Bulk Water Samples Research Articles

Comparison of surface freshwater PFAS sampling methods to evaluate potential for bias due to PFAS enrichment in the surface microlayer.

Per- and polyfluoroalkyl substances (PFAS) accumulate at the air-water interface of the surface microlayer (SML) on marine and freshwater bodies. In order to determine if including the SML when sampling bulk surface water leads to a high bias in measured PFAS concentrations, a pilot study and a full field study were conducted. The pilot study conducted at two sites was aimed at determining the analytical precision and small-scale (~1 m) spatial variability in concentrations of PFAS in bulk water and the SML. The full field study was performed at 11 sites, where three commonly used bulk surface water sampling methods were compared: (1) a peristaltic pump with tubing that excludes the SML, (2) a fully submerged sample bottle that excludes the SML, and (3) a partially submerged sample bottle that allows inclusion of the SML. The SML was sampled using the glass plate method. The samples were analyzed by liquid chromatography tandem mass spectrometry. The pilot study indicated that sampling variation was greater than analytical variation (although Levene's tests indicated that the differences were not statistically significant) and that relatively small differences in the mean concentration among sampling methods could be detected. The full investigation indicated that there was no evidence of high bias of PFAS concentrations in bulk surface water resulting from inclusion of SML using the partially submerged bottle sampling method. Unexpectedly, there was evidence that samples collected using the partially submerged bottle had slightly lower PFAS concentrations, particularly for less hydrophobic PFAS, than bulk water samples that excluded the SML. Additionally, the PFAS enrichment factor in the SML increased with increasing retention time, although the increase was not evident at all sampling sites for all PFAS. Integr Environ Assess Manag 2024;20:2271-2282. © 2024 SETAC.

Systematic underestimation of polycyclic aromatic hydrocarbon aqueous concentrations in rivers

Polycyclic aromatic hydrocarbons (PAHs) are a widespread group of organic contaminants whose presence in water bodies is cause of severe concern. With few exceptions, the majority of PAHs is hydrophobic, presents a high adsorption affinity, and is thus primarily transported within river systems during high-flow events together with suspended particulate matter (SPM). Evidence exists of analytical challenges related to the incomplete extraction of PAHs adsorbed to solids and thus to a potential negative bias in the chemical analysis of PAHs in bulk water samples with high SPM content. Despite this, partly due to the elevated efforts required to collect representative samples containing sufficient SPM for the separate PAH analysis in this matrix, several investigations rely on the analysis of aqueous samples. This study tests the hypothesis that surveys based exclusively on bulk water may lead to a systematic underestimation of the real contamination level and transport of PAHs in rivers. Six high-turbidity events were examined in three Austrian rivers applying time-integrated sampling and simultaneously analyzing PAHs in total bulk water, filtered water, SPM, and supernatant. Despite an unavoidable degree of uncertainty in such challenging sampling scheme, the results indicate that measurements performed with best available standard methods in bulk water samples determined in average only about 40% of the theoretically expected total PAHs concentrations derived from the analyses in SPM. Such deviation has important implications for the reliable assessment of the compliance with environmental quality standards as well as for surveys aimed to estimate riverine loads, validate emission models, and understand the transport dynamics of PAHs in rivers. Whereas the first objective, e.g., in European countries, is alternatively achieved via monitoring in biota, the latter ones require efforts directed to complement monitoring campaigns with separate sampling of SPM, with monitoring of suspended solids transport to appropriately select and interpret the results of water samples and to improve the chemical analysis of PAHs in bulk water samples with high solids content.

Microelectrode evaluation of in situ oxidant reactivity and pH variability at new ductile iron and copper coupon surfaces.

