensors and acoustic Doppler current profilers (ADCP) to measure suspended-sediment concentrations (SSC), waves and tidal currents in coastal water off the Choshui River estuarine mouth [16]. Their field results indicated that the high-SSC region distributed in the coastal area was strongly influenced by the tidal current speed. The stronger the tidal current off shore, the higher the SSC region. Their results also indicated that the suspended sediment load in the water column was dominated by the resuspension effect because the tidal current could reach 1.5–2.0 m/s during spring tides and the tidal in the western central Taiwan can reach 4–5 m. In addition, due to being located in northeastern Asia, Taiwan is frequently hit by the western Pacific typhoon. The Choshui River has frequently suffered from the hyperpycnal events (when suspended sediment concentrations exceeds 40 g/L) and the sediment load can easily exceed 100 Mt during the typhoon period [30,31]. The large fluctuation of daily tidal and strong tidal current in the western central Taiwan coast induces the re-distribution of the sediment load during the different seasons, complicating the distribution of sediment grain size in the Mailiao coastal environment.
The TOC contents in surface sediments of the Mailiao coast obtained in the present study generally ranged from 0.1–0.3%, with a few exceptions at stations 14–16 (of which grain sizes were relatively finer and were generally dominated by mud). The TOC contents in surface sediments of the coastal environment generally ranged from 0.2–1.0%, with an average of 0.4–0.6% [32,33]. However, the relatively higher TOC contents, 5–14%, in marine sediments have been reported in the Romanian Black Sea coastal sediments, which is attributed to the influence of the wastewater treatment plant discharge [34]. The TOC contents in the Mailiao coastal sediment are relatively lower than those, generally ranging from 0.5–1.0%, observed in the coastal sediments along China, such as the Bohai Sea, the Yellow Sea and the Leizhou Peninsula [33].
The metals total concentrations in marine sediment are generally relevant to the grain size (GS), and the finer the GS, the higher the concentration [29]. The increased surface charge and the exponential increase in surface area with decreasing particle size in the clay-sized particles enhance these finer particles, as they have the strong adsorbed ability and the strong affinity to the chemical contaminants in the water column [35,36,37]. Thus, the trace metal concentrations inversely correlate with the GS in marine sediment [28,38]. In addition, the dissolved organic carbon (DOC) has the high affinity to form the organo-metal complexes with some trace metals, especially for Hg, Cu, Fe and Zn and particulate organic carbon (POC) has the higher adsorption capacity to adsorb trace metals in the water column [7,29]. Thus, the TOC contents positively correlated with the trace metal concentrations in marine sediment is commonly reported in marine sediment [28,38,39,40].
Excel software was used to examine the correlations between the pairs of the trace metals, TOC and grain size, and the calculated results are tabulated in Table 3, which shows that metals total concentrations generally positively correlated with TOC contents in the Mailiao coastal sediments in most surveys, except the 13 July 2017 survey. In contrast, only one survey, 17 November 2017, showed that the metals total concentrations inversely correlated with the GS and Cu concentrations generally inversely correlated with the GS in the different surveys. These results may suggest that the metals total concentrations in the Mailiao coastal sediments were more influenced by the TOC content than the GS. In addition, the concentrations of trace metals also generally positively correlated well with each other.

