Metal/metalloid accumulation/remobilization during aquatic litter decomposition in freshwater: a review

Soil Cd increased the leaf litter Cd remains of Solanum nigrum and Solanum lycopersicum

Plant litter decomposition is a natural pathway of heavy metal cycling in soil ecosystems, but the dynamics of heavy metal release during litter decomposition are relatively poorly understood. The purpose of this study was to investigate the effects of species, soil fauna and soil Cd addition on litter decomposition and Cd release dynamics. Therefore, we selected two plants, Solanum nigrum and S. lycopersicum with large differences in Cd accumulation capacity. First, they were enriched with Cd during the growing period and leaf litter was harvested after 6 months of pretreatment. Then, the decomposition of leaf litter was conducted with or without soil Cd and Eisenia fetida through lab pot tests. Our results showed that leaf litter Cd led to a significant decrease in litter decomposition rate (K value), with a maximum decrease of 32.1% in S. nigrum and 30.1% in S. lycopersicum. We observed that the presence of E. fetida significantly increased K value, but the effect was similar in the +leaf Cd treatment and the -leaf Cd treatment, both for S. nigrum and S. lycopersicum. Interestingly, the litter Cd concentration did not decrease during decomposition, but showed an increasing trend, especially for S. nigrum in the +soil Cd treatment. Moreover, the litter Cd remains was higher in the +soil Cd treatment compared to the -soil Cd treatment for both S. nigrum and S. lycopersicum, no matter whether with or without E. fetida. This result suggests that the Cd may be transferred from soil to litter, thus increasing the litter Cd remains. Overall, our study shows that leaf litter Cd slowed down the carbon cycling in ecosystems. In addition, the release of litter Cd has a lag, and the litter has a certain adsorption capacity for soil Cd, which intensifies the harm to the ecology during litter transfer.

Effects of copper and cadmium on stream leaf decomposition: evidence from a microcosm study

We seek to understand how copper and cadmium act on leaf litter decomposition by their effects on microbial conditioning and litter fragmentation by invertebrates. In this study, we evaluated, in an integrated manner, different biological elements responsible for functioning of streams. Thus, we performed a microcosm assay with different concentrations for the two metals and their combination, evaluating their effects on fungi sporulation rate, consumption rate by shredders, and, consequently, the leaf litter decomposition rates. Sporulation rates were affected by all copper concentrations tested 10 ×  = 16 µg L-1 and 25 ×  = 40 µg L-1) but significantly reduced only at the highest concentration of cadmium (25 ×  = 22.5 µg L-1). Increased copper and cadmium concentrations reduced the consumption of leaf litter by Phylloicus at 60%. The concentrations (10 × and 25 ×) of both metals resulted in a reduction in decomposition rates. When combined, copper and cadmium negatively affected microbial conditioning, consumption by shredders, and leaf litter decomposition. Increases in concentrations of copper and cadmium directly affected organic matter decomposition in aquatic environments. Thus, the presence of a high concentration of heavy metals in aquatic environments alters the functioning of ecosystems. As trace-elements occur in a combined manner in environments, our results show that the combined effects of different metals potentiate the negative effects on ecosystem processes.

Vegetated urban streams have sufficient purification ability but high internal nutrient loadings: Microbial communities and nutrient release dynamics

The release of nutrients back into the water column due to macrophyte litter decay could offset the benefits of nutrient removal by hydrophytes within urban streams. However, the influence of this internal nutrient cycling on the overlying water quality and bacterial community structure is still an open question. Hence, litter decomposition trials using six hydrophytes, Typha latifolia (TL), Phragmites australis (PAU), Hydrilla verticillata (HV), Oenanthe javanica (OJ), Myriophyllum aquaticum (MA), and Potamogeton crispus (PC), were performed using the litterbag approach to mimic a 150-day plant litter decay in sediment-water systems. Field assessment using simple in/out mass balances and uptake by plant species was carried out to show the potential for phytoremediation and its mechanisms. Results from two years of monitoring (2020-2021) indicated mean total nitrogen (TN) retention efficiencies of 7.2-60.14 % and 9.5-55.6 % for total phosphorus (TP) in the studied vegetated urban streams. Nutrient retention efficiencies showed temporal variations, which depended on seasonal temperature. Mass balance analysis indicated that macrophyte assimilation, sediment adsorption, and microbial transformation accounted for 10.31-41.74 %, 0.84-3.00 %, and 6.92-48.24 % removal of the inlet TN loading, respectively. Hydrophyte detritus decay induced alterations in physicochemical parameters while significantly increasing the N and P levels in the overlying water and sediment. Decay rates varied among macrophytes in the order of HV (0.00436 g day^-1) > MA (0.00284 g day^-1) > PC (0.00251 g day^-1) > OJ (0.00135 g day^-1) > TL (0.00095 g day^-1) > PAU (0.00057 g day^-1). 16S rRNA gene sequencing analysis showed an increase in microbial species richness and diversity in the early phase of litter decay. The abundances of denitrification (nirS and nirK) and nitrification (AOA and AOB) genes also increased in the early stage and then decreased during the decay process. Results of this study conducted in seven urban streams in northern China demonstrate the direct effects of hydrophytes in encouraging nutrient transformation and stream self-purification. Results also demonstrate that macrophyte detritus decay could drive not only the nutrient conversions but also the microbial community structure and activities in sediment-water systems. Consequently, to manage internal sources and conversions of nutrients, hydrophytic detritus (e.g., floating/submerged macrophytes) must be suppressed and harvested.

Macroinvertebrates as engineers for bioturbation in freshwater ecosystem

Bioturbation is recognized as a deterministic process that sustains the physicochemical properties of the freshwater ecosystem. Irrigation, ventilation, and particle reworking activities made by biotic components on sediment beds influence the flow of nutrients and transport of particles in the sediment-water interface. Thus, the biogenic disturbances in sediment are acknowledged as pivotal mechanism nutrient cycling in the aquatic system. The macroinvertebrates of diverse taxonomic identity qualify as potent bioturbators due to their abundance and activities in the freshwater. Of particular relevance are the bioturbation activities by the sediment-dwelling biota, which introduce changes in both sediment and water profile. Multiple outcomes of the macroinvertebrate-mediated bioturbation are recognized in the form of modified sediment architecture, changed redox potential in the sediment-water interface, and elicited nutrient fluxes. The physical movement and physiological activities of benthic macroinvertebrates influence organic deposition in sediment and remobilize sediment-bound pollutants and heavy metals, as well as community composition of microbes. As ecosystem engineers, the benthic macroinvertebrates execute multiple functional roles through bioturbation that facilitate maintaining the freshwater as self-sustaining and self-stabilizing system. The likely consequences of bioturbation on the freshwater ecosystems facilitated by various macroinvertebrates - the ecosystem engineers. Among the macroinvertebrates, varied species of molluscs, insects, and annelids are the key facilitators for the movement of the nutrients and shaping of the sediment of the freshwater ecosystem.

Arsenic Bioaccumulation and Identification of Low-Arsenic-Accumulating Food Fishes for Aquaculture in Arsenic-Contaminated Ponds and Associated Aquatic Ecosystems

Arsenic-contaminated food including farmed fish is one of the main routes of human exposure. Fish farmed in contaminated environment accumulates arsenic in different tissues with great variability. Thus, it is utmost important to quantify the risk associated with different farmed fish species in arsenic-contaminated aquaculture systems. In the present study, arsenic content was measured in twelve fish species (Labeo rohita, L. catla, Cirrhinus mrigala, Oreochromis niloticus, O. mossambicus, Liza tade, Puntius javanicus, L. calbasu, Glossogobius giuris, Macrobrachium rosenbergii, Ctenopharyngodon idella, and Bellamya bengalensis (gastropod)) collected from arsenic-contaminated aquaculture systems. Among the studied finfishes, C. idella was found to accumulate the lowest amount of arsenic (< 0.05 ± 0.00 mg kg^-1) whereas the highest accumulation was noticed in O. mossambicus (1.0 ± 0.18 mg kg^-1). However, the estimated carcinogenic and non-carcinogenic risks of human were found to be low for all the studied fishes. The calculated target hazard quotient (THQ) value for adults ranged from 0.01 to 0.08 whereas for children it ranged from 0.05 to 0.27 for low-arsenic-accumulating fishes (arsenic conc. < 0.5 mg kg^-1). Based on these findings, C. mrigala, C. idella, and M. rosenbergii could be recommended as the candidate species for aquaculture in the arsenic-contaminated areas as farming of the low-arsenic-accumulating food fishes would also lower the risk of human exposure through food chain.

