Distributions, cycling and recovery of amino acids in estuarine waters and sediments

Acid hydrolysis of estuarine water samples for the determination of amino acids (AAs) was tested and found to be effective at high (250 μM) nitrate concentrations when the anti-oxidant, ascorbic acid, was added to the samples. Hydrolysable AA concentrations were then determined in surface sediments collected from low and high salinity regions of the Tamar Estuary (UK) during winter 2003 and 2004, and in overlying water when simulated resuspension of sediment particles was performed. Concentrations of AAs in sediment samples comprised <50% of particulate nitrogen, fitting the paradigm that most sedimentary nitrogen is preserved within an organic matrix. When sediment samples were resuspended in overlying water (salinity 17.5), the rapid, measured increase in dissolved AA concentrations almost equalled the reported nitrate concentration in the lower estuary, with the subsequent decrease in the total dissolved AA levels suggested that bacterial uptake was occurring. Our data concur with previous studies on nitrogen desorption from sediments and suggest that an understanding of organic nitrogen cycling will be an important aspect of future effective estuarine management.     

Unexpected removal of the most neutral cationic pharmaceutical in river waters

Contamination of surface waters by pharmaceuticals is now widespread. There are few data on their environmental behaviour, particularly for those which are cationic at typical surface water pH. As the external surfaces of bacterio-plankton cells are hydrophilic with a net negative charge, it was anticipated that bacterio-plankton in surface-waters would preferentially remove the most extensively-ionised cation at a given pH. To test this hypothesis, the persistence of four, widely-used, cationic pharmaceuticals, chloroquine, quinine, fluphenazine and levamisole, was assessed in batch microcosms, comprising water and bacterio-plankton, to which pharmaceuticals were added and incubated for 21 days. Results show that levamisole concentrations decreased by 19 % in microcosms containing bacterio-plankton, and by 13 % in a parallel microcosm containing tripeptide as a priming agent. In contrast to levamisole, concentrations of quinine, chloroquine and fluphenazine were unchanged over 21 days in microcosms containing bacterio-plankton. At the river-water pH, levamisole is 28 % cationic, while quinine is 91–98 % cationic, chloroquine 99 % cationic and fluphenazine 72–86 % cationic. Thus, the most neutral compound, levamisole, showed greatest removal, contradicting the expected bacterio-plankton preference for ionised molecules. However, levamisole was the most hydrophilic molecule, based on its octanol–water solubility coefficient (K _ow). Overall, the pattern of pharmaceutical behaviour within the incubations did not reflect the relative hydrophilicity of the pharmaceuticals predicted by the octanol–water distribution coefficient, D _ow, suggesting that improved predictive power, with respect to modelling bioaccumulation, may be needed to develop robust environmental risk assessments for cationic pharmaceuticals.     

Temporal variability in nutrient concentrations and loads in the River Tamar and its catchment (SW England) between 1974 and 2004

This study reports the results from the analyses of a 30-year (1974–2004) river water quality monitoring dataset for NO _x –N (NO₃–N?+?NO₂–N), NH₄–N, PO₄–P and SiO₂–Si at the tidal limit of the River Tamar (SW England), an agriculturally dominated and sparsely populated catchment. Annual mean concentrations of NH₄–N, PO₄–P and SiO₂–Si were similar to other rural UK rivers, while annual mean concentrations of NO _x –N were clearly lower. Estimated values for the 1940s were much lower than for those of post-1974, at least for NO₃–N and PO₄–P. Flow-weighted mean concentrations of PO₄–P decreased by approximately 60 % between 1974 and 2004, although this change cannot be unequivocally ascribed to either PO₄–P stripping from sewage treatment work effluents or reductions in phosphate fertiliser applications. Lower-resolution sampling (to once per month) in the late 1990s may also have led to the apparent decline; a similar trend was also seen for NH₄–N. There were no temporal trends in the mean concentrations of NO _x –N, emphasising the continuing difficulty in controlling diffuse pollution from agriculture. Concentrations of SiO₂–Si and NO _x –N were significantly and positively correlated with river flows ≤15 m³?s^?1, showing that diffuse inputs from the catchment were important, particularly during the wet winter periods. In contrast, concentrations of PO₄–P and NH₄–N did not correlate across any flow window, despite the apparent importance of diffuse inputs for these constituents. This observation, coupled with the absence of a seasonal (monthly) cycle for these nutrients, indicates that, for PO₄–P and NH₄–N, there were no dominant sources and/or both undergo extensive within-catchment processing. Analyses of nutrient fluxes reveal net losses for NO₃–N and SiO₂–Si during the non-winter months; for NO₃–N, this may be due to denitrification. Areal fluxes of NO _x –N from the catchment were towards the higher end of the range for the UK, while NH₄–N and PO₄–P were closer to the lower end of the ranges for these nutrients. These data, taken together with information on sestonic chlorophyll a, suggest that water quality in the lower River Tamar is satisfactory with respect to nutrients. Analyses of these monitoring data, which were collected at considerable logistical and monetary cost, have revealed unique insights into the environmental behaviour of key nutrients within the Tamar catchment over a 30-year period.     

Does carbon limitation reduce nitrogen retention in soil?

Environmental Chemistry Letters - Artificial soils made from waste materials offer an alternative to imported natural topsoils, notably in large-scale groundwork and reclamation projects. Benefits...     

