Benin’s waterways are affected by several forms of pollution that are linked in particular to anthropic activities. This study aims to detect the presence of antibiotic residues, the frequency of antibiotic resistant bacteria and the levels of heavy metals in Benin’s waterways. 160 surface water samples from streams in Benin were collected. They were filtered by the membrane filtration method, then incubated on different media. The isolated bacterial species were identified by API 20E gallery and specific biochemical tests. After detection of the resistance profile of the latter, the antibiotic residues were quantified in the samples by the ELISA technique on plate and the physicochemical analyses were performed by Multi 3630 IDS SET KS2 multimeter. Finally, heavy metal levels were detected by the MERCK test kit method specific to each metal. The bacterial species mostly identified were Klebsiella pneumoniae (56.59%), Klebsiella spp. (18.68%), Enterobacter spp. (12.63%). The most abundant resistance of bacterial strains was to amoxicillin + clavulanic acid (92%), followed by metronidazole (86%). Metronidazole was the antibiotic with the highest residue concentration in the samples (6.578 to 6.829 µg/L), followed by ciprofloxacin (2.142 to 9.299 µg/L). Benin streams contain heavy metals such as mercury (0.454±0.129 µg/L), lead (0.040±0.50 mg/L), zinc (6.120±16.017 mg/L), nickel (0.155±0.233 mg/L) and cadmium (0.154±0.132 mg/L). The analysis of the physico-chemical parameters showed that, apart from electrical conductivity, all parameters comply with Beninese and World Health Organization standards. Actions must be taken to clean up these rivers to preserve the integrity of aquatic ecosystems in Benin.

Forest management can alter the mobilization of mercury (Hg) into headwater streams and its conversion to methylmercury (MeHg), the form that bioaccumulates in aquatic biota and biomagnifies through food webs. As headwater streams are important sources of organic materials and nutrients to larger systems, this connectivity may also increase MeHg in downstream biota through direct or indirect effects of forestry on water quality or food web structure. In this study, we collected water, seston, food sources (biofilm, leaves, organic matter), five macroinvertebrate taxa and fish (slimy sculpin; Cottus cognata) at 6 sites representing different stream orders (1–5) within three river basins with different total disturbances from forestry (both harvesting and silviculture). Methylmercury levels were highest in water and some food sources from the basin with moderate disturbance (greater clearcutting but less silviculture). Water, leaves, stoneflies and fish increased in MeHg or total Hg along the river continuum in the least disturbed basin, and there were some dissipative effects of forest management on these spatial patterns. Trophic level (δ¹⁵N) was a significant predictor of MeHg (and total Hg in fish) within food webs across all 18 sites, and biomagnification slopes were significantly lower in the basin with moderate total disturbance but not different in the other two basins. The elevated MeHg in lower trophic levels but its reduced trophic transfer in the basin with moderate disturbance was likely due to greater inputs of sediments and of dissolved organic carbon that is more humic, as these factors are known to both increase transport of Hg to streams and its uptake in primary producers but to also decrease MeHg bioaccumulation in consumers. Overall, these results suggest that the type of disturbance from forestry affects MeHg bioaccumulation and trophic transfer in stream food webs and some longitudinal patterns along a river continuum.

The presence of microplastics (MPs) in freshwater systems that receive discharge of urban effluent implies a great environmental impact. In order to be able to generate proposals that solve this problem, it is necessary to know in detail the contributions of different MPs sources. The aim of this work was to study the contribution of urban sewage discharge to MPs pollution in a stream that runs through a medium-sized city. The spatial distribution of MPs with sizes between 100 μm and 1.5 mm present in surface water was measured and their characteristics, dimensions, shapes and identification were determined. Physical-chemical parameters of the stream water were measured, and a decrease in water quality was found due to wastewater treatment plants. The main source of MPs was effluent from the plants (97% of the total MPs), while the rest came from storm drains and discharge of tributaries. The maximum concentration of MPs found was around 72,000 MP/L (equivalent to 53 million MPs/s), at a point after discharge from both plants. Around 70% of MPs correspond to microfibers with a mean length of around 300 μm and a mean width of around 15 μm, and they are mainly polyethylene fibers. The remaining 30% of MPs are particles with lengths of around 140 μm. The transport of MPs between a point located after discharge of the plants and another point located about 3 km further on was studied, and no significant variation was found in the concentration of MPs. Electrical conductivity was used as a conservative tracer of MPs concentration. This work presents for the first time a detailed analysis of different contributions of MPs to a freshwater system in South America, which receives discharge of wastewater treatment plants, evidencing its important role in pollution.

