Estimation of WHAM7 constants for GaIII, InIII, SbIII and BiIII from linear free energy relationships, and speciation calculations for natural waters

We compiled the equilibrium constants for the interactions of the technology-critical elements (TCEs) GaIII, InIII, SbIII and BiIII with ammonia, fluoride, hydroxyl and ligands with oxygen atoms. We then combined them with predictive equations to estimate parameters for Humic Ion-Binding Model VII, which permits the calculation of metal binding by natural organic matter (fulvic acid, FA, and humic acid, HA). Derived values of the Model VII parameter quantifying the interaction of metal ions with carboxyl-type groups (log KMA) were among the highest estimated so far, as were the values for the parameter (ΔLK2) that quantifies the tendency of the metal ion to interact with softer ligand atoms (N and S). The Windermere Humic Aqueous Model, version 7 (WHAM7), which incorporates Model VII, was then used to estimate the chemical speciation of each TCE element

WHAM-FTOXβ – An aquatic toxicity model based on intrinsic metal toxic potency and intrinsic species sensitivity

We developed a model that quantifies aquatic cationic toxicity by a combination of the intrinsic toxicities of metals and protons and the intrinsic sensitivities of the test species. It is based on the WHAM-FTOX model, which combines the calculated binding of cations by the organism with toxicity coefficients (αH, αM) to estimate the variable FTOX, a measure of toxic effect; the key parameter αM,max (applying at infinite time) depends upon both the metal and the test species. In our new model, WHAM-FTOXβ, values of αM,max are given by the product αM* × β, where αM* has a single value for each metal, and β a single value for each species. To parameterise WHAM-FTOXβ, we assembled a set of 2182 estimates of αM,max obtained by applying the basic model to laboratory toxicity data for 76 different test species, covering 15 different metals, and including results for metal mixtures. Then we fitted the log10 αM,max values with αM* and β values (a total of 91 parameters). The resulting model accounted for 72% of the variance in log10 αM,max. The values of αM* increased markedly as the chemical character of the metal changed from hard (average αM* = 4.4) to intermediate (average αM* = 25) to soft (average αM* = 560). The values of log10 β were normally distributed, with a 5–95 percentile range of -0.73 to +0.56, corresponding to β values of 0.18 to 3.62. The WHAM-FTOXβ model entails the assumption that test species exhibit common relative sensitivity, i.e. the ratio αM,max / αM* is constant across all metals. This was tested with data from studies in which the toxic responses of a single organism towards two or more metals had been measured (179 examples for the most-tested metals Ni, Cu, Zn, Ag, Cd, Pb), and statistically-significant (p < 0.003) results were obtained

The Effect of Adsorbed Humic Substances on the Uptake of Copper(II) by Goethite

The uptake of Cu by particles of goethite to which humic substances (HS) were adsorbed was measured as a function of pH at fixed Cu concentration, and as a function of [Cu] at pH 5.5, at an ionic strength of 0.01 mol dm-3• Uptake was enhanced, compared to that by goethite alone, in the pH range 4-7 and at [Cuz+] ; 10-5 mol dm-3• The results at pH 5.5 show that the enhancement is not due simply to the adsorbed HS increasing the concentration of particulate sites able to interact with Cu, but also to the creation of extra uptake sites of relatively high affinity when the goethite and HS interact

Proton binding by groundwater fulvic acids of different age, origins, and structure modeled with the model V and NICA-Donnan model

The proton binding properties of four fulvic acids from pristine groundwater and leachate-polluted groundwater were measured at four different ionic strengths (0.005−0.12 M) and modeled by the Model V and the NICA−Donnan model in order to evaluate the necessity of detailed proton binding parameters for groundwater fulvic acids. The proton binding parameters derived from the various fulvic acids were very similar, and on the basis of these parameters, it was not possible to distinguish between pristine and polluted groundwater. Normalization of the proton charge density by the proton charge density at pH 7 for each fulvic acid made all four fulvic acids regress to the same curve. The effects of varying the proton binding parameters were evaluated by simulating cadmium complexation using sets of proton binding parameters for the four fulvic acids and default sets of proton binding parameters available in the models WHAM (based on Model V) and Ecosat (based on NICA−Donnan). The Model V was rather indifferent with respect to specific characteristics of fulvic acids proton binding, and for most practical uses, the default values available in the model can be used. The NICA−Donnan model resulted in larger deviations between simulations based on default values and specific parameters. However, the NICA−Donnan database is still rather limited, and specific proton binding parameters should be used until the database providing default values has been extended

The Effect of Adsorbed Humic Substances on the Uptake of Copper(II) by Goethite

The uptake of Cu by particles of goethite to which humic substances (HS) were adsorbed was measured as a function of pH at fixed Cu concentration, and as a function of [Cu] at pH 5.5, at an ionic strength of 0.01 mol dm-3• Uptake was enhanced, compared to that by goethite alone, in the pH range 4-7 and at [Cuz+] ; 10-5 mol dm-3• The results at pH 5.5 show that the enhancement is not due simply to the adsorbed HS increasing the concentration of particulate sites able to interact with Cu, but also to the creation of extra uptake sites of relatively high affinity when the goethite and HS interact

