Surface Water Characteristics in the Vicinity of Abandoned...

Keywords: abandoned mine, heavy metals, mercury, physicochemical properties, pit lake

Surface Water Characteristics in the Vicinity of Abandoned Mercury Mine Site in

Puerto Princesa City, Philippines

Philippine Nuclear Research InstituteDepartment of Science and Technology

Quezon City 1101 Philippines

*Corresponding Author: [email protected]

Jessie O. Samaniego*, Cris Reven L. Gibaga, Alexandria M. Tanciongco, Rasty M. Rastrullo, and Ma. Azileira V. Costa

This study was part of an ongoing research project aimed to trace the pathways of possible mercury (Hg) contamination in an abandoned Hg mine site formerly operated by Palawan Quicksilver Mines, Inc. (PQMI) in Puerto Princesa City, Palawan. This mined-out area has been identified as the possible cause for the recent reported Hg poisoning cases among the residents living near the vicinity. To evaluate the water quality in the area, water samples collected from pit lake, river, coast, other nearby streams, leachate from landfill, and hot spring were analyzed for physicochemical parameters and heavy metal concentrations. Results showed that the physicochemical characteristics of freshwater (pit lake and river) and coastal water were generally within the water quality guidelines. Heavy metals in pit lake and river – except for Mn and Ni, Fe, and Mn – were measured within the guidelines, respectively. Hg concentrations in pit lake and river were not detected while low Hg concentrations were measured in coastal water near the jetty (0.001 mg/L) and in hot spring (≤0.0004 mg/L). A landfill near the pit lake was releasing partially-treated leachate with high total suspended solids (TSS) and heavy metal concentrations that contribute to the pollution in the area.

Philippine Journal of Science148 (3): 493-498, September 2019ISSN 0031 - 7683Date Received: 05 Apr 2019

INTRODUCTIONFrom 1953 to 1976, mining of cinnabar (HgS) ore – a naturally-occurring form of Hg hosted by the Tagburos Opalite formation in Central Palawan Island – was carried out by PQMI and produced about 2,900 metric tons of Hg (Gray et al. 2003, Williams et al. 1996). Currently, the open pit area is filled with water (Figure 1) and it is included in the list of abandoned and inactive mines in the country that is high risk to human health and the environment (Tetra Tech 2001). The site is approximately 3 km inland from the

Honda Bay coast and situated within the catchment of the Tagburos River, which is a local fishery and recreational area. Approximately 2,000,000 metric tons of mine waste calcines were produced during mining and about half of these calcines were transported to Honda Bay to construct a jetty, which was used as an operational port for the mine (Gray et al. 2003). Today, the area is home to approximately 10,000 residents combined from Barangays Sta. Lourdes and Tagburos in Puerto Princesa City, including people living in the busy Honda Bay Wharf.

Cases of Hg poisoning via exposure to mine tailings and ingestion of marine products have been reported among the residents living near PQMI were reported as early as 1996

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(Williams et al. 1996). A study by Gray and co-authors (2003) on the measurement of Hg methylation at the Palawan mine was found elevated similar to other Hg mines worldwide. Likewise, results of statistical analysis from Maramba and co-authors (2004) presented methylmercury (MeHg) levels in local fishes exceeding recommended levels. A food pathway of Hg from fishes to human is most likely in this area, especially since the population is generally fish-consuming. Studies on Hg concentration on surface waters of the pit lake and surrounding rivers, sea water, and drinking water were undergone by several researchers since early 1980s (Kapauan et al. 1982, Benoit et al. 1994, Williams et al. 1996, Gray et al. 2003). The high concentration of Hg (570 ppm) measured in the Honda Bay Wharf is traced from the HgS mine tailings used to build the jetty (Benoit et al. 1994).

Some 500 m above the pit lake, the Puerto Princesa City sanitary landfill is situated and it releases partially-treated leachate, which is believed to be one of the sources of heavy metals pollution in the pit lake and rivers that drains to the Honda Bay.

This study is part of a project to determine the pathways of Hg concentration in the abandoned PQMI mined-out area. The objective of this study is to characterize the physicochemical parameters and heavy metal concentrations of the different surface waters in and around the vicinity of PQMI mined-out area.