In 2018, over 30,000 L of fluorine-free firefighting foam was used to extinguish an industrial warehouse fire of uncharacterized chemical and industrial waste. Contaminated firewater and runoff were discharged to an adjacent freshwater creek in Melbourne, Australia. In this study, we applied nontarget analysis using liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) to 15 surface water samples to investigate the presence of legacy, novel and emerging per-and polyfluoroalkyl substances (PFAS). We identified six novel and emerging fluorotelomer-based fluorosurfactants in the Australian environment for the first time, including: fluorotelomer sulfonamido betaines (FTABs or FTSA-PrB), fluorotelomer thioether amido sulfonic acids (FTSASs), and fluorotelomer sulfonyl amido sulfonic acids (FTSAS-So). Legacy PFAS including C₆–C₈ perfluoroalkyl sulfonic acids, C₄–C₁₀ perfluoroalkyl carboxylic acids, and perfluoro-4-ethylcyclohexanesulfonate were also detected in surface water. Of note, we report the first environmental detection of ethyl 2-ethenyl-2-fluoro-1-(trifluoromethyl) cyclopropane-1-carboxylate. Analysis of several Class B certified fluorine-free foam formulations allowed for use in Australia revealed that there was no detectable PFAS. Patterns in the homologue profiles of fluorotelomers detected in surface water are consistent with environments impacted by fluorinated aqueous film-forming foams. These results provide strong evidence that firewater runoff of stockpiled fluorinated firefighting foam was the dominant source of detectable PFAS to the surrounding environment.

Japan receives nitrogenous air pollutants via long-range transport from China. However, emissions of nitrogenous air pollutants in China have stabilized or decreased in recent years. This study examined both the long-term trends in atmospheric nitrogen (N) deposition from the 1990s to the 2010s and the response of stream water nitrate (NO₃⁻) leaching from forested areas in western Japan. A long-term (1992–2018) temporal analysis of atmospheric N deposition in Fukuoka (western Japan) was conducted. Atmospheric bulk N deposition was collected at forested sites in a suburban forest (Swₑₛₜ) and a rural forest (Rwₑₛₜ) in western Japan during 2009–2018. Stream water samples were also collected from four locations at sites Swₑₛₜ and Rwₑₛₜ during the same period. Results showed that atmospheric N deposition in Fukuoka started to decrease from the mid-2000s at an annual rate of −2.5% yr⁻¹. The decrease in atmospheric N deposition was attributable mainly to decreased atmospheric ammonium (NH₄⁺) deposition, which caused greater contribution of NO₃⁻ deposition to atmospheric N deposition. Concentrations of NO₃⁻ in the stream water samples from three of the four locations decreased significantly at an annual rate of −3.7 to −0.7% yr⁻¹. However, stream water NO₃⁻ concentrations increased in one watershed where understory vegetation has been deteriorating owing to the increased deer population. This might weaken the recovery of N leaching from forested areas.

