Origin and distribution of hydrocarbons and organic matter in the surficial sediments of the Sfax-Kerkennah channel (Tunisia, Southern Mediterranean Sea)

Sources of hydrocarbons and their risk assessment in seawater and sediment samples collected from the Nile Delta coast of the Mediterranean Sea

The aim of this work is to examine the levels, distribution, bases, and hazards of n-alkanes (n-C9 to n-C20) and PAHs in the seawater and sediments around oil production locations in the whole delta region. The variations in the levels of PAHs and n-alkanes in seawater and sediment of the Nile delta coast of the Mediterranean were investigated using GC-MS/MS. The Σn-alkanes residues ranged between 12.05 and 93.51 mg/L (mean: 50.45 ± 17.49 mg/L) and 4.70 to 84.03 µg/g (mean: 31.02 ± 27.995 µg/g) in seawater and sediments, respectively. Total PAHs concentrations ranged between 4.485 and 16.337 μg/L (average: 9.47 ± 3.69 μg/L) and 1.32 to 28.38 ng/g (average 8.61 ± 7.57 ng/g) in seawater and sediment samples, respectively. The CPI (carbon preference index) values fluctuated between 0.62 and 1.72 (seawater) and from 0.234 to 2.175 (sediment), proposing the variation sources of n-alkane in the studied area. PAHs concentrations were lower than the Effective Range Low (ERL) and Effective Range Median (ERM) levels. The Toxic Equivalent Quotient (TEQ) values oscillated between 0.002 and 6.84 ng/L and from 3.72 to 13.48 ng/g for the seawater and sediment samples, respectively. The Ant/(Ant + Phe) ratio in sediment and seawater samples indicated a pyrolytic source while the BaA/(BaA + Chry) ratio indicates petrogenic sources in most of the studied stations.

Distribution, composition and risk assessment of hydrocarbon residue in surficial sediments of El-Dakhla, El-Kharga and El-Farafra oases, Egypt

This work examined the polycyclic aromatic hydrocarbons (PAHs) and n-alkanes quantities, sources, and hazards in sediments collected from the Egyptian Western Desert Oases namely: Dakhla, Kharga and Farafra oases. The n-alkane (C9-C20) residue concentrations have ranged from 0.66 to 2417.91 µg/g recorded for the three Oases. On the other hand, the total n-alkane ranged from 448.54 µg/g to 8442.60 µg/g. Higher carbon preference index (CPI) values (> 1.0) proposed that the natural sources could be the main contributor to n-alkanes in the Oases sediment. GC-MS/MS (selected reaction monitoring (SRM) method) was used for the determination of the ΣPAHs concentrations in the studied sediments. The ΣPAHs concentrations (ng/g, dry weight) in the studied three Oases varied from 10.18 to 790.14, 10.55 to 667.72, and from 38.27 to 362.77 for the Kharga, Dakhla and Farafra Oases, respectively. The higher molecular weight PAHs were the most abundant compounds in the collected samples. Assessing potential ecological and human health issues highlighted serious dangers for living things and people. All the investigated PAHs had cancer risk values between 1.43 × 10-4 and 1.64 × 10-1, this finding suggests that PAHs in the samples under study pose a moderate risk of cancer. The main sources of PAHs in this study are biomass, natural gas, and gasoline/diesel burning emissions.

Preliminary data on the occurrence of PAH and Anisakis spp. in Moroccan anchovies: Environmental parasitology and human health risk

This survey focuses on an environmental parasitology study by investigating Polycyclic Aromatic Hydrocarbons (PAH) bioaccumulation and the occurrence of Anisakis spp. on common anchovies collected from Moroccan coasts over 9 months through chemical (PAH) and Biological (Biometrics and parasitic) analysis. Obtained results were statistically analyzed and human health risks from anchovies consumption were assessed. The results obtained highlighted the good biological and chemical status of this fish in all stations of Morocco's coasts. Anisakis spp. was present in only four stations in the Atlantic fringe (maximum prevalence 22.22 %). Results have shown non-significant differences for tissue nature (Muscle, viscera) or spatial variation and were within a low range of concentrations well below the European Commission standards. Results have shown no serious harmful risk for humans from this fish consumption (ILCR and HI), and statistical analysis had shown positive correlations between prevalence and Chr, prevalence and sex-ratio, and prevalence and weight.