Presented in Table 1 are the results of the physicochemical parameters and heavy metal concentrations gathered from the study. These results are compared with the water quality guidelines for Class C freshwater and Class SB marine waters based on water body classification guidelines (DENR 2016). Same parameters measured from both hot spring and leachate samples are also reported hereunder.

Depths vs. concentration profiles for pH, EC, temperature, and dissolved oxygen (DO) in the deep area of pit lake are shown in Figure 2. Low temperature and low DO values observed in the bottom water (hypolimnion) – both increased towards the upper waters (epilimnion) and the atmosphere. Lower DO in the bottom water is caused by bacterial respiration that depletes the available DO and releases CO2, thereby decreasing the pH as shown in Figure 2a. Electrical conductivity (EC) in the pit lake increases with water depth with the range of 0.842–0.912 mS/cm. These values were in agreement with non-detected salinity level and low total dissolved solids (TDS) at 0.61 g/L. The measured TSS of the pit lake water was within the guidelines, while the negative oxidation-reduction potential (ORP) reading in the entire profile – which coincides with the alkalinity and low DO – indicates that the water was a reducing environment. This results in bacteria being unable to efficiently break down the waste products present in the water. This can lead to accumulation of more contaminants through time, especially since some of the leachates are

Figure 1. PQMI pit lake and the calcine deposit in the background.

Philippine Journal of ScienceVol. 148 No. 3, September 2019

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allegedly draining from the Puerto Princesa City Landfill towards the pit lake. Of all the heavy metals analyzed, only Mn and Ni exhibited high concentrations compared to the guidelines. Hg concentration in the PQMI Lake determined to be below the detection limit shows the low solubility of Hg from the tailings and sediments. Presence of Mn and Ni is attributed to the natural ophiolitic rocks in the area rich in both elements, which can easily be weathered.

Low concentrations of Hg in pit lake (<0.20 µg/L) in the present study is identical to the Hg concentrations reported in the previous study on PQMI pit lake, which is 0.029 µg/L (Gray et al. 2003). These values are within the regulatory limit (2.0 µg/L) for Class C freshwaters.

The measured temperature, pH, and TSS levels were within the guidelines, while DO concentrations are low

Table 1. Physico-chemical characteristics and heavy metal concentrations of different surface waters in the PQMI mined-out area with corresponding water quality guidelines.

