The Role of Spring Flood and Landscape Type in the Terrestrial Export of Polycyclic Aromatic Compounds to Streamwater

Polycyclic aromatic compounds in a northern freshwater ecosystem: Patterns, sources, and the influences of environmental factors

Polycyclic aromatic compounds (PACs) - a large group of organic chemicals naturally present in petroleum deposits (i.e., petrogenic) or released into the environment by incomplete combustion of organic materials (i.e., pyrogenic) - represent a potential risk to the health of aquatic ecosystems. In high latitude freshwater ecosystems, concentrations of PACs may be increasing, yet there are limited studies in such systems to assess change and to understand threats. Using 10 years of contemporary data from passive samplers deployed across five regions (n = 43 sites) in the Mackenzie River Basin, we (i) describe baseline levels of PACs, (ii) assess spatiotemporal patterns, and (iii) evaluate the extent to which environmental factors (fire, snowmelt, and proximity to oil infrastructure) influence concentrations in this system. Measured concentrations were low, relative to those in more southern systems, with mixtures primarily being dominated by non-alkylated, low molecular weight compounds. Concentrations were spatially consistent, except for two sites near Norman Wells (an area of active oil extraction) with increased levels. Similarly, observed annual variation was minimal, with 2014 having generally higher levels of PACs. We did not detect effects of fire, snowmelt, or oil infrastructure on concentrations. Taken together, our findings suggest that PACs in the Mackenzie River are currently at low levels and are primarily petrogenic in origin. They further indicate that ongoing monitoring and testing of environmental drivers (especially at finer spatial scales) are needed to better predict how ecosystem change will influence PAC levels in the basin and in other northern systems.

Seasonal trends and retention of polycyclic aromatic compounds (PACs) in a remote sub-Arctic catchment

Atmospheric deposition is the most dominant source of polycyclic aromatic hydrocarbons (PAHs) in remote and pristine areas. Despite low bioaccumulation potential, PAHs and their persistent transformation products (PAH-derivatives) are chemicals of concern as they can harm human and animal health through chronic low dose exposure. In this study, atmospheric deposition fluxes of polycyclic aromatic compounds (PACs) were measured on a seasonal basis (3-month periods) from 2012 to 2016 in a remote subarctic forest catchment in northern Europe. The target PACs included 19 PAHs and 15 PAH-derivatives (oxygenated, nitrogenated, and methylated PAHs). The deposition fluxes of ƩPAHs and ƩPAH-derivatives were in the same range and averaged 530 and 500 ng m2 day-1, respectively. The fluxes were found to be higher with a factor of 2.5 for ƩPAHs and a factor of 3 for ƩPAH-derivatives during cold (<0 °C) in comparison to warm (>10 °C) periods. PAHs and PAH-derivatives showed similar seasonal patterns, which suggests that these two compound classes have similar sources and deposition mechanisms, and that the source strength of the PAH-derivatives in air follows that of the PAHs. The terrestrial export of PACs via the outlet of the catchment stream was estimated to be 1.1% for ƩPAHs and 1.7% for ƩPAH-derivatives in relation to the annual amounts deposited to the catchment, which suggests that boreal forests are sinks for PACs derived from the atmosphere. Some individual PACs showed higher export than others (i.e. chrysene, cyclopenta(c,d)pyrene, carbazole, quinoline, and benzo(f)quinoline), with high export PACs mostly characterized by low molecular weight and low hydrophobicity (2-3 benzene rings; log Kow<6.0).

Analysis of polycyclic aromatic hydrocarbons (PAHs) and their derivatives in biochar treated stormwater

Polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs (oxy-PAHs) and nitrogen heterocyclic polycyclic aromatic compounds (N-PACs) are persistent and semi-volatile organic compounds primarily formed due to incomplete combustion of organic material or, in the case of the derivatives, through transformation reactions of PAHs. Their presence in the environment is ubiquitous and many of them have been proven carcinogenic, teratogenic, and mutagenic. These toxic pollutants can therefore pose a threat to both ecosystem and human health and urges for remediation strategies for PAHs and derivatives from water bodies. Biochar is a carbon-rich material resulting from the pyrolysis of biomass resulting in a very porous matter with high surface area for an enhanced interaction with chemicals. This makes biochar a promising alternative for filtering micropollutants from contaminated aquatic bodies. In this work, a previously developed and validated methodology for the analysis of PAHs, oxy-PAHs and N-PACs in surface water samples was adapted for its utilization in biochar treated stormwater with special emphasis on scaling down the solid-phase extraction as well as including an additional filtering step for the removal of particulate matter in the media.•Optimized extraction method for PAHs, oxy-PAHs and N-PACs from stormwater treated with biochar.•Biochar strongly impacts the stormwater matrix and, therefore, additional steps are required in the extraction methodology.•Solid-phase extraction combined with GC-MS have been used to analyse PAHs, oxy-PAHs and N-PACs in stormwater treated with biochar.