Hydrocarbons in size-fractionated plankton of the Mediterranean Sea (MERITE-HIPPOCAMPE campaign)

Aliphatic and polycyclic aromatic hydrocarbons (AHs and PAHs, respectively) were analyzed in the dissolved fraction (<0.7 μm) of surface water and in various particulate/planktonic size fractions (0.7-60, 60-200, 200-500 and 500-1000 μm) collected at the deep chlorophyll maximum, along a North-South transect in the Mediterranean Sea in spring 2019 (MERITE-HIPPOCAMPE campaign). Suspended particulate matter, biomass, total chlorophyll a, particulate organic carbon, C and N isotopic ratios, and lipid biomarkers were also determined to help characterizing the size-fractionated plankton and highlight the potential link with the content in AHs and PAHs in these size fractions. Ʃ28AH concentrations ranged 18-489 ng L-1 for water, 3.9-72 μg g-1 dry weight (dw) for the size fraction 0.7-60 μm, and 3.4-55 μg g-1 dw for the fractions 60-200, 200-500 and 500-1000 μm. AH molecular profiles revealed that they were mainly of biogenic origin. Ʃ14PAH concentrations were 0.9-16 ng L-1 for water, and Ʃ27PAH concentrations were 53-220 ng g-1 dw for the fraction 0.7-60 μm and 35-255 ng g-1 dw for the three higher fractions, phenanthrene being the most abundant compound in planktonic compartment. Two processes were evidenced concerning the PAH patterns, the bioreduction, i.e., the decrease in concentrations from the small size fractions (0.7-60 and 60-200 μm) to the higher ones (200-500 μm and 500-1000 μm), and the biodilution, i.e., the decrease in concentrations in plankton at higher suspended matter or biomass, especially for the 0.7-60 and 60-200-μm size fractions. We estimated the biological pump fluxes of Ʃ27PAHs below 100-m depth in the Western Mediterranean Sea at 15 ± 10 ng m-2 day-1, which is comparable to those previously reported in the South Pacific and Indian Ocean.

Spatial distribution, sources and risk assessment of polycyclic aromatic hydrocarbons in the surficial sediments of the Egyptian Mediterranean coast

The Egyptian Mediterranean coast (EMC) receives a considerable quantity of polycyclic aromatic hydrocarbons (PAHs). PAHs from EMC sediments were assessed to understand the effects of marine and riverine currents on their distribution. The concentrations of total PAHs ranged between 13,156-34,852 ng/g dw. PAH levels have increased even in areas far from the shoreline under the influence of riverine inputs from the Nile River; this is attributed to the tidally induced riverine freshwater re-suspension of surface sediments in the shallow near-shore section and re-precipitation in the fare stations. PAH levels generally increase as one moves from the western to the eastern part of the studied area, owing to the effect of the marine current. Diagnostic ratios pointed toward different pyrogenic sources. SQGs were used to assess the probability of observing adverse biological effects in benthic organisms in sediment samples. The toxic and mutagenic equivalent quotient for carcinogenic PAHs was extremely high.

Prokaryotic Diversity and Dynamics during Dinoflagellate Bloom Decays in Coastal Tunisian Waters

(1) Background: Harmful algal blooms (HABs) can negatively impact marine ecosystems, but few studies have evaluated the microbial diversity associated with HABs and its potential role in the fates of these proliferations. (2) Methods: Marine prokaryotic diversity was investigated using high-throughput sequencing of the 16S rRNA gene during the bloom declines of two dinoflagellates detected in the summer of 2019 along the northern and southern Tunisian coasts (South Mediterranean Sea). The species Gymnodinium impudicum (Carthage, Tunis Gulf) and Alexandrium minutum (Sfax, Gabes Gulf) were identified using microscopy and molecular methods and were related to physicochemical factors and prokaryotic compositions. (3) Results: The abundance of G. impudicum decreased over time with decreasing phosphate concentrations. During the G. impudicum bloom decay, prokaryotes were predominated by the archaeal MGII group (Thalassarchaeaceae), Pelagibacterales (SAR11), Rhodobacterales, and Flavobacteriales. At Sfax, the abundance of A. minutum declined with decreasing phosphate concentrations and increasing pH. At the A. minutum peak, prokaryotic communities were largely dominated by anoxygenic phototrophic sulfur-oxidizing Chromatiaceae (Gammaproteobacteria) before decreasing at the end of the survey. Both the ubiquitous archaeal MGII group and Pelagibacterales were found in low proportions during the A. minutum decay. Contrary to the photosynthetic Cyanobacteria, the photo-autotrophic and -heterotrophic Rhodobacterales and Flavobacteriales contents remained stable during the dinoflagellate bloom decays. (4) Conclusions: These results indicated changes in prokaryotic community diversity during dinoflagellate bloom decays, suggesting different bacterial adaptations to environmental conditions, with stable core populations that were potentially able to degrade HABs.

