The most common type of petroleum mulch that has been successfully used for over thirty years to combat desertification in vast areas of Iran is produced from heavy residual petroleum cuts. This petroleum mulch contains a wide range of various heavy hydrocarbons, including polycyclic aromatic hydrocarbons (PAHs). PAHs are present in low concentrations in petroleum mulch, particularly where it comes into contact with water and soil, creating the potential for these compounds to be transferred into the environment. Some PAHs, especially benzo(a)pyrene (BaP), have been recommended for evaluation and comparison against carcinogenicity standards.

Although Iran has long-standing experience in stabilizing sand dunes using petroleum-based products, no adequate studies have yet been conducted—neither in Iran nor in other countries—on the potential environmental impacts of petroleum mulch use.

In this study, it was assumed that precipitation and temperature influence the decomposition of mulch. Based on this assumption, different climatic regions in three provinces—Khuzestan, Kerman, and Sistan & Baluchestan—were selected. Soil samples were collected from multiple locations within each province, including both mulched and unmulched (control) sites. To estimate PAHs content, several soil samples were taken from different depths at the selected sites.

PAHs were analyzed using solvent extraction and HPLC with UV fluorescence detection. The results, compared against national standards, showed that the concentrations of PAHs, particularly BaP, in petroleum mulch and in the soil beneath the mulch, were below the permissible limits defined by national standards. In fact, this compound was reduced to 1/40 of its initial concentration at a depth of 5 cm, even after several years, indicating very limited penetration. Therefore, petroleum mulch and the contaminated soils can be considered environmentally safe.

Authors:

• H. Akbarnia (Scientific Member, Research Institute of Petroleum Industry, National Iranian Oil Company, Tehran, Iran)

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