4.2. Trace Metals

4.2.1. Metals Total Concentrations

The analyzed data of the present study show that the total concentrations of trace metals in the Mailiao coastal sediments were generally lower than the sediment quality guidelines, effects range low (ERL), of the US EPA [6], except most Ni data and some Pb data. The Ni total concentrations in the Mailiao coastal sediments mostly exceeded the ERL value, which was not a surprise in the present study and is consistent with many studies [28,40,41,42,43]. The Ni total concentrations in the marine sediments exceeding the ERL value seems to be the global issue [23,40]. Rudnick and Gao [44] reviewed the Ni concentration, ranging from 19–60 mg/kg, of the upper continental crust shown in ten pieces of literature published from 1967 to 2003. Birch [23] comprehensively reviewed the published paper to evaluate the background concentration and enrichment of trace metals in marine sediment. He indicated that the Ni total concentrations of the upper continental crust range between 18.6–75 mg/kg, and the global mean values in the crust and soil are 47 mg/kg and 49.7 mg/kg, respectively. These Ni concentrations were two to three folds higher than the ERL value. In addition, the particulate nickel concentrations in the large rivers worldwide, such as the Changjiang River (range within 54–59 mg/kg, have a mean of 56 mg/kg, [45]), the Yellow River (28.2–45.6 mg/kg, mean 37.3 mg/kg, [46]), the Amazon River (21.8–87.2 mg/kg, with two relatively high values > 200 mg/kg, [47]), and the Congo River (53.4–141.4 mg/kg, [48]), are also much higher than the ERL value. Thus, the Ni total concentrations in the marine sediments worldwide exceeding the ERL value was not surprising and was probably not related to the anthropogenic influence. A similar result was also indicated by Fang and Lien [40] who suggested that Ni ranks as the most polluted element among trace metals in surface sediments of East China Sea, because the guideline ERL value of Ni in the marine sediment is set too low to obey, maybe lower than the background concentration of some marine environments.
Unlike the other trace metals, the guideline ERL values of some trace metals are much higher than the concentrations of the upper continental crust, inducing that the metal concentration in the marine sediment is very unlikely to exceed the ERL value, even though the metal is obviously polluted. For example, the guideline ERL values of Cd in the marine sediment are 1.2 mg/kg [6], of which value the is 10–15 (folds higher than the concentration in the upper continental crust), ranging from 0.075–0.102 mg/kg [44]. Thus, the metal background concentration should be taken into consideration when employing the guideline ERL values to interpret the contamination status of trace metals in marine sediment.

4.2.2. Trace Metals Speciation

The metals’ concentrations in different fractions of the Mailiao coastal sediments may vary from the different elements, different sediments and different surveys in the present study. The general patterns of the dominant fraction of trace metals in the sediments can be divided into three groups, as mentioned above. Precisely examining the sequence of the average concentration of trace metals in each fraction in the sediment, the fraction sequence of the studied metals is follows as:
  • Fe, Ni, and Zn: F5 > F3 > F4 > F2 > F1
  • Cr: F5 > F2 > F4 > F3 > F1
  • Cu: F5 > F4 > F3 > F2 > F1
  • Mn: F2 > F3 > F5 > F4 > F1
  • Pb: F5 > F4 > F2 > F3 > F1
It is commonly found that the fractions of trace metals in marine sediment analyzed by the Tessier’s sequential extraction method generally follow the order: residual (F5) > Fe-Mn oxides (F3) > organic (F4) > carbonate (F2) > exchangeable (F1), except Mn and Pb [27,39,42,49,50,51,52,53]. However, the organic fraction of Cu frequently ranks as the second important fraction and contributes a significant portion of the total concentrations in some marine environments [27,28,41,49,54]. The reason for this is Cu ranking the second highest stability constant with organic compounds of the Irving-Williams order [29]. Thus, the organic Cu could contribute a significant portion of the total Cu pool in the marine sediments. The sedimentary Mn in the Mailiao coastal sediments is generally dominated by three fractions: carbonate (25–51%, average 37%), Fe-Mn oxides (21–41%, av. 27%) and the residual (16–38%, av. 27%), as observed in many studies [28,38,55,56,57]. The mechanisms elucidating that the sedimentary Mn is dominated by these labile fractions in marine sediment can be found elsewhere [28,38]. The mechanisms are mainly attributed to fact that Mn is a redox-sensitive element and the transformation of Mn species and phase will naturally occur under the different redox conditions and during the diagenetic processes in the sediment. In addition, the formation of dissolved Mn+2 reacts with carbonate to form the rhodochrosite (MnCO3) and particulate Mn is adsorbed onto CaCO3 surface in seawater [58,59]. These reactions may enhance the contribution of carbonate fraction to the total Mn pool in sediment.
The Pb total concentrations in the Mailiao coastal sediments are shared by nearly four fractions: carbonate (12–40%, average 21%), Fe-Mn oxides (7–33%, av. 20%), organic (16–51%, av. 25%) and residual (16–58%, av. 35%). The prestige of the residual fraction of sedimentary Pb is much lower than the other metals, except Mn. This result slightly differs from the previous studies which indicate that the Pb total concentrations in marine sediment are mainly dominated by carbonate, Fe-Mn oxides and residual fractions and the organic fraction is relatively minor [27,28,41,49,54]. However, it has been reported that the organic fraction of Pb ranked as the second important species, lower than the Fe-Mn oxides fraction and exceeded 30% of total concentrations in the estuarine sediment of the Pearl River Estuary, China [60]. A similar result was also observed in the lagoon sediments of the Rio de Janeiro, Brazil, and was attributed to the diagenetic processes which may potentially increase the metal content in the organic fraction or precipitated as sulfides [61]. Due to analyzing the surface sediments, the diagenetic processes increasing the metal content in the organic fraction may not be suitable for the present study. Further investigation is needed into why the Mailiao coastal sediments contain a relatively higher proportion of organic fraction of Pb, as observed in the present study.