Sampling group Pit Lake River Coastal Hot spring Leachate Regulatory limits

for river and lake*Regulatory limits for

coastal water**

No. of samples 11 20 6 2 2

pH 7.90–10.2 7.42–7.96 6.75 5.89–6.47 6.67 6.5–9.0 7.0–8.5

EC (mS/cm) 0.842–0.912 0.394–1.205 50.12 5.43–6.20 5.94 – –

DO (mg/L) 0.02–6.95 1.14–2.56 2.93 3.88 1.14 5 (min.) ≥ 6

Temp. (°C) 28.2–31.6 24.8 – 28.2 29.57 >60 26.3 25–31 26–30

Salinity (%) 0 0 3.28 0.3 0.3 – –

TDS (g/L) 0.61 0.32 30.33 4 3.7 – –

ORP (mV) –200.9 74.42 8 –275 29 – –

TSS (mg/L) 65.00 8.53 3.75 0.10 540.5 80 50

As (mg/L) ND ND ND ND ND–0.01 0.02 0.01

Ba (mg/L) 0.02–0.03 ND–0.1 ND–0.007 2.4–3.0 0.06–0.2 3.0 0.7

Cd (mg/L) ND ND ND ND ND–0.002 0.005 0.003

Cr (mg/L) ND–0.006 ND–0.01 ND–0.008 ND 0.1–0.3 0.01 0.05

Cu (mg/L) ND ND–0.009 ND ND 0.04–0.1 0.02 0.02

Fe (mg/L) 0.1–0.2 0.03–2.3 0.04–1.7 0.07–0.1 5.5–15.0 1.5 1.5

Hg (mg/L) ND ND ND–0.001 ND–0.0004 0.002–0.003 0.002 0.001

Mn (mg/L) 0.2–0.4 0.01–0.4 ND–0.04 0.02 1.2–1.6 0.2 0.4

Ni (mg/L) 0.02–0.03 ND–0.05 ND–0.01 ND 0.6-0.8 0.2 0.04

Pb (mg/L) ND ND ND ND 0.007–0.01 0.05 0.01

Zn (mg/L) ND–0.02 ND–0.04 ND–0.01 0.006–0.007 0.1 2.00 0.05

Notes:Detection limit for As, Ba, Cd, Cr, Cu, Hg, Mn, Ni, Pb, and Zn are 0.008 mg/L, 0.005 mg/L, 0.001 mg/L, 0.005 mg/L, 0.003 mg/L, 0.0002 mg/L, 0.003 mg/L, 0.003 mg/L, 0.005 mg/L, and 0.005 mg/L, respectively.*DAO 2016-08 Guidelines (Class C)**DAO 2016-08 Guidelines (Class SB)

Figure 2. Depth profiles of (a) pH, (b) temperature, (c) EC, and (d) DO in PQMI pit lake in Feb 2019.



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for the fish population (1.14–2.56 mg/L). EC of the river has low ability to carry electric current with a range of 0.394–1.205 mS/cm. It is correlated to low TDS (0.32 mg/L) and undetected salinity level in the water. Hg concentration was not detected along Tagburos River and other tributaries, as shown in Figure 3. All heavy metals analyzed, except for Fe and Mn in some parts of the river, were measured within the guidelines.

Like the low concentrations of Hg in pit lake, Tagburos River has measured <0.20 µg/L of Hg, which is identical to the Hg concentrations (0.013 µg/L) reported in the previous studies on Tagburos River (Gray et al. 2003) and it is within the regulatory limit (2.0 µg/L) for Class C freshwaters. The measured Hg concentrations in Tagburos River is lower than the Hg concentrations in stream waters measured near the abandoned mines in Monte Amiata District, Italy with 1.4 µg/L (Rimondi et al. 2012), and in San Benito County, CA, USA with Hg concentration of 2.9–12.4 µg/L (Fortner 2010).

The measured level of pH, temperature, and TSS were within the guidelines for seawater, while DO is below the required concentration. Other parameters – EC, salinity, and TDS, though not regulated – showed concentrations that were within their respective typical values on seawater (Pawlowicz 2013, Rusydi 2018). Measured ORP, meanwhile, indicates that the seawater is a weakly

oxidizing agent. All heavy metals analyzed, except for Fe, were either undetected or within Class SB guidelines. Hg concentration (0.001 mg/L) detected in the seawater near the Honda Bay jetty suggests leaching of elemental Hg from HgS tailings in Honda Bay Wharf. However, much-localized distribution exhibits a low diffusion rate or easy dilution of the metal.

Water samples collected from the hot spring resort near the PQMI area were classified as hyperthermal spring with a surface temperature of >60 °C and weak acidic at pH 5.89–6.47. The hot spring was a strongly reducing environment yielding ORP levels of –275 mV, which may be attributed to the thermophilic bacteria that survive the >60 °C anaerobic environment. Water samples yielded relatively low TSS levels versus that of typical groundwater. Measured DO of hot spring was slightly higher compared with the typical groundwater due to the interface with the atmosphere. Low concentrations of Hg (≤0.0004 mg/L), Ba (2.4–3.0 mg/L), Fe (0.07–0.1 mg/L), Mn (0.02 mg/L), and Zn (0.006–0.007 mg/L) were found to be present in the water samples gathered from hot spring.

Leachate samples collected from the outflow of the landfill during the dry season (November–February) were found to be at near neutral pH (6.67) and is weakly oxidizing with an ORP of 29 mV. The electric conductivity of the leachate

Figure 3. Hg concentrations in surface waters at different sampling sites in the study area.



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reaches up to 5.94 mS/cm, which can be correlated to its high TDS levels. DO of leachate was low (1.14 mg/L) measured at a water temperature of 26.3 °C. The leachate with high TSS (540.5 mg/L) can pollute the receiving bodies of water if untreated. The common heavy metals found from the leachate in order of abundance were Fe, Mn, Ni, Cr, Ba, Zn, Cu, Pb, Hg, As, and Cd (Table 1).