Identifying risks to ecosystems from contaminants needs a diversity of bioindicators, to understand the effects of these contaminants on a range of taxa. Molluscs are an ideal bioindicator because they are one of the largest phyla with extremely high ecological and economic importance. The aim of this study was to evaluate if laboratory bred Potamopyrgus antipodarum has the potential to show the impact of contaminants from various land use activities and degree of pollution on a freshwater ecosystem. We assessed the impact of contaminants arising from runoff and direct discharges in Merri Creek by measuring organism level responses (survival, growth, and reproduction), and sub-organism level responses (glutathione S-transferase (GST) activity, lipid peroxidation (LPO) activity and catalase (CAT) activity) in snails after 28-d of deployment at nine sites in Merri Creek and one site in Cardinia Creek. In Merri Creek, the top two sites were reference sites (with low impact from human activities), while the rest were impact sites (impacted by various anthropogenic land uses). Cardinia Creek (an additional reference site) had lower human activity. High concentrations of heavy metals, nutrients, and/or synthetic pyrethroids (bifenthrin) dominated these sites, which are likely to have contributed towards the negative responses observed in the snails. There was little influence from environmental conditions and site location on the endpoints because we found a similar response at an additional reference site compared to the reference sites in Merri Creek. At the organism level, reproduction increased and/or reduced, while CAT was affected at the sub-organism level. Potamopyrgus antipodarum has the potential to be a sensitive bioindicator for Australian conditions because the snails responded to varying concentrations of contaminants across different land use activities and showed similar sensitivity to P. antipodarum found in other regions of the globe and other bioindicators.

Pollution of riverine ecosystems through the multidimensional impact of human footprints around the world poses a serious challenge. Research studies that communicate potential repercussions of landscape structure metrics on snowmelt riverine water quality particularly, in climatically fragile Himalayan watersheds are very scarce. Though, worldwide, grasping the influence of land-use practices on water quality (WQ) has received renewed attention yet, the relevance of spatial scale linked to landscape pattern is still elusive due to its heterogenic nature across diverse geomorphic regions. In this work, therefore, we tried to capture the insights on landscape-aquascape interface by juxtapositioning the impacts of landscape structure pattern on snowmelt stream WQ of the whole Jhelum River Basin (JRB) under three varying spatial scales viz., watershed scale, riparian corridor (1000 m wide) and reach buffer (500 m wide). The percentage of landscape pattern composition and configuration metrics in the JRB were computed in GIS utilizing Landsat-8 OLI/TIRS satellite image having 30 m resolution. To better explicate the influence of land-use metrics on riverine WQ with space and time, we used Redundancy analysis (RDA) and multilinear regression (MLR) modeling. MLR selected land-use structure metrics revealed the varied response of WQ parameters to multi-scale factors except for total faecal coliform bacteria (TC) which showed perpetual presence. The reach-scale explained slightly better (76%) variations in WQ than riparian (75%) and watershed (70%) scales. Likewise, across seasonal scale, autumn (75%), winter (83%), and summer (77%) captured the most WQ variation at catchment, riparian, and reach scales respectively. We observed impairing WQ linkages with agriculture, built-up and barren rocky areas across watersheds, besides, pastures in riparian buffer areas, and fragmentation of landscape patches at the reach scale. Due to little appearance of spatial scale differences, a multi scale perspective landscape planning is emphasized to ensure future sustainability of Kashmir Himalayan water resources.

Forest and agricultural land use affects the concentration and composition of dissolved organic carbon (DOC) in streams and rivers. To elucidate the impacts of forest and agricultural land use on stream DOC during storm events, we investigated DOC concentration ([DOC]), optical properties of dissolved organic matter (DOM), and Δ¹⁴C-DOC in both forest- and agriculture-dominated headwater streams in South Korea in the summer of 2012. One forested and five agricultural streams were investigated. During storms, the peak [DOC] of forest stream increased to 5.8 mg L⁻¹, approximately two times larger than that of the most agricultural stream (3.2 mg L⁻¹), demonstrating the weaker storm responses of the [DOC] of agricultural streams to hydrological change. Five PARAFAC components were identified, including three terrestrial humic-like substances (C1, C2, C3), one microbial humic substance (C4), and one microbial protein-like substances (C5). The mean (C4+C5)/(C1+C2+C3) of all storm events at the most agricultural stream was 1.5 times larger than that of the most forested stream, suggesting that more protein-like DOM is exported from agricultural watersheds. Whereas a forest stream was primarily composed of terrestrially derived and ¹⁴C-enriched modern DOC, the ¹⁴C-age of the most agricultural stream was up to ∼1000 years old. The results suggest that agricultural practices could decrease the old organic carbon pools from soils. However, how quickly the aged DOC can be degraded to CO₂ in streams is unknown, warranting future investigation on lability of the aged DOC and their effects on CO₂ evasion from rivers and estuaries downstream.