Evaluation of negative effect of Naphthenic acids (NAs) on physiological metabolism and polycyclic aromatic hydrocarbons adsorption of Phragmites australis

Toxic substances in the environment disturb the adsorption of pollutants in plants but little is known about the underlying mechanisms of these processes. This study evaluated the PAH adsorption by Phragmites australis under NAs stress. Results showed that Naphthenic acids (NAs) significantly decreased the adsorption of PAHs and had higher selectivity for type and structure. P. australis root cell growth and mitosis were significantly affected by NAs, which was accompanied by serious disturbances in mitochondrial function. The physiological evaluation showed the NAs could increase Reactive Oxygen Species (ROS) accumulation by around 16-fold and cause damage to the root cell normal redox equilibrium. The levels of three key related antioxidants, PLA, CAT and POD, decreased significantly to 35-50% under NAs stress and were dependent upon NAs concentration. Furthermore, NAs could significantly change the concentration and species of root exudates of P. ausralis. Autotoxic substances, including alcohol and amines, increased by 28.63% and 23.96, respectively. Sixteen compounds were identified and assumed as potential biomarkers. Galactonic, glyceric, and octadecanoic acid had the general effect of activating PAH in soil. The global view of the metabolic pathway suggests that NAs influenced the citric acid cycle, fatty acid synthesis, amino acid metabolism and the phenylpropanoid pathway. Detection data results indicated that the energy products cause hypoxia and oxidative stress, which are the main processes under the NAs. Furthermore, verification of these processes was fulfilled through gene expression and biomarkers quantification. Our results provide novel metabolic insights into the mechanisms of PAHs adsorption by P. australis under NAs disturbance, suggesting that monitoring NAs in phytoremediation applications is necessary.

Oxygenated polycyclic aromatic hydrocarbons in the surface water environment: Occurrence, ecotoxicity, and sources

Oxygenated polycyclic aromatic hydrocarbons (OPAHs) have been ubiquitously detected in atmospheric, soil, sediment, and water environments, some of which show higher concentrations and toxicities than the parent polycyclic aromatic hydrocarbons (PAHs). The occurrence, source, fate, risks and methods of analysis for OPAHs in the atmosphere, soil, and the whole environment (comprising the atmosphere, soil, water, and biota) have been reviewed, but reviews focusing on OPAHs in the water environment have been lacking. Due to the higher polarity and water solubility of OPAHs than PAHs, OPAHs exist preferentially in water environments. In this review, the occurrence, ecological toxicity and source of OPAHs in surface water environments are investigated in detail. Most OPAHs show higher concentrations than the corresponding PAHs in surface water environments. OPAHs pose non-ignorable ecological risks to surface water ecosystems. Wastewater treatment plant effluent, atmospheric deposition, surface runoff, photochemical and microbiological transformation, and sediment release are possible sources for OPAHs in surface water. This review will fill important knowledge gaps on the migration and transformation of typical OPAHs in multiple media and their environmental impact on surface water environments. Further studies on OPAHs in the surface environment, including their ecotoxicity with the co-existing PAHs and mass flows of OPAHs from atmospheric deposition, surface runoff, transformation from PAHs, and sediment release, are also encouraged.

Seasonal trends of legacy and alternative flame retardants in river water in a boreal catchment

Boreal forests store large amounts of atmospherically deposited (semi-)persistent organic pollutants (POPs). The terrestrial POPs may be exported to streams and rivers through processes that are heavily impacted by seasonality. In this screening study, concentrations of 4 legacy and 45 alternative flame retardants (FRs) were determined in the dissolved and particulate phase in streams within a relatively pristine boreal catchment in northern Europe (Krycklan Catchment Study; 3 sites) and in rivers more impacted by human activities further downstream towards the Baltic Sea (3 sites). The sampling included the main hydrological seasons (snow-free, snow-covered, and spring flood) and was conducted during two consecutive years (2014-2016). Of the 49 analyzed FRs, 11 alternative halogenated FRs (HFRs), 13 alternative organophosphorus FRs (OPFRs), and 4 legacy polybrominated diphenyl ethers (PBDEs) were detected in at least one sample. The average bulk (dissolved + particulate) concentrations of ∑FRs (including all sites) were highest for ∑HFRs (38 ± 70 ng L^-1), followed by the ∑OPFRs (3.9 ± 4.9 ng L^-1) and the ∑PBDEs (0.0040 ± 0.016 ng L^-1). Bulk concentrations of HFRs, OPFRs, and PBDEs were highly variable with season and sampling location, e.g., during spring flood, bulk concentrations were up to 600 times, 3.7 times, and 4.9 times higher for HFRs, OPFRs and PBDEs, respectively, than during periods of lower flow. Bulk concentrations of ∑OPFRs, were elevated at all sites ~6 days before the actual start of the spring flood in 2015, suggesting that hydrophobicity fractionation had occurred within the snowpack. Similar to previous studies of other POPs in the same headwater catchment, there was a general trend that levels of ∑FRs were higher at the mire site than at the forested site. Annual fluxes of FRs were found to be ~15 times higher downstream the city of Umeå compared to at the outlet of the pristine catchment. This study should be regarded as a screening study considering the large number of diverse FRs analyzed and variability in the results.