Explaining PAH desorption from sediments using Rock Eval analysis

Characterisation of former manufactured gas plant soils using parent and alkylated polycyclic aromatic hydrocarbons and Rock-Eval(6) pyrolysis

Soils sampled from 10 former manufactured gas plants (MGP) in the UK were investigated using gas chromatography mass spectrometry (GC-MS/MS) and Rock-Eval (6) Pyrolysis (RE). RE is a screening tool used to characterise bulk organic matter in soils via the release of carbon compounds during pyrolysis and oxidation. Both the distributions and concentrations of 30 parent and 21 alkylated polycyclic aromatic hydrocarbons (PAHs) and the parameters of RE were analysed to establish relationships between soils and the MGP processes history. Principal component analysis (PCA) using the PAHs distributions and RE parameters can assist with differentiating between MGP processes. MGP processes utilizing oil provided the clearest results, attributed to petrogenic signatures with high proportions of low molecular weight PAHs. Processes using lower temperature processes were distinguished by higher proportions of high molecular weight PAHs. RE parameters alone were unable to distinguish MGP processes but showed potential in estimating the lability and thus the amount of PAH that could be released from soils. This research provides new insights that may be useful in understanding and characterising the risks posed to human health from PAHs in soils.

Dynamic process and mechanism of crude oil release from silty intertidal sediment under different influencing factors

Under tidal scouring, residual petroleum in the intertidal sediment after oil spills could release again, causing secondary pollution in the marine ecosystem. The current study aimed to investigate the dynamic process and principles of crude oil release from silty intertidal sediment under different influencing factors and screened for the key factors. In this paper, the fitting equations and correlation between the release amount and various factors were explored through the single-factor and orthogonal experiments. Then, the key influencing factors were selected for multi-factor fitting of the release amount. The results showed that the oil release amount rose with the increase in oil concentration, oscillation frequency, and release time, but decreased with an increase in salinity. As the pH decreased, the oil release amount increased. The relationship between release amount and concentration/oscillation frequency can be equipped by the polynomial equation, and the average R² was 0.95 and 0.84, respectively. The release amount can be fitted by the Lagergren pseudo-second-order kinetic equation with time, with the average R² 0.89. The pH was negatively correlated with the release amount in the fresh contaminated sediment but positively correlated with the weathered one. The correlation between each factor and oil release amount was ranked (from large to small) as oil concentration, oscillation frequency, salinity, time, and pH. At last, a polynomial equation can be fitted between the key influencing factors (oil concentration and oscillation frequency) and the release amount. The results can provide a theoretical basis for predicting the secondary pollution owing to the oil re-release from intertidal sediment.

Historical and post-ban releases of organochlorine pesticides recorded in sediment deposits in an agricultural watershed, France

Agricultural use of organochlorine pesticides (OCPs) increased during the twentieth century but many of them have been progressively banned several decades after their introduction. Nevertheless, these lipophilic chemical compounds may persist in soils and sediments. From sediment deposits, it is possible to reconstruct the chronology of OCP releases in relation to former applications through time. Nevertheless, long-term fate of OCPs i.e. source, transfer, and storage through the watershed, is also related to the OCPs-sediment characteristics interactions, and our study showed the significant links between OCPs and labile or refractory organic matter. From sediment cores collected in a mainly agricultural watershed, the Eure River watershed (France), aldrin and lindane widespread applications during the 1950s-1970s have been recorded. While lindane applications declined after that date, according to the temporal trend of the stable isomer of hexachlorocyclohexane (β-HCH), α-, and γ-HCH have been recorded at significant levels in the 2000s, suggesting first local post-ban applications. Nevertheless, the relationships between these OCPs and labile organic matter resulted in an overestimation of the post-ban releases. Also, the detection of stable metabolites of dichlorodiphenyltrichloroethane (DDT) (i.e. 4,4'-DDE) and heptachlor (i.e. heptachlor epoxide) several decades after their ban, revealed the role of old deep soils erosion in the chronology of OCP releases and thus the reemergence of stable transformation products from historical OCPs.