Trace metals and polycyclic aromatic hydrocarbons in the Eastern Mediterranean sediments: Concentration ranges as a tool for quality control of large data collections

Assessing the status of marine pollution at regional and sub-regional scales requires the use of comparable and harmonized data provided by multiple institutions, located in several countries. Standardized data management and quality control are crucial for supporting a coherent evaluation of marine pollution. Taking the Eastern Mediterranean Sea as a case study, we propose an approach to improve the quality control procedures used for sediment pollution data, thus supporting a harmonized environmental assessment. The regional ranges of contaminant concentrations in sediments were identified based on an in-depth literature review, and the lowest measured concentrations were evaluated to determine the "background concentrations" of chemical substances not yet targeted in the Mediterranean Sea. In addition, to verify the suitability of the approach for validating large data collections provided by multiple sources, the determined ranges were used to validate a regional dataset available through EMODnet data infrastructure.

Polycyclic Aromatic Hydrocarbons (PAHs) in the Dissolved Phase, Particulate Matter, and Sediment of the Sele River, Southern Italy: A Focus on Distribution, Risk Assessment, and Sources

The Sele River, located in the Campania Region (southern Italy), is one of the most important rivers and the second in the region by average water volume, behind the Volturno River. To understand the distribution and sources of polycyclic aromatic hydrocarbons (PAHs) in the Sele River, water sediment samples were collected from areas around the Sele plain at 10 sites in four seasons. In addition, the ecosystem health risk and the seasonal and spatial distribution of PAHs in samples of water and sediment were assessed. Contaminant discharges of PAHs into the sea were calculated at about 1807.9 kg/year. The concentration ranges of 16 PAHs in surface water (DP), suspended particulate matter (SPM), and sediment were 10.1–567.23 ng/L, 121.23–654.36 ng/L, and 331.75–871.96 ng/g, respectively. Isomeric ratio and principal component analyses indicated that the PAH concentrations in the water and sediment near the Sele River were influenced by industrial wastewater and vehicle emissions. The fugacity fraction approach was applied to determine the trends for the water-sediment exchange of 16 priority PAHs; the results indicated that fluxes, for the most part, were from the water into the sediment. The toxic equivalent concentration (TEQ) of carcinogenic PAHs ranged from 137.3 to 292.6 ngTEQ g⁻¹, suggesting that the Sele River basin presents a definite carcinogenic risk.

Spatial distribution, compositional pattern and source apportionment of n-alkanes in surface sediments of the Bohai Sea, Yellow Sea, and East China Sea and implications of carbon sink

China's marginal seas (CMSs, including the Bohai Sea, Yellow Sea, East China Sea) are a significant sink for both terrestrial organic matter (OM) and marine OM, and they play an important role in the global biogeochemical carbon cycle. The spatial distribution and origin of organic matter based on n-alkanes in the surface sediments of CMSs and the implications of carbon sinks were comparatively analyzed. The n-alkane content in surface sediment from the Bohai Sea was higher than that of the Yellow Sea and the East China Sea. The spatial distribution trends of marine and terrestrial organic matter are obviously different in the surface sediments of China's marginal seas. The n-alkanes in the sediments of the Yellow Sea and the East China Sea were mainly derived from terrestrial higher plants, and land-based influence gradually decreased from the near shore to the open sea. Higher concentration of terrigenous OM are concentrated nearshore, especially near estuaries, such as the Yellow River Estuary, the Old Yellow River Estuary and the Yangtze River Estuary. The input of n-alkanes from woody plants in the Bohai Sea area was slightly higher than that of herbaceous plants, and the input of herbaceous plants in the Yellow Sea and East China Sea was slightly dominant. The distribution of marine organic matter is controlled by marine productivity and the sedimentary environment. Due to climate change, the decomposition and enrichment of organic matter also show the climate effect of carbon molecular combinations. As a semiclosed sea area, the Bohai Sea was beneficial to the growth and reproduction of marine phytoplankton. From the perspective of petroleum pollution, the Bohai Sea was the most serious, followed by the Yellow Sea, and the East China Sea was the lightest. The carbon burial amount of terrestrial organic matter accounts for approximately 7% of the terrestrial organic matter burial amount of global marginal sea sediments, indicating that China's marginal sea plays an important role in the global carbon cycle. The result provide a basis for further understanding the source pattern and burial preservation of sedimentary organic matter in this sea area.