Effect of metal pollution from mining on litter decomposition in streams

Litter decomposition is critical to stream biogeochemical cycles. Metal pollution from past or present mining activities seriously threatens stream ecosystems. However, its effects on litter decomposition in streams remain unclear. A field litterbag experiment was conducted to determine the direct (i.e., via changes in stream water quality: a mine-affected vs. forest stream) and indirect (i.e., via changes in litter traits: polluted vs. non-polluted litter) effects of metal pollution from mining activities on leaf litter decomposition (total vs. microbial-driven) and the associated microbial activity and community composition in streams. Platanus acerifolia leaf litter collected from a polluted and a non-polluted site was enclosed in fine and coarse mesh bags and incubated in a mine-affected stream and a forest stream. The litter from the polluted site had a higher Pb, Zn, Cd, N, soluble sugar concentrations, specific leaf area and pH, and lower leaf toughness and lignin concentration than the litter from the non-polluted site. After incubation in situ, litter mass loss did not significantly differ between streams, but the mine-affected stream had a greater impact on total-driven decomposition rates than microbial-driven decomposition rates. Polluted litter had a significantly higher decomposition rate than non-polluted litter. The decomposition potential of polluted litter produces faster nutrient cycling and supports higher microbial colonization. Litter traits and decomposer community type modulate the influence of metal pollution on litter decomposition. The results suggest that the indirect effects of mining activities on litter decomposition were stronger than the direct effects.

Response of Chlorophyll Fluorescence Characteristics and Dissolved Organic Matter for Marine Diatom Skeletonema dohrnii under Stress from Penicillin and Zn2

Skeletonema dohrnii is a good model diatom for studying environmental stress and has promising applications and prospects in various fields. Antibiotics and heavy metals are commonly exceeded in the nearshore marine habitats. In this work, we investigated the effects of an antibiotic (penicillin, 2 µg/L) and a heavy metal ion (Zn2+, 10 µmol/L) stress on marine diatom S. dohrnii, mainly using excitation-emission matrices (EEMs) fluorescence methods and OJIP test. Results indicated that algal cells grown with the antibiotic showed higher biomass, specific growth rate, doubling time, chlorophyll a, and chlorophyll fluorescence variables. Moreover, excess zinc had negative effects on S. dohrnii. We found that zinc not only inhibited the relative photosynthetic electron transfer efficiency but also reduced the Chl a content, which ultimately affected algal growth and organic matter production. In addition, the combined effect of penicillin and Zn2+ further affected the physiological state of S. dohrnii. The dissolved organic matter (DOM) characteristics of the four cultures were also different, including fluorescence indices (fluorescence index, biological index, β/α, and humification index) and fluorescence peaks (peaks A, C, M and T). In brief, characterization of chlorophyll fluorescence characteristics and DOM-related variables are important for understanding the effects of environmental stress on microalgae.

Bioaccumulation and release of heavy metals during growth and decomposition of cultivated Gracilaria lemaneiformis

Seaweeds are important primary producers and bioremediation materials, but its litter produced during growth and harvest is one of the restrictions to the sustainable development of seaweed cultivation. In this study, we conducted field investigation and indoor experiments to analyze the bioaccumulation and release of metals in Gracilaria lemaneiformis during the growth and decaying. The investigation revealed the 3.5 × 10⁵ t (wet weight) G. lemaneiformis from a 1500 ha cultivation area bioaccumulated 1925-2353 kg Zn, 233.5-251 kg Cu, 70.5-80.5 kg Pb and 25.5-47 kg Cd, indicating that G. lemaneiformis is a good metals remover. The growth and decaying period of G. lemaneiformis releases, absorbs or adsorbs metals. It has the function of a "heavy metal pool", simultaneously accumulate and release metals. G. lemaneiformis has a strong influence on heavy metals cycling in the seaweed cultivation ecosystem and provides a very good sample for biogeochemistry study for the globally seaweed sustainable development.

How efficient is graphene-based nanocomposite to adsorb Hg from seawater. A laboratory assay to assess the toxicological impacts induced by remediated water towards marine bivalves

Advanced investigations on the use of graphene based nanomaterials have highlighted the capacity of these materials for wastewater treatment. Research on this topic revealed the efficiency of the nanocomposite synthetized by graphene oxide functionalized with polyethyleneimine (GO-PEI) to adsorb mercury (Hg) from contaminated seawater. However, information on the environmental risks associated with these approaches are still lacking. The focus of this study was to evaluate the effects of Hg in contaminated seawater and seawater remediated by GO-PEI, using the species Ruditapes philippinarum, maintained at two different warming scenarios: control (17 °C) and increased (22 °C) temperatures. The results obtained showed that organisms exposed to non-contaminated and remediated seawaters at control temperature presented similar biological patterns, with no considerable differences expressed in terms of biochemical and histopathological alterations. Moreover, the present findings revealed increased toxicological effects in clams under remediated seawater at 22 °C in comparison to those subjected to the equivalent treatment at 17 °C. These results confirm the capability of GO-PEI to adsorb Hg from water with no noticeable toxic effects, although temperature could alter the responses of mussels to remediated seawater. These materials seem to be a promise eco-friendly approach to remediate wastewater, with low toxicity evidenced by remediated seawater and high regenerative capacity of this nanomaterial, keeping its high removal performance after successive sorption-desorption cycles.

Abundance and mobility of metal(loid)s in reservoir sediments of Singe Tsangpo and Yarlung Tsangpo in Tibet, China: Implications for ecological risk

Geogenic arsenic enrichment in soil and river sediments of Tibet compared to its upper crustal abundance has been observed, raising the question whether other trace elements are also enriched and thus may pose ecological risks. Because human activities are limited, the reservoir sediments after the recent construction of the Shiquan dam on the Singe Tsangpo (ST) and the Zam dam on the Yarlung Tsangpo (YT) collect and thus represent material sourced from 14,870 km² and 157,668 km² of drainage areas, respectively. Bulk concentrations of the metalloid (As) and 13 metals (Li, Be, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Cs, and Pb) are analyzed for 123 samples from 9 mostly silty sediment cores (depth: 11-20 cm) from the Shiquan Reservoir and for 250 samples from 13 mostly sandy sediment cores (depth: 9-28 cm) from the Zam Reservoir. These elemental concentrations are normalized to the upper crustal Fe abundance of 3.9% to arrive at a regional sediment geochemical background value for each element. The regional background values of most elements in the ST drainage and the YT drainage are comparable with the upper crustal abundance. However, three elements (Li, As, and Cs) in both drainage basins display significant enrichment compared to their respective upper crustal abundance. Sequential leaching of a subset of sediment samples from the ST (n = 18) and YT (n = 29) drainages reveals that chemical fractions of metals and metalloids in these two reservoirs are similar, with most of the elements dominated by the residual fraction with low mobility. Taken together, the ecological risks of the most studied elements in the reservoir sediments are likely low pending further aquatic bioavailability investigations, except that As, Cu, Pb, and Be deserve more attention due to their elevated levels in mobile fractions.

Genome-Wide Identification of the Nramp Gene Family in Spirodela polyrhiza and Expression Analysis under Cadmium Stress

Natural resistance-associated macrophage proteins (Nramps) are specific metal transporters in plants with different functions among various species. The evolutionary and functional information of the Nramp gene family in Spirodela polyrhiza has not been previously reported in detail. To identify the Nramp genes in S. polyrhiza, we performed genome-wide identification, characterization, classification, and cis-elements analysis among 22 species with 138 amino acid sequences. We also conducted chromosomal localization and analyzed the synteny relationship, promoter, subcellular localization, and expression patterns in S. polyrhiza. β-Glucuronidase staining indicated that SpNramp1 and SpNramp3 mainly accumulated in the root and joint between mother and daughter frond. Moreover, SpNramp1 was also widely displayed in the frond. SpNramp2 was intensively distributed in the root and frond. Quantitative real-time PCR results proved that the SpNramp gene expression level was influenced by Cd stress, especially in response to Fe or Mn deficiency. The study provides detailed information on the SpNramp gene family and their distribution and expression, laying a beneficial foundation for functional research.

Seasonal variation of heavy metals in seagrasses along Thondi coast, Palk Bay, India

The present study deals with the bioaccumulation of heavy metals in different seagrass species (Syringodium isoetifolium, Halodule pinifolia, Cymodocea serrulata, Halophila ovalis) along Thondi coast and decaying seagrass offshore. Heavy metal concentrations in the seagrass samples were analysed during the period of April 2019 to March 2020 using atomic absorption spectrophotometry. Among the heavy metals assayed, the level of manganese was higher (15.62 ± 1.02 mg/kg) and chromium was the least metal observed (0.002 mg/kg). One-way ANOVA revealed significantly higher level of heavy metals in summer season, while it gradually decreased through pre-monsoon to monsoon season (P < 0.05). Cadmium and chromium were observed to be below detectable levels in the seagrass species. S. isoetifolium was found to bioaccumulate higher levels of heavy metals than the other seagrass species studied. Elucidation of heavy metal levels in the dead and decayed seagrass offshore revealed a higher level of heavy metals than live seagrass species.