Thirty-two short term (∼7.5h) abiotic experiments were conducted with new ductile iron and copper coupons exposed to various water qualities, including pH (7 or 9), dissolved inorganic carbon (DIC, 10 or 50mgCL-1) and phosphate (0 or 3mgPL-1) concentrations and 4mgCl2L-1 free chlorine or monochloramine. To quantify oxidant reactivity with the new metal coupons, microelectrodes were used to obtain oxidant (free chlorine or monochloramine and dissolved oxygen (DO)) concentration and pH microprofiles from the bulk water to near the metal coupon surface. From the microprofiles, apparent surface reaction rate constants (k) were determined for each oxidant. An ANOVA analysis evaluated if the five variables (Material, Oxidant, Phosphate, DIC, and pH) significantly affected estimates of k, finding that the Material and Oxidant variables and their interaction were statistically significant (p<0.05), but the effect of variables of Phosphate, DIC, and pH on k values were not significant in this study. In general, both ductile iron and copper coupons showed significant surface reactivity towards free chlorine and monochloramine. For ductile iron, DO consumption was greater than for copper, which showed minimal DO reactivity, and DO was less reactive towards the copper surface than either free chlorine or monochloramine. Furthermore, pH microprofiles provided insight into the complexity that might exist near corroding metal surfaces where the bulk water pH may be substantially different from that measured near metal surfaces which is significant as pH is a controlling variable in terms of scale formation and metal solubility. This study represents an important first step towards using microelectrodes to (1) understand and provide direct measurement of oxidant microprofiles from the bulk water to the metal surface; (2) determine pipe wall reactivity using the directly measured concentrations profiles versus estimated pipe wall reactivity from bulk water measurements, and (3) understand how variables measured by bulk water samples (e.g., pH) may be drastically different from what is occurring at and near the metal surface. Together, these insights will assist in understanding disinfectant residual maintenance, corrosion, and metal release.

Effect of Sodium Dodecyl Benzene Sulfonate on the Production of Cloud Condensation Nuclei from Breaking Waves.

While sea spray particles are highly soluble by nature, and are thus excellent seeds for nascent cloud droplets, organic compounds such as surfactants have previously been identified within aerosol particles, bulk seawater, and the sea-surface microlayer in various oceans and seas. As the presence of dissolved surfactants within spray particles may limit their ability to act as cloud condensation nuclei (CCN), and since the abundance of CCN available during cloud formation is known to affect cloud albedo, the presence of surfactants in the marine environment can affect the local radiation balance. In this work, we added a model surfactant commonly used in households and industry (sodium dodecyl benzene sulfonate, SDBS) to a control solution of NaCl and observed its effects on the number of CCN produced by artificial breaking waves. We found that the addition of SDBS modified the number of CCN produced by a breaking wave analogue in three main ways: (I) by reducing the hygroscopicity of the resulting particulate; (II) by producing finer particulates than the control NaCl solution; and (III) by reducing the total number of particles produced overall. In addition, measurements of the absorption of ultraviolet light (λ = 224 nm) were used to quantify the concentration of SDBS in bulk water samples and aerosol extracts. We found that SDBS was significantly enriched in aerosol extracts relative to the bulk water even when the concentration of SDBS in the bulk water was below the limit of detection (LOD) of our quantitation methods. Thus, the surfactant studied will influence the production of CCN even when present in minute concentrations.

Diel variations in the estimated refractive index of bulk oceanic particles.

The index of refraction (n) of particles is an important parameter in optical models that aims to extract particle size and carbon concentrations from light scattering measurements. An inadequate choice of n can critically affect the characterization and interpretation of optically-derived parameters, including those from satellite-based models which provide the current view of how biogeochemical processes vary over the global ocean. Yet, little is known about how n varies over time and space to inform such models. Particularly, in situ estimates of n for bulk water samples and at diel-resolving time scales are rare. Here, we demonstrate a method to estimate n using simultaneously and independently collected particulate beam attenuation coefficients, particle size distribution data, and a Mie theory model. We apply this method to surface waters of the North Pacific Subtropical Gyre (NPSG) at hourly resolution. Clear diel cycles in n were observed, marked by minima around local sunrise and maxima around sunset, qualitatively consistent with several laboratory-based estimates of n for specific phytoplankton species. A sensitivity analysis showed that the daily oscillation in n amplitude was somewhat insensitive to broad variations in method assumptions, ranging from 11.3 ± 4.3% to 16.9 ± 2.9%. Such estimates are crucial for improvement of algorithms that extract the particle size and production from bulk optical measurements, and could potentially help establish a link between n variations and changes in cellular composition of in situ particles.

