Preliminary Water and Sediment Quality Assessment of the Meycauayan River Segment of the Marilao-Meycauayan-Obando River System in Bulacan, the Philippines

Background. The Meycauayan River is considered one of the most severely polluted rivers in the Philippines due to heavy metal and organic pollution that has caused environmental degradation. Objectives. The aim of the present study was to provide insight on the current status of the Meycauayan River and outline an appropriate strategy to solve problems of organic and heavy metal contamination. Methods. The physical, chemical and biological characteristics of the water and sediments were analyzed and evaluated based on available local and international standards. Three sites (upstream, midstream and downstream) of the river were considered for the evaluation of water and sediment quality. Results. Dissolved oxygen, measured in the morning, was very low at the upstream sampling station (1.87 ppm) and even lower at the downstream site (0.49 ppm). The temperature for the three sites ranged from 28.03°C (upstream) to 30.75°C (downstream). Visual inspection indicated that the color of the water was gray upstream and midstream, and black at the downstream station. Biochemical oxygen demand exceeded the recommended limits of the Department of Environment and Natural Resources (DENR) of 7.0 ppm with values of 13.22 ppm (upstream) and 12.02 ppm (downstream). Chemical oxygen demand exceeded the limit of 20 ppm at the downstream site at 84 ppm. Dissolved oxygen did not reach the recommended limit of 5.0 ppm of the DENR. There was a high coliform count at both the upstream (3.5 × 104 colony-forming unit (cfu)/ml) and downstream (2.5 × 104) sites, which exceeded the limit of the United States Environmental Protection Agency (USEPA) of 126 cfu/100 ml. Heavy metals such lead (Pb), zinc (Zn), copper (Cu), manganese (Mn) and chromium (Cr) exceeded the severe effect level of the National Oceanic and Atmospheric Administration (NOAA), which could be detrimental to humans and aquatic life. The results of one-way analysis of variance showed significant differences (p <0.001) in pH, temperature, dissolved oxygen, conductivity, total dissolved solids, chemical oxygen demand, nitrates and phosphates for water quality and Pb, Zn, Cu, Mn and Cr for sediment quality across the study sites. Conclusions. The results of the present study indicate that the downstream site was more polluted, possibly due to the accumulation of pollutants coming from the upstream site. The deterioration of the Meycauayan River is a result of rapid industrialization, urbanization and population growth. Examination of the water quality of the Meycauayan River indicates that it is very polluted and requires an immediate solution. The results of the present study should be used as a basis for crafting strategies to rehabilitate the Meycauayan River. Competing Interests. The authors declare no competing financial interests. This study was funded by Pure Earth.

Research pollution are severe in this river system and have caused environmental degradation such as decreased quality of fish harvest and degraded water quality for aquaculture ponds. Water pollution can also pose public health problems such as accumulation of heavy metals in fish, which can affect human consumers of fish from this river system through increased blood lead levels of heavy metals, which can be fatal. The river system is heavily polluted due to many industrial and domestic sources, including untreated municipal wastewater from sewers and poorly operated septic tanks; heavy metals (chromium (Cr), lead (Pb), cadmium (Cd), etc.) and chemical discharges from formal and informal industries such as used Pb-acid battery recycling, leather tanning industries, gold and precious metals refining and jewelry making, solid waste dumped into the rivers or drainage, as well as silt, wastes, oil and other contaminants discharged as part of the runoff in the area. 3 Water pollution due to industrial activities and technological development poses significant threats to the environment and public health because of its toxicity, nonbiodegradability and bioaccumulation. The degraded state of the water resources in the Philippines arises from the absence of an effective system to stop the uncontrolled dumping of untreated sewage, garbage and industrial effluents into water bodies. In light of these problems, it is important to determine and assess the condition of the surrounding environment. A river's water quality is caused by several interrelated compounds which are subjected to spatial and temporal variation and affected by water volume. 4 Water quality assessment is an important ecological investigation to determine the current condition of a river. This preliminary study can serve as a basis for the crafting of strategies to revive, rehabilitate, and protect the river system in Bulacan.
The general objective of the present study was to assess the physicochemical, microbiological and sediment quality of the river system. The study specifically aimed to examine physico-chemical water quality variables (dissolved oxygen, temperature, pH, conductivity, total dissolved solids, nitrate, phosphate, and biochemical and chemical oxygen demand) and biological quality (total bacterial and total coliform count) of the Meycauayan River. In addition, the present study aimed to determine the heavy metal content of the river sediment and identify the site with the highest pollution load in the river system.