Effects of heavy metal-mediated intraspecific variation in leaf litter on the feeding preferences of stream detritivores

Plant litter inputs from terrestrial ecosystems are indispensable resources for stream ecosystems. Heavy metal pollution in the environment may indirectly affect the food webs of streams by changing the traits of leaf litter. In the present study, willow leaf litter was collected in polluted and non-polluted sites (natural willow), and leaf litter was produced in the lab by exposing willow saplings to different concentrations of heavy metals in water (cultivated willow). The collected willow leaf litter was used for feeding preference experiments with stream detritivores (shrimps and snails). Metal pollution significantly decreased the lignin concentration and toughness of litter and increased Zn and Cd concentrations. Both detritivores preferred to consume metal-enriched litter, with their consumption rates of this litter being significantly higher than those of non-enriched litter. The toughness of the willow litter was the key factor determining the feeding preferences of shrimps and snails. The detritivores that consumed metal-enriched leaf litter contained more Zn and Cd in their bodies than those that consumed non-enriched litter. The Zn and Cd concentrations in shrimp faeces were higher for shrimps that consumed metal-enriched litter than for those that consumed non-enriched litter. The heavy metal concentrations and chemical oxygen demand (COD) of the water following litter consumption were significantly higher for the metal-enriched litter than for the non-enriched litter, resulting in decreased water quality in the former context. The specific resource allocation patterns that result from heavy metal pollution in the environment will have ecological consequences.

Role of Biofilms in Contaminant Bioaccumulation and Trophic Transfer in Aquatic Ecosystems: Current State of Knowledge and Future Challenges

In freshwater environments, microbial assemblages attached to submerged substrates play an essential role in ecosystem processes such as primary production, supported by periphyton, or organic matter decomposition, supported by microbial communities attached to leaf litter or sediments. These microbial assemblages, also called biofilms, are not only involved in nutrients fluxes but also in contaminants dynamics. Biofilms can accumulate metals and organic contaminants transported by the water flow and/or adsorbed onto substrates. Furthermore, due to their high metabolic activity and their role in aquatic food webs, microbial biofilms are also likely to influence contaminant fate in aquatic ecosystems. In this review, we provide (1) a critical overview of the analytical methods currently in use for detecting and quantifying metals and organic micropollutants in microbial biofilms attached to benthic substrata (rocks, sediments, leaf litter); (2) a review of the distribution of those contaminants within aquatic biofilms and the role of these benthic microbial communities in contaminant fate; (3) a set of future challenges concerning the role of biofilms in contaminant accumulation and trophic transfers in the aquatic food web. This literature review highlighted that most knowledge on the interaction between biofilm and contaminants is focused on contaminants dynamics in periphyton while technical limitations are still preventing a thorough estimation of contaminants accumulation in biofilms attached to leaf litter or sediments. In addition, microbial biofilms represent an important food resource in freshwater ecosystems, yet their role in dietary contaminant exposure has been neglected for a long time, and the importance of biofilms in trophic transfer of contaminants is still understudied.

Selenium removal by clam shells and gravels amended with cattail and reed litter

Increasing selenium (Se) levels in aquatic environments raise concerns all over the world. This study investigated effects of organic amendments (cattail and reed litter) and porous media (gravels and clam shells) on Se removal efficiency of horizontal subsurface flow constructed wetlands. Our results show clam shells reduced Se (by mass) up to 2.4-fold faster than gravels within 19 days. Using clam shells as the sole substrate, 96.3% removal efficiency was obtained for cattail litter as an amendment, compared to 88.7% for reed litter over 10 days, although the latter released carbon and nitrogen at least 1.4-fold faster than the former. Meanwhile, speciation analysis suggests Se⁰ (~75%) and organo-Se (~94%) dominated the biofilms on shells and plant litter, respectively, as substrates. Overall, this study suggests clam shells and cattail litter as an effective medium and carbon source, respectively, can enhance microbial Se removal without posing risks to wildlife health.

Microstructure Analysis and Chemical and Mechanical Characterization of the Shells of Three Freshwater Snails

The shells of freshwater snails are discarded as waste, which qualify as biological materials with prospective multiple uses. To substantiate this proposition, an attempt was made to elucidate the physical and chemical properties of the shells of three freshwater snails, namely, Bellamya bengalensis, Pila globosa, and Brotia costula. The shells were prepared for electron microscopy and assessment of the calcium carbonate content, apart from the Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and nanoindentation studies. The results indicated that the calcium carbonate content (y) of the shells ranged between 87 and 96% of the total weight (x) and complied with a power regression equation: y = 0.801x 1.016; R 2 = 0.994; r = +0.998; P < 0.001. Observations through SEM depicted different snail species-specific arrangement patterns of calcium carbonate crystals in the diverse layers of shells. The XRD, FTIR, and EDS observations revealed the dominance of the aragonite form of the calcium carbonate crystal in the microstructures of each snail shell with the occurrence of different shell surface functional groups. The Brunauer-Emmett-Teller analysis elucidated the surface textures of shell dust taken from each snail species; in addition, the nanohardness properties indicate the shells as a tough biocomposite exoskeleton. Species-specific variations in the shell morphology, microstructure, and calcium carbonate content were prominent for the three freshwater snails considered for the study. Nonetheless, the physical and chemical properties substantiate that the shells of B. bengalensis, P. globosa, and B. costula qualify as biological materials for sustainable use in various fields including bioremediation, biocatalyst, biomedical applications, and a source of lime. Since the shells of the freshwater snails are discarded as aquaculture waste, subsequent use as a biological material will support the "waste made useful" paradigm in sustainability, both from ecological and economic perspectives.

Online Simulation Model to Estimate the Total Costs of Tobacco Product Waste in Large U.S. Cities

Tobacco product waste (TPW) is one of the most ubiquitous forms of litter, accumulating in large amounts on streets, highways, sidewalks, beaches, parks, and other public places, and flowing into storm water drains, waste treatment plants, and solid waste collection facilities. In this paper, we evaluate the direct and indirect costs associated with TPW in the 30 largest U.S. cities. We first developed a conceptual framework for the analysis of direct and indirect costs of TPW abatement. Next, we applied a simulation model to estimate the total costs of TPW in major U.S. cities. This model includes data on city population, smoking prevalence rates, and per capita litter mitigation costs. Total annual TPW-attributable mean costs for large US cities range from US$4.7 million to US$90 million per year. Costs are generally proportional to population size, but there are exceptions in cities that have lower smoking prevalence rates. The annual mean per capita TPW cost for the 30 cities was US$6.46, and the total TPW cost for all 30 cities combined was US$264.5 million per year. These estimates for the TPW-attributable cost are an important data point in understanding the negative economic externalities created by cigarette smoking and resultant TPW cleanup costs. This model provides a useful tool for states, cities, and other jurisdictions with which to evaluate a new economic cost outcome of smoking and to develop new laws and regulations to reduce this burden.

Nutrients release and greenhouse gas emission during decomposition of Myriophyllum aquaticum in a sediment-water system

Aquatic macrophytes play a significant role in nutrients removal in constructed wetlands, yet nutrients could be re-released due to plant debris decomposition. In this study, Myriophyllum aquaticum was used as a model plant debris and three debris biomass levels of 3 g, 9 g dry biomass, and 20 g fresh biomass (D3, D9, and F20, respectively) were used to simulate 120-d plant debris decomposition in a sediment-water system. The biomass first-order decomposition rate constants of D3, D9, and F20 treatments were 0.0058, 0.0117, and 0.0201 d^-1, respectively with no significant difference of decomposition rate among three mass groups (p > 0.05). Plant debris decomposition decreased nitrate and total nitrogen concentrations but increased ammonium, organic nitrogen, and dissolved organic carbon (DOC) concentrations in overlying water. The parallel factor analysis confirms that three components of DOC in overlying water changed over decomposition time. Emission fluxes of methane and nitrous oxide in the plant debris treatments were several to thousands of times higher than the control group within the initial 0-45 d, which was mainly attributed to DOC released from the plant debris. Plant debris decomposition can affect the gas emission fluxes for relatively shorter time (30-60 d) than water quality (>120 d). The 16S rRNA, nirK, nirS and hazA gene abundance increased in the early stage for plant debris treatments, and then decreased to the end of 120-d incubation time while ammonia monooxygenase α-subunit A gene abundance of ammonia-oxidizing archaea and bacteria had no large variations during the entire decay time compared with no plant debris treatment. The results demonstrate that decomposition of M. aquaticum debris could affect greenhouse gas emission fluxes and microbial gene abundance in the sediment-water system besides overlying water quality.

