Geographically, the Sekotong mangrove ecosystem is located in West Lombok Regency, West Nusa Tenggara Province, Indonesia Figure. 1. The research was carried out in May – July 2025 in an area of ± 36 ha mangrove ecosystem located in the Central Sekotong ecotourism area, namely the Tanjung Batu and Bagek Kembar mangrove ecosystems, adjacent to conventional gold ore mining and processing.

This study used a global positioning system (GPS), pH meter, hand refractometer, analytical balance, oven, sample bottles, digital thermometer, and spectrophotometer (Perkin Elmer Spectrophotometer). The materials used inclused mangrove leaves, mangrove roots, water, substrate, HClO4, and HNO3. The research began with the identification of mangrove species using mangrove identification guide by (Noor et al., 2006), followed by measurement s of physicochemical water parameters, including water temperature, substrate temperature, substrate pH, water salinity, and water pH. Environmental parameter measurements were conducted repeatedly over a three-month period (May – July 2025).

Leaf, root, and substrate samples were collected using a purposive random sampling method. Leaf and root samples were obtained from trees with stem diameters of 5 – 30 cm or stem circumferences of 15 – 95 cm. Sampling was conducted three times for nine mangrove species at different locations and tree stands within the study area. Repeated sampling of each organ and species was performed to improve data robustness and minimize analytical bias. Substrate samples were collected at the base of the same trees from which leaf and root samples were obtained.

Mercury concentrations in leaf, root, and substrate samples were determined using atomic absorption spectrophotometry. Laboratory analyses were conducted at the Agricultural Instrument Standardization Agency, which complies with SNI ISO/IEC 17025:2017 and is accredited by the National Accreditation Committee (certificate number LP-394-IDN) for chemical analysis of soil and plant tissues.

Approximately 2.5 g of plant samples (leaves and roots) and mangrove soil with particles sizes < 0.5 mm were weighed and placed into digestion tubes. Each sample was treated with 5 mL of concentrated HNO3 and allowed to stand for 24 hours. The samples were then heated at 100 oC for 1 hour 30 minutes, cooled and supplemented with an additional 5 mL of HNO3 and 1 mL of HClO4. The mixture was heated to 130 °C for 1 hour, followed by heating at 150 °C for 2 hours and 30 minutes until yellow fumes disappeared; heating time was extended if yellow fumes persisted. Afterwards, the temperature was increased from 113 °C to 170 °C for 1 hour, followed by another temperature increase to 200 °C for 1hour until white fume appeared. The extraction process was considered complete when a white residue formed or approximately 1 mL of clear solution remained.

After cooling, the extract was diluted with deionized water to a final volume of 25 mL, shaken thoroughly until homogeneous, and allowed to stand overnight (Petunjuk Teknis: Analisis Kimia Tanah, 2009); (Horwitz, 2010); (Lisle et al., 1991); (Agriculture, 2004). Clear extracts were analyzed for mercury using atomic absorption spectrophotomery equipped with a vapor generation system at a wavelength of 253.7 nm using a mercury standard series for calibration. The carrier gas, SnCl2 rexative, diluted H2SO4 solution, and standards or samples were introduced into the generator through separate inlet lines. Mercury concentrations in the extracts were calculated using the atomic absorption spectrophotometric method according to the following formula:

Hg heavy = ppb curve x mL extract metal content 1,000/mL x 1,000 g/sample (ppm) x fp x fk(ppm)

= ppb curve x 25 mL/1,000 x 1,000/2.5 g/sample x fp xfk = ppb curve x 10 x fp x fk

where:

ppb = The sample rate derived from the regression curve represents the connection between the standard

series rate and its value after subtracting the blank readings.

1,000 = Conversion faktor to ppm (mg/kg)

fp = Dilution factor.

fk = Water content coreection factor (100/100-% moisture contect))

Further calculations were performed using data from laboratory analysis on each leaf, root and substrate sample to determine Translocation Factor (TSF), Biological Accumamulation Factor (BAF) and Phytoremediation (FTD) values, as indicators to evaluate the capacity of each mangrove species to remediate heavy metals in Sekotong Tengah(Mellem et al., 2012);(Supriyantini et al., 2017); (Rachmawati et al., 2018); (Manikasari & Mahayani, 2019), using the following formulas:

(a) Translocation factors (TSF)

TSF = Mercury heavy metal in leaves / Mercury heavy metal in root (1)

Category:

TSF value < 1: phytostabilization

TFS value > 1: phytoextraction

(b) Bioaccumulation Factors (BAF)

Leaf BAF = Hg heavy metal in leaves / Hg heavy metal in substrates (2)

Root BAF = Hg heavy metal in root / Hg heavy metal in substrates (3)

Category:

BAF > 1 : Accumulator BAF = 1 : Indicator BAF < 1 : Excluded

(c) Phytoremediation (FTD)