Methods
The study area was the Meycauayan River segment of the Marilao-Meycauayan-Obando river system in Bulacan. Bulacan is located immediately north of the National Capital Region. Three sampling points were chosen to be representative of the river. The sampling sites were chosen  Figure 1 presents a map of the study area.

Water sample collection
Water samples were collected from upstream, midstream and downstream locations of the river segment on October 10, 2014 from 9:00 am to 10:00 am. Four replicate samples were obtained for the determination of the in-situ water quality indicators. Four replicate samples were obtained and pooled equally into two 1 L polyethylene bottles for analysis. The samples were placed in an ice chest for transport to the Central Analytical Services Laboratory, BIOTECH,

University of the Philippines Los
Baños for the ex-situ analysis. Table 1 presents the analytical methods and instruments used for the determination of the different variables.

Total bacterial and total coliform count
Four replicate samples were obtained and pooled equally into one sterilized dilution bottle. The dilution bottle was placed in an ice chest during transport to the laboratory. Serial dilutions of the water sample were prepared. Each dilution was plated on three replicates of solidified freshly prepared nutrient agar and violet red bile agar (for total coliform count) and spread using a sterile glass rod and incubated at room temperature (30°C) for 24 hours after which the colonies that developed on the plates were counted. Those counts with 25-250 colony-forming units (cfu) were reported as total viable count. 9

Sediment collection and analysis
Surface sediments were collected at each site along the river using a grab sampler. Replicate samples were collected and pooled to represent the site. Samples were brought to the laboratory for heavy metal analysis. Prior to analysis, the samples were air dried for 24-48 hours. After air drying, the sediments were analyzed using X-ray fluorescence spectrometry (Niton-XRF analyzer).

Data and statistical analysis
The water quality indicators at the upstream and downstream sites were compared and analyzed. Physicochemical and microbiological results were compared to different water quality standards for freshwater to determine whether they were within the recommended safe limits based on Pleto, Migo, Arboleda

Table 1 -Analytical Methods Used for Determinations of Water Quality Variables
Research the DENR administrative order 2016-08. 10 Sediment quality was assessed using the standard set by the National Oceanographic and Atmospheric Administration (NOAA) for sediment quality. 11 One-way analysis of variance (ANOVA) and post-hoc Tukey's test were used to determine significant differences across the sites for the study variables.

Results
The mean physico-chemical variables and water quality criteria from different agencies are presented in Table 2. The visual color of the water at the upstream site was gray, while water at the downstream site appeared black. The water was slightly alkaline in nature as indicated by its pH. The mean pH of the upstream site was 7.49, while the midstream and downstream sites had a pH of 7.28 and 7.35, respectively. According to DENR 2016-08, it was within the recommended limits of 6.5-9.0. 10 The temperature from upstream to downstream was within the recommended range of 25-31°C set by the DENR during the sampling time. The dissolved oxygen levels at the three sites were very low and did not meet the standard level of 5.0 ppm. The upstream dissolved oxygen level was low (1.87 ppm) with a saturation of 23%, which is unsatisfactory for aquatic life. In addition, the mean dissolved oxygen level at the midstream site was only 0.98 ppm with a saturation of 12%, while downstream had the lowest dissolved oxygen level with 0.49 ppm and saturation of only 6%. In terms of electrical conductivity, the downstream site had the highest conductivity of 738.80 mS/cm, followed by the midstream site (642.33 mS/cm) and the upstream site (391.59 mS/cm). The recommended conductivity level for aquatic organisms is only 0.15-0.50 mS/cm. 12 Total dissolved solids (TDS) are directly related with conductivity.
The present study showed that TDS increased from upstream towards downstream. The oxidation reduction potential (ORP) was positive, but relatively low upstream (30 mV) and midstream (15 mV) and negative downstream (-190.75 mV). The recommended ORP limit for aquatic life is 300-500 mV. 13, 14 The biochemical oxygen demand for both upstream (13.22 ppm) and downstream (12.02 ppm) exceeded the recommended limit of 7.00 ppm by the DENR. 10 The chemical oxygen demand level was higher at the downstream site (84 ppm) than the upstream site (20 ppm). Downstream exceeded the recommended chemical oxygen demand limit of 20 ppm. 15