To reduce direct discharges of surface runoff to receiving waters, separate sewer systems have been implemented, with runoff retention basins (RRB) for pollutant pretreatment by sedimentation and infiltration. However, due to frequent and intense precipitation events, most RRBs are overwhelmed by runoff resulting in overflow into the receiving freshwater bodies. Hence, the present study evaluates the impact of traffic-related runoff overflow on metal concentrations in sediment and Gammarus sp. Downstream of the RRB outfall in the receiving stream. Samples were collected from the RRB, upstream (reference site) and at different distances downstream from the RRB outfall in the stream. The samples were analyzed for the presence and distribution of metals using ICP-MS. Furthermore, ecotoxicological effects of the overflow on benthic species were assessed using Lumbriculus variegatus exposed to the field sediments. Our findings reveal that overflow of the RRB results in elevated traffic-related metal concentrations in sediment and biota of the stream. Within the first 50 m downstream increased sediment metal concentrations were found. The gammarids downstream of the RRB outfall showed an increased accumulation of several metals. Similarly, the metals were found to be taken up by the endobenthic L. variegatus under laboratory conditions and the bioaccumulation pattern was related to the sediment concentrations. Bioaccumulation by both organisms is an indication that overflow of the RRB also leads to uptake of increased element amounts in organisms downstream. Laboratory-based studies addressing standard toxicity endpoints showed no clear toxic effects on growth and reproduction. However, elevated levels of metallothioneins were measured in the annelids during the test period. This indicates a physiological response induced by increased metal concentrations due to RRB overflow. Hence, the results of this study show that discharges by the RRB increase the metal concentration in the receiving stream with the possibility of adverse effects on organisms.

Given extensive use of pesticides in agriculture, there is concern for unintended consequences to non-target species. The non-target freshwater amphipod, Hyalella azteca has been found to show resistance to the organophosphate (OP) pesticide, chlorpyrifos, resulting from an amino acid substitution in acetylcholinesterase (AChE), suggesting a selective pressure of unintended pesticide exposure. Since resistant organisms can survive in contaminated habitats, there is potential for them to accumulate higher concentrations of insecticides, increasing the risk for trophic transfer. In the present study, we estimated the uptake and elimination of chlorpyrifos in non-resistant US Lab, and resistant Ulatis Creek (ULC Resistant), H. azteca populations by conducting 24-h uptake and 48-h elimination toxicokinetic experiments with ¹⁴C-chlorpyrifos. Our results indicated that non-resistant H. azteca had a larger uptake clearance coefficient (1467 mL g⁻¹ h⁻¹) than resistant animals (557 mL g⁻¹ h⁻¹). The half-life derived from the toxicokinetic models also estimated that steady state conditions were reached at 13.5 and 32.5 h for US Lab and ULC, respectively. Bioaccumulation was compared between non-resistant and resistant H. azteca by exposing animals to six different environmentally relevant concentrations for 28 h. Detection of chlorpyrifos in animal tissues indicated that resistant animals exposed to high concentrations of chlorpyrifos were capable of accumulating the insecticide up to 10-fold higher compared to non-resistant animals. Metabolite analysis from the 28-h concentration experiments showed that between 20 and 50 % parent compound was detected in H. azteca. These results imply that bioaccumulation potential can be more significant in chlorpyrifos resistant H. azteca and may be an essential factor in assessing the full impacts of toxicants on critical food webs, especially in the face of increasing pesticide and chemical runoff.