Environmental Assessment of Hydrocarbon Accumulation and its Correlation with Dissolved Organic Matter in the Tigris River

Abstract

In this research study, it was attempted to determine the levels of organic and hydrocarbon pollutants in the Tigris River due to the effluents from industries and thermal sources, as well as to estimate the capacity of the river's self-purification. Four representative sampling stations were chosen on the course of the river: Station 1 being used as the control point, Station 2 situated near the outlet of a vegetable oils factory, Station 3 downstream of the South Baghdad Thermal Power Plant (Al-Zaafaraniya), and Station 4 in the Tuwaitha area. High-Performance Liquid Chromatography (HPLC) was used to identify and to calculate the concentration of the following three most dangerous PAHs: naphthalene, anthracene and benzo[a]pyrene. The analytical method was combined with environmental analyses using Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD5).The results have shown significant differences between the COD (up to 115 ppm) and BOD5 (46.0 ppm) values at the vegetable oils factory station, which speaks to the complex structure of the organic contaminants not being easily decomposable. Analysis of pollutants using chromatography showed spatial variations in their concentration. Station 3 was the power plant, and it had the highest amount of pollution. The increase in pollutants such as naphthalene (84.91 ppm) and benzo[a]pyrene (7.05 ppm) can be attributed to thermal pollution and hydrocarbon contamination in the water. In contrast, the river had partial self-purification and attenuation between stations 1 and 2, but the assimilative capacity of the river was completely lost in subsequent stations, ending in Station 4 (Tuwaitha). In Station 4, pollutants were numerically stabilized at 61.25 ppm for naphthalene with overlap, suggesting a situation of cumulative organic load. Thus, the research shows that the waters of the Tigris River in the zones of investigation have significant pollution from chemical organics, which exceed internationally recognized standards and thresholds, especially benzo[a]pyrene—a potent carcinogen. This poses an immediate danger to the biological system of the river and humans, implying the necessity to implement primary treatment plants and constant monitoring systems.