4.2.3. Trace Metals Contamination Assessment

The results of the two assessment indices, EF and Igeo, indicated that the Mailiao coastal sediments were not some minor contamination of trace metals, especially for Ni and Pb, because some EF values of both metals exceeded 4. In addition, the RAC values of Cu, Pb and Mn, generally exceeded 30% and 50%, respectively, exhibiting high risk to very high risk to marine organisms. The RAC result was not consistent with the assessment results of the EF and Igeo index. The RAC value of Mn generally presented the highest among the trace metals in the marine sediment study [28]. However, it was not necessary to worry too much about the Mn toxicity to marine organisms in the marine environment. Manganese is an essential micronutrient for most organisms and the toxicity level of Mn to marine organisms is four to six orders of magnitude higher than the seawater concentration [62,63]. This is probably the reason why most countries in the world do not set the guideline value of Mn in the marine sediments [22].
The RAC values of Cu and Pb generally surpassed 30%, indicating high risk to marine organisms in the Mailiao coastal sediments. The Cu total concentrations in the analyzed sediment samples range from 3.75–26.64 mg/kg, with an average concentration of 11.4 mg/kg, meaning the value was much lower than the ERL value (34 mg/kg), USA. Copper is an essential element for marine organisms and ranks as the fifth most abundant concentration of trace metals of marine phytoplankton [64]. In crustaceans, Cu is an integral component of the respiratory pigment, hemocyanin. It was indicated that Cu has a relatively high toxicity toward aquatic organisms and could cause sublethal and lethal effect towards various groups of aquatic invertebrates and fishes from approximately 5 µg/L and 30 µg/L, respectively [8]. The LC50 of dissolved inorganic Cu concentration of some macro-algae generally ranges within 4–100 µg/L [65]. However, dissolved free Cu ion in aquatic environment generally less than 1% of total amount of Cu was present because Cu has a high binding affinity for organic chelators, such as humic and fulvic acids, and algal exudates [29,65]. As a result, the dissolved Cu in the coastal seawater was generally less than 1 µg/L [7,66]. However, the dissolved Cu concentration, exceeding 10 µg/L, in inshore seawater of South China has been frequently observed in the last decade due to heavy contamination by industry activities [67,68]. Such a pollution means that the Cu content in oyster of the surrounding seawater can reach as high as 19,000 µg/g (dry weigh) and the economic loss of the oyster aquaculture has surpassed tens of millions US dollars. However, the oyster still can survive and grow up in such a polluted marine environment [68,69]. The dissolved Cu concentration in the Mailiao coastal seawater is generally less than 1 µg/L [70], and the Cu total concentrations in the Mailiao coastal sediment analyzed in the present study were also much lower than the ERL value, suggesting that the Cu contamination in the Mailiao coastal environment was not significant. Thus, the RAC indice of Cu in the Mailiao coastal sediment may provide a warning signal which indicates that Cu poses a potentially high risk to marine organisms. The corresponding result is also seen for Ni, of which total concentrations mostly exceeded the ERL value. The Ni total concentrations in the analyzed sediments were mainly dominated by the residual fraction, averagely accounting for 75% of the total pool, suggesting that the Ni in the sediments is chiefly derived from lithogenic origin rather than from the anthropogenic sources.
Lead is probably the most threatening metal to marine organisms among the metals studied in the Mailiao coastal sediments because the Pb total concentrations at some sediments exceed the ERL value (46.7 mg/kg), USA and the RAC values generally surpass 30%, indicating high risk to marine organisms. Figure 1d,e indicate that Pb concentration in sediments of the Choshui River and the New Huwei River ranged between 8.66–24.3 mg/kg, approaching Pb concentration, 17–18 mg/kg, of the upper continental crust [44]. These values were much lower than the ERL value (46.7 mg/kg), USA. Thus, Pb total concentrations in the Mailiao coastal sediment exceeded the ERL value, which may imply that it is a significantly anthropogenic source input to the environment. The increasing concentration of Pb in sediments of the East China Sea since 2003 has been confirmed by the Pb isotopic analysis and attributed to the increasing coal consumption due to the economic development [71]. One coal fired power plant, located at the Mailliao Industrial Zone, produces a total of 1.8 GW with three electricity generators (http://www.mimpc.com.tw, accessed on 1 August 2022). Thus, it is assumed that Pb elevated concentration in the Mailiao coastal sediment may partly attribute to the emission of this coal fired power plant, as found in the literature. This assumption needs further verification.
Dissolved Pb ion in seawater is easily adsorbed by Fe-Mn oxides [7]. It is found that the suspended particulate Pb in the marine environment is present primarily as the hydroxyl and carbonate complexes that readily adsorb to particles [72,73] which finally precipitate to the sediments. Thus, many studies have indicated that the Fe-Mn oxides fraction, or the reducible fraction, controlled the Pb total concentrations in the marine sediments [41,47,54]. Lead is considered as a non-essential element for living organisms [7,8]. The toxicity of Pb to marine organisms, such as macro algae and fishes, exposed in different levels of Pb concentration in culture works of the laboratory has been addressed in many studies which indicated that the sub-lethal and lethal concentrations of Pb to marine organisms were generally at mg/L and μM level, varying from the different species of algae and fishes [74,75,76,77]. The Pb dissolved concentration in the coastal water is generally < 0.1μg/L [7,66] of which the value is three to four orders of magnitude lower than the threshold concentration of Pb to marine organisms. Fang and Dai [70] investigated the trace metals in the water column of the Mailiao harbor and indicated that the Pb dissolved concentration in the Mailiao harbor ranged from 0.025–0.124 μg/L, which corresponds well with reported data of the literature [7]. The results obtained from the bench experiments demonstrated that the Pb toxicity to the marine organisms may not really be reflected in the marine environment because Pb dissolved concentration in inshore environment is much lower than the threshold concentration of Pb to marine organisms, except the inshore is severely polluted by trace metals, such as the Minamata Bay disaster which occurred five decades ago. Even so, it should be kept in mind that marine organisms have a strong ability to accumulate trace metals and have the bio-magnification effect through the food web. In addition, the trace metals can persistently reside in the marine environment no matter whether they are from the natural source or from the anthropogenic source. Thus, Pb and Ni data obtained in the present study provide an alarming signal to the Mailiao coastal environment.