Free-Living Amoeba and Associated Pathogenic Bacteria in Well-Chlorinated Drinking Water Storage Tanks

Free-living amoebae (FLA) and amoeba-resistant bacteria (ARB) are of increasing concern for water utilities as they cause diseases in humans. To protect consumers, disinfectants are used to prevent colonization by these pathogens in drinking water; however, FLA possess inherent defence mechanisms that can protect them from disinfection. This study investigated the presence and abundance of these amoebae and bacteria in chlorinated drinking water storage tanks in Western Australia. Viability and molecular testing methods, in the form of culturing, quantitative polymerase chain reaction, and 16S rRNA gene amplicon sequencing, were employed to detect amoebae and bacteria present in bulk water and sediment samples. FLA and ARB were detected in water storage tanks that had free chlorine residuals above 0.5 mg/L. Viable Acanthamoeba spp. and Vermamoeba sp. were isolated from the tanks along with various other FLA also detected molecularly. Nontuberculous mycobacteria, a known ARB and opportunistic pathogen, was isolated from all tanks and sample types as well as in the growth fronts of the viable amoebae. This study illustrates the presence and persistence of FLA, ARB, and associated bacterial communities in well-chlorinated water storage tanks, highlighting the need for continued surveillance and risk management.

Bacterial Genes Encoding Resistance Against Antibiotics and Metals in Well-Maintained Drinking Water Distribution Systems in Finland.

Information on the co-occurrence of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) among bacterial communities in drinking water distribution systems (DWDSs) is scarce. This study characterized ARGs and MRGs in five well-maintained DWDSs in Finland. The studied DWDSs had different raw water sources and treatment methods. Two of the waterworks employed artificially recharged groundwater (ARGW) and used no disinfection in the treatment process. The other three waterworks (two surface and one groundwater source) used UV light and chlorine during the treatment process. Ten bulk water samples (two from each DWDS) were collected, and environmental DNA was extracted and then sequenced using the Illumina HiSeq platform for high-throughput shotgun metagenome sequencing. A total of 430 ARGs were characterized among all samples with the highest diversity of ARGs identified from samples collected from non-disinfected DWDSs. Furthermore, non-disinfected DWDSs contained the highest diversity of bacterial communities. However, samples from DWDSs using disinfectants contained over double the ratio of ARG reads to 16S rRNA gene reads and most of the MRG (namely mercury and arsenic resistance genes). The total reads and types of ARGs conferring genes associated with antibiotic groups namely multidrug resistance, and bacitracin, beta-lactam, and aminoglycoside and mercury resistance genes increased in waterworks treating surface water with disinfection. The findings of this study contribute toward a comprehensive understanding of ARGs and MRGs in DWDSs. The occurrence of bacteria carrying antibiotic or metal resistance genes in drinking water causes direct exposure to people, and thus, more systematic investigation is needed to decipher the potential effect of these resistomes on human health.

Microplastic pollution in the Yangtze River Basin: Heterogeneity of abundances and characteristics in different environments

Microplastic pollution in the Yangtze River Basin has become a major concern; however, the variations in different environmental compartments are unknown. Here, we compiled published information including detection methods, occurrence, and characterization of microplastics from 624 sampling sites in river water, river sediment, lake and reservoir water, and lake and reservoir sediment in the Yangtze River Basin. The spatial distribution of sampling sites shows fractal pattern and was uniformly concentrated around the main stream of the Yangtze River and the lake geographical zone. Collection, pretreatment, identification, and quantification processes varied among different studies. Non-parametric tests were performed to compare the different microplastic indices. A Pearson correlation analysis was used to study the relationship between microplastic pollution and local socioeconomic conditions. We found that the microplastic size and abundance distribution in river water and lake and reservoir water showed different patterns for different sampling methods, indicating that different methods influenced the results. Population density and urbanization rate are suggested to be important factors influencing the spatial heterogeneity of microplastic abundances in water, rather than in sediment. The microplastic abundances in lake and reservoir water were higher than that in river water in bulk samples. However, microplastic abundances among different sediment environments shows no significant difference. For bulk water samples and sediment samples overall, the proportion of small microplastics (<1 mm, i.e. SMP), fibers, transparent debris, and polypropylene (PP) were 65.1%, 67.8%, 31.8%, and 29.7%, respectively. The microplastic characteristics of lake and reservoir water and sediment were similar, differing from those of river water and sediment. This study provides the first basin scale insight into microplastic occurrence and characteristics in different environments in the Yangtze River Basin.

