Transport of sediment borne contaminants in a Mediterranean river during a high flow event

Distribution, levels, sources and risk assessment of polycyclic aromatic hydrocarbons in the bottom sediments of a Mediterranean river under multiple anthropopressures (Soummam River), Algeria

The Soummam River, a vital watercourse in Algeria is threatened by anthropogenic activities despite its protected wetland status. This study is the first to assess sediment pollution in the Soummam River, examining levels, compositions, sources of 16 PAHs and their effects on the environment and human health. Analysis employing Principal Component Analysis (PCA) and molecular diagnostic ratios pointed to petrogenic sources, likely stemming from petroleum leaks originating from aging pipeline and vehicles, as well as pyrogenic sources arising from vehicle exhaust and biomass combustion. Environmental and health risks were assessed through risk quotients (RQ), Sediments Quality Guidelines (SQG) and Total Lifetime Cancer Risk (TLCR). Ecological risk was found to range from moderate to high, with anticipated biological impacts, while cancer risk was deemed low. Toxicity assessment, measured by TEQ, revealed that the majority of monitoring stations exceeded safe levels. Consequently, urgent action by local authorities is warranted to implement ecosystem rehabilitation measures.

New insights into pesticide occurrence and multicompartmental monitoring strategies in stream ecosystems using periphyton and suspended sediment

Streams are susceptible to pesticide pollutants which are transported outside of the intended area of application from surrounding agricultural fields. It is essential to monitor the occurrence and levels of pesticides in aquatic ecosystems to comprehend their effects on the aquatic environment. The common sampling strategy used for monitoring pesticides in stream ecosystems is through the collection and analysis of grab water samples. However, grab water sampling may not effectively monitor pesticides due to its limited ability to capture temporal and spatial variability, potentially missing fluctuations and uneven distribution of pesticides in aquatic environments. Monitoring using periphyton and sediment sampling may offer a more comprehensive approach by accounting for accumulative processes and temporal variations. Periphyton are a collective of microorganisms that grow on hard surfaces in aquatic ecosystems. They are responsive to chemical and biological changes in the environment, and therefore have the potential to act as a cost-effective, integrated sampling tool to monitor pesticide exposures in aquatic ecosystems. The objective of this study was to assess pesticides detected through periphyton, suspended sediment, and conventional grab water sampling methods and identify the matrix that offers a more comprehensive characterization of a stream's pesticide exposure profile. Ten streams across Southern Ontario were sampled in 2021 and 2022. At each stream site, water, sediment and periphyton, colonizing both artificial and natural substrates, were collected and analyzed for the presence of ~500 pesticides. Each of the three matrices detected distinctive pesticide exposure profiles. The frequency of detection in periphyton, sediment and water matrices were related to pesticides' log Kow and log Koc (P < 0.05). In addition, periphyton bioconcentrated 22 pesticides above levels observed in the ambient water. The bioconcentration factors of pesticides in periphyton can be predicted from their log Kow (simple linear regressions, P < 0.05). The results demonstrate that sediment and periphyton accumulate pesticides in stream environments. This highlights the importance of monitoring pesticide exposure using these matrices to ensure a complete and comprehensive characterization of exposure in stream ecosystems.

Association of drought conditions and heavy rainfalls with the quality of drinking water in Barcelona (2010-2022)

BACKGROUND

Climate change influences the incidence and scope of climate extreme events that affect communities and the environment around the world. In an urban context such as Barcelona, these climate extremes can have a negative impact on drinking water quality. The worsening of drinking water quality can have important repercussions on human health, leading to the appearance of different diseases.

OBJECTIVE

Investigate the association between climate extremes, in particular heavy rainfall events and drought conditions, and the drinking water quality in the city of Barcelona from 2010 to 2022.

METHODS

We conducted a daily retrospective time-series study using data covering 13 years of daily monitoring of conductivity, nickel, turbidity and trihalomethanes parameters of raw water in the Llobregat River catchment area and treated water in the Drinking Water Treatment Plant (DWTP) Sant Joan Despí. We used river flow as a proxy for drought conditions and heavy rainfall events. We analyzed short-term associations between river flow rate and quality parameters in raw and treated water using generalized linear regression with distributed lag-non-linear models (DLNM).