Simulation for dynamic release of oil from oil-contaminated marine sediment

Dynamic oil release from oil-contaminated sediment to seawater was investigated in kinetic and factor experiments. Oil-release kinetic was described using a two-compartment first-order equation with rapid- and slow-release steps. The rapid-desorption-fraction rate (k_r) was not affected by the ratio of solid-liquid, but significantly affected by sediment pollution level and salinity. The slow-desorption-fraction rate constant (k_s) was affected by sediment pollution level, the ratio of solid-liquid, and salinity. Desorption efficiencies were 1.09-4.04%, increasing as the sediment pollution level and salinity increased and the ratio of solid-liquid decreased. Oil desorption was critically affected by sediment suspension (or lack of). The desorption kinetics curves were unaffected with the shear force for unsuspended sediment, and the desorption efficiency and k_r were increasing with the shear force for suspended sediment, and no significant correlations were found between k_s and hydrodynamic conditions. The results provide a theoretical basis for evaluating ecological risks posed by oil in sediment.

Effects of Wave Conditions and Particle Size on the Release of Oil from Oil-Contaminated Sediments in a Wave Tank

The floating oil can drift to the coastal areas and interact with the shoreline substrates after oil spill accidents. This process is demonstrated to be the cause of the formation of oil-contaminated sediments, which has attracted much attention. However, no systematic study has concerned the desorption process of oil from oil-contaminated sediments when the coastal hydrodynamic conditions change. This work determines the effects of wave conditions and particle size on the release of oil from artificially prepared sediments in a wave tank. Nonlinear fitting results show that the oil release kinetic curves can be correctly estimated with the Lagrangian first-order (LFO) first-order equation. Under different test conditions. The oil concentration in the water increases rapidly within 6 h. However, the oil desorption is inhibited thereafter and the process of sorption occurs dominantly. Under higher wave energy, the process of desorption is significantly enhanced and more large oil droplets release from sediments. Under the same wave condition, small oil droplets firstly release from the sediments. Besides, more oil especially with a larger size can release from larger sediment while oil releases more quickly from smaller sediment.

Bioaccumulation of polycyclic aromatic hydrocarbons by arctic and temperate benthic species

Increasing oil and gas activities may substantially increase chemical stress to benthic ecosystems in the Arctic, and it is necessary to evaluate such environmental risks in these systems. Risk assessment procedures for oil-related compounds (e.g., polycyclic aromatic hydrocarbons [PAHs]) should address differences in exposure between Arctic and temperate benthos. We compare for the first time the bioaccumulation of PAHs by Arctic benthic invertebrate species with that of temperate species, based on their biota-sediment accumulation factors (BSAFs). Measured PAH BSAFs were generally higher in temperate bivalves (Limecola balthica) than in Arctic bivalves (Macoma calcarea), whereas BSAFs in Arctic polychaetes (Nephtys ciliata) were higher than in temperate polychaetes (Alitta virens). Differences in measured BSAFs were explained by species-specific feeding modes and traits. However, modeled BSAFs revealed that steady state was not likely to be reached in the 28-d tests for all PAHs and organisms. Due to the low numbers of individuals, most species-specific parameters were too uncertain to reveal differences between Arctic and temperate species. The results of the present study suggest that data from temperate species could be used as a surrogate for Arctic species in risk assessment. Environ Toxicol Chem 2019;38:883-895. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Simulated oil release from oil-contaminated marine sediment in the Bohai Sea, China

There is a high degree of heavy oil partitioning into marine sediments when an oil spill occurs. Contaminated sediment, as an endogenous pollution source, can re-pollute overlying water slowly. In this study, a static oil release process and its effects in marine sediment was investigated through a series of experiments with reproductive heavy oil-contaminated marine sediment. The oil release process was accurately simulated with a Lagergren first-order equation and reached equilibration after 48h. The fitted curve for equilibrium concentration (C₀) and first-order rate constant (k₁) for sediment pollution levels exhibited a first-order log relationship. The instantaneous release rate (dC_tdt) was also calculated. The C₀ increased with increases in temperature and dissolved organic matter (DOM), and decreasing salinity. The k₁ increased with temperature, but was not affected by DOM and salinity. These results can be used to better understand the fate of heavy oil in contaminated sediments of the Bohai Sea.