Leaf FTD = BAF of leaf - TSF

Root FTD = BAF of root - TSF

Environmental parameters in the Sekotong Tengah mangrove ecosystem show considerable variations in physicochemical conditions across sampling points. Water temperature ranged from 31.70 °C to 33.50 °C, with an average of 32.69 ± 0.79 °C, remaining within the tolerance range for mangrove organisms. Salinity was relatively stable (31.00 - 31.50 ppt; 31.25 ± 0.29 ppt), reflecting an estuarine environment that supports typical tropical mangrove species. Water pH was alkaline (8.04 - 8.56), while soil pH was more acidic (5.75 - 6.70), a common feature of mangrove substrates resulting from organic matter accumulation and decomposition. Dissolved oxygen (DO) fluctuated widely (4.81 - 8.90 ppm; 6.87 ± 2.30 ppm), reflecting variations in photosynthetic activity and organic matter degradation. Biochemical oxygen demand (BOD) also varied (3.32 - 8.87 ppm), indicating differences in microbial activity and organic matter load among sites.

The physicochemical conditions of the Sekotong mangrove waters are suitable for mangrove growth and development, according to Government Regulation of the Republic of Indonesia Number 22 year 2021 on the Implementation of Environmental Protection and Management with National Water Quality Standard Specifications. Previous studies reported that water physicochemistry can influence mangrove physiology, affecting nutrient absorption and limiting the uptake of heavy metals accumulated in the substrate and water column (Tang et al., 2010); (Kumar et al., 2015); (Liu et al., 2016).

Mercury (Hg) concentrations in the leaves of nine mangrove species varied significantly, ranging from 0.01 to 2.36 ppm, with an average of 0.48 ± 0.716 ppm Table 3. The highest concentration was observed in Bruguiera cylindrica leaves (2.36 ppm), while the lowest was recorded in Bruguiera gymnorrhiza leaves (0.01 ppm), both species belonging to the Rhizophoraceae family. This wide range suggests generally low leaf absorption efficiency for mercury. Other species, such as Scyphiphora hydrophyllacea (0.38 ppm), Avicennia marina (0.37 ppm), and Clerodendrum inerme (0.36 ppm) exhibited mercury levels above 0.35 ppm, indicating relatively efficient metal translocation from roots to leaves. In contrast, Rhizophora mucronata (0.23 ppm), Rhizophora stylosa (0.21 ppm), and Lumnitzera racemosa (0.08 ppm) showed lower leaf accumulation, suggesting preferential retention of mercury in the roots.

Mercury accumulation in the roots of nine mangrove species ranged from 0.02 to 0.78 ppm, with an average of 0.33 ± 0.204 ppm. The highest concentration was observed in Clerodendrom inerma (0.78 ppm) and lowest in Bruguiera gymnorrhiza (0.02 ppm). In five species (Avicennia marina, Bruguiera cylindrica, Rhizophora apiculata, Rhizophora mucronata, and Rhizophora stylosa), root mercury concentrations were lower than those in the leaves, whereas in four species (Bruguiera gymnorrhiza, Clerodendrom inerma, Lumnitzera racemosa, and Scyphiphora hydrophyllacea), root accumulation exceeded leaf levels. Higher mercury accumulation in roots indicates the capacity of mangroves to adsorb and retain metals in the root zone, functioning as phytostabilizing agents. Species of the Rhizophoraceae family generally showed lower root accumulation (< 0.35 ppm), suggesting efficient translocation of mercury to aerial tissues. These data provide an important basis for selecting mangrove species for root-based phytoremediation strategies.

Mercury concentrations in the substrate beneath each mangrove stand averaged 0.30 ± 0.122 ppm, lower than the average concentrations in leaves (0.48 ± 0.716 ppm) and roots (0.33 ± 0.204 ppm). However, certain species exhibited higher substrate accumulation than in plant tissues. For example, Avicennia marina (0.16 ppm), Bruguiera cylindrica (0.15 ppm), Clerodendrom inerma (0.18 ppm), and Scyphiphora hydrophyllacea (0.33 ppm) accumulated less mercury in substrate than in plant tissues, whereas Bruguiera gymnorrhiza (0.46 ppm), Lumnitzera racemosa (0.43 ppm), Rhizophora apiculata (0.43 ppm), Rhizophora mucronata (0.28 ppm), and Rhizophora stylosa (0.25 ppm) showed higher substrate accumulation. Variations in substrate mercury concentrations are influenced by particle size and deposition mechanisms (Brady et al., 2014);(Rezania et al., 2016);(Baran et al., 2019);(Harmesa et al., 2020), consistent with previous studies in Lembar Bay, West Lombok, where substrate lead concentrations exceeded leaf and root levels (Rahman et al., 2025).

Seveeral species exceeded the SNI 7387:2009 threshold for mercury contamination in plant tissues; Bruguiera cylindrica leaves (2.36 ppm) and Clerodendrom inerma roots (0.78 ppm), whereas no substrate samples exceeded 0.50 ppm. Compared with the Decree of the Minister of Environment of the Republic of Indonesia No. 51 year 2004 on the Quality of Marine Tourism Health, mercury concentrations in both plant tissues and substrates indicate a polluted condition (> 0.001 ppm).