RESULTS

A low flow, as an indicator of drought condition or low rainfall, was significantly associated with an increase in conductivity in raw water and nickel in both raw and treated water. A high flow, as an indicator of heavy rainfall events, was significantly associated with an increase of turbidity in raw water, and a decrease in all other quality parameters.

IMPACT STATEMENT

This study provides novel evidence that climate extremes have an impact on the quality of drinking water in urban areas with a Mediterranean climate. The findings of this study are significant because they suggest that as the frequency and intensity of climate extremes increase due to climate change, there will be further challenges in managing and treating drinking water, which could have a detrimental effect on public health. This study serves as an important reminder of the need to strengthen and accelerate adaptation actions in water management to ensure an adequate supply of drinking water that protects the people's health.

Bioaccumulation and fate of pharmaceuticals in a Mediterranean coastal lagoon: Temporal variation and impact of a flash flood event

Coastal ecosystems are particularly vulnerable to terrestrial inputs from human-impacted areas. The prevalence of wastewater treatment plants, unable to remove contaminants such as pharmaceuticals (PhACs), leads to their continuous input into the marine environment. In this paper, the seasonal occurrence of PhACs in a semi-confined coastal lagoon (the Mar Menor, south-eastern Spain) was studied during 2018 and 2019 by evaluating their presence in seawater and sediments, and their bioaccumulation in aquatic organisms. Temporal variation in the contamination levels was evaluated by comparison to a previous study carried out between 2010 and 2011 before the cessation of permanent discharges of treated wastewater into the lagoon. The impact of a flash flood event (September 2019) on PhACs pollution was also assessed. A total of seven compounds (out of 69 PhACs analysed) were found in seawater during 2018-2019, with a limited detection frequency (<33%) and concentrations (up to 11 ng/L of clarithromycin). Only carbamazepine was found in sediments (ND-1.2 ng/g dw), suggesting an improved environmental quality in comparison to 2010-2011 (when 24 and 13 compounds were detected in seawater and sediments, respectively). However, the biomonitoring of fish and molluscs showed a still remarkable accumulation of analgesic/anti-inflammatory drugs, lipid regulators, psychiatric drugs and β-blocking agents, albeit not higher than in 2010. The flash flood event from 2019 increased the prevalence of PhACs in the lagoon, compared to the 2018-2019 sampling campaigns, especially in the upper water layer. After the flash flood the antibiotics clarithromycin and sulfapyridine yielded the highest concentrations ever reported in the lagoon (297 and 145 ng/L, respectively), alongside azithromycin in 2011 (155 ng/L). Flash flood events associated with sewer overflows and soil mobilisation, which are expected to increase under climate change scenarios, should be considered when assessing the risks posed by pharmaceuticals to vulnerable aquatic ecosystems in the coastal areas.

Toxicity effects of ciprofloxacin on biochemical parameters, histological characteristics, and behaviors of Corbicula fluminea in different substrates

Antibiotic toxicity and antibiotic resistance have become significant challenges to human health. However, the potential ecotoxicity of sediment-associated antibiotics remains unknown. In this study, biochemical responses, histological changes, and behavioral responses of Corbicula fluminea exposed to sediment-associated ciprofloxacin (CIP) were systemically investigated. Special attention was paid to the influence of different substrate types. Biochemical analyses revealed that the balance of the antioxidant system was disrupted, eventually leading to oxidative damage to the gills and digestive gland with increasing CIP concentration. Severe histopathological changes appeared along with the oxidative damage. An enlargement of the tubule lumen and thinning of the epithelium in the digestive gland were observed under exposure to high CIP concentrations (0.5 and 2.5 μg/g CIP). In a behavioral assay, the filtration rate of C. fluminea in high concentration exposure groups was clearly inhibited. Moreover, from the integrated biomarker response (IBR) index, the toxicity response gradients of the digestive gland (no substrate--NOS > Sand > Sand and kaolinite clay-- SKC > Sand, kaolinite clay, and organic matter--SCO) and gills (NOS > SCO > SKC > Sand) were different among substrate exposure groups. The most serious histopathological damage and highest siphoning inhibition were observed in the NOS group. The changes in the morphological structure of digestive gland cells in C. fluminea were similar in the other three substrate groups. The inhibition of the filtration rate in the higher concentration groups decreased in the order Sand > SKC > SCO.