5. Conclusions

The metals total concentrations, except Ni and Pb, in the Mailiao coastal sediments were generally lower than the sediment quality guidelines, effects range low (ERL), of the US EPA. Whereas total concentrations of most Ni and some Pb exceeded the ERL value. The result for Ni probably reflects that the guideline ERL value of Ni is set too low to obey, as was suggested by Fang and Lien [40]. The result for Pb may be attributed to the coal-fired power plant located inside of MIZ, which needs to be further verified. The Pb total concentrations in sediments of the Choshui River and the New Huwei River ranged from 8.66–8.88 mg/kg and 9.78–24.3 mg/kg, respectively, of which values were much lower than ERL value (46.7 mg/kg), EPA USA.
The metals total concentrations, except Mn, in the sediments were mainly dominated by the residual fraction, averagely exceeding 75% of the total Fe, Cr, Ni, Zn. Whereas, the residual fraction of Cu and Pb reduced to 38% and 35% of their total pool, respectively. In contrast, the Mn total concentrations in sediments were dominated by carbonate (F2) and Fe-Mn oxides (F3) fractions, averagely accounting for 65% of the total pool. This result means that the RAC value of Mn poses a very high risk to marine organisms, but such a risk may pose a fault signal because the geochemical characteristics of Mn in the marine sediment were present in the labile fraction rather than the residual fraction, which was contrast to the other trace metals. Overall, the results of the three assessment indices indicate that the Mailiao coastal sediments is minorly contaminated by Pb, which is not the essential metal for living organisms.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/w15020250/s1.

Author Contributions

T.-H.F.: Conceptualization, Supervison, Resource, Writing. J.-R.C.: Methodology, Formal analysis, Data Curation. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Ministry of Science and Technology of the Republic of China under grants MOST 109-2611-M-008 and MOST 110-2611-M-019-014.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data of this study can be found in the Supplementary File.

Acknowledgments

This research was financially supported by the Ministry of Science and Technology of the Republic of China under grants MOST 109-2611-M-019-008 and 110-2611-M-019-014 and also supported by the Formosa Petrochemical Corporation.

