Copper complexation in English Rivers

Are sustainable drainage systems (SuDS) effective at retaining dissolved trace elements?

Sustainable drainage systems (SuDS) are increasingly deployed to mitigate against increased trace element contaminant loads associated with urban and road runoff. However, there is a lack of research on their capabilities in removing these trace elements, particularly from the dissolved phase. Water samples were taken, following various rainfall events, from three different SuDS in Devon; one wetland pond adjacent to a busy dual carriageway, a new SuDS serving a housing estate and an established SuDS draining a mixed housing/light industrial area. A total of 15 elements were studied over the course of six rain events including the first flush of runoff. Removal rates varied within and between rain events as well as between types of SuDS. Although there was a general (modest) removal of dissolved elements within any given SuDS, this was not the case for all of the elements studied. Highest observed element concentrations entering the SuDS occurred at the onset of a rain event (first flush), the intensity of which, was related to the antecedent dry period. During high flows associated with intense rainfall, the SuDS could also act as a source of trace elements associated with fine particulates (e.g. lead) owing to resuspension of fine particulate material. Mature ponds with an abundance of macrophytes help retain solids and particulate metals, however poor maintenance leading to successional growth of shrubs and trees, reduces the efficiency of metal removal. This study highlighted the importance of long-term management planning to be included within any SuDs scheme.

Temporal assessment of copper speciation, bioavailability and toxicity in UK freshwaters using chemical equilibrium and biotic ligand models: Implications for compliance with copper environmental quality standards

Although significant progress has been made in understanding how environmental factors modify the speciation, bioavailability and toxicity of metals such as copper in aquatic environments, the current methods used to establish water quality standards do not necessarily consider the different geological and geochemical characteristics of a given site and the factors that affect copper fate, bioavailability potential and toxicity. In addition, the temporal variation in the concentration and bioavailable metal fraction is also important in freshwater systems. The work presented in this paper illustrates the temporal and seasonal variability of a range of water quality parameters, and Cu speciation, bioavailability and toxicity at four freshwaters sites in the UK. Rivers Coquet, Cree, Lower Clyde and Eden (Kent) were selected to cover a broad range of different geochemical environments and site characteristics. The monitoring data used covered a period of around six years at almost monthly intervals. Chemical equilibrium modelling was used to study temporal variations in Cu speciation and was combined with acute toxicity modelling to assess Cu bioavailability for two aquatic species, Daphnia magna and Daphnia pulex. The estimated copper bioavailability, toxicity levels and the corresponding ecosystem risks were analysed in relation to key water quality parameters (alkalinity, pH and DOC). Although copper concentrations did not vary much during the sampling period or between the seasons at the different sites; copper bioavailability varied markedly. In addition, through the chronic-Cu BLM-based on the voluntary risk assessment approach, the potential environmental risk in terms of the chronic toxicity was assessed. A much higher likelihood of toxicity effects was found during the cold period at all sites. It is suggested that besides the metal (copper) concentration in the surface water environment, the variability and seasonality of other important water quality parameters should be considered in setting appropriately protective environmental quality standards for metals.

Toxicity of uranium and copper individually, and in combination, to a tropical freshwater macrophyte (Lemna aequinoctialis)

Copper (Cu) and uranium (U) are of potential ecotoxicological concern to tropical freshwater biota in northern Australia, as a result of mining activities. Few data are available on the toxicity of U, and no data are available on the toxic interaction of Cu and U, to freshwater biota. This study determined the toxicity of Cu and U individually, and in combination, to a tropical freshwater macrophyte, Lemna aequinoctialis (duckweed), in a synthetic soft water (27 degrees C; pH, 6.5; hardness, 40 mg CaCO3 l-1, alkalinity, 16 mg CaCO3 l-1), typical of many fresh surface waters in coastal northern Australia. The growth rate of L. aequinoctialis decreased with increasing Cu or U concentrations, with the concentration of Cu inhibiting growth by 50% (EC50) being 16+/-1.0 microg l-1, with a minimum detectable effect concentration (MDEC) of 3.2 microg l-1. The concentration of U inhibiting growth by 50% (EC50) was 758+/-35 microg l-1 with a MDEC of 112 microg l-1. The EC50 value for the exposure of L. aequinoctialis to equitoxic mixtures of Cu and U was significantly (P0.05) higher than one toxic unit (1.35; 95% confidence interval, 1.18-1.52), indicating that the combined effects of Cu and U are less than additive (antagonistic). Therefore, inhibition of the growth rate of L. aequinoctialis was reduced when Cu and U were present in equitoxic mixtures, relative to individual metal exposures. Since non-additive (e.g. antagonistic) interactions of metal mixtures cannot be predicted using current mixture models, these results have important potential implications for the protection of freshwater ecosystems through the derivation of national water quality guidelines.

The Protonation of Polyacrylate in Seawater. Analysis of Concentration Effects

The protonation of polyacrylate (PAA, MW 2 kDa) was studied potentiometrically at 25 degrees C, in mixed electrolyte aqueous solution simulating the composition of seawater, in the salinity range 30 < or = S < or = 40. The salt composition of different solutions was varied in order to study its effect on apparent protonation constants. Results were analysed using two fairly different approaches: by simple regression analysis on a combination of concentration parameters and salinity, and by canonical correlation analysis. Unexpectedly we found that variations on protonation constants, due to the different relative component concentrations, are fairly low, revealing a sort of buffering capacity of seawater respect to protonation properties of polyacrylate (and likely for other HMW and LMW polycarboxylates). The intrinsic protonation constant of polyacrylate 2 kDa at 25 degrees C and 35 salinity is log K(H*) = log K(int) = 4.399 +/- 0.004. The use of different pH scales and standard seawater compositions is also discussed.