Occurrence and depositional history of organochlorine pesticides in the sediments of the Zayandehrud River in the arid region of Central Iran.

In this study, surface sediments along the Zayandehrud River (14 samples), and two dated core sediments (46 samples) from small artificial urban lakes at the middle section of the Zayandehrud River in the Gavkhooni basin in the central arid regions of Iran were analyzed for residual levels of 20 organochlorine pesticide (OCP) compounds. Total OCP concentrations ranged from 0.1 to 50.1 ng g-1 dry weight and from 1.9 to 51.5 ng g-1 dry weight in surface and core sediments, respectively. Dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD) were found to be the predominant OCPs in these sediments. The calculated metabolic and isomeric ratios confirmed the aged nature of residual dichlorodiphenyltrichloroethane (DDT) in sediments. Moreover, the isomeric ratios indicated the aged nature of technical HCH (hexachlorocyclohexane), while the contribution of γ- HCH (lindane) as a main source has increased, especially in the last two decades. Past usage, as well as current usage of endosulfan technical mixture in the Gavkhooni basin, has been found in the last four decades. Analyses of sedimentary cores, as natural archives, have shown the successful ban on the use of organochlorine pesticides (especially DDT) in the Gavkhooni basin, and to some extent, in the central plateau of Iran. In general, it can be concluded that natural factors (i.e., floods and wet years) lead to soil leachate and play an essential role in remobilization and transfer of residual OCPs from soil to inland aquatic ecosystems in the Gavkhooni basin, which is an arid region.

Distribution and characteristic of PAHs in sediments from the southwest Caspian Sea, Guilan Province, Iran.

Contamination by polycyclic aromatic hydrocarbons (PAHs) in the southwest Caspian Sea was assessed by examination of 45 sediment samples, collected from the coasts of the Guilan Province in 2012 and analyzed for 29 PAHs. The concentrations of PAHs were in the range of 232.1-1,014 ng g(-1) dry weight (mean 520±246.4 ng g(-1)). The predominance of alkyl-substituted naphthalenes and phenanthrenes and the higher contributions of petrogenic compounds (NPD=35.4-74.4%) compared to pyrogenic PAH compounds (COM=18.1-47.4%) reveal a petrogenic source for PAHs with ubiquitous distribution in the study area. Offshore increase of total PAH concentrations was found to be correlated with increase of organic matter content of sediments, but no correlations with particle size fractions were found. The evaluation of ecotoxicological risk by sediment quality guidelines indicated that total PAH concentrations at all sites were below the effects range-low (ERL), but some individual petrogenic PAHs at some stations were significantly above their ERL and likely to adversely affect benthic biota. According to the diagnostic ratios used, most stations revealed the major source of the PAHs to be petrogenic, but some stations suggested a mixed petrogenic-pyrogenic source.

Vertical distribution and source identification of polycyclic aromatic hydrocarbons (PAHs) in southwest of the Caspian Sea: most petrogenic events during the late Little Ice Age.

In this study, 75 samples of two (210)Pb-dated cores from the southwest of the Caspian Sea were analysed for 30 compounds of polycyclic aromatic hydrocarbons (PAHs). The TPAH29 flux of the last six centuries ranged from 16.3 to 177.3 and 22.3 to 426.2 ng cm(-2)y(-1) in the Rezvanshahr and Anzali core sediments, respectively. Prior to 1840, four distinct maxima in PAH fluxes (61-426.2 ng cm(-2)y(-1)) with a low weathered petrogenic pattern were found in each of the core sediments. Simultaneity of distinct peaks of PAH fluxes before 1840 and Caspian Sea level high-stands during the Little Ice Age (LIA), revealed the high importance of this phenomenon in washing and transport of land-based oil pollution into the Caspian Sea. An overall increase in some diagnostic ratios (Flu/202, IP/276 and BaA/228), especially after 1940, indicated increase of pyrogenic PAHs as a result of industrial development in the catchment area.

Perylene as an indicator of land-based plant biomarkers in the southwest Caspian Sea.

In this study, 84 surface sediment samples, from 28 Iranian rivers, 45 surface sediment samples and 31 samples from one core in the southwest of the Caspian Sea were collected and analyzed for polycyclic aromatic hydrocarbons (PAHs). The results showed high variability of perylene in coastal surface sediments (1.3-123.6 ng g⁻¹ dw) and river sediments (0.5-111.1 ng g⁻¹ dw). Core samples revealed high levels of perylene which increased with depth. Three diagnostic ratios (DRs) for source identification of perylene (Per/TPAH, Per/PAI and Py/Per) revealed a dominance of biogenic inputs to the surface layers (coasts and rivers) and diagenetic production of perylene in the sediment core. Hyrcanian forests with humid climates favor wood-degrading fungi and the production of perylene and its precursors. Biogenic production of perylene as a land plant derived biomarker can be used for the reconstruction of paleoclimatic conditions of the southwest Caspian Sea.