Conflicts of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be constructed as a potential conflict of interest.

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Figure 1. (a) The monthly flow rate of the Choshui River during the years 2012–2017, (b) the daily particle flux of the Choshui River during the years 2016–2017, (c) the particle flux vs. the flow rate of the Choshui River during the years 2016–2017, (d) the concentrations of trace metals in sediments of the Choshui River during the 2015-year survey, and (e) the concentrations of trace metals in sediments of the New Huwei River during the 2019-year survey.
Figure 1. (a) The monthly flow rate of the Choshui River during the years 2012–2017, (b) the daily particle flux of the Choshui River during the years 2016–2017, (c) the particle flux vs. the flow rate of the Choshui River during the years 2016–2017, (d) the concentrations of trace metals in sediments of the Choshui River during the 2015-year survey, and (e) the concentrations of trace metals in sediments of the New Huwei River during the 2019-year survey.
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Figure 2. The sampling stations in the coastal sediments off the central western Taiwan.
Figure 2. The sampling stations in the coastal sediments off the central western Taiwan.
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Figure 3. (a) The grain size (GS) and (b) the TOC content of the surface sediments at each station, (c) the plot of grain size (GS) against the TOC content in all data.
Figure 3. (a) The grain size (GS) and (b) the TOC content of the surface sediments at each station, (c) the plot of grain size (GS) against the TOC content in all data.
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Figure 4. The Percentage distributions of four grain size fractions in surface sediment at each station. (MS: medium sand, >177 μm; FS: fine sand, 125–177 μm; VFS: very fine sand, 63–125 μm; and mud, <63 μm). The sampled time (a) 6 Jan. 2017, (b) 14 April 2017, (c) 13 July 2017, (d) 17 Nov. 2017.
Figure 4. The Percentage distributions of four grain size fractions in surface sediment at each station. (MS: medium sand, >177 μm; FS: fine sand, 125–177 μm; VFS: very fine sand, 63–125 μm; and mud, <63 μm). The sampled time (a) 6 Jan. 2017, (b) 14 April 2017, (c) 13 July 2017, (d) 17 Nov. 2017.
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Figure 5. The distributions of the five geochemical fractions of trace metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The dash line is the ERL (effects range low) value of the sediment quality guidelines, USA (Long et al., 1995). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
Figure 5. The distributions of the five geochemical fractions of trace metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The dash line is the ERL (effects range low) value of the sediment quality guidelines, USA (Long et al., 1995). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
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Figure 6. The distributions of the five geochemical fractions of trace metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The dash line is the ERL (effects range low) value of the sediment quality guidelines, USA (Long et al., 1995). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
Figure 6. The distributions of the five geochemical fractions of trace metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The dash line is the ERL (effects range low) value of the sediment quality guidelines, USA (Long et al., 1995). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
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Figure 7. The distributions of the five geochemical fractions of trace metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The dash line is the ERL (effects range low) value of the sediment quality guidelines, USA (Long et al., 1995). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
Figure 7. The distributions of the five geochemical fractions of trace metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The dash line is the ERL (effects range low) value of the sediment quality guidelines, USA (Long et al., 1995). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