Effects of organic matter on polycyclic aromatic hydrocarbons in riverine sediments affected by human activities

Organic matter (OM) is an important component of riverine environments and a major factor in the migration and transformation of hydrophobic organic substances, such as polycyclic aromatic hydrocarbons (PAHs), to sediments. We studied the distributions, sources, and correlations between PAHs and OM in sediments from the Duliujian and the Beiyun rivers in North China. Sixteen PAHs were detected in the surface sediments at total concentrations ranging from 356 to 4652 ng·g^-1 dry weight, which caused a moderate to high level of pollution. The PAH distributions were significantly and positively correlated with OM (p < 0.01) and higher concentrations were detected downstream of areas affected by human activity. Petroleum, coal, and wood combustion were the main sources of PAHs in riverine sediments, and the sources of OM in sediment included terrestrial and aquatic higher plants, soil, and sewage discharge. The OM accumulated and aged along the river, with increases in the degree of aromaticity and condensation, which led to stronger adsorption of PAHs. Our results will help to promote the management and restoration of contaminated riverine sediments.

Co-occurrence and potential ecological risk of parent and oxygenated polycyclic aromatic hydrocarbons in coastal sediments of the Taiwan Strait

Thirty-two surface sediment samples, collected from the Taiwan Strait (TWS), were investigated for the occurrence, composition profile, and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs). PAHs were ubiquity in the TWS with a total concentration (∑PAHs, excluding naphthalene due to its high volatility) ranging from 17.8-213 ng g^-1. Benzo[b] fluoranthene, fluoranthene, phenanthrene, and pyrene were the predominant PAHs. Also, eight OPAHs were detected, having a cumulative concentration range (∑OPAHs) of 10.5-118 ng g^-1, predominated by anthraquinone and 6H-Benzo[c,d]Pyren-6-one. Higher concentrations of ∑PAHs and ∑OPAHs were detected at sampling sites adjacent to the mainland and in the northwest part of the TWS. The results suggested important continental input, and particle sedimentation under the specific hydrodynamic conditions of the region. Based on the measured concentrations and sediment quality guidelines, PAHs had a limited ecological impact on the area.

Integrated Biomarker Response for Environmental Assessment Using the Gastropod Phorcus turbinatus along the Northern and the Northeastern Coasts of Tunisia

This work aims to assess the spatial and temporal variations of four biomarkers activities and to integrate their biological responses in a battery using the gastropod Phorcus turbinatus. The monitoring was carried out during the period between April 2014 and January 2015 at six stations along the northern and the northeastern coasts of Tunisia. The Fulton condition factor was estimated and the activities of catalase, acetylcholinesterase and glutathione-S-transferase were evaluated by spectrophotometry. A multi-biomarker battery approach was used to assess ecosystems' condition and to identify environmental impacts on the organisms. The results suggest that the enzymatic activities of CAT and GST depend especially on seasons. As for AChE activity, it was similar between seasons and stations. The values of the integrated biological response were maximal at Jarzouna in summer and at Sidi Daoued in winter, indicating the presence of severe stressors suffered by the organisms. This perturbation may be due to the enrichment of the waters by xenobiotics, namely polycyclic aromatic hydrocarbons, insecticides, phosphate wastes, PCBs and pesticides. Thus, P. turbinatus seems to be a good bioindicator of chemical pollution, constituting an adequate tool for a bio-monitoring program.

Organic pollutants in marine samples from Tunisian coast: Occurrence and associated human health risks

140 contaminants belonging to various classes (organochlorine and organophosphorus pesticides, pyrethroid insecticides, carbamates, fungicides, acaricides, herbicides, synergists, insect growth regulators, polychlorobiphenyls, polycyclic aromatic hydrocarbons) were simultaneously analysed by GC-MS/MS in marine sediments, aquatic plant leaves and fish tissues samples. A total of 260 samples from five stations along the coast of Tunisia were evaluated. The results highlight that only 28 residues (12 polychlorobiphenyls, 8 organochlorine pesticides, 7 polycyclic aromatic hydrocarbons and triphenyl phosphate) were detected at levels higher than relative LOQ values. The amounts in sediment samples were compared with Sediment Quality Guidelines (SQGs) showing that the values are acceptable and no toxic effect is expected on aquatic organisms. A little variation of contaminant residues in sediment samples among coastal stations was recorded. Namely, with respect to almost all polychlorobiphenyls and organochlorine pesticides, higher values were recorder in summer. With respect to almost all polycyclic aromatic hydrocarbons, higher values were recorder in autumn. Aquatic plant leaves showed a residue accumulation higher than that of other compartments of marine system. The data about fish samples (Sparus aurata and Sarpa salpa, the two most frequently caught fish species at five sites on the central coast of Tunisia) do not pose direct hazard to human health because values were lower than protection limits.