The low concentrations of Hg in Tagburos River and PQMI pit lake (<0.20 µg/L) can be associated with the low solubility of Hg from the tailings and sediments by its slightly alkaline to alkaline waters (pH 7.42–10.2). The results are in agreement with the very low solubility of HgS in water, which is set at 1.04 x 10–25 g/100 mL water (Myers 1986). Transport of soil particles with Hg by heavy runoff to surface waters is another pathway of contamination in river and pit lake, but sedimentation – which resulted to low measured TSS in the surface waters – contribute to the low Hg concentration in the water. This suggests that the Hg is adsorbed to the soil particles that settle in the bottom of the river and pit lake. Several studies reported that Hg was positively associated with the fine particles (Kelly and Rudd 2018, Samaniego and Tanchuling 2018) that are settled in the bottom of the water bodies. Also, dissolution of HgS can be enhanced by the presence of dissolved organic matter at oxic condition (Stallings 2013), but the product of this reaction will eventually settle in the bottom that will leave the surface water free from Hg concentration.

ACKNOWLEDGMENTSThe authors acknowledge the Department of Science and Technology – Philippine Council for Industry, Energy and Emerging Technology Research and Development (DOST-PCIEERD) and Grants-in-Aid Program (DOST-GIA) for funding the project.

NOTE ON APPENDIXThe methodology section of this study can be accessed online in the Appendix section at http://www.philjournalsci.dost.gov.ph

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[DENR] Department of Environment and Natural Resources. 2016. Water Quality Guidelines and General Effluent Standards of 2016 [DENR Administrative Order No. 2016-08]. Quezon City, Philippines, Department of Environment and Natural Resources. 25p.

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near the Abbadia San Salvatore mercury mine, Monte Amiata district, Italy. Science of the Total Environment 414: 318–327.

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SAMANIEGO JO, TANCHULING MAN. 2018. Physico-chemical Characteristics of Wastewater from a Ball Mill Facility in Small-Scale Gold Mining Area of Paracale, Camarines Norte, Philippines. Philippine Journal of Science 147(3): 343–356.

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WILLIAMS TM, WEEKS JM, APOSTOL A, MIRANDA C. 1996. Assessment of toxicity hazard associated with former cinnabar mining and tailings disposal in Honda Bay, Palawan, Philippines [Overseas Geology Series Technical Report WC/96/31]. Keyworth, UK: British Geological Survey. 57p.

[TETRA TECH] Tetra Tech EM Inc. 2001. Semi-detailed Assessment of Abandoned Mines in the Philippines. 50p. Retrieved from http://pcij.org/blog/wp-docs/Tetra_Tech_Assessment_of_20_Abandoned_mines.pdf on 16 Nov 2017.



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Figure 1. Procedure chart for water quality assessment in and around the vicinity of the abandoned PQMI mined-out area in Puerto Princesa City, Palawan, Philippines from Nov 2018 to Feb 2019.

A total of 41 samples were collected in 1000-mL polyethylene bottles – 6 coastal water bodies, two hot springs, two leachate puddles, 20 river waters, and 11 PQMI pit lake samples. All of the coastal waters were obtained on areas north and south of the Honda Bay Wharf. For river waters, 13 samples were collected from upstream to downstream of Tagburos River, and the remaining seven from other rivers and creeks in the vicinity of PQMI. Seven (7) surface water samples were obtained in the circumference and center of the pit lake, and the remaining four (4) were sampled at depths 2, 5, 10, and 12 m.

Measurement of physicochemical parameters of all samples was done on-site using Horiba Multi-Probe Water Quality Monitor. TSS was analyzed in the laboratory using the gravimetric method.

Water samples were preserved by acidification using 5 mL HNO3 and were stored in iced styrofoam containers during transport from site to laboratory. Flame atomic

absorption spectrophotometer was used to analyze As, Ba, Cd, Cr, Cu, Fe, Pb, Mn, Ni, and Zn. Cold vapor atomic absorption spectrophotometer was used to determine Hg. APHA-AWWA Standard Method for the Examination of Water and Wastewater (1998) was used as a reference in conducting the analyses.

All physicochemical parameters and heavy metal concentrations were compared to the freshwater (Class C) and marine water (Class SB) quality guidelines (DENR 2016). Class C waters are intended for propagation of fish and other aquatic resources as well as recreational activities such as boating, fishing, and for agriculture use. Class SB seawater guidelines are intended for commercial propagation of fish and shellfish and are applicable for ecotourism and other activities such as bathing, swimming, and diving.



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