Pollution levels in Sri Lanka’s west-south coastal waters: Making progress toward a cleaner environment

Sri Lanka’s Western-Southern coastal area, home to more than 40% of the country’s population and the commercial capital city of Colombo, receives the most attention. Fisheries, tourism, hotel and restaurant, commercials, and administrations are among the government and non-government enterprises established in the area, demonstrating localization that impacts people’s lifestyles. This study aimed to identify point sources of coastal water pollution in the west-south coastal belt using the standard physico-chemical and microbiological methods, for 65 sampling sites from Negombo to Mirissa. The study area was divided into 11 land segments based on the environment type. 6 land segments and 5 land segments were used to cover the Western province and Southern province respectively. Each parameter was compared by province. Temperature and pH fluctuated less over the coastal belt between Negombo and Mirissa. The average temperature was 28.89 ±1.5 °C, and the pH ranged from 7.41 ± 1.5 to 9.64 ± 1.6. Electrical Conductivity (EC) and Dissolved Oxygen (DO) displayed dynamic changes, with average values of 40.88 ± 16.90 mS/cm and 7.66 ± 2.78 mg/L, respectively. The chemical limiting factor of the study areas was nitrogen. Nitrate was 0.01 mg/dm3 for almost all sampling locations and the highest Nitrite was 2.94 ± 0.8 μg/dm3. The highest Ammonia was 62.18 ±6.1μg/dm3, and Total Phosphorus (TP) was ranged from 92.41 ± 6.4 to 421 ±7.2μg/dm3. The Chemical Oxygen Demand (COD) was recorded between 112.5 ± 8.7 and 7318 ± 8.9 mg/dm3 and the maximum oil and grease concentration of 192.34 ± 7.6 mg/dm3. Unsurprisingly, fecal coliform was found in practically all of the coastal waterways, indicating fecal contamination, and the discovery of Salmonella sp. pathogenic bacteria from the Dehiwala canal and Rathmalana sampling locations drew additional attention. The highest level of Tributyltin (TBT) pollution was found in the Dikkovita fishery harbor (241 ± 4 ng/L), with TBT levels ranging from 51 ± 2 to 158 ± 2 ng/L in the remaining locations. The findings revealed that the study area has begun to decline due to anthropogenic activities and that there is less care for environmental friendliness as development stories progress.