Table 2 -Mean Physico-Chemical Water Quality Variables of the Study Site and the Recommended Standards for Each Variable
Water and Sediment Quality of the Meycauayan River, Philippines

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(1.04 ppm) was high compared to upstream (0.42 ppm). The phosphates at the downstream site exceeded the recommended limit of 0.5 ppm.
Aside from physico-chemical variables, the quality of the water samples was also determined through microbial indicators. The most common group of bacteria used for monitoring and assessing water quality are coliform bacteria. The coliform counts obtained at the upstream and downstream sites of the river were 3.5 x 10 4 cfu/ml and 2.5 x 10 4 cfu/ml, respectively. Based on the standards set by the United States Environmental Protection Agency (USEPA) for freshwater bodies of water that are used for recreational activities such as bathing, which is a criterion of Class C water, the water samples from the downstream and upstream sites exceeded the allowed limit of 126 cfu/ml. 16 A bacterial count for water samples from the same sources was also obtained and the results showed that the bacterial counts obtained at the upstream and downstream locations of the river were 1.4 x 10 6 cfu/ml and 7.5 x 10 5 cfu/ml, respectively.

Heavy metal content of sediment
The results of the sediment quality analysis of heavy metals using X-ray fluorescence spectrometry and their assessment with different sediment quality guidelines are shown in Table  4  and midstream (178 ppm) locations and below the limit of detection at the downstream site. They also exceeded the severe effect level of 75 ppm. The manganese (Mn) level of the midstream and downstream sites was high and exceeded the severe effect level of 1100 ppm. The Cr level increased from upstream to downstream. It also exceeded the severe effect level of 110 ppm. The other heavy metals such as arsenic (As), mercury (Hg) and Cd were below the limit of detection.

