By Freddie Rabelas Obligacion, Ph.D.
The Pasig River, one of the major Philippine river systems, connects Laguna de Bay to Manila Bay. Spanning 25.2 kilometers (15.7 miles), it bisects the Philippine capital of Manila and its surrounding urban area into northern and southern halves. Its major tributaries are the Marikina River and San Juan River. The total drainage basin of Pasig River, including the basin of Laguna de Bay, covers 4,678 square kilometers (1,806 square miles).
The Pasig River figured as an important transport route and source of water for Manila during the Spanish era. Unfortunately, as a result of negligence and industrial development, the river evolved into a highly polluted water body. In fact, it is considered by many ecologists as biologically dead or is unable to sustain life.
The Pasig River Rehabilitation Commission (PRRC), a state entity under the Office of the President, was tasked with rehabilitating the Pasig River. The commission served for 20 years, from 1999 until its dissolution by President Rodrigo Duterte in November 2019. The commission’s powers and functions were transferred to the Manila Bay Task Force and the Department of Environment and Natural Resources (DENR).
This report presents quantitative water quality data in the Pasig River tributary communities (esteros) of Maypajo, Sunog Apog, Vitas, San Lazaro, Kabulusan, Magdalena, Binondo, and De la Reina all situated within the Metro-Manila area. Scientific data came from the PRRC’s Environmental Division that performed on-site, laboratory, and sedimentary analyses.
According to the California State Water Resources Board, the “vital signs” or the five basic water quality parameters that are basic to life within aquatic systems are dissolved oxygen (DO), temperature, electrical conductivity/salinity, pH, and turbidity. Impairments of these can be observed as impacts to flora and fauna in a given water body. Additional water quality parameters such as biochemical oxygen demand (BOD), total coliform and total fecal coliform will also be discussed.
Dissolved oxygen (DO) refers to the amount of oxygen dissolved in water. Because fish and other aquatic organisms cannot survive without oxygen, DO is the most important water quality parameter. The DENR standard for DO is at least 60% saturation. All 8 esteros failed to satisfy the DENR standard of at least 60% saturation with their very low saturation levels ranging from a low of 7.58% in Binondo to a high of merely 38.04% in Maypajo.
Temperature is a measure of the average kinetic energy of water molecules. It is one of the most important water quality indicators because it influences DO concentration, photosynthetic rates of algae and other aquatic plants, the metabolic rates of organisms and their sensitivity to toxic wastes, parasites and diseases. The DENR standard for Class C waters (used for propagation of fish and other aquatic resources, boating, fishing, agriculture, irrigation and livestock watering) is an allowable temperature increase over the average ambient temperature for each month or a maximum rise of 3 degrees Celsius. All eight esteros far exceeded 3 degrees Celsius and hence failed to meet the prescribed DENR standard. The highest excess in temperature was noted in Sunog Apog (28.7 degrees Celsius), while the lowest was seen in Maypajo (26.45 degrees).
Electrical conductivity is the ability of water to conduct an electrical current. Significant changes in conductivity, whether due to natural flooding, evaporation or man-made pollution can be very detrimental to water quality. There is no DENR standard for conductivity. However, the U.S. standard for drinking water set by the Environmental Protection Agency’s (EPA) National Secondary water standards is less than or equal to 900 microSiemens/micromhos per centimeter. Viewed against the EPA criterion, all eight esteros met the benchmark with their low conductivity values ranging from a low of 0.77 in De la Reina to a high of 24.39 in Sunog Apog.
Salinity is an estimate of the level of salt in a water sample. The higher the salinity, the lower the DO concentration. The waters of Sunog Apog with a salinity of 2.44 ppt falls in the brackish/estuary category, indicating a relatively low DO concentration.The waters of Maypajo, Kabulusan, Magdalena with salinity values less than 0.5 ppt belong to the freshwater category, implying higher DO concentration.
pH is a measure of how acidic or basic (alkaline) a water source is. pH values less than 4.8 or greater than 9.2 can be harmful to aquatic life. The DENR pH standard for Class C waters establishes the optimum range of 6.5 to 8.5. Only Binondo met such standard. The other 7 esteros showed acidic levels with pH values lower than the prescribed lower limit of 6.5. The most acidic waters came from Magdalena which had a pH of 6.05.
Turbidity is a measure of the amount of suspended particles in water. When turbidity is high, water loses its ability to support a diversity of aquatic organisms. There are no specific standards for turbidity. However, Mitchell and Stapp (1986) suggested a guideline level of 23 NTUs. Viewed against this standard, all 8 esteros have substantially higher values. Among the 8 esteros, the most turbid or murkiest water came from San Lazaro (158.94), while the least turbid was Sunog Apog (26.91).
Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms (those requiring oxygen for their metabolism) to break down organic material present in a given water sample. High BOD levels indicate a reduction of oxygen availability in a water sample. The DENR standard for Class C waters is a BOD level equal to or less than 7.0 milligrams per liter. Compared with the DENR standard, all 8 esteros’ relatively high values exceeded the 7.0 upper limit which imply low oxygen availability. The lowest BOD reading was observed in Sunog Apog (32 mg/L), while the highest was in San Lazaro (121.67).
Coliform is a very common rod-shaped bacterium. Total coliform is viewed as a general indicator of potential contamination of a water source with pathogenic and disease-causing organisms. The DENR standard for Class C waters, is less than or equal to 5,000 MPN (Most Probable Number) per 100 milliliters of water. All 8 esteros failed to meet this standard, as shown by counts way exceeding the prescribed maximum limit. San Lazaro had the highest total coliform (13,300,000 MPN/100 ml. of water), hence the worst water quality. Binondo showed the lowest count (2,160,000 MPN/100 ml. of water, thus the best water quality according to the total coliform criterion.
Fecal coliforms are the coliform bacteria that originate specifically from the intestinal tract of warm-blooded animals (e.g. humans, raccoons, beavers). Fecal coliform provides stronger evidence of fecal contamination than total coliform counts. The DENR standard for Class C waters is less than or equal to 200 Most Probable Number (MPN)/100 ml. water. All 8 esteros far exceeded such total fecal coliform criteria. The highest total fecal count, hence the worst water quality, was seen in Maypajo (7,040,000 MPN/100 ml. water). The lowest, thus relatively the best water quality, was in Binondo (4,800,000 MPN).
In conclusion, most of the numerical water quality indicators reveal a high level of pollution. All 8 esteros failed 3 of the 5 vital signs of water quality, namely, dissolved oxygen, temperature and turbidity. Moreover, BOD level, total coliform and total fecal coliform counts far exceed benchmarks. These findings indicate an urgent need to immediately reduce the influx of human and industrial wastes into the Pasig River. To do this, residents of esteros must be encouraged to connect to sanitary sewage systems. Equally important is the strict implementation of laws prohibiting the discharge of industrial wastes into the river, a task easier said than done.