The occurrence and levels of polycyclic aromatic hydrocarbons (PAHs) in African environments-a systematic review

In the African continent, several studies have been conducted to determine PAH pollution levels with their associated health risks in the environment. However, these studies are very much disconnected. The objective of this study is to conduct a systematic review that serves as a comprehensive report on the PAH-related studies conducted in the African continent. Data sources are from Google Scholar and PubMed. English language studies that reported on PAH levels in smoked fish and meat, soils and dust, aquatic environments, indoor and outdoor air, and ready-to-eat food items were selected. Specific PAHs included the following: 33 PAHs comprising of the 16 USEPA PAHs, non-alkylated PAHs, non-alkylated PAHs, oxygenated PAHs (OPAHs), and azaarenes (AZAs). Study appraisal and synthesis methods: The Newcastle-Ottawa Scale (NOS) was adapted to assess the quality of the selected studies basing on their sampling methods, analytical techniques, and results. A total of 121 studies were reviewed, with the majority (56) being from Nigeria. PAH levels in smoked fish and meat, soils and dust, aquatic environments, indoor and outdoor air, and ready-to-eat food items recorded total concentrations of PAHs ranging from 5 to 3585 μg/kg, BDL to 6,950,000 μg/kg, 0 to 10,469,000 μg/kg, 0 to 7.82 ± 0.85 μg/m³, and 2.5 to 7889 ± 730 μg/kg respectively. Carcinogenic risk assessment for children and adults ranged from very low to very high levels when compared to the ILCR range (10^-6 to 10^-4) defined by the USEPA. Out of 54 African countries, only 19 were represented. The majority of selected studies failed to apply any standard protocols for sample collection and analysis. The low to very high PAH levels reported in studies calls for effective actions on environmental health. Similar systematic reviews are expected to be performed in other continents for a global assessment of PAH pollution.

One century of historical deposition and flux of hydrocarbons in a sediment core from a South Atlantic RAMSAR subtropical estuary

Levels and fluxes of Polycyclic aromatic hydrocarbons (PAHs) and aliphatic hydrocarbons (AHs), including n-alkanes and petroleum biomarkers (PBMs), were measured in a sedimentary core from a nominated RAMSAR (Guaratuba Bay, Brazil) subtropical estuary experiencing relatively low human impacts, to describe the evolution of anthropogenic activities over the last century. TOC contents varied from 0.80 to 1.25%. No significant correlation between hydrocarbons and TOC with grain size (predominantly sand) was observed. Concentration and flux of total AHs ranged from 65.5 to 195 μg g^-1 and 27.6 to 82.0 μg cm^-2 y^-1, respectively, with the highest levels found in 1960-1966, when access routes to Guaratuba city were improved. Diagnostic ratios based on AH components showed an apparent change in the sources over time, with biogenic origins prevailing until 1966-1971, followed by subsequent increases in petroleum sources. Petroleum tricyclic terpanes were detected in the core (0.40 to 3.0 μg g^-1), suggesting the use of lubricating oil in the bay area. Hopanes were mainly attributed to biological sources. Concentration and flux of total PAHs ranged from 8.65 to 35.9 ng g^-1 and 3.64 to 15.1 ng cm^-2 y^-1, respectively, with the highest levels found in the top core section, reflecting recently increased human activity, while a peak PAH concentration at approximately 1977-1983 can be assumed to be a delayed signal of increased human occupation as a consequence of the improvement of access roads to the area, which started in the 1960s. Alkylated were the most abundant group of PAHs throughout the core. Despite relatively low concentrations of hydrocarbon deposition over approximately 90 years, this study highlights the influence of human occupation and slight petroleum contamination in this preserved area, mainly in recent core sections.

