A summary of river water quality data collected within the Land-Ocean Interaction Study: core data for eastern UK rivers draining to the North Sea

Boron contamination and its risk management in terrestrial and aquatic environmental settings

Boron (B) is released to terrestrial and aquatic environments through both natural and anthropogenic sources. This review describes the current knowledge on B contamination in soil and aquatic environments in relation to its geogenic and anthropogenic sources, biogeochemistry, environmental and human health impacts, remediation approaches, and regulatory practices. The common naturally occurring sources of B include borosilicate minerals, volcanic eruptions, geothermal and groundwater streams, and marine water. Boron is extensively used to manufacture fiberglass, thermal-resistant borosilicate glass and porcelain, cleaning detergents, vitreous enamels, weedicides, fertilizers, and B-based steel for nuclear shields. Anthropogenic sources of B released into the environment include wastewater for irrigation, B fertilizer application, and waste from mining and processing industries. Boron is an essential element for plant nutrition and is taken up mainly as boric acid molecules. Although B deficiency in agricultural soils has been observed, B toxicity can inhibit plant growth in soils under arid and semiarid regions. High B intake by humans can be detrimental to the stomach, liver, kidneys and brain, and eventually results in death. Amelioration of soils and water sources enriched with B can be achieved by immobilization, leaching, adsorption, phytoremediation, reverse osmosis, and nanofiltration. The development of cost-effective technologies for B removal from B-rich irrigation water including electrodialysis and electrocoagulation techniques is likely to help control the predominant anthropogenic input of B to the soil. Future research initiatives for the sustainable remediation of B contamination using advanced technologies in soil and water environments are also recommended.

Composition and Functional Characteristics and Influencing Factors of Bacterioplankton Community in the Huangshui River, China

Bacterial community plays a key role in environmental and ecological processes of river ecosystems. Given the special climatic and geographical conditions, studying the compositional characteristics of microorganisms in highland rivers and the relationship between such microorganisms and water physicochemical factors is important for an in-depth understanding of microbial ecological mechanisms. In the present study, high-throughput sequencing was used to investigate and study the bacterioplankton community of the Huangshui River in the ecotone zone of the Qinghai Plateau and Loess Plateau. The results showed that the Huangshui River had significantly lower alpha diversity than the plain rivers. Despite the similarity in their environmental conditions, the main taxonomic compositions of the bacterial communities were distinct between the Huangshui River and polar regions (the Arctic and Antarctica). Proteobacteria accounted for the largest proportion (30.79–99.98%) of all the sequences, followed by Firmicutes (0–49.38%). Acidiphilium was the most numerous genera, which accounted for 0.03–86.16% of the assigned 16S reads, followed by Acidocella (0–95.9%), both belonging to Alphaproteobacteria. The diverse taxa of potential pathogens, such as Acinetobacter, Pseudomonas, and Aeromonas, were also identified. A principal coordinates analysis, coupled with a canonical correspondence analysis, showed spatial variations in the bacterial community composition. The water physical properties (e.g., Cr⁶⁺, total phosphorus, and COD_Mn); altitude; and land use (e.g., urban land cover and aquaculture) determined the distribution of the bacterioplankton composition. PICRUSt2 revealed that the overall functional profiles of the bacterial communities in different samples were similar, and our results suggested the potential health risks of water sources in this area. This work provided valuable insight into the composition of the plankton bacterial community and its relationship with the environmental factors in the Huangshui River in the ecotone zone of the Qinghai Plateau and Loess Plateau and a theoretical foundation for ecological health management.

Transcriptome analysis provides insights into copper toxicology in piebald naked carp (Gymnocypris eckloni)

Background

Copper was used for many years in aquaculture operations as an effective algaecide or a parasite treatment of fish. It is an essential nutrient with numerous functions in organisms, but is toxic at high concentrations. However, the toxicity of copper to fish remains unclear. In this study, we used the piebald naked carp, Gymnocypris eckloni, as a model. RNA-seq data from different tissues, including gills, kidney, and liver, were used to investigate the underlying mechanism of copper toxicology in G. eckloni.

Results

We compared the transcriptomes from different tissues with different time durations of copper ion treatment. After 72 h copper ion treatment, the number of genes with different expression in gills and liver changed dramatically, but not in kidneys. In KEGG functional enrichment, the pattern of differentially expressed genes (DEGs) was also similar in the gills and liver. The most enriched pathway of DEGs was “Ribosome” in both tissues. Furthermore, we analyzed the expression levels of genes involved in oxidative stress response and protein synthesis using qPCR and RNA-seq data. Our results showed that several genes involved in oxidative stress response were up-regulated both in gills and liver. Up-regulation of these genes indicated that copper treatment caused oxidative stress, which is likely to result in ribosome damage. In addition, our results showed that the expression of Eef1b2, a transcription elongation factor, was decreased in the liver under oxidative stress, and the expression of translation initiation factors Eif4ebp1 and eIF2α, and elongation factor eEF2 was up-regulated. These results supported the idea that oxidative stress inhibits protein synthesis in cells.

Conclusions

Our results indicate that copper exposure caused different responses in different tissues, since the gene expression patterns changed substantially either in the gills or liver, while the effect on the kidney was relatively weak. Furthermore, our results indicated that the expression pattern of the genes involved in the ribosome, which is a complex molecular machine orchestrating protein synthesis in the cell, together with translation initiation factor and elongation factors, were affected by copper exposure both in the gills and liver of piebald naked carp. This result leads us to speculate that the downregulation of global protein synthesis is an acute response strategy of fish to metal-induced oxidative stress. Moreover, we speculate that this strategy not only exists in the selective translation of proteins but also exists in the specific translation of functional proteins in tissues and cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07673-4.

Arsenic Fixation in Polluted Soils by Peat Applications

Soil arsenic (As) pollution is still a major concern due to its high toxicity and carcinogenicity, thus, the study of decontamination techniques, as the organic amendment applications, keeps upgrading. This research evaluates the potential remediation of peat in different As-polluted soils, by assessing the decrease of As solubility and its toxicity through bioassays. Obtained reduction in As solubility by peat addition was strongly related to the increase of humic substances, providing colloids that allow the complexation of As compounds. Calcareous soils have been the least effective at buffering As pollution, with higher As concentrations and worse biological response (lower soil respiration and inhibition of lettuce germination). Non-calcareous soils showed lower As concentrations due to the higher iron content, which promotes As fixation. Although in both cases, peat addition improves the biological response, it also showed negative effects, hypothetically due to peat containing toxic polyphenolic compounds, which in the presence of carbonates appears to be concealed. Both peat dose tested (2% and 5%) decreased drastically As mobility; however, for calcareous soils, as there is no phytotoxic effect, the 5% dose is the most recommended; while for non-calcareous soils the efficient peat dose for As decontamination could be lower.

Highly variable iron content modulates iceberg-ocean fertilisation and potential carbon export

Marine phytoplankton growth at high latitudes is extensively limited by iron availability. Icebergs are a vector transporting the bioessential micronutrient iron into polar oceans. Therefore, increasing iceberg fluxes due to global warming have the potential to increase marine productivity and carbon export, creating a negative climate feedback. However, the magnitude of the iceberg iron flux, the subsequent fertilization effect and the resultant carbon export have not been quantified. Using a global analysis of iceberg samples, we reveal that iceberg iron concentrations vary over 6 orders of magnitude. Our results demonstrate that, whilst icebergs are the largest source of iron to the polar oceans, the heterogeneous iron distribution within ice moderates iron delivery to offshore waters and likely also affects the subsequent ocean iron enrichment. Future marine productivity may therefore be not only sensitive to increasing total iceberg fluxes, but also to changing iceberg properties, internal sediment distribution and melt dynamics.