Dependence of ombrotrophic peat nitrogen on phosphorus and climate

Nitrogen (N) is a key, possibly limiting, nutrient in ombrotrophic peat ecosystems, and enrichment by pollutant N in atmospheric deposition (Ndep, g m-2 a-1) is of concern with regard to peatland damage. We collated data on the N content of surface (depth ≤ 25 cm, mean 15 cm) ombrotrophic peat (Nsp) for 215 sites in the UK and 62 other sites around the world, including boreal, temperate and tropical locations (wider global data), and found Nsp to range from 0.5 % to 4%. We examined the dependences of Nsp on surface peat phosphorus (P) content (Psp), mean annual precipitation (MAP), mean annual temperature (MAT) and Ndep. Linear regression on individual independent variables showed highly significant (p < 0.001) correlations of Nsp with Psp (r2 = 0.23) and MAP (r2 = 0.14), and significant (p < 0.01) but weaker correlations with MAT (r2 = 0.03) and Ndep (r2 = 0.03). A multiple regression model using log-transformed values explained 36% of the variance of the UK data, 84% of the variance of the wider global data, and 47% of the variance of the combined data, all with high significance (p < 0.001). In all three cases, most of the variance was explained by Psp and MAP, but in view of a positive correlation between MAP and MAT for many of the sites, a role for MAT in controlling Nsp cannot be ruled out. There is little evidence for an effect of Ndep on Nsp. The results point to a key role of P in N fixation, and thereby C fixation, in ombrotrophic peats

Aged riverine particulate organic carbon in four UK catchments

The riverine transport of particulate organic matter (POM) is a significant flux in the carbon cycle, and affects macronutrients and contaminants. We used radiocarbon to characterise POM in 9 rivers of four UK catchments (Avon, Conwy, Dee, Ribble) over a one-year period. High-discharge samples were collected on three or four occasions at each site. Suspended particulate matter (SPM) was obtained by centrifugation, and the samples were analysed for carbon isotopes. Concentrations of SPM and SPM organic carbon (OC) contents were also determined, and were found to have a significant negative correlation. For the 7 rivers draining predominantly rural catchments, PO14C values, expressed as percent modern carbon absolute (pMC), varied little among samplings at each site, and there was no significant difference in the average values among the sites. The overall average PO14C value for all 7 sites of 91.2 pMC corresponded to an average age of 680 14C years, but this value arises from the mixing of differently-aged components, and therefore significant amounts of organic matter older than the average value are present in the samples. Although topsoil erosion is probably the major source of the riverine POM, the average PO14C value is appreciably lower than topsoil values (which are typically 100 pMC). This is most likely explained by inputs of older subsoil OC from bank erosion, or the preferential loss of high-14C topsoil organic matter by mineralisation during riverine transport. The significantly lower average PO14C of samples from the River Calder (76.6 pMC), can be ascribed to components containing little or no radiocarbon, derived either from industrial sources or historical coal mining, and this effect is also seen in the River Ribble, downstream of its confluence with the Calder. At the global scale, the results significantly expand available information for PO14C in rivers draining catchments with low erosion rates

An investigation of the distribution of phosphorus between free and mineral associated soil organic matter, using density fractionation

We investigated whether density fractionation can be used to determine the distribution of organic phosphorus (OP) between free and mineral-associated soil organic matter (SOM)

Nutrient fluxes from domestic wastewater: a national-scale historical perspective for the UK 1800–2010

Nutrient emissions in human waste and wastewater effluent fluxes from domestic sources are quantified for the UK over the period 1800-2010 based on population data from UK Census returns. The most important drivers of change have been the introduction of the water closet (flush toilet) along with population growth, urbanisation, connection to sewer, improvements in wastewater treatment and use of phosphorus in detergents. In 1800, the population of the UK was about 12 million and estimated emissions in human waste were 37 kt N, 6.2 kt P and 205 kt organic C per year. This would have been recycled to land with little or no sewage going directly to rivers or coastal waters. By 1900, population had increased to 35.6 million and some 145 kt N were emitted in human waste but, with only the major urban areas connected to sewers, only about 19 kt N were discharged in sewage effluent. With the use of phosphorus in detergents, estimated phosphorus emissions peaked at around 63.5 kt P/year in the 1980s, with about 28 kt P/year being discharged in sewage effluent. By 2010, population had increased to 63 million with estimated emissions of 263 kt N, 43.6 kt P and 1460 kt organic C per year, and an estimated effluent flux of 104kt N, 14.8 kt P and 63 kt organic C. Despite improvements in wastewater treatment, current levels of nutrient fluxes in sewage effluent are substantially higher than those in the early 20th century