Occurrence of Antibiotics and Pharmaceutical Residues in the Coastal Waters of Mabini, Batangas

The presence of antibiotics in natural waters pose an emerging threat to the immediate environment and communities in contact with it. In an era where most antibiotics are losing effectivity and multidrug-resistant genes proliferate, the importance of assessing and monitoring antibiotic assemblage and concentration levels in the natural waters is of utmost importance. Mabini, Batangas is an area of interest for the occurrence of antibiotics in its coastal waters due to its proximity from the “Center of the Center of Marine Biodiversity” which is the Verde Island Passage. There are many well-known diving sites, hence, the coasts are actively being developed for tourism purposes. Given the high relief of the area and land use, transport of possible pollutants from higher grounds to the coasts is also perceived to be fast and efficient. Due to the geological characteristic of the area, several submarine groundwater discharge outlets that could serve as a pathway are also present near the coasts. Surface, drainage, and coastal waters were collected for analysis. Duplicates of 500 mL samples were filtered, added with 50 ppb surrogate standards, and processed through solid-phase extraction. Extracts were then injected with 1 ppb internal standards and subjected to liquid chromatography-tandem mass spectrometry analysis for the identification and quantification of selected antibiotics and pharmaceutical residues. Acetaminophen and caffeine were found to be present in the majority of the sites, reaching at most over 100,000 ng/L. Sulfamethazine, oxolinic acid and ciprofloxacin were detected separately in the coastal waters ranging from less than 10 ng/L to over 4,000 ng/L. The total levels of detected antibiotics and pharmaceutical residues are generally lower compared to Manila Bay, but the emerging presence of antibiotics present a concern on the management of run-off draining into the coasts.