Discussion
The river water was gray at the upstream location and almost black downstream. This might be due to the color of sediments, which were gray to black in color, and the presence of pollutants. Temperature is an important indicator because it could have an effect on other physical phenomena, such as the rate of biochemical and chemical changes, reduction in solubility of gases and amplification of taste and odor of water. 17 Temperature affects organisms present in the water since every living organism has its own tolerance range. It can affect other water quality variables such as dissolved oxygen, pH, ORP and conductivity. The pH level of the sites was slightly alkaline, which is desirable for aquatic organisms. Aquatic organisms function efficiently at a pH range of 6.5-9.0.
Dissolved oxygen is regarded as one of the most important indicators of water quality. It is essential for the survival and physiological function of fish and other aquatic organisms. A number of factors that could affect dissolved oxygen concentrations include water movement, presence of photosynthetic organisms (algae and aquatic plants) and bacteria, temperature and pollution. One cause of decreased dissolved oxygen concentration is pollution, due to effluents or runoff water with constituents that have high oxygen demand for decomposition. 18 Based on the obtained results, the dissolved oxygen level did not meet the standard of the DENR, which is 5.0 ppm. The dissolved oxygen level was very low and unsatisfactory for aquatic life. It indicates that there is very low abundance of photosynthetic organisms in the river system due to pollution. In addition, the water on the upstream side was stagnant, which resulted in a decreased dissolved oxygen level. In terms of temperature level, dissolved oxygen is inversely related, and the solubility of gases decreases as temperature increases. 19 The results agreed that a higher temperature site demonstrated relatively low dissolved oxygen levels. A decrease in dissolved oxygen level might also be due to the consumption of bacteria during decomposition. The Meycauayan River is classified as hypoxic, with a dissolved oxygen level < 2.0 ppm. During the assessment of the National Water Quality Status Report, the annual average dissolved oxygen in the Meycauayan River was 1.5 ppm (2003)  Biochemical oxygen demand determines the amount of oxygen required for the decomposition of organic matter from a pollution source. The demand for oxygen does not occur directly where the effluent or runoff water is discharged, but is manifested somewhere downstream where decomposition finally occurs. Thus, a higher O value indicates more pollution. 18 The results showed that river water exceeded the recommended limit of 7 ppm. Biochemical oxygen demand has an inverse relationship with dissolved oxygen. The higher the biochemical oxygen demand, the more rapidly oxygen is depleted in water. Hence, less oxygen is available to aquatic organisms. Different sources of biochemical oxygen demand in the river system might come from effluents from industries, wastewater treatment plants, domestic waste and water runoff. Aside from the physico-chemical variables, water sample quality was also determined through microbial indicators. The most common group of bacteria used in monitoring and assessing water quality are coliform bacteria. Coliforms are non-sporeforming, rod-shaped bacteria which are commonly found in the environment and in the feces of warm-blooded organisms. Due to the characteristics of coliforms, they are used in detecting human and animal fecal contamination in bodies of water. The World Health Organization uses coliforms as a microbiological parameter for assessing water quality due to high occurrence of the bacteria in the feces of humans and warmblooded animals, high counts in wastewater and polluted waters and absence from pure water and other

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Pleto, Migo, Arboleda environments which do not have any contact or intervention with humans and other animals. 25 Coliform count is one of the most important water quality indicators related to human health. Existing studies have monitored heavy metals in water, but not in sediments in the Philippines. It is essential that sediment quality be considered to determine overall environmental health because of the importance of benthic organisms. A study was conducted to determine the heavy metal concentration of sediments from Manila Bay and its inflow rivers. The Meycauayan River discharges into Manila Bay. The study showed that Pb, Cd, Zn and Cu were elevated in riverine sediments. 29 Few studies have addressed sediment heavy metal pollution in river quality assessments in the Philippines.

Statistical analysis
The results of one-way analysis of variance (ANOVA) for water quality shows significant differences in variables such as pH, temperature, dissolved oxygen, conductivity, total dissolved solids, chemical oxygen demand, nitrates and phosphates. The post-hoc Tukey test showed significant differences for these variables across the three study sites. In the analysis of sediment quality, one-way ANOVA and post-hoc Tukey test showed significant differences in sediment for Pb, Zn, Cu, Mn and Cr across the three study sites.

Conclusions
The results of the present study indicate the presence of severe heavy metal pollution in sediments. Lead, Zn, Cu, Mn and Cr exceeded the severe effect level by NOAA for the three stations. One-way ANOVA showed significant differences (p < 0.001) in sediment heavy metal concentrations across the three sites. The deterioration of the Meycauayan River has been a result of rapid industrialization, urbanization and population growth.
The present study provides preliminary information on the severity of pollution in the Meycauayan River. Hence, a further, more comprehensive study of the Meycauayan River is recommended to determine its environmental health status. A water quality index assessment would help to determine which water quality variable should be prioritized. Further studies should include all of the abiotic and biotic elements of the river system. In addition, sediment quality index assessment must be included and highlighted because of the importance of sediment to the health of surrounding water bodies. This will provide a better vision of the current status of the Meycauayan River. The present study could be used as a basis for the development of strategies for reviving, rehabilitating and protecting the Meycauayan River.