Toxic PAH Pollution Soars in Iraqi Rivers, Winter Samples Reveal Alarming Hotspots

In the mountain-ringed governorate of Sulaymaniyah in Iraqi Kurdistan, the freshwater systems that supply drinking water, irrigation, and fish for hundreds of thousands of people are carrying a chemical burden far heavier than most residents realize. A new study published in Environmental Monitoring and Assessment by Danial B. Tahir and Rezan O. Rasheed of the University of Sulaimani has delivered the most detailed picture yet of polycyclic aromatic hydrocarbon, or PAH, contamination across eight interconnected shoreline sites in the region. The results are stark: total PAH concentrations ranged from 37.61 to 217.30 micrograms per liter throughout the winter and spring 2025 sampling campaigns, with maximum values exceeding established international water quality guidelines by several orders of magnitude. For a region that has long lacked systematic monitoring of these persistent organic pollutants, the findings amount to both a warning and a baseline.

PAHs are a family of fused-ring hydrocarbons produced whenever organic material burns incompletely or when petroleum products leak and spill into the environment. Compounds such as naphthalene, phenanthrene, benzo[a]pyrene, and fluoranthene are of intense concern to environmental chemists because many are carcinogenic, mutagenic, or endocrine-disrupting, and because their hydrophobic, persistent character allows them to linger in sediments and accumulate in aquatic food webs. Once released into a river system, low molecular weight PAHs can dissolve and travel with the water column, while heavier congeners bind to suspended particles and settle, creating long-term reservoirs of contamination that can be remobilized during floods or sediment disturbance. The World Health Organization and the United States Environmental Protection Agency have set guidelines and regulatory limits for only a handful of these compounds, which makes comprehensive regional surveys like this one especially valuable.

The study focused on the freshwater systems of Sulaymaniyah Governorate, a semi-arid mountainous region whose rivers and reservoirs are shaped by dramatic seasonal hydrology. Rainfall concentrates in the winter months, feeding spring snowmelt that swells rivers through the Zagros foothills, while summers bring low flows and high evaporation. Eight shoreline sites were selected across interconnected waterbodies, including reaches affected by the Tanjaro River, a waterway the authors describe as severely deteriorated. Raw sewage, massive local agriculture, municipal waste, and a variety of toxic industrial effluents all flow into the Tanjaro, making it a focal point for understanding how urban and industrial pressures translate into chemical signatures in the water. Samples were collected during winter and spring 2025 and analyzed for PAHs alongside major anions such as nitrate, nitrite, phosphate, sulfate, and chloride, and a suite of physicochemical parameters including pH, temperature, dissolved oxygen, and oxidation-reduction potential.

The analytical approach combined standard spectrophotometric and instrumental methods for the anions and physicochemical variables with gas chromatography–mass spectrometry for the semivolatile PAH fraction, following established protocols for environmental water analysis. The researchers then applied multivariate statistical tools, including non-parametric analyses of variance and clustering methods widely used in community ecology, to tease apart spatial and seasonal patterns in the data. Diagnostic molecular ratios, which compare the relative abundance of specific PAH congeners to distinguish combustion-derived from petroleum-derived inputs, were used to fingerprint the pollution sources. This combination of chemical measurement and statistical inference allowed the team to move beyond simple concentration tables toward a mechanistic picture of where the pollution comes from and how it moves through the system.

What the numbers revealed was a waterway network under sustained chemical assault. Total PAH concentrations were notably high at every one of the eight sites, spanning nearly a sixfold range from the cleanest to the most contaminated location. The maximum recorded concentrations exceeded established international water quality guidelines by several orders of magnitude, a margin so large that the authors characterize the contamination as severe. The Tanjaro River emerged as a critical hotspot, consistent with its role as the receiving water for Sulaimani City’s untreated sewage, industrial discharges, and agricultural runoff. Yet the study also highlights a sobering regulatory gap: the majority of the PAH compounds detected currently lack established surface water quality guidelines, meaning that for many of the chemicals found in these waters there is no legal benchmark against which to judge them, and no direct regulatory comparison is possible.