Acute exposure to copper induces variable intensity of oxidative stress in goldfish tissues

Copper is an essential element, but at high concentrations, it is toxic for living organisms. The present study investigated the responses of goldfish, Carassius auratus, to 96 h exposure to 30, 300, or 700 μg L^-1 of copper II chloride (Cu²⁺). The content of protein carbonyls was higher in kidney (by 158%) after exposure to 700 mg L^-1 copper, whereas in gills, liver, and brain, we observed lower content of protein carbonyls after exposure to copper compared with control values. Exposure to copper resulted in increased levels of lipid peroxides in gills (76%) and liver (95-110%) after exposure to 300 and 700 μg L^-1 Cu²⁺. Low molecular mass thiols were depleted by 23-40% in liver and by 29-67% in kidney in response to copper treatment and can be used as biomarkers toxicity of copper. The activities of primary antioxidant enzymes, superoxide dismutase and catalase, were increased in liver as a result of Cu²⁺ exposure, whereas in kidney catalase activity was decreased. The activities of glutathione-related enzymes, glutathione peroxidase, glutathione-S-transferase, and glutathione reductase were decreased as a result of copper exposure, but glutathione reductase activity increased by 25-40% in liver. Taken together, these data show that exposure of fish to Cu²⁺ ions results in the development of low/high intensity oxidative stress reflected in enhanced activities of antioxidant and associated enzymes in different goldfish tissues.

An alternative approach to risk rank chemicals on the threat they pose to the aquatic environment

This work presents a new and unbiased method of risk ranking chemicals based on the threat they pose to the aquatic environment. The study ranked 12 metals, 23 pesticides, 11 other persistent organic pollutants (POPs), 13 pharmaceuticals, 10 surfactants and similar compounds and 2 nanoparticles (total of 71) of concern against one another by comparing their median UK river water and median ecotoxicity effect concentrations. To complement this, by giving an assessment on potential wildlife impacts, risk ranking was also carried out by comparing the lowest 10th percentile of the effects data with the highest 90th percentile of the exposure data. In other words, risk was pared down to just toxicity versus exposure. Further modifications included incorporating bioconcentration factors, using only recent water measurements and excluding either lethal or sub-lethal effects. The top ten chemicals, based on the medians, which emerged as having the highest risk to organisms in UK surface waters using all the ecotoxicity data were copper, aluminium, zinc, ethinylestradiol (EE2), linear alkylbenzene sulfonate (LAS), triclosan, manganese, iron, methomyl and chlorpyrifos. By way of contrast, using current UK environmental quality standards as the comparator to median UK river water concentrations would have selected 6 different chemicals in the top ten. This approach revealed big differences in relative risk; for example, zinc presented a million times greater risk then metoprolol and LAS 550 times greater risk than nanosilver. With the exception of EE2, most pharmaceuticals were ranked as having a relatively low risk.

Orthophosphate-P in the nutrient impacted River Taw and its catchment (SW England) between 1990 and 2013

Excess dissolved phosphorus (as orthophosphate-P) contributes to reduced river water quality within Europe and elsewhere. This study reports results from analysis of a 23 year (1990-2013) water quality dataset for orthophosphate-P in the rural Taw catchment (SW England). Orthophosphate-P and river flow relationships and temporal variations in orthophosphate-P concentrations indicate the significant contribution of sewage (across the catchment) and industrial effluent (upper R. Taw) to orthophosphate-P concentrations (up to 96%), particularly during the low flow summer months when maximum algal growth occurs. In contrast, concentrations of orthophosphate-P from diffuse sources within the catchment were more important (>80%) at highest river flows. The results from a 3 end-member mixing model incorporating effluent, groundwater and diffuse orthophosphate-P source terms suggested that sewage and/or industrial effluent contributes ≥50% of the orthophosphate-P load for 27-48% of the time across the catchment. The Water Framework Directive (WFD) Phase 2 standards for reactive phosphorus, introduced in 2015, showed the R. Taw to be generally classified as Poor to Moderate Ecological Status, with a Good Status occurring more frequently in the tributary rivers. Failure to achieve Good Ecological Status occurred even though, since the early-2000s, riverine orthophosphate-P concentrations have decreased (although the mechanism(s) responsible for this could not be identified). For the first time it has been demonstrated that sewage and industrial effluent sources of alkalinity to the river can give erroneous boundary concentrations of orthophosphate-P for WFD Ecological Status classification, the extent of which is dependent on the proportion of effluent alkalinity present. This is likely to be a European - wide issue which should be examined in more detail.

Food web modeling of a river ecosystem for risk assessment of down-the-drain chemicals: a case study with AQUATOX

Conventional approaches to estimating protective ecotoxicological thresholds of chemicals, i.e. predicted no-effect concentrations (PNEC), for an entire ecosystem are based on the use of assessment factors to extrapolate from single-species toxicity data derived in the laboratory to community-level effects on ecosystems. Aquatic food web models may be a useful tool to improve the ecological realism of chemical risk assessment because they enable a more insightful evaluation of the fate and effects of chemicals in dynamic trophic networks. A case study was developed in AQUATOX to simulate the effects of the anionic surfactant linear alkylbenzene sulfonate and the antimicrobial triclosan on a lowland riverine ecosystem. The model was built for a section of the River Thames (UK), for which detailed ecological surveys were available, allowing for a quantification of energy flows through the whole ecosystem. A control scenario was successfully calibrated for a simulation period of one year, and tested for stability over six years. Then, the model ecosystem was perturbed with varying inputs of the two chemicals. Simulations showed that both chemicals rapidly approach steady-state, with internal concentrations in line with the input bioconcentration factors throughout the year. At realistic environmental concentrations, both chemicals have insignificant effects on biomass trends. At hypothetical higher concentrations, direct and indirect effects of chemicals on the ecosystem dynamics emerged from the simulations. Indirect effects due to competition for food sources and predation can lead to responses in biomass density of the same magnitude as those caused by direct toxicity. Indirect effects can both exacerbate or compensate for direct toxicity. Uncertainties in key model assumptions are high as the validation of perturbed simulations remains extremely challenging. Nevertheless, the study is a step towards the development of realistic ecological scenarios and their potential use in prospective risk assessment of down-the-drain chemicals.

Removal of phosphorus from trickling filter effluent by electrocoagulation

As regulatory requirements for contaminants in wastewater discharged to the environment get stricter, alternative or additional treatment processes to those already being used are necessary. One contaminant of particular concern associated with discharging treated municipal wastewater to a receiving water body is phosphorus (P). A continuous scale electrocoagulation (EC) system was investigated as an alternative to conventional chemical addition for P removal from municipal wastewater. The EC process was optimized for iron dose delivery by changing the electrical current, electrode spacing and the reactor contact time, and a comparison was made with conventional ferric dosing through jar testing. Results showed that EC could achieve P removal to meet a P consent of 1 mg L⁻¹ at a dose of 154 mg L⁻¹ Fe. The process was shown to provide a supplementary benefit for chemical and biological oxygen demand removal of 86% and 82%, respectively, but gave no significant removal of other sanitary pollutants. When compared directly with conventional iron dosing, EC required approximately twice the iron dose. When electrical costs were also factored into the comparison, EC was shown to be approximately double the cost of conventional dosing and at present is not a feasible alternative to conventional coagulation using ferric chloride.