Concentrations and origin of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in sediments of western Spitsbergen fjords (Kongsfjorden, Hornsund, and Adventfjorden)

Contaminant profiles in sediment cores represent valuable natural archives of environmental contamination, by which contaminant sources and historical changes in contaminant input and cycling may be recognized. In the present study, we discuss the sedimentary profiles and historical trends of organic contaminants - polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) - in three fjords of the Svalbard archipelago differing in environmental conditions and anthropogenic impact. The obtained results revealed no significant differences between the fjords Hornsund and Kongsfjorden, in the average levels of the analyzed contaminants. Levels ranging from 0.05 to 1.47 ng/g d.w. for ∑7 PCBs and from 37.3 to 1973 ng/g d.w. for ∑12 PAHs were measured. The observed spatial and temporal differences in contaminant levels are rather related to local variations in the fjords associated with the location of sampling stations. Higher concentrations of the ∑7 PCBs exceeding 1.00 ng/g d.w. were measured in sediment cores collected in the inner parts of both fjords, which remain under the influence of melting glacier outflows. Important concentrations of these contaminants were noticed in layers deposited recently, suggesting intensive supply of these substances from secondary sources. The observed levels are generally low and well below known established no effect levels. Only the concentration of fluoranthene exceeded the threshold effect level at several sampling stations. Moreover, fluoranthene concentrations in almost all Adventfjorden sediment layer samples were above probable effect levels, which can indicate a risk of adverse effects in exposed benthic organisms. The fluoranthene/pyrene and phenthrene/anthracene ratios, which are used for identification of hydrocarbon sources, suggest a dominance of PAHs of pyrolytic genesis in Kongsfjorden and Hornsund. In Adventfjorden, hydrocarbons of petrogenic origin were predominant. However, other sources like coal dust from stores on land are also possible at this location.

Spatial-temporal and multi-media variations of polycyclic aromatic hydrocarbons in a highly urbanized river from South China

Comprehensive studies on polycyclic aromatic hydrocarbons (PAHs) within an urban river are urgently needed to carry out strategies to limit their contamination and dispersal. Here, we analyzed 16 PAH occurrences in water, suspended particulate matter (SPM), and sediment monthly for a year in the Maozhou River mainstream (Shenzhen, South China). Monthly rainfall positively correlated with both total PAH concentrations in filtered water (water PAHs) and SPM. Sediment PAH concentration increased from the river source to estuary. Compared to the earlier record, the sediment PAHs decreased at almost all sites due to the high-molecular-weight PAH (≥4 rings; especially the 4-ring PAH) degradation, except the estuary site that accumulated more low-molecular-weight PAHs (<4 rings). Results suggest that the water and SPM PAHs had similar and recent sources (e.g., rainfall and storm runoff) and actively exchanged with each other. The sediment PAHs had relatively different and complicated sources (fossil fuel combustion: 44.0%; oil pollution: 28.4%; biomass burning: 27.6%), and showed a long-term accumulation effect and increasingly weaker source-sink relation with both water and SPM PAHs from river source to estuary. This study highlights a disconnection in the source and migration mechanism between the water body (including water and SPM) and sediment PAHs.