Translocation factor (TSF) values for mercury in the nine mangrove species ranged from 0.23 to 7.61, with an average of 1.55 ± 2.296. The highest TSF was observed in Bruguiera cylindrica (7.61) and the lowest in Lumnitzera racemosa (0.23), reflecting interspecific differences in metal transport from roots to aerial tisues (Analuddin et al. 2017; Arumugam et al. 2018). Four species (Bruguiera gymnorrhiza, Clerodendrom inerma, Lumnitzera racemosa, Scyphiphora hydrophyllacea) had TSF values < 1, functioning primarily as phytostabilazers, while five species (Avicennia marina, Bruguiera cylindrica, Rhizophora mucronata, Rhizophora apiculata, and Rhizophora stylosa) exhibited TSF > 1, indicating phytoextraction capacity Table 4.

Phytostablization in roots is mediated by binding of metal ions through root mucilage or cell walls, followed by chelation with phytochelatins or metallothioneins and storage in vacuoles (Abreu & Magalhães, 2009);(Shackira & Puthur, 2019); (Phytoextraction as a tool for green chemistry, 2014); (Nedjimi, 2021). This is supported by higher average mercury concentrations in roots (0.39 ± 0.311 ppm) compared with leaves (0.21 ± 0.190 ppm) in the four phytostabilizing species.

The Rhizophoraceae family, including Bruguiera cylindrica, Rhizophora mucronata, Rhizophora apiculata, and Rhizophora stylosa, and the Acanthaceae family (Avicennia marina) exhibited ecological capabilities as phytoextractors (TSF > 1), supported by higher mercury accumulation in leaves than in roots. Similarly, Rahman et al. (2025) reported that R. stylosa in Lembar Bay, West Lombok, functions as phytoextractor, with leaf lead concentrations (4,230 ppm) exceeding root concentrations (2,843 ppm; TSF= 1.488). Other studies also indicate that Rhizophoraceae species predominantly function in phytoextraction (Majid et al. 2014; (Takarina & Pin, 2017); (Baharvand et al., 2021); (Mentari et al., 2022).

Bioaccumulation factors (BAF) indicate the capacity of mangroves to absorb and accumulate heavy metals from the environment into plant tissues (Dajam et al., 2024). In this study, leaf BAF values ranged from 0.02 to 15.73, with an average of 2.65 ± 4.961, while root BAF values ranged from 0.04 to 4.33, with an average of 1.45 ± 1.280. Leaf BAF values were generally higher than root BAF values, indicating preferential translocation of mercury to aboveground tissues. This pattern aligns with observed mercury accumulation in leaves of Bruguiera gymnorrhiza, Clerodendrom inerma, Lumnitzera racemosa, Scyphiphora hydrophyllacea and Avicennia marina, whereas the other five species showed higher root BAF values. Bruguiera cylindrica exhibited the highest leaf BAF (15.73), indicating strong accumulation in aerial tissues, whereas Bruguiera gymnorrhiza showed very low BAF values (< 0.05) in both tissues, reflecting minimal mercury accumulation.

Four mangrove species (Avicennia marina, Bruguiera cylindrica, Clerodendrom inerma, and Scyphiphora hydrophyllacea) had BAF value > 1 in both leaves and roots, indicating their role as accumulator plants. Accumulators transfer metals from roots to leaves and store them in aboveground tissues (Baker & Walker, 1990);(Tam et al., 1998);(Analuddin et al., 2017). Physiologically, metal ions are absorbed through roots, transported via xylem, chelated by phytochelatins or metallothioneins, and sequestered in vacuoles of stems or leaves (Cobbett & Goldsbrough, 2002);(Nair, 2022);(Sharma et al., 2023).

Meanwhile, five mangrove species (Rhizophora mucronata, Rhizophora stylosa, Rhizophora apiculata, Bruguiera gymnorrhiza, Lumnitzera racemosa) had BAF values < 1 in both organs, functioning as excluders. Excluder plants limit metal accumulation in aboveground biomass, concentrating metals primarily in (Phytoextraction as a tool for green chemistry, 2014); (Santana et al., 2018). This may also reflect mercury distribution in the substrate, as root uptake and translocation occur through xylem-mediated transport (Ariesabeth, 2005); (Hao et al., 2012).

The Factor of Translocation and Distribution (FTD) reflects the efficiency of heavy metal distribution between roots and leaves. FTD values in leaves ranged from -0.48 to 8.12 (mean 1.10 ± 2.275), while root FTD values ranged from -5.55 to 3.87 (mean -0.10 ± 2.449). Negative mean FTD in roots suggests preferential accumulation in leaves. For example, Bruguiera cylindrica exhibited the highest leaf FTD value (8.12), consistent with high BAF and TSF values. In contrast, Rhizophora mucronata, Rhizophora stylosa, Rhizophora apiculata, and Bruguiera gymnorrhiza showed negative FTD values in both organs, indicating low accumulation in aboveground tissues and a stronger phytoextraction function.