The cotton-strip assay as an environmental surveillance tool for ecological integrity assessment of rivers affected by WWTP effluents

Environmental impact studies of rivers affected by wastewater treatment plant (WWTP) effluents have been greatly restricted by the difficulties associated with carrying out bioassays in the field and also by the complex interactions between the pollutants contained in the discharges. The cotton-strip assay (CSA) enables study of the organic matter decomposition potential, an important ecosystem process in rivers, by taking all of the factors affecting this process into account. However, the CSA has never been used for assessment of WWTP effluents. In the present study, we selected six fluvial zones affected by discharges from small WWTPs and placed cotton strips at increasing distances from the discharge points in each zone. After 17 days, we evaluated decay of the strips by measuring cotton tensile strength loss (CTSL) and cotton mass loss (CML). We then determined the relationships between these parameters and various physico-chemical and biological properties in the water, as well as the δ¹⁵N isotopic signal and metal contents of aquatic mosses transplanted in the same sampling sites and used as biomonitors. Although the WWTPs were similar, some of the discharges stimulated and others inhibited decomposition of the cotton strips. This was probably due to differences in the proportions of various types of pollutants (with trophic or toxic effects) in the discharges. The CSA proved to be a simple, practical and economic bioassay and suitable for evaluating the ecological integrity of fluvial ecosystems.

Removal of metals from wastewaters by mineral and biomass-based sorbents applied in continuous-flow continuous stirred tank reactors followed by sedimentation

Numerous studies have examined the performance of mineral and biomass-based sorbents for metal removal under laboratory conditions, but few pilot-scale tests have been performed on possible water purification systems in which these sorbents can be used. This study addressed this issue by evaluating the suitability of selected sorbents for use in continuous-flow continuous stirred tank reactors (CSTR) followed by sedimentation in laboratory and in situ pilot-scale experiments. Acid (HCl)-modified peat (M-Peat), a commercially available mineral sorbent containing mainly magnesium (Mg) carbonates, Mg oxides and Mg silicates (Mineral-P) and a calcium-rich ground granular blast furnace slag (by-product of stainless steel production (Slag) were tested for treatment of metallurgical industry wastewater (laboratory, pilot). Overall, higher metal removal was achieved from samples with higher initial metal concentrations. M-Peat achieved good removal of Zn (50-70%) and Ni (30-50%) in laboratory and pilot experiments. However, the poor settling characteristics of M-Peat can restrict its application in systems where sedimentation is the solid-liquid separation process applied. Mineral-P showed good performance in removing 65-85% of Zn present in the water and it performed similarly in laboratory and pilot tests. However, low concentrations of As and Ni leached from Mineral-P in all tests. Slag achieved good performance in treatment of the industrial wastewater, removing 65-80% of Zn and 60-80% of Pb during pilot tests. However, low concentrations of Cr and Cu were leached from Slag in a few tests. As a by-product of the same (metallurgical) industry, ground granular blast furnace slag is an excellent candidate for reducing Zn concentrations from industrial wastewater flows.

Exposure pathway dependent effects of titanium dioxide and silver nanoparticles on the benthic amphipod Gammarus fossarum

The increasing production of engineered inorganic nanoparticles (EINPs) elevates their release into aquatic ecosystems raising concerns about associated environmental risks. Numerous investigations indicate sediments as the final sink, facilitating the exposure of benthic species to EINPs. Although reports of sub-lethal EINP effects on benthic species are increasing, the importance of exposure pathways (either waterborne or dietary) is poorly understood. This study investigates the influence of two EINPs, namely titanium dioxide (nTiO₂) and silver (nAg), on the benthic model organism Gammarus fossarum specifically addressing the relative relevance of these pathways. For each type of EINP an individual 30-day long bioassay was conducted, applying a two-factorial test design. The factors include the presence or absence of the EINPs (nTiO₂: ∼80 nm, 4 mg/L or nAg: ∼30 nm, 0.125 mg/L; n = 30) in the water phase (waterborne), combined with a preceding 6-day long aging of their diet (black alder leaves) also in presence or absence of the EINPs (dietary). Response variables were mortality, food consumption, feces production and energy assimilation. Additionally, the physiological fitness was examined using lipid content and dry weight of the organisms as measures. Results revealed a significantly reduced energy assimilation (up to ∼30%) in G. fossarum induced by waterborne exposure towards nTiO₂. In contrast, the dietary exposure towards nAg significantly increased the organisms' energy assimilation (up to ∼50%). Hence, exposure pathway dependent effects of EINPs cannot be generalized and remain particle specific resting upon their intrinsic properties affecting their potential to interact with the surrounding environment. As a result of the different properties of the EINPs used in this study, we clearly demonstrated variations in type and direction of observed effects in G. fossarum. The results of the present study are thus supporting current approaches for nano-specific grouping that might enable an enhanced accuracy in predicting EINP effects facilitating their environmental risk assessment.

Migration and distribution of cadmium in aquatic environment: The important role of natural biofilms

For a better understanding of the migration process of trace metals in aquatic environment with multiple phases, dynamic processes of Cd reaching quasi-equilibrium among different phases, including water, natural biofilms and surficial sediments, were investigated, using microcosmic simulating systems. The processes of the re-equilibrium of Cd after a supplement of Cd and after an adjustment of solution pH were also investigated. The results showed both the migration of Cd from water to the solid materials, and the accumulation of Cd in the solid materials. (Modified) pseudo-second-order kinetic model can be used to simulate such processes. However, Cd content in biofilms and sediments varied in different ways: Cd in biofilms increased rapidly at first, then decreased, and finally approached constancy, while Cd in sediments increased slowly and continuously. The more the Cd was added in the water, the higher the Cd contents in solid phases, and the quicker the Cd accumulation and decrease process would be. The decrease of solution pH promoted the release of adsorbed Cd from the solid phases, especially from biofilms, while the increase of pH stimulated the migration of Cd to the solids. Therefore, as an indicator and temporary reservoir of trace metals in water, which respond rapidly to the variation of trace metal concentration in water, biofilms play a role in indicating and buffering the variation of trace metals in water. Although the response of sediments to the variation of metal concentration in water is very slow, most trace metals migrate to sediments eventually, thus sediments play a role as a more stable and massive reservoir for trace metals in water.

Decomposition of Spartina alterniflora and concomitant metal release dynamics in a tidal environment

The decomposition of salt marsh plants is affected by the variation of physiochemical factors caused by the change of tide level. In the present study, plant tissues of Spartina alterniflora from controlled metal exposure experiments were subjected to a field decomposition trial at different tidal levels in a tidal flat of Chongming Island, Shanghai. The contents of the metals and Pb stable isotope ratios of the plant litter and the adjacent sediment were followed. The mass loss rate of the root and leaf litters of S. alterniflora decreased with the increase of burial time. Leaf had the highest decomposition rate (0.009 day^-1 to 0.020 day^-1) compared to that of the roots (0.004 day^-1 to 0.005 day^-1) and stems (0.002 day^-1 to 0.006 day^-1). Leaf had the highest decomposition rate possibly due to the significantly lower C/N ratio (16.0-44.6) compared to that of the roots (32.8-88.9) and stems (43.7-120.9). The mass loss rate of the roots and leaves of S. alterniflora was higher in the high tidal marsh than that in the low tidal marsh, especially at the late stages of decomposition. The concentrations of metals in leaf litter of S. alterniflora increased, whereas the pools of metals in most of the plant litters decreased significantly with the increasing of the decomposition time. The ratios of ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb in the root litters decreased significantly in the first 290 days of decomposition and then increased significantly at Day 350, while the Pb isotope ratios in adjacent sediment showed no significant changes. Fast mass loss of plant litters induced the significant decrease in metals' pools at early stages of decomposition, and release of the plant tissue Pb was greatly inhibited due to the slowed mass loss at the late stages of decomposition.

Black carbon yields highest nutrient and lowest arsenic release when using rice residuals in paddy soils

Rice straw increasingly remains on the fields for nutrient supply to the next generation of crop plants. It can be applied either fresh or after burning to black carbon or ash. A central concern during rice cultivation is accumulation of carcinogenic arsenic and the question arises how much rice straw application contributes to nutrient versus arsenic supply in paddy fields. Laboratory incubation experiments were performed to assess the effect of rice straw, black carbon and ash on element mobilization. Our experiments showed initially higher silicon and phosphorus release from black carbon compared to fresh straw amendments. However, more re-sorption to soil lead to finally slightly lower pore water concentrations for black carbon versus fresh straw amendments. Highest arsenic, iron, manganese and dissolved organic carbon concentrations were observed after fresh rice straw application. Black carbon and ash application lead to only minor increases of arsenic compared to controls without amendments. Overall, for silicon and phosphorus the soil acts as sink while for iron and arsenic it was the main source. In summary, burning of rice straw to black carbon prior to application seems to yield a high increase in desired nutrient and a decrease in undesired arsenic mobilization in paddy soils.