Micro-gas column assisted laser induced breakdown spectroscopy (MGC-LIBS): A metal elements detection method for bulk water in-situ analysis

This manuscript introduces a newly developed method for in situ analysis of bulk water samples, called micro-gas column assisted LIBS (MGC-LIBS). A specially designed MGC assistance system was employed to generate a 1.28 mm diameter stable micro-gas column in situ underwater and laser pulses were focused on the gas-liquid interface of the column to improve LIBS spectral signal of metal elements in water sample. The detection experiments on metal elements in the solution showed that the intensity of ion line in the signal was enhanced by up to 14 times, and the signal RSD value was less than 1%. The detection limits (LOD) of Mg, Ca, Sr, Na, K and Li were all less than 1 mg/L. Compared with the results obtained by direct breakdown experiments in bulk water, the LODs of MGC-LIBS were significantly improved, in which the LOD of Mg element could be reduced by nearly 7.6 times. The concentration calibration curves of the above 6 elements were obtained in the possible concentration ranges of seawater samples, and quantitative inversion experiments were carried out. The results show that the estimated value using MGC-LIBS was basically consistent with the actual value, and the minimum error was 0.12%. This method is expected to be developed into an in situ, online, real-time and highly sensitive detection method for marine investigation or natural water environment monitoring.

Impact of phosphate dosing on the microbial ecology of drinking water distribution systems: Fieldwork studies in chlorinated networks

Phosphate is routinely dosed to ensure regulatory compliance for lead in drinking water distribution systems. Little is known about the impact of the phosphate dose on the microbial ecology in these systems and in particular the endemic biofilms. Disturbance of the biofilms and embedded material in distribution can cause regulatory failures for turbidity and metals. To investigate the impact of phosphate on developing biofilms, pipe wall material from four independent pipe sections was mobilised and collected using two twin-flushing operations a year apart in a chlorinated UK network pre- and post-phosphate dosing. Intensive monitoring was undertaken, including turbidity and water physico-chemistry, traditional microbial culture-based indicators, and microbial community structure via sequencing the 16S rRNA gene for bacteria and the ITS2 gene for fungi. Whole metagenome sequencing was used to study shifts in functional characteristics following the addition of phosphate.As an operational consequence, turbidity responses from the phosphate-enriched water were increased, particularly from cast iron pipes. Differences in the taxonomic composition of both bacteria and fungi were also observed, emphasising a community shift towards microorganisms able to use or metabolise phosphate. Phosphate increased the relative abundance of bacteria such as Pseudomonas, Paenibacillus, Massilia, Acinetobacter and the fungi Cadophora, Rhizophagus and Eupenicillium. Whole metagenome sequencing showed with phosphate a favouring of sequences related to Gram-negative bacterium type cell wall function, virions and thylakoids, but a reduction in the number of sequences associated to vitamin binding, methanogenesis and toxin biosynthesis. With current faecal indicator tests only providing risk detection in bulk water samples, this work improves understanding of how network changes effect microbial ecology and highlights the potential for new approaches to inform future monitoring or control strategies to protect drinking water quality.

Microbial abundance and community composition in biofilms on in-pipe sensors in a drinking water distribution system

Collecting biofilm samples from drinking water distribution systems (DWDSs) is challenging due to limited access to the pipes during regular operations. We report here the analysis of microbial communities in biofilm and water samples collected from sensors installed in a DWDS where monochloramine is used as a residual disinfectant. A total of 52 biofilm samples and 14 bulk water samples were collected from 17 pipe sections representing different water ages. Prokaryotic genome copies (bacterial and archaeal 16S rRNA genes, Mycobacterium spp., ammonia-oxidizing bacteria (AOB), and cyanobacteria) were quantified with droplet digital PCR, which revealed the abundance of these genes in both biofilm and water samples. Prokaryotic 16S rRNA gene sequencing analysis was carried out for a subset of the samples (12 samples from four sites). Mycobacterium and AOB species were dominant in the DWDS sections with low water age and sufficient residual monochloramine, whereas Nitrospira species (nitrite-oxidizing bacteria) dominated in the sections with higher water age and depleted monochloramine level, suggesting the occurrence of nitrification in the studied DWDS. The present study provides novel information on the abundance and identity of prokaryotes in biofilms and water in a full-scale operational DWDS.