Prospective Environmental Risk Assessment for Sediment-Bound Organic Chemicals: A Proposal for Tiered Effect Assessment

A broadly accepted framework for prospective environmental risk assessment (ERA) of sediment-bound organic chemicals is currently lacking. Such a framework requires clear protection goals, evidence-based concepts that link exposure to effects and a transparent tiered-effect assessment. In this paper, we provide a tiered prospective sediment ERA procedure for organic chemicals in sediment, with a focus on the applicable European regulations and the underlying data requirements. Using the ecosystem services concept, we derived specific protection goals for ecosystem service providing units: microorganisms, benthic algae, sediment-rooted macrophytes, benthic invertebrates and benthic vertebrates. Triggers for sediment toxicity testing are discussed.We recommend a tiered approach (Tier 0 through Tier 3). Tier-0 is a cost-effective screening based on chronic water-exposure toxicity data for pelagic species and equilibrium partitioning. Tier-1 is based on spiked sediment laboratory toxicity tests with standard benthic test species and standardised test methods. If comparable chronic toxicity data for both standard and additional benthic test species are available, the Species Sensitivity Distribution (SSD) approach is a more viable Tier-2 option than the geometric mean approach. This paper includes criteria for accepting results of sediment-spiked single species toxicity tests in prospective ERA, and for the application of the SSD approach. We propose micro/mesocosm experiments with spiked sediment, to study colonisation success by benthic organisms, as a Tier-3 option. Ecological effect models can be used to supplement the experimental tiers. A strategy for unifying information from various tiers by experimental work and exposure-and effect modelling is provided.

Relationship between the water-exchangeable fraction of PAH and the organic matter composition of sediments

The sorption of PAH on 12 different sediments was investigated and was correlated to their corresponding organic matter (OM) content and quality. For this purpose, the OM was precisely characterized using thermal analysis consisting in the successive combustion and quantification of the increasingly thermostable fractions of the OM. Simultaneously, the water-exchangeable fraction of the sorbed PAH defined as the amount of PAH freely exchanged between the water and the sediment (by opposition to the PAH harshly sorbed to the sediments particles) was determined using a passive sampler methodology recently developed. The water concentrations, when the sediment-water system is equilibrated, were also assessed which allows the determination of the sediment-water distribution coefficients without artifacts introduced by the non water-exchangeable fraction of PAH. Hence, the present study provides the distribution coefficients of PAH between the water and 4 different OM fractions combusted at a specific temperature range. The calculated distribution coefficients demonstrate that the sedimentary OM combusted at the intermediate temperature range (between 300 °C and 450 °C) drives the reversible sorption of PAH while the inferred sorption to the OM combusted at a lower and higher temperature range does not dominate the partitioning process.

Bioaccumulation of polycyclic aromatic hydrocarbons, polychlorinated biphenyls and hexachlorobenzene by three Arctic benthic species from Kongsfjorden (Svalbard, Norway)

The predicted expansion of oil and gas (O&G) activities in the Arctic urges for a better understanding of impacts of these activities in this region. Here we investigated the influence of location, feeding strategy and animal size on the bioaccumulation of Polycyclic Aromatic Hydrocarbons (PAHs), Polychlorinated Biphenyls (PCBs) and Hexachlorobenzene (HCB) by three Arctic benthic species in Kongsfjorden (Svalbard, Norway). No toxicity was expected based on biota PAH critical body residues. Biota PCB levels were mainly below limit of detection, whereas samples were moderately polluted by HCB. PAH concentrations in biota and Biota Sediment Accumulation Factors (BSAFs) were generally higher in Blomstrandhalvøya than in Ny-Ålesund, which was explained by a higher abundance of black carbon in Ny-Ålesund harbour. BSAFs differed significantly among species and stations. We conclude that contaminant body residues are a less variable and more straightforward monitoring parameter than sediment concentrations or BSAFs in Arctic benthos.