Molybdenum distributions and variability in drinking water from England and Wales

An investigation has been carried out of molybdenum in drinking water from a selection of public supply sources and domestic taps across England and Wales. This was to assess concentrations in relation to the World Health Organization (WHO) health-based value for Mo in drinking water of 70 μg/l and the decision to remove the element from the list of formal guideline values. Samples of treated drinking water from 12 water supply works were monitored up to four times over an 18-month period, and 24 domestic taps were sampled from three of their supply areas. Significant (p < 0.05) differences were apparent in Mo concentration between sources. Highest concentrations were derived from groundwater from a sulphide-mineralised catchment, although concentrations were only 1.5 μg/l. Temporal variability within sites was small, and no seasonal effects (p > 0.05) were detected. Tap water samples collected from three towns (North Wales, the English Midlands, and South East England) supplied uniquely by upland reservoir water, river water, and Chalk groundwater, respectively, also showed a remarkable uniformity in Mo concentrations at each location. Within each, the variability was very small between houses (old and new), between pre-flush and post-flush samples, and between the tap water and respective source water samples. The results indicate that water distribution pipework has a negligible effect on supplied tap water Mo concentrations. The findings contrast with those for Cu, Zn, Ni, Pb, and Cd, which showed significant differences (p < 0.05) in concentrations between pre-flush and post-flush tap water samples. In two pre-flush samples, concentrations of Ni or Pb were above drinking water limits, although in all cases, post-flush waters were compliant. The high concentrations, most likely derived from metal pipework in the domestic distribution system, accumulated during overnight stagnation. The concentrations of Mo observed in British drinking water, in all cases less than 2 μg/l, were more than an order of magnitude below the WHO health-based value and suggest that Mo is unlikely to pose a significant health or water supply problem in England and Wales.

Coastal Zone Ecosystem Services: from science to values and decision making; a case study

This research is concerned with the following environmental research questions: socio-ecological system complexity, especially when valuing ecosystem services; ecosystems stock and services flow sustainability and valuation; the incorporation of scale issues when valuing ecosystem services; and the integration of knowledge from diverse disciplines for governance and decision making. In this case study, we focused on ecosystem services that can be jointly supplied but independently valued in economic terms: healthy climate (via carbon sequestration and storage), food (via fisheries production in nursery grounds), and nature recreation (nature watching and enjoyment). We also explored the issue of ecosystem stock and services flow, and we provide recommendations on how to value stock and flows of ecosystem services via accounting and economic values respectively. We considered broadly comparable estuarine systems located on the English North Sea coast: the Blackwater estuary and the Humber estuary. In the past, these two estuaries have undergone major land-claim. Managed realignment is a policy through which previously claimed intertidal habitats are recreated allowing the enhancement of the ecosystem services provided by saltmarshes. In this context, we investigated ecosystem service values, through biophysical estimates and welfare value estimates. Using an optimistic (extended conservation of coastal ecosystems) and a pessimistic (loss of coastal ecosystems because of, for example, European policy reversal) scenario, we find that context dependency, and hence value transfer possibilities, vary among ecosystem services and benefits. As a result, careful consideration in the use and application of value transfer, both in biophysical estimates and welfare value estimates, is advocated to supply reliable information for policy making.

Combining phosphate and bacteria removal on chemically active filter membranes allows prolonged storage of drinking water

A chemically active filtration membrane with incorporated lanthanum oxide nanoparticles enables the removal of bacteria and phosphate at the same time and thus provides a simple device for preparation of drinking water and subsequent safe storage without using any kind of disinfectants.

What impact might mitigation of diffuse nitrate pollution have on river water quality in a rural catchment?

Observations of river flow, river quality and solar radiation were collated to assess the degree to which light and nutrients may be limiting phytoplankton growth at seven sites in the River Ouse catchment in NE England under average conditions. Hydraulic information derived from river network model applications was then used to determine where river water has sufficient residence time above the tidal limit to facilitate bloom development. A nitrate model (NALTRACES) was developed to estimate the impact of land management change on mean river nitrate concentrations. Applications of this model showed that although agricultural activity contributes substantially to nitrate loads in the Ouse it is likely to have little impact on phytoplankton growth, which could still occur extensively in its absence given favourable sunny and dry conditions. As an example of a means of controlling light availability, establishing full riparian tree cover would appear to be a considerably more effective management scenario than suppressing inputs to the river of nitrate or phosphorus. Any actions should be prioritised in headwater areas such as the upper reaches of the Swale and Ure tributaries. These conclusions are in broad agreement with those arising from more detailed simulations at daily resolution using the QUESTOR river quality model. The combination of simple modelling approaches applied here allows an initial identification of suitable spatially-targeted options for mitigating against phytoplankton blooms which can be applied more widely at a regional or national level.

The effect of metals on condition and pathologies of European eel (Anguilla anguilla): in situ and laboratory experiments

Forty-nine wild eels (Anguilla anguilla) caught in the Albufera Lake (Spain), measuring 24.0-75.0 cm in length and 25.0-637.7 g in weight, were examined for metals (Cd, Co, Cr, Cu, Fe, Hg, Mn, Pb, Se and Zn), condition (CI and HSI indices), as well as for diseases (Anguillicola infestation; bacterial infections). Total metal load significantly increased in eel liver tissue parallel to total length and body weight (log), while silvering females (W(B) > 200 g; L ≥ 500 mm) exhibited the highest amounts of Co, Cu, Hg, Se and Zn. Diverse effects may be expected in these big eels due to long-term metal exposure. In fact, IMBI (individual mean (multi-metal) bioaccumulation index) and copper load (Ln) in particular, were significantly related with a decrease in the HSI, reflecting lower eel fitness. In addition, most silvering females (75%) showed a CI below 0.2, and this size group presented the highest prevalence of chronic diseases, at significant levels, that are non-lethal in the short term, but degenerative in the long term. Amounts of hepatic iron were not correlated with eel size; however, a significant, strong negative correlation between this metal (Ln) and HSI and CI was found for wild eels suffering from diseases of any aetiology. This also included small eels (W(B) <67 g; L < 350 mm), as this size group presented a significant prevalence of acute diseases caused by single virulent bacterial pathogens (i.e. Edwardsiella tarda and Vibrio vulnificus biotype 2). To assess the effect of metals on susceptibility to disease, yellow eels were maintained and exposed to iron, copper, and pathogens, in captivity under laboratory conditions. Co-exposure of eels to iron (9 μg of Fe/g of fish) and bacterial pathogens by intraperitoneal injection (IP), yielded a hundred-fold reduction in the LD50 of all bacteria assayed (i.e. E. tarda, V. vulnificus, and motile Aeromonas), and also the time taken to cause eel death. Short-term aqueous exposure of eels to 0.4, 0.7, 1.7 and 3.9 μM of copper, yielded increasing mortality among eels IP challenged by a single dose of 1.90 × 10(6) E. tarda cells, and this effect was significant for 1.7 μM of copper. These results suggest a synergistic interaction among copper and iron, and bacterial disease agents, with respect to their effect on eel health, considering sublethal levels of metals that are currently found in natural waters.

Chorda tympani nerve modulates the rat's avoidance of calcium chloride

Calcium intake depends on orosensory factors, implying the presence of a mechanism for calcium detection in the mouth. To better understand how information about oral calcium is conveyed to the brain, we examined the effects of chorda tympani nerve transection on calcium chloride (CaCl(2)) taste preferences and thresholds in male Wistar rats. The rats were given bilateral transections of the chorda tympani nerve (CTX) or control surgery. After recovery, they received 48-h two-bottle tests with an ascending concentration series of CaCl(2). Whereas control rats avoided CaCl(2) at concentrations of 0.1mM and higher, rats with CTX were indifferent to CaCl(2) concentrations up to 10mM. Rats with CTX had significantly higher preference scores for 0.316 and 3.16 mM CaCl(2) than did control rats. The results imply that the chorda tympani nerve is required for the normal avoidance of CaCl(2) solution.