Episodic surges in titanium dioxide engineered particle concentrations in surface waters following rainfall events

Quantifying and characterizing engineered particles in environmental systems is key for assessing their risk but remains challenging and requires the distinction between natural and engineered particles. The objective of this study was to characterize and quantify the concentrations of titanium dioxide engineered particles in the Broad River, Columbia, South Carolina, United States during and following rainfall events. The elemental ratio distributions of Ti/Nb, Ti/Fe, and Ti/Al, determined on a single particle basis using inductively coupled plasma-time of flight-mass spectrometry (SP-ICP-TOF-MS), were similar between samples during the different rainfall events, indicating that naturally occurring particles had the same elemental ratios and origin. Therefore, the changes in the Ti/Nb ratios in the bulk water samples were attributed to the introduction of titanium dioxide engineered particles into the Broad River with urban runoff during and following rainfall events. The total concentrations of Ti, Fe, Al, Nb, Ce, and La in the Broad River followed the same trend of rise and fall as the discharge/runoff. The elemental ratios of Ti/Nb were higher (e.g., 330 to 565) than the average crustal values (e.g., 320) and the natural background elemental ratios in surface waters in Columbia, SC (e.g., 266.4 ± 8.9), suggesting contamination with titanium dioxide engineered particles. The concentration of titanium dioxide engineered particles were estimated by mass balance calculations using total titanium concentrations and increases in Ti/Nb ratios above the natural background ratios. The concentrations of titanium dioxide engineered particles in the Broad River varied between 20 and 140 μg TiO2 L−1 following rainfall events. The source of titanium dioxide was attributed to urban runoff due to the absence of sewage contamination as indicated by the low size of the gadolinium anomaly. The findings of this study demonstrate that urban runoff is a major source of titanium dioxide engineered particles to urban rivers, which results in episodic high concentrations of titanium dioxide engineered particles, which may pose environmental risks during and following rainfall events. This study also highlights the importance of determining the temporal variations in engineered particle concentrations in surface waters for a more comprehensive risk assessment of engineered particles.

Bacterial community including opportunistic pathogens dynamics in a chlorine tablet-dosed chloraminated service reservoir and reticulation pipes

This study reports even minimal changes of chloramine (measured as total chlorine) residual by chlorine tablets dosing in a service reservoir modify the bacterial community composition. The study was carried out by characterising the bacterial community composition in bulk water samples collected from the inlet, outlet, and downstream of a service reservoir. A regular dose of chlorine tablets to increase the chloramine by about 0.15 mg/L in the service reservoir increases total chlorine to ammonia nitrogen ratio and induces locally breakpoint chlorination within the proximity of the chlorine tablets. This, in turn, selects the specific bacterial groups despite smaller changes in the chloramine concentration. The dominated bacterial genera (87.1–93.8%) in the service reservoir were Methylobacterium and unclassified Rhizobiales whereas Methylobacterium, unclassified Rhizobiales, and Hyphomicrobium dominated (71.8–93.4%) downstream distribution pipelines of the service reservoir. E.Coli was not detected during the study period. Total chlorine residuals, nitrification, and temperature did not influence the presence/absence including the relative abundances of the majority of the opportunistic pathogens (characterized using the MiSeq Illumina platform). However, the presence of Burkholderia and Legionella increased at low total chlorine residuals and high temperatures in a small number of samples. Although this might indicate the importance of higher total chlorine residuals, more studies are needed to confirm if it is a valid strategy/or if there is health significance.