PAH Accessibility in Particulate Matter from Road-Impacted Environments

Snowmelt, surface runoff, or stormwater releases in urban environments can result in significant discharges of particulate matter-bound polycyclic aromatic hydrocarbons (PAHs) into aquatic environments. Recently, more-specific activities such as road-tunnel washing have been identified as contributing to contaminant load to surface waters. However, knowledge of PAH accessibility in particulate matter (PM) of urban origin that may ultimately be released into urban surface waters is limited. In the present study, we evaluated the accessibility of PAHs associated with seven distinct (suspended) particulate matter samples collected from different urban sources. Laboratory-based infinite sink extractions with silicone rubber (SR) as the extractor phase demonstrated a similar pattern of PAH accessibility for most PM samples. Substantially higher accessible fractions were observed for the less-hydrophobic PAHs (between 40 and 80% of total concentrations) compared with those measured for the most-hydrophobic PAHs (<5% of total concentrations). When we focused on PAHs bound to PM from tunnel-wash waters, first-order desorption rates for PAHs with log Kow > 5.5 were found in line with those commonly found for slowly or very slowly desorbing sediment-associated contaminants. PAHs with log Kow < 5.5 were found at higher desorbing rates. The addition of detergents did not influence the extractability of lighter PAHs but increased desorption rates for the heavier PAHs, potentially contributing to increases in the toxicity of tunnel-wash waters when surfactants are used. The implications of total and accessible PAH concentrations measured in our urban PM samples are discussed in a context of management of PAH and PM emission to the surrounding aquatic environment. Although we only fully assessed PAHs in this work, further study should consider other contaminants such as OPAHs, which were also detected in all PM samples.

Predicting seasonal fate of phenanthrene in aquatic environment with a Markov chain

Phenanthrene (Phe) with carcinogenicity is ubiquitous in the environment, especially in aquatic environment; its toxicity is greater. To help determine toxicity risk and remediation strategies, this study predicted seasonal fate of Phe in aquatic environment. Candidate mechanisms including biodegradation, sorption, desorption, photodegradation, hydrolysis and volatility were studied; the results for experiments under simulated conditions for normal, wet and dry seasons in the Yinma River Basin indicated that biodegradation in sediment, sorption, desorption, and volatility were important pathways for elimination of Phe from aquatic environment and showed seasonal variations. A microcosm which was used to mimic sediment/water system was set up to illustrate seasonal distribution and transport of Phe. A Markov chain was applied to predict seasonal fate of Phe in air/water/sediment environment, the predicted results were perfectly agreed with results of microcosm experiments. Predicted results with a Markov chain suggested that volatility and biodegradation in sediment were main elimination pathways, and contributions of elimination pathways showed seasonal variations; Phe was eliminated from water and sediment to negligible levels over around 250 h in August and over 1000 h in May; in November, Phe was eliminated from water to a negligible level while about 31 % of Phe amount still remained in sediment over 1000 h.

Dynamics and recovery of a sediment-exposed Chironomus riparius population: A modelling approach

Models can be used to assess long-term risks of sediment-bound contaminants at the population level. However, these models usually lack the coupling between chemical fate in the sediment, toxicokinetic-toxicodynamic processes in individuals and propagation of individual-level effects to the population. We developed a population model that includes all these processes, and used it to assess the importance of chemical uptake routes on a Chironomus riparius population after pulsed exposure to the pesticide chlorpyrifos. We show that particle ingestion is an important additional exposure pathway affecting C. riparius population dynamics and recovery. Models ignoring particle ingestion underestimate the impact and the required recovery times, which implies that they underestimate risks of sediment-bound chemicals. Additional scenario studies showed the importance of selecting the biologically relevant sediment layer and showed population effects in the long term.