Water quality of medium size watercourse under baseflow conditions: the case study of river Sutla in Croatia

The study on medium size river Sutla in Croatia indicated considerable water contamination at specific sites during the baseflow period, probably associated to low flow-rate (0.73-68.8 m3 s(-1)), and consequently low dilution capacity of this river. Various aspects of contamination were observed: increased conductivity to 1,000 microS cm(-1), decreased dissolved oxygen level to 50%, 4-5 degrees C increased water temperature, increased concentrations of several dissolved trace elements (e.g., maximal values of Li: 45.4 microg l(-1); Rb: 10.4 microg l(-1); Mo: 20.1 microg l(-1); Cd: 0.31 microg l(-1); Sn: 30.2 microg l(-1); Sb: 11.8 microg l(-1); Pb: 1.18 microg l(-1); Ti: 1.03 microg l(-1); Mn: 261.1 microg l(-1); and Fe: 80.5 microg l(-1)) and macro elements (e.g., maximal values of Na: 107.5 mg l(-1); and K: 17.3 mg l(-1)), as well as moderate or even critical fecal (E. coli: 4,888 MPN/100 ml; total coliforms: 45,307 MPN/100 ml; enterococci: 1,303 MPN/100 ml) and organic pollution (heterotrophic bacteria: 94,000 cfu/ml). Although metal concentrations still have not exceeded the limits considered as hazardous for aquatic life or eventually for human health, the observed prominent increases of both metal concentrations and bacterial counts in the river water should be considered as a warning and incentive to protect the small and medium size rivers from the future deterioration, as recommended by EU Water Framework Directive.

Titanium in UK rural, agricultural and urban/industrial rivers: geogenic and anthropogenic colloidal/sub-colloidal sources and the significance of within-river retention

Operationally defined dissolved Titanium [Ti] (the <0.45μm filtered fraction) in rivers draining rural, agricultural, urban and industrial land-use types in the UK averaged 2.1μg/l with a range in average of 0.55 to 6.48μg/l. The lowest averages occurred for the upland areas of mid-Wales the highest just downstream of major sewage treatment works (STWs). [Ti] in rainfall and cloud water in mid-Wales averaged 0.2 and 0.7μg/l, respectively. Average, baseflow and stormflow [Ti] were compared with two markers of sewage effluent and thus human population: soluble reactive phosphorus (SRP) and boron (B). While B reflects chemically conservative mixing, SRP declined downstream of STW inputs due to in-stream physico-chemical and biological uptake. The results are related to colloidal and sub-colloidal Ti inputs from urban/industrial conurbations coupled with diffuse background (geological) sources and within-river removal/retention under low flows as a result of processes of aggregation and sedimentation. The urban/industrial inputs increased background [Ti] by up to eleven fold, but the total anthropogenic Ti input might well have been underestimated owing to within-river retention. A baseline survey using cross-flow ultrafiltration revealed that up to 79% of the [Ti] was colloidal/nanoparticulate (>1kDa i.e. >c. 1-2nm) for the rural areas, but as low as 28% for the urban/industrial rivers. This raises fundamental issues of the pollutant inputs of Ti, with the possibility of significant complexation of Ti in the sewage effluents and subsequent breakdown within the rivers, as well as the physical dispersion of fine colloids down to the macro-molecular scale. Although not directly measured, the particulate Ti can make an important contribution to the net Ti flux.

A review and model assessment of (32)P and (33)P uptake to biota in freshwater systems

Bioaccumulation of key short-lived radionuclides such as (131)I and (32,33)P may be over-estimated since concentration ratios (CRs) are often based on values for the corresponding stable isotope which do not account for radioactive decay during uptake via the food chain. This study presents estimates for bioaccumulation of radioactive phosphorus which account for both radioactive decay and varying ambient levels of stable P in the environment. Recommended interim CR values for radioactive forms of P as a function of bioavailable stable phosphorus in the water body are presented. Values of CR are presented for three different trophic levels of the aquatic food chain; foodstuffs from all three trophic levels may potentially be consumed by humans. It is concluded that current recommended values of the CR are likely to be significantly over-estimated for radioactive phosphorus in many freshwater systems, particularly lowland rivers. Further research is recommended to field-validate these models and assess their uncertainty. The relative importance of food-chain uptake and direct uptake from water are also assessed from a review of the literature. It can be concluded that food-chain uptake is the dominant accumulation pathway in fish and hence accumulation factors for radioactive phosphorus in farmed fish are likely to be significantly lower than those for wild fish.

The biogeochemistry of arsenic in a remote UK upland site: trends in rainfall and runoff, and comparisons with urban rivers

Ten years of monitoring of rainfall and streams in the remote acidic and acid sensitive moorland and afforested moorland of upland mid-Wales reveals concentrations of arsenic (As) typically <1 µg L(-1). On average, the lowest concentrations occur within rainfall and they have declined over time probably in response to reductions in global emissions. There is a corresponding reduction within the streams except for forested systems where concentrations up to doubled following clear-fell. Within the streams there are both annual cycling and diurnal cycling of As. The annual cycling gives maxima during the summer months and this probably reflects the importance of groundwater inputs and mineralisation/desorption from the surface soil layers. Correspondingly, the diurnal cycling occurs during the summer months at low flow periods with As concentrations highest in the afternoon/evening. For the urban/industrial basins of northern England with historically a much higher As deposition, land contamination and effluent discharges, comparative data indicate As concentrations around three fold higher: strong seasonal patterns are observed for the same reasons as with the uplands. Across the sites, the As concentrations are over an order of magnitude lower than that of environmental concern. Nonetheless, the results clearly show the effects of declining emissions on rainfall deposition and some indication of areas of historic contamination. Arsenic is mainly present in the <0.45 fraction, but cross-flow filtration indicates that approx. 43% is in the colloidal phase at the clean water sites, and 16% in the colloidal phase at the contaminated sites. Part of this colloidal component may well be associated with organic carbon.

The Ribble/Wyre observatory: major, minor and trace elements in rivers draining from rural headwaters to the heartlands of the NW England historic industrial base

Information on a new observatory study of the water quality of two major river basins in northwestern England (the Ribble and Wyre) is presented. It covers upland, intermediate and lowland environments of contrasting pollution history with sufficient detail to examine transitional gradients. The upland rivers drain acidic soils subjected to long-term acidic deposition. Nonetheless, the acidic runoff from the soils is largely neutralised by high alkalinity groundwaters, although the rivers retain, perhaps as colloids, elements such as Al and Fe that are mobilised under acid conditions. The lowland rivers are contaminated and have variable water quality due to variable urban/industrial point and diffuse inputs reflecting local and regional differences in historic and contemporary sources. For most determinands, pollutant concentrations are not a major cause for concern although phosphate levels remain high. Set against earlier studies for other regions, there may be a general decline in pollutant levels and this is most clearly observed for boron where effluent inputs have declined significantly due to reductions in household products that are flushed down the drain. High concentrations of sodium and chloride occurred briefly after a severe cold spell due to flushing of road salts. A major inventory for water quality within rural, urban, industrial and agricultural typologies is provided within data summary attachments for over 50 water quality determinands. Within the next year, the full dataset will be made available from the CEH website. This, with ongoing monitoring, represents a platform for water quality studies across a wide range of catchment typologies pertinent to environmental management of clean and impacted systems within the UK. The study provides a base of research "from source to sea" including extensions to the estuary and open sea for a semi-confined basin, the Irish Sea, where there are many issues of pollution inputs and contamination.