Can cold-season macrophytes at the senescence stage improve nitrogen removal in integrated constructed wetland systems treating low carbon/nitrogen effluent?

Cold-season macrophytes were configured in a system of stabilization ponds (SPs) and batch operation constructed wetlands (BCWs) to supply a carbon source for low carbon/nitrogen (C/N) effluent in spring and summer without generating secondary pollution during the decomposition process. For eutrophic water, the macrophyte configuration increased the average removal efficiency (RE) from 41.6% to 68.6% and from 70.2% to 83.7% for NO₃^--N and TN in the final BCW effluent, respectively, with the concentrations decreasing from 3.08 mg/L to 1.04 mg/L and from 4.94 mg/L to 3.12 mg/L, respectively. In the early decomposition stages, the RE and concentrations were 82.9% and 0.53 mg/L and 89.4% and 2.38 mg/L for NO₃^--N and TN, respectively. Thus, cold-season macrophytes can improve N removal in SP-BCW systems at the senescence stage, especially at the early decomposition stage.

Anaerobic end-products and mitochondrial parameters as physiological biomarkers to assess the impact of urban pollutants on a key bioturbator

The impact of long-term exposure (6 months) to highly or slightly polluted sediments on the energy metabolism of an ecosystem engineer (the oligochaete Limnodrilus hoffmeisteri) was investigated in laboratory conditions. We evaluated some mitochondrial parameters (respiratory chain activity and ATP production rate) and the accumulation of anaerobic end-products (lactate, alanine, succinate, and propionate). The sediments were collected from stormwater infiltration basins and presented high levels of heavy metals and polycyclic aromatic hydrocarbons (PAHs). These compounds had been drained by the runoff water on impervious surfaces of urban areas during rainfall events. A decrease in the activity of the mitochondrial electron transport chain was observed in worms exposed to the most polluted sediment. Urban contaminants disrupted both aerobic metabolism and mitochondrial functioning, forcing organisms to shift from aerobic to anaerobic metabolism (which is characteristic of a situation of functional hypoxia). Although L. hoffmeisteri is very tolerant to urban pollutants, long-term exposure to high concentrations can cause disruption in mitochondrial activity and therefore energy production. Finally, this study demonstrated that anaerobic end-products could be used as biomarkers to evaluate the impact of a mixture of urban pollutants on invertebrates.

Shoot litter breakdown and zinc dynamics of an aquatic plant, Schoenoplectus californicus

Decomposition of plant debris is an important process in determining the structure and function of aquatic ecosystems. The aims were to find a mathematic model fitting the decomposition process of Schoenoplectus californicus shoots containing different Zn concentrations; compare the decomposition rates; and assess metal accumulation/mobilization during decomposition. A litterbag technique was applied with shoots containing three levels of Zn: collected from an unpolluted river (RIV) and from experimental populations at low (LoZn) and high (HiZn) Zn supply. The double exponential model explained S. californicus shoot decomposition, at first, higher initial proportion of refractory fraction in RIV detritus determined a lower decay rate and until 68 days, RIV and LoZn detritus behaved like a source of metal, releasing soluble/weakly bound zinc into the water; after 68 days, they became like a sink. However, HiZn detritus showed rapid release into the water during the first 8 days, changing to the sink condition up to 68 days, and then returning to the source condition up to 369 days. The knowledge of the role of detritus (sink/source) will allow defining a correct management of the vegetation used for zinc removal and providing a valuable tool for environmental remediation and rehabilitation planning.

Incorporation of zinc and copper by insects of different functional feeding groups in agricultural streams

Metals from agricultural areas are responsible for soil contamination and are carried into aquatic ecosystems. In this context, we evaluated the incorporation of zinc and copper via three feeding strategies (shredding, herbivory and predators) in assemblages of stream insects. We collected aquatic insects in five agricultural streams and five natural streams in Atlantic forest biome to investigate the accumulation of copper and zinc in insects with different feeding strategies. We found no significant differences in the concentrations of copper and zinc between stream types among all insect-feeding groups compared. However, we observed that copper accumulate concentrations differed significantly among the shredders and predators in relation to their resource in streams, while zinc concentrations differed in the two feeding strategy. Therefore, the investigation of the transfer of copper and zinc by different feeding strategies in streams can contribute to the understanding of changes in aquatic insect assemblages related to agricultural activities around streams.

Beyond the mean: A comparison of trace- and macroelement correlation profiles of two lacustrine populations of the crayfish Procambarus clarkii

In invertebrate biomonitors of chemical pollution, emphasis has been generally given to mean accumulation patterns and how they reflect varying environmental levels of contamination. Intra-population variability, and how it relates with individual phenotypic traits, has received less attention. Here, a set of analytes including trace elements (B, Ba, Cd, Cr, Cu, Fe, Li, Mn, Ni, Pb, Sr, V, and Zn), macroelements (C, Ca, K, Mg, N, Na), and carbon and nitrogen stable isotopes (δ¹³C and δ¹⁵N) was measured in two populations of the crayfish Procambarus clarkii from Lake Trasimeno and Lake Bolsena (Central Italy). The influence of location, sex, body size, and condition factor was assessed; in addition, the analyte correlation profiles of the two populations were compared to verify their congruence. In general, significant inter-lake differences were observed in the concentration of both trace- and macroelements in crayfish tissues, generally mirroring the local chemistry of water and of benthic non-living matrices (sediment and plant detritus). Crayfish CN isotopic signatures excluded the occurrence of inter-lake variations in their omnivorous trophic habits. Correlation profiles varied considerably between the two populations in the nature and strength of bivariate relationships. However, Mantel tests and procrustean analyses indicated a general, significant congruence; C, N, and, to a lesser extent K, Li, Ni, Pb, and δ¹³C showed the highest procrustean residuals, suggesting that their associations with other analytes may be partially influenced by inter-population differences in growing phases. Our study indicates that the local geochemistry of the lacustrine environment influences the elemental fingerprint of Procambarus clarkii; the considerable inter-individual variability in the concentration of analytes, however, does not significantly reflect on their association, thus corroborating its effectiveness as an indicator species.

Influence of heavy metal ions on the spectra and charge characteristics of DOM of municipal sewage secondary effluent

The spectral and charged characteristics of dissolved organic matter (DOM) in municipal sewage secondary effluent influenced by heavy metal ions were studied by three-dimensional fluorescence spectroscopy, ultraviolet spectrometry, etc. As the Cu(II) concentration increased, the fluorescence intensity of the DOM's fluorescence peak reduced. When the Cu(II) concentration was 100 μmol/L, the fluorescence intensity of the humic-like acid in the DOM reduced by 19.5%-27.6%. However, there was no obvious change in the fluorescence intensity when Cd(II) was added. According to the modified Stern-Volmer equation, the conditional stability constant lgK and the proportion of the fluorescent functional groups of the DOM binding with Cu(II) were 2.19-2.69 and 16%-48%, respectively. The UV₂₅₃/UV₂₀₃ value changed little with the additional dosage of metal ions below 10 μmol/L, which increased as the concentration of Cu(II) or Pb(II) increased from 10-100 μmol/L. As the metal concentrations increase, the absolute values of the Zeta potential and the particle sizes of the DOM basically increased. The results showed that Cu(II) had the strongest binding ability to the groups that emitted fluorescence in the secondary effluent DOM compared to Pb(II) and Cd(II).