Impact assessment of a large river on the sediments and fish from its continental shelf: using Solea solea as sentinel in the Ebro river mouth (NW Mediterranean, Spain)

Many studies have been carried out along mighty rivers with heavily industrialized watersheds to evaluate pollutants and their effects on freshwater organisms. However, their impact on marine organisms is virtually unknown. In order to cover this gap, Solea solea, one of the most important commercial fish species, together with sediments, were sampled during 2013-2015 offshore from the Ebro Delta river mouth. Fish health indicators (condition indices, histological tissue alterations, and parasite descriptors) were used to assess the potential effect of pollutants, an issue of particular interest in the area following the dredging activities taking place in the river upstream in 2013. No major histopathological alterations were detected, but perivascular inflammatory foci (PIF) were frequently observed, especially in 2014. The most prevalent and abundant parasites were acanthocephalans and digeneans within the digestive tract and copepods on the gills. Levels of trace metals from sediments and fish muscle were below the effects range median and reference levels accepted for human consumption, respectively. However, the lower levels of the hepatosomatic index, higher numbers of PIF, and variations in the abundance of parasites in 2014 and 2015 could suggest a pollutant exposure during these years. These results warn signs of toxicity, which could be associated with sediment leaks during the dredging activities.

Effects of seasonal contaminant remobilization on the community trophic dynamics in a Brazilian tropical estuary

In tropical estuaries, wet seasons are responsible for the downstream transport of allochthonous material from the upper basin and flooded plains. Although allochthonous matter is commonly associated to nutrient and detritus input, pollutants are also transported throughout the basin or suspended from the river bottom via strong streamflow remobilization and rainfall dynamics. We assessed community and population trophic niche-based patterns using organisms' stable isotopes signatures in the wet and the dry seasons to test if estuarine trophic diversity is affected by remobilization of metal-contaminated material from a mining dam collapse that occurred in the Doce river basin, Brazil. Trophic depletion was detected community-wide and in a key consumer group (bottom-dwelling fishes) at the end of the wet season in the impacted Doce river estuary (DRE). Conversely, higher trophic diversity values were recorded in a well-preserved estuary used as control site. Stable isotopes mixing models indicated in the DRE that G. genidens, a predator fish species, presented poor-quality diet based on pollutant-tolerant tiny organisms, a finding that strongly contrasts from diet described in other, little-impacted Brazilian estuaries. Although wet seasons are expected to increase trophic, functional and taxonomic diversity in tropical estuaries, in the DRE the rainfall-driven dynamics poses a threat to the community due to the presence of ore tailings.

Using Sr-Nd-Pb isotope systems to trace sources of sediment and trace metals to the Weser River system (Germany) and assessment of input to the North Sea