Prevalence of antibiotic resistance genes in drinking water and biofilms: The correlation with the microbial community and opportunistic pathogens

The emergence of antibiotic resistance genes (ARGs) and opportunistic pathogens (OPs) in drinking water system posed potential risks to human health. However, the occurrence of ARGs and OPs in drinking water biofilms is still at its infancy. In this study, we investigated the occurrence of ARGs and OPs in both water and biofilm samples from a drinking water system, and the correlation between ARGs and microbial communities was analyzed. The quantitative PCR results showed that the drinking water treatment process effectively decreased the absolute abundances of ARGs. However, the relative concentration of ARGs did not show a significant difference between raw water and treated water samples. Compared with bulk water and tap water samples, biofilms had higher relative abundances of ARGs. 16 S Illumina Miseq sequencing results showed that microbial communities of biofilms were distinguished with water samples. Meanwhile, qPCR results of OPs also showed that biofilms had higher relative abundances of OPs compared with water samples. Furthermore, the Spearman correlation analysis indicated that Dechloromonas, Desulfovibrio, Methylobacterium and Propionivibrio correlated well with the relative abundance of ARGs. The absolute concentrations of OPs and ARGs also showed a significant correlation. Results of this study suggest that biofilms could serve as the reservoirs for the spread of ARGs and the interaction between biofilms and bulk water requires further research.

Removal behavior of microplastics using alum coagulant and its enhancement using polyamine-coated sand

In recent years, microplastics (MPs) smaller than 100μm have been reported to be abundant in bulk water samples from drinking water treatment plants (WTPs). In this study, the removal behavior of MPs for different sizes (10–100μm), shape and surface morphology were investigated using alum coagulant and alum combined with cationic polyamine-coated (PC) sand. For identification and quantification, MPs were stained with Nile Red dye and observed under a laser scanning fluorescent microscope. The removal of MPs increases with increasing doses of alum up to 30mgL–1 (70.7%). Further increases in the doses resulted in a sharp decrease in the removal of MPs. The analysis for different sizes showed lower removal of smaller MPs (10–30μm) for all doses of alum. PC sand (500mgL–1) combined with 20mgL–1 of alum dose showed the highest removal (92.7%) of MPs. The removal was enhanced by 26.8% when compared with alum alone. The removal of MPs followed the behavior of elongated-rough (ER)>elongated-smooth (ES) >spherical-rough (SR)>spherical-smooth (SS) and was supported by a flocculation kinetic study. This study revealed that size, shape and surface morphology of MPs play important roles in the removal of MPs from drinking WTPs.

Limited long-distance transport of plastic pollution by the Orange-Vaal River system, South Africa

Much of the plastic waste entering the sea is thought to be transported from land by rivers, yet little is known about the distances over which rivers transport plastic. To address this knowledge gap, we collected surface water samples from the Orange-Vaal River at the end of the wet and dry seasons. The Vaal River drains South Africa's main urban-industrial centre, whereas the upper Orange River is sparsely populated. Below their confluence, the river flows through increasingly arid regions with very low human populations before entering the Atlantic Ocean. We collected bulk water samples from 33 bridges to test for microplastic and microfibre (0.025–1 mm) pollution and conducted observations for macrodebris (>50 mm). Where possible, we sampled for plastic fragments (>1 mm) using a neuston net. Microfibres and microplastics were found at every site (1.7 ± 5.1 L−1, >99% fibres) and accounted for 99% of the number of items recorded. Microfibres and microplastics were particularly abundant in the lower reaches during the period of low flow prior to the wet season flush. Macrodebris and larger microplastics were orders of magnitude less abundant (observations: 0.0002 ± 0.0007 items·m−2; neuston net: 0.34 ± 0.93 items·m−2). However, at sites where larger items were found, they comprised most of the mass of plastic. Larger plastics were found mostly at sites in the upper reaches of the Vaal River. Our results suggest that, while the Orange-Vaal River system may be a source of microfibres to the Atlantic Ocean, larger plastic items typically only travel short distances. The Orange-Vaal River system therefore does not appear to be a major source of plastics into the Atlantic Ocean, at least under regular flow conditions.

Preliminary survey of Aphanomyces sp. associated with native and invasive crayfish in the Lower Susquehanna watershed of South Central Pennsylvania

The oomycete species, Aphanomyces astaci, is well known as the devastating causal agent of European crayfish plague. Despite assumptions of a North American origin, the prevalence and distribution of A. astaci in its presumed native range is unknown. In this study, we modified published PCR-based diagnostic methods to detect Aphanomyces sp. in both whole crayfish and in environmental DNA from bulk water samples. Putatively positive samples were sequence-verified as A. astaci, and pure cultures were obtained from four individual crayfish. Our results suggest that a single genotype of A. astaci is present in at least six out of ten locations sampled within the Lower Susquehanna watershed, and is associated with three non-native species, including Faxonius rusticus, the rusty crayfish. Aphanomyces were not detected directly from native crayfish, Cambarus bartonii, but both A. astaci and an unknown Aphanomyces species were detected from corresponding environmental DNA samples. Although North American crayfish are considered less susceptible to A. astaci infection, future studies should interrogate the impact of invasive species, such as the rusty crayfish, and land use changes on potential host-pathogen dynamics.