Behavioural and biochemical responses to metals tested alone or in mixture (Cd-Cu-Ni-Pb-Zn) in Gammarus fossarum: From a multi-biomarker approach to modelling metal mixture toxicity

Metals are usually present as mixtures at low concentrations in aquatic ecosystems. However, the toxicity and sub-lethal effects of metal mixtures on organisms are still poorly addressed in environmental risk assessment. Here we investigated the biochemical and behavioural responses of Gammarus fossarum to Cu, Cd, Ni, Pb and Zn tested individually or in mixture (M2X) at concentrations twice the levels of environmental quality standards (EQSs) from the European Water Framework Directive. The same metal mixture was also tested with concentrations equivalent to EQSs (M1X), thus in a regulatory context, as EQSs are proposed to protect aquatic biota. For each exposure condition, mortality, locomotion, respiration and enzymatic activities involved in digestive metabolism and moult were monitored over a 120h exposure period. Multi-metric variations were summarized by the integrated biomarker response index (IBR). Mono-metallic exposures shed light on biological alterations occurring at environmental exposure levels in gammarids and depending on the considered metal and gender. As regards mixtures, biomarkers were altered for both M2X and M1X. However, no additive or synergistic effect of metals was observed comparing to mono-metallic exposures. Indeed, bioaccumulation data highlighted competitive interactions between metals in M2X, decreasing subsequently their internalisation and toxicity. IBR values indicated that the health of gammarids was more impacted by M1X than M2X, because of reduced competitions and enhanced uptakes of metals for the mixture at lower, EQS-like concentrations. Models using bioconcentration data obtained from mono-metallic exposures generated successful predictions of global toxicity both for M1X and M2X. We conclude that sub-lethal effects of mixtures identified by the multi-biomarker approach can lead to disturbances in population dynamics of gammarids. Although IBR-based models offer promising lines of enquiry to predict metal mixture toxicity, further studies are needed to confirm their predictive quality on larger ranges of metallic combinations before their use in field conditions.

Occurrence and risk assessment of trace metals and metalloids in sediments and benthic invertebrates from Dianshan Lake, China

The present study measured concentrations of Cr, Ni, Cu, Zn, As, Cd, Sb, and Pb in surface sediments and two benthic invertebrate species (Anodonta woodiana and Bellamya aeruginosa) collected from Dianshan Lake, located in the Yangtze River Delta. The Dianshan Lake acts as one of the most important drinking water sources to Shanghai, the biggest city in China. Concentrations of trace metals and metalloids ranged from 0.04 mg/kg for Cd to 288.0 mg/kg for Zn. Substantial bioaccumulation in invertebrates was observed for Zn and Cu based on the biota-sediment accumulation factor (BSAF) measurements. The results revealed that concentrations of metals and metalloids in sediments from Dianshan Lake were at the lower end of the range of levels found in other regions of China. The assessment of three significantly inter-related evaluation indices, including the geo-accumulation Index (I_geo), potential ecological risk factor (Erⁱ), and mean probable effect concentration quotients (Q_m-PEC), suggested that sediment-associated trace elements exhibited no considerable ecological risks in the studied watershed. However, the target hazard quotient and hazard index analysis suggested that selected elements (particularly As) accumulation in edible tissues of benthic invertebrates could pose potential health risks to local populations, especially fishermen. Given that wild aquatic organisms (e.g., fish and bivalves) constitute the diet of local populations as popular food/protein choices, further investigations are needed to better elucidate human health risks from metal and metalloid exposure via edible freshwater organisms.

The filter feeder Dreissena polymorpha affects nutrient, silicon, and metal(loid) mobilization from freshwater sediments

Organic sediments in aquatic ecosystems are well known sinks for nutrients, silicon, and metal(loid)s. Organic matter-consuming organisms like invertebrate shredders, grazers, and bioturbators significantly affect element fixation or remobilization by changing redox conditions or binding properties of organic sediments. Little is known about the effect of filter feeders, like the zebra mussel Dreissena polymorpha, an invasive organism in North American and European freshwater ecosystems. A laboratory batch experiment exposing D. polymorpha (∼1200 organisms per m²) to organic sediment from a site contaminated with arsenic, copper, lead, and uranium revealed a significant uptake and accumulation of arsenic, copper, iron, and especially uranium both into the soft body tissues and the seashell. This is in line with previous observations of metal(loid) accumulation from biomonitoring studies. Regarding its environmental impact, D. polymorpha significantly contributed to mobilization of silicon, iron, phosphorus, arsenic, and copper and to immobilization of uranium (p < 0.001), probably driven by redox conditions, microbial activity within the gut system, or active control of element homeostasis. No net mobilization or immobilization was observed for zinc and lead, because of their low mobility at the prevailing pH of 7.5-8.5. The present results suggest that D. polymorpha can both ameliorate (nutrient mobilization, immobilization of toxicants mobile under oxic conditions) or aggravate negative effects (mobilization of toxicants mobile under reducing conditions) in ecosystems. Relating the results of the present study to observed population densities in natural freshwater ecosystems suggests a significant influence of D. polymorpha on element cycling and needs to be considered in future studies.

Input, behaviour and distribution of multiple elements in abiotic matrices along a transect within the Okavango Delta, northern Botswana

Wetlands fed by rivers can be a sink for elements depending on elemental concentrations, wetland hydrology, geochemistry, vegetation and climate. In the case of the Okavango Delta, northern Botswana, the outflow discharge is a small fraction (2-5%) of the inflow. This has strong potential consequences for the Delta, as it strongly affects element cycling and storage within the Delta. We estimated the inputs, behaviour and distribution of multiple elements along a longitudinal transect within the Okavango Delta, to show potential effects of retention mechanisms of different elements. High annual element input is rather attributed to discharge than to the concentration within the water, which is generally extremely low. We observed minimal enrichment of the elements within the water pathway along the transect from inflow to outlets, implying that element output is negligible. For most elements, we observed a high correlation between storage and sediment organic matter content. The organic matter content within the sediments was higher in the vegetated sediments than in non-vegetated sediments (factor ∼ 10), and a similar trend was found for most elements. In conclusion, organic matter dominated in sediments from vegetated plots and thus plays an important role in retaining the elements within the sediments of the Delta. This finding has major implications for e.g. planning constructed wetlands for water purification or element retention especially in areas with high evapotranspiration.

Metal and Metalloid Size-Fractionation Strategies in Spatial High-Resolution Sediment Pore Water Profiles

Sediment water interfaces (SWIs) are often characterized by steep biogeochemical gradients determining the fate of inorganic and organic substances. Important transport processes at the SWI are sedimentation and resuspension of particulate matter and fluxes of dissolved materials. A microprofiling and micro sampling system (missy), enabling high resolution measurements of sediment parameters in parallel to a direct sampling of sediment pore waters (SPWs), was combined with two fractionation approaches (ultrafiltration (UF) and cloud point extraction (CPE)) to differentiate between colloidal and dissolved fractions at a millimeter scale. An inductively coupled plasma-quadrupole mass spectrometry method established for volumes of 300 μL enabled the combination of the high resolution fractionation with multi-element analyzes. UF and CPE comparably indicated that manganese is predominantly present in dissolved fractions of SPW profiles. Differences found for cobalt and iron showed that the results obtained by size-dependent UF and micelle-mediated CPE do not necessarily coincide, probably due to different fractionation mechanisms. Both methods were identified as suitable for investigating fraction-related element concentrations in SPW along sediment depth profiles at a millimeter scale. The two approaches are discussed with regard to their advantages, limitations, potential sources of errors, further improvements, and potential future applications.

Effects of Lumbriculus variegatus (Annelida, Oligochaete) bioturbation on zinc sediment chemistry and toxicity to the epi-benthic invertebrate Chironomus tepperi (Diptera: Chironomidae)

Classical laboratory-based single-species sediment bioassays do not account for modifications to toxicity from bioturbation by benthic organisms which may impact predictions of contaminated sediment risk to biota in the field. This study aims to determine the effects of bioturbation on the toxicity of zinc measured in a standard laboratory bioassay conducted with chironomid larvae (Chironomus tepperi). The epi-benthic chironomid larvae were exposed to two different levels of sediment contamination (1600 and 1980 mg/kg of dry weight zinc) in the presence or absence of annelid worms (Lumbriculus variegatus) which are known to be tolerant to metal and to have a large impact on sediment properties through bioturbation. Chironomids had 5-6x higher survival in the presence of L. variegatus which shows that bioturbation had a beneficial effect on the chironomid larvae. Chemical analyses showed that bioturbation induced a flux of zinc from the pore water into the water column, thereby reducing the bioavailability of zinc in pore water to the chironomid larvae. This also suggested that pore water was the major exposure path for the chironomids to metals in sediment. During the study, annelid worms (Oligochaetes) produced a thin layer of faecal pellets at the sediment surface, a process known to: (i) create additional adsorption sites for zinc, thus reducing its availability, (ii) increase the microbial abundance that in turn could represent an additional food source for opportunistic C. tepperi larvae, and (iii) modify the microbial community's structure and alter the biogeochemical processes it governs thus indirectly impact zinc toxicity. This study represents a contribution in recognising bioturbating organisms as "ecological engineers" as they directly and indirectly influence metal bioavailability and impact other sediment-inhabiting species. This is significant and should be considered in risk assessment of zinc levels (and other metals) in contaminated sediment when extrapolating from laboratory studies to the field.