Bioavailability-based assessment of aryl hydrocarbon receptor-mediated activity in Lake Tai Basin from Eastern China

Coupling polydimethylsiloxane (PDMS)-based equilibrium passive sampling with chemical and bioassay analysis, we assessed aryl hydrocarbon receptor (AhR)-mediated activity and contributing chemicals in sediment from Lake Tai Basin, Eastern China. The bioanalytical equivalent concentrations (BEQs) of AhR-active chemicals for the exhaustive (total burden) and PDMS extracts (bioavailable fractions) ranged from <9.5-300 ng TCDD-EQ/ kgdry weight (dw) and <0.096-2.2 ng TCDD-EQ/kgdw, respectively, which were of average levels compared to those reported elsewhere. The total concentrations of PAHs in sediment and PDMS were 17-4700 μg/kgdw and 0.61-10 μg/kgdw, respectively. The majority of the exhaustive extracts subject to acid treatment showed >70% decline in AhR-mediated activity, suggesting the minor contribution by persistent AhR ligands. Targeted analysis of polycyclic aromatic hydrocarbons (PAHs) showed, however, that these chemicals contributed <40% to the overall effect in both exhaustive and PDMS extracts, indicating the presence of other labile AhR ligands. The concentrations of PAHs and BEQs of the AhR-mediated activity attributed to these chemicals in the exhaustive extracts can be back calculated from those in the PDMS extracts via a general organic carbon-PDMS partition coefficient. Similar quantitative conversion between PDMS and aquatic organisms was also verified for aquatic organisms via the lipid-PDMS partition coefficient. Therefore, our study provided a first insight into the quantitative links between bulk chemical burdens in sediment, chemical bioavailability, bioaccumulation potential and resulting mixture effects, as an integral part of predictive environmental risk assessment of contaminated sediment.

Modeling of Bioaccumulation in Marine Benthic Invertebrates Using a Multispecies Experimental Approach

The causal links between species traits and bioaccumulation by marine invertebrates are poorly understood. We assessed these links by measuring and modeling polychlorinated biphenyl bioaccumulation by four marine benthic species. Uniformity of exposure was achieved by testing each species in the same aquarium, separated by enclosures, to ensure that the observed variability in bioaccumulation was due to species traits. The relative importance of chemical uptake from pore water or food (organic matter, OM) ingestion was manipulated by using artificial sediment with different OM contents. Biota sediment accumulation factors (BSAFs) ranged from 5 to 318, in the order Nereis virens < Arenicola marina ≈ Macoma balthica < Corophium volutator. Calibration of a kinetic model provided species-specific parameters that represented the key species traits, thus illustrating how models provide an opportunity to read across benthic species with different feeding strategies. Key traits included species-specific differentiation between (1) ingestion rates, (2) ingestion of suspended and settled OM, and (3) elimination rates. The high BSAF values and their concomitant variability across the species challenges approaches for exposure assessment based on pore water concentration analysis and equilibrium partition theory. We propose that combining multienclosure testing and modeling will substantially improve exposure assessment in sediment toxicity tests.

Analysis of organic contaminant desorption kinetic data for sediments and soils: implications for the Tenax extraction time for the determination of bioavailable concentrations

Solid-phase extractions with adsorbents like Tenax have been widely used to assess bioaccessible or bioavailable concentrations and non-extractable residues (NER) of organic contaminants in soils or sediments. This paper presents an analysis of literature rate constants and fractions for rapid, slow and very slow contaminant desorption from soils and sediments. Contaminant fractions desorbed from sediment to Tenax in 6 or 24h were evaluated as to their adequacy as a proxy for rapidly desorbing fractions, which have been shown to correlate with bioavailable concentrations. Desorption rate constants appear to decrease with increasing contaminant n-octanol-water partition coefficient. The ratio of the fraction of contaminant desorbed from sediment to Tenax in 6h and the rapidly desorbing fraction appeared to slightly decrease on increasing contaminant hydrophobicity. This was not the case for the extraction for 24h. Rapidly desorbing fractions or bioavailable fractions can be estimated, within a factor of 1.4, by multiplying the fraction desorbed in 24h by a factor of 0.7.