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Figure 8. The distributions of the five geochemical fractions of trace metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The dash line is the ERL (effects range low) value of the sediment quality guidelines, USA (Long et al., 1995). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
Figure 8. The distributions of the five geochemical fractions of trace metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The dash line is the ERL (effects range low) value of the sediment quality guidelines, USA (Long et al., 1995). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
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Figure 9. Percentage of each fraction of metal concentration to the total metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
Figure 9. Percentage of each fraction of metal concentration to the total metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
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Figure 10. Percentage of each fraction of metal concentration to the total metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
Figure 10. Percentage of each fraction of metal concentration to the total metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
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Figure 11. Percentage of each fraction of metal concentration to the total metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
Figure 11. Percentage of each fraction of metal concentration to the total metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
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Figure 12. Percentage of each fraction of metal concentration to the total metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
Figure 12. Percentage of each fraction of metal concentration to the total metal concentrations in surface sediment at each station. (F1, exchangeable; F2, bound to carbonate; F3, bound to Fe-Mn oxides; F4, bound to organic; and F5, residual). The sampled time (a) 6 Jan. 2017 (b) 14 April 2017 (c) 13 July 2017 (d) 17 Nov. 2017 (e) 6 Jan. 2017 (f) 14 April 2017 (g) 13 July 2017 (h) 17 Nov. 2017.
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Figure 13. The enrichment factor of the studied metal in surface sediment at each station. (a) Cr, (b) Cu, (c) Fe, (d) Mn, (e) Ni, (f) Pb, (g) Zn. (1< EF < 3 not or minorly contaminated).
Figure 13. The enrichment factor of the studied metal in surface sediment at each station. (a) Cr, (b) Cu, (c) Fe, (d) Mn, (e) Ni, (f) Pb, (g) Zn. (1< EF < 3 not or minorly contaminated).
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Figure 14. The Igeo value of the studied metal in surface sediment at each station. (a) Cr, (b) Cu, (c) Fe, (d) Mn, (e) Ni, (f) Pb, (g) Zn. (Igeo < 0 not contaminated).
Figure 14. The Igeo value of the studied metal in surface sediment at each station. (a) Cr, (b) Cu, (c) Fe, (d) Mn, (e) Ni, (f) Pb, (g) Zn. (Igeo < 0 not contaminated).
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Figure 15. The risk assessment code (RAC) value of the studied metal in surface sediment at each station. (<10%, low risk, 10% < RAC ≤ 30%, medium risk; 30% < RAC ≤ 50%, high risk; and RAC > 50%, very high risk). (a) Cr, (b) Cu, (c) Fe, (d) Mn, (e) Ni, (f) Pb, (g) Zn.
Figure 15. The risk assessment code (RAC) value of the studied metal in surface sediment at each station. (<10%, low risk, 10% < RAC ≤ 30%, medium risk; 30% < RAC ≤ 50%, high risk; and RAC > 50%, very high risk). (a) Cr, (b) Cu, (c) Fe, (d) Mn, (e) Ni, (f) Pb, (g) Zn.
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Table 1. The analytical accuracy and precision (1std) of trace metals of the MESS-3 reference materials are triplicate analyzed using the Tissue’s method. (Concentration unit, in mg/kg; except Al and Fe in %, and Hg in μg/kg).
Table 1. The analytical accuracy and precision (1std) of trace metals of the MESS-3 reference materials are triplicate analyzed using the Tissue’s method. (Concentration unit, in mg/kg; except Al and Fe in %, and Hg in μg/kg).
Species
Element
F1
Exchangeable
F2
Carbonate
F3
Fe-Mn Oxides
F4
Organic
F5
Residue
Total Conc.Certified
Values
Accuracy
(%)
Al<0.001<0.0030.044 ± 0.0010.061 ± 0.0015.78. ± 0.025.89 ± 0.048.59 ± 0.2368.6 ± 0.25