Targeted metabolomics of Gammarus pulex following controlled exposures to selected pharmaceuticals in water

The effects of pharmaceuticals and personal care products (PPCPs) on aquatic organisms represent a significant current concern. Herein, a targeted metabolomics approach using liquid chromatography-high resolution mass spectrometry (LC-HRMS) is presented to characterise concentration changes in 29 selected metabolites following exposures of aquatic invertebrates, Gammarus pulex, to pharmaceuticals. Method performance revealed excellent linearity (R(2)>0.99), precision (0.1-19%) and lower instrumental limits of detection (0.002-0.20ng) for all metabolites studied. Three pharmaceuticals were selected representing the low, middle and high range of measured acute measured toxicities (of a total of 26 compounds). Gammarids were exposed to both the no-observed-adverse-effect-level (NOAEL) and the lowest-observed-adverse-effect-level (LOAEL) of triclosan (0.1 and 0.3mgL(-1)), nimesulide (0.5 and 1.4mgL(-1)) and propranolol (100 and 153mgL(-1)) over 24h. Quantitative metabolite profiling was then performed. Significant changes in metabolite concentrations relative to controls are presented and display distinct clustered trends for each pharmaceutical. Approximately 37% (triclosan), 33% (nimesulide) and 46% (propranolol) of metabolites showed statistically significant time-related effects. Observed changes are also discussed with respect to internal concentrations of the three pharmaceuticals measured using a method based on pulverised liquid extraction, solid phase extraction and LC-MS/MS. Potential metabolic pathways that may be affected by such exposures are also discussed. This represents the first study focussing on quantitative, targeted metabolomics of this lower trophic level benthic invertebrate that may elucidate biomarkers for future risk assessment.

Controls on metal exposure to aquatic organisms in urban streams

Streams in urban ecosystems receive metal inputs primarily from stormwater runoff and wastewater effluent. The relative contribution of these metal sources to stream impairment is difficult to discern based on simple water characteristics and biological surveys. Stream impairment in these systems is often indicated by reduced abundance and diversity of aquatic insects, which tend to be more sensitive to chronic metal exposures. Metal species and controls on metal species in both the waterborne and dietborne exposure pathways to aquatic organisms are reviewed here. In addition, ecological changes that can control dietborne species are discussed. A main focus is on how organic matter from different anthropogenic sources may control both aqueous metal speciation as well as interaction with various inorganic or microbiological surfaces in streams. Most of the reviewed research focuses on Cu, Zn or Pb as those are the primary metals of concern in developed systems and Cu and Pb have unique and strong interactions with organic matter. Recommendations for further research are described in the context of exposure species, dynamics of exposure, stoichiometry, or advanced analytical tools, and regulatory implications are discussed.

Contribution of aqueous and dietary uptakes to lead (Pb) bioaccumulation in Gammarus pulex: From multipathway modeling to in situ validation

Although dynamic approaches are nowadays used increasingly to describe metal bioaccumulation in aquatic organisms, the validation of such laboratory-derived modeling is rarely assessed under environmental conditions. Furthermore, information on bioaccumulation kinetics of Pb and the significance of its uptake by dietary route is scarce in freshwater species. This study aims at modeling aqueous and dietary uptakes of Pb in the litter-degrader Gammarus pulex and assessing the predictive quality of multipathway modeling from in situ bioaccumulation data. In microcosms, G. pulex were exposed to environmentally realistic concentrations of Pb (from 0.1 to 10µg/L) in the presence of Pb-contaminated poplar leaves, which were enclosed or not in a net to distinguish aqueous and dietary uptakes. Results show that water and food both constitute contamination sources for gammarids. Establishing biodynamic parameters involved in Pb aqueous and dietary uptake and elimination rates enabled to construct a multipathway model to describe Pb bioaccumulation in gammarids. This laboratory-derived model successfully predicted bioaccumulation measured in native populations of G. pulex collected in situ when local litter was used as dietary exposure source. This study demonstrates not only the suitable applicability of biodynamic parameters for predicting Pb bioaccumulation but also the necessity of taking dietary uptake into account for a better interpretation of the gammarids' contamination in natural conditions.

Accumulation of Trace Metal Elements (Cu, Zn, Cd, and Pb) in Surface Sediment via Decomposed Seagrass Leaves: A Mesocosm Experiment Using Zostera marina L

Accumulation of Cu, Zn, Cd, and Pb in the sediment of seagrass ecosystems was examined using mesocosm experiments containing Zostera marina (eelgrass) and reference pools. Lead was approximately 20-fold higher in the surface sediment in the eelgrass pool than in eelgrass leaves and epiphytes on the eelgrass leaves, whereas zinc and cadmium were significantly lower in the surface sediment than in the leaves, with intermediate concentrations in epiphytes. Copper concentrations were similar in both the surface sediment and leaves but significantly lower in epiphytes. Carbon and nitrogen contents increased significantly with increasing δ13C in surface sediments of both the eelgrass and reference pools. Copper, Zn, Cd, and Pb also increased significantly with increasing δ13C in the surface sediment in the eelgrass pool but not in the reference pool. By decomposition of eelgrass leaves with epiphytes, which was examined in the eelgrass pool, copper and lead concentrations increased more than 2-fold and approximately a 10-fold, whereas zinc and cadmium concentrations decreased. The high copper and lead concentrations in the surface sediment result from accumulation in decomposed, shed leaves, whereas zinc and cadmium remobilized from decomposed shed leaves but may remain at higher concentrations in the leaves than in the original sediments. The results of our mesocosm study demonstrate that whether the accumulation or remobilization of trace metals during the decomposition of seagrass leaves is trace metal dependent, and that the decomposed seagrass leaves can cause copper and lead accumulation in sediments in seagrass ecosystems.

Bioturbation effects on heavy metals fluxes from sediment treated with activated carbon

Adding activated carbon (AC) to sediment has been proposed as an in situ sediment remediation technique. To date, it is not clear whether this technique is effective in the treatment of heavy metal-contaminated sediment in the presence of bioturbators. In the present study, we compare the ability of granular-activated carbon (GAC) and powder-activated carbon (PAC) to reduce Cu, Zn, and Pb pore water concentrations at environmentally relevant concentrations in the absence and presence of Chironomid larvae. Compared to untreated sediment, PAC and GAC addition in the absence of Chironomid larvae resulted in reductions of free Cu concentrations of 78 and 66 % just below the sediment-water interface after 28 days, respectively. While for Pb and Zn these concentration reductions were only 40 and 38, 19 and 25 %, respectively. The presence of Chironomid larvae in untreated, and GAC sediment generally increased the free heavy metals concentrations in pore water, especially in the deeper layers. In comparison with untreated sediment, the coexistence of AC enhanced the accumulation of heavy metals, especially for PAC. This increased bioaccumulation may decrease the survival of Chironomid larvae. The result indicated that ACs may not be suitable for the remediation of heavy metal-contaminated sediments.

Metal release/accumulation during the decomposition of Potamogeton crispus in a shallow macrophytic lake

Changes in metal concentrations in the litter of Potamogeton crispus were monitored during a consecutive 40-day in situ decomposition experiment using the litterbag method. The accumulation index was calculated and used to indicate the changes in the metals in litter. The results showed that the concentrations of Al, Cd, Cr, Fe, Mn, and Pb in litter increased significantly during the decomposition, while Cu and Zn concentrations decreased dramatically. Significant positive correlations were found between the concentrations of Al, Cr, Fe, and Mn and between Cu and Zn. Moreover, Cu and Zn both negatively correlated with Al and Fe. The remaining dry mass was negatively correlated with Al and Fe concentrations but positively correlated with Cu and Zn concentrations. Generally the accumulation index values of metals other than Al were less than one, indicating that the litter of P. crispus acted as a source of metals to the surrounding water body. Al was the only metal that showed continuous net accumulation in litter. The net accumulation of Fe and Mn in litter during the last 10 days of the experiment may indicate the precipitation of Fe- and Mn-oxides. It was estimated that 160 g/m(2) (dry weight) P. crispus was decomposed in 40 days. This was equivalent to releasing the following amounts of metals: 0.01 mg Cd, 0.03 mg Cr, 0.71 mg Cu, 0.55 mg Mn, 0.02 mg Pb and 13.8 mg Zn into surrounding water, and accumulating 149 mg Al and 11 mg Fe, in a 1m(2) area.