Processes of distribution of pharmaceuticals in surface freshwaters: implications for risk assessment

The global consumption and production of pharmaceuticals is increasing concomitantly with concern regarding their environmental fate and effects. Active pharmaceutical ingredients are mainly released into the aquatic environment through wastewater effluent discharge. Once in the environment, pharmaceuticals can undergo processes of natural attenuation, i.e. dilution, sorption, transformation, depending on physico-chemical properties of the compound, such as water solubility, lipophilicity, vapour pressure, and environmental conditions, such as pH, temperature and ionic strength. A major natural attenuation process is the sorption on dissolved organic matter, colloids, suspended solids and sediments, which in turn control pharmaceuticals distribution, residence time and persistence in aquatic systems. Here we review studies of sorption capacity of natural sorbents to pharmaceuticals. These report on the importance of several environmental and sorbent-specific properties, such as the composition, quality, and amount of the sorbent, and the environmental pH, which determines the speciation of both the sorbent and compound. The importance of accounting for distribution processes on freshwater sorbents for any determination of environmental concentrations of pharmaceuticals is apparent, while the reliability of surrogate standards for measuring dissolved organic matter (DOM) distribution is evaluated in the context of the need for robust environmental risk assessment protocols.     

A comparison of SEM-EDS with ICP-AES for the quantitative elemental determination of estuarine particles

Suspended particulate matter (SPM) is a key component regulating the biogeochemistry of natural and contaminant moieties in estuaries. Individual particle analyses can complement conventional bulk analyses of SPM, but are rarely undertaken. This study used scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS) of particles to quantify a range of elements in the reference estuarine sediment PACS-2. This approach was compared with a bulk SPM analysis based on inductively coupled plasma-atomic emission spectrometry (ICP-AES). The median concentrations of Al, Fe, Mg, and Ca for the two approaches were similar, and accuracy for both methods was good. SEM-EDS analysis was also satisfactory for K. Agreement was poorer for Mn and Ti, which were present at trace concentrations. Increasing the number of particles examined by SEM-EDS should improve the analysis. SEM-EDS analysis of SPM from the Tamar Estuary, UK, revealed marked geochemical differences between particle sub-populations.Selected article from 6th European Meeting on Environmental Chemistry, Belgrade, 2005, organised by Prof. Dr. Branimir Jovancicevic and the European Association of Chemistry and the Environment (ACE, www.research.plymouth.ac.uk/ace)     

Temporal variability in dynamic and colloidal metal fractions determined by high resolution in situ measurements in a UK estuary

In recent environmental legislation, such as the Water Framework Directive in the European Union (WFD, 2000/60/EC), the importance of metal speciation and biological availability is acknowledged, although analytical challenges remain. In this study, the Voltammetric In situ Profiler (VIP) was used for high temporal resolution in situ metal speciation measurements in estuarine waters. This instrument simultaneously determines Cd, Cu and Pb species within a size range (ca. <4 nm) that is highly relevant for uptake by organisms. The colloidal metal fraction can be quantified through a combination of VIP measurements and analyses of total dissolved metal concentrations.VIP systems were deployed over tidal cycles in a seasonal study of metal speciation in the Fal Estuary, southwest England. Total dissolved concentrations were 4.97-315 nM Cu, 0.13-8.53 nM Cd and 0.35-5.75 nM Pb. High proportions of Pb (77 ± 17%) and Cu (60 ± 25%) were present as colloids, which constituted a less important fraction for Cd (37 ± 30%). The study elucidated variations in the potentially toxic metal fraction related to river flow, complexation by organic ligands and exchanges between dissolved and colloidal phases and the sediment. Based on published toxicity data, the bioavailable Cu concentrations (1.7-190 nM) in this estuary are likely to severely compromise the ecosystem structure and functioning with respect to species diversity and recruitment of juveniles. The study illustrates the importance of in situ speciation studies at high resolution in pursuit of a better understanding of metal (bio)geochemistry in dynamic coastal systems.     

Removal of atrazine from river waters by indigenous microorganisms

We report the first data for atrazine removal in low-turbidity freshwaters. Atrazine is a globally applied herbicide, contamination by which may lead to direct and indirect ecotoxicological impacts. Although a common contaminant of surface waters, microbial biodegradation of atrazine in this environment has been little studied, with most work focused on soils by means of selected, atrazine-degrading bacteria-enriched cultures. Here, we measured atrazine removal from river water using a batch incubation system designed to represent environmental conditions, with water from two contrasting UK rivers, the Tamar and Mersey. Atrazine and bacterial inocula prepared from the source water were added to cleaned river water for 21-day incubations that were analysed directly by electrospray ionisation-mass spectrometry. The experimental approach was validated using peptides of different molecular mass. Results show that atrazine concentrations decreased by 11% over 21 days in Tamar samples, a rural catchment with low population density, when atrazine was the only substrate added. In contrast no removal was evident in Mersey samples, an urban catchment with high population density. When a tripeptide was added as a co-substrate, atrazine removal in the Tamar water remained at 11% while that for the Mersey water increased from 0 to 37%. Although degradation of atrazine in aerobic freshwaters is predicted according to its chemical structure, our data suggest that the composition of the bacterial population determines whether removal occurs under these conditions and at these environmentally realistic concentrations.