Background and purpose: Shadegan wetland as the largest wetland in Iran is constantly exposed to hydrocarbons entering through the main entrance of the lagoon including Jarahi River, outbursts of seasonal rivers from upstream, Persian Gulf tides from downstream, atmospheric deposition, and possible leaks from oil pipelines. The aim of this study was to investigate toxicity and identifying the sources and spatial distribution of polycyclic aromatic hydrocarbon (PAH) in surface sediments of the study area for its appropriate management.

Materials and methods: Sediment samples were collected (in 2015) from 202 stations at the top 5 cm of the sediment according to a systematic-random sampling design. The concentrations of PAHs were analyzed by GC–MS.

Results: The total PAHs (sum of 30 PAH compounds) ranged from 593.74 to 53393.86 ng/g dw. The results of diagnostic ratios indicated that the study area was highly contaminated by petrogenic hydrocarbon sources. The concentrations of PAHs in this research were substantially higher than those found in many other aquatic systems and significantly more than current sediment quality criteria (ERL).

Conclusion: High levels of petrogenic contamination were found in sediments of Shadegan wetland. A vast majority of the study area (90%) is subjected to chronic pollution of oil contaminants that could adversely affect benthic biota.