Effects of low arsenic concentration exposure on freshwater fish in the presence of fluvial biofilms

Arsenic (As) is a highly toxic element and its carcinogenic effect on living organisms is well known. However, predicting real effects in the environment requires an ecological approach since toxicity is influenced by many environmental and biological factors. The purpose of this paper was to evaluate if environmentally-realistic arsenic exposure causes toxicity to fish. An experiment with four different treatments (control (C), biofilm (B), arsenic (+As) and biofilm with arsenic (B+As)) was conducted and each one included sediment to enhance environmental realism, allowing the testing of the interactive effects of biofilm and arsenic on the toxicity to fish. Average arsenic exposure to Eastern mosquitofish (Gambusia holbrooki) was 40.5 ± 7.5 μg/L for +As treatment and 34.4 ± 1.4 μg/L for B+As treatment for 56 days. Fish were affected directly and indirectly by this low arsenic concentration since exposure did not only affect fish but also the function of periphytic biofilms. Arsenic effects on the superoxide dismutase (SOD) and glutathione reductase (GR) activities in the liver of mosquitofish were ameliorated in the presence of biofilms at the beginning of exposure (day 9). Moreover, fish weight gaining was only affected in the treatment without biofilm. After longer exposure (56 days), effects of exposure were clearly seen. Fish showed a marked increase in the catalase (CAT) activity in the liver but the interactive influence of biofilms was not further observed since the arsenic-affected biofilm had lost its role in water purification. Our results highlight the interest and application of incorporating some of the complexity of natural systems in ecotoxicology and support the use of criterion continuous concentration (CCC) for arsenic lower than 150 μg/L and closer to the water quality criteria to protect aquatic life recommended by the Canadian government which is 5 μg As/L.

Natural origin arsenic in aquatic organisms from a deep oligotrophic lake under the influence of volcanic eruptions

Volcanic eruptions are recognized sources of toxic elements to freshwater, including arsenic (As). In order to study the short term changes in the bioaccumulation of naturally occurring As by aquatic organisms in Lake Nahuel Huapi (Argentina), located close to the Puyehue-Cordón Caulle volcanic complex (PCCVC), we described As concentrations at different trophic levels and food web transfer patterns in three sites of the lake prior to the last PCCVC eruption (June 2011), and compared As concentrations in biota before and after the eruption. The highest As concentrations and greater variations both between sites and position in the water column, were observed in phytoplankton (3.9-64.8 µg g(-1) dry weight, DW) and small zooplankton (4.3-22.3 µg g(-1) DW). The pattern of As accumulation in aquatic organisms (whole body or muscle) was: primary producers (phytoplankton) > scrapper mollusks (9.3-15.3 µg g(-1) DW) > filter feeding mollusks (5.4-15.6 µg g(-1) DW) > omnivorous invertebrates (0.4-9.2 µg g(-1) DW) > zooplankton (1.2-3.5 µg g(-1) DW) > fish (0.2-1.9 µg g(-1) DW). We observed As biodilution in the whole food web, and in salmonids food chains, feeding on fish prey; but biomagnification in the food chain of creole perch, feeding on benthic crayfish. The impact of the 2011 PCCVC eruption on the As levels of biota was more evident in pelagic-associated organisms (zooplankton and planktivorous fish), but only in the short term, suggesting a brief high bioavailability of As in water after ash deposition. In benthic organisms As variations likely responded to shift in diet due to coverage of the littoral zone with ashes.

Strategies of Gammarus pulex L. to cope with arsenic--Results from speciation analyses by IC-ICP-MS and XAS micro-mapping

The invertebrate shredder Gammarus pulex L. is a key species for aquatic carbon turnover via litter decomposition and can thrive in high-arsenic (As) environments. To understand their strategies for coping with increased As concentrations while fulfilling their ecosystem functions, we analyzed the As concentration and speciation in their aquatic habitat and in leaves with heterotrophic biofilms as their natural food source. We also followed the As distribution and speciation on the cuticle and within the body of G. pulex by X-ray absorption spectroscopic imaging. Half of the total As on G. pulex was found to be associated with the cuticle but was not taken up. Removing this externally bound As yielded only arsenate in the wash solution which reflects the speciation of the surrounding aquatic phase and shows that this As does not undergo any biotransformation. The major pathway into the organism is suggested to be incorporation via food intake, but only very low amounts of As were taken up or translocated from the gut system to other tissues. In one of the main food sources, leaves, 68% arsenate and 29% monomethylarsenate were found. After ingestion into the gut system, up to 23% of the more toxic arsenite was seen, but a substantial share was methylated to dimethylarsenate (46-56%). Little arsenate and arsenite were found in the adjacent tissues. Besides 76-80% mono- and di-methylarsenate, 10-21% of the As was complexed as As(III)-S species. G. pulex plays an important role in As cycling and our results indicate that As translocation from the gut to other tissues is minimized, but a transformation to other As-species occurred.

The relative importance of diet-related and waterborne effects of copper for a leaf-shredding invertebrate

Copper (Cu) exposure can increase leaf-associated fungal biomass, an important food component for leaf-shredding macroinvertebrates. To test if this positive nutritional effect supports the physiological fitness of these animals and to assess its importance compared to waterborne toxicity, we performed a 24-day-bioassay in combination with a 2×2 factorial design using the amphipod shredder Gammarus fossarum and a field-relevant Cu concentration of 25 μg/L (n = 65). Waterborne toxicity was negligible, while gammarids fed leaves exposed to Cu during microbial colonization exhibited a near-significant impairment in growth (∼30%) and a significantly reduced lipid content (∼20%). These effects appear to be governed by dietary uptake of Cu, which accumulated in leaves as well as gammarids and likely overrode the positive nutritional effect of the increased fungal biomass. Our results suggest that for adsorptive freshwater contaminants dietary uptake should be evaluated already during the registration process to safeguard the integrity of detritus-based ecosystems.

Does the presence of titanium dioxide nanoparticles reduce copper toxicity? A factorial approach with the benthic amphipod Gammarus fossarum

In aquatic ecosystems, titanium dioxide nanoparticles (nano-TiO2) may adsorb co-occurring chemical stressors, such as copper (Cu). This interaction has the potential to reduce the concentration of dissolved Cu due to surface binding to the nanoparticles. The subsequent sedimentation of nano-TiO2 agglomerates may increase the exposure of benthic species towards the associated Cu. This scenario was assessed by employing the amphipod Gammarus fossarum as model species and taking advantage of a 2×2-factorial design investigating absence and presence of 2mg nano-TiO2/L and 40μg Cu/L (n=45; t=24d) in darkness, respectively. Nano-TiO2 alone did not affect mortality and leaf consumption, whereas Cu alone caused high mortality (>70%), reduced leaf consumption (25%) and feces production (30%) relative to the control. In presence of nano-TiO2, Cu-induced toxicity was largely eliminated. However, independent of Cu, nano-TiO2 decreased the gammarids' assimilation and weight. Hence, nano-TiO2 may be applicable as Cu-remediation agent, while its potential long-term effects need further attention.

Distribution and relationship of uranium and radium along an allochthonously dominated wetland gradient

Uranium mining may pose a large threat for freshwater ecosystems, caused by elevated concentrations of metals/radionuclides in drainage water. Important pollutants of such waters are uranium (U) and radium (Ra), because of their impact due to both radio- as well as chemo-toxicity. Despite the comprehensive knowledge about specific element speciation as well as fixation processes, less is known about the retention of U and Ra at a higher level of complexity (within allochthonous ecosystems as predominant for low order streams). Consequently, we investigated the distribution and retention potential of allochthonous ecosystems regarding U and Ra as well as changing U/Ra ratios. We found U predominantly transported over long distances, whereas Ra mainly precipitates immediately after reaching the surface, i.e. in the spring area. Although high U accumulation in organic rich sediments is found, still high transport rates are detected. Low overall fixation of U within the allochthonously dominated wetland results in an U transport over long distances. Consequently, large areas are affected by U mining activities and its post-mining impact, with U being more relevant compared to Ra.

Invertebrate grazers affect metal/metalloid fixation during litter decomposition

Plant litter and organic sediments are main sinks for metals and metalloids in aquatic ecosystems. The effect of invertebrates as key species in aquatic litter decomposition on metal/metalloid fixation by organic matter is described only for shredders, but for grazers as another important animal group less is known. Consequently, a laboratory batch experiment was conducted to examine the effect of invertebrate grazers (Lymnaea stagnalis L.) on metal/metalloid fixation/remobilization during aquatic litter decomposition. It could be shown that invertebrate grazers facilitate significantly the formation of smaller sizes of particulate organic matter (POM), as shown previously for invertebrate shredders. The metal/metalloid binding capacity of these smaller particles of POM is higher compared to leaf litter residuals. But element enrichment is not as high as shown previously for the effect by invertebrate shredders. Invertebrate grazers enhance also the mobilization of selected elements to the water, in the range also proven for invertebrate shredders but different for the different elements. Nonetheless invertebrate grazers activity during aquatic litter decomposition leads to a metal/metalloid fixation into leaf litter as part of sediment organic matter. Hence, the effect of invertebrate grazers on metal/metalloid fixation/remobilization contrasts partly with former assessments revealing the possibility of an enhanced metal/metalloid fixation.