In order to trace the sources of sediment materials and trace metals in the Weser River system (Germany), and the riverine input to the North Sea, Sr, Nd and Pb isotopes, together with multi-elemental compositions, were measured for sediments collected over the entire Weser River Basin, from headwaters to the estuary. Mass fractions of metals, including Ag, Cd, and Pb, and of one metalloid, Sb, higher than their crustal abundance, were observed within the entire Weser Basin. Isotope-amount ratio n(⁸⁷Sr)/n(⁸⁶Sr) and ε_Nd ranged from 0.71182 ± 0.00005 to 0.72880 ± 0.00009 and -11.3 ± 0.3 to -21.0 ± 0.3, respectively. n(²⁰⁶Pb)/n(²⁰⁴Pb), n(²⁰⁷Pb)/n(²⁰⁴Pb), and n(²⁰⁸Pb)/n(²⁰⁴Pb) ranged from 18.226 ± 0.008 to 18.703 ± 0.012, 15.613 ± 0.007 to 15.653 ± 0.012 and 38.14 ± 0.02 to 38.84 ± 0.02, respectively. Sr and Nd isotope compositions reflected primarily a mixture of natural materials derived from the Weser Basin. Pb isotope signatures indicated strong anthropogenic influences in the middle-lower Weser region. Pb isotopic compositions in the sediments from the Aller (tributary of the Weser) and its tributary suggested influence from historical Pb-Zn ore mining in the Harz Mountains that might contribute to the observed elevated mass fractions of Ag, Cd, Sb and Pb in that region. K-means cluster and principal component analysis of the Sr, Nd, and Pb isotope data yielded results consistent with their isotope systematics, supporting statistical analysis as an unsupervised tool in isotope fingerprinting studies. Sr, Nd, and Pb isotopic signatures in the sediments of the Weser were distinctively different from those of another major river discharging into the North Sea, the Elbe. This suggested that this Sr, Nd, and Pb isotope dataset can be used to distinguish riverine input of sediment materials and metals between the two rivers, thereby assessing their individual contribution to materials transported into the North Sea.

Climate change impacts on contaminant loads delivered with sediment yields from different land use types in a Carpathian basin

Soil runoff and sediment transport are considered as an important vector for particle-bound contaminant transfer from source to receiving waters. Under changing climate conditions and rapid basin development, identification of sediment origins is critical for planning further action to reduce erosion effects, and further pollution to surface waters. The goal of this study was to distinguish sediment sources in a Carpathian basin (Wolnica River, southern Poland) and to perform source-oriented contaminant load estimations. Sediment yields (SYLD) and land use specific sediment yields (LUSY) were modeled with the use of the Macromodel DNS/SWAT (Discharge-Nutrients-Sea/Soil and Water Assessment Tool). Sorting of sediment sources was performed by the fingerprinting method using variability of the geochemical composition of soils (Pb, Zn, Cd, Cu, Mn, Ni, Fe, Hg, total N and P, Σ16 PAHs, and 137Cs) of four land use (LU) types: arable lands (A), grasslands (G), residential areas (R), and forests (F). Statistical analysis revealed six metals (Pb, Zn, Cd, Cu, Ni, and Hg) as fingerprint properties providing the best source discrimination in this basin. The contribution of particular land use origin assessed with the use of the mixing model varied in the range of 20-30%. Finally, estimation of land use specific contaminant loads in suspended sediments was performed as a result of a modeling and sediment fingerprinting combination. The final estimates revealed yearly LUSY values varying between 716 t/y for A, 12 t/y for F, and metal loads from 31 kg/y for Zn to values below 100 g/y for Cd and Hg. Long-term predictions (2046-2055) of the metal loads revealed an increase by 75% under the combined RCP 8.5 climate change and land use scenarios. These findings are of great value for land management in the Carpathian basins, especially with regards to the predicted increase of forest cover which significantly alters contaminant signals conveyed through the system.

Current advisory interventions for grazing ruminant farming cannot close exceedance of modern background sediment loss - Assessment using an instrumented farm platform and modelled scaling out