The diagnostic ratios told a story of mixed origins. Rather than pointing to a single culprit, the congener patterns indicated both pyrogenic sources, meaning PAHs formed during the incomplete combustion of coal, wood, fuel, and waste, and petrogenic sources, meaning PAHs introduced directly through petroleum products, oils, and fuels. This dual signature fits the local landscape, where vehicle emissions, generators, waste burning, and fuel handling coexist with industrial activity and agricultural operations. Correlation analysis between the major anions and the physicochemical parameters further reinforced the picture of multiple anthropogenic pressures acting simultaneously on water quality, with nutrient enrichment from sewage and fertilizers tracking alongside the organic pollutant load.

Seasonality emerged as one of the most striking findings. PAH burdens were consistently higher in winter than in spring, a pattern with clear physical explanations. Winter rains wash accumulated pollutants from roads, soils, and urban surfaces into the rivers, a process environmental scientists call runoff-driven mobilization. Lower water temperatures also slow the volatilization, photodegradation, and microbial breakdown that would otherwise remove PAHs from the water column, so the same input lingers longer in winter. Lower river flows provide less dilution capacity, concentrating whatever contaminants enter the system. The spring decline, while welcome, should not be mistaken for recovery; it reflects dilution and degradation rather than any reduction in the underlying sources, which remain active year-round.

The ecological and public health implications are considerable. PAHs are known to impair fish reproduction and development, damage hepatic tissue, and induce oxidative stress in aquatic organisms, and related work by one of the authors has documented PAH accumulation in the muscle tissue of fish from the Derbendikhan Reservoir in the same region. Communities in Sulaymaniyah Governorate depend on these interconnected waters for drinking water, fishing, and agriculture, and previous regional studies have linked environmental contamination in the area to elevated serum heavy metals and cancer incidence. Because many PAHs are lipophilic, they bioaccumulate in fatty tissues and can biomagnify up the food chain, meaning that concentrations measured in water today may foreshadow exposures in fish and, ultimately, in people. The winter peaks identified in this study are particularly concerning for water treatment systems that may not be designed to remove semivolatile organic compounds.

Beyond the immediate findings, the study fills a genuine gap in global environmental data. While PAH contamination has been extensively surveyed in the Euphrates system, the Danube, the Yangtze, and major South and East Asian rivers, the freshwater systems of the Kurdistan Region of Iraq have remained largely unstudied, despite hosting a UNESCO City of Literature and a growing urban population. By establishing a critical baseline for 2025, the research gives future monitoring programs a reference point against which to measure improvement or decline, and it demonstrates a transferable methodology for understudied regions worldwide that face similar combinations of rapid urbanization, weak wastewater infrastructure, and industrial emissions.

The authors argue that the evidence now justifies stronger pollution control measures, including wastewater treatment for Sulaimani City, regulation of industrial discharges into the Tanjaro River, and the development of surface water quality guidelines for the PAH compounds that currently escape regulatory scrutiny. As climate change alters the precipitation regime of the Zagros Mountains and intensifies the seasonal extremes that govern pollutant transport in these rivers, the window for effective intervention may be narrowing. What this study makes unmistakably clear is that the waters of Sulaymaniyah are not merely dirty in a general sense; they carry a chemically specific, seasonally patterned, and traceable burden of some of the most well-characterized carcinogens in environmental science, and the tools to identify, monitor, and ultimately reduce that burden are now demonstrably in hand.

Subject of Research: Polycyclic aromatic hydrocarbon contamination and seasonal water quality in the freshwater systems of Sulaymaniyah Governorate, Iraq

Article Title: Surface water quality monitoring in Sulaymaniyah Governorate, Iraq: polycyclic aromatic hydrocarbons, major anions, physicochemical parameters, and seasonal trends

Article References: Tahir, D. B., & Rasheed, R. O. (2026). Surface water quality monitoring in Sulaymaniyah Governorate, Iraq: polycyclic aromatic hydrocarbons, major anions, physicochemical parameters, and seasonal trends. Environmental Monitoring and Assessment, 198(10), Article 1052. https://doi.org/10.1007/s10661-026-15784-2

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15784-2

Keywords: polycyclic aromatic hydrocarbons, water quality, Sulaymaniyah, Iraq, Tanjaro River, freshwater pollution, seasonal variation, pyrogenic sources, petrogenic sources, persistent organic pollutants, environmental monitoring, major anions