Occurrence, sources and effects of polycyclic aromatic hydrocarbons in the Tunis lagoon, Tunisia: an integrated approach using multi-level biological responses in Ruditapes decussatus

Coastal lagoons are critical ecosystems presenting a strategic economic importance, but they are subjected to potential anthropogenic impact. As part of the Tunis lagoon (Tunisia) biomonitoring study, levels, composition pattern and sources of polycyclic aromatic hydrocarbons (PAHs) in surface sediments along with their bioavailability in clam Ruditapes decussatus were investigated in polluted (S2-S4) and reference (S1) sites. In order to investigate the contamination effects at different biological levels in clams, a wide set of biomarkers, including gene expression changes, enzymatic activities disruption and histopathological alterations, was analysed. Biomarkers were integrated in a biomarker index (IBR index) to allow a global assessment of the biological response. Principal component analysis (PCA) was used for chemical and biological data integration to rank the sampling sites according to their global environmental quality. Sediment PAHs levels ranged between 144.5 and 3887.0 ng g^-1 dw in the Tunis lagoon sites versus 92.6 ng g^-1 dw in the reference site. The high PAH concentrations are due to anthropogenic activities around the lagoon. PAH composition profiles and diagnostic isomer ratios analysis indicated that PAHs were of both pyrolitic and petrogenic origins. Clams sampled from S2 and S3 exhibited the highest PAH contents with 2192.6 ng g^-1 dw and 2371.4 ng g^-1 dw, respectively. Elevated levels of tissue PAHs were associated to an increase in biotransformation and antioxidant activities, and lipid peroxidation levels along with an overexpression of different genes encoding for general stress response, mitochondrial metabolism and antioxidant defence, in addition to the emergence of severe and diverse histopathological alterations in the clams' digestive glands. IBR index was suitable for sampling sites ranking (S1 = 0 < S4 = 0.4 < S3 = 1.15 < S2 = 1.27) based on the level of PAH-induced stress in clams. PCA approach produced two components (PC1, 83.8% and PC2, 12.2%) that describe 96% of the variance in the data and thus highlighted the importance of integrating contaminants in sediments, their bioaccumulation and a battery of biomarkers of different dimensions for the assessment of global health status of coastal and lagoon areas.

First Investigation of Seasonal Concentration Behaviors and Sources Assessment of Aliphatic Hydrocarbon in Waters and Sediments from Wadi El Bey, Tunisia

The contents, composition profiles, and sources of aliphatic hydrocarbons were examined in surface sediment and water samples collected from Wadi El Bey, in Tunisia, during different year seasons in 14 stations receiving domestic effluent, industrial discharge, and agricultural drainage wastes. The target substances were analyzed by gas chromatography coupled with mass spectrometric detection (GC/MS). Total concentrations of n-alkanes (n-C₁₄-n-C₃₈) ranged from 0.08 ± 0.01 to 18.14 ± 0.1 µg/L in waters and 0.22 ± 0.04 to 31.9 ± 24.6 µg/g in sediments, while total aliphatic fraction ranged from 0.08 ± 0.01 to 196 ± 140 µg/L in waters and 0.22 ± 0.04 to 1977 ± 1219 µg/g in sediments, which means that almost all sites were affected by hydrocarbon contents in sediments exceeding the recommended limit (100 µg/g). Various diagnostic indices (ADIs) were used to identify the hydrocarbon sources, namely the concentration ratios of individual compounds (n-C₁₇/pristane, n-C₁₈/phytane, pristane/phytane, n-C₂₉/n-C₁₇, n-C₃₁/n-C₁₉) as well as cumulative quantities (Carbon Preference Index, natural n-alkanes ratio, terrigenous/aquatic compounds ratio, unresolved complex mixture percentage, low molecular weight vs. high molecular weight homologues, Alkane Proxy and Terrestrial Marine Discriminants). In general, these indexes indicated that the origin of aliphatic hydrocarbons affecting sediments and waters of Wadi El Bey were linked to both biogenic and petrogenic inputs, attesting the impact of plankton and terrestrial plants and of oil contamination, respectively. The average carbon chain length computation (ACL), used to further index the chemical environment, ranged from 25.5 to 31.1 in sediments and 47.9-116 in waters. This finding could depend on the severe disturbances suffered by the ecosystem as a consequence of heavy anthropogenic inputs. Petroleum contamination associated with high eutrophication rates in Wadi El Bey must be strictly controlled, due to possible harmful effects induced on ecosystem and humans.

Microplastic pollution in the sediments of Sidi Mansour Harbor in Southeast Tunisia

Despite the increasing interest in microplastic (MP) research, the accurate prevalence, distribution and fate of these materials in the environment is yet poorly known and, consequently, a focus of debate. Hence, to better ascertain the presence of microplastics in specific environments, samples from 35 random sites distributed across a 4200-meter long section from the area of Sidi Mansour, Sfax-Tunisia, were collected and analyzed. MPs were extracted, digested with potassium hydroxide and dyed with Eosin B, for visual microscopy counting and sorting. Polymer composition and surface morphology were identified by FTIR-ATR spectroscopy and SEM microscopy. Total abundances ranged from 252 to-5332 particles per m² where fragments and granules were the most frequent types of microplastics. These findings highlight the considerable presence of these materials in the studied harbor region and underscore the density dependence on the distribution and occurrence of MPs and how these tend to accumulate in the sandy sediments.