Water quality impairment by elevated sediment loss is a pervasive problem for global water resources. Sediment management targets identify exceedance or the sediment loss 'gap' requiring mitigation. In the UK, palaeo-limnological reconstruction of sediment loss during the 100-150 years pre-dating the post-World War II intensification of agriculture, has identified management targets (0.20-0.35 t ha^-1 yr^-1) representing 'modern background sediment delivery to rivers'. To assess exceedance on land for grazing ruminant farming, an integrated approach combined new mechanistic evidence from a heavily-instrumented experimental farm platform and a scaling out framework of modelled commercial grazing ruminant farms in similar environmental settings. Monitoring (2012-2016) on the instrumented farm platform returned sediment loss ranges of 0.11-0.14 t ha^-1 yr^-1 and 0.21-0.25 t ha^-1 yr^-1 on permanent pasture, compared with between 0.19-0.23 t ha^-1 yr^-1 and 0.43-0.50 t ha^-1 yr^-1and 0.10-0.13 t ha^-1 yr^-1and 0.25-0.30 t ha^-1 yr^-1 on pasture with scheduled plough and reseeds. Excess sediment loss existed on all three farm platform treatments but was more extensive on the two treatments with scheduled plough and reseeds. Excessive sediment loss from land used by grazing ruminant farming more strategically across England, was estimated to be up to >0.2 t ha^-1 yr^-1. Modelled scenarios of alternative farming futures, based on either increased uptake of interventions typically recommended by visual farm audits, or interventions selected using new mechanistic understanding for sediment loss from the instrumented farm platform, returned minimum sediment loss reductions. On the farm platform these were 2.1 % (up to 0.007 t ha^-1 yr^-1) and 5.1 % (up to 0.018 t ha^-1 yr-1). More strategically, these were up to 2.8 % (0.014 t ha^-1 yr^-1) and 4.1 % (0.023 t ha^-1 yr^-1). Conventional on-farm measures will therefore not fully mitigate the sediment loss gap, meaning that more severe land cover change is required.

The use of Hediste diversicolor in the study of emerging contaminants

The contamination of aquatic environments has been the focus of research to understand effects on ecosystems and its species. Benthic organisms are considered potential targets since sediments act as sources and sinks for environmental contaminants. This review presents information on the effects of three types of emerging contaminants: pharmaceuticals (tested concentrations between 0.1 ng/L - 250 mg/L and 0.01 ng/g - 2.5 μg/g), metal-based nanoparticles (<100 nm) (tested concentrations between 10 μg/L - 1 mg/L and 5 - 140 μg/g) and micro(nano)plastics (tested concentrations between 5 μg/L - 50 mg/L and 10 - 50 mg/kg), on the polychaete Hediste diversicolor, a key species in estuarine/coastal ecosystems. Data shows that these contaminants promote alterations in burrowing activity (lowest concentration inducing effects: 10 ng/L), neurotransmission and damage related parameters (lowest concentration inducing effects: 100 ng/L). The characteristics of this polychaete, such as regenerative capacity, make the use of this species in biomedical studies involving environmental contaminants valuable.

Multivariate statistical analyses for water and sediment quality index development: A study of susceptibility in an urban river

In this study, multivariate statistical analyses were performed to develop water and sediment quality indexes, allowing us (i) to select with reliability the most appropriate chemical variables for the evaluation of river quality susceptibility; (ii) to weight the influence of each variable based on monitored data; (iii) to consider possible synergism or antagonism derived from the combined effect of several pollutants; and (iv) to express the quality as a deviation from selected site-specific reference conditions. For the establishment of these threshold/maximum values, combining two biological indicators related to denitrifying bacteria in sediments turned out to be applicable to ensure compliance with the European water quality standard. The joint implementation of water and sediment quality indexes assisted us in the rapid detection of the deleterious effect of different anthropogenic contamination sources, as well as the influence of hydrological regime seasonality on river quality. In addition, metal-dependent water quality appeared to be coupled to sediment dynamics, since they were preferentially adsorbed onto sediments during low flow seasons, whereas there was potential for metal mobilization to water during sediment resuspension in high flow seasons. Therefore, an annual determination of sediment quality index was also recommended as suitable tool for prospective monitoring water quality, identifying those sites which could deserve special attention during certain periods, and planning future strategies for river quality improvement. However, two limitations were found: (1) sediment was not appropriate for water physicochemical quality early monitoring due to organic matter and nutrient continuous transformation; and (2) a multimetric index did not provide a concise and definitive quality information, thus a new tool for combining with quality index was proposed for specifically evaluate the water and sediment quality by identifying pollutant/s of concern at each location.