Decreasing boron concentrations in UK rivers: insights into reductions in detergent formulations since the 1990s and within-catchment storage issues

The changing patterns of riverine boron concentration are examined for the Thames catchment in southern/southeastern England using data from 1997 to 2007. Boron concentrations are related to an independent marker for sewage effluent, sodium. The results show that boron concentrations in the main river channels have declined with time especially under baseflow conditions when sewage effluent dilution potential is at its lowest. While boron concentrations have reduced, especially under low-flow conditions, this does not fully translate to a corresponding reduction in boron flux and it seems that the "within-catchment" supplies of boron to the river are contaminated by urban sources. The estimated boron reduction in the effluent input to the river based on the changes in river chemistry is typically around 60% and this figure matches with an initial survey of more limited data for the industrial north of England. Data for effluent concentrations at eight sewage treatment works within the Kennet also indicate substantial reductions in boron concentrations: 80% reduction occurred between 2001 and 2008. For the more contaminated rivers there are issues of localised rather than catchment-wide sources and uncertainties over the extent and nature of water/boron stores. Atmospheric sources average around 32 to 61% for the cleaner and 4 to 14% for the more polluted parts. The substantial decreases in the boron concentrations correspond extremely well with the timing and extent of European wide trends for reductions in the industrial and domestic usage of boron-bearing compounds. It clearly indicates that such reductions have translated into lower average and peak concentrations of boron in the river although the full extent of these reductions has probably not yet occurred due to localised stores that are still to deplete.

Water quality, nutrients and the European union's Water Framework Directive in a lowland agricultural region: Suffolk, south-east England

The water quality of 13 rivers in the lowland, agricultural county of Suffolk is investigated using routine monitoring data for the period 1981 to 2006 collected by the Environment Agency of England and Wales (EA), and its predecessors, with particular emphasis on phosphorus (as total reactive phosphorus, TRP) and total (dissolved and particulate) oxidised nitrogen (TOxN--predominantly nitrate NO3). Major ion and flow data are used to outline fundamental hydrochemical characteristics related to the groundwater provenance of base-flow waters. Relative load contributions from point and diffuse sources are approximated using Load Apportionment Modelling for both TRP and TOxN where concurrent flow and concentration data are available. Analyses indicate a mixture of point and diffuse sources of TRP, with the former being dominant during low flow periods, while for TOxN diffuse sources dominate. Out of 59 sites considered, 53 (90%) were found to have annual average TRP concentrations greater than 0.05 mg P l(-1), and 36 (61%) had average concentrations over 0.120 mg P l(-1), the upper thresholds for 'High' and 'Good' ecological status, respectively. Correspondingly, for TOxN, most of the rivers are already within 70% of the 11.3 mg N l(-1) threshold, with two rivers (Wang and Ore) being consistently greater than this. It is suggested that the major challenge is to characterise and control point-source TRP inputs which, being predominant during the late spring and summer low-flow period, coincide with the peak of primary biological production, thus presenting the major challenge to achieving 'good' ecological status under the Water Framework Directive. Results show that considerable effort is still required to ensure appropriate management and develop tools for decision-support.

European eel (Anguilla anguilla L.) metallothionein, endocrine, metabolic and genotoxic responses to copper exposure

This study investigated Anguilla anguilla (European eel) physiological and genotoxic responses to copper (Cu) and their relation with metallothionein (MT) protection. Eels were exposed during 7 days to Cu 0.2 micromol/L. MT induction was assessed in gill and liver, revealing significant response only in liver. Endocrine responses displayed a plasma free triiodothyronine (T3) and cortisol significant decrease, though the thyroid-stimulating hormone (TSH) and free thyroxine (T4) concentrations were unaltered. A significant plasma glucose increase was observed whereas lactate was significantly decreased. Despite the absence of DNA integrity decrease in blood, gill, liver and kidney, erythrocytic nuclear abnormalities (ENA) frequency significantly increased in Cu exposed group. MT induction was insufficient to prevent endocrine and metabolic alterations as well as genotoxicity/clastogenicity in blood. However, MT protection was evident in liver by preventing DNA integrity loss. Globally, it was demonstrated that Cu environmentally realistic levels may pose a serious ecological risk to fish.

Biomagnification of trace elements in the aquatic food web in the Mekong Delta, South Vietnam using stable carbon and nitrogen isotope analysis

In the present study, we report the concentrations of 21 trace elements (V, Cr, Mn, Co, Cu, Zn, As, Se, Rb, Sr, Mo, Ag, Cd, Sn, Sb, Cs, Ba, Hg, Tl, Pb, and Bi), as well as the results of the analysis of stable carbon and nitrogen isotopes, of the various biota that make up the food web in the main stream of the Mekong Delta near Can Tho, South Vietnam. A significant trophic level-dependent increase was found in concentrations of Se, Rb, and Hg with increasing delta(15)N, indicating that an overall biomagnification of these elements occurred. However, the increase of Hg concentration per trophic level was lower than in previous studies. In contrast, the concentration of Mn showed an opposite trend in the food web of the Mekong Delta. In addition to these overall trends, the present study revealed that the biomagnification profiles of trace metals differ between crustaceans and fishes; concentrations of Mn, Cu, Zn, As, Sr, Mo, Ag, Cd, Sb, Cs, Ba, Tl, and Pb were significantly higher in crustaceans, whereas fishes showed higher concentrations of Cr, Rb, and Hg (trophic level determined by delta(15)N). The differences in the biomagnification profile between the major taxa might be attributed to differences in metal accumulation and in detoxification abilities such as possessing a metal-binding protein, e.g., metallothionein (MT).

Arsenic in the environment: Biology and Chemistry

Arsenic (As) distribution and toxicology in the environment is a serious issue, with millions of individuals worldwide being affected by As toxicosis. Sources of As contamination are both natural and anthropogenic and the scale of contamination ranges from local to regional. There are many areas of research that are being actively pursued to address the As contamination problem. These include new methods of screening for As in the field, determining the epidemiology of As in humans, and identifying the risk of As uptake in agriculture. Remediation of As-affected water supplies is important and research includes assessing natural remediation potential as well as phytoremediation. Another area of active research is on the microbially mediated biogeochemical interactions of As in the environment. In 2005, a conference was convened to bring together scientists involved in many of the different areas of As research. In this paper, we present a synthesis of the As issues in the light of long-standing research and with regards to the new findings presented at this conference. This contribution provides a backdrop to the issues raised at the conference together with an overview of contemporary and historical issues of As contamination and health impacts.

Long-term investigations of radiocaesium activity concentrations in carp in North Croatia after the Chernobyl accident

Long-term investigations of radiocaesium activity concentrations in carp in the Republic of Croatia are presented. The radiocaesium levels in carp decreased exponentially and the effective ecological half-life of (137)Cs was estimated to be about 1 year during 1987-2002 and 5 years during 1993-2005. The observed (134)Cs:(137)Cs activity ratio in carp was found to be similar to the ratio observed in other environmental samples. The concentration factor for carp (wet weight) was estimated to be 128+/-74 Lkg(-1), which is in reasonable agreement with model prediction based on K(+) concentrations in water. Estimated annual effective dose received by adult members of the Croatian population due to consumption of carp contaminated with (134)Cs and (137)Cs are small: per capita dose from this source during 1987-2005 was estimated to be 0.5+/-0.2 microSv. Due to minor freshwater fish consumption in Croatia and low radiocaesium activity concentrations in carp, it can be concluded that carp consumption was not a critical pathway for the transfer of radiocaesium from fallout to humans after the Chernobyl accident.