Geochemical imprints of occurrence, vertical distribution and sources of aliphatic hydrocarbons, aliphatic ketones, hopanes and steranes in sediment cores from ten Iranian Coral Islands, Persian Gulf

The levels, vertical distribution and sources of hydrocarbons and petroleum biomarkers were estimated for the first time in sediment cores (0-40 cm) from ten coral Islands of the Persian Gulf, Iran. Discrepant hydrocarbons, including linear n-alkanes (n-C₁₁ to n-C₄₀) and isoprenoids (AHs), aliphatic ketones (AKs), hopanes and steranes were measured in all core samples, showing mean concentrations ranging from 209 to 5388 μg g^-1dw (∑₃₀AH), 2-244 μg g^-1-dw (∑₁₃AK), 189-3713 ng g^-1dw (∑₃₁hopane) and 42-3864 ng g^-1dw (∑₁₅sterane), respectively. All sediment cores were found to be petroleum polluted, with ∑₃₀AH > ∑₃₁hopane > ∑₁₅sterane > ∑₁₃AK, with higher levels recorded at 10-20 cm, mainly at industrial sites. Various diagnostic indices revealed that hydrocarbons derived mainly from anthropogenic inputs, with significant contribution of biogenic origin at sites less polluted. Moreover, total organic carbon (0.24-23.45 mg g^-1-dw), terrestrial and marine organic matter had an overwhelming effect on hydrocarbons deposition in sediment cores. Overall, findings provide relevant information for monitoring and preventing petroleum pollution in the sensitive ecosystems of the Persian Gulf.

Occurrence and origins of biomarker aliphatic hydrocarbons and their indications in surface sediments of the East China Sea

The composition, distribution, indexes and budget of saturated lipid biomarker aliphatic hydrocarbons (AHs) in sediments of the East China Sea (ESC) were analyzed to identify their indications and sources. The resolved n-alkane (R) contents were 0.70-2.89 μg/g, with long-chain n-alkanes as the dominant composition in the ECS. The high R values mainly appeared at south inner shelf and north outer upwelling area, corresponding to the high mud, total organic carbon (TOC) and Chl a contents there. The composition, distribution pattern, combined with indexes of AHs, suggested no petroleum contamination and predominant biogenic sources in the ECS. The biogenic sources mainly were the mixed terrestrial higher plant, marine plankton and bacteria and aquatic macrophyte origins. Biotic source apportionment suggested that terrestrial higher plants were the dominant source of AHs, followed by marine planktons, with the lowest of submerged/floating macrophytes. Quantitative evaluation of R sources suggested that the Changjiang River input was the primary terrestrial contributor, accounting for 67.9% of total terrestrial input. The burial flux of R was 1.11 × 10³ t/yr, with inner shelf and estuary as main accumulation areas. Although there was a huge amount of R influx from terrestrial and marine sources, only 9.8% could be preserved in sediments.

Evaluating polar pesticide pollution with a combined approach: a survey of agricultural practices and POCIS passive samplers in a Tunisian lagoon watershed

A study of pesticides in the Bizerte lagoon watershed on the Mediterranean coast of Tunisia showed that herbicides and fungicides are the most commonly used compounds. A survey was made of selected farmers. Pesticide contamination was monitored in the water column and sediments at four selected sampling sites (lagoon (A) and in three oueds-Chegui (B), Garaa (C), and Tinja (D)). Polar organic chemical integrative samplers (POCIS) were used to assess pesticide contamination. Thirty-two pesticides were investigated; the total concentration of active ingredients ranged from 35.9 ng L^-1 in Tinja oued to 1246 ng L^-1 in Chegui oued. In the lagoon, the total concentration of pesticides was 67.7 ng L^-1. In the sediments, the highest concentration was measured in Chegui oued in the spring (31 ng g^-1 dw). The main compounds found in the analyzed sediments were prosulfocarb and tebuconazole molecules.