Occurrence of organic plastic additives in surface waters of the Rhône River (France)

We present here a comprehensive study (1-year regular sampling) on the occurrence of major families of organic plastic additives in the Rhône River surface waters. Potential sources and contaminant export are also discussed. A total of 22 dissolved phase samples were analyzed for 22 organic additives mainly used in the plastic industry, including organophosphate esters (OPEs), phthalates (PAEs) and bisphenols (BPs). Our results indicate that PAEs were the most abundant class, with concentrations ranging from 97 to 541 ng L^-1, followed by OPEs (85-265 ng L^-1) and BPs (4-21 ng L^-1). Among PAEs, diethylhexyl phthalate (DEHP) was the most abundant compound, whereas TCPP (Tris(1-chloro-2-propyl) phosphate) and TnBP (Tri(n-butyl)phosphate) were the predominant OPEs. Bisphenol S was the only BP detected. 5-54 metric tons year^-1 of dissolved organic plastic additives of emerging concern are estimated to be exported to the Gulf of Lion by the Rhône River, which is the main freshwater source of the Mediterranean Sea.

The hydrological regime of a large Mediterranean river influences the availability of pollutants to mussels at the adjacent marine coastal area: Implications for temporal and spatial trends

The present study reports the levels and trends (1993-2013) of DDTs, PCBs and metals in mussels collected at two coastal sites influenced by the River Ebro discharges. Results showed that levels of PCBs, DDTs, Cd and Hg were related to water inputs from the river, while these did not seem to be the main source for the Pb, Zn, Cu and As levels observed. Significant relationships were observed between PCBs and DDTs levels and the river flowrate in the fast-flowing months, suggesting that overflow periods promoted the mobilization of contaminants from sediments, and their subsequent discharge and spreading across the sea. Results indicated that PCBs were effectively southwestern transported, probably in relation to their soluble behavior in stream waters, while DDTs were limitedly spread in seawater, likely due to their particulate behavior. Significant declining trends observed for some metals, PCBs and p,p' DDE may reflect the reduction of pollutants inputs along the river basin. However, the results also showed significant relationships between the river's flowrate in the fast-flowing months and PCBs and DDTs levels, and significant decreases on the river flowrate in some fast-flowing months during the long-term series studies. Both facts suggested that the reduction on overflow periods influenced the decreasing pollutants trends observed in mussels. The present study advises that decreasing trends in contaminant levels in Mediterranean estuarine coastal areas may be related not only to successful remediation works/policies, but also to the fluctuations on the hydrological regime of the rivers, which are directly linked to current climatic trends.

First determination of high levels of organophosphorus flame retardants and plasticizers in dolphins from Southern European waters

This study evaluates for the first time organophosphorus flame retardant (OPFR) occurrence in the Alboran Sea delphinids (Spain). OPFRs were detected in all the individuals with concentration levels up to 24.7 µg/g lw. Twelve out of sixteen tested analytes were detected, being TBOEP which presented the highest detection frequency, and IDPP which presented the highest levels of concentration. OPFR distribution in different tissues (blubber, brain, kidney, muscle and liver) was evaluated. The pattern distribution showed the highest contribution for blubber (mean value of 68%) and the lowest contribution for liver (mean value of 2%). Seven OPFRs were detected in brain samples showing their capacity to surpass the blood-brain barrier and reach the brain. Moreover, high affinity for the brain tissue was observed. This is extremely important due to the neurotoxic effects of several compounds such as TCEP and TNBP. OPFR levels were compared with previously published PBDE concentrations, and no significant differences were observed. Taking into account the lower use and lower bioaccumulation and biomagnification capacities of OPFRs, this could indicate an additional OPFR source of pollution in addition to their use as FRs.