Oxidative stress, liver biotransformation and genotoxic effects induced by copper in Anguilla anguilla L.--the influence of pre-exposure to beta-naphthoflavone

Fish are exposed in the aquatic ecosystems to different classes of pollutants. Polycyclic aromatic hydrocarbons (PAHs) and heavy metals represent two important classes of aquatic contaminants. Thus, one lot of European eels (Anguilla anguilla L.) was pre-exposed during 24 h to 2.7 microM beta-naphthoflavone (BNF; a PAH-like compound), and subsequently exposed during 24 h to 0, 1 and 2.5 microM copper (Cu). Additionally, another lot not pre-exposed to BNF was exposed to the same Cu concentrations. BNF pre-exposure promoted a significant increase in liver ethoxyresorufin O-deethylase (EROD) activity, but did not change the other responses investigated in eels. On the other hand, both Cu concentrations did not modify the liver EROD activity either in eels pre-exposed to BNF or not. Liver total cytochrome P450 was increased in eels exposed to Cu 2.5 microM, being significantly only in eels not pre-exposed to BNF. Free sulfhydryl group content was decreased by 1 and 2.5 microM in eels pre-exposed to BNF or not pre-exposed, being significant at 2.5 microM Cu in eels not pre-exposed compared to its control. Liver total glutathione (TG), reduced glutathione (GSH) and GSH/oxidized glutathione (GSSG) levels were slightly decreased by 1 and 2.5 microM Cu in eels pre-exposed to BNF, whereas a slight tendency to increase was observed in eels not pre-exposed. Thus, liver TG and GSH significantly decreased in 2.5 microM Cu BNF pre-exposed eels compared to eels not pre-exposed to BNF. Liver glutathione reductase and catalase activities were significantly inhibited by 1 and 2.5 microM Cu in eels pre-exposed to BNF, concomitantly with a slight liver glutathione peroxidase tendency to decrease. Lipid peroxidation was significantly increased by 1 microM Cu in eels either pre-exposed or not pre-exposed to BNF. Liver H(2)O(2) was significantly increased by 1 microM Cu in eels pre-exposed to BNF. Liver DNA integrity was significantly decreased by 1 and 2.5 microM Cu in eels pre-exposed to BNF. The oxidative stress and genotoxic effects induced by Cu in eels pre-exposed to BNF revealed that the metal effects are potentiated by previous exposure to BNF.

Modelling the dispersion of radionuclides following short duration releases to rivers: Part 2. Uptake by fish

This paper evaluates and generalizes state-of-the-art approaches for dynamic modelling of bioaccumulation in fish resulting from short duration liquid discharges of radionuclides ((3)H, (14)C, (60)Co, (134)Cs, (137)Cs, (65)Zn, (89)Sr, (90)Sr, (125)I, (131)I, (241)Am, isotopes of Pu and U) to rivers. Based on a review of model parameter values, predictions are made of maximum and time-integrated activity concentrations in fish. A simplified version of the model was developed and presented as "look-up" graphs. The influence of various environmental parameters on model output was evaluated by sensitivity analysis. Maximum and time-integrated concentrations in fish may be predicted for rivers based on the river volumetric flow rate and water temperature. It is demonstrated that the dynamic model gives lower and more realistic predictions of maximum concentrations in fish than the simpler "Concentration Factor" approach. However, for time-integrated concentration in fish, and estimation of radiation dose to humans from consumption of the fish, the Concentration Factor approach gives similar predictions to the dynamic model.

Modelling the dispersion of radionuclides following short duration releases to rivers: Part 1. Water and sediment

This paper evaluates and generalises state-of-the-art approaches for modelling short duration liquid discharges of radionuclides ((3)H, (14)C, (60)Co, (134)Cs, (137)Cs, (65)Zn, (89)Sr, (90)Sr, (125)I, (131)I, (241)Am, isotopes of Pu and U) to rivers. An advection-dispersion model was parameterised and used to predict the concentrations of radionuclides in the river environment, i.e. in river water, river bed sediment and fish (Part II of this paper covers uptake to fish). The coupled transport and bio-uptake model was used to predict the concentrations of radionuclides in the River Thames, UK, and one of its tributaries as a result of hypothetical short duration discharges. A simplified version of this model was developed and presented as "look-up" graphs. The influence of various environmental parameters on model output was evaluated by sensitivity analysis. Time-integrated water and sediment concentrations and maximum sediment concentrations may be predicted for all rivers on the basis of the river volumetric flow rate only. Maximum concentration in water is, however, also dependent on other river characteristics. For this latter case, generalised modelling approaches are tested for use in situations where detailed hydrological and dispersion data are not available.

Nitrate concentrations in river waters of the upper Thames and its tributaries

The spatial and temporal patterns of in-stream nitrate concentrations for the upper Thames and selected tributaries are described in relation to point and diffuse sources for these rural catchments. The rivers associated with catchments dominated by permeable (Cretaceous Chalk) bedrock show a smaller range in nitrate concentrations than those associated with clay and mixed sedimentary bedrock of lower permeability. The differences reflect the contrasting nature of water storage within the catchments and the influence of point and diffuse sources of nitrate. Nitrate concentrations often increase in a gradual way as a function of flow for the rivers draining the permeable catchments, although there is usually a minor dip in nitrate concentrations at low to intermediate flow due to (1) within-river uptake of nitrate during the spring and the summer when biological activity is particularly high and (2) a seasonal fall in the water table and a change in preferential flow-pathway in the Chalk. There is also a decrease in the average nitrate concentration downstream for the Kennet where average concentrations decrease from around 35 to 25 mg NO(3) l(-1). For the lower permeability catchments, when point source inputs are not of major significance, nitrate concentrations in the rivers increase strongly with increasing flow and level off and in some cases then decline at higher flows. When point source inputs are important, the initial increase in nitrate concentrations do not always occur and there can even be an initial dilution, since the dilution of point sources of nitrate will be lowest under low-flow conditions. For the only two tributaries of the Thames which we have monitored for over 5 years (the Pang and the Kennet), nitrate concentrations have increased over time. For the main stem of the Thames, which was also monitored for over 5 years, there is no clear increase over time. As the Pang and the Kennet river water is mainly supplied from the Chalk, the increasing nitrate concentrations over time clearly reflect increasing nitrate concentrations within the groundwater. It primarily reflects long-term trends for agricultural fertilizer inputs and significant aquifer storage and long water residence times. The results are discussed in terms of hydrogeochemical processes and the Water Framework Directive and are compared with data from other eastern UK rivers. The importance of diffuse sources of nitrate contamination is highlighted. On a flow weighted basis, the average diffuse component of nitrate is around 95% for the Thames Basin rivers draining Chalk and for the corresponding rivers draining less permeable strata, there is a more significant but not major point source component (at least in terms of flux); the average diffuse component is 79% in this case. These data fit well with earlier assessments of agricultural sources to UK surface waters. Under baseflow conditions the diffuse sources remain dominant for the Chalk fed Thames Basin rivers, but point sources can be dominant for the low permeability cases. On a proportionate basis, the Thames Basin rivers are similar to the rural rivers of the Tweed and Humber Basins in terms of percentage diffuse components although the lower intensity agriculture occurring for the rivers monitored means that the average nitrate concentrations are lower for the rural rivers of central and northern England and the borders with Scotland: the Humber and Tweed.

Chlorophyll-a in the rivers of eastern England

Chlorophyll-a concentration variations are described for two major river basins in England, the Humber and the Thames and related to catchment characteristics and nutrient concentrations across a range of rural, agricultural and urban/industrial settings. For all the rivers there are strong seasonal variations, with concentrations peaking in the spring and summer time when biological activity is at its highest. However, there are large variations in the magnitude of the seasonal effects across the rivers. For the spring-summer low-flow periods, average concentrations of chlorophyll-a correlate with soluble reactive phosphorus (SRP). Chlorophyll-a is also correlated with particulate nitrogen (PN), organic carbon (POC) and suspended sediments. However, the strongest relationships are with catchment area and flow, where two straight line relationships are observed. The results indicate the importance of residence times for determining planktonic growth within the rivers. This is also indicated by the lack of chlorophyll-a response to lowering of SRP concentrations in several of the rivers in the area due to phosphorus stripping of effluents at major sewage treatment works. A key control on chlorophyll-a concentration may be the input of canal and reservoir waters during the growing period: this too relates to issues of residence times. However, there may well be a complex series of factors influencing residence time across the catchments due to features such as inhomogeneous flow within the catchments, a fractal distribution of stream channels that leads to a distribution of residence times and differences in planktonic inoculation sources. Industrial pollution on the Aire and Calder seems to have affected the relationship of chlorophyll-a with PN and POC. The results are discussed in relation to the Water Framework Directive.