Little evidence that dams in the Orange–Vaal River system trap floating microplastics or microfibres

Abstract Rivers can be major sources of plastics into coastal seas, but it is unclear whether dams retain floating plastics, thus reducing the amount reaching the sea. To test if dams trap microplastics, we collected bulk water and neuston net samples from five dams on the Orange–Vaal River system, South Africa. Most manufactured items were microfibres and densities of microplastics were modest (bulk water: 0.21 ± 0.27 items·L−1; net: 0.04 ± 0.16 items·m−2). There was an interaction between dam and season: dams on the densely populated Vaal River had higher microplastic concentrations during dry than wet conditions, whereas the opposite pattern occurred on the less industrialised Orange River. Overall there was no difference in microplastic concentration at sites above vs below dam walls nor was there a strong correlation between microplastic concentration and distance to the wall. Our results therefore suggest that dams do not trap floating microplastics or microfibres.

Sampling microfibres at the sea surface: The effects of mesh size, sample volume and water depth

Microfibres are one of the most ubiquitous particulate pollutants, occurring in all environmental compartments. They are often assumed to be microplastics, but include natural as well as synthetic textile fibres and are perhaps best treated as a separate class of pollutants given the challenges they pose in terms of identification and contamination. Microfibres have been largely ignored by traditional methods used to sample floating microplastics at sea, which use 300–500 μm mesh nets that are too coarse to sample most textile fibres. There is thus a need for a consistent set of methods for sampling microfibres in seawater. We processed bulk water samples through 0.7–63 μm filters to collect microfibres in three ocean basins. Fibre density increased as mesh size decreased: 20 μm mesh sampled 41% more fibres than 63 μm, and 0.7 μm filters sampled 44% more fibres than 25 μm mesh, but mesh size (20–63 μm) had little effect on the size of fibres retained. Fibre density decreased with sample volume when processed through larger mesh filters, presumably because more fibres were flushed through the filters. Microfibres averaged 2.5 times more abundant at the sea surface than in water sampled 5 m sub-surface. However, the data were noisy; counts of replicate 10-L samples had low repeatability (0.15–0.36; CV = 56%), suggesting that single samples provide only a rough estimate of microfibre abundance. We propose that sampling for microfibres should use a combination of <1 μm and 20–25 μm filters and process multiple samples to offset high within-site variability in microfibre densities.

Glucose as a Potential Chemical Marker for Ice Nucleating Activity in Arctic Seawater and Melt Pond Samples.

Recent studies pointed to a high ice nucleating activity (INA) in the Arctic sea surface microlayer (SML). However, related chemical information is still sparse. In the present study, INA and free glucose concentrations were quantified in Arctic SML and bulk water samples from the marginal ice zone, the ice-free ocean, melt ponds, and open waters within the ice pack. T50 (defining INA) ranged from -17.4 to -26.8 °C. Glucose concentrations varied from 0.6 to 51 μg/L with highest values in the SML from the marginal ice zone and melt ponds (median 16.3 and 13.5 μg/L) and lower values in the SML from the ice pack and the ice-free ocean (median 3.9 and 4.0 μg/L). Enrichment factors between the SML and the bulk ranged from 0.4 to 17. A positive correlation was observed between free glucose concentration and INA in Arctic water samples (T50(°C) = (-25.6 ± 0.6) + (0.15 ± 0.04)·Glucose(μg/L), RP = 0.66, n = 74). Clustering water samples based on phytoplankton pigment composition resulted in robust but different correlations within the four clusters (RP between 0.67 and 0.96), indicating a strong link to phytoplankton-related processes. Since glucose did not show significant INA itself, free glucose may serve as a potential tracer for INA in Arctic water samples.