Influences of Catchment and River Channel Characteristics on the Magnitude and Dynamics of Storage and Re-Suspension of Fine Sediments in River Beds

Fine particles or sediments are one of the important variables that should be considered for the proper management of water quality and aquatic ecosystems. In the present study, the effect of catchment characteristics on the performance of an already developed model for the estimation of fine sediments dynamics between the water column and sediment bed was tested, using 13 catchments distributed worldwide. The model was calibrated to determine two optimal model parameters. The first is the filtration parameter, which represents the filtration of fine sediments through pores of the stream bed during the recession period of a flood event. The second parameter is the bed erosion parameter that represents the active layer, directly related to the re-suspension of fine sediments during a flood event. A dependency of the filtration parameter with the catchment area was observed in catchments smaller than ~100 km2, whereas no particular relationship was observed for larger catchments (>100 km2). In contrast, the bed erosion parameter does not show a noticeable dependency with the area or other environmental characteristics. The model estimated the mass of fine sediments released from the sediment bed to the water column during flood events in the 13 catchments within ~23% bias.

Pollution from azithromycin-manufacturing promotes macrolide-resistance gene propagation and induces spatial and seasonal bacterial community shifts in receiving river sediments

Effluents from antibiotic manufacturing may contain high concentrations of antibiotics, which are the main driving force behind the selection and spread of antibiotic resistance genes in the environment. However, our knowledge about the impact of such effluent discharges on the antibiotic resistome and bacterial communities is still limited. To gain insight into this impact, we collected effluents from an azithromycin-manufacturing industry discharge site as well as upstream and downstream sediments from the receiving Sava river during both winter and summer season. Chemical analyses of sediment and effluent samples indicated that the effluent discharge significantly increased the amount of macrolide antibiotics, heavy metals and nutrients in the receiving river sediments. Quantitative PCR revealed a significant increase of relative abundances of macrolide-resistance genes and class 1 integrons in effluent-impacted sediments. Amplicon sequencing of 16S rRNA genes showed spatial and seasonal bacterial community shifts in the receiving sediments. Redundancy analysis and Mantel test indicated that macrolides and copper together with nutrients significantly correlated with community shift close to the effluent discharge site. The number of taxa that were significantly increased in relative abundance at the discharge site decreased rapidly at the downstream sites, showing the resilience of the indigenous sediment bacterial community. Seasonal changes in the chemical properties of the sediment along with changes in effluent community composition could be responsible for sediment community shifts between winter and summer. Altogether, this study showed that the discharge of pharmaceutical effluents altered physicochemical characteristics and bacterial community of receiving river sediments, which contributed to the enrichment of macrolide-resistance genes and integrons.

Particle bound pollutants in rivers: Results from suspended sediment sampling in Globaqua River Basins

Transport of hydrophobic pollutants in rivers such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and heavy metals is often facilitated by suspended sediment particles, which are typically mobilized during high discharge events. Suspended sediments thus represent a means of transport for particle related pollutants within river reaches and may represent a suitable proxy for average pollutant concentrations estimation in a river reach or catchment. In this study, multiple high discharge/turbidity events were sampled at high temporal resolution in the Globaqua River Basins Sava (Slovenia, Serbia), Adige (Italy), and Evrotas (Greece) and analysed for persistent organic pollutants such as PAHs (polycyclic aromatic hydrocarbons) or PCBs (polychlorinated biphenyls) and heavy metals. For comparison, river bed sediment samples were analysed as well. Further, results are compared to previous studies in contrasting catchments in Germany, Iran, Spain, and beyond. Overall results show that loadings of suspended sediments with pollutants are catchment-specific and relatively stable over time at a given location. For PAHs, loadings on suspended particles mainly correlate to urban pressures (potentially diluted by sediment mass fluxes) in the rivers, whereas metal concentrations mainly display a geogenic origin. By cross-comparison with known urban pressure/sediment yield relationships (e.g. for PAHs) or soil background values (for metals) anthropogenic impact - e.g. caused by industrial activities - may be identified. Sampling of suspended sediments gives much more reliable results compared to sediment grab samples which typically show a more heterogeneous contaminant distribution. Based on mean annual suspended sediment concentrations and distribution coefficients of pollutants the fraction of particle facilitated transport versus dissolved fluxes can be calculated.