Factors influencing development of management strategies for the Abou Ali River in Lebanon II: seasonal and annual variation

The water quality of a river at any point reflects several major influences including but are not limited to climatic conditions and anthropogenic inputs. Assessing these influences is essential for managing land and water resources within a particular river catchment. The objectives of this study were to identify the causes of increasing or decreasing trends in the concentrations of various water quality parameters in the Abou Ali River in North Lebanon and to account for the consequential variations both annual and seasonal (low/high flow). The assessment was conducted at the end of the dry season in October 2002 and 2003 and the end of the wet season in March 2003 and 2004. Results established that dissolved oxygen levels were consistently higher at the end of the wet season. The concentrations of biochemical oxygen demand, ammonia nitrogen and ortho-phosphates did not exhibit a clear seasonal or annual variation. While the levels of total dissolved solids and nitrate nitrogen exhibited a decreasing trend in urban catchments, an increasing trend was observed in rural, agricultural and forested areas. The findings of this study reinforce the notion that management of point and non-point sources should be integrated as the combination of both sources connected with land use results in deleterious effects on water quality. The lack of good quality water hinders economic development and the potential for long term sustainability.

The water quality of the River Thame in the Thames Basin of south/south-eastern England

The water quality of the River Thame, a tributary of the River Thames in the Thames basin, is described in relation to point and diffuse contaminant inputs and runoff from permeable and impermeable bedrock geology with their own characteristic water quality. The data is examined to see if the market town of Aylesbury in the upper part of the catchment influences water quality. Previous studies highlighted the influence of Aylesbury sewage treatment works (STW) on soluble reactive phosphorus (SRP) concentrations in the river before and after phosphorus (P) stripping at the STW. Variations in water quality along the river are described and the study indicates that, apart from SRP, water quality determinants seem to be relatively unaffected by Aylesbury. The Thame water quality is compared with other catchment typologies and it is very similar to that of the main stem of the Thames even though the Thames is mainly Chalk groundwater fed. Differences in water quality largely link to the amount of STW effluent within the rivers and to the endmember compositions of the groundwater and near surface water sources.

The "AQUASCOPE" simplified model for predicting 89,90Sr, 131I, and 134,137Cs in surface waters after a large-scale radioactive fallout

Simplified dynamic models have been developed for predicting the concentrations of radiocesium, radiostrontium, and I in surface waters and freshwater fish following a large-scale radioactive fallout. The models are intended to give averaged estimates for radionuclides in water bodies and in fish for all times after a radioactive fallout event. The models are parameterized using empirical data collected for many lakes and rivers in Belarus, Russia, Ukraine, UK, Finland, Italy, The Netherlands, and Germany. These measurements span a long time period after fallout from atmospheric nuclear weapons testing and following the Chernobyl accident. The models thus developed were tested against independent measurements from the Kiev Reservoir and Chernobyl Cooling Pond (Ukraine) and the Sozh River (Belarus) after the Chernobyl accident, from Lake Uruskul (Russia), following the Kyshtym accident in 1957, and from Haweswater Reservoir (UK), following atmospheric nuclear weapons testing. The AQUASCOPE models (implemented in EXCEL spreadsheets) and model documentation are available free of charge from the corresponding author.

Anguilla anguilla L. oxidative stress biomarkers responses to copper exposure with or without beta-naphthoflavone pre-exposure

The redox cycling of heavy metals as well as their interactions with organic pollutants is a major contributor to the oxidative stress resulting from aquatic pollution. Therefore, in order to evaluate beta-naphthoflavone (BNF), Cu and BNF/Cu-induced oxidative stress with single and subsequent exposures, research was carried out in European eel (Anguilla anguilla L.). Eel gill and kidney oxidative stress biomarker responses such as lipid peroxidation (LPO), glutathione peroxidase (GPX), catalase (CAT), glutathione S-transferase (GST) and total reduced glutathione (GSH) to a single 24 h exposure to two copper concentrations (Cu-1 microM, 2.5 microM) and BNF (2.7 microM) with or without 24 h BNF (2.7 microM) pre-exposure were investigated. Cu exposure alone showed a significant gill GST increase at the lowest concentration and GSH content decrease for the highest concentration. Double BNF exposure in gill demonstrated a significant increase in LPO, CAT, GPX and GST, as well as a decrease in GSH content. However, in sequential BNF/Cu exposures, only the highest Cu concentration exhibited a significant increase in LPO and GSH as well as a decrease in GPX (vs. BNF + CW). In kidney, Cu exposure alone showed a significant CAT and GSH contents decrease for both concentrations, and at highest concentration in GPX; as well as GST increase at the lowest concentration. Double BNF exposure showed a significant increase in LPO and GST. Nevertheless, in sequential BNF/Cu exposures, both concentrations exhibited a significant increase in LPO and decrease in GSH contents. Moreover, LPO was also increased significantly in comparison to BNF+CW and the equivalent Cu exposures without BNF pre-exposure. Concerning GPX, a significant increase was observed at highest Cu concentration. In GST, a significant decrease at the lowest Cu concentration and increase at the highest Cu concentration was observed. Summarizing, a simple copper or BNF exposures have no ability to induce LPO in both gill and kidney. However, double BNF exposure induced LPO in both organs and sequential BNF/Cu exposures potentiated the risk of peroxidative damage occurrence in both organs. BNF/Cu interference on antioxidant responses differs between the studied organs. In gill, antagonistic effects were denoted with probable reflex in terms of peroxidative damage increase. In kidney, BNF pre-exposure prevented CAT and GPX inhibition by copper; though, no advantage of this effect was perceptible as defence against LPO generation. Considering BNF as a surrogate for a PAH and the detected interactions with copper, as well as the likelihood that these effects would be observed in polluted ecosystems, current results demonstrate their relevance to actual ecological exposures contributing to a better knowledge on oxidative stress mechanisms in fish.

The water quality of the River Carnon, west Cornwall, November 1992 to March 1994: the impacts of Wheal Jane discharges

In January 1992, there was a major pollutant event for the River Carnon and downstream with its confluence to the River Fal and the Fal estuary in the west Cornwall. This incident was associated with the discharge of several million gallons of highly polluted water from the abandoned Wheal Jane tin mine that also extracted Ag, Cu and Zn ore. Later that year, the Centre for Ecology and Hydrology (CEH; then Institute of Hydrology) Wallingford undertook daily monitoring of the River Carnon for a range of major, minor and trace elements to assess the nature and the dynamics of the pollutant discharges. These data cover an 18-month period when there remained major water-quality problems after the initial phase of surface water contamination. Here, a summary is provided of the water quality found, as a backdrop to set against subsequent remediation. Two types of water-quality determinant grouping were observed. The first type comprises the determinants B, Cs, Ca, Li, K, Na, SO4, Rb and Sr, and their concentrations are positively correlated with each other but inversely correlated with flow. This type of water-quality determinant shows variations in concentration that broadly link to the normal hydrogeochemical processes within the catchment, with limited confounding issues associated with mine drainage. The second type of water-quality determinant comprises Al, Be, Cd, Ce, Co, Cu, Fe, La, Pb, Pr, Nd, Ni, Si, Sb, U, Y and Zn, and concentrations for all this group are positively correlated. The determinants in this second group all have concentrations that are negatively correlated with pH. This group links primarily to pollutant mine discharge. The water-quality variations in the River Carnon are described in relation to these two distinct hydrogeochemical groupings.