Cr<DL<DL3.99 ± 0.226.81 ± 0.3675.3 ± 1.2986.1 ± 1.88105 ± 481.9 ± 1.79
Cu1.33 ± 0.191.01 ± 0.051.58 ± 0.128.90 ± 0.4218.13 ± 0.0730.96 ± 0.5233.9 ± 1.691.3 ± 1.5
Fe<DL0.042 ± 0.0000.698 ± 0.0070.068 ± 0.0123.029 ± 0.0443.837 ± 0.0494.34 ± 0.1188.4 ± 1.1
Mn42.22 ± 0.6766.41 ± 1.5078.48 ± 2.1313.44 ± 0.57105.8 ± 0.69306.4 ± 1.42324 ± 1294.6 ± 1.4
Ni0.27 ± 0.102.99 ± 0.3510.78 ± 0.945.32 ± 0.1032.28 ± 0.0251.65 ± 1.3146.9 ± 2.2110.1 ± 2.8
Pb<DL3.81 ± 0.314.47 ± 0.16<DL13.42 ± 0.5721.69 ± 0.1021.1 ± 0.7102.8 ± 0.5
Zn2.26 ± 0.0814.47 ± 0.6742.75 ± 0.9713.07 ± 0.58101.57 ± 0.14174.12 ± 1.00159 ± 8109.5 ± 0.6
Note(s): DL: detection limit.
Table 2. The total concentrations range of sedimentary trace metals, the percentage range of each fraction of trace metals to the total concentrations and the ranges of enrichment factor, Igeo and risk code assessment of trace metals obtained in the present study. (Conc. unit: mg kg−1, except Al and Fe in %).
Table 2. The total concentrations range of sedimentary trace metals, the percentage range of each fraction of trace metals to the total concentrations and the ranges of enrichment factor, Igeo and risk code assessment of trace metals obtained in the present study. (Conc. unit: mg kg−1, except Al and Fe in %).
AlCrCuFeMnNiPbZn
Total conc.4.13~7.8432.3~76.73.75~26.63.18~8.85234~62220.8~61.217.4~62.358.0~154
Fraction 1 (%)<0.01<0.1<0.1~0.43<0.10.3~10.5<0.1~2.6<0.1<0.1
Fraction 2 (%)0.04~0.311.4~16.32.1~15.00.23~2.3425.8~51.30.3~9.311.9~40.52.5~10.0
Fraction 3 (%)0.78~2.86<0.1~5.01.0~57.20.57~14.321.3~40.67.8~37.97.2~33.39.7~35.1
Fraction 4 (%)0.42~1.321.7~19.51.3~55.30.2~1.991.2~10.10.8~13.23.3~51.04.9~16.2
Fraction 5 (%)95.9~98.767.7~90.317.7~68.083.1~98.616.0~38.452.0~86.016.4~58.046.7~82.7
Enrichment factor 1.21~3.650.23~1.691.19~3.430.49~1.731.35~4.091.06~5.061.06~3.00
Igeo −0.70~0.55−3.32~−0.49−0.72~0.75−1.95~−0.53−0.53~1.03−0.79~1.05−0.88~0.54
Risk assessment code 2.9~19.09.1~72.21.0~16.256.0~78.611.1~40.221.0~55.912.3~42.1
Table 3. The correlations among the sediment grains size (GS), TOC and trace metal total concentrations in coastal surface sediments of the central Taiwan.
Table 3. The correlations among the sediment grains size (GS), TOC and trace metal total concentrations in coastal surface sediments of the central Taiwan.
TOCAlCrCuFeMnNiPbZn
Sampled time 6 Jan. 2017
GS−0.46−0.30−0.36−0.63−0.31−0.29−0.55−0.11−0.54
TOC 0.240.710.860.650.850.700.020.88
Al 0.060.210.120.240.08−0.0030.26
Cr 0.580.680.470.460.090.48
Cu 0.710.850.840.100.95
Fe 0.720.66−0.090.66
Mn 0.760.120.92
Ni 0.300.80
Pb 0.00
Sampled time 14 April 2017
GS−0.41−0.12−0.13−0.31−0.03−0.22−0.28−0.40−0.34
TOC 0.600.710.850.760.860.890.820.92
Al 0.520.600.710.670.640.460.68
Cr 0.790.720.770.830.720.77
Cu 0.790.930.910.770.94
Fe 0.820.830.700.85
Mn 0.890.760.96
Ni 0.830.94
Pb 0.80
Sampled time 13 July 2017
GS−0.37−0.21−0.46−0.570.070.14−0.310.00−0.34
TOC 0.260.590.690.310.260.34−0.230.49
Al 0.470.460.310.550.690.450.66
Cr 0.900.290.660.860.390.86
Cu 0.330.530.750.080.82
Fe 0.470.420.170.36
Mn 0.800.520.76
Ni 0.630.89
Pb 0.37
Sampled time 17 Nov. 2017
GS−0.50−0.49−0.59−0.57−0.21−0.41−0.67−0.68−0.64
TOC 0.340.810.670.480.750.790.630.80
Al 0.580.670.100.480.600.620.56
Cr 0.830.480.850.950.860.90
Cu 0.520.910.880.700.93
Fe 0.730.500.260.62
Mn 0.870.670.93
Ni 0.890.96
Pb 0.78
Note(s): The values in bold and underline represent the significance < 0.05.
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Fang, T.-H.; Chang, J.-R. The Geochemical and Environmental Characteristics of Trace Metals in Coastal Sediment Discharge off the Mailiao Industrial Zone of Central Western Taiwan. Water 2023, 15, 250. https://doi.org/10.3390/w15020250

AMA Style

Fang T-H, Chang J-R. The Geochemical and Environmental Characteristics of Trace Metals in Coastal Sediment Discharge off the Mailiao Industrial Zone of Central Western Taiwan. Water. 2023; 15(2):250. https://doi.org/10.3390/w15020250

Chicago/Turabian Style

Fang, Tien-Hsi, and Jie-Ren Chang. 2023. "The Geochemical and Environmental Characteristics of Trace Metals in Coastal Sediment Discharge off the Mailiao Industrial Zone of Central Western Taiwan" Water 15, no. 2: 250. https://doi.org/10.3390/w15020250

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