Natural and anthropogenic particulate-bound aliphatic and polycyclic aromatic hydrocarbons in surface waters of the Gulf of Gabès (Tunisia, southern Mediterranean Sea)

Particulate-bound aliphatic and polycyclic aromatic hydrocarbons (AHs and PAHs) were investigated in the surface waters of the Gulf of Gabès (Tunisia, southern Mediterranean Sea). Samples were collected off the Sfax and Gabès-Ghannouch coasts. Concentrations in total resolved n-alkanes ranged from 0.03 to 3.2 μg L^-1, and concentrations in total parents + alkylated PAHs ranged from bdl to 108.6 ng L^-1. The highest concentrations were recorded in the southern Sfax. AHs were mainly of biogenic origin with odd n-alkane predominance, although an anthropogenic contribution was also detected. The PAH molecular patterns revealed a mixed origin with the presence of low molecular weight and alkylated compounds, characteristic of uncombusted oil-derived products, and the presence of high molecular weight compounds, typical of combustion residues. Rainfall events induced an increase in PAH concentrations by a factor 1.5-23.5. The particle-water partition coefficients (K_oc) suggest that the partitioning of PAHs between the particulate and dissolved phases is driven by hydrophobicity and organic matter composition.

Remobilization of polycyclic aromatic hydrocarbons and organic matter in seawater during sediment resuspension experiments from a polluted coastal environment: Insights from Toulon Bay (France)

Polycyclic aromatic hydrocarbons (PAHs) and organic matter contents were measured in seawater during resuspension experiments using sediments collected from Toulon Bay (Northwestern Mediterranean Sea, France). The studied sediments were very highly contaminated in PAHs, especially in 4-ring compounds emitted from combustion processes. The sediments used for resuspension experiments were collected at 0-2 cm (diagenetically new organic matter, OM) and 30-32 cm depths (diagenetically transformed OM). They were both mostly composed of fine particles (<63 μm), enriched in organic carbon (8.2 and 6.3%, respectively) and in PAHs (concentration of Σ34 PAHs: 38.2 and 35.7 × 10³ ng g^-1, respectively). The resuspension of these sediments led to an increase in concentrations of dissolved Σ34 PAHs, dissolved organic carbon (DOC) and dissolved humic- and tryptophan-like fluorophores in seawater up to 10-, 1.3-, 4.4- and 5.7-fold, respectively. The remobilization in seawater was higher for 4-6 ring PAHs, especially benzo(g,h,i)perylene, whose concentration exceeded the threshold values of the European Water Framework Directive. This noted the potential harmful effects of sediment resuspension on marine biota. From these sediment resuspension experiments, we determined OC-normalized partition coefficients of PAHs between sediment and water (K_oc) and found that during such events, the transfer of PAHs from sediment particles to seawater was lower than that predicted from octanol-water partition coefficients (K_ow) (i.e., measured K_oc > K_oc predicted from K_ow). The results confirmed the sequestration role of sedimentary OC quality and grain size on PAHs; the OM diagenetic state seemed to impact the partition process but in a relatively minor way. Furthermore, differences were observed between 2-4 ring and 5-6 ring PAHs, with the latter displaying a relatively higher mobility towards seawater. These differences may be explained by the distribution of these two PAH pools within different OM moieties, such as humic substances and black carbon.

Microbial Diversity in Sulfate-Reducing Marine Sediment Enrichment Cultures Associated with Anaerobic Biotransformation of Coastal Stockpiled Phosphogypsum (Sfax, Tunisia)

Anaerobic biotechnology using sulfate-reducing bacteria (SRB) is a promising alternative for reducing long-term stockpiling of phosphogypsum (PG), an acidic (pH ~3) by-product of the phosphate fertilizer industries containing high amounts of sulfate. The main objective of this study was to evaluate, for the first time, the diversity and ability of anaerobic marine microorganisms to convert sulfate from PG into sulfide, in order to look for marine SRB of biotechnological interest. A series of sulfate-reducing enrichment cultures were performed using different electron donors (i.e., acetate, formate, or lactate) and sulfate sources (i.e., sodium sulfate or PG) as electron acceptors. Significant sulfide production was observed from enrichment cultures inoculated with marine sediments, collected near the effluent discharge point of a Tunisian fertilizer industry (Sfax, Tunisia). Sulfate sources impacted sulfide production rates from marine sediments as well as the diversity of SRB species belonging to Deltaproteobacteria. When PG was used as sulfate source, Desulfovibrio species dominated microbial communities of marine sediments, while Desulfobacter species were mainly detected using sodium sulfate. Sulfide production was also affected depending on the electron donor used, with the highest production obtained using formate. In contrast, low sulfide production (acetate-containing cultures) was associated with an increase in the population of Firmicutes. These results suggested that marine Desulfovibrio species, to be further isolated, are potential candidates for bioremediation of PG by immobilizing metals and metalloids thanks to sulfide production by these SRB.