Nutrient chemistry of River Pinios (Thessalia, Greece)

The impact of human activities with 3-year monitoring on the fluctuation of nutrients along the Pinios River and its tributaries were studied. Their seasonal variations throughout the years 1996-1998 were also presented. High temperatures, from June to August, cause a restriction of the water flow, an enhancement of nutrient concentration with the subsequent increase of eutrophication. High concentrations of nutrients were observed first in winter (wet period), caused by leaching of fertilizers from terrestrial systems after heavy rainfall, later during the warm months due to low water flow of the river, and at last in autumn when plant organisms began to decompose. The intensive algal and macrophyte growth (spring, summer) resulted in severe depletion of nutrients. Organic carbon showed no seasonal trend but its values were high near the estuaries. Nitrate fluxes were high at the initial station (sources) and the Titarisios tributary, whereas nitrites and ammonium were low. In contrary, the Kalentzis tributary with relatively low nitrate values showed increased values of nitrite ammonium or total nitrogen. On the other hand, the Enipeas tributary showed high SO4 values. Phosphates are remarkably present mainly after the city of Larissa, where sewage and industrial discharges occur. None of the nutrients measured in the Pinios River and its tributaries showed a clear seasonal cycle of concentration. Concentrations of nutrients and organic carbon increased as a consequence of anthropogenic inputs, particularly point discharges from sewage treatment plants (i.e. showing distinct, but variable, concentration peaks), as well as diffuse urban and/or agricultural runoff over long areas during storm events. The agricultural management, the urban pollution, mainly from Larissa City, and the climate conditions in the catchment basin (Thessalia Plain) of Pinios River and its tributaries greatly affect the chemical composition of their waters.

Copper detection in the Asiatic clam Corbicula fluminea: optimum valve closure response

When exposed to a contaminant, bivalves close their shell as a protective strategy. The aim of the present study was to estimate the maximum expected dissolved copper sensitivity in the freshwater bivalve Corbicula fluminea using a new approach to determine their potential and limit to detect contaminants. To take into account the rate of spontaneous closures, we integrated stress problems associated with fixation by a valve in usual valvometers and the spontaneous rhythm associated with nycthemeral activity, to optimize the response in conditions where the probability of spontaneous closing was lowest. Moreover, we used an original system with impedance valvometry, using lightweight impedance electrodes, to study free-ranging animals in low stress conditions combined with an analytical approach describing dose-response curves by logistic regression, with valve closure reaction as a function of response time and concentration of contaminant. In C. fluminea, we estimated that copper concentrations > 4 microg/l (95% confidence interval (CI95%), 2.3-8.8 microg/l) must be detected within 5 h after Cu addition. Lower values could not be distinguished from background noise. The threshold values were 2.5 times lower than the values reported in the literature.

Copper detection in the Asiatic clam Corbicula fluminea: optimum valve closure response

When exposed to a contaminant, bivalves close their shell as a protective strategy. The aim of the present study was to estimate the maximum expected dissolved copper sensitivity in the freshwater bivalve Corbicula fluminea using a new approach to determine their potential and limit to detect contaminants. To take into account the rate of spontaneous closures, we integrated stress problems associated with fixation by a valve in usual valvometers and the spontaneous rhythm associated with nycthemeral activity, to optimize the response in conditions where the probability of spontaneous closing was lowest. Moreover, we used an original system with impedance valvometry, using lightweight impedance electrodes, to study free-ranging animals in low stress conditions combined with an analytical approach describing dose-response curves by logistic regression, with valve closure reaction as a function of response time and concentration of contaminant. In C. fluminea, we estimated that copper concentrations >4 microg/l (95% confidence interval (CI(95%)), 2.3-8.8 microg/l) must be detected within 5 h after Cu addition. Lower values could not be distinguished from background noise. The threshold values were 2.5 times higher than the values reported in the literature.

Water quality functioning of lowland permeable catchments: inferences from an intensive study of the RIVER KENNEt and upper River Thames

This paper brings together information on the water quality functioning of the River Kennet and other parts of the upper River Thames in the south east of England. The Kennet represents a groundwater fed riverine environment impacted by agricultural and sewage sources of nutrient pollution. Descriptions of the general water quality of the area, nutrient sources, sinks and within river processes are provided together with biological responses to driving issues of agriculture, sewage treatment and climatic change. Models are developed and applied to assess the key processes involved for a highly dynamic system and to provide initial estimates of the likely responses to environmental change. Furthermore, the economic aspects of pollution control are reviewed, together with legislation issues, which are presented within the context of a landmark case known as the 'Axford Inquiry', the implications of which extend to regional and national dimensions. The paper concludes with a discussion on the present state of knowledge, key issues and future research on the science and management of groundwater fed nutrient impacted riverine systems.

Calcite saturation in eastern UK rivers

Calcite saturation in eastern UK rivers is assessed in relation to the potential kinetic inhibition of calcite precipitation. Two well established inhibitors are considered: soluble reactive phosphorus (SRP, i.e. inorganic monomeric phosphorus); and dissolved organic carbon (DOC). The rivers show a range of calcite saturation levels from approximately 1hundredth to approximately 100-fold. The greatest range occurs for the northernmost river considered, the Tweed, where the waters range from highly unsaturated to highly oversaturated. The lowest range occurs for the most southerly rivers (the Great Ouse and the Thames) where the waters are consistently oversaturated with respect to calcite. The contrasting patterns relate to a greater diversity of water quality within the northern regions. Thus, during the winter, the main waters are derived from the upland areas with acidic soils and low weathering rates. During the summer baseflow periods, groundwater inputs are more important and high photosynthesis results in particularly high pHs and calcite oversaturation. In contrast, for the southern rivers, the main source of water during both the summer baseflow and the winter highflow periods comes from calcium carbonate rich aquifer sources. Statistical analysis of pH vs. the logarithm of the calcite saturation index for each river indicates strong linear features with individual gradients of approximately 1. This linearity results from an autocorrelation (the logarithm of the saturation index is calculated from the pH) and this indicates that calcite solubility controls are not operative in any of the rivers examined. A comparison of calcite saturation levels and SRP and DOC concentrations show a pattern inconsistent with kinetic hindrance, although some structure is observed, probably due to the mixing reactions between point and diffuse sources of water with contrasting chemistry.

Total phosphorus content of river sediments in relationship to calcium, iron and organic matter concentrations

Data on the total concentrations of phosphorus, calcium, iron and organic matter in surface bed-sediments taken from rivers in the Thames catchment (Wey, Blackwater, Thame and Kennet), the River Swale in Yorkshire (data excludes the organic matter content) as well as the headwaters of the Great Ouse, are collated and compared. Total concentrations of phosphorus, iron and calcium range from 1.7-649, 12-8,333 and 9-4,605 micromol g(-1) (dry weight), respectively, with organic matter in the range of 0.6-19% by dry weight. For the Wey, Blackwater and Great Ouse, sewage inflows had no detectable effect on the sediment concentrations of total calcium, iron and organic matter whereas for the Blackwater and Great Ouse, the total phosphorus contents of the sediment were higher downstream of the effluent input in comparison with a less impacted upstream location. Relationships between the total phosphorus content of the sediments and contents of iron, calcium and organic matter indicated marked differences between the rivers. Although the organic matter content of the sediments was found to be a significant predictor for the total phosphorus concentration for the Blackwater and Great Ouse, the total iron content was also useful for the Blackwater and total calcium for the Great Ouse. It is postulated that this difference is a result of the sediment processes that are known to occur in these two systems, i.e. co-precipitation of phosphate with calcite in the Great Ouse and the formation of vivianite in